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Journal of Cleaner Production 27 (2012) 103e108

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Journal of Cleaner Production

journal homepage: www.elsevier .com/locate/ jc lepro

Environmental impact assessment of caprolactam production e a case studyin China

Jinglan Hong*, Xu XuShandong Provincial Key Laboratory of Water Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Shandong University, Shanda South Road 27,Jinan 250100, China

a r t i c l e i n f o

Article history:Received 26 March 2011Received in revised form6 December 2011Accepted 30 December 2011Available online 8 January 2012

Keywords:Life cycle assessmentCaprolactamEnergy generationRecoveryEnvironmental potential impact

* Corresponding author. Tel.: þ86 531 88362328; faE-mail address: hongjing@sdu.edu.cn (J. Hong).

0959-6526/$ e see front matter � 2012 Elsevier Ltd.doi:10.1016/j.jclepro.2011.12.037

a b s t r a c t

A life cycle assessment was carried out using IMPACT2002þ to estimate the environmental impacts ofcaprolactam production in China. The technology highly contributed to the potential impacts ofcarcinogens, respiratory inorganic matters, global warming, and non-renewable energy. The technologyplayed a limited role in the categories of non-carcinogens and terrestrial ecotoxicity. Specifically, theemissions from the steam, electricity, benzene, sodium hydroxide, hydrogen peroxide, ammonia, andsulfuric acid production processes involved played important roles, whereas the potential impactgenerated from other elements was quite small. Caprolactam recovery from nylon filament yarn, the useof natural gas-based energy generation system, and increasing the efficiency of nitrogen oxide andammonia emission control systems are the key factors for reducing the overall potential environmentalimpact of caprolactam production in China.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

Caprolactam is an organic compound mainly produced duringNylon 6 productions, one of the most widely used types ofcommercial nylons. Due to vast population growth and urbaniza-tion, the consumption of caprolactam in China has dramaticallyincreased. For instance, approximately 3.6�105 and 7.4�105 tonsof the caprolactam had been consumed in China in 2000 and 2008,respectively (Li and Li, 2007; Cui, 2009), corresponding to anincrease of 105.6% in just a span of 9 years. However, caprolactamproduction in China is a new, immature economy. The ratio ofimport dependence in the Chinese caprolactam market is approx-imately 60% (Jin, 2009). Recently, Chinese government leaders havepaid significant attention to the construction of caprolactam plantsbecause of the relatively low energy efficiency and high environ-mental pollution associated with caprolactam production sites.

Life cycle assessment (LCA) is well-known as an effective tool foranalyzing environmental impact associated with all the stages ofa product, process, or activity from cradle to grave. Today, the LCAapplications are used as the basis of marketing, consumer educa-tion, process improvement, eco-labeling program, strategic plan-ning, and product design throughout the world. However, few

x: þ86 531 88364513.

All rights reserved.

studies have been performed on the environmental impacts ofcaprolactam production using the LCA method (Binder et al., 2010).In particular, no research efforts have focused on caprolactamproduction in China. China is recognized as one of the largestenergy consumers and emitters of greenhouse gases worldwide.The energy and water consumption of Chinese textile industries,accounting for the national total industrial energy consumptionand total water consumption, are 4.4% and 8.5%, respectively (Feng,2010). The environmental performance of caprolactam productionsites, which are among the largest textile industrial consumers ofenergy in China, is quite important to the worldwide carbonreduction. The industry needs to be characterized to reduce itsenvironmental impacts. The goals of the current study are tointroduce a Chinese database of caprolactam production to theworld to encourage the right decisions for caprolactam productionand to identify the significant potential for improving the efficiencyof energy, process, and waste treatment in caprolactam industriesin China.

2. Scope definition

2.1. Functional unit

The functional unit is 1 ton of caprolactam. In the current study,all emissions, transport, waste treatment, chemical, energy, andmaterial consumption are based on this functional unit.

