a review: utilization of food wastes for hydrogen production under hydrothermal gasification

This article was downloaded by: [Texas State University, San Marcos]On: 02 October 2013, At: 21:19Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

Environmental Technology ReviewsPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/tetr20

A review: utilization of food wastes for hydrogenproduction under hydrothermal gasificationRattana Muangrataa Department of Food Engineering, Faculty of Agro-Industry, Chiang Mai University, ChiangMai, ThailandPublished online: 27 Sep 2013.

To cite this article: Rattana Muangrat , Environmental Technology Reviews (2013): A review: utilization offood wastes for hydrogen production under hydrothermal gasification, Environmental Technology Reviews, DOI:10.1080/21622515.2013.840682

To link to this article: http://dx.doi.org/10.1080/21622515.2013.840682

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the Content) containedin the publications on our platform. However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of theContent. Any opinions and views expressed in this publication are the opinions and views of the authors, andare not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon andshould be independently verified with primary sources of information. Taylor and Francis shall not be liable forany losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoeveror howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use ofthe Content.

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

Environmental Technology Reviews, 2013http://dx.doi.org/10.1080/21622515.2013.840682

A review: utilization of food wastes for hydrogen production under hydrothermal gasication

Rattana Muangrat

Department of Food Engineering, Faculty of Agro-Industry, Chiang Mai University, Chiang Mai, Thailand

(Received 8 May 2012; nal version received 25 August 2013 )

Biorenewable energy sources have received considerable attention in recent years. They are used instead of fossil fuels asthe main energy sources which have led to fuels depletion and environmental problems. Large quantities of food processingwastes are generated annually from dierent food industries. Most of food wastes contain high moisture content and arecomposed of mainly contents of carbohydrates, proteins and lipids which are considered as a possible renewable sourcetogether with the possible other food processing waste conversion techniques into useful energy such as syngas, ethanol,bio-oil and biodiesel. This paper reviews food waste utilization for hydrogen production under hydrothermal gasication. Itis concluded that food wastes give a great potential for biorenewable energy resource which could still contribute to reductionof environmental pollution.

Keywords: biorenewable energy; fossil fuels; food wastes; hydrothermal gasication; syngas

1. IntroductionFood wastes could come from several sources such as foodprocessing industries, domestic or commercial kitchens.The quantity of food wastes is included in statistics relatedto four dierent types of waste sectors such as the manufac-turing sector and the municipal solid waste (MSW) sectorincluding wholesale/retail, food service and the householdsector. These food waste sectors cover the solid and liq-uid food wastes which have a great number of organiccompounds and high moisture content. Lawrence et al. [1]reported on the treatment of waste from the manufactur-ing sector and municipalities including food industry wasteand household waste, respectively. Among the four sectorsconsidered and based on EUROSTAT 2006, the largest offood waste was produced from the household and manufac-turing sector, respectively. There were an estimated 38 and35 million tonnes per year of the household and manufac-turing food waste, respectively, in the 27 European Union(EU-27).[2]

There are many types of wastes in MSW such as foodwaste, garden and park waste, paper and cardboard, wood,textiles, nappies, rubber and leather, plastics, metal, glass,ash, dust, soil and electricwaste.[3] Figure 1 summarizes thewaste composition of MSW without industrial waste in dif-ferent regions and countries (Asia, Africa, Europe, Oceanicand America). The composition data were given by per centweight based on a wet basis. Some regions were short ofwaste data causing the percentage of waste composition tobe reported as less than 100%. From Figure 1, it is notable

Corresponding author. Email: [email protected]

that the percentage composition of foodwaste is higher thanthat of other types of wastes.

Due to the rapid growth of population in the world, it isundoubtable that food demand will certainly increase. Thefood and drink industry is the largest industry in the world-wide manufacturing sectors to support the growing demandfor food.[4] During industrial food processing, large quan-tities of food processing wastes have been produced fromthe food and drink industry.[4] There are ve main sectorsof the food processing industry which were considered bythe Agro-Food Wastes Reduction Network (AWARENET)as meat processing, sh processing, milk processing, veg-etable and fruit processing and wine processing.[57] Thewaste residues produced within the food and drink process-ing industry are deemed to be a large and ever-increasingproblem.

The volume of the food wastes being processed inEurope is a large problem which is growing. Food wasteis mainly composed of an organic material with a highmoisture content. According to the report from the SwedishInstitute for Food and Biotechnology (SIK)/the Food andAgriculture Organization (FAO) of the United Nations in2011, approximately 1.3 billion tonnes of food is wastedannually in the world and the total amount of food wasteand by-products produced in the European Union hasbeen estimated at approximately 222 million tonnes peryear.[5,8,9] Moreover, FAO of the United Nations of theUnited Nations analyses food balance sheets for 2007 andestimated that food waste in North America and Europe and

2013 Taylor & Francis

Dow

nloa

ded

by [T

exas

State

Univ

ersity

, San

Marc

os] a

t 21:1

9 02 O

ctobe

r 201

3

2 R. Muangrat

Figure 1. The percentage of dierent waste types in MSW in dierent regions and countries.[3]

in South/Southeast Asia and Sub-SaharanAfrica is roughly95115 and 611 kg/capita/year, respectively.[6] In EU,food waste is expected to increase from about 89 milliontonnes in 2006 to about 126 million tonnes in 2020 of whichthe data are based on anticipated EU population growthand increasing auence only.[2,10] It could be concludedthat there is an increasing trend in food wastes, which hasbecome an increasingly large issue. It is essential that foodwaste should be reduced.

Currently, food wastes are disposed of by various meth-ods such as landlling, incineration and recovery or recycle.There are many methods to convert food waste into gaseousand liquid fuels such as hydrogen via fermentation orgasication.[11] The major problem in using biologicalprocesses is the length of the microbial reaction. This cou-pled with variations in carbohydrates and protein typescan result in unstable concentrations of the waste mix-ture. Further, each component requires dierent conditionsof biological stability and microbial activity.[12] Althoughfood wastes have highly varied compositions depending ontheir sources, the carbonaceous contents of food processingwastes attract a great deal of attention as a potential energysource.

However, the actual volume of food wastes producedfrom the food processing industries is quite dicult to deter-mine. Signicant amounts of food waste originate from theindustrial production of food at various stages along the pro-duction line.[13]This is because each individual food indus-try produces dierent quantities and qualities of waste. In a2004 European research project such as AWARENET, the

food waste problem thoroughly investigated and quantiedwas focused on ve main industrial sectors for Europeanagro-food production (meat, sh, dairy, wine and fruit andvegetables processing). The AWARENET has been set upto collect and evaluate the amount of residues produced inthese ve main food processing industries from 19 selectedproduction processes shown in Table 1 and in dierentEuropean countries as illustrated in Figure 2.

The wastewater discarded comes from the cleaning ofraw materials, treatment and cooking of food. The cleaningof equipment contains an oxygen demand and high organiccontent solid residues. There are dierent sources of liquidwastes produced from the main processing operations suchasmeat processing, dairy processing, seafood including shprocessing, bread, sugar and confectionery processing, veg-etable and animal oils and fats processing, and beverage,alcohol and non-alcoholic processing.[6,14] The contentsof euents vary with each food processing operation andvary on a daily, weekly or seasonal basis.[15] Wastewaterreleased from food industries is turbid with high concentra-tions of biochemical oxygen demand (BOD), fats, oils andgrease, suspended solids (SS), nitrogen (N) and phosphorus(P). In contrast, the hazardous chemical content is generallylow.[1] The SS concentration varies from negligible to ashigh as 120 g L1. Wastewater from, for example, the meatand dairy sectors contains high concentrations of edible fatsand oils. Other characteristics of wastewater for food pro-cessing are seasonal variation and concentration variationin a day. Signicantly, wastewater from Food, Drink andMilk industries is extremely variable in composition. It is

Dow

nloa

ded

by [T

exas

State

Univ

ersity

, San

Marc

os] a

t 21:1

9 02 O

ctobe

r 201

3

Environmental Technology Reviews 3

Table 1. Average quantities of food wastes or by-productsfrom 19 selected production processes in Europe.[57]

Food processing wastes or by-products

Food processing Production In 103sector Production tonnes

Fish Fish canning 1543Fish lleting, salting and

smoking3166

Crustaceans processing 328Molluscs processing 180

Meat Beef slaughtering 4534Pig slaughtering 7339Poultry slaughtering 3482

Dairy Milk, butter and creamproduction

Negligible

Yoghurt production 335Fresh, soft and cooked cheese

production45,004

Wine White wine production 1862Red wine production 2036

Fruits andvegetables

Fruit and vegetables juiceproduction

5096

Fruit and vegetablesprocessing and preservation

3991

Vegetable oil production 12,698Corn starch production 579Potato starch production 2943Wheat starch production 487Sugar beet production 80,022Total 175,625

high in both chemical oxygen demand (COD) and BODwith levels as high as 10100 times higher than those ofdomestic wastewater.

2. Principal contents of food wastesFood waste composition is assumed to be C21.53H 34.21O12.66N1.00.[16,17] Food waste is made up of 30% solidresidue and 70%water.[16]Additionally,many foodwastesfrom the food processing industries have common charac-teristics such as a high moisture content, for instance, meatand vegetable wastes have moisture contents between 70%and 95%.[15,18] Food waste consists of abundant quanti-ties of organic materials which can be classied into threemain biological groups represented by carbohydrates, pro-teins and lipids. The carbohydrate group includes cellulose,starch and sugars and is a major composition of biodegrad-able wastes. For instance, the food industry wastes containstarch and cellulose which are rich in terms of carbohydratecontent.[12,19] The solid waste contains starch which iseasier to process for carbohydrate. Cellulose and hemicellu-loses can be hydrolyzed to carbohydrates.[12] Furthermore,biological wastes still contain large amounts of SS, highBOD or COD content, high nitrogen concentration, highsuspended oil or grease contents and a highly varied pHvalue. From the general information for the content of foodwastes and euents, the main composition of food wastecan be represented as in Figure 3.

