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Journal of Cleaner Production 68 (2014) 272e278

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Journal of Cleaner Production

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

An integrated environmental impact assessment of corn-based polyolscompared with petroleum-based polyols production

Yan Zhao a,b,*, Jia Xu a, Xianxian Xie a, Hongwen Yu b

a School of Chemical and Environmental Engineering, Changchun University of Science and Technology, Weixing Road 7989, Changchun 130022, PR ChinabKey Laboratory of Soybean Molecular Design Breeding, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, PR China

a r t i c l e i n f o

Article history:Received 10 April 2013Received in revised form19 November 2013Accepted 18 December 2013Available online 28 December 2013

Keywords:Environmental impactSystem dynamicsCornPolyols

* Corresponding author. School of Chemical andChangchun University of Science and Technology, We130022, PR China. Tel.: þ86 13039118667.

E-mail address: zhaoyan_xx@163.com (Y. Zhao).

0959-6526/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.jclepro.2013.12.049

a b s t r a c t

Various aspects of bio-ethanol technology have been studied for decades; however the previous liter-atures do not have a detailed assessment of a whole corn-based polyols system and its integrated impacton the environment. The evaluation system used to analyze the impact of adopting corn-based polyolsfrom an environmental point of view was the system dynamics innovatively. Consequential models wereapplied to evaluate the environmental impact in four polyols production stages: raw material planting,corn-based polyols production, corn-based polyols products utilization and disposal process. N2Oemission from nitrogen fertilizers was important contributor of greenhouse gases produced duringagricultural activities. Growing corn was capable of absorbing a lot of CO2 which showed carbon sink.Pollutants discharged during the conversion of corn into polyols were highly dependent on processingtechnology alternatives. There also existed some worse impacts such as discharged N2O, CO, SO2 and HClin waste disposal process. Findings from the systemic simulation might be utilized in identifying envi-ronmental pollution bottlenecks within the process. The results demonstrated that multiple scientificand technological improvements in polyols production could reduce 1/3 of the production cost per ton incomparison to petrochemical polyols. Through optimal parameter selection, the corn consumption perton of polyols production could be controlled from 1.68 to 1.42 tons. These findings could provideimpetus for further technological advancement of corn-based polyols by reducing the overall environ-mental impacts of the bio-polyols process.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Non-renewable fossil fuels accounted for about 88% of totalenergy used in 2008 (Brennan and Owende, 2010). This resulted inboth excessively large emissions of greenhouse gases as well as theprogressive depletion of non-renewable resources (Gomes andMuylaert de Araújo, 2009). The past decade has witnessed anincreased consumer and government interest in replacing petro-leum-based products with those made from or with bio-based re-sources. Production from grass straws, corn, wheat, and sugar beetwas the largest source of bio-ethanol (Nanaki and Koroneos, 2012;Spatari et al., 2010; Bai et al., 2010; Luo et al., 2009a,b; Schmer et al.,2008; Nguyen and Gheewala, 2008a,b). The environmental impactof bio-based ethanol was well documented, for example, theethanol production from lignocelluloses feed stocks (Morais et al.,

Environmental Engineering,ixing Road 7989, Changchun

All rights reserved.

2010; Kiwjaroun et al., 2009) produced less greenhouse gas emis-sions and needed fossil energy consumption compared to petro-leum fuels (Melamu and von Blottnitz, 2011; Nguyen andGheewala, 2008a,b; Spatari et al., 2005).

Recent studies have been focused on the conversion of plantmaterials into polyols. Researchers investigated starch polyols,polyhydroxyalkanoates, polylactides and other bio-based polyolsbased on flax, hemp, and china reed (Corbière et al., 2001; Martinet al., 2004). The findings indicated that bio-based polyols mightcontribute substantially to reducing the environmental impactwhich was related to resource use. Furthermore, the cradle-to-gatelife cycle assessments demonstrated the environmental benefits forflexible foam polyols from soy or castor oil in comparison topetrochemical based polyols. It was found that seed oil based pol-yols used 33e64% of the fossil resources and had the potential tolower greenhouse gas emissions (Richard and David, 2009). Thecommercial implications of using natural, renewable oil initiatorsfor polyols production were examined with particular emphasis tothe resultant environmental and financial advantages gainedwhere low cost oils were found in abundance (Colvin, 2011).

