Environmental assessment of thermo-chemical processes for bio-ethylene production in comparison with bio-chemical and fossil-based ethylene

The University of Manchester Research Environmental assessment of thermo-chemical processes for bio-ethylene production in comparison with biochemical and fossil-based ethylene DOI: 10.1016/j.jclepro.2018.08.147 Document Version Accepted author manuscript Link to publication record in Manchester Research Explorer Citation for published version (APA): Alonso-fariñas, B., Gallego-schmid, A., Haro, P., & Azapagic, A. (2018). Environmental assessment of thermochemical processes for bio-ethylene production in comparison with bio-chemical and fossil-based ethylene. Journal of Cleaner Production, 202, 817-829. https://doi.org/10.1016/j.jclepro.2018.08.147 Published in: Journal of Cleaner Production Citing this paper Please note that where the full-text provided on Manchester Research Explorer is the Author Accepted Manuscript or Proof version this may differ from the final Published version. If citing, it is advised that you check and use the publisher's definitive version. 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Download date:29. may.. 2023 Journal of Cleaner Production 202 (2018) 817-829 https://doi.org/10.1016/j.jclepro.2018.08.147 Environmental assessment of thermo-chemical processes for bio-ethylene production in comparison with bio-chemical and fossil-based ethylene Bernabé Alonso-Fariñasa*, Alejandro Gallego-Schmidb*, Pedro Haroa, Adisa Azapagicb a Departamento de Ingeniería Química y Ambiental, Escuela Técnica Superior de Ingeniería, Universidad de Sevilla, Camino de los Descubrimientos s/n. 41092 Seville, Spain. b Sustainable Industrial Systems, School of Chemical Engineering and Analytical Science, The University of Manchester, The Mill, Sackville Street, Manchester M13 9PL, UK *Corresponding authors: be[email protected]; [email protected] Abstract The use of biomass for production of chemicals is gaining interest because of its potential to contribute towards a reduction in greenhouse gas emissions and other environmental benefits linked to the substitution of fossil resources. But, conversely to biofuels, studies focusing on environmental impacts of biomass-derived chemicals are scarce. This paper uses life cycle assessment to evaluate the environmental sustainability of bio-ethylene from poplar produced by the following three thermo-chemical routes: direct and indirect dehydration of ethanol and production of olefins via dimethyl ether. The indirect route is the best option for most impact categories for all three allocation methods considered: system expansion, economic and energy basis. However, the dimethyl ether-to-olefins route has the lowest global warming potential. In comparison to ethylene produced bio-chemically from sugar beet, the thermo-chemical indirect route has lower impacts for all categories except human, terrestrial and freshwater toxicities. All three thermo-chemical alternatives show a significant reduction in global warming potential (up to 105% in the case of dimethyl ether-to-olefins) and depletion of fossil fuels when compared to conventional ethylene production from fossil fuels. However, the results also suggest that bioethylene produced by any of the three thermo-chemical routes would lead to a significant increase in most other impact categories relative to fossil fuels. Therefore, while trying to reduce greenhouse gas emissions, the overall environmental sustainability of bio-ethylene suffers from the increase in other environmental impacts. Keywords: Bio-chemical production; climate change; environmental sustainability; ethylene; life cycle assessment. 1 Introduction The European chemicals industry is committed to a gradual increase in the utilization of renewable feedstocks, with the objective of producing 25% of biomass-derived chemicals in 2030 (DSBC, 2012). Biomass-derived chemicals act as a storage of biogenic carbon (Haro et al., 2014) and could potentially have negative net greenhouse gas emissions (The Royal Society, 2016). This makes them an appealing target for reducing the impact on climate change from the chemicals industry. Among the candidates for producing bio-chemicals, ethylene stands out as the largest chemical commodity with the global demand of 150 million tonnes in 2016 (Mitsubishi Chemical, 2017). Ethylene is currently largely produced by steam cracking using different hydrocarbon feedstocks (ethane, propane, naphtha and gas oils), although the use of ethane is being favoured, especially in Europe (Ethylene Profile, 2015). Even though bio-ethylene production is still far from playing an important role in the near future, it can complement production of fossil-based olefins (Amghizar et al., 2017; Braskem Company, 2017). Compared to other biomass-derived chemicals, the production of bio-ethylene has an advantage that it can be introduced directly into existing value chains, infrastructure and markets (Arvidsson, 2016). Ethylene can be produced from biomass following two different pathways: bio- 2 chemical and thermo-chemical. In the former, ethanol produced from the fermentation of sugars is dehydrated into ethylene. The Brazilian company Braskem is already producing 200,000 t/y of polymer-grade bio-ethylene using sugarcane bio-ethanol as an intermediate (Braskem Company, 2017). In the thermo-chemical pathway, lignocellulosic biomass is converted into ethylene prior to thermal treatment (pyrolysis and/or gasification) and further chemical conversion of produced syngas into ethylene. There are two alternatives for the chemical conversion, either the production of methanol/dimethyl ether (DME) or ethanol as chemical intermediates. In the case of methanol/DME, a methanol-to-olefins reactor is used. For ethanol, the same dehydration process as in the bio-chemical pathway is utilized. Several studies have evaluated techno-economic feasibility of ethylene production via the bio-chemical route, including Kamzon et