Life Cycle Assessment of Polyol Fuel from Corn Stover via Fast

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Life cycle assessment of polyol fuel from corn stover via fast pyrolysis and upgrading Lijun Heng, Huiyan Zhang, Jun Xiao, and Rui Xiao ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b04378 • Publication Date (Web): 03 Jan 2018 Downloaded from http://pubs.acs.org on January 3, 2018

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ACS Sustainable Chemistry & Engineering

Life Cycle Assessment of Polyol Fuel from Corn Stover via Fast Pyrolysis and Upgrading Lijun Henga, b, Huiyan Zhanga, Jun Xiaoa, Rui Xiaoa,* a

Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, School of Energy and Environment, Southeast University, No.2, Xuefu Road, Nanjing 210096, China b

School of Energy and Architectural Environment Engineering, Henan University of Urban Construction, No.10, Longxiang Road, Pingdingshan 467036, China

*Corresponding Author: [email protected].

Abstract The purpose of this study is to evaluate the fossil energy consumption and the greenhouse gas (GHG) emissions of polyol fuel produced via corn stover fast pyrolysis and bio-oil upgrading based on life cycle assessment (LCA). The required material and energy inputs involved in the unit processes of LCA are taken from Aspen Plus simulation models established according to a demonstration plant with annual polyol output of 1,000 tonnes. The eBalance software with a Chinese Life Cycle Database (CLCD) is employed to perform this task. The research results show the net fossil energy input (FEI) and the net global warming potential (GWP) of polyol fuel are respectively 0.760 MJ and 0.0444 kgCO2 eq. per MJ energy output under the proposed production pathway. Compared to petroleum-based gasoline and diesel, the net FEI of polyol fuel reduces by 42.9% and 42.2% respectively and the net GWP of polyol fuel decreases by 55.1% and 56.9% accordingly. Sensitivity analysis indicates the data uncertainty of the polyol yield and the electricity consumption for bio-oil production has significant impact on the GHG emissions. The polyol fuel is expected to partly replace petroleum-based fuels. 1

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Keywords: Life cycle assessment, Polyol fuel, Bio-oil upgrading, Fossil energy input, Global warming potential

Introduction Fast-growing consumption of fossil fuels and feedstocks has led to increasingly serious environmental problems. Especially global warming has caused worldwide attention. It is necessary that much effort be made to reduce anthropogenic GHG emissions because global warming can result in increasingly unpredictable and dangerous impacts on human and ecosystems. This has aroused great interest in exploiting new technologies to produce sustainable biofuels and bio-based chemicals from renewable biomass.1 Biomass is an inexpensive renewable resource abundant in the nature. Among renewable resources, only biomass can provide the sustainable carbon source converted into fuels or chemicals.2 Production of alternative fuels or chemicals from biomass is one of the most promising ways to reduce the dependence on fossil fuels and CO2 emission.3 Agricultural residues are considered to be promising feedstock of alternative fuel or chemicals production for they are by-products with higher energy in the crop production. China is one of the countries with the most abundant crop straw resources. The annual total yield of agricultural straw is more than 700 million tonnes in recent years, of which corn stover is most abundant and its average annual yield is more than 220 million tonnes. 4 The biomass fast pyrolysis is one of the most promising options to convert biomass into liquid products owing to its high-efficiency and low-cost compared to the technologies of gasification and fermentation.5 Furthermore it is relatively mature and is close to commercialization.6 However, the pyrolysis bio-oil cannot directly substitute for the 2