Fig. 1. The framework of environmental impact analysis of corn-based polyols.

Table 1The carbon emissions of corn planting (/hm2).

Input Xi EFi/kg C/hm2 Carbon emissions/kg C

1 Seedlings 30 kg 1.050 31.502 Nitrogen fertilizer (N) 187.5 kg 0.857 160.693 Phosphate fertilizer (P2O5) 75 kg 0.165 12.384 Potash fertilizer (K2O) 75 kg 0.120 9.005 Machinery 7.53 kg 0.68 5.126 Diesel 63.53 L 0.849 53.947 Electric power 225 kWh 0.355 79.888 Pesticides 0.99 kg 4.932 4.889 Herbicides 2.71 kg 4.702 12.74Total 370.12

Y. Zhao et al. / Journal of Cleaner Production 68 (2014) 272e278 273

An integrated environmental impact assessment would supportthe further development of bio-based polyols composites based onrenewable resource. Regular monitoring and assessment of poten-tial environmental impacts was needed for the continuousimprovement of the environmental performance of bio-polyols. Sosystem dynamics was applied in life cycle assessment innovatively.Bysystemic simulation, theenvironmental protectionand scientific-technological effect factors could be adjusted which resulted in thereduced resources consumption and pollutants discharge.

The largest ethanol producers in the world are the United States(US), Brazil and China. TheUS corn ethanol production has exceeded12 billion gallons as of 2011 (http://www.mczx.moa.gov.cn/, 2012).Meanwhile, China has high consumption of polyols (more than 20million t/year) whichweremade of 50million t petroleum resource.Chinese authorities face a growing environmental and energychallenge resulting fromthehigh consumptionof polyols. This studylooks at a typical corn-based polyols production as a study case. Theproduction factory is owned to Changchun DaCheng Group Co., Ltdof China with independent intellectual property rights. This inno-vative technology produced polyols such as glycol, propylene glycoland 1,2-butylene glycol based on corn as rawmaterial. This researchhopes to outline the environmental and commercial advantages ofthese polyols in comparison to fossil-based polyols. This report aimsto present an integrated environmental impact assessment of apractical corn-based polyols system carried out using the systemdynamics innovatively. The results couldprovide impetus for furthertechnological advancement of corn-based polyols and reduceoverall environmental impacts of the future bio-polyols process.

2. Methods

One common method of measuring environmental impact wasto conduct an environmental impact simulation, which was avaluable tool to evaluate the potential environmental costs andbenefits of new production options for chemicals and materials(Dong et al., 2012). System dynamics (SD) was a powerful meth-odology and computer simulation modeling technique for framing,understanding, and discussing complex issues and problems. Withcasual loops and standard mathematical program, Vensim, a visualmodeling tool, was able to conceptualize record, simulate, analyze,and optimize models of SD. The SD models were setup forcomputation simulation to aid in the study of an integrated envi-ronmental impact assessment with regard to the alternative sci-entific and technological changes within the system.

The environmental impact of corn-based polyols was analyzed inthe whole life cycle. A unit process was defined as the “smallestelement of a product system for which data are collected when per-forming a life cycle assessment.” (ISO 14040). The production of corn-basedpolyolsneeded solar and fossil energyasdriving forceaswell asother material input. The unit processes updated for this studyincluded: Raw materials production, polyols production, differenti-ated polyester production and products waste disposal. These foursub-processes specifically comprised stages of corn planting, cornprocessing and distribution, corn-based polyols production, polyolsdistribution, differentiated polyester polyols production, and thefinalincineration disposal of products waste, shown in Fig. 1. Trans-portation aspects for each unit process were also included.

3. Results and discussion

3.1. Environmental impact in corn planting process

3.1.1. Carbon emissions of com plantingThe greenhouse gas emissions in corn planting process included

CO2 (C1) discharged in planting process, due to use of irrigation

electricity, diesel fuel for farm machinery, nitrogen, phosphorous,potash fertilizers, pesticides and herbicides.