al. (2016), Becerra et al. (2017) and Nitzsche et al. (2016). Equivalent studies of thermo-chemical pathways have also been carried out (Haro et al., 2013; McKechnie et al., 2015; Sharifzadeh et al., 2015). In this study, we focus on the thermo-chemical route to evaluate the environmental sustainability of producing bio-ethylene from biomass. The results are compared with bio-chemical ethylene produced by dehydration of first-generation bio-ethanol and with ethylene obtained by steam cracking of fossil resources. The following three main alternative pathways are considered: direct ethanol dehydration, indirect ethanol dehydration and DME-to-olefins. Therefore, the scope of the work covers the most promising alternatives for bio-ethylene production via thermo-chemical conversion (Haro et al., 2013). In contrast to biofuels, there are scarce examples of life cycle assessment (LCA) studies of biomass-derived chemicals. Most existing studies are focused on specialty chemicals produced via the bio-chemical pathway (e.g. Fiorentino et al., 2017) and only a few on chemical commodities like ethylene (e.g. Cheali et al., 2015). Studies of life cycle impacts of ethylene production using the thermo-chemical pathway are rare and the number of impacts considered is limited. For example, Karka et al. (2017) considered only three categories: cumulative energy demand, global warming potential and water consumption. A couple of other studies discussed the key environmental issues in the production of bio-ethylene focusing on second-generation ethanol (Belboom and Leonard, 2016; Liptow et al., 2013). First-generation bio-chemical ethanol was studied by Ghanta et al. (2014) who considered corn as a feedstock in a US context while Tsiropoulos et al. (2015) evaluated the use of sugarcane in Brazil and India. Sugarcane from Brazil was also considered by Kikuchi et al. (2017) for the production of ethanol in Japan, alongside the use of domestic sugarcane-molasses. Other studies assessed the economic and environmental implications of using bio-ethanol for ethylene production instead of utilizing it as a transportation fuel (McKechnie et al., 2015; Posen et al., 2015). Finally, Horváth et al. (2017) analysed the carbon efficiency of the conversion of bio-ethanol into different chemicals, including ethylene. Therefore, there is a lack of comprehensive studies of environmental impacts of thermo-chemical production of ethylene from biomass. This study aims to fill this knowledge gap. The results are compared to the impacts from ethylene produced by bio-chemical conversion as well as with ethylene produced from fossil feedstocks to provide a comprehensive multi-criteria analysis of the environmental performance of bio-ethylene. As far as we are aware, this is the first study of its kind internationally. 2 Methodology The study involves a comparative attributional LCA, based on the guidelines of the ISO 14040/44 standards (2006a, 2006b). The goal and scope of the study are described next, followed by the inventory data and an overview of the impact assessment method used in the study. 2.1 Goal and scope The main goal of the study is to estimate and compare life cycle environmental impacts of the three alternative methods for producing bio-ethylene from biomass via thermo-chemical conversion: direct ethanol dehydration (Case 1); indirect ethanol dehydration (Case 2); and DME to olefins 3 (Case 3). A further goal is to compare these thermo-chemical routes with ethylene produced from first-generation ethanol via the bio-chemical route and with ethylene from fossil-based resources. As indicated in Figure 1, the scope of the study is from ‘cradle to gate’, with two main stages considered: biomass supply (cultivation, collection and transportation to the processing plant); and production of bio-ethylene and its co-products. The use of bio-ethylene and the co-products, as well as their distribution, are excluded from the system boundaries. The construction and decommissioning of the production plant are also excluded as the impacts of infrastructure per unit of product are negligible over the (long) lifespan of industrial plants (Reyes Valle et al., 2015). The functional unit is defined as the production of 1 tonne of ethylene. Figure 1 Systems boundaries considered for the production of bio-ethylene via the thermochemical route. (Case 1: direct ethanol dehydration; Case 2: indirect ethanol dehydration; Case 3: dimethyl ether to ethylene.) 2.2 System description The plant size chosen is equivalent to 500 MWth in terms of the energy content of the feedstock processed, based on the higher heating value (HHV). This plant size is typically considered in studies of biomass-to-liquids (BTL) plants (Villanueva et al., 2011). The type of biomass processed in the plant is the same for each of the three cases considered. However, the amount of biomass required per tonne of ethylene produced and the output of the co-products vary depending of the Cultivation and collection Transportation Biomass to bioslurry Bioslurry to ethanol Biomass to ethanol Ethanol to ethylene Bioslurry to olefins Methanol Propanol Ethylene Ethylene Propylene Liquefied Petroleum Gas (LPG) CASE 2 CASE 1 CASE 3 Biomass supply Production Fertilizers /Pesticides Fuel / Electricity Catalysts Bed materials Solvents Other chemicals Water Energy Waste to Landfill Emissions to air, soil and water Emissions to air Wastewaster to treatment 4 production route due to the different efficiency and selectivity of the three routes. The feedstock is poplar as detailed in the next section. 