J. Hong, X. Xu / Journal of Cleaner Production 27 (2012) 103e108104

2.2. System boundary

Fig. 1 presents system boundary for caprolactam production.Processes included are summarized as follows:

1) Infrastructure of each life cycle stage;2) Road transport of chemical and raw materials to caprolactam

production site;3) Waste treatment processes;4) Direct emissions generated from caprolactam production site;5) Material- and coal-based energy production;

2.3. Methodology

The results of the life cycle impact assessment (LCIA) werecalculated at the mid-point and damage level using theIMPACT2002þ method (Jolliet et al., 2003), due to the fact thatIMPACT2002þmodel is one of the most widely used models in LCAanalysis, the fate exposure in consistent way based on multimediamodeling. This method is a combination of results of theIMPACT2002 model for human health (Pennington et al., 2005),Eco-indicator 99 (Goedkoop and Spriensma, 2000) and CML(Guinée et al., 2001). This approach defines 15 mid-point categoriesincluding carcinogens, non-carcinogens, respiratory inorganics,ionizing radiation, ozone layer depletion, respiratory organics,aquatic ecotoxicity, terrestrial ecotoxicity, terrestrial acidification/nutrification, land occupation, aquatic acidification, aquatic eutro-phication, global warming, non-renewable energy and mineralextraction, all of which are connected to the inventory results.According to Jolliet et al. (2003), these mid-point categories arestructured into 4 damage categories: human health (includingcarcinogens, non-carcinogens, respiratory inorganics, ionizingradiation, ozone layer depletion, and respiratory organics mid-points), ecosystem quality (including aquatic ecotoxicity, terrestrialecotoxicity, terrestrial acidification/nitrification, and land occupa-tion mid-points), climate change (including global warming mid-point) and the resources depletion (including non-renewableenergy and mineral extraction mid-points). In addition, tocompare the mid-point impact to each other and to analyze the

Cyclohexanone (0.90 t)

Cyclohexane (1.01 t)

Cyclohexanone oxime (1.02 t)

Caprolactam (1.0 t)

Benzene (0.94 t)H2 (957.34 Nm3)

NaOH (0.15 t)

Liquid ammonia(165 kg)Toluene (0.5 kg)TBA (0.5 kg)

H2O2 ( 27.5%, 1.26 t)

Liquid ammonia(0.45 t)

Benzene (10 kg)

NaOH (12 kg)

HNO3(36%, 14 kg)

H2(99%, 2.62 Nm3)

Chemicals , raw materials, and energy p

Fuming sulfuric acid (1.17 t)

NaOH (2.86 kg)

HNO3(36%, 0.33 kg)

S

Natural gas (14.90 Nm3)68.74 Nm3

Fig. 1. System bounda

respective share of each mid-point impact to the overall impact aswell, normalization was applied in present study. The normalizedfactor of mid-point impact is determined by the ratio of the impactper unit of emission divided by the total impact generated fromEuropean emissions per person per year (Jolliet et al., 2003).Moreover, ReCiPe (mid-point E, Goedkoop et al., 2009; De Schryveret al., 2009) and TRACI (tool for the reduction and assessment ofchemical and other environmental impacts, U.S EPA) methods areused as a comparison to complement IMPACT2002þ and check therobustness of the obtained results from IMPACT2002þ.

2.4. Inventory data sources

The life cycle inventory data related to the operation processes(e.g., electricity, steam, direct emissions, chemicals, and waterconsumption) of a caprolactam production site in south Chinawereutilized in the current study (Hu, 2009; China Petroleum &Chemical Corporation, 2010). The caprolactam production site isunder one of the most famous and high-grade petrochemicalproduction enterprises in the nation. The technology of capro-lactam produced from the oxidation of cyclohexane technologyinvolved in the present study (with a total capacity of 200 kt/year)approximately accounted for 40% of the total caprolactamproduction of China in 2010. Due to limited information on gasemissions in the caprolactam production site, the data on gasemissions from Juhua caprolactam production site (Juhua GroupCorporation, 2011), which also uses cyclohexane oxidation tech-nology in the production of caprolactam, was utilized in the currentstudy. In addition, the integrated emission of air pollutant standardin China (GB16297, 1996) was used to determine N2O emissions.Coal-based electricity production was considered in the currentresearch because coal plays a vital role in the electricity generationof China. The data of solid waste landfilling and coal-based elec-tricity production in China were taken from the references (Honget al., 2010; Huang and Wu, 2009). The data of infrastructure, rawmaterials, chemicals, and wastewater treatment processes weretaken from Europe (Ecoinvent Centre, 2007) because of the limitedinformation in the China life cycle inventory database. The inven-tory data of energy, raw materials, and waste are shown in Table 1.