When food is decomposed, generally it is convertedinto basic food substances such as carbohydrates, pro-teins and lipids which are the highest sources of energyin a diet. Figure 4 demonstrates that food wastes havea similar conversion characteristic to real food. In addi-tion, Chu et al. [21] reviewed and reported that foodwaste is a carbohydrate-rich representative of the mostimportant organic wastes generated within China. Quitainet al. [22] studied the hydrothermal treatment from variousorganic wastes such as proteinaceous wastes and cellulose

Figure 2. Percent contribution of individual European countries to the total food wastes and by-products of Europe (220 million tonesper year total) according to the report from SIK/FAO in 2011.[5,8,9]

Dow

nloa

ded

by [T

exas

State

Univ

ersity

, San

Marc

os] a

t 21:1

9 02 O

ctobe

r 201

3

4 R. Muangrat

Figure 3. Main contents of food wastes.[20]

Figure 4. General simplied reaction under hydrothermal con-ditions for the treatment of various organic wastes.[22]

wastes converted into smaller compounds and illustratedin Figure 4. Carboxylic acids as low-molecular weightcompounds formed during this process are oxidized toend products such as volatile compounds, carbon, water,synthesis gases, etc.

3. General methods for the reuse of food wastesA great number of food wastes are mainly composedof organic materials with high moisture content andare disposed currently by various methods such as

landlling, incineration, anaerobic fermentation, compost-ing and recovery or recycle. The method of landlling useslarge areas and generates landll leachate which is dicultto treat and creates odour nuisances. Incineration can pro-duce dioxins and heavy metals which are harmful to theenvironment. In addition, food waste has a high portion oforganicmaterial, variousminerals and a highwater content;therefore, incineration may not be an appropriate solution.Regarding the composting of foodwaste, themajor problemis the variation in carbohydrates and proteins that result inan unstable concentration of the waste mixture. Also eachcomponent requires dierent conditions of biological sta-bility and optimal microbial activity.[12] Furthermore, thesales of the best quality compost have a high capital costthat are often not protable.[23] In the European Union of27 countries (EU-27), the municipal waste including foodwastes landlled, incinerated, recycled and composted in2009 were 96, 51, 59 and 45 million tonnes, respectively.Themunicipalwaste dumped into landlls has reduced from141 million tonnes in 1995 to 96 million tonnes in 2009as a result of incineration, recycling and composting. Theamount of MSW sent to incinerators has increased from 31million tonnes in 1995 to 51 million tonnes in 2009.[24]Recycling and recovery have risen by 22 million tonnesto 59 million tonnes in the same period.[24] It has beenreported that food wastes generation can be reduced orrecycled for energy or fuel or chemical production.[2531]

4. Energy recovery methods for food processing andeuents

Food processingwastes include complexmixedwastes pro-duced from dierent processing units. Food wastes andeuents derived from biological raw materials are rich inbiodegradable components with a high biological oxygen(BOD) and COD content. If food wastes are untreated orare not treated properly, they will be hazardous to the envi-ronment and cause problems in landlls and wastewater

Dow

nloa

ded

by [T

exas

State

Univ

ersity

, San

Marc

os] a

t 21:1

9 02 O

ctobe

r 201

3


treatment systems. Moreover, disposal of food wastes inlandlls uses valuable space and may cause water, ground-water, soil and air pollution. Food processing may includethe food processing of solid wastes, meat processing solidwastes, vegetable crop residues, food waste in MSW andfood processing uidwastes. To reduce the problemof thesewastes, there are many processes developed not only tominimize the amount of food processing wastes but alsoto maximize the recovery of valuable products.

There are several energy conversion techniques suchas biological conversion, thermochemical conversion andchemical conversion. These conversion processes can trans-form dierent food processing wastes into dierent formsof energy products including heat and power, gaseous fuels(biogas and synthesis gases) and liquid fuels (bioethanol,biodiesel and bio-oil). Thermochemical conversion pro-cesses include pyrolysis, gasication, combustion andhydrothermal liquefaction.[3235] During thermochemicalconversion, organic food processing wastes are decom-posed to gaseous or liquid molecules at a high temperatureand in the presence or absence of air or oxygen. Gasicationis a process used to produce synthesis gases under partialoxidizing conditions. The synthesis gases are a mixture ofcarbon monoxide, carbon dioxide, methane and hydrogen.The pyrolysis process produces mainly liquid tar and solidchar in the absence of oxygen. Thermochemical conver-sion of food processing wastes into directly usable fuels togenerate steam and electricity is possible, or as gaseous, liq-uid fuels for energy. Anaerobic digestion and fermentationare two primary biological conversion processes to convertwastes into energy. During anaerobic digestion, microor-ganisms break down organic waste materials to producebiogas, which is a gaseous mixture mainly consisting ofmethane and carbon dioxide. The selection of an appropri-ate process is dependent on (1) the physical and chemicalproperties of wastes such as the moisture content and heatvalue; (2) the quantity of wastes; (3) the desired form ofenergy products; (4) the eciency of the energy conver-sion method; (5) energy demands for the process; and (6)economical feasibility. Food wastes containing high mois-ture content (approximately > 50%) are usually convertedinto useful energy by biological processes such as anaero-bic digestion while wastes containing low moisture contentare suitable for thermochemical conversion processes suchas combustion, gasication and pyrolysis. Thermochemicalliquefaction can also be used to break down wet food pro-cessing wastes at high pressure and a moderate temperatureinto a bio-oil of partly oxygenated hydrocarbons. However,thermochemical liquefaction may be more complicated andexpensive than a pyrolysis conversion process, which isanother process to break down the organic matter into bio-oil as reported by Mckendry.[36] However, the pyrolysisis a rapidly developing technology with great potential toproduce liquid oil from dry biomass as the main product.Combustion, gasication and anaerobic digestion generate

gaseous energy products such as hot gases for steamgenera-tion, synthesis gas and biogas, which are suitable to be usedat the production location. For hydrogen gaseous fuel, gasi-cation is likely to be commercially viable because it hasthe highest overall conversion eciency for gaseous fuelproduction. For real biomass, food wastes or wastewatercontaining a high moisture content, subcritical and super-critical water gasication has become a benign methodto generate hydrogen from real biomass and food wastesor domestic wastewater.[3739] Moreover, hydrothermalgasication can directly deal with wet biomass without adrying step and obtained high gasication eciency at lowtemperatures.[38,40,41]

Gasication and pyrolysis have disadvantage which ischar and tar formation leading to a low yield of hydro-gen gas.[42] There is great interest in developing novelconversion technologies that would cope with high mois-ture contents.[4349] Various energy conversion processesfrom main food processing wastes have been investigatedand are shown in Figure 5.

There are many reports about gasication of biomassinvolving hydrogen production in subcritical and super-critical water with many researchers suggesting that thisprocess has advantages and high potential. Compared withother biomass thermochemical gasication processes suchas air gasication or steam gasication that do requirea drying step, hydrothermal (subcritical and supercriticalwater) gasication is a process involving partial or lim-ited oxidation and can be used directly with wet biomasseswithout the need for a drying step.[38,5052] Drying steprequires energy intensive, when biomass has a moisturecontent higher than 50wt% (on a wet basis).[53,54] Ahigh moisture content in the raw material or food wastesunder supercritical conditions would promote gasicationreactions and production of hydrogen gas; as a result, thisgasication has a higher eciency than that of traditionalgasication.[44,5557] Kruse [58] noted that the energyrequirement to attain hydrothermal gasication conditionswhich are temperatures of 600C and a pressure of 30MPais lower than that to dry wet biomass for conventionaldry gasication at a temperature of 600C and a pressureof 0.1MPa. Kruse [58] further presented that the energyused in hydrothermal gasication of wet feedstock becomessignicantly lower when compared with evaporation anddry gasication in a low temperature range from 200C to450C. This is an obvious advantage and the fact that theenergy required for the hydrothermal gasication processis held at a high pressure making it largely recoverable.[58]Therefore, subcritical and supercritical water gasicationhas high gasication eciency at lower temperatures.[38,5052] Moreover, the subcritical and supercritical watergasication does not use any methods to maintain micro-bial cultures and enzymes like other biofuel processingtechniques or fermentation.[59] Systematic experimentalinvestigations for biomass gasication under the conditions

Dow

nloa

ded

by [T

exas

State

Univ

ersity

, San

Marc

os] a

t 21:1

9 02 O

ctobe

r 201

3

6 R. Muangrat

Figure 5. Summation of dierent types of food processing wastes and energy conversion techniques.

of supercritical water were examined by many researchgroups.[6079]

5. Properties of subcritical and supercritical waterIn comparison with other solvents, water is an environ-mentally benign non-toxic, low cost and most abundantsolvent and acidbase catalyst.[80,81] When both temper-ature and pressure are raised to near its critical point (Tc =374C,Pc = 22.1MPaandc = 320 kgm3), its propertieschange and dier signicantly from those of ambient water.Water heated below its critical point under a pressurizedcondition to maintain a liquid state is known as subcriti-cal water.[81,82] The supercritical water region is abovethe critical point.[78,83] The subcritical and supercriticalwater region could be presented in relation to temperatureand pressure as shown in Figure 6 which is a simple phasediagram. It is notable that the higher temperature and pres-sure cause the liquid phase to become less dense becauseof thermal expansion and the gas phase becomes denserwith rising pressure.[81] The densities of the liquid and gasphases become identical and the distinction between theliquid and gas disappears.[81] The supercritical water stateshares the physical propertieswith the liquid and gas phases.Above the critical water point the interface line separatingthe two phases disappears as shown in Figure 6.

Figure 6. A simple phase diagram of water (Tc is criticaltemperature and Pc is critical pressure).