C1 ¼

P

iðXi � EFiÞ

Y(1)

In equation (1), C1 is the CO2 discharged in corn planting pro-cess; Xi is the ith substance consumed in corn planting process; EFiis the carbon emission coefficient of the ith substance.

Y (corn yield): The estimated value of average summer cornyield is 7500 kg/hm2 in China main corn production areas (Lu et al.,2003).

Other data for input materials came from Chinese Sino Center,Chinese Database for Materials Life Cycle Assessment. The resultswere shown in Table 1. Equation (2) was cited from foreign litera-tures (Tristram and Gregg, 2002).

CN2O ¼ a� XN � GWPY

� 1228

(2)

In equation (2), XN is the consumption of nitrogen fertilizer incorn planting; a is the N2O formation proportion caused by nitro-gen fertilizer application effect, which is estimated to be 1.25%(Tristram and Gregg, 2002); GWP is the global warming potentialcoefficient of N2O, and its value is 310 (Zhang and Yuan, 2006).

3.1.2. Carbon emissions of com transportation

C2 ¼ D� TE� TEF (3)

In equation (3), D (average distance of corn transportation): Thematerials are transported by diesel trucks inmost of the timewhichhave traveled an average distance of 300 km.

Table 2The total greenhouse gas emissions (CT) of corn planting process (kg CO2/kg corn).

C1 CN2O C2 C3 CT

0.049 0.0969 (kg N2O/kg corn) 0.0258 �0.204 �0.032

Fig. 3. Simulation model of wastewater subsystem. J e crystal sugar production unit; He polyols production unit; P e PDT (polybutylene terephthalate glycol ester) polyesterproduction unit.

Y. Zhao et al. / Journal of Cleaner Production 68 (2014) 272e278274

TE (consumption intensity of transportation fuel): The dieselconsumption intensity was 0.0315 L/t km indicated by the maineconomic and technical index of transportation enterprises ofchina.

TEF (carbon emission coefficient of corn transportation): Thecarbon emission coefficient of diesel fuel is 2.73 kg CO2/L (IPCC,2006).

3.1.3. Absorption of carbon emissions by corn plantingAccording to the study of “Dynamics of carbon dioxide flux in a

maize agro-ecosystem”, the CO2 flux of Chinese main corn agro-ecosystem was measured continuously using the eddy covariancetechnique. The result indicated that the net ecosystem carbon ex-change was �652.8 g/m2 and 499.8 g/m2 during the growth seasonand the non-growth season in the corn agro-ecosystem, respec-tively (Liang et al., 2012). So the carbon budget was �153.0 g/m2

which meant carbon sink C3.The total greenhouse gas emissions (CT) of corn planting process

were calculated in Table 2. Although some components of cornagriculture were excluded due to lack of available data, the resultdisplayed the significant impact that corn planting had on theenvironment. As growing corn was capable of absorbing a lot ofCO2, the total greenhouse gas emissions (CT) of corn planting pro-cess turned to negative value, which contributed to the beneficialenvironmental impact of corn-based polyols.

3.2. Environmental impact in corn-based polyols production andutilization process

3.2.1. SD simulation on corn-based polyols productionThe SD method aimed to find out how policies, decisions mak-

ing, structure, and time delay correlated with each other andaffected the growth and stability of a given system. The dynamicmodels were converted to the causaleloop diagrams or stock flowdiagrams, which were based on the interactions of different com-ponents associated within the system (Talyan et al., 2007).

Herein, we discussed the environmental impact of bio-polyolsusing a typical corn-based polyols production technology as anexample. This innovative technology produced sorbose usingstarch sugar from corn as raw material. Meanwhile, hydrogen wasmade by end’s powdered coal fluidized bed gasification technol-ogy, shown as Fig. 2. The main environmental impact of this corn-

Fig. 2. The corn-based polyols production process.

based polyols system could be categorized into four subsystems:wastewater, exhausted gas, and solid waste and noise subsystems.The relationships within and among those subsystems could befurther classified according to the characteristics of elementcomponents, and the systemic behavior and effect were simulatedand optimized.