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petroleum-based fuels to date because of its poor physical and chemical properties and needs to be upgraded through catalytic upgrading methods.7, 8 The bio-oil hydrotreatment is considered to be feasible for alternative fuel or chemicals production.9, 10 The researchers from America have proposed the production of both hydrogen and alkanes from the aqueous phase organics of bio-oil.11, 12 The study from Twente University indicates the upgraded products from the aqueous fraction of bio-oil have higher calorific value and lower coking tendency compared to either the organic fraction of bio-oil or the whole bio-oil.13 The aqueous phase bio-oil (APB) is easy to be converted into alcohols via hydrogenation process.14 However, the non-aqueous phase bio-oil (NAPB) containing phenols and its derivatives is difficult to be upgraded into fuels through

hydrotreatment.15,16 Additionally, there still exist many difficulties to hydrodeoxygenate the bio-oil completely owing to the lower yield of single target product and lots of worthless water produced. Considering the factors above-mentioned and for achieving the utilization of the whole bio-oil, a new upgrading pathway has been proposed by our research group. This upgrading technology mainly includes the esterification reaction and the catalytic hydrotreatment of APB for polyol production, and the chemical-looping hydrogen production (CLHP) using NAPB as fuel.17,18 The target products mainly compose of C2 to C6 polyols and hydrogen gas. The pilot-scale production of polyols supported by the National 863 Project (No. 2012AA051801) has offered the technical feasibility of the proposed upgrading pathway. However, the well-to-wheel FEI and the well-to-wheel potential environmental impacts of polyol fuel are currently unclear. Life cycle assessment (LCA) is a standard evaluation method seeking to evaluate the FEI and the potential environmental impacts of a product throughout its life cycle. LCA has been widely utilized for assessing various biofuels derived from biomass.19-22 This work 3



of LCA is conducted to quantify the FEI and the GWP of polyol fuel produced from corn stover from cradle to grave. The Aspen Plus software used for process simulation and the eBalance software with a Chinese Life Cycle Database (CLCD) are employed to perform this LCA task.

Description of Polyol Production Pathway The polyol production technology mainly includes bio-oil production and upgrading, which is illustrated in Figure S1 in Supporting Information (SI). The fast pyrolysis plant capacity is 25 tonnes/day based on the dry basis of corn stover according to the annual polyol output of 1,000 tonnes and 6,000 operation hours per year in the pilot plant. The ultimate and proximate analysis of corn stover, the lower calorific value (LHV) of corn stover, the pyrolysis product compositions and their yields are respectively listed in Table S1 and Table S2 in SI. The bio-oil yield is 69.15 wt. % based on the dry basis of biomass. The bio-oil production is comprised of biomass pretreatment, biomass fast pyrolysis, solid removal, bio-oil recovery, and process heat production. For improving the bio-oil yield, the biomass needs to be pretreated including drying and smashing. The biomass with 25wt. % moisture (M) is chopped to 10 mm particle diameter, dried to 7wt. % M and then ground to 3 mm particle diameter.23 The preprocessed biomass is pyrolyzed into bio-oil vapors, non-condensable gases (NCGs), and char in a ﬂuidized bed reactor operating at 500 o

C and ambient pressure.10, 24 It is assumed that 99 wt. % of the entrained char and ash particles in

the pyrolysis gas are removed through a set of cyclones and baghouse filters in turn. The bio-oil vapors are recovered via staged condensers. The process heat required by the pyrolysis reactor, steam generation, preheating the combustion air, and preheating the reactants for the esterification reactor is supplied by all the NCGs and about 74 wt. % of the char via combusting in a combustor. A portion of flue gas from the combustor is compressed and sent to the pyrolyzer as carrier gas. 4


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The surplus char acts as an alternative fuel locally consumed. The bio-oil is separated into APB and NAPB via forced water separation in a liquid–liquid (L–L) extractor. The dry bio-oil is defined as the bio-oil without water, which is composed of about 62.0 wt. % of water-free APB and 38.0 wt. % of water-free NAPB according to the simulation results. The APB is mainly converted into polyol fuel and esters through supercritical methanol catalytic esterification effectively decreasing the acidity of the APB and subsequent two-stage low temperature hydrotreating processes. 25, 26 In this study, the esterification reactor operates at 240 oC and 8.5 MPa. The first stage hydrotreatment reactor is set at 140 oC and 6.0 MPa (hydrogen cold pressure) with Ru/C catalyst. The second stage hydrotreatment reactor is set at 250 oC and 6.0 MPa (hydrogen cold pressure) with Pt/C catalyst. The polyol composition and their outputs are shown in Table S3 in SI. The hydrogen gas used for hydrogenation of APB is produced via an iron-based CLHP process with CO2 capture using NAPB as fuel. The process flow diagram, the key assumptions and the operation parameters used in the CLHP sub-process are respectively shown in Figure S2 and Table S4 in SI, which have been published in the literature.18 The new simulation results of CLHP using NAPB derived from corn stover as fuel are listed in Table S5 in SI.