The properties of water inuenced by subcritical andsupercritical conditions include dielectric constant, ionproducts, density, thermal conductivity and viscosity. Theseproperties can be changed by varyingwater temperature andpressure. Increasing the temperature and pressure causessignicant change in the properties of water, namely dielec-tric strength, ionic product anddensity,when comparedwithambient water.[81,84] The dielectric constant is a measure

Dow

nloa

ded

by [T

exas

State

Univ

ersity

, San

Marc

os] a

t 21:1

9 02 O

ctobe

r 201

3


of the polarity of the solvent. The solvent can dissolveany solutes with the dielectric constant close to that ofthe solvent.[85] When water is heated from the ambientcondition to higher temperatures, the density of the liq-uid phase decreases and that of the gas phase increases.Near the critical point, water decreases rapidly in its den-sity when it approaches its critical point. At the criticalpoint, the densities of liquid and gas phases are equaland become a homogeneous medium. The value of theionic product for water near the subcritical water regionis approximately three orders of magnitude larger than thatof ambient water.[86,87] Consequently, subcritical waterconditions have a higher concentration of hydrogen ions(H+) and hydroxide ions (OH) than in ambient condi-tions. The ionic product property of water in a subcriticalstate has a stronger tendency to ionize than ambient water.In the subcritical water region, it is possible to make waternot only as a polar solvent but also as a potential acidbase catalyst to decompose organic compounds via variouscatalyst reactions and hydrolysis.[59,8088] Generally, theionic product and dielectric constant are considered as themain properties that inuence and control the reactionsof organic compounds under subcritical water.[89] Withincreasing temperature, the dielectric constant decreasesand the number of hydrogen bonds decrease leading toa decrease in their strength (or the decrease of densityat a higher temperature).[46,90] For example, at approx-imately 250C, the dielectric constant decreases from 80(at 25C) to 25 which is almost equal to that of ethanol atambient temperature.[91,92] At 280C, the ionic productand dielectric constant of water are 6.34 1012 and 33,respectively, which equal those of methane at 25C.[91,92]Subcritical water behaves more like an excellent polarsolvent for polar organic compounds.[86,93,94]

Above the critical point, a supercritical water reactionenvironment provides an opportunity to conduct chemistryin a single uid phase that would otherwise occur in a mul-tiphase system under more conventional conditions. Afterthis critical point, the density of the supercritical water canbe turned continuously from high (liquid-like) to low (gas-like) values without a change in phase by adjusting thetemperature and pressure.[90,95,96] The phase separationcan no longer be observed by compression of vapour phaseor expansion of liquid phase.[97] The densities, dielectricconstant and ionic products further decrease in supercriti-cal water with increasing temperature. Supercritical wateris thus an ecient solvent for non-polar organic com-pounds which have very low solubility at subcritical waterconditions. This solvent property will allow non-polar com-pounds to dissolve and gases such as oxygen, nitrogen,ammonia, carbonmonoxide and carbon dioxide also exhibitcomplete miscibility in supercritical water.[59,90,98100]Subcritical and supercritical water conditions can dissolvemany types of biomass or biomass wastes. The advan-tages of a single supercritical phase reaction medium arethat higher concentrations of reactants can often be attained

Table 2. The properties of water under dierentconditions.[80,83,102]

Water under Subcritical Supercriticalambient water water

Properties condition region region

Temperature, T(C)

25 250 400 400

Pressure, P (MPa) 0.1 5 25 50Density, (kgm3) 1000 800 170 580Dielectric constant,

78.5 27.1 5.9 10.5

Ionic product, Kw 14.0 11.2 19.4 11.9Heat capacity, cp

(kJ kg1C1)4.22 4.86 13.0 6.8

Viscosity, (mPa s)

0.89 0.11 0.03 0.07

Heat conductivity, (mWm1C1)

608 620 160 438

and that there is no interphase mass transport processes toobstruct reaction rates. The reaction rates are intrinsicallyfast in subcritical and supercritical water conditions.[101]Therefore, many processes have been studied under sub-critical and supercritical water conditions such as gasica-tion, oxidation, hydrolysis and extraction.[80,87,95,99]Theproperties of subcritical and supercritical water as interme-diates between the liquid and gas phases are summarized inTable 2.

The gasication process in subcritical and supercrit-ical water is a technique to produce high-energy valuegases including hydrogen or methane from various kinds ofbiodegradable wastes or mixed feedstock such as agricul-tural wastes, crops, municipal wastes,[59,103] sewage,[49,76,104] wastewater from metalworking industries [57] andfood processingwastes such as alcohol distilleries,[57] pulpresidue waste of tofu production[37,105] and bean curdrefuse.[51] Many researchers [77,106,107] have shown thatamong the food classes, carbohydrate-like materials appearto be better suited for hydrothermal conversion to produceH2 gaseous yield. Wastes from the agricultural and foodindustries are composed mainly of carbohydrates that canbe converted to gaseous or liquid fuels via hydrothermalprocessing.[78] Experimental research related to the gasi-cation process under subcritical and supercritical waterconditions for production of energy has started to receiveincreasing attention. Hence, it is a challenge to apply sub-critical and supercritical water gasication as an alternativeenergy conversion technique for hydrogen production fromvarious food wastes.

From the advantages stated previously, supercriticalwater has been widely used as an eective medium. TheISI Web of Knowledge database shown in Figure 7 demon-strates that the number of studies on the application ofsupercritical water with catalysts follows an increasingexponential trend from 2001 to 2012. It is clear thatsupercritical water has attracted much recent interest for

Dow

nloa

ded

by [T

exas

State

Univ

ersity

, San

Marc

os] a

t 21:1

9 02 O

ctobe

r 201

3

8 R. Muangrat

0

20

40

60

80

100

120

140

160

180

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012Year Period

raeyhcae

nis

metIdehsilb

uP

Figure 7. The application tendency of supercritical water con-ditions using catalysts represented by ISI Web of Knowledgedatabase from 2001 to 2012.

a research into the conversion of biomass under hydrother-mal gasication for the production ofH2 and other synthesisgases.

6. Subcritical and supercritical water gasicationused with model compounds, real biomass, foodwastes and wastewater

Many researchers did not start with real biomass or foodwaste consisting of various types of organic material ofdierent compositions but have studied compounds derivedfrom biomass such as glucose, cellulose or fructose.[41,53]

6.1. Model compounds hydrothermal gasicationHao et al. [79] studied supercritical water gasication usingglucose as a model compound to produce hydrogen. Thereactor was a continuous tubular system which used a solu-tion or slurry of materials without drying and was designedfor a temperature and pressure of up to 650C and 35MPa,respectively. The results show that glucose as a model com-pound of biomass formed H2, CO, CH4 and CO2 with asmall amount of C2H4 and C2H6 (based on mass of gasproduct per mass of feed stock). Moreover, temperaturehas an eect on the process of supercritical water gasi-cation. When the temperature increased, the gasicationeciency, hydrogen yield potential, carbon eciency andCO increased while CH4 decreased. The gasication e-ciency was reported to be in excess of 100% when thetemperature was 650C with a pressure of 25MPa, theresident time of approximately 3.6min and a glucose con-centration of 0.1M. This condition produced no char or tar.In addition, increasing the pressure from 25 to 35MPa ata temperature between 500C and 550C had no eect onthe glucose gasication eciency. The hydrogen fraction inthe gas products and the gasication eciency decreasedwhile the CO increased as the glucose concentration in thewater solution increased from 0.1 to 0.8M (temperature650Candpressure 25MPa). Itwas found that extending theresidence time longer than 3.6min did not increase the gasi-cation eciency. The alkali addition of KOH and Na2CO3

inuenced thewater-gas shift reaction; as a result, it reducedthe CO fraction and increased the CO2 fraction in the gasproduct for glucose gasication and sawdust mixed withsodium carboxymethyl cellulose gasication.

Between 2003 and 2007, Kruse and co-workers [77,78,104,108,109] investigated wet biomass conversion usingexperimental conditions of 330410C, 3050MPa and15min of reaction time. The wet biomass called phytomass(CH1.87O0.98N0.02S0.001) was used in the study as baby foodwhich consists mainly of cooked carrots and potatoes. Ahigher temperature led to an increase in the gasication e-ciency resulting in the yields of carbon in the gas productto increase. Kruse and Dinjus [106] studied the hydrother-mal gasication of glucose with added K2CO3 and twobiomass feedstocks in a continuous stirred tank reactor at500C, 30MPa and a varied reaction time. One biomassfeedstock came from plant material, a mixture of carrotsandpotatoes as carbohydrates. Theother contained zoomass(animal constituents) which was a mixture of cooked riceand chicken consisting of proteins and carbohydrates. Theresult showed that most of the gases were formed by free-radical reactions. The gas products of the glucose/K2CO3and the phytomass were similar, while the gas product ofthe zoomass was lower. The gasication of proteins con-tained in the zoomass has unexpected eects such as lowergas yields. A higher concentration of dissolved organiccarbon, oil formation, higher phenol content and a lowerformic acid concentration in the aqueous phase than thatof the glucose/K2CO3 mixture and plant mass. Protein inthe zoomass may be resistant to gas formation. Also, theaddition of K2CO3 decreased CO formation but increasedthe gasication eciency.

Kruse et al. [109] also studied the hydrogen gasicationof (1) glucose; (2) glucose with the addition of KHCO3representing a model system for plant mass and (3) glucosewith the addition of KHCO3 and also amino acid alanineas a model system for zoomass. Alanine in the zoomasshas a similar eect to the protein contained within the realbiomass. From this series of experiments, the protein degra-dation products were seen to react with the carbohydratedegradation products via a Maillard reaction. The reactionproduces free-radical scavengers which inhibit the free-radical chain reactions and suppress the gas formation. Itis likely that the proteins in biomass or alanine in glucosesolution (zoomass) had an eect on the gas yields from thehydrothermal gasication. Protein waste is composed ofmany amino acids or nitrogen atoms which combine withother free radicals to form stable products, as a result ofwhich the gasication reaction is inhibited. Therefore, thereis a limitation for gasication of protein waste.