3.2.1.1. Wastewater subsystem. The wastewater subsystem in Fig. 3comprised CODcr, BOD5, SS (suspended solid) and ammonia nitro-gen wastewater mainly from two procedures, namely the crystalsugar unit and chemical polyols production equipment unit. Itcould be seen that the total wastewater volume was appointed aslevel variable; wastewater generation and reduction amount wereused as rate variables to adjust the systemic balance. In designedfeedback system, the integrated reduction treatment includedanaerobic treatment, acidification, coagulation and sedimentation.Meanwhile, gray water reuse system, environmental protectionand scientific-technological effect factors were introduced asauxiliary variables to express the mitigatory impact. Theimprovement of wastewater subsystem was adjusted by therespective reduction of total pollutants and wastewater amount.

3.2.1.2. Exhausted gas subsystem. As shown in Fig. 4, the exhaustedgas pollutants from corn-based polyols production processincluded CO2, NH3, SO2, H2S, fume, dust, alcohols gas, ether, etc.Hence the organic pollutants and mephitic gases not only pollutedthe environment but also caused harm to human health. Fume anddust were generally purified by bag filter with relatively low energyconsumption and cost. Other positive measures were taken asfollow: SO2 was removed through desulphurization; CO2 emissionwas reduced by liquid alkali absorption. Further, realizing of pol-lutants source control was much appreciated. Furnace combustionand low nitrogen combustion were adopted as reduction methods,

Fig. 4. Simulation model of exhausted gas subsystem.

Y. Zhao et al. / Journal of Cleaner Production 68 (2014) 272e278 275

and in the latter the nitrogen in fuel was kept in a free state orformed N2 rather than NO and NO2 as far as possible. H2S was gotrid of via closed and bio-filter pool methods. In addition, solventrecovery such as n-hexane and so on could achieve recycling.Environmental protection and scientific-technological effect factorswere beneficial to enhance the dust removal efficiency by adjustingscientific-technological investment.

3.2.1.3. Solid waste subsystem. The solid waste from corn-basedpolyols production process could be classified into two types:general solid waste and hazardous waste. In this subsystem, mostwaste belonged to general waste with a relatively higher recyclingvalue. Therefore, it could be made full use of by delivering to cor-responding processing place for recycle and reuse, shown in Fig. 5.But some catalyst and toxic sludge used in production process, ashazardous solid waste, had to be sent to the designated qualifieddepartment for special treatment. Therefore, it could be made fulluse of by delivering it to a corresponding processing place forrecycling and reuse (shown in Fig. 5). Catalyst and toxic sludge usedin the production process, as hazardous solid waste, were sent tothe designated department for special treatment.

3.2.1.4. Noise subsystem. In the corn-based polyols productionprocess, the source of the majority of the noise came from the stoneremoval machine, grain conveyor, crusher, centrifuges, blender,turbo generator and various pumps. The noise sources appearedcontinuous and steady. Buffering vibration parts were adopted asnoise mitigation measures which conformed to the noise attenu-ation rules. Noise insulation materials such as double compositeboard, double-layer doors and windows were also applied toreduce environmental impact from workshop equipment. In addi-tion, noise reduction by foliage was carried out.

3.2.2. SD simulation on corn-based polyols productsCorn-based polyols had extensive usages, especially in the

synthesis of chemical fibers. Herein simulation on the manufactureof polyester by glycol was analyzed as an example, so as to discussthe environmental impact of corn-based polyols productsutilization.

Fig. 6 showed the production process of converting glycol intopolyester fiber mainly involved esterification, pre-polycondensation, final polycondensation, melt transfer, slice pro-duction and spinning. Most wastewater pollutants came frompolyester manufacturing equipment. Through unified burning aftersteam gas stripping, nearly all the glycol, acetaldehyde, and part ofCODcr, BOD5 could be removed. Other measures were alsoemployed to reduce exhausted gas pollutants, such as water spray

Fig. 5. Simulation model of solid waste subsystem.

stripping for exhausted gas from the filter cleaning process. As aresult, the volatile poisonous and harmful substances could diffuseinto a gas phase for pollutant separation purposes.