2.2.1. Feedstock supply Poplar is selected as the feedstock, which has recently attracted significant interest as an energy crop (Guo, 2014). The production plant is assumed to be based in the Duero Valley (Castilla y León, Spain) as there is extensive cultivation of poplar there due to favourable climatic conditions. For these reasons, land use change is not considered. The life cycle of a poplar crop spans 16 years. In the first year, land preparation and the planting of cuttings take place. This is followed by three tree-growing cycles of five years each (Gasol et al., 2009), with the trees being cut to the ground after each cycle. At the end of the third cycle, the trunks are treated with insecticide to remove the roots and, after three months, new cuttings are planted. The average production of biomass is 216 t/ha on a dry basis for the three cycles as a whole. Further description of the feedstock supply can be found in Reyes Valle et al. (2015). 2.2.2. Case 1: Direct ethanol dehydration This process involves three main steps: i) bioslurry production from biomass (Figure 2); ii) production of ethanol from bioslurry by direct route through gasification and catalytic conversion of syngas (Figure 3); and iii) production of ethylene by ethanol dehydration (Figure 4), based on a commercial technology (Chematur Engineering AB, 2017). A detailed description of this route is given in the Supporting Information (SI). 2.2.3. Case 2: Indirect ethanol dehydration In this case, there are two main stages: i) production of ethanol from biomass by indirect route; and ii) production of ethylene by ethanol dehydration. i) The process for producing ethanol is detailed in Figure 5 (Haro et al., 2012). It follows the following sequence: first, a fraction of the syngas is used for methanol synthesis; the methanol is then dehydrated to DME and water; and finally, DME and the rest of the syngas are reacted to produce ethanol via methyl acetate. Methanol is also produced in this last step. For further details, see the SI. ii) The production of ethylene follows the same process as in Figure 4. 2.2.4. Case 3: DME to olefins Case 3 comprises two main steps: i) bioslurry production; and ii) production of olefins. The bioslurry and the olefins are produced in the processes outlined in Figure 2 and Figure 6 (Haro et al., 2013), respectively. A detailed description is provided in the SI. 5 Figure 2 Bioslurry production used in the direct ethanol dehydration route (Case 1) and in the DME-to-olefins route (Case 3). (Adapted from Villanueva et al. (2011). The green colour (in the online version of the paper) refers to the main input and output from the process. The red colour (online version) signifies the outputs from the process, including co-products.) Figure 3 Ethanol production via the direct route (Case 1). (Adapted from Villanueva et al. (2011). WGS: water-gas shift; WWT: wastewater treatment; ATR: autothermal reformer; LO-CAT: liquid-phase oxidation catalytic unit. The green colour (in the online version of the paper) refers to the main input and output from the process. The red colour (online version) signifies the outputs from the process, including coproducts.) Figure 4 Ethylene production by dehydration of ethanol. (Adapted from Villanueva et al. (2011). WWT: wastewater treatment. The green colour (in the online version of the paper) refers to the main input and output from the process. The red colour (online version) signifies the outputs from the process, including co-products.) CycloneFast pyrolysis Combustor Milling Gas-liquid separation Combustor and power generation Air Biochar Bioslurry Air Flue gas Grinding Biomass Drying Flue gas Ash Flue gas Bio-oil Air Electricity ReactorSelexol Gas-liquid separation ZnO bedATR H2OO2 Stabilizer Combined cycle Methanol Ethanol Propanol Lights Dewatering unit Distillation columns Fluegas To WWT Bioslurry Ash Gasification Candle filter Sour WGS Scrubber H2O O2 Ash CO2 Sulphur cake LO-CAT To WWT To WWT Electricity Dehydration reactor Ethanol Gas-liquid separator Gas-liquid separator To WWT Dewatering unit To WWT Fractionation column Fractionation column Ethylene To WWT Water Fuel gas Coke combustor Flue gas Combustor Fuel gas Natural gas Flue gas Air Air 6 Figure 5 Ethanol production via the indirect route (Case 2). (Adapted from Haro et al. (2012). HRSG: heat recovery steam generator; LPMEOH: liquid-phase methanol; LO-CAT: liquid-phase oxidation catalytic unit; SMR: steam methane reformer; MEA: monoethanolamine; DME: dimethyl ether. The green colour (in the online version of the paper) refers to the main input and output from the process. The red colour (online version) signifies the outputs from the process, including co-products.) Methanol WaterAirOil Mediumpressure steam Biomass MillingDryer Gasification bed Combustor Sand Sand & biochar Sand Ash Flue gas Flue gas Cleaning Cyclone Ash HRSG OLGA Dust Tars Scrubber Air & tars HRSG Low-pressure steam SMR LPMEOH LO-CAT Sulphur cake Guard bed Combustor CO2 Air Purge AirPurge and lights Syngas to hydrocarbonylation Dewatering unit Hydrocarbonylation reactor DME Column Ethanol MEA CO2 capture CO2 Gas-liquid separation Dehydration reactor Purge Unreacted syngas Syngas from SMR Stabilizer column MeOH-EtOH column Methyl acetate Lights Raw methanol Flue gas Flue gas Raw methanol Gas-liquid separation Unreacted syngas To WWT Combustor and power generation Water Water To WWT To WWT To WWT Electricity Low-pressure steam Medium-pressure steam 7 Figure 6 Production of olefins via dimethyl ether (Case 3). (Adapted from Haro et al. (2012). WGS: water-gas shift; WWT: wastewater treatment; DME: dimethyl ether; LO-CAT: liquid-phase oxidation catalytic unit; LPG: liquefied petroleum gas. The green colour (in the online version of the paper) refers to the main input and output from the process. The red colour (online version) signifies the outputs from the process, including co-products.) 2.3 Life cycle inventory All background LCA data have been obtained from the Ecoinvent database V3.3 (Moreno Ruiz et al., 2016), except for NPK fertilizers, which have been sourced from the agri-footprint database (Durlinger et al., 2014). The 2016 Spanish electricity mix has been considered in the analysis (REE, 2017). The storage of biogenic carbon is not included since the end-use of ethylene is not considered and it is not known how long the carbon would be stored before being released back to the atmosphere. However, the influence of carbon storage on the results is discussed in section 3.3. 