Resende et al. [110] investigated gasication of cellu-lose in supercritical water by using quartz reactors (metal-free reactors) without catalysts. The eects of temperature,cellulose concentration, water density and reaction time ongas production were studied. The results show that the totalgas yields of H2, CH4, CO and CO2 are lower in quartz

Dow

nloa

ded

by [T

exas

State

Univ

ersity

, San

Marc

os] a

t 21:1

9 02 O

ctobe

r 201

3


reactors than in stainless steel reactors with no added cata-lysts. The signicant gas yields from stainless steel reactorsmay be attributable to heterogeneous reactions catalyzed onthe reactor wall. Moreover, Resende et al. [110] found thathigher temperatures increased the rate of formation of allgases. In addition, the higher H2 was obtained at a longerreaction time, higher water density and higher celluloseloading. Cellulose loading and water density were used tocontrol the product selectivity and have a strong inuenceon the amounts of H2 and CH4 produced.

Williams and Onwudili [111] studied the gasicationof glucose as a biomass model compound under subcriti-cal and supercritical water. The results show that a higherconcentration of oxidant (hydrogen peroxide) decreasedthe amounts of char, oil and water soluble product pro-duced from subcritical and supercritical water gasication.The yield and product composition did not signicantlychange with temperature and pressure. The formation ofcompounds found in the oil product was described bythe reaction mechanism route. Subcritical and supercriticalwater gasication was also investigated in a heated batchreactor of cellulose, starch and glucose set as biomassmodelcompounds and real biomass (cassava waste). In addition,temperature was found to have an eect on the yield of theproduct gases, oil, char and water. The model compoundsand cassavawaste in subcritical and supercriticalwater gasi-cation produced oil, char and the gases carbon dioxide,carbon monoxide, hydrogen, methane and other hydrocar-bons. Cellulose produced higher char, carbon monoxideand hydrocarbons gases (C1C4) than starch and glucose.However, the hydrogen gas converted was the highest forglucose, followedby starch and cellulose, respectively.Cas-sava waste was slightly converted to hydrogen gas but thisconversionwas similar to that found for cellulose. Oils anal-ysed from this study had the same compositions for themodel biomass compounds as the cassava biomass wastebut the concentration of the chemical groups varied.

Sinag et al. [112] studied the hydropyrolysis of glucoseas a model compound of cellulose with a K2CO3 catalystat a temperature of 400C and 500C with a pressure of 30and 50MPa with a reaction time between 1.8 and 16.3min.It was found that increasing temperature leads to higheryields of carbon in the gas phase rather than in the aqueousphase. Above the critical point of water (above 374C and22.1MPa), its density and dielectric constant decrease andas a result the ionic reactions are depressed and free-radicalreaction increases. The increasing radical reactions resultin a higher formation of CH4. Moreover, the alkaline saltsaect the gas yield from the hydropyrolysis of glucose insupercritical water. Adding K2CO3 to glucose leads to alower formation of CO and a higher formation of H2, CO2and CH4 per mole of glucose. An increasing reaction timeresults in an increase of H2 yields.

Watanabe et al. [113] studied batch gasication experi-ments for hydrogen production from cellulose and glucosewith ZrO2 catalyst in supercritical water (400440C and

3035MPa). It was found that the supercritical water gasi-cation with ZrO2 produced a hydrogen yield which wasdoubled in comparison with the absence of ZrO2 in allexperimental conditions. Watanabe et al. [114] used a batchreactor to investigate the eects of the catalysts NaOHand ZrO2 or the partial oxidative supercritical water gasi-cation of n-hexadecane (n-C16) and lignin (40MPa and400C). The results show that the yield of H2 from n-C16and lignin with zirconia was twice that without catalystsunder the same conditions. The H2 gas produced by usingNaOH was four times higher than that without a cata-lyst. In the case of n-C16, NaOH and ZrO2 enhanced thedecomposition of intermediate compounds (aldehyde andketone) into CO. The catalytic eect of NaOH and ZrO2promoted decomposition of the carbonyl compounds andinhibited char formation and enhanced CO and H2 forma-tion. Lee et al. [45] used a tubular ow reactor to gasifyglucose at temperatures between 480C and 750C and ata pressure of approximately 28MPa. With an increasingtemperature over 660C, the level of the hydrogen yieldsignicantly increased. Meanwhile the methane yield wasquite stable at a temperature as high as 700C. For thereaction time of 1015 s, the carbon gasication eciencyobtained was 100%.[45] An increased hydrogen productionwas obtained with an increasing temperature and pressurein further results shown by Demirbas.[115]

Kersten et al. [116] researched the supercritical watergasication of glycerol, glucose and pinewood. They stud-ied the supercritical water gasication without adding cat-alysts. The results found that complete gasication to thegas phase is possible at low concentrations of solution sam-ples (< 2wt%). The addition of Ru/TiO2 gasied glucosesolution by up to 17wt%.

6.2. Real biomass and food wastes hydrothermalgasication

Gasication under subcritical and supercritical water of realbiomass or food wastes to enhance hydrogen production,for instance, the addition of catalysts, has been investi-gated. Okajima et al. [57] used waste biomass (pig sludge,paper sludge, garbage and strained lees of distilled spirits)to investigate the eects of reaction temperature, pres-sure, reaction time, molar ratio of water to carbon in thesebiomass and catalysts on the decomposition eciency ofwaste biomass. Experiments were conducted under super-critical water gasication conditions using batch-type andow-type reactors. The catalysts employed were nickel(Ni-5132P), KOH, NaOH, K2CO3, Na2CO3 and KCl. Thisresearch produced hydrogen yield from these biomass.Hightemperatures, low pressures and high molar ratio of waterto carbon produced high hydrogen gas yields. The optimumconditions were 700C, 10MPa, 20min and a molar ratioof water to carbon equating to approximately 20 produc-ing hydrogen gas of 15002300mL from 1 g of dry wastebiomass. The order of volume of hydrogen gas produced

Dow

nloa

ded

by [T

exas

State

Univ

ersity

, San

Marc

os] a

t 21:1

9 02 O

ctobe

r 201

3

10 R. Muangrat

was distilled spirits, garbage, pig sludge and paper sludge,respectively. In addition, all alkali catalysts had higherpotentiality than nickel catalyst.

Schmieder et al. [76] showed that wet biomass (woodas saw dust, straw) and organic waste (sewage sludgeand lignin) were gasied under hydrothermal conditionsin two tubular ow reactors and in two batch autoclaveswith glucose, catechol and vanillin, and glycine as modelcompounds of carbohydrates, lignin and protein, respec-tively. Moreover, the hydrothermal gasication of thesecompounds investigated the eects of temperature, pres-sure, residence time and the addition of the alkali metalsKOH or K2CO3. The results found that carbohydrates, aro-matic compounds, glycine (amodel compound for proteins)and real biomass completely gasied to a H2-rich prod-uct containing CO2 as the main carbon compound in thepresence of KOH and K2CO3.

Izumizaki et al. [49] researched hydrogen productionunder supercritical water conditions using biomass anddomestic wastes with the addition of ruthenium oxide(RuO2) as a catalyst. This research had a set reaction temper-ature and pressure ranging from 400C to 500C and 30 to50MPa, respectively. It was concluded that the RuO2 addedcould produce hydrogen in the supercritical water gasica-tion of biomass including sewage disposals. Moreover, thehigher reaction temperature promotes a higher hydrogenproduction.

Jarana et al. [117] studied supercritical water gasi-cation of two dierent industrial wastewaters, cutting oilwastes (oleaginous wastewater from metalworking indus-tries), and vinasses and alcohol distillery wastewater. Theseindustrial organic wastes have a high concentration oforganics and have a high-energy potential. The experimentsused hydrogen peroxide and KOH as oxidant and cata-lyst, respectively. The presence of KOH in all experimentsincreased the rate of the water-gas shift reaction leadingto a higher amount of hydrogen. In addition, the increas-ing oxidant concentration resulted in an increased amountof hydrogen produced in the gas phase. The highest yieldof hydrogen, methane and carbon dioxide were obtainedat 550C where the lowest yield for carbon monoxide wasobserved.

Fang et al. [118] investigated the hydrothermal gasi-cation of cellulose and glucose using a catalyst in anoptical micro-reactor (50 nL), an autoclave (120mL) and aow reactor (11.3mL). In the micro-reactor experiments,the Ni catalyst had a low gasication rate, but 96wt%cellulose could be gasied to a 35mol% of H2 in theautoclave. The high gasication rate was attributed to awell-mixed Ni/silicaalumina catalyst and cellulose com-bination during slow heating to 350C for 30min. From themicro-reactor, it was found that cellulose completely dis-solved in water at 318Cduring fast heating, and that Pt wasthe most active catalyst for glucose reactions. Gasicationof glucose with Pt/ -alumina catalyst was investigated inow experiments, and 67wt% glucose was converted to

main gases (CO2, H2 and CH4), with up to 44mol% H2produced at 360C and 30MPa.

In recent years it has been demonstrated that biomassgasication using CO2 sorbent is a promising technique toenhance the hydrogen yield. Lin et al. [119,120] used HyPr-RING (Hydrogen Production by Reaction Integrated NovelGasication)with supercritical water at a temperature rangeof 600700C and pressure between 12 and 105MPa forgenerating hydrogen gas from coals, organic waste, wood,sludge and polyvinyl chloride. This method used calciumhydroxideCa(OH)2 as a sorbent for capturingCO2 and usedsodium hydroxide, NaOH, as the catalyst.