Wastewater treatment (8.38 t)

roduction

Emissions

(CO2, SO2…)

aponification waste alkali

liquortreatment

Byproduct: Na2CO3(0.12 t)

Steam

(1.61 t)

Byproduct:

(NH4)2SO4 (1.56 t)

ry and mass flow.

Table 1Main inventory data (values are presented per functional unit).

Category Substance Amount Unit

Raw materials Benzene 0.95 tonElectricity 1026 kWhNatural gas 83.64 Nm3

Vapor (4.4 MPa) 4.19 tonVapor (1.0 MPa) 1.31 tonHydrogen 959.96 Nm3

Sodium hydroxide 0.16 tonLiquid ammonia 0.61 tonToluene 0.5 kgTBA 0.5 kgH2O2 (27.5%) 1.26 tonHNO3 (36%) 14.33 kgFuming sulfuric acid 1.17 tFresh water 16.72 tonSewage 8.38 ton

Gas emissions Methanol 0.12 kgAcetone 0.29 kgSulfur dioxide 4.41 kgNitrogen oxides 2.38 kgDinitrogen monoxide 0.37 kgParticle matter 3.18 kgBenzene 1.14 kgCarbon tetrachloride 0.75 kgCaprolactam 0.15 kgFluoride 69.58 gAmmonia 5.88 kgCyclohexylamine 0.18 kgCyclohexanone 0.27 kgHydrogen chloride 0.49 kg

J. Hong, X. Xu / Journal of Cleaner Production 27 (2012) 103e108 105

3. Results

3.1. Mid-point results

The phase defined by the impact assessment of classification,characterization, and normalization was considered in the currentstudy. Table 2 presents the mid-point assessment results using theIMPACT2002þ method. Hydrogen peroxide and ammonia produc-tion processes represented an important role in each category,whereas the steam generation process represented the dominantcontribution in most categories, except for the carcinogens andmineral extraction categories. Benzene production also played animportant role in most categories, except for the ionizing radiation,ozone layer depletion, land occupation, and mineral extractioncategories, whereas direct emissions from the caprolactamproduction stage represented the dominant contribution in thenon-carcinogens, respiratory inorganics, respiratory organics,terrestrial acidification/nitrification, and aquatic acidification

Table 2LCIA results.

IMPACT2002þ R

Carcinogens 408.5 kg C2H3Cl eqNon-carcinogens 69.8 kg C2H3Cl eqRespiratory inorganics 8.7 kg PM2.5 eq 1Ionizing radiation 6.6� 104 Bq C-14 eqOzone layer depletion 3.8� 10�4 kg CFC-11 eq 3Respiratory organics 3.1 kg C2H4 eqAquatic ecotoxicity 3.2� 105 kg TEG water 1Terrestrial ecotoxicity 7.6� 104 kg TEG soil 5Terrestrial acid/nutri 207.0 kg SO2 eqLand occupation 15.6 m2org.arable UAquatic acidification 61.4 kg SO2 eq TAquatic eutrophication 0.17 kg PO4 P-lim 0Global warming 6.90� 103 kg CO2 eq 6Non-renewable energy 1.56� 105 MJ primary 3Mineral extraction 67.2 MJ surplus

categories. Sodium hydroxide production had an effective role inmost categories, except for the carcinogens and respiratory organiccategories. The potential impact generated from the rest of theprocesses was minimal.

ReCiPe and TRACI methods were used for comparison withIMPACT2002þ to confirm and add credibility to the currentresearch. The mid-point assessment results of the ReCiPe methodtended to be similar to those of the IMPACT2002þ analysis resultsfor the ozone layer depletion, acidification, eutrophication, andglobal warming categories. For the respiratory inorganics, the lifecycle impact assessment (LCIA) result using the IMPACT2002þmethod (8.7 kg PM2.5 eq) was less than the result obtained usingthe ReCiPe method (18.3 kg PM10 eq). This finding can be attrib-uted to the fact that the particulate matter with a diameter largerthan 10 mm had no effect; thus, it was not considered by theIMPACT2002þ method. For the energy category, the ReCiPe anal-ysis result was approximately 1.5�105 MJ (change rate at 42.62 MJ/kg oil eq), which is consistent with the result obtained by theIMPACT2002þ method. Similarly, the LCIA mid-point results of theTRACI method tended to be similar to that of the IMPACT2002þanalysis results in ozone layer depletion. For the respiratory inor-ganics category, the LCIA result using the TRACI method (12.8 kgPM2.5 eq) was higher than that using IMPACT2002þ method(8.7 kg PM2.5 eq), which may be due to the relatively larger char-acterization factor value for sulfur dioxide emission in the TRACImethod. For the global warming category, the TRACI LCIA result(7.5�103 kg CO2 eq) was higher than that obtained using theReCiPe and IMPACT2002þ methods (6.9�103 kg CO2 eq) becausethe two methods considered a 500-year time horizon in the globalwarming category. If the global warming potential impact of a 100-year time horizon is used in the study, the global warming potentialimpact of the current research will be 7.5�103 kg CO2 eq./t, whichis similar to the TRACI analysis results. The rest of the LCIA resultswere difficult to compare because the categories or label substanceswere significantly different. Overall, ReCiPe and TRACI achievedresults similar to those of IMPACT2002þ, but several substancesplayed a significant role. These results indicate that IMPACT2002þis reliable as far as the current research is concerned.