2.3.1. Biomass supply The inventory data for the biomass supply stage are summarised in Table 1. The data refer to the annual production of 1 Mt of biomass (wet) needed for the chosen size of the ethylene plant (equivalent to the HHV of the feedstock of 500 MWth). The requirements for fertilizers, pesticides, diesel, electricity and the transport have been calculated following the biomass supply model described in Reyes Valle et al. (2015). The amounts of pesticides and their emissions to soil have been calculated according to Nemecek and Schnetzer (2012) and Sutter (2010). Emissions to water have been estimated using the average lixiviation fractions given in Franke et al. (2013). The concentration of metals in the fertilizers for the lixiviation calculations and the emissions to air from To WWT Bioslurry Ash Gasification Candle filter Sour WGS Scrubber H2O O2 Selexol CO2 Sulphur cake Ash LO-CAT To WWT CO2 DME synthesis reactor Syngas Olefins synthesis reactor Distillation column Gas-liquid separator Gas-liquid separator Rectisol unit Dewatering unit Fractionation column Fractionation column Ethylene Fuel gas Fractionation column LPG Fractionation column LPG Fractionation column LPG Propylene Fuel gas Combined cycle To WWT To WWT To WWT LO-CAT CO2 Sulphur cake Fluegas Fuel gas Electricity 8 the use of fertilizers have been determined using data and methodologies proposed in Nemecek and Schnetzer (2012). According to these authors, the nutrients supplied to the soil are assumed to be taken up by the biomass or lost to the air or water, so the quantity of nutrients in the soil should not change in the long term. Therefore, no emissions to the soil from the use of fertilizers are considered. Table 1 Life cycle inventory data for annual production of 1 Mt (500 MWth) of poplar (wet) Category Sub-category Amount Fertilizers NPK (9-18-27) 6,098 t/y N fertilizer (ammonium nitrate) 2,541 t/y Pesticides Metil pirimifos (insecticide) 6 t/y Gliphosate (herbicide) 50 t/y Propineb (fungicide) 4 t/y Diesel 843 t/y Electricity 20 MWh/y Emissions to air Diesel emissionsa Carbon dioxide Carbon monoxide Methane NMVOCb Nitrous oxide Nitrogen oxides Particulates Sulphur dioxide Ammonia Polycyclic aromatic hydrocarbons 2,630 t/y 9.58 t/y 0.14 t/y 4.36 t/y 0.1 t/y 37.11 t/y 3.77 t/y 0.85 t/y 16.8 kg/y 2.8 kg/y Ammoniac 47 t/y Nitrous oxidec 24 t/y Nitrogen oxidesc 5 t/y Emissions to water Nitrate 615 t/y Phosphate 11 t/y Cadmium 13 kg/y Copper 51 kg/y Zinc 306 kg/y Lead 20 kg/y Nickel 59 kg/y Chromium 195 kg/y Emissions to soil Metil pirimifosd 6 t/y Gliphosated 50 t/y Propinebd 4 t/y Transport Feedstock to the production plant 1.4·107 t·km/y a Emissions from the combustion of diesel in the machinery. b Non-methane volatile organic compounds. c Emissions from the use of fertilizers. d Active components: C11H20N3O3PS (metil pirimifos); C3H8NO5P (glyphosate); C5H8N2S4Zn (propineb). 2.3.2. Ethylene production The inventory data for the production stage are summarised in Table 2 for the three production routes considered. These data have been obtained through simulation in Aspen Plus (Haro et al., 2012, 2013; Villanueva et al., 2011). The simulations are based on the best available data from existing commercial (i.e. dehydration stage) and experimental plants. It can be seen from Table 2 that, for the same plant size (500 MWth), the requirements for biomass and the type and amount of co-products per tonne of ethylene are different for each route. 15 Figure 9 Life cycle environmental impacts of bio-ethylene produced via three thermo-chemical route for allocation on the economic basis. (Economic basis: market prices of ethylene and the co-products. Case 1: direct ethanol dehydration; Case 2: indirect ethanol dehydration; Case 3: dimethyl ether (DME) to olefins. For the impacts nomenclature, see Figure 7. Some impacts have been scaled to fit. To obtain the original values, multiply by the factor shown on the x-axis for the relevant impacts.) 2.1 8.4 6.8 8.8 3.4 3.1 8.3 4.7 5.4 4.4 2.9 0.5 10.6 7.9 10.5 3.6 1.8 3.8 4.7 0.1 3.6 3.3 3.4 7.2 6.3 8.6 3.8 2.9 8.9 4.3 1.8 4.9 2.9 0 2 4 6 8 10 12 ADP e. (g Sb eq./t) ADP f. (GJ/t) GWP (t CO2 eq./t) x0.1 ODP (g CFC-11 eq./t) x0.01 HTP (t DCB eq./t) x0.1 FAETP (t DCB eq./t) x0.1 MAETP (t DCB eq./t) x100 TETP (kg DCB eq./t) POCP (kg C2H4 eq./t) AP (kg SO2 eq./t) EP (kg PO4 eq./t) Case 1 Case 2 Case 3 16 Figure 10 Comparison of thermo-chemical and bio-chemical bio-ethylene for system expansion. (Case 1: direct ethanol dehydration; Case 2: indirect ethanol dehydration; Case 3: dimethyl ether (DME) to olefins. Bio-chemical ethylene: dehydration of ethanol produced from sugar beet by fermentation. For the impacts nomenclature, see Figure 7. Some impacts have been scaled to fit. To obtain the original values, multiply by the factor shown on the x-axis for the relevant impacts.) 36.8 -2.3 4.8 7.0 4.5 4.3 9.5 8.0 59.7 3.7 3.9 4.8 10.6 7.9 10.5 3.6 1.8 3.8 4.7 1.3 3.6 3.3 75.1 -62.4 -0.7 -5.9 7.6 6.2 18.0 9.4 37.5 5.3 5.8 11.3 15.2 14.4 13.7 1.6 1.0 5.1 -7.2 4.6 10.8 8.8 -90 -70 -50 -30 -10 10 30 50 70 90 ADP e. (g Sb eq./t) x0.1 ADP f. (GJ/t) GWP (t CO2 eq./t) x0.1 ODP (g CFC-11 eq./t) x0.01 HTP (t DCB eq./t) x0.1 FAETP (t DCB eq./t x0.1 MAETP (t DCB eq./t) x100 TETP (kg DCB eq./t) POCP (kg C2H4 eq./t) x0.1 AP (kg SO2 eq./t) EP (kg PO4 eq./t) Thermo-chemical ethylene (Case 1) Thermo-chemical ethylene (Case 2) Thermo-chemical ethylene (Case 3) Bio-chemical ethylene 17 3.3 Comparison of thermo-chemical and bio-chemical ethylene Figure 10 shows that, for system expansion, the bio-chemical route using sugar beet as the feedstock for ethanol, is a better option than the thermo-chemical route for only three impacts across the three cases considered: HTP, FAETP and TETP. For the remaining eight impacts, it is less sustainable than at least one of the thermo-chemical cases. The higher ADPfossil, GWP and ODP for the bio-chemical