Onwudili and Williams [103] studied the inuence ofsodium hydroxide (NaOH), water density and reaction tem-perature on the hydrothermal gasication of MSW materialin the form of refuse-derived fuel (RDF) including veg-etables and food wastes. Hydrogen gas production fromRDF increased dramatically with an increasing NaOH/C(based on the amount of NaOH and carbon content of RDF)mass ratio up to 0.8 but decreased slightly when the ratiowas increased to 1.2. CO2 and CO concentrations decreasedwith an increasing NaOH/C mass ratio. This indicated thatthe NaOH catalyzed the gasication via the removal ofCO2 as sodium carbonate. Hydrogen production was alsoenhanced with an increasing water density. Moreover, thisresearch compared the hydrothermal gasication of RDFwith biomass model compounds such as glucose, cellu-lose and starch at a temperature of 375C, with a NaOH/Cmass ratio of 0.6 and a water density of 0.15 g cm3. Itwas found that the RDF produced a higher hydrogen yieldthan glucose, cellulose and starch, respectively. In addition,tars produced by glucose, cellulose and starch contained ahigher content of carbon than RDF residues. As a resultglucose, cellulose and starch lost carbon atoms through tarformation which aected the availability of carbon for COproduction and conversion to hydrogen via the water-gasshift reaction.

Okajima et al. [51] also studied hydrogen productionfrom four food wastes: bean curd refuse, strained lees ofdistilled spirits, barley husk of distilled spirits and garbage.Researchwas conducted byusing high pressure superheatedsteamwith the presence of an alkali catalyst.Ahighpressuresuperheated stream condition in this researchwas dened asan experimental regionwhich uses thewater property abovethe critical temperature and below the critical pressure.Hydrogenproductionwas about 1.82.0mmol from1mmolof carbon in the wastes at the experimental conditions of700C, 10MPa, 30min, ratio of water to organic carbonapproximately 20% followed by a 20wt% of potassiumhydroxide to the organic carbon in the waste. Hydrogen gasproduction increased when the temperature and molar ratioof water to carbon atoms increased and pressure decreased.However, a higher temperature suppressed ammonia andtotal organic carbon (TOC) dissolved in water. On theother hand, increasing pressure accelerated the formationof ammonia but decreased insignicantly TOC production.

Dow

nloa

ded

by [T

exas

State

Univ

ersity

, San

Marc

os] a

t 21:1

9 02 O

ctobe

r 201

3


Supercritical water gasication of municipal sludge wascarried out to produce gaseous fuel consisting of H2, CO,CO2 and CH4. Zhang et al. [121] applied partial oxidativesupercritical water gasication of municipal sludge in thepresence of NaOH catalyst. Hydrogen peroxide was usedas the oxygen source. They studied gasication of sludge inthe ranges of 350450C, 2428MPa and a reaction timeof 540min. The results indicated that the NaOH catalystsignicantly aects the gasication by promoting H2 prod-uct via the water-gas shift reaction and inhibiting char andtar formation. The H2 production with NaOH was twicethat without this catalyst. The longer reaction time andhigher temperature are favourable to gaseous yields. Partialoxidation with the proper amount of oxidant added couldimprove gasication eciency with a great yield of H2 andCO produced from the gasied sludge.[121]

In another study, Ishida et al. [37] produced hydro-gen gas from okara, food waste separated from soya beanmilk in the production of tofu. The experimental work usedhydrothermal gasication at 400C with the addition of aninorganic alkali (Na2CO3) and Ni catalyst. The additionof Na2CO3 and Ni catalyst resulted in a high hydrogengas molar yield (mmol) with a decreased molar yield ofCO2 (mmol) being released into the gas phase at a lowtemperature of approximately 400C. Ishida reported thatthe combination of Na2CO3 and Ni catalyst led to thedissolution of CO2 into the liquid layer.[37]

Between 2010 and 2011, Muangrat et al. [2629,122]studied the hydrothermal gasication of organic foodwastes into hydrogen at low temperatures. The main studyinvestigated catalytic and partial oxidative hydrothermalgasication of organic materials as model food waste com-pounds (glucose, glutamic acid and sunower oil) andrepresentative food samples (corn, carrot, bean, beef, may-onnaise, dried mixed food waste, chicken soup, tropicalfruit salad and cat food). The by-products from food pro-cessing such as molasses, rice bran and whey were alsoinvestigated. Further, the inuence of reaction temperature,reaction time, model compounds or food waste concen-tration, oxidant concentration and types of catalysts wereexamined in relation to the yields of gases and other prod-ucts such as solid residues/char, tar/oil and liquid euents.The hydrogen production from various representative foodwastes using hydrothermal gasication has been investi-gated in the presence of NaOH and H2O2. The combinationof NaOH and H2O2 led not only to a high production of H2gas by promoting the water-gas shift reaction with subse-quent CO2 capture, but also led to an inhibition of char andtar/oil formation. Alkaline hydrothermal conditions ini-tially converted organic materials to water soluble productscontaining important intermediate compounds, sodium for-mate and sodium acetate which subsequently decomposedto hydrogen and methane gases. Increasing the concentra-tion of H2O2 could oxidize organic compounds and themain intermediates (organic salts) to form more CO2 gasleading to the reduction of H2 gas production. In general,

hydrogen gas increased with increased temperature andreaction time.With increasing feed concentration, the yieldsof other gases such as CO, CO2, CH4 and C2C4 increased,while the H2 gas production dropped. Comparing hydrogengas yields in relation to various alkali additives, the fol-lowing order was NaOH > KOH > Ca(OH)2 > K2CO3 >Na2CO3 > NaHCO3. Comparison of dierent catalysts forhydrogen production showed that NaOH additivewas supe-rior to Ni/Al2O3 and Ni/SiO2 catalysts. The reactionof NaOH additive with Ni/Al2O3 could form dawsonite(NaAlCO3(OH)2) leading to a reduction of catalytic activ-ity. The dierent chemical structure and compositions ofmodel foodwastes have a signicant eect on hydrogenpro-duction. The hydrogen production from carbohydrate-richwasteswas comparatively higher than that fromprotein- andlipid-rich wastes. The main hydrogen production reactionsfor hydrothermal gasication of food wastes using bothNaOH and H2O2 were investigated in relation to glucoseas a representative carbohydrate waste. The maximum totaleciency of hydrogen production achieved from glucosewas approximately 66.3% of the theoretical yield.

In 2012, Tian et al. [105] studied the conversion of tofuwaste under supercriticalwater below390C in abatch reac-tor. Four experimental parameters including water density,the ratio of tofu towater, reaction time and reaction tempera-ture were investigated. The results showed that CO2 was themajor component of the produced gas, ameasurable amountof H2 was produced above 300C and 6575% or more oftofu waste can be converted into water-soluble fraction. Itwas found that the inuence of the treatment temperatureon tofu waste conversion was the most signicant.

6.3. Wastewater hydrothermal gasicationThe supercritical water gasication process is an attractivetechnique not only for the treatment of wet biomass butalso for liquid euents produced from biomass gasicationplants.[39,123] Di Blasi et al. [123] researched supercriticalwater gasication downstream of an updraft wood gasi-cation plant containing wood tar and compounds of aceticacid, anhydroglucose and 1-hydroxy-2-propanone. Duringthe gasication processes, sugars and complex phenolsare degraded to furfurals and simpler phenols, respec-tively. Some compounds such as acetic acid, propionic acid,1,2-ethanediol, ketone, cresol and phenols were thermallyresistant. Moreover, the gasication of TOC is describedby an irreversible, rst-order, Arrhenius rate reaction withan activation energy of 75.7 22 kJmol1 and a pre-exponential factor of 897 30 s1 at reaction temperaturesof 450548C, residence times of about 60120 s and initialTOC contents of about 715 g L1. From the experiment,it was observed that the yield of gas produced varies fromabout 0.4 to 1 L for each gram of initial TOC content. Themaximumconversion of TOCwas 70%. Itwas similar to theresult of glucose under supercritical water gasication.[45]However, it was not the direct degradation of glucose but it

Dow

nloa

ded

by [T

exas

State

Univ

ersity

, San

Marc

os] a

t 21:1

9 02 O

ctobe

r 201

3

12 R. Muangrat

was attributed to the degradation of the intermediates duringsupercritical water gasication of glucose.

Yan et al. [124] used wastewater containing polyvinylalcohol (PVA) for gasifyingunder supercriticalwater condi-tions in a continuous ow reactor at 450600C, 2036MPaand residence time of 2060 s. The main gaseous productswere H2, CH4, CO and CO2. The eect of pressure wasinsignicant on the gasication eciency. The gasicationeciency was enhanced when temperature and residencetime increased. Lower temperature favoured the produc-tion of H2 and the amount of H2 decreased as a result of theacceleration of methanation reactions with the increase oftemperature. The eects of KOH catalyst on gas productionwere studied, and itwas found thatCOdecreased in the pres-ence of KOH leading to an increase in hydrogen formationvia the water-gas shift reaction. The hydrogen gasicationratio was 126% based on the hydrogen amount in organiccompounds and theTOCgasiedwas approximately 96%at25MPa, 600Cand60 s.The results indicated that supercrit-ical water gasication for hydrogen generationwas possibleto treat wastewater containing PVA.