Fig. 2 shows the normalized mid-point categories, highlightingthe contribution of each stage of the life cycle using IMPACT2002þmethod. In addition, to better understand and describe the domi-nant pollutants in each dominant normalizedmid-point categories,the contributions of most significant substances to these mid-points are shown in Fig. 3. The impact of the carcinogens, respira-tory inorganics, global warming, and non-renewable energy cate-gories had an important contribution; the impact of non-carcinogens and terrestrial ecotoxicity played relatively small

eCiPe TRACI

17.2 benzene eq2.1� 105 toluene eq

8.3 kg PM10 eq 12.8 kg PM2.5 eq

.9� 10�4 kg CFC-11 eq 3.8� 10�4 kg CFC-11 eq

.6� 104 kg 1,4-DB eq 1.3� 104 kg 2,4-D eq

.5 kg 1,4-DB eq

rban land occupation: 21.3 m2aerrestrial acidification 66.7 kg SO2 eq.13 kg P eq 2.7 kg N eq.91� 103 kg CO2 eq 7.52� 103 kg CO2 eq.46� 103 kg oil eq

Fig. 2. Normalized mid-point scores for the full life cycle.

J. Hong, X. Xu / Journal of Cleaner Production 27 (2012) 103e108106

roles; the impact of the remaining categories was negligible.Specifically, the contributions of hydrogen peroxide (79%) andbenzene (14%) production processes had effective roles on thecarcinogens potential impact category. The direct hydrocarbonemitted from the electric steel production stage for the infra-structure construction of chemical plants (i.e., hydrogen peroxideand benzene) yielded the highest contributions. Similarly, steamand chemical generation processes (i.e., hydrogen peroxide,benzene, sodium hydroxide, sulfuric acid, and ammonia) weremainly responsible for the contributions to the non-carcinogens,respiratory inorganics, and terrestrial ecotoxicity impact cate-gories. For the non-carcinogens impact category, the dominantsubstance was arsenic to water, followed by arsenic, benzene, anddioxin to air. These pollutants mainly came from the coal-basedsteam and chemical production stages. For the respiratory inor-ganics, the direct emissions of sulfur dioxide, nitrogen oxides, andparticulate matters yielded the highest contribution, which weremainly generated from caprolactam production and the use of coal

0%

20%

40%

60%

80%

100%

Subs

tanc

e co

ntri

butio

n

Others

Dioxins to air

Arsenic to water

Hydrocarbons to air

a

0%

20%

40%

60%

80%

100%

Others

Zn to soil

Ni to air

Al to soil

Al to air

d

Fig. 3. Contribution of most significant substances to the mid-point score of a) carcinogwarming, and f) non-renewable energy.

and diesel for steam generation stages. Similarly, the substancewith the largest contribution to the terrestrial ecotoxicity wasaluminum to air, followed by aluminum to soil, nickel to air, andzinc to soil, which were also mainly from the coal-based steam andchemical production stages. For the global warming impact cate-gory, the carbon dioxide generated from coal-based energy (i.e.,electricity and steam) generation and chemical productionprocesses (i.e., hydrogen peroxide, benzene, ammonia, and sodiumhydroxide) represented the dominant contribution, whereas directglobal warming gas emissions, such as dinitrogen monoxide fromthe caprolactam production process, were negligible becauseapproximately 99% of dinitrogen monoxide could be generallyremoved using highly effective catalysis and active carbonabsorption technologies. For the non-renewable energy impactcategory, the largest contributing processes were chemical (i.e.,hydrogen peroxide, benzene, ammonia, and sodium hydroxide),hydrogen, electricity, and steam generation, whereas the maincontributors were coal, natural gas, and crude oil.