route than any of the three thermochemical cases are due to the heat demand in the biological reactor, supplied mainly by fossil-fuel resources, and the higher specific biomass consumption per tonne of ethylene involving higher diesel consumption in the agricultural activities. GWP is also higher due to the higher emissions of nitrous oxide from the use of fertilizers. The higher values of AP and EP are related respectively to the higher emissions of ammonia to air and nitrate to water from the use of fertilizers for sugar beet than for poplar. For ADPelements, MAETP and POCP, bio-chemical ethylene has higher impacts than Case 2 but lower than Cases 1 and 3. For ADPelements, the higher impact than for Case 2 is due to the higher consumption of pesticides and biocides for the sugar beet and the higher biomass requirement per unit of ethylene produced. The lower impact with respect to Cases 1 and 3 is related to their utilization of metal catalysts. The higher MAETP and POCP relative to Case 2 is due to the heat consumed in the fermentation reactor. Cases 1 and 3 show higher values for MAETP and POCP because of the higher electricity consumption and CO emissions from Selexol, respectively. 3.4 Comparison of thermo-chemical bio-ethylene and fossil-based ethylene Compared to ethylene from fossil resources, thermo-chemical bio-ethylene reduces ADPfossil by 84%-196% and GWP by 66%-105% across the three cases considered (Figure 11). These results are not surprising given the use of biomass for bio-ethylene. Furthermore, the electricity consumption per unit ethylene produced is lower for bio-ethylene (0.39-2.1 MWh/t; see Table 2) than for its fossil-based equivalent (3.5-6.8 MWh/t (Deloite, 2013)). In addition, the reduction in these two impacts is greater for Cases 1 and 3 due to the credits for the coproducts. The reduction in GWP would be much higher if the biogenic carbon storage in bio-ethylene was considered, due to the carbon sequestration by the feedstock. If all the carbon contained in 1 tonne of bio-ethylene is considered as stored carbon, 3.14 t CO2 eq./t would need to be subtracted from the GWP values shown in Figure 9 for each of the three routes. In that case, the GWP would range from –3.21 t CO2 eq./t for Case 3 to –2.36 t CO2 eq./t for Case 2. However, these potential savings in GHG should be interpreted with caution as processing of ethylene into an end product would lead to additional GHG emissions and, depending on the type of the product and its longevity, potential release of the stored carbon back to the atmosphere. Extrapolating the results (without considering biogenic carbon) to the global levels, and assuming that 20% of the demand of 150 Mt/y (Mitsubishi Chemical, 2017) is supplied by thermo-chemical bio-ethylene, would lead to the reductions in GWP shown in Figure 12. These reductions have been calculated considering the current supply of fossil-based ethylene. For system expansion, the savings would range from 18,300 kt CO2 eq./y in Case 2 to 43,950 kt CO2 eq./y in Case 3. The latter is higher than the annual CO2 eq. emissions of Sweden in 2015 (JRC, 2017). These savings would be reduced by almost two times for the energy and 22%-48% for the economic allocation for Cases 1 and 3 (there would be no change for Case 2 due to insignificant credits for the sulphur as fertilizer). However, six other impacts would be higher for bio-ethylene than its equivalent produced by steam cracking (Figure 11): ADPelements, HTP, FAETP, MAETP, TETP and EP. These impacts 18 would increase from three (MAETP) to 39 times (ADPelements) due to the use of metal catalysts, pesticides, fertilizers and MEA which are not required in the production of ethylene from fossil resources. For POCP, Cases 1 and 3 have higher POCP values than fossil-based ethylene (16 and 3.5 times, respectively) because of the CO emissions from the Selexol process. However, the fossil option has a higher impact than Case 2 due to methane leakage from the equipment, pipes, etc. (Berdowski et al., 1995). Furthermore, ODP is higher for Cases 1 and 2 (17 and 25 times) but Case 3 has a 14.6 times lower impact due to the system credits. Finally, Cases 1 and 2 have a similar AP to the fossil option, which is lower than the value in Case 3. These impacts could be reduced by developing more efficient catalysts with longer lifespans. This would reduce the biomass requirements per tonne of ethylene and reduce the amount of both the catalyst needed and solid waste generated at the end of its useful lifetime. In summary, switching from fossil to bio-ethylene would lead to substantial reductions in GWP but would also increase significantly a number of other impacts. This is congruent with the results in Liptow et al. (2015), who reported lower GWP and POCP but higher EP and AP for bio-ethylene from wood produced via thermo-chemical route (methanol to olefins) compared to ethylene from fossil resources. Case 3 offers the greatest potential for reducing GWP (105%) but it also has higher impacts for six other categories. Case 2 also provides a considerable reduction in GWP (44%) but shows a lower or no increase in other categories compared to ethylene from fossil resources. 