Research ArticleCarbon-Based Catalyst from Pyrolysis of Waste Tire for CatalyticEthanol Dehydration to Ethylene and Diethyl Ether

Ekrachan Chaichana,1 Weeraphat Wiwatthanodom,2 and Bunjerd Jongsomjit 2

1Research Center of Natural Materials and Products, Chemistry Program, Faculty of Science and Technology,Nakhon Pathom Rajabhat University, Muang, Nakhon Pathom 73000, %ailand2Center of Excellence on Catalysis and Catalytic Reaction Engineering, Department of Chemical Engineering,Faculty of Engineering, Chulalongkorn University, Bangkok 10330, %ailand

Correspondence should be addressed to Bunjerd Jongsomjit; bunjerd.j@chula.ac.th

Received 12 November 2018; Revised 1 January 2019; Accepted 8 January 2019; Published 5 February 2019

Guest Editor: Hu Li

Copyright © 2019 Ekrachan Chaichana et al. *is is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work isproperly cited.

*is work investigated the use of waste tire as a source of carbon in preparation of carbon-based catalysts for applying inethanol dehydration. *e pyrolysis of waste tire was performed to obtain the solid carbon, and then it was treated with twodifferent acids including HCl and HNO3 prior to the activation process with different temperatures to gain suitable carboncatalysts. All carbon catalysts were characterized using nitrogen physisorption, XRD, FTIR, and acid-base titration. *ecatalysts were tested for catalytic ethanol dehydration in a micropacked-bed reactor under the temperature range from 200°C to400°C. It revealed that the ethanol conversion increased with increasing the reaction temperature for all catalysts. *e carboncatalyst treated with HCl and calcined at 420°C (AC_H420) exhibited the highest ethanol conversion of 36.2% at 400°C havingethylene and diethyl ether selectivity of 65.9 and 33.5%, respectively. *e high activity of this catalyst can be attributed to thehigh acid density at the surface (18.5 μmol/m2), which was significantly higher than those of most other catalysts (lessthan 8.0 μmol/m2).

1. Introduction

It has been reported that global tire manufacturing output isestimated to be over 17 million tons in 2016 and is growingnearly by 4% per year through 2022 [1]. *is leads to largeamounts of waste tires produced annually. A commonway fordisposal of these waste tires is land filling. However, due totheir large volume and high void space (about 75%), theyconsume a considerable amount of space if directly dumpedinto landfill [2]. Burning waste tires also release variousharmful gases such as CO2 and CO, and volatile organiccompounds such as benzene, styrene, butadiene, and phenol-like substances [3].

One of the most interesting and dynamically developingmethods for reducing waste tires is a pyrolysis process [4].*e pyrolysis process is not only the waste disposal, but alsoproduces alternative fuel for internal combustion engines.In addition, the pyrolysis is nontoxic without emission of

harmful gas, unlike incineration [5]. *e proportions ofpyrolysis products including gas, oil, and solid carbon de-pend on the rate of temperature rise, time of decomposition,temperature, and pressure [6].

In general, flash pyrolysis process (heating rate around100°C/s to 10,000°C/s) produces 45–75wt% of liquid, 15–25wt% of solid, and 10–20wt% of noncondensable gases [7].*e obtained pyrolysis gas and liquid can be efficiently usedas fuel. In general, the pyrolysis liquid has an average heatingvalue of 12MJ/kg and the pyrolysis gas has an averageheating value of 23–26.3MJ/kg. For the obtained pyrolysissolid (solid carbon), it can be used to produce low-gradecarbon black, and also adsorbent materials after applying anactivation step (known as activated carbon, AC) [8]. *us,the use of solid carbon from waste tire as a catalyst or acatalyst support is also an alternative way for valorization ofwaste tires. Sanchez-Olmos et al. [9] prepared a new acidcatalyst based from a solid carbon from waste tire pyrolysis.