LCA Scope Definition and Methods of Dealing with Co-products LCA scope definition The integrated refinery scenario is widely adopted compared to the distributed one in the research of bioenergy conversion because the difference between them has an insignificant impact on LCA results.27-29 Therefore, this study focuses on the integrated case. The integrated refinery is located in the corn belt of central China. The LCA system in this work includes seven unit 5



processes: biomass production, biomass collection and transportation, biomass pre-treatment, bio-oil production, bio-oil upgrading, product transportation and distribution, and product consumption. The LCA system boundary is illustrated in Figure 1. The material and energy flows entering into the LCA system boundary are included in. The fossil energy consumption for their production and corresponding GHG emissions are traced to the exploitation of raw materials. The electric energy required for all the unit processes is assumed to come from the national electricity grid in China. The crop stover harvested for biofuel production may lower the equilibrium amount of carbon in the soil. However, it is difficult to accurately quantify the effects of crop stover removal on soil organic carbon (SOC) loss because of various uncertainties and the limited available information.30 The specific proportion of corn stover sustainably harvested is still under dispute and is influenced by multiple factors including cropping practices, climate, topography, and soil type.30-33 There is a wide range of 20–80% for the sustainable stover removal rate.32, 34, 35 In this study, the availability coefficient of corn stover for biofuel production is about 0.40 according to the statistical data. About 60 percent of corn stover serves as the organic fertilizer to sustain the soil properties. Therefore, the changes in SOC from corn stover removal are not considered in this LCA study. The indirect land use change (ILUC) effects are not included in this study owing to the lack of standard evaluation rules and much difficulty of measuring GHG emission associated with ILUC.36 Additionally, the material and energy associated with the physical infrastructures are not included in this work. The required primary material and energy inputs associated with the unit processes of LCA are from the simulation results. The Aspen Plus simulation models for bio-oil production are adapted 6


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from the process models established and developed by Ringer and Wright et al. 23, 27 The Aspen Plus simulation models for the production of polyols and hydrogen gas are established according to the design parameters of the pilot-plant. The CLCD can provide the secondary material and energy required. It is assumed all the weights in LCA inventories are on a dry basis, otherwise they are stated specially. The functional unit (FU) used is 1 MJ energy output in this LCA work. The method of 100-year time horizon GWP (IPCC 2007) is utilized to quantify life cycle GHG emissions of polyol fuel and hydrogen gas. The cumulative energy demand method is applied to calculate the FEI for the polyol and hydrogen production.

Methods of dealing with co-products The polyol fuel production process is a typical co-production system with multiple intermediate and final products. The fossil energy use and waste emissions produced during all of unit processes need to be allocated among products. The chosen allocation method of energy use and emission loads can significantly influence the LCA results of bio-fuels, but there is no agreement on which method should be applied in biofuel LCA.37, 38 The allocation methods (based on mass output share, energy output share or economic revenue share) and the displacement method are generally utilized in bio-fuel LCA.38 A hybrid approach is employed to solve the allocation problem in this study. The market-value-based allocation method is used for corn grain and corn stover in this study. In the past five years, the average market prices of corn grain and corn stover are respectively $301.3 and $67.8. Thus the price allocation factor of corn stover is about 0.184. The energy allocation method is utilized for the energy products including APB and NAPB while the mass allocation method is applied to the products of polyols (as biofuels) and esters (as chemicals). The outputs of APB and NAPB are respectively 0.622 kg and 0.378 kg per 7