4 Conclusions This paper has discussed the environmental performance of three thermo-chemical processes for ethylene production from a lignocellulosic feedstock: direct and indirect dehydration of ethanol and dimethyl (DME)-to-olefins route. Three approaches have been considered for apportioning the impacts among the co-products: system expansion, and energy and economic allocation. When system expansion is applied, the indirect route (Case 2) has the lowest values for eight out of the 11 impact categories (ADPelements, HTP, FAETP, MAETP, TETP, POCP, AP and EP), mostly because of the lower requirement of biomass, catalysts and electricity per unit of bio-ethylene produced. On the other hand, the DME-to-olefins route (Case 3) has the lowest impacts for GWP, ADPfossil and ODP due to the system credits for the co-products. Similar conclusions regarding the best alternative are reached when energy or economic allocation is applied. The main difference with the results from system expansion is that the direct dehydration route (Case 1) is the worst option for most of the impact categories for energy allocation due to the lower energy content of the co-product methanol compared to ethylene. Compared to bio-chemical ethylene produced from sugar-beet ethanol, the indirect route reduces the impacts by 23%-73% for most categories, except for HTP, FAETP, and TETP. The other two thermo-chemical routes have lower ADPfossil, ODP, GWP and, to a lesser extent, AP and EP. However, bio-chemical ethylene is the best option for FAETP, HTP and TETP, POCP and ADPelements. All the thermo-chemical processes offer a great potential for reducing GWP (44%-105%) and ADPfossil (104%-196%) relative to ethylene produced from fossil resources. However, for most of the other categories, bio-ethylene has higher impacts. Therefore, the substitution of ethylene produced from fossil fuel resources with thermo-chemical bio-ethylene to reduce greenhouse gas emission could result in an increase in other environmental impacts. 19 Figure 11 Comparison of thermo-chemical bio-ethylene and fossil-based ethylene for system expansion. (Case 1: direct ethanol dehydration; Case 2: indirect ethanol dehydration; Case 3: dimethyl ether (DME) to olefins. Fossil: steam cracking. For the impacts nomenclature, see Figure 7. Some impacts have been scaled to fit. To obtain the original values, multiply by the factor shown on the x-axis for the relevant impacts.) 36.8 -2.3 4.8 7.0 4.5 4.3 9.5 8.0 59.7 3.7 3.9 4.8 10.6 7.9 10.5 3.6 1.8 3.8 4.7 1.3 3.6 3.3 75.1 -62.4 -0.7 -5.9 7.6 6.2 18.0 9.4 37.5 5.3 5.8 0.2 65.2 14.0 4.3·10-2 0.3 0.3 1.3 0.1 2.3 3.8 0.3 -80 -60 -40 -20 0 20 40 60 80 ADP e. (g Sb eq./t) x0.1 ADP f. (GJ/t) GWP (t CO2 eq./t) x0.1 ODP (g CFC-11 eq./t) x0.01 HTP (t DCB eq./t) x0.1 FAETP (t DCB eq./t x0.1 MAETP (t DCB eq./t) x100 TETP (kg DCB eq./t) POCP (kg C2H4 eq./t) x0.1 AP (kg SO2 eq./t) EP (kg PO4 eq./t) Thermo-chemical ethylene (Case 1) Thermo-chemical ethylene (Case 2) Thermo-chemical ethylene (Case 3) Fossil 20 Figure 12 Reduction in global warming potential (GWP) assuming 20% of the global demand was supplied by thermo-chemical bioethylene instead of fossil-based ethylene. (The rest of the demand supplied by ethylene produced by steam cracking. Case 1: direct ethanol dehydration; Case 2: indirect ethanol dehydration; Case 3: dimethyl ether (DME) to olefins. For the impacts nomenclature, see Figure 7.) 27,509 14,270 21,561 18,314 18,314 18,314 43,949 22,833 23,030 0 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 45,000 50,000 System expansion Energy allocation Economic allocation GWP reducion (kt CO2 eq./y) Case 1 Case 2 Case 3 21 Acknowledgements Bernabé Alonso-Fariñas thanks the members of the Sustainable Industrial Systems research group for their kind support during his post-doctoral stay at the University of Manchester. Pedro Haro is grateful to the Universidad de Sevilla for the post-doctoral Grant Contrato de Acceso al Sistema Español de Ciencia, Tecnología e Innovación (VPPI-US). References Amghizar, I., Vandewalle, L.A., Van Geem, K.M., Marin, G.B., 2017. New Trends in Olefin Production. Engineering. 3(2), 171-178. https://doi.org/10.1016/J.ENG.2017.02.006 Arvidsson, M., 2016. Assessing Integrated Gasification-Based Biorefinery Concepts for Decarbonisation of the Basic Chemicals Industry. Industrial Energy Systems and Technologies, Department of Energy and Environment, Chalmers University of Technology. Göteborg. ISBN 978-91-7597-410-1 Aspen, 2007. Aspen Physical Property System. Physical Property Methods, Aspen Technology. Becerra, J., Figueredo, M., Cobo, M., 2017. Thermodynamic and economic assessment of the production of light olefins from bio-ethanol. Journal of Environmental Chemical Engineering 5(2), 1554-1564. https://doi.org/10.1016/j.jece.2017.02.035 Belboom, S., and Léonard, A., 2016. Does biobased polymer achieve better environmental impacts than fossil polymer? Comparison of fossil HDPE and biobased HDPE produced from sugar beet and wheat. Biomass & Bioenergy 85:159-167. https://doi.org/10.1016/j.biombioe.2015.12.014 Berdowski, J. J. M., van der Most, P.F.J., Mulder, W., 1995. Production proccess-Ethylene, code 040501. TNO Company. The Netherlands. BOE, 2014. Spanish Official Gazette (in Spanish). 145-6339 pp 45187-45189. Available at http://www.boe.es. Braskem Company, 2017. http://www.braskem.com/site.aspx/Im-greenTM-Polyethylene Cheali, P., Posada, J.A., Gernaey, K.V., Sin, G., 2015. Upgrading of lignocellulosic biorefinery to value-added chemicals: Sustainability and economics of bio-ethanol- derivatives. Biomass & Bioenergy 75, 282-300. https://doi.org/10.1016/j.biombioe.2015.02.030 Chematur Engineering AB, 2017. Ethylene from ethanol. Available at: http://chematur.se/downloads. Clifford, C.B, 2017. EGEE 439, Alternative fuels from biomass sources, 7.1 Ethanol production-general information. PennState College of Earh and Meneral Sciences and John A. dutton e-Education Institute. Available at: https://www.eeducation.psu.edu/egee439/node/646. Deloite, 2013. Report on Developing Baseline Specific Energy Consumption in Petrochemicals Industry in India. www.deloitte.com/in. Durlinger, B., Tyszler, M., Scholten, J., Broekema, R., Blonk, H., 2014. Agri-Footprint; a Life Cycle Inventory database covering food and feed production and processing. Proceedings of the 9th International Conference on Life Cycle Assessment in the Agri- Food Sector (LCA Food 2014), 8-10 October 2014, San Francisco, USA. ACLCA, Vashon, WA, USA. ISBN: 978-0-9882145-7-6. Available at: http://lcacenter.org/lcafood2014/proceedings/LCA_Food_2014_Proceedings.pdf DSBC, 2012. Dutch Sustainable Biomass Commission (Commissie Duurzaamheidsvraagstukken Biomassa). Sustainable biomass in the chemical industry. The Netherlands Deloitte, 2013. Report on Developing Baseline Specific Energy Consumption in Petrochemicals Industry in India. Available at: www.deloitte.con/in ECOBION project, 2009. Compared life cycle assessments of biomass feedstocks at subregional scale Livrable L7 – Résultats. Agro ParisTech, INRA, PNRB. Ethylene Profile, 2015. ICIS Chemical Business. 