Waste streams like black liquor from pulp and the paper-making industry were gasied in supercritical water toconvert the waste into value-added fuel products.[125] Theexperiments were conducted using miniature scale cap-illaries as a batch reactor. Parameters such as pressure,temperature, residence time and feed concentration wereinvestigated. Pressure between 220 and 400 atm had aninsignicant inuence on gas production and carbon con-version. The operating temperature and reaction time werecarried out between 375C and 650C and between 5 and120 s, respectively. The results indicated that increasingthe temperature and reaction time signicantly increasedthe gaseous product yields, overall carbon conversion andenergy eciency. The highest conversion to H2, CO,CH4 and C2Hx was obtained at the maximum temper-ature and the longest reaction time. The overall carbonconversion, gas energy content and energy conversionratio obtained were 84.8% (based on the total mass ofcarbon in feed), 9.4MJm3 and 1.2, respectively. Eventhough the higher carbon conversion and energy conver-sion ratio were obtained from dilute black liquor, thegas energy content was lower than that of high solidcontents.[125]

From the literature review, subcritical and supercriti-cal water gasication has possibilities to generate gaseousfuel products such as hydrogen or methane from biomass.Biomass includes the residues or by-products of agricultureor the food industries, especially biomass containing highmoisture content up to 95% or biomass in wastewater eu-ent. The use of wet biomass, food wastes or wastewater viathis process can be not only an alternative renewable andgreen energy but also an environmentally sustainable treat-ment. Energy from such wastes decreases CO2 emissionand reduces consumption of fossil energy. To enhance theprocess improvement in hydrogen gaseous yield, decrease

or inhibition of tar/oil and char formation was investigatedusing catalysts.

7. ConclusionBiomass is expected to be an important energy resourcesince it has several environmental and economical benetsand has potential under a wide range of situations to sub-stantially contribute to fuel and renewable energy demands.Innovations and developments are likely to improve theprospects of biomass energy technologies which are receiv-ing increasing interest. Therefore, the pace of researchand development for the commercialization of biomassenergy technologies and future biomass energy use islikely to increase in the eld of thermochemical conver-sion processes for various biomass types. Food wastes area signicant proportion of the total waste stream and areproduced from dierent sources such as food industriesand municipal sectors. Food wastes have a high mois-ture content consisting of a complex mixture of organicmaterials composed principally of carbohydrates, proteinsand lipids. There are many dierent percentage contentsdepending on the characteristics of each food waste. Oneenergy source that has been described as a future fuel ishydrogen; therefore, conversion of food wastes to hydro-genwould be of value and sustainable as currently hydrogenis produced mainly from fossil fuel sources. Food wastescontaining high moisture content are not suitable for con-ventional thermochemical gasication processes becausethe process capital and operating costs for processing such awet waste will become increasingly expensive. The highermoisture content results in lower heating value and thuscannot be used as a combustion fuel when food wastesare to be gasied by conventional methods. This prob-lem can be avoided by applying hydrothermal gasicationwhich can employ water not only as a solvent but also asa reaction medium. In this review, hydrothermal (subcrit-ical and supercritical water) gasication with or withoutcatalysts has been identied as a possible technique for pro-ducing renewable hydrogen gas. Thus, food wastes havethe potential to provide renewable energy and reduce theenvironmental impact of waste and also promote sustain-able development. Despite the potential of hydrothermalgasication this review has shown that improvements ineciency and environmental performance of conversionsystems and development are needed. Further research isstill required to increase hydrogen gas production and eco-nomic analysis of the hydrothermal gasication process. Inthis review, it has been demonstrated that food wastes havea good potential for the sustainable production of hydrogenas a clean energy of the future via hydrothermal gasication.

AcknowledgementsThe author thanks Professor Paul T. Williams and Dr Jude A.Onwudili of the University of Leeds for providing valuableknowledge and suggestions.

Dow

nloa

ded

by [T

exas

State

Univ

ersity

, San

Marc

os] a

t 21:1

9 02 O

ctobe

r 201

3


References[1] Lawrence KW, Yung-Tse H, Howard HL, Costantine Y.

Waste treatment in the food processing industry. 2nd ed.New York: CRC Press; 2006.

[2] European Commission. Final report preparatory study onfood waste across EU27. Paris: Bio Intelligence Service;2010.

[3] IPCC (Intergovernmental Panel onClimateChange).Wastegeneration, composition and management data, Chapter 2.In: Eggleston S, Buendia L, Miwa K, Ngara T, TanabeK, editors. 2006 IPCC guidelines for national greenhousegas inventories, Volume 5. Hayama, Japan: The Institutefor Global Environmental Strategies (IGES); 2006 [cited2012 Aug 30]. Available from: http://www.ipccnggip.iges.or.jp/public/2006gl/pdf/5_Volume5/V5_2_Ch2_Waste_Data.pdf

[4] Waldron K. Handbook of waste management and co-product recovery in food processing: volume 1. Cambridge:Woodhead Publishing; 2007.

[5] AWARENET. Handbook for the prevention and minimiza-tion of waste and valorization of by-products in Euro-pean agro-food industries; 2004. Available from: http://eea.eionet.europa.eu/Public/irc/envirowindows/awarenet/library?l=/awarenet_handbook&vm=detailed&sb=Title(cited 2012 Aug 30).

[6] Gustavsson J, Cederberg C, Sonesson U, van Otter-dijk R, Meybeck A. Global food losses and foodwaste: extent causes and prevention. Rome: Food andAgriculture Organization (FAO) of the United Nations;2011.

[7] FAO-Food and Agriculture Organization. Global foodlosses and food waste extent, causes and prevention.Rome: Food and Agriculture Organization; 2011.

[8] Mahro B, Timm M. Potential of biowaste from the foodindustry as a biomass resource. Eng Life Sci. 2007;7:457468.

[9] Gustavsson J, Cederberg C, Sonesson U, van OtterdijkR, Meybeck A. SIK/FAO. Global food losses and foodwaste: extent, causes and prevention. Study conducted bythe Swedish Institute for Food and Biotechnology (SIK)and FAO at the International Congress Safe Food atInterpack 2011, Dsseldorf, Germany. Gothenburg; 2011[cited 2012 Aug 30]. Available from: http://www.fao.org/leadmin/user_upload/ags/publications/GFL_web.pdf

[10] Eurostat Data Explore. In: Eurostat European Commis-sion [cited2012Sep17].Available from:http://epp.eurostat.ec.europa.eu/portal/page/portal/statistics/search_database

[11] Tanaka M, Ozaki H, Ando A, Kambara S, MoritomiH. Basic characteristics of food waste and food ashon steam gasication. Ind Eng Chem Res. 2008;47:24142419.

[12] Kapdan IK, Kargi F. Bio-hydrogen production fromwaste materials. Enzyme Microb Technol. 2006;38:569582.

[13] Salhofer S, Obersteiner G, Schneider F, Lebersorger S.Potentials for the prevention of municipal solid waste.Waste Manag. 2008;28:245259.

[14] EuropeanCommission. IntegratedPollutionPrevention andControl. Reference document on best avail-able techniquesin the food, drink and milk industries. Seville, ES: WITPress; 2006.

[15] RussW,Meyer-PittroR.Utilizingwaste products from thefood production and processing industries. Crit Rev FoodSci. 2004;44:5762.

[16] Diggelman C, Ham RK. Household food waste to wastew-ater or to solid waste? That is the question. Waste ManagRes. 2003;21:501514.

[17] Tchobanoglous G, Theisen H, Vigil SA. Integrated solidwaste management: engineering principles and manage-ment issues. New York: McGraw-Hill, Inc.; 1993.

[18] Chang JI, Hsu TE. Eects of compositions on food wastecomposting. Bioresour Technol. 2008;99:80688074.

[19] Ding HB, Liu XY, Stabnikova O, Wang JY. Eect of pro-tein on biohydrogen production from starch of food waste.Water Sci Technol. 2008;57:10311036.

[20] RussW.Waste as a renewable energy resource in renewableenergy resource. Workshop in the Sixth Framework Pro-gram Integrated European Network for Biomass Co-ringNETBIOCOF (Timisoara (Romania), 2006 June 1517),Timisoara (Romania); 2006.

[21] Chu CF, Li YY, Xu KQ, Ebie Y, Inamori Y, Kong HN. ApH- and temperature-phased two-stage process for hydro-gen and methane production from food waste. Int J HydrogEnergy 2008;33:47394746.

[22] Quitain AT, Faisal M, Kang K, Daimon H, Fujie K.Low-molecular-weight carboxylic acids produced fromhydrothermal treatment of organic wastes. J Hazard Mater.2002;93:209220.

[23] OreopoulouV,RussW.Utilization of by-products and treat-ment of waste in the food industry. New York: Springer;2007.

[24] Blumenthal K. Generation and treatment of municipalwaste. In Eurostat European Commission; 2011 [cited2012Aug30].Available from:http://epp.eurostat.ec.europa.eu/cache/ITY_OFFPUB/KS-SF-11-031/EN/KS-SF-11-031-EN.pdf

[25] Kim MH, Song HB, Song Y, Jeong IT, Kim JW. Evaluationof food waste disposal options in terms of global warm-ing and energy recovery. Korea Int J Energy Environ Eng.2013;4(1):112.

[26] Muangrat R, Onwudili JA, Williams PT. Reaction prod-ucts from the subcritical water gasication of food wastesand glucose with NaOH and H2O2. Bioresour Technol.2010;101:68126821.

[27] Muangrat R, Onwudili JA, Williams PT. Inuence of alkalicatalysts on the production of hydrogen-rich gas from thehydrothermal gasication of food processing waste. ApplCatal B. 2010;100:440449.

[28] Muangrat R, Onwudili JA, Williams PT. Alkaline sub-critical water gasication of dairy industry waste (Whey).Bioresour Technol. 2011;102:63316335.

[29] Muangrat R, Onwudili JA, Williams PT. Reactions ofdierent food classes during subcritical water gasica-tion for hydrogen gas production. Int J Hydrog Energy.2012;37:22482259.

[30] He W, Li G, Kong L, H.Wang, Huang J, Xu J. Applicationof hydrothermal reaction in resource recovery of organicwaste. Resour Conserv Recycl. 2008;52:691699.

[31] JS Van Dyk, Gama R, Morrison D, Swart S, Pletschke BI.Food processing waste: problems, current management andprospects for utilization of the lignocellulose componentthrough enzyme synergistic degradation. Renew SustainEnergy Rev. 2013;26:521531.

[32] Demirbas A. Sub- and super-critical water depolymeriza-tion of biomass. Energy Sources Part A. 2010;32:11001110.