1.0 kg dry bio-oil output. The LHVs of APB and NAPB are respectively 15.20 MJ/kg dry APB and 30.33 MJ/kg dry NAPB. Therefore the energy allocation factor calculated is 0.452 for dry APB and 0.548 for dry NAPB. The mass allocation factor of polyols and esters is separately 0.587 and 0.413. The FEI and GWP of hydrogen gas are calculated independently and hydrogen gas does not be treated as a substitute for fossil fuels to avoid distorting the data accuracy of polyol fuel. The displacement method is only applied to char. According to the displacement method, the estimated energy use and emission burdens of raw coal production are treated as the credits that are subtracted from the total energy consumption and the total emission loads of the biofuel production cycle.38, 39

Inventory Analysis The inventory analysis can present the basic data which are the basis of LCA. Its basic task is to establish system inputs and outputs for each unit process according to various data sources aforementioned. The inventory data are listed in Table S6 to Table S12 in SI and are standardized on the basis of FU in the section of Results and Discussion.

Biomass production The FEI and GHG emissions associated with the production of corn stover are included in the inventory analysis. The average output of dry corn stover is about 5382 kg per hectare according to the average mass ratio of the corn stover to the corn grain of 1.09 in China agriculture.40-42 Considering 40 percent of corn stover removal, three kinds of chemical fertilizers (namely nitrogen(N), phosphorus(P), and potassium(K) fertilizers) are utilized to replenish the soil nutrient content for sustaining the good soil properties.31 The inputs of N, P, and K fertilizers are respectively 175 kg N, 60 kg P2O5, and 60 kg K2O per hectare farmland. The emissions of N2O 8


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and NO from soil nitrification and denitrification reactions as a result of N fertilizer application are included in the data inventory. The total emission factor of N2O and NO including direct and indirect emissions from the soil owing to N fertilizer application is respectively 13.75 g N2O–N/kg N and 6.5 g NO–N/kg N.43, 44 The electric energy of 105 kWh for irrigation, 0.99 kg pesticides, and 2.70 kg herbicides are consumed per hectare farmland during the growth of corn. The fossil energy consumption from the production of fertilizers, electric energy, pesticides and herbicides and all of waste emissions needs to be distributed between corn grain and corn stover. As agricultural residue, the market-value-based allocation method aforementioned is used for dealing with corn stover allocation problem. The calculated data allocated to corn stover production are listed in Table S6 in SI.

Biomass collection and transportation In china, the reaped biomass is usually transported to the adjacent collection stations by tractor and then baled to increase the mass density of biomass for centralized transportation by truck. Therefore the reaping, baling, and stevedoring processes are involved in the collection task. The diesel fuel is consumed during the collection and transportation of biomass except that the electricity is expended on the baling of corn stover. The biomass transportation includes both transporting biomass to the pyrolysis plant and a return trip with empty load. The total weight of delivered biomass containing 25wt. % M is 33.5tonnes/day. The corn planting region is assumed to be a circular area taking the pyrolysis plant as the center. The coverage rate of corn field is about 30% in central China. The availability ratio of corn stover is about 0.40. The theoretical collection radius of corn stover is a function of many variables including biomass yield per unit area, the plant capacity, the coverage rate of corn field, and the availability of corn stover, the 9



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value of which is about 5.6 km calculated according to the data aforementioned. Main inventory data for biomass collection transportation are listed in Table S7 in SI.

Biomass pre-treatment The biomass pretreatment includes chopping, drying and grinding of feedstock. The electricity is consumed during chopping and grinding of corn stover. About 17.02 kWh of electric energy is expended on one tonne of corn stover with 25wt. % M for chopping it from the original length to 10 mm particle diameter. About 0.081kg of superheated steam is used for drying 1kg of the chopped corn stover in order to decrease its water content to 7 wt. %. The superheated steam is generated from waste heat utilization of high temperature flue gas. Then 50 kWh of electricity energy is required to grind one tonne of the dried corn stover with 7 wt. % moisture content

45

.