27 July-9 August. Page 32. 22 Fiorentino, G., Ripa, M., Ulgiati, S., 2017. Chemicals from biomass: Technological versus environmental feasibility. A review. Biofuels, Bioproducts and Biorefining 11(1), 195-214. https://doi.org/10.1002/bbb.1729 Franke, N.A., Boyaciosglu, H., Hoekstra, A.Y., 2013. Grey water footprint accounting. Tier 1 Supporting guidelines. Value of Water, Research report series n. 65. UNESCO-IHE Institute for Water Education. Delft, The Netherlands. Gasol, C.M., Gabarrell, X., Anton, A., Rigola, M., Carrasco, J., Ciria, P., Rieradevall, J., 2009. LCA of poplar bioenergy system compared with Brassica carinata energy crop and natural gas in regional scenario. Biomass and bioenergy 33, 119–129. http://doi.org/10.1016/j.biombioe.2008.04.020. Ghanta, M., Fahey, D., Subramaniam, B., 2014. Environmental impacts of ethylene production from diverse feedstocks and energy sources. Applied petrochemical research, 4, 167–179. http://doi.org/10.1007/s13203-013-0029-7 Guinée, J.B., Gorrée, M., Heijungs, R., Huppes, G., Kleijn, R., van Oers, L. Sleeswijk A.W., Suh S., Udo de Haes H.A., de Bruijn H., van Duin R., Huijbregts M.A.J., 2001. Life Cycle Assessment: An Operational Guide to the ISO Standards. Parts 1, 2a & 2b. Kluwer Academic Publishers, Dordrecht, The Netherlands. Guo, M., Littlewood, J., Joyce, J., Murphy, R., 2014. The environmental profile of bio-ethanol produced from current and potential future poplar feedstocks in the EU. Green Chemistry 16, 4680-4695. https://doi.org/10.1039/C4GC01124D Haro, P., Ollero, P., Villanueva Perales, A.L., Reyes Valle, C., 2012. Technoeconomic assessment of lignocellulosic ethanol production via DME (dimethyl ether) hydrocarbonylation. Energy 44(1), 891-901. https://doi.org/10.1016/j.energy.2012.05.004 Haro, P., Ollero, P., Trippe, F., 2013. Technoeconomic assessment of potential processes for bio-ethylene production. Fuel Processing Technology 114, 35-48. http://dx.doi.org/10.1016/j.fuproc.2013.03.024 Haro, P., Villanueva Perales, A.L., Arjona, R., Ollero, P., 2014. Thermochemical biorefineries with multiproduction using a platform chemical. Biofuels, Bioproducts and Biorefining 8(2), 155-170. http://dx.doi.org/10.1002/bbb.1409 Horváth, I.T., Cséfalvay, E., Mika, L.T., Debreczeni, M., 2017. Sustainability Metrics for Biomass-Based Carbon Chemicals. ACS Sustainable Chemistry & Engineering 5(3), 2734-2740. https://doi.org/10.1021/acssuschemeng.6b03074 ICIS Pricing Data, 2014. Available at: www.icis.com ISO, 2006a. ISO14040:2006 - Environmental Management - Life Cycle Assessment: Principles and Framework. International Standard Organization, Geneva, Switzerland. ISO, 2006b. ISO14044:2006 - Environmental Management - Life Cycle Assessment: Requirements and Guidelines. International Standard Organization, Geneva, Switzerland. JRC (Joint Research Centre), 2017. Emission Database for Global Atmospheric Research (EDGAR). Emissions time series, CO2 1990-2015. Available at: http://edgar.jrc.ec.europa.eu/overview.php?v=CO2ts1990-2015 Kamzon, M.A., Abderafi, S., Bounahmidi, T., 2016. Promising bio-ethanol processes for developing a biorefinery in the Moroccan sugar industry. International Journal of Hydrogen Energy 41(45), 20880-20896. https://doi.org/10.1016/j.ijhydene.2016.07.035 Karka, P., Papadokonstantakis, S., Kokossis, A., 2017. Cradle-to-gate assessment of environmental impacts for a broad set of biomass-to-product process chains. The International Journal of Life Cycle assessment 22(9), 1418-1440. https://doi.org/10.1007/s11367-017-1262-6 Kikuchi, Y., Oshita, Y., Mayumi, K., & Hirao, M., 2017. Greenhouse gas emissions and socioeconomic effects of biomass-derived products based on structural path and life cycle analyses: A case study of polyethylene and polypropylene in Japan. Journal of Cleaner Production, 167, 289-305. http://dx.doi.org/10.1016/j.jclepro.2017.08.179 Liptow, C., Tillman, A., Janssen, M., Wallberg, O., Taylor, G.A., 2013. Ethylene based on woody biomass - What are environmental key issues of a possible future Swedish production on industrial scale. The International Journal of Life Cycle assessment 18(5), 1071-1081. https://doi.org/10.1007/s11367-013-0564-6 23 Liptow, C., Tillman, A.M., Janssen, M., 2015. Life cycle assessment of biomass-based ethylene production in Sweden - is gasification or fermentation the environmentally preferable route? The International Journal of Life Cycle Assessment. 20(5), 632–644. McKechnie, J., Pourbafrani, M., Saville, B.A., MacLean, H.L., 2015. Environmental and financial implications of ethanol as a bioethylene feedstock versus as a transportation fuel. Environmental Research Letters 10, 124018. https://doi.org/10.1088/1748- 9326/10/12/124018 Mitsubishi Chemical, 2017. Global Supply and Demand of Petrochemical Products relied on LPG as Feedstock. Mitsubishi Chemical Techno-Research. Mohsenzadeh, A., Zamani, A., Taherzadeh, M.J., 2017. Bioethylene Production from Ethanol: A review and techno-economical evaluation. ChemBioEng Reviews 4(2), 75-91. https://doi.org/10.1002/cben.201600025 Moreno Ruiz, E., Lévová T., Reinhard J., Valsasina L., Bourgault G., Wernet G., 2016. Documentation of changes implemented in ecoinvent Data 3.3. Ecoinvent, Zurich, Switzerland. NREL (National Renewable Energy Laboratory), 2006. Equipment Design and Cost Estimation for Small Modular Biomass Systems, Synthesis Gas Cleanup, and Oxygen Separation Equipment, Task 2.3: Sulfur Primer. Nexant Inc. San Francisco, California, USA. Muñoz, I., Flury, K., Jungbluth, N., Rigarlsford, G., Mila i Canals, L., Kimg, H., 2014. Life cycle assessment of bio-based ethanol produced from different agricultural feedstocks. The international journal of life cycle assessment, 19(1), 109-119. http://doi.org/10.1007/s11367-013-0613-1 Nemecek, T., Schnetzer, J., 2012. Methods of assessment of direct field emissions for LCIs of agricultural production systems (Data v3.0). Agroscope Reckenholz-Tänikon Research Station ART, Zurich, Switzerland. Nitzsche, R., Budzinski, M., Gröngröft, A., 2016. Techno-economic assessment of a woodbased biorefinery concept for the production of polymer-grade ethylene, organosolv lignin and fuel. Bioresource Technology 200, 928-939. https://doi.org/10.1016/j.biortech.2015.11.008 Posen, I.D., Griffin, W.M., Matthews, H.S., Azevedo, I.L., 2015. Changing the renewable fuel standard to a renewable material standard: Bioethylene case study. Environmental Science & Technology. 