HindawiInternational Journal of Chemical EngineeringVolume 2019, Article ID 4102646, 10 pageshttps://doi.org/10.1155/2019/4102646

*e solid carbon was functionalized using sulfuric acid assource of −SO3H acid groups prior using in biodieselproduction. It was found that this catalyst exhibited a highcatalytic performance, which required shorter times, lowtemperature, and significantly a low amount of methanolcompared to other studies for the biodiesel production.Hood et al. [10] compared waste tire-derived carbons pre-pared using two different methods including the treatmentwith concentrated sulfuric and a newly developed methodinvolving the sequential treatment with L-cysteine, dithio-threitol, and H2O2 under mild conditions.*e catalysts wereapplied for the waste to biofuel conversion. It was found thatboth catalysts could also effectively convert oleic acid or amixture of fatty acids and soybean oil to usable biofuels.

In addition, one of the interesting reactions in whichcarbon-based catalyst from pyrolysis could be employed iscatalytic ethanol dehydration that converts ethanol intoethylene and diethyl ether (DEE) [11–14]. *is reactionundergoes via suitable solid acid catalysts. Ethylene is oneof the most usable upstream chemicals, while DEE ismostly used as a solvent in chemical processes includingfragrance and pharmaceutical processes. However, only afew research works studied in the catalytic ethanol de-hydration with using the carbon-based catalyst. Bedia et al.[15] used acid carbon catalyst derived from olive stoneactivated with phosphoric acid (H3PO4) for catalytic de-composition of ethanol, which yields mainly dehydrationproducts, mostly ethylene with lower amounts of diethylether. It was also found that characteristic of the carboncatalyst such as surface functional groups significantlyaffected the catalytic activity during the reactions. *ementioned characteristics varied with the activationtemperature and the chemical concentration in impreg-nation step. *erefore, adjusting conditions in preparationprocesses of carbon catalyst can tailor the reaction andobtain the desired products.

Hence, in this study, waste tires were used to preparecarbon-based catalysts via pyrolysis with various conditionsincluding activation temperatures and types of treatmentacid (HCl and H2SO4). All prepared carbons were thenactivated with H3PO4 prior to sulfonating with H2SO4 toobtain the acidic carbon-based catalysts for ethanol de-hydration to ethylene and diethyl ether. *e carbon catalystswere characterized with different techniques such as N2physisorption, acid-based titration, Fourier transform in-frared spectroscopy (FTIR), and X-ray diffraction (XRD).*e catalysts were then tested in the gas-phase ethanoldehydration under a reaction temperature of 200°C to 400°C.*e catalytic performance for all catalysts in terms of cat-alytic activity and product selectivity was determined andfurther discussed.

2. Materials and Methods

2.1. Materials. Waste tires were obtained from the localsupplier in Bangkok, *ailand. Hydrochloric acid (HCl),nitric acid (HNO3), and phosphoric acid (H3PO4) werepurchased from QReC, New Zealand. *e proximateanalysis of waste tire is shown in Table 1.

2.2. Pyrolysis of Waste Tire. Waste tires were washed, dried,and cut into pieces. *ey were then pyrolyzed at 400°C innitrogen with a heating rate of 10°C/min and held at thattemperature for 1 h. Products from pyrolysis included threephases: liquid (bio-oil), solid (carbon), and gas. In this study,only solid carbon was further investigated.

2.3. Preparation of CarbonCatalyst. At first, waste tires werepyrolyzed at 420°C in 0.5 batch reactor with N2 flowing at50mL/min. *e pyrolysis process was conducted as illus-trated in Scheme 1.

All solid material from the pyrolysis of waste tires knownas solid carbon was brought into a magnetic separator toremove the tire wire. After that, the carbon was treated with3M hydrochloric (HCl) or nitric acid (HNO3) at 125°C for1 h, neutralized with water, and dried.*e activation processwas carried out with 1M phosphoric acid (1 : 2 w/v) at threedifferent temperatures including 420, 520, and 620°C for 3 hin a vacuum oven.

Six carbon catalysts are donated as follows:

AC XY, (1)

where X refers to hydrochloric (H) or nitric acid (N)treatment and Y is the activation temperatures. For instance,AC_H420 refers to the catalyst obtained using hydrochloricacid, activated at 420°C.