Detailed input data are showed in Table S8 in SI.

Bio-oil production The pyrolysis plant pyrolyzing 26.9 tonnes/day of corn stover with 7 wt. % M has been modeled using Aspen Plus software to obtain the basic mass and energy flows for LCA. In this study, the bio-oil output containing water is 19.18 tonnes/d and the detailed compositions of bio-oil are shown in Table S2 in SI. The char and the NCGs are treated as by-products. All the NCGs and about 74 wt. % of char are burned out as fuel. The LHV of char is about 20.3 MJ/kg calculated according to ultimate analysis and proximate analysis of char. The surplus char is treated as a substitute for raw coal with a LHV of 20.908 MJ/kg and is assumed to be consumed locally, so its transportation does not be considered.20 The electricity is consumed by the devices including draught fans, pumps, gas-solid separators, et al. The process water is employed to quench the hot pyrolysis gases to recover bio-oil and the air is used for combusting NCGs and 10


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char. During combustion, a lot of waste gases are discharged, e.g. carbon dioxide, carbon monoxide, sulfur dioxide, nitrogen oxides, and so on. The inventory analysis for bio-oil production is shown in Table S9 in SI.

Bio-oil upgrading The polyol output is 4.091tonnes/d corresponding to a yield of 16.4 wt. % based on the dry basis of corn stover. The esters output is 2.881 tonnes/d. The mass ratio of methanol input to the water-free APB input is 3 for improving the effect of removing acids, the consumption of which is 50.92 kg/h. The Ru/C and Pt/C catalysts are employed in the hydrotreatment of APB and their application amounts are calculated according to 3wt. % of the mass of water-free APB. The annual supplement quantity of catalysts is assumed to be 20 percent of their application amounts in view of various losses. The net hydrogen output is 0.576 tonnes/d. The process heat required by the fuel reactor (FR) is totally provided by the air reactor (AR) by virtue of the circulating oxygen carrier. The electricity consumed can be wholly provided by waste heat generation of high temperature gas under the self-sustaining operation mode in the CLHP sub-process.18 During hydrogen production, some waste gases from AR are directly emitted into the air while 90 percent of CO2 from FR is conservatively assumed to be captured. However the transportation and sequestration of CO2 captured are not included in this study. The mixture of hematite and alumina (Fe2O3+Al2O3) is utilized as oxygen carrier in the CLHP process, the service life of which is assumed to be 2,000 hours considering its reactivity inactivation. The purified water is employed as working medium for waste heat power generation and acts as a reactant in the steam reactor (SR) in the CLHP process. The vast majority of process water is used for condensing water vapor mixed with CO2 11



and hydrogen gas in the CLHP sub-process. The waste water produced during the bio-oil upgrading is purified firstly and then sent into the public emission system. The fossil energy consumption for organic wastewater treatment and its greenhouse gas emissions are included in. The detailed inventory data are listed in Table S10 in SI.

Product transportation and distribution Considering small-scale production of polyols, it is assumed that the polyol fuel is consumed locally. The polyol transportation to the bulk terminals is by 8-tonne truck. The one-way transportation distance is assumed to be 100 km. The polyol fuel is distributed by truck with an average travel distance of 30 km.20 The factors of energy consumption and emissions from the transport vehicle are from CLCD. The inventory analysis is listed in Table S11 in SI.

Polyol application The ethylene glycol, as a main component of polyol fuel, has been successfully tested in the diesel engine with no obvious difference in brake specific fuel consumption under an addition of 10% volume in diesel.46 Additionally, the test results indicate it can contribute to reducing the emissions of CO, NOx and soot. It is promising that the polyol fuel partly replaces the petroleum fuels. The LHV of polyol fuel is about 22.19 MJ/kg calculated according to the components of polyols. The inventory data for 1 MJ energy output are shown in Table S12 in SI.