49(1), 93-102. https://doi.org/10.1021/es503521r Pré Consultants B.V., 2017. SimaPro v.8.3. The Netherlands. REE (Red Eléctrica Española), 2017. The electric system in Spain 2016 (in Spanish). Available in www.ree.es. Reyes Valle, C., Villanueva Perales, Vidal-Barrero, F., A.L., Ollero, P., 2015. Integrated economic and life cycle assessment of thermochemical production of bio-ethanol to reduce production cost by exploiting excess of greenhouse gas savings. Applied Energy 148, 466-475. http://dx.doi.org/10.1016/j.apenergy.2015.03.113 Sharifzadeh, M., Wang, L., Shah, N., 2015. Decarbonisation of olefin processes using biomass pyrolysis oil. Applied Energy 149, 404-414. https://doi.org/10.1016/j.apenergy.2015.03.081 Sutter, J., 2010. Life cycle inventories of pesticides (Data v2.2). Swiss Centre for Life Cycle Inventories, St. Gallen, Switzerland. The Royal Society, 2016. The potential and limitations of using carbon dioxide. London. Tsiropoulos, I., Faaij, A.P.C., Lundquist, L., Schenker, U., Briois, J.F., Patel, M.K., 2015. Life cycle impact assessment of bio-based plastics from sugarcane ethanol. Journal of Cleaner Production, 90, 114-127. http://dx.doi.org/10.1016/j.jclepro.2014.11.071 Villanueva, A.L., Reyes Valle, C., Ollero, P., Gómez Barea, A., 2011. Technoeconomic assessment of ethanol production via thermochemical conversion of biomass by entrained flow gasification. Energy 36(7), 4097-4108. http://dx.doi.org/doi:10.1016/j.energy.2011.04.037. S1 Environmental assessment of thermo-chemical processes for bio-ethylene production in comparison with bio-chemical and fossil-based ethylene Bernabé Alonso-Fariñas, Alejandro Gallego-Schmid, Pedro Haro, Adisa Azapagic Supporting information 1. Case 1: Direct ethanol dehydration Case 1 consists of three main steps: i) bioslurry production from biomass; ii) production of ethanol from bioslurry by direct route through gasification and catalytic conversion of the syngas; and iii) production of ethylene by ethanol dehydration. i) Bioslurry production This section is show in Figure 2 in the paper. After it has been dried and grinded, the biomass is fed to a fast pyrolysis reactor in which it is converted into light gas, heavy hydrocarbons and biochar. The system is designed to be energy self-sufficient. A fraction of the biochar is burnt to supply the thermal energy required by the pyrolysis reactor. The light gas is purged and burned to produce electricity in a steam cycle. Flue gases from biochar and light gas combustion are used for drying. The bioslurry is composed of the remaining biochar and the bio-oil obtained from heavy hydrocarbon condensation. Due to the energy self-sufficiency, only 80% of the biomass energy is recovered in the bioslurry (Villanueva et al., 2011). ii) Production of ethanol from bioslurry The bioslurry is then fed to the gasifier (1300 ºC and 70 bar); see Figure 3 in the paper. The oxygen supplied to the gasifier is generated in a cryogenic air separation unit. The produced syngas is cooled and then cleaned up and conditioned before being fed to the synthesis loop. Particles (including alkalis) and NH3 (also possible traces of NH4Cl) are removed with a candle filter and a Venturi scrubber, respectively. The H2/CO mole ratio is adjusted in a sour water-gas shift (WGS) reactor employing a sulphur-resistant Co-Mo catalyst. The synthesis loop comprises four stages: Selexol plant, synthesis reactor, autothermal reformer (ATR) and gas-liquid separator. The CO2 concentration is adjusted in the Selexol unit before feeding into the synthesis reactor. The sulphur contained in the acid gas from the Selexol process as H2S is removed in a liquid-phase oxidation catalytic (LO-CAT) unit. The synthesis reactor utilizes a MoS2 catalyst for alcohols production. The effluent of the reactor is sequentially cooled, including a cryogenic stage, to separate the condensable products from the gas phase that comprises unreacted syngas and light products. This gas phase is sent to the ATR unit with steam and oxygen before recirculating. A ZnO bed is placed upstream of the ATR unit to remove all sulphur contained in the gas as it is a poison for the Ni reforming catalyst. The condensates from the gas-liquid separator are fed to a stabilizer where methanol (>98% mol) and dissolved gases are recovered. The water is completely removed in the dehydrator (zeolite molecular sieve). Finally, ethanol (>98% mol) and propanol (>98% mol) are separated by distillation. Therefore, methanol and propanol are generated as coproducts in this process. Dissolved gases recovered in the stabilizer and the purge from the synthesis loop (including unreacted syngas and light products) are sent to the combined cycle for power generation. Despite power generation in the combined cycle, this is not sufficient and additional electricity is imported from the grid. iii) Production of ethylene by ethanol dehydration Finally, the bioethanol is dehydrated to obtain ethylene (Figure 4 in the paper). The ethanol feedstock is mixed with water and preheated before entering the dehydration reactor train. The reaction train consists of a series of three adiabatic fixed-bed reactors filled with alumina catalyst (Cameron et al., 2012). Two gas-liquid separators, a dewatering unit (zeolite