2.4. Sulfonating of Catalyst. *e prepared carbon catalystwas mixed with sulfuric acid (98 %) in the ratio of 1 g carbonper 1mL acid. *e mixture was stirred at 125°C for 20 h. *eobtained catalyst was washed with water until it becomeneutral, and then dried at 125°C for 6 h.

2.5. Characterization of Carbon Catalyst

2.5.1. Nitrogen Physisorption. *e surface area and porecharacteristics of all catalysts were determined by the ni-trogen physisorption technique using Micromeritics ASAP2020 surface area and porosity analyzer. *e catalyst samplewas thermally heated at 150°C for 1 h before nitrogen ad-sorption at the temperature of −196°C.

2.5.2. Iodine Adsorption Test. *e adsorption of iodine wasdetermined using 0.5N standardized iodine solution andconducted according to ASTM D1510 [16].

2.5.3. X-Ray Diffraction (XRD). XRD was used to determinethe bulk crystalline phases of all catalysts using a SIEMENS

Table 1: Proximate analysis of waste tires.

Item Value (%)Moisture 2.81Volatile matter 1.86Ash 15.42Fixed carbon 79.91

2 International Journal of Chemical Engineering

D5000 X-ray di�ractometer with CuKα radiation through anNi �lter in the 2θ range of 20° to 80° [17].

2.5.4. Acidity Determination. 0.1 g of catalyst was soaked in60ml of 0.08M sodium hydroxide (NaOH) for 24 h at roomtemperature. A few drops of phenolphthalein were addedinto the mixture, and then titrated with 0.02MHCl until theequivalent point was reached.

2.5.5. Scanning Electron Microscopy (SEM). �e morphol-ogy of the catalysts was investigated with using JEOL JSM-35F scanning electron microscope (SEM). �e sample wasconductive to prevent charging by coating with gold particleby ion 45 sputtering device.

2.5.6. Fourier Transform Infrared Spectroscopy (FTIR).�e functional groups of the catalysts were determined by aNicolet 6700 FTIR spectrometer. �e infrared spectra wererecorded under the wavenumber scanning from 400 to4,000 cm−1 with a scanning frequency of 64 times.

2.6. Reaction Study. �e ethanol dehydration process wasconducted in a �xed-bed continuous �ow reactor with0.7 cm inside diameter. First, 0.01 g of quartz wool and 0.05 gof catalyst were packed into the middle of reactor. �eprocess began with pretreating the catalyst with argon(50ml/min) at 200°C for 1 h under atmospheric pressure(WHSV� 8.4 h−1). �e reaction was carried out in thetemperature range from 200°C to 400°C. �e obtainedproducts were analyzed by a Shimadzu GC14B gas chro-matographer with capillary column (DB-5 for separation ofethylene, diethyl ether, and acetaldehyde) and FID detector.�e catalytic ethanol dehydration system (Scheme 2) wasconducted as reported in our previous work [12].

3. Results and Discussion

3.1. Characterization. Characterization results of the carboncatalysts prepared from pyrolysis of waste tires treated with

two di�erent acids (HCl and HNO3), and activated withphosphoric acid at various temperatures are shown in Ta-ble 2. From a nitrogen adsorption-desorption technique,which gave details of surface and pore characteristics, it wasfound that surface areas and pore volume of all activatedcarbons increased with increasing the activation tempera-ture indicating no sintering occurred. �e higher temper-atures enhance a removal of organic volatile compounds andalso noncarbon atom remained in the activated carbonsresulting in the additional pores inside the structure, thusleading to the higher pore volume and the larger surface [18].However, the small new pores dragged the average porevalues of the activated carbons down as seen from the result.Similar trends were found for both types of activated car-bons, treated with HCl or HNO3.

It was observed that iodine adsorption capacities of thecatalysts did not linearly increase with increasing ofsurface area. Change in pore size could a�ect the ad-sorption capacity of the catalyst. Decrease of pore size inthe catalysts activated at higher temperature obstructs theadsorption of iodine molecules onto the catalyst surface.Even though the iodine molecules are relatively smaller(0.6 nm, [19]) than the average pore sizes of the catalyst,the new pores generated at the high activation tempera-ture may be smaller than or nearly the same size as theiodine molecules, thus hindering the adsorption process.Shimada et al. [20] also found a remarkable decrease in theiodine adsorption number which is attributed to thecollapse of pores by the excessive activation and an in-crease in the ash content in the activated carbon. Changein adsorption characteristic could in�uence the perfor-mance of catalysts, especially when catalysts have to beimmobilized prior to use.