Results and Discussion Fossil energy inputs The FEI of each unit process is calculated based on the FU according to the inventory data in SI, the allocation factors and the basic data from CLCD, as shown in Figure 2. The net FEI include the fossil energy required by all the unit processes and the credit of char shown as a 12


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negative value.20, 47 The total positive FEI is the sum of the fossil energy consumed by all the unit processes, its value being 0.864 MJ per MJ energy output. Figure 2 indicates the largest FEI is used for bio-oil upgrading, accounting for 42.1% of the total positive FEI. This mainly results from the consumption of methanol, hydrogen gas, electricity and water steam. Approximately 34.0% of the total positive FEI is consumed by bio-oil production, which is the second largest FEI because of the electricity consumption for many pumps, draught fans, solid cyclones, etc. The FEI for biomass pre-treatment accounting for about 13.2% of the total positive FEI is nearly caused by the electricity consumption for biomass chopping, grinding and conveying. The corn stover production contributes about 5.0% of the total positive FEI, which mainly results from use of pesticides and fertilizers (especially nitrogen fertilizer). About 3.8% the total positive FEI is spent on the biomass collection and transportation. The fossil energy used for polyol transportation contributes about 1.9 % of the total positive FEI owing to local consumption. The surplus char contributes to 0.104 MJ reductions per MJ energy output to the total positive FEI. Finally the net FEI is 0.760 MJ per MJ energy output. Additionally, the net FEI of hydrogen gas calculated is about 0.596 MJ per MJ hydrogen gas.

GHG emission In this study, the GWP is a sum of CO2 equivalent from the GHGs including CO2, carbon monoxide (CO), methane (CH4), nitrous oxide (N2O) and describes the overall contribution to the potential global climate change. Based on the FU, the GWP of polyol fuel from each unit process is calculated and the results are shown in Figure 3. The reduction in GHG emissions is mainly attributed to the biogenic CO2 credit from the uptake of atmospheric CO2 during growth of biomass. The biogenic CO2 credit can offset the biogenic carbon emissions from biomass 13



pyrolysis, bio-oil upgrading, biofuel consumption, and the disposal of carbonaceous organics in waste water. Obviously, if the atmospheric CO2 absorbed by biomass is returned to the atmosphere, the net greenhouse effect is nearly zero. If these biogenic carbon emissions and credits are included in, they would dominate Figure 3.39 Therefore, Figure 3 only includes all of carbon emissions including indirect and direct from fossil energy use in various unit processes and the equivalent carbon credits resulting from char replacing raw coal and H2 consumption from the CLHP with CO2 capture. The GWP of each unit process allocated to the polyol fuel is calculated according to the allocation methods aforementioned. The total positive GWP is 0.0737 kg CO2, eq. per MJ energy output. The unit process of bio-oil production contributes about 38.1 % of the total positive GWP, which is the largest GHG emission owing to electricity consumption. The unit process of APB upgrading makes a contribution of 33.1 % to the total positive GWP as the second largest GHG emission largely resulting from the consumption of methanol and electricity. The third largest contribution to the total positive GWP, accounting for 14.8% of the total positive GWP, primarily comes from the electricity consumption for biomass pre-treatment. Another contributor is the unit process of biomass production contributing 8.4% of the total positive GWP, which is mainly caused by the nitrogen fertilizer application. The collection and transportation of biomass and the polyol transportation respectively offer 3.6% and 2.0% of the total positive GWP. The net GWP of hydrogen production is -0.0769 kg CO2, eq. per MJ hydrogen gas, which is attributed to CO2 capture and bio-based fuel used by the CLHP sub-process. The equivalent carbon credit from hydrogen gas consumption is -0.0209 kg CO2, eq. per MJ energy output. The equivalent carbon credit from char is about -0.0084 kg CO2, eq. per MJ energy output. As a result, the net GWP of 14


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polyol fuel is 0.0444 kgCO2, eq. per MJ energy output.