3.2. End-point results

Fig. 4 shows the contribution of the most significant processesand pollutants to the damage score, combining all the mid-pointcategories into damages on human health, ecosystems, climatechange, and abiotic resources. The steam and chemical productionprocesses (i.e., hydrogen peroxide, benzene, sodium hydroxide,sulfuric acid, or ammonia) represented an important role in eachdamage category, whereas the direct emission generated fromcaprolactam production process represented the dominant contri-bution in human health and ecosystem quality categories. Forclimate change and resource damage categories, electricity gener-ation process was also a dominant contributor. In the human healthdamage category, direct emissions of sulfur dioxide, nitrogen oxide,particulate matters, hydrocarbon, and ammonia yielded an effec-tive contribution, which were mainly generated from caprolactamproduction and use of coal and diesel for steam generation. In theecosystem quality damage category, the most significant substancewas aluminum to air, followed by aluminum and zinc to soil, andlastly, ammonia, nickel, nitrogen oxides, and sulfur dioxide to air. In

Others

As to air

Benzene to airDioxins to air

As to water

Others

Methane

Dinitrogen monoxideCarbon dioxide

Others

Nitrogen oxidesParticulates

Sulfur dioxide

Others

Crude oil

Natural gas

Coal

cb

e f

ens, b) non-carcinogens, c) respiratory inorganics, d) terrestrial ecotoxicity, e) global

Fig. 4. Contribution of most significant processes and pollutants to damage score. a) Processes and b) pollutants.

J. Hong, X. Xu / Journal of Cleaner Production 27 (2012) 103e108 107

the climate change damage category, the main contributors werecarbon dioxide seen from energy and chemical production. In theresources damage category, the use of coal, natural gas, and crudeoil were the main contributors. Results shown in the damage levelwere consistent with those presented at the mid-point level.

3.3. Sensitivity analysis

Table 3 presents the analysis of the sensitivity of the maincontributors. In the non-renewable energy mid-point and resourcedamage point categories, the efficiency of benzene consumptionhad the highest environmental benefit, mainly due to the decreaseof crude oil and natural gas consumption in the benzene productionstage. For the rest of the categories except for carcinogens, theefficiency of steam consumption had the highest environmentalbenefit, mainly due to the decrease of coal consumption in thesteam production stage. In carcinogens, the decrease of directhydrocarbon emission had the highest environmental benefit. By

Table 3Sensitivity of main contributors.

Benzene Hydrogen peroxide Sod

Variation 2% 2% 2%Non-renewable energy (MJ primary) 1.30� 103 323.56 140Respiratory inorganics(kg PM2.5) 1.53� 10�2 8.14� 10�3 5.38Carcinogens (kg SO2 eq) 1.13 6.52 0Global warming (kg CO2 eq) 29.41 15.27 6Human health (Daly) 1.41� 10�5 2.47� 10�5 4.29Ecosystem quality (PDFm2 yr) 1.07 1.46 1Resources (MJ primary) 1.30� 103 324.07 140

contrast, the efficiency of sulfuric acid consumption had the lowestenvironmental benefit in non-renewable energy, global warming,and resources, mainly due to the low energy consumption in thesulfuric acid production stage. For the other categories, the elec-tricity generation process had the lowest environmental benefitdue to its relatively low pollutant emissions (e.g., particles matter,heavy metals, carbon dioxide, sulfur dioxide, nitrogen oxides).

4. Discussion

The LCIA results presented that electricity, steam, benzene,sodium hydroxide, hydrogen peroxide, sulfuric acid, and ammoniaproduction processes played important roles in the carcinogens,non-carcinogens, respiratory inorganics, terrestrial ecotoxicity,global warming, and non-renewable energy potential scores,whereas the potential impact generated from the infrastructure,transport, wastewater treatment, water supply, hydrogen, toluene,TBA, coal, and nitric acid production processes was quite small.

ium hydroxide Ammonia Sulfuric acid Electricity Steam

2% 2% 2% 2%.57 528.42 52.98 179.64 385.2� 10�3 1.50� 10�2 2.72� 10�2 4.62� 10�3 3.39� 10�2