[33] Zhang Y. Chapter 10, hydrothermal liquefaction to con-vert biomass into crude oil. In: Blaschek HP, Ezeji TC,Scheran J, editors. Biofuels from agricultural wastes andbyproducts. Iowa: Blackwell Publishing; 2010. p. 201232.ISBN: 978-0-813-80252-7.

[34] Menon V, Rao M. Trends in bioconversion of lignocellu-lose: biofuels, platform chemicals and biorenery concept.Prog Energy Combust. 2012;38:522550.

Dow

nloa

ded

by [T

exas

State

Univ

ersity

, San

Marc

os] a

t 21:1

9 02 O

ctobe

r 201

3

14 R. Muangrat

[35] Wang L, Food processing wastes and utilizations, energyeciency and management in food processing facilities.London: CRC Press, Taylor & Francis Group, LLC; 2009.

[36] McKendry P. Energy production from biomass (part2): conversion technologies. Bioresour Technol. 2002;83:4754.

[37] Ishida Y, Kumabe K, Hata K, Tanifuji K, Hasegawa T,Kitagawa K, Isu N, Funahashi Y, Asai T. Selective hydro-gen generation from real biomass through hydrothermalreaction at relatively low temperatures. Biomass Bioenerg.2009;33:813.

[38] Kong L, Li G, Zhang B, He W, Wang H. Hydrogen pro-duction from biomass wastes by hydrothermal gasication.Energy Sources Part A 2008;30:11661178.

[39] Sawai O, Nunoura T, Yamamoto K. Application of sub-critical water liquefaction as pretreatment for supercriticalwater gasication system in domestic wastewater treatmentplant. J Supercrit Fluid. 2013;77:2532.

[40] Kruse A. Hydrothermal biomass gasication. J SupercritFluid. 2009;47:391399.

[41] Snag A, Kruse A, Maniam P. Hydrothermal conversion ofbiomass and dierent model compounds. J Supercrit Fluid.2012;71:8085.

[42] Swami SM, Chaudhari V, Kim DS, Sim SJ, Abraham MA.Production of hydrogen from glucose as a biomass simu-lant: integrated biological and thermochemical approach.Ind Eng Chem Res. 2008;47:36453651.

[43] Antal MJ, Allen SG, Schulman D, Xu XD, Divilio RJ.Biomass gasication in supercritical water. Ind Eng ChemRes. 2000;39:40404053.

[44] Calzavara Y, Joussot-Dubien C, Boissonnet G, Sarrade S.Evaluation of biomass gasication in supercritical waterprocess for hydrogen production. Energy Convers Manage.2005;46:615631.

[45] Lee IG, Kim MS, Ihm SK. Gasication of glucose in super-critical water. Ind Eng Chem Res. 2002;41:11821188.

[46] Lu YJ, Guo LJ, Ji CM, Zhang XM, Hao XH, Yan QH.Hydrogen production by biomass gasication in super-critical water: a parametric study. Int J Hydrog Energy.2006;31:822831.

[47] Matsumura Y, Minowa T, Potic B, Kersten SRA, PrinsW, van Swaaij WPM, van de Beld B, Elliott DC, Neuen-schwander GG, Kruse A, Antal MJ. Biomass gasicationin near- and super-critical water: status and prospects.Biomass Bioenerg. 2005;29:269292.

[48] Tang HQ, Kitagawa K. Supercritical water gasication ofbiomass: thermodynamic analysis with direct Gibbs freeenergy minimization. Chem Eng J. 2005;106:261267.

[49] Izumizaki Y, Park KC, Yamamura T, Tomiyasu H, Goda B,Fujii Y. Exothermic hydrogen production system in super-critical water from biomass and usual domestic wasteswith an exploitation of RuO2 catalyst. Prog Nucl Energy.2008;50:438442.

[50] YanQH,GuoLJ,LuYJ.Thermodynamic analysis of hydro-gen production from biomass gasication in supercriticalwater. Energy Convers Manage. 2006;47:15151528.

[51] Okajima I, Shimoyama D, Sako T. Gasication and hydro-gen production from food wastes using high pressuresuperheated steam in the presence of alkali catalyst. J ChemEng Jpn. 2007;40:356364.

[52] Lu YJ, Li S, Guo LJ, Zhang XM. Hydrogen production bybiomass gasication in supercritical water over Ni/gammaAl2O3 and Ni/CeO2-gamma Al2O3 catalysts. Int J HydrogEnergy. 2010;35:71617168.

[53] Elliott DC. Catalytic hydrothermal gasication of biomass.Biofuels Bioprod Bioren. 2008;2:254265.

[54] Toonssen R, Aravind PV, Smit G, Woudstra N, VerkooijenAHM. System study on hydrothermal gasication com-bined with a hybrid solid oxide fuel cell gas turbine. FuelCell. 2010;10:643653.

[55] Guo Y, Wang SZ, Xu DH, Gong YM, Ma HH, TangXY. Review of catalytic supercritical water gasication forhydrogen production from biomass. Renew Sustain EnergyRev. 2010;14:334343.

[56] Williams PT, Onwudili JA. Subcritical and supercriticalwater gasication of cellulose, starch, glucose, and biomasswaste. Energy Fuel. 2006;20:12591265.

[57] Okajima I, Shimoyama D, Sako T. Gasication and hydro-gen production from waste biomass with supercriticalwater. Proceeding of 10th the Asian Pacic Confer-ence of Chemical Engineering Congress, A-270; 2004;Kitakyushu, Japan.

[58] Kruse A. Supercritical water gasication. Biofuels BioprodBioren. 2008;2:415437.

[59] Peterson AA, Vogel F, Lachance RP, Froling M, AntalMJ, Tester JW. Thermochemical biofuel production inhydrothermal media: a review of sub- and supercrit-ical water technologies. Energy Environ Sci. 2008;1:3265.

[60] Antal MJ, Manarungson S, Mok WS. Hydrogen produc-tion by steam reforming glucose in supercritical water.In: Bridgwater AV, editor. Advances in thermochemi-cal biomass conversion. London: Blackie Academic &Professional; 1994. p. 13671377.

[61] Yu DH, Aihara M, Antal MJ. Hydrogen-production bysteam reforming glucose in supercritical water. EnergyFuel. 1993;7: 574577.

[62] Antal MJ, Matsumura Y, Xu XD, Stenberg J, Lipnik P.Catalytic gasication of wet biomass in supercritical water.Prepr Pap - Am Chem, Div Fuel Chem. 1995;40(2):304307.

[63] Xu XD, Matsumura Y, Stenberg J, Antal MJ. Carbon-catalyzed gasication of organic feedstocks in supercriticalwater. Ind Eng Chem Res. 1996;35:25222530.

[64] Xu XD, Antal MJ. Gasication of sewage sludge and otherbiomass for hydrogen production in supercritical water.Environ Prog. 1998;17:215220.

[65] Elliott DC, Sealock LJ. Chemical processing in high-pressure aqueous environments: low-temperature catalyticgasication. Chem Eng Res Des. 1996;74:563566.

[66] Sealock LJ, Elliott DC, Baker EG, Butner RS. Chemical-processing in high-pressure aqueous environments. 1.Historical-perspective and continuing developments. IndEng Chem Res. 1993;32:15351541.

[67] Elliott DC, Butner RS, Sealock LJ, Jr. Low-temperaturegasication of high-moisture biomass. In: Bridgwater AV,Kuester JL, editors. Research in thermochemical biomassconversion. Barking. England: Elsevier Science Publishers,Ltd.; 1988. p. 696710.

[68] Elliott DC, Neuenschwander GG, Hart TR, Butner RS,Zacher AH, Engelhard MH, Young JS, McCready DE.Chemical processing in high-pressure aqueous environ-ments. 7. Process development for catalytic gasication ofwet biomass feedstocks. IndEngChemRes. 2004;43:19992004.

[69] Elliott DC, Sealock LJ, Baker EG. Chemical-processingin high-pressure aqueous environments. 3. Batch reactorprocess-development experiments for organics destruction.Ind Eng Chem Res. 1994;33:558565.

[70] Elliott DC, Phelps MR, Sealock LJ, Baker EG. Chemical-processing in high-pressure aqueous environments .4.Continuous-ow reactor process-development experiments

Dow

nloa

ded

by [T

exas

State

Univ

ersity

, San

Marc

os] a

t 21:1

9 02 O

ctobe

r 201

3


for organics destruction. Ind Eng Chem Res. 1994;33:566574.

[71] Minowa T, Ogi T. Hydrogen production from celluloseusing a reduced nickel catalyst. Catal Today. 1998;45:411416.

[72] Minowa T, Fang Z, Ogi T, Varhegyi G. Decomposi-tion of cellulose and glucose in hot-compressed waterunder catalyst-free conditions. J Chem Eng Jpn. 1998;31:131134.

[73] Minowa T, Zhen F, Ogi T. Cellulose decomposition in hot-compressed water with alkali or nickel catalyst. J SupercritFluid. 1998;13:253259.

[74] Usui Y, Minowa T, Inoue S, Ogi T. Selective hydrogenproduction from cellulose at low temperature catalyzedby supported group 10 metal. Chem Lett. 2000;10:11661167.

[75] Minowa T, Fang Z. Hydrogen production from cellulose inhot compressed water using reduced nickel catalyst: prod-uct distribution at dierent reaction temperatures. J ChemEng Jpn. 1998;31:488491.

[76] Schmieder H, Abeln J, Boukis N, Dinjus E, Kruse A, KluthM, Petrich G, Sadri E, Schacht M. Hydrothermal gasi-cation of biomass and organic wastes. J Supercrit Fluid.2000;17:145153.

[77] Kruse A, Henningsen T, Sinag A, Pfeier J. Biomass gasi-cation in supercritical water: inuence of the dry mattercontent and the formation of phenols. Ind Eng Chem Res.2003;42:37113717.