Adsorption isotherms of the catalysts were also obtainedfrom a nitrogen adsorption-desorption technique. It can beobserved that all samples exhibited type IV isotherm with ahysteresis loop indicating to a mesoporous structure of thematerials according to the IUPAC classi�cation (Figure 1).

Crystal structures of the catalyst samples were detectedwith an X-ray di�ractometer (XRD). It can be seen from the

Nitrogen Pyrolysis reactor

Flow meter

Temperaturecontroller

Condenser Gas

Bio-oil

Solid carbon

Scheme 1: Pyrolysis process.

International Journal of Chemical Engineering 3

XRD patterns in Figure 2 that all samples exhibited thesimilar crystal structures revealing the characteristic peaks ofgraphite at around 2θ� 26 [21]. �e sharper peaks appearedwith the higher activation temperature. �is suggests thatthe higher activation temperature causes more crystallinityto the samples.

Morphologies of the catalysts were investigated with ascanning electron microscope (SEM) as shown in the SEMmicrographs in Figure 3. It can be observed that all catalystsexhibited spherical-like particles with smooth surface. Nodi�erences in morphologies caused by di�erent activationtemperatures or acids were observed.

For e§cient use in the ethanol dehydration, the acidity ofthe catalysts was improved by sulfonating with H2SO4 ontothe carbon. �e �nished catalysts were then investigatedwith the FTIR to detect functional groups on the catalystsurface. �e FTIR spectra of all catalysts are shown inFigure 4. It can be seen that all catalysts clearly exhibitedpeaks around 1184 cm1, which are attributed to sulfategroups (S�O) from the substitution of hydrogen in surfacehydroxyl groups (−O−H). �is is evident for the presence ofacid groups derived from sulfonation with H2SO4 on thecatalyst surfaces. �e peaks attributed to alcohols (R−OH)around 3400–3600 cm−1 and carboxylic (C�O) around1711 cm−1 were also observed in all catalysts.

�e acidity of the catalysts was determined by backtitration with NaOH. �e result of acidity determinationwith regard to surface acidity (moles of acidic sites) andacid density is shown in Table 3. It was observed that thesurface acidities of all catalysts are nearly similar probablydue to same amount of sulfonic acid sites present on allcatalysts. �is indicates that all catalysts have similaradsorption capacities for sulfonic acid, in consistent withthe adsorption capacities of iodine as observed previously.�e di�erences in surface areas of the catalysts in-signi�cantly a�ected the acidity of the catalyst. However,as a result of the di�erences in surface areas of the cat-alysts, it leads to the variation of acid density among allcatalysts. �e highest acid density belonged to the catalystsactivated at the low temperature (400°C) for both series ofcatalysts (previously treated with HCl or HNO3) due totheir low surface areas. �ese acid properties may in�u-ence catalytic performances of the catalyst during ethanoldehydration, which will be further discussed in the nextpart.

3.2. Reaction Study. �e catalytic ethanol dehydration wasconducted under temperature programming from 200°C to400°C for all catalysts to evaluate their catalytic performance

Temperaturecontroller

Temperaturecontroller

Bypass

Reaction line

Ethanolinjector

Mass flowcontroller

Ar

Vent

Thermocouple

Glassreactor

Furn

ace

Vapo

rizer

syste

mBubbleflow

meter

Injection

H2 N2 GC-14B Sampling

Scheme 2: Ethanol dehydration system.

Table 2: Surface areas, pore characteristics, and iodine adsorption of carbon catalysts.