Comparative analysis on hydrogen sources and different fuels As shown in Table 1, compared with natural gas steam reforming (NGSR) and coal gasification (CG) for hydrogen production, the net FEI of hydrogen gas is significantly reduced via the CLHP process using NAPB as fuel, which is only 18.4% of that from CG for hydrogen production. More remarkably, the hydrogen gas from the CLHP process has a negative net GWP due to the bio-based fuel and CO2 capture. This CLHP sub-process with CO2 capture plays a role of carbon sink. According to Table 1, the different hydrogen source has significant influence on the net FEI and especially the net GWP of polyol fuel. The net GWP of polyol fuel in the baseline case reduces by 37.4% and 49.9% respectively compared to those of the cases consuming hydrogen from NGSR and CG. Table 1 shows the net FEI of the polyol fuel decreases by 42.9% and 42.2% respectively compared with petroleum-based gasoline and diesel, and correspondingly the net GWP has a reduction of 55.1% and a reduction of 56.9% respectively. It indicates that the bio-based polyol fuel has significant advantages of lower fossil energy consumption and GHG emissions over the petroleum-based fuels. These are mainly attributed to the renewable biomass feedstock, the relatively moderate reaction conditions of APB upgrading, the CLHP process with inherent CO2 separation, and waste heat recovery of the overall system.

Sensitivity analysis Sensitivity analysis is aimed to ascertain whether the results obtained are significantly affected by the uncertainty of the data variation. Sensitivity analysis of GHG emission is performed via changing operation parameters within a prescribed range (±25%) versus the 15



baseline case in this study. The discussed parameters include the application amount of nitrogen fertilizer, the biomass collection radius, the dry APB yield, the polyol yield and the electricity consumption required by biomass pre-treatment, biomass pyrolysis and bio-oil upgrading. The sensitivity analysis of GHG emission from polyol fuel is shown in Figure 4 in the form of relative deviation. The overall relative deviation of the net GWP ranges from -21.8% to 22.1%. The greatest impact on GHG emission is from the polyol yield, a variation of ±25% of which respectively leads to a GWP deviation of -21.8% and 22.1% versus the baseline case. When the electricity consumption used for bio-oil production varies ±25% off that of the baseline case, the net GWP increases by 15.8% and decreases by 15.8% respectively. The electricity consumption for biomass pre-treatment and APB upgrading has a relatively smaller effect on the net GWP of polyols, a variation of ±25% of which respectively leads to a net GWP change from -6.3% to 6.1% and from -4.3% to 4.1%. A variation of ±25% in the dry APB yield produces a net GWP change from -8.3% to 8.4%. The application amount of nitrogen fertilizer has a small impact on the net GWP, a variation of ±25% corresponding to a net GWP change of ±2.9%. Additionally, the biomass collection radium has a negligible effect on the net GWP of polyols, a variation of ±25% producing a variation of ±0.05% in the net GWP. The sensitivity analysis results indicate that the data uncertainty of the polyol yield, the electricity consumption for bio-oil production have obvious impact on the net GWP of polyol fuel.

Conclusions The fossil energy consumption and GHG emissions of polyol fuel produced from corn stover fast pyrolysis and bio-oil upgrading are mainly investigated based on LCA in this study. The study results indicate the co-production technology of hydrogen gas and polyols can greatly reduce the 16


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FEI and the GHG emissions than the scenario where the polyol fuel is the only product and hydrogen gas required for hydrogenation of APB comes from NGSR or CG. Among seven unit processes, the upgrading process of APB has the largest FEI while the bio-oil production contributes the largest GHG emissions. All the NCGs and about 74 wt. % of char are combusted to supply the process heat required for the whole system to reduce the external FEI. The net FEI and the net GWP of polyol fuel are respectively 0.760 MJ and 0.0444 kg CO2, eq per MJ polyols via the proposed production pathway. According to the comparative analysis, the polyol fuel has significant advantage of low carbon emission over petroleum-based fuels. The sensitivity analysis results indicate the polyol fuel yield and the electricity consumption for bio-oil production have significant influence on the GHG emissions. It is possible to decrease the GHG emissions through improving the polyol yield, the dry bio-oil yield, and waste heat utilization in the overall system.