[78] Kruse A, Gawlik A. Biomass conversion in water at 330410Cand 3050MPa. Identication of key compounds forindicating dierent chemical reaction pathways. Ind EngChem Res. 2003;42:267279.

[79] Hao XH, Guo LJ, Mao X, Zhang XM, Chen XJ. Hydro-gen production from glucose used as a model compound ofbiomass gasied in supercriticalwater. Int JHydrogEnergy.2003;28:5564.

[80] GalkinAA, LuninVV.Water in sub- and supercritical statesas a universal medium for chemical reactions. Usp Khim.2005;74:2440.

[81] Lindstrom UM, Organic Reactions in water: principles,strategies and applications. Oxford: Blackwell Publishing;2007.

[82] Adams DJ, Dyson PJ, Tavener SJ. Chemistry in alternativereaction media. Chichester: John Wiley & Sons; 2004.

[83] Krammer P, Vogel H. Hydrolysis of esters in subcritical andsupercritical water. J Supercrit Fluid. 2000;16:189206.

[84] Alenezi R, Leeke GA, Santos RCD, Khan AR. Hydrolysiskinetics of sunower oil under subcritical water conditions.Chem Eng Res Des. 2009;87:867873.

[85] Anslyn EV, Dougherty DA. Modern physical organicchemistry. Sausalito, CA: University Science Books; 2005.

[86] Akiya N, Savage PE. Roles of water for chemical reactionsin high-temperature water. Chem Rev. 2002;102:27252750.

[87] Kruse A, Dinjus E. Hot compressed water as reactionmedium and reactant properties and synthesis reactions.J Supercrit Fluid. 2007;39:362380.

[88] Zhu G, Zhu X, Fan Q, Wan X. Recovery of biomass wastesby hydrolysis in sub-critical water. Resour Conserv Recycl.2011;55:409416.

[89] Cliord T. Fundamentals of supercritical uids. New York:Oxford University Press; 1998.

[90] Basu P, Mettanant V. Biomass gasication in supercriticalwater a review. Int J Chem React Eng. 2009;7:161.

[91] Khedr AA, Selim IZ, El-Sobki KM, Shehata OS. Corrosionbehaviour of stainless steel in acidic water-organic solventmixtures. J Mater Sci Technol. 1994;10:411417

[92] Kim WJ, Kim J, Veriansyah B, Kim JD, Lee YW, OhSG,TjandrawinataRR. Extraction of bioactive componentsfrom Centella asiatica using subcritical water. J SupercritFluid. 2009;48:211216.

[93] Heimbuch JA, Wilhelmi AR. Wet air oxidation a treat-mentmeans for aqueous hazardous-waste streams. JHazardMater. 1985;12:187200.

[94] Dietrich MJ, Randall TL, Canney PJ. Wet air oxida-tion of hazardous organics in wastewater. Environ Prog.1985;4:171177.

[95] Loppinet-Serani A, Aymonier C, Cansell F. Supercriticalwater for environmental technologies. J Chem TechnolBiotechnol. 2010;85:583589.

[96] Franck EU. Thermophysical properties of supercritical u-ids with special consideration of aqueous systems. FluidPhase Equilib. 1983;10:211222.

[97] Arai K, Adschiri T, Watanabe M. Hydrogenation of hydro-carbons through partial oxidation in supercritical water. IndEng Chem Res. 2000;39:46974701.

[98] KrajncM,Levec J. The role of catalyst in supercriticalwateroxidation of acetic acid. Appl Catal B. 1997;13:93103.

[99] Brunner G. Near critical and supercritical water. Part Ihydrolytic and hydrothermal processes. J Supercrit Fluid.2009;47:373381.

[100] Okajima I, Sako T. Energy conversion of biomasswith supercritical and subcritical water using large-scale plants. J Biosci Bioeng. 2013:19. Available from:http://dx.doi.org/10.1016/j.jbiosc.2013.06.010

[101] Savage PE. Organic chemical reactions in supercriticalwater. Chem Rev. 1999;99:603621.

[102] Yu Y, Lou X, Wu HW. Some recent advances in hydrolysisof biomass in hot-compressed, water and its comparisonswith other hydrolysis methods. Energy Fuel. 2008;22:4660.

[103] Onwudili JA, Williams PT. Hydrothermal catalyticgasication of municipal solid waste. Energy Fuel.2007;21:36763683.

[104] Fiori L, Valbusa M, Castello D. Supercritical water gasi-cation of biomass for H2 production: process design.Bioresour Technol. 2012;121:139147.

[105] Tian Y, Kumabe K, Matsumoto K, Takeuchi H, Xie Y,Hasegawa T. Hydrolysis behavior of tofu waste in hotcompressed water. Biomass Bioenerg. 2012;39:112119.

[106] Kruse A, Dinjus E. Inuence of salts during hydrothermalbiomass gasication: the role of the catalysed water-gasshift reaction. Z Phys Chem. 2005;219:341366.

[107] Onwudili JA, Williams PT. Hydrothermal reforming ofbio-diesel plant waste: products distribution and charac-terization. Fuel. 2010;89:501509.

[108] Kruse A, Krupka A, Schwarzkopf V, Gamard C, Hen-ningsen T. Inuence of proteins on the hydrothermal gasi-cation and liquefaction of biomass. 1. Comparison ofdierent feedstocks. Ind Eng Chem Res. 2005;44:30133020.

[109] Kruse A, Maniam P, Spieler F. Inuence of proteins on thehydrothermal gasication and liquefaction of biomass. 2.Model compounds. Ind Eng Chem Res. 2007;46:8796.

[110] Resende FLP, Ne ME, Savage PE. Noncatalytic gasi-cation of cellulose in supercritical water. Energy Fuel.2007;21:36373643.

[111] Williams PT, Onwudili JA. Composition of productsfrom the supercritical water gasication of glucose: amodel biomass compound. Ind Eng Chem Res. 2005;44:87398749.

[112] Sinag A, Kruse A, Schwarzkopf V. Key compounds of thehydropyrolysis of glucose in supercritical water in the pres-ence of K2CO3. Ind Eng Chem Res. 2003;42:35163521.

Dow

nloa

ded

by [T

exas

State

Univ

ersity

, San

Marc

os] a

t 21:1

9 02 O

ctobe

r 201

3

16 R. Muangrat

[113] Watanabe M, Inomata H, Arai K. Catalytic hydrogengeneration from biomass (glucose and cellulose) withZrO2 in supercritical water. Biomass Bioenerg. 2002;22:405410.

[114] Watanabe M, Inomata H, Osada M, Sato T, Adschiri T, AraiK. Catalytic eects of NaOH and ZrO2 for partial oxida-tive gasication of n-hexadecane and lignin in supercriticalwater. Fuel. 2003;82:545552.

[115] Demirbas A. Hydrogen-rich gas from fruit shells viasupercritical water extraction. Int J Hydrog Energy.2004;29:12371243.

[116] Kersten SRA, Potic B, Prins W, van Swaaij WPM. Gasi-cation of model compounds and wood in hot compressedwater. Ind Eng Chem Res. 2006;45:41694177.

[117] Jarana MBG, Saanchez-Oneto J, Portela JR, Sanz EN,de la Ossa EJM. Supercritical water gasication ofindustrial organic wastes. J Supercrit Fluid. 2008;46:329334.

[118] Fang Z, Minowa T, Fang C, Smith RL, Inomata H,Kozinski JA. Catalytic hydrothermal gasication of cel-lulose and glucose. Int J Hydrog Energy. 2008;33:981990.

[119] Lin S, Suzuki Y, Hatano H, Oya M, Harada M. Inno-vative hydrogen production by reaction integrated novelgasication process (HyPr-RING). J S Afr Inst Min Metall.2001;101:5359.

[120] Lin SY, Suzuki Y, Hatano H, Harada M. Hydrogen pro-duction from hydrocarbon by integration of water-carbonreaction and carbondioxide removal (HyPr-RINGmethod).Energy Fuels. 2001;15:339343.

[121] Zhang QM, Wang SZ, Wang L, Xu DH. Catalytic hydro-gen production frommunicipal sludge in supercriticalwaterwith partial oxidation. In International conference on powerengineering (ICOPE-2007), challenges of power engi-neering and environment. Oct 2327; Hangzhou, China:Springer; 2007. p. 12521255.

[122] The National Institute of Advanced Industrial Science andTechnology (AIST). Mechanism of peculiar chemical reac-tions in supercritical water claried; 2004 [cited 2012Aug 30]. Available from: http://www.aist.go.jp/aist_e/latest_research/2004/20040520/20040520.html

[123] Di Blasi C, Branca C, Galgano A, Meier D, Brodzin-ski I, Malmros O. Supercritical gasication of wastewaterfrom updraft wood gasiers. Biomass Bioenerg. 2007;31:802811.

[124] Yan B, Wei CH, Hu CS, Xie C, Wu JZ. Hydrogen gener-ation from polyvinyl alcohol-contaminated wastewater bya process of supercritical water gasication. J Environ Sci.2007;19:14241429.

[125] Sricharoenchaikul V. Assessment of black liquor gasica-tion in supercritical water. Bioresour Technol. 2009;100:638643.

Dow

nloa

ded

by [T

exas

State

Univ

ersity

, San

Marc

os] a

t 21:1

9 02 O

ctobe

r 201

3

IntroductionPrincipal contents of food wastesGeneral methods for the reuse of food wastesEnergy recovery methods for food processing and effluentsProperties of subcritical and supercritical waterSubcritical and supercritical water gasification used with model compounds, real biomass, food wastes and wastewaterModel compounds hydrothermal gasificationReal biomass and food wastes hydrothermal gasificationWastewater hydrothermal gasification

ConclusionAcknowledgementsReferences

a review: utilization of food wastes for hydrogen production under hydrothermal gasification

Documents