Sample Surface area (m2/g) Pore volume (cm3/g) Pore size (nm) Iodine adsorption (mg/g)AC_H420 119.2 0.85 28.3 125AC_H520 273.6 1.49 23.4 129AC_H620 293.3 1.81 20.4 139AC_N420 105.8 0.85 32 124AC_N520 263.6 1.34 23.9 126AC_N620 290.0 1.62 21.3 129

4 International Journal of Chemical Engineering

in terms of catalytic activity (% ethanol conversion) andproduct selectivity.�e ethanol conversions of all catalysts atvarious temperatures are shown in Figure 5. �e ethanolconversions at 400°C (the best condition) are also listed inTable 3 along with the product selectivities at thistemperature.

From Figure 5, it can be observed that for all catalystsexcept AC_N620, the ethanol conversion increased withreaction temperatures. �is could be an e�ect of an endo-thermic reaction which favors high temperature. �e syn-thesis pathway of ethanol into ethylene is considered anendothermic reaction as proposed in reaction (2) [22].�erefore, the results con�rm the existence of this reaction.

C2H5OH⟶ C2H4 +H2O⟶ (ΔH � +44.9 kJ/mol)(2)

10 20 30 40 50 60 70 802θ (°)

Inte

nsity

(a.u

.)

AC_N620

AC_N520

AC_N420

AC_H620

AC_H520

AC_H420

Figure 2: XRD patterns of the catalysts.

0

100

200

300

400

500

600Vo

lum

e (cc

/g)

0.20 0.40 0.60 0.80 1.000.00Relative pressure (P/P0)

(a)

0

100

200

300

400

500

600

Volu

me (

cc/g

)

0.20 0.40 0.60 0.80 1.000.00Relative pressure (P/P0)

(b)

0100200300400500600700800900

1000

Volu

me (

cc/g

)

0.20 0.40 0.60 0.80 1.000.00Relative pressure (P/P0)

(c)

0100200300400500600700800900

1000

Volu

me (

cc/g

)

0.20 0.40 0.60 0.80 1.000.00Relative pressure (P/P0)

(d)

0200400600800

10001200140016001800200022002400

Volu

me (

cc/g

)

0.20 0.40 0.60 0.80 1.000.00Relative pressure (P/P0)

(e)

0100200300400500600700800900

100011001200

Volu

me (

cc/g

)

0.20 0.40 0.60 0.80 1.000.00Relative pressure (P/P0)

(f )

Figure 1: N2 adsorption/desorption isotherms of the catalysts.

International Journal of Chemical Engineering 5

Considering the ethanol conversions at 400°C in Table 3,it was found that for both series of catalysts, the ethanolconversions increased with surface acidity and acid densityof the catalysts. Nevertheless, the acid density apparentlyin�uenced the ethanol conversion more than the totalacidity. It has been known that the dehydration processincreases with increased total acidity of the carbon surfacesand takes place mainly at the active centers of the Brønstedacid. Accordingly, sulfonic groups on the catalysts, whicheasily give up a proton can be classi�ed as the Brønsted acid,essentially enhance catalytic activities of the catalysts. �us,high acidity (Brønsted acid sites) of the catalysts increasedthe ethanol conversion as expected. �e reaction pathway ofethanol dehydration with the sulfonic acid carbon-basedcatalyst can be proposed as Figure 6. In the �rst step,protonation takes place at alcoholic oxygen in the ethanol

(a) (b)

(c) (d)

(e) (f )

Figure 3: SEM micrographs of the catalysts: (a) AC_H420, (b) AC_H520, (c) AC_H620, (d) AC_N420, (e) AC_N520, and (f) AC_N620.

AC_N620

AC_N520

AC_N420

AC_H620

AC_H520

AC_H420

Tran

smitt

ance

(a.u

.)

700

900

1,10

01,

300

1,50

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1,90

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2,30

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500

2,70

02,

900

3,10

03,

300

3,50

03,

700

3,90

0

500

Wavenumber (cm–1)

Figure 4: FTIR spectra of the catalysts.

6 International Journal of Chemical Engineering

molecule.�en, the C-O bond is broken causing the loss of awater molecule and resulting in a carbocation intermediate.Finally, a hydrogen ion is removed from the carbocation,forming a double bond of ethylene.