3.2.3. Results and comparisonsAccording to the feedback relationships among constituent el-

ements of wastewater, exhausted gas, solid waste and noise sub-systems, a series of level variables, rate variables, auxiliary variablesand constants were set respectively. Table functions were used torepresent the dynamic parameters changing with time. Being theprimary part, level variables represented the systems state atcertain times during the dynamic change process. Level variableswere expressed by differential equations in models. Both rate andauxiliary equations were built based on the causal feedback re-lationships among variables. Basic models data of corn-based pol-yols production and utilization under different schemes wereshown in Table 3.

Table 3 displayed the environmental impact of polyols produc-tion process accounted for a large proportion of the entire impact inthe life cycle. In the synthesis of polyester fibers by polyhydricalcohol, the main pollutant contributing factors were terephthalicacid, CODcr, BOD5, oil stain and NOx emission. Impact reductionthrough the decrease use of raw material as well as strengtheningwater purification needed to be implemented in order to lower theconcentration of these pollution factors. Regular check, monitoringand maintenance of excessive noise equipments were suggested tobe performed timely under the direction of environmental pro-tection personnel.

The corn-based polyols production technology could reducenearly 1/3 production cost per ton compared with petrochemicalpolyols (The production of 1 t polyols needed 1.42 t corn as rawmaterial. Corn price: 365 dollars/t; corn processing cost: 325 dol-lars/t. The total cost of corn-based polyols was 843 dollars/t. The 1 tpetrochemical polyols cost was 1250 dollars/t (China Agriculturefor Trade and Economy Information Network, 2012)). It showed asignificant advantage from the point of view of alternative energyand economic feasibility. Control measures and their ability toreduce the pollutants were presented in Table 4. The most signifi-cant finding was that when the environmental protection andscientific-technological effect factors were adjusted, resulting in areduced corn consumption and pollutants discharge.

3.3. Environmental impact in corn-based polyols products disposalprocess

Corn-based polyols, such as glycol, propylene glycol and 1,2-butylene glycol were the raw material of industrial polymers. Take

Fig. 6. Simulation model of corn-based polyols products.

Table 3The environmental impact data of corn-based polyols production and utilization process (polyols product/t).

Pollutants Crystal sugar unit/kg Polyols unit/kg PDT polyester unit/kg Reduction amount/kg Final discharge/kg

Wastewater CODcr 16.57 1.77 3.33 21.34 0.33BOD5 8.28 0.71 0.88 9.81 0.06SS 4.56 0.22 0.023 4.57 0.23Ammonia nitrogen 0.19 3.5 � 10�4 5.9 � 10�4 0.17 0.021

Exhausted gas SO2 0.59 1.21 0.91 1.79 0.92Smoke dust 0.02 24.51 2 26.42 0.11Dust 12.3 12.24 0.06H2S 0.44 kg/h 0.027 kg/h 0.44 kg/h 0.027 kg/hAcetaldehyde 0.91 0.91 0Hexane 0.05 0 0.05NO2 0.36 0 0.36

Solid waste Ash/slag 0.076 634 30 664.08 0Washing gas sludge 35 35 0Waste activated carbon 13.2 2 15.2 0Others 11.25 0.25 11.5 0Catalyst (hazardous waste) 0.74 0.74 0Sludge (hazardous waste) 6 6 0

Note: the basic pollutants data of crystal sugar, polyols and PDT polyester unit were quoted from the monitoring data of corn-based polyols production technology ofChangchun DaCheng Group Co., Ltd of China.

Y. Zhao et al. / Journal of Cleaner Production 68 (2014) 272e278276

polyester fiber production for instance, the post-process mainlyincluded esterification, pre-polycondensation and final poly-condensation, melt transfer and slice production, spinning and soon. These processes were similar with those of petrochemicalpolyols. The discharged pollutants mainly comprised of CODcr,BOD5, CO2, SO2 and NOx. Alkali liquor was known for carbonemission absorption and dilution.

Corn-based polyols products were generally applied in poly-ester, unsaturated polyester, food processing, daily commodity

Table 4Control measures and their effect to reduce the pollutants.

Items Measures Reduction Final discharge

Wastewater Strengtheningwastewaterpurification system;efficient fiber filtration;gray water reuse forgasification washing;dry ash humidifyingand water supplement;rainwater and sewageseparation.

The amount ofterephthalic acid,CODcr, BOD5,ammonianitrogen and SS.