Supporting Information Please refer to Supplement Information of this paper for detailed information including the ultimate analysis and proximate analysis of corn stover, the compositions and yields of fast pyrolysis products, the polyol compositions and their outputs, the process diagram, the modeling assumptions, the operation parameters and the simulation results of hydrogen production, and life cycle inventory data of seven unit processes.

Acknowledgements This work was supported by the National Science Foundation for Distinguished Young Scholars of China [Grant No. 51525601] and the National Natural Science Foundation of China 17



(NSFC)-the National Research Council of Thailand (NRCT) Project (Grant No.51661145011).

Nomenclature APB

Aqueous Phase Bio-oil

AR

Air Reactor

CG

Coal Gasification

CLCD

Chinese Life Cycle Database

CLHP

Chemical-Looping Hydrogen Production

FEI

Fossil Energy Input

FR

Fuel Reactor

FU

Functional Unit

GHG

Greenhouse Gas

GWP

Global Warming Potential

ILUC

Indirect Land Use Change

IPCC

Intergovernmental Panel on Climate Change

LCA

Life Cycle Assessment

NAPB

Non-aqueous Phase Bio-oil

NCGs

Non-condensable Gases

NGSR

Natural Gas Steam Reforming

SI

Supporting Information

SOC

Soil Organic Carbon

SR

Steam Reactor

References 18


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For Table of Contents Use Only LCA Separator APB

Polyols Upgrading

Biomass

Fast Pyrolysis

Bio-oil H2 NAPB

CLHP

H2

Synopsis: The polyol fuel is a renewable biofuel produced from biomass fast pyrolysis and upgrading contributing to the sustainable development.

25



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Biomass Production

Biomass Collection and Transportation

Biomass Pretreatment Bio-oil Production Biomass Fast Pyrolysis

Fluidizing Gas & Process Heat

Process Stream Char

Solids Removal

Heat Production

Process Stream  Energy Resources  Material Resources

Non-condensable Gases

Bio-oil Recovery

 Air Emission  Water Emission  Solid Waste

Bio-oil Upgrading Phase Separation of Bio-oil

Surplus Char

Aqueous Phase Bio-oil Non-aqueous Phase Bio-oil Iron-based Chemical Looping Hydrogen Production

Esterification & Hydrogenation of Aqueous Phase Bio-oil H2 Polyols Product Transportation & Distribution

Surplus H2

Delivered Polyols

Waste Treatment

Product Application

Figure 1. Life cycle system boundary diagram for polyol fuel from corn stover via fast pyrolysis and upgrading

Figure 2. Fossil energy inputs of various unit processes based on per MJ energy output


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Figure 3. GWP of various unit processes based on per MJ energy output

Figure 4. Sensitivity of GHG emissions caused by the variations of various operation parameters versus the baseline case



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Table 1. Net fossil energy input and net GWP of different hydrogen sources and different fuels Net fossil energy input

Net GWP

(MJ/MJ Fuel)

(kg CO2,eq/MJ Fuel)

Hydrogen from CLHP using NAPB as fuel

0.596

-0.0769

Hydrogen from natural gas steam reforming 48

1.527

0.0991

Hydrogen from coal gasification (initial data from CLCD)

3.242

0.2160

Polyol production using H2 from CLHP (baseline case)

0.760

0.0444

Polyol production using H2 from natural gas steam reforming

0.901

0.0709

Polyol production using H2 from coal gasification

1.159

0.0886

Petroleum-based gasoline 49

1.331

0.0989

Petroleum-based diesel 49

1.316

0.1030

Item

1


Life Cycle Assessment of Polyol Fuel from Corn Stover via Fast

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