For the e�ect of acid density, it can be seen that theethanol conversion of the catalysts signi�cantly increasedwith the acid density. �is e�ect was also observed in ourprevious study [23], which revealed that high acid density of

the alumina catalysts apparently results in high catalyticactivity in the ethanol dehydration. �is is because theshorter distances between two nearby neighboring acid sites(high acid density) probably lead to rapidly react to formdiethyl ether. �e diethyl ether can be formed through abimolecular nucleophilic substitution mechanism which ispreferred with two adjacent ethanol molecules adsorbed onthe catalyst surface as shown in Figure 7. It can be see that

Table 3: Surface acidity, total conversion, and product selectivity of carbon-based catalysts at 400°C.

Sample Acidity (μmol/g) Acid density (μmol/m2) Ethanol conversion (%)Selectivity (%)

Ethylene Diethyl ether AcetaldehydeAC_H420 2210 18.5 36.2 65.9 33.5 0.6AC_H520 2200 8.0 19.9 66.2 33.1 0.7AC_H620 2170 7.4 14.3 69.0 30.5 0.4AC_N420 2270 21.5 29.1 69.4 29.9 0.7AC_N520 2040 7.7 22.7 75.6 23.6 0.8AC_N620 1980 6.8 22.1 73.9 25.5 0.6

200°C300°C400°C

AC_H

420

AC_H

520

AC_H

620

AC_N

620

AC_N

520

AC_N

420

0

5

10

15

20

25

30

35

40

Etha

nol c

onve

rsio

n (%

)

Figure 5: Ethanol conversion of the catalysts for ethanol dehydration at various temperatures.

S

O

O

OH

O

H

CH2CH2

HO3S

AC

ACS

OO

O

H

CH2 C

+ +H2O CH2H2C

ACS

OHO

O

H2O

Figure 6: �e mechanism of ethanol dehydration to ethylene.

International Journal of Chemical Engineering 7

the intermediate carbocation combines with the near eth-anol molecule and then produces diethyl ether. Convertingthe ethanol into diethyl ether can increase the ethanolconversion. In addition, diethyl ether also acts as reactionintermediate and is subsequently decomposed to ethylene[24]. Nevertheless, this process still increased the catalyticactivity anyway.

It should be noted that the catalytic activity also de-creased with increasing of the activation temperature ofthe catalysts. �e reason may be a gradual decompositionof carboxyl groups present on the carbon surface prior tosulfonation, which already becomes unstable at 180°C [25].It has also been reported that heat treatment will createunsaturated surfaces as a result of thermal desorption ofacidic functional groups [26]. Several researchers foundthat the decomposition of oxygen functional groups occursat elevated temperatures and leads to an increase in ba-sicity of the carbon surface [27–29]. �erefore, an increaseof the activation temperature led to lower acidity on thecatalyst and consequently reduced the ethanol conversion.�is indicates that the other acidic functional groups suchas carboxyl group could involve in the reaction mechanismof the ethanol dehydration besides sulfonic acid on thecatalyst surface.

When comparing between two series of the catalysts, itwas found that with the high activation temperatures(520°C and 620°C) the HNO3-treated catalysts gave thehigher catalytic activity than the HCl-treated catalysts.However, at 420°C, the HCl-treated catalyst (AC_H420)conversely gave the higher catalytic activity than theHNO3-treated catalyst (AC_N420). �is was because atthe same activation temperatures (520°C and 620°C), theHNO3-treated activated carbons have a slightly largerpore diameter than the HCl-treated activated carbons(Table 1). �erefore, after sulfonation the sulfonic acidsites located inside the pores of the HNO3-treated cata-lysts could be more easily access than those of the HCl-treated catalysts. �is is attributed to the higher catalyticactivity of the HNO3-treated catalysts. Nevertheless, at420°C both types of activated carbons (AC_H420 andAC_N420) have the relatively larger pore diameter, thusan e�ect of pore diameter becoming lower. �e highercatalytic activity of AC_H420 than AC_N420 was due tothat HNO3 having a higher oxidizing strength thatdestroyed the pore walls to a large extent, �xing a largeamount of oxygen surface groups [30]. �e higher degreeof oxidization at the catalyst surface could convert surfacehydroxyl groups into other oxygen contained groups, thus

consequently a�ecting the addition of the sulfonic groupsthrough hydroxyl groups during sulfonation. �is leads tothe higher active acidic centers on the surface of AC_H420than AC_N420, and then provided the higher catalyticactivity.