Meeting dischargestandard

Exhausted gas Desulphurization; lownitrogen combustion;bio-filter pool andsolvent recovery.

The amount ofCO2, NH3, SO2,H2S, fume, dustand alcohols gas.

Meeting dischargestandard

Solid waste Recycle and reuse, suchas ash, cinders andsludge for wall-buildingmaterial; discardedactivated carbon to thethermal power stationsfor combustiondisposal.

The amount ofgeneral solidwaste

Zero discharge

Noise Designing noisereduction structure andinstalling mufflerdevice on condensatepumps, electricfeedwater pumps andsteam turbinegenerator; regularcheck, monitoring andmaintenance.

10e15 dB (A) 75e80 dB(A)

Rawmaterialconsumption

Optimizing productionline; catalyst yieldimprovement;technique innovation.

15% (1.68 t cornfor 1 t polyols)

1.42 t corn for 1 tpolyols

production and pharmaceutical industry, etc. The main materials ofthe wastes were synthetic fiber, textile, food and food additives,rubber, cosmetic and pharmaceutical intermediates, most of whichcould be considered as domestic rubbish.

Cities with a population over one million in China basicallyqualified for the “Waste power generationmature phrase standard”regulated by the United Nations Environment Programme (UNEP),namely: ① More than 0.5e1.0 kg/d rubbish output per person. ②The organic matter proportion in rubbish is less than 40%. ③ Thewater content proportion in rubbish is less than 50%.④ The averagegross calorific value of rubbish is over 3349.44e7117.56 kJ/kg. ⑤Considering the feasibility and cost of reduction, reuse and recy-cling, it is hard to achieve the target of keeping remainder at 35%. Bythe end of 2007, China’s total number of waste incineration powerplant had reached 75. China’s annual investment of waste powerindustry was predicted to reach 80 billion RMB in 2010 (ChineseInvestment Advisory Industry Research Center, 2011). By 2020,China’s waste power generation capacity will increase by 3.3million kilowatts or so. Therefore, we chose waste incineration asthe appropriate way to deal with the corn-based polyols productswaste.

The environmental impact of polyols waste products mainlycontained the exhausted gas emission derived from waste incin-eration, in which the pollutants included CO, SO2, NOx, HCl, dioxinsand so on. The calculation formula was shown as:

Q ¼ ðX þ 0:0161Þð0:0889Cþ 0:0333Sþ 0:265H� 0:0333OÞþ 0:0554Hþ 0:007Oþ 0:0124Wþ 0:008N

(4)

In equation (4): Q was the exhaust volume derived from wasteincineration (per ton) in standard state, m3/kg;

X e Excess air coefficient: According to measured statistics of400 boilers, 75.5% X value focused on 2.51e3.50, herein 3.0 wasassigned to X value;

C, H, S, O, W, N e The respective content of carbon, hydrogen,sulfur, oxygen, water and nitrogen of waste (%).

The calculated exhausted emission of waste incineration was7.6 m3/kg. The contaminants content from waste incinerationexhaust in different countries was show in Table 5.

Hereinto HF emission adopted the aviation waste incinerationemissions standard of Beijing Capital International Airport, thatwas HF < 2 mg/m3. PCDD (polychlorinated dibenzo-p-dioxin)emission complied with China’s “Domestic rubbish incineration

Table 5The contaminants content of waste incineration exhaust in different countries (mg/m3).

Country Smoke and dust CO HCl SO2 NOx Pb Cd Hg PCDD

Britain 16e2800 6e640 345e950 180e670 0.1e0.5 <0.1e3.5 0.21e0.39 0.73e1225Switzerland 1.2 25 17 0.05 0.002 0.09 0.04Russia 15 <2 0.358 0.026 0.067China 180 60 17.6 15 7.6

Y. Zhao et al. / Journal of Cleaner Production 68 (2014) 272e278 277

pollution control standard” (GB 18485-2001), which wasPCDD � 1.0 ng TEQ/m3. The waste products of corn-based polyolswaste incineration (100 kg) emission were calculated according tothe standards above and the result was shown in Table 6.