.05 0.30 0.06 4.8� 10�4 0.12

.97 24.94 3.15 18.54 34.76� 10�6 1.18� 10�5 1.95� 10�5 3.26� 10�6 2.57� 10�5

.26 2.70 1.21 0.26 6.33

.76 528.69 53.29 179.64 385.22

J. Hong, X. Xu / Journal of Cleaner Production 27 (2012) 103e108108

Binder et al. (2010) reported the potential impact of the capro-lactam production site of Shaw Inc. in the U.S. on energy (135 GJprimary/t), which was slightly lower than the result obtained forthe caprolactam production site in China (156 GJ primary/t). Binderet al. (2010) also studied the potential impact of virgin caprolactamproduction process on global warming (7.1 t CO2 eq./t), acidification(1.1�103 mol Hþ eq./t), eutrophication (1.6 kg N eq./t), and smogair (1.1�10�2 kg NOx eq./t) categories using the TRACI method. Inthe current study, mid-point LCIA results (using the TRACI method)showed that the global warming (7.5 t CO2 eq./t), acidification(3.2�103 mol Hþeq./t), eutrophication (2.7 kg N eq./t), and smogair (15.2 kg NOx eq./t) impacts seen from the China caprolactamproduction process were quite high; energy consumption wasconsidered as the main reason. Coal-based electricity and steamgeneration were considered in the current study. If natural gas-based electricity and steam generation are involved, the potentialimpact per ton of caprolactam on global warming, acidification,eutrophication, and smog air categories of the caprolactamproduction process will be reduced to 6.4 t CO2 eq./t, 2.7�103 molHþ eq./t, 2.5 kg N eq./t, and 12.3 kg NOx eq./t, respectively. Theglobal warming potential impact result is consistent with theresults of the previous study (Binder et al., 2010). The potentialscore on the rest of the categories indicates that a more efficientnitrogen oxide and ammonia emission control system is highlyrecommended for the Chinese caprolactam production site.However, to avoid secondary pollutant, a life cycle perspective ofcaprolactam production with/without nitrogen oxides andammonia emissions control systems is highly recommended.Similarly, around 15.8%, 11.1%, and 14.3% of the respiratory inor-ganics, terrestrial ecotoxicity, and global warming potential scorescalculated by IMPACT2002þ method will be reduced, respectively.Environmental-friendly energy (including electricity and steam)generation is a key factor for reducing the overall environmentalimpact.

Compared with virgin caprolactam production, the use of thereclamation of end-of-life carpet and the recycling of the NylonType 6 face fiber into caprolactam approaches can reduce approx-imately 30.7%, 13.5%, 12.2%, 67.6%, and 14.4% of non-renewableenergy, global warming, acidification, eutrophication, and smogair impact, respectively (Binder et al., 2010). Therefore, caprolactamrecovery from nylon filament yarn is also a key factor for reducingthe potential impact of the overall environmental score.

5. Conclusions

The current study introduces the environmental impactsgenerated from the caprolactam production site in China. Sensi-tivity analysis of the key factors and LCIA methods were used toconfirm and add credibility to the current study. The results ob-tained could be very helpful to increase the life cycle inventorydatabase of China’s caprolactam production and provide useful andscientific information for policymakers in China to make theirdecisions regarding to the construction of caprolactam productionplants. The main conclusions drawn from the current study are asfollows:

� The LCIA method of IMPACT2002þ is reliable as far as thecurrent research is concerned.

� The impact generated from carcinogens, respiratory inorganics,global warming, and non-renewable energy categories hada dominant contribution.

� The impacts on non-carcinogens and terrestrial ecotoxicityplayed a relatively small role and the impacts on the rest of thecategories were negligible.

� Energy (i.e., steam, electricity) and chemical productionprocesses (i.e., benzene, sodium hydroxide, hydrogen peroxide,ammonia, and sulfuric acid) were the main contributors on theenvironmental impact of the caprolactam production sites inChina.

� Themid-point LCIA results in the global warming, acidification,eutrophication, and smog air categories were higher than thoseof previous study;

� Caprolactam recovery from nylon filament yarn, natural gas-based electricity and steam generation system usage, andincreasing the efficiency of nitrogen oxides and ammoniaemission control systems are highly recommended for thereduction of the potential impact of the overall environmentalscore.

Acknowledgments

We gratefully acknowledge financial support from the nationalnatural science foundation of China (No.41101554).

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