With regard to the product selectivity of the catalyst, itwas found that all HNO3-treated catalysts had higherethylene selectivities than those obtained from HCl-treated catalysts. �e opposite was true for the diethylether selectivities. �e acetaldehyde selectivities wereinsigni�cant for both series of catalysts. �e di�erentnatures of catalysts, which were previously treated withdi�erent acids, may be the reasons for the di�erent se-lectivities. It is generally accepted that the ethanol con-version to ethylene occurs on weak acid sites [24, 31].�erefore, this suggests that the HNO3-treated catalystshave the higher proportion of weak acid sites than theHCl-treated catalysts. From the results of the reactionstudy, it can be concluded that the types of acid used intreatment process, and also the activation temperatures,in�uence the catalytic performance of the solid carboncatalysts prepared from the pyrolysis of waste tire.�erefore, tuning the ethanol dehydration productionwith solid carbon catalysts by variation of the acid typeswould be plausible and worth further investigation.

In Table 4, summarized reports of catalytic performancefor ethanol dehydration to ethylene over various catalysts arecompared. It can be seen that the solid carbon catalysts inthis study exhibited the lower catalytic activity than mostcatalysts in the previous studies. Nevertheless, when com-paring among the carbon-based catalysts, the waste tire-derived carbon is still comparable. �us, waste tires have theconsiderable potential to be developed as a catalyst forethanol dehydration.

4. Conclusion

Waste tires were pyrolyzed to obtain carbon and thensulfonated to achieve the carbon-based catalysts. �e cata-lysts were divided into two series according to the acid typesin the treatment process. Both series of catalysts have thesame trends that increasing the activation temperaturedecreased the catalytic activity due to the reduction of aciddensity. �e HNO3-treated catalysts had higher catalyticactivities than the HCl-treated catalysts except at the acti-vation temperature of 400°C. �e ethylene selectivities of theHNO3-treated catalysts were rather higher than those of

O

H

CH2 C CH3H2C O

H

CH2CH2

+

ACS

OO

O

CH2CH3 CH3CH2OCH2CH3

ACS

OHO

O

+

Figure 7: �e mechanism of ethanol dehydration to diethyl ether.

8 International Journal of Chemical Engineering

HCl-treated catalysts. *is was probably resulted from thehigher proportion of weak acid sites.

Data Availability

*e data used to support the findings of this study are in-cluded within the article.

Conflicts of Interest

*e authors declare that they have no conflicts of interest.

Acknowledgments

*e authors thank the Grant for International Research In-tegration: Chula Research Scholar, RatchadaphiseksomphotEndowment Fund for financial support of this project.

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Table 4: Comparison of catalysts for ethylene dehydration and their catalytic ability.

Catalyst Reaction temperature (°C) Ethanol conversion (%) Ethylene selectivity (%) Ref.HBZ 200–400 7–100 1–100 [17]Al-HBZ 200–400 9–92 0–98 [17]M-Al 200–400 12–92 0–96 [17]H-ZSM-5 400 99 10 [32]20HP-ZSM-5 250–450 25–100 3–98 [32]c-Al2O3 400–550 70–100 40–95 [11]TiO2/c-Al2O3 360–550 70–100 50–99 [11]SAPO-34 500 100 100 [33]Carbon based Activator ModifierBacterial cellulose 200–400 41–65 0–65 [34]Olive stone Steam (NH4)2S2O8 180 1–22 16–26 [35]

Polish brown coal HCl, HF

HNO3 150–450 n.a. 0–50∗ [24]CH3COOOH 150–450 n.a. 0–15∗ [25]

H2SO4 150–450 n.a. 0–14∗ [25]Air 150–450 n.a. 0–18∗ [25]Cl2 150–450 n.a. 0–5∗ [25]

Waste tire HCl H2SO4 200–400 14–36 65–69 *is workHNO3 H2SO4 200–400 22–29 69–75 *is work

∗Based on the ethanol conversion to ethylene only and the values are approximate.

International Journal of Chemical Engineering 9

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