On the other hand, the transport impact from the generationplant to the incinerator was calculated as follow:

In the waste incineration treatment process, the average wastecollection distance was 2 km and average transport distance was500 km (National Bureau of Statistics of China, 2012). According tothe equation (3) C2 ¼ D � TE � TEF, the transport impact from thegeneration place to the incinerator was C4 ¼ 0.0432 (kg CO2/kg).

3.4. Discussion

Compared with the petrochemical polyols, the corn-based pol-yols could reduce the dependence on fossil fuels, greenhouse gasesemission as well as other environmental impact in the whole lifecycle. The environmental performance of petrochemical polyolsproduction included the energy produced from nuclear, hydro, so-lar, wind, and wood, plus any of these sources used to produce anddeliver any fuel or feedstock. Air emissions such as CO2 equivalents,SOx, NOx, hydrocarbon and volatile organic compounds, these weresums of all the calculated emissions for both energy use andchemical production. Also, the water pollutants and solid wastesproduced in polyols production and disposal process. With prop-erties of being environment friendly, renewable, and rich in stock,corn resource could enhance the independence and energy securityof local polyols system. In corn planting process, N2O emission fromthe nitrogen fertilizers was found to be a major contributor togreenhouse gases during life cycle. It should be noticed that thegrowing corn had environmental benefit shown as absorbing a lot ofCO2 called carbon sink. There were still some worse impacts interms of relatively high carbon emission coefficient and dischargedN2O, CO, SO2 and HCl in corn-based polyols production process.Thus, the discharged pollutants could be decreased by adoptingoptimized alternatives. Further, multiple scientific and technolog-ical improvements in polyols production could reduce rawmaterialconsumption and production cost. Incineration was used as aneffective disposal way for corn-based polyols waste; the mainenvironmental impact came from gas pollutants.

Firstly, efforts should be made to promote the corn planting forsustainable cultivation so as to reduce greenhouse gases emission.For example, control of nitrogen fertilizer application and reductionof energy consumptionwere to be emphasized. Secondly, scenarios

Table 6The waste products of corn-based polyols waste incinera-tion (100 kg) emission.

Exhausted emission 760 m3

Smoke and dust 137 gSO2 11.4 gNOx 5.7 gCO 45.6 gHCL 13.4 gHF 2 gPCDD 760 ng

of corn-based polyols production and utilization process could beevaluated in order to find the best model from an environmentalpoint of view. This could be seen from the feedback results of SDsimulation, technological development in gray water reuse, biopool filtering, bag filter and wet flue gas desulfurization wasbeneficial to improve the environmental profile in the corn-basedpolyols life cycle. Furthermore, it was significant to advance tech-nology improvements in catalysis and hydrogen decompositioncondition control, which would contribute to promoting the con-version efficiency of resource and energy. “3R” rules should beadvocated in polyols products utilization. In addition, technologicaladvances in polyols products conversion and disposal could alsohelp to improve the environmental profile.

4. Conclusions

The goal of this integrated environmental impact was toestablish baseline information for the process of making corn-based polyols, to which other impact of petrochemical polyolscould be compared. Understanding the environmental burdens ofthe corn-based polyols production would allow insight intoinherent sustainability. Compared with petrochemical polyols, thecorn-based polyols would reduce the overall environmental impactin life cycle. N2O emission from nitrogen fertilizers was importantcontributor of greenhouse gases produced during agricultural ac-tivities. As could be seen from the SD simulation, pollutants dis-charged during the conversion of corn into polyols were highlydependent on technology alternatives. It was concluded that themost preferred production options were modification process, re-covery technology and hazardous chemical replacement. As aneffective disposal way, incineration was used to deal with corn-based polyols waste. Furthermore, distinct environmental protec-tion policy was also suggested.

The integrated environmental impact assessment of corn-basedpolyols was a complex issue. It not only included the resourcesconsumption, pollutants emission, energy efficiency and wastepollution problems discussed above, but also involved otherecological problems such as soil degradation, water tables decline,pesticide pollution and so on. Therefore, more influence factors anddeeper study needed to be considered systematically. From thewhole life cycle, the introduction of corn-based polyols was asubject of large interest as its implementation would bring a greatreduction in fuel resource and pollution discharges.

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