Resources, Conservation and Recycling 95 (2015) 174–182 Contents lists available at ScienceDirect Resources, Conservation and Recycling journal homepage: www.elsevier.com/locate/resconrec Synthesis of 2-methyl tetrahydrofuran from various lignocellulosic feedstocks: Sustainability assessment via LCA Hsien H. Khoo ∗ , Loretta L. Wong, Jonathan Tan, Valerio Isoni, Paul Sharratt Institute of Chemical and Engineering Sciences, 1 Pesek Road, Singapore 207683, Singapore a r t i c l e i n f o Article history: Received 9 July 2014 Received in revised form 2 December 2014 Accepted 29 December 2014 Available online 24 January 2015 Keywords: Sustainability Biomass LCA Land footprint a b s t r a c t This work highlights that bio-based chemicals may not automatically be synonymous with “green”, and efforts to generate the quantitative environmental performance of bio-products via LCA are crucial in ensuring their sustainable attributes. 2-Methyl tetrahydrofuran (2-MeTHF) is a new solvent derived from natural product sources. A relative LCA comparing 2-MeTHF manufacture originating from different biomass resources was carried out to investigate the sustainability of each feedstock. The biofine process was employed as a model for the production of levulinic acid from a mixture of C5 and C6 sugars before the final synthesis of 2-MeTHF. A new perspective of LCA impact, land footprint (total land area required), is proposed as a result of our evaluation, taking into account the viewpoint of competing land use options in the LCAs of green chemicals. © 2015 Elsevier B.V. All rights reserved. 1. Introduction The chemical industry has grown in size and technological maturity through the 20th century and is currently facing pressure to rethink its operations to adapt to a changing world. Amidst concerns of global warming and decreasing fossil fuel reserves, the manufacturing of environmentally friendly and green chemical products has emerged (Clark, 2007). Some of the new bio-based materials include new developments in the synthesis of chemicals and cellulosic biofuels. However, the transition from a petroleum-based economy to one that exploits the potential of biomass requires new strategies (Serrano-Ruiz et al., 2011). In order to be sustainable, biomass utilization demands the successful deployment of innovative, new technologies now known as biorefineries. Large scale utilization of biomass for the production of fuels and chemicals is associated with a number of important environmental issues, namely land footprint (area utilized), energy inputs and the application of fertilizers during the stage of agriculture (Dornburg et al., 2004; Luo et al., 2009). Along with the option to switch from fossil to bio-based chemicals comes the selection of biomass resources based on their availability, sustainability and the available methods that can be applied to process them into useful products. Lignocellulosic ∗ Corresponding author. +65 67967341. E-mail address: khoo hsien hui@ices.a-star.edu.sg (H.H. Khoo). http://dx.doi.org/10.1016/j.resconrec.2014.12.013 0921-3449/© 2015 Elsevier B.V. All rights reserved. biomass is the target feedstock in this paper due to the fact that it is an agriculture residue or crop by-product; hence no land competition for food is expected. This paper seeks to take into account different biomass feedstocks: sugarcane bagasse, rice straw and corn stover from different geographical locations. 1.1. Sugars (C5 /C6 ) from biomass Lignocellulosic biomass has a variable content of cellulose, hemicelluloses and lignin depending on the type of feedstock, country of origin and a number of other factors. However, the content of cellulose is generally in the range of 29–45%, hemicellulose in the range of 18–30%. These two polymers are among the most abundant in nature, representing a form of renewable feedstock trapped in a complex matrix, lignin (Yu et al., 2013a; Zhang et al., 2013; Gu et al., 2013). The presence of lignin reduces the availability of such a great energy reservoir dramatically since its complex phenolic polymeric nature, prevents the direct access to hemicelluloses and cellulose. Harsh conditions are generally required to breakdown lignin, such as high temperature and high pressure or chemical treatment. After separation of the solid residue (from lignin), the acidic solution containing a mixture of both hemicelluloses and cellulose is subject to hydrolysis of the polysaccharides into monomeric C5 (pentoses) and C6 (hexoses) sugars. Hexoses can be converted into levulinic acid, whereas pentoses can undergo dehydration to form furfural. Both levulinic acid and furfural can be converted to 2-MeTHF, but in this work the effort was focused on the levulinic acid pathway. H.H. Khoo et al. / Resources, Conservation and Recycling 95 (2015) 174–182 Three different types of non-edible biomass were considered for the study: bagasse, rice straw and corn stover. The glucan contents were extracted from various references (Yu et al., 2013a,b; Zhang et al., 2013; Gu et al., 2013; Yang et al., 2013; Liu et al., 2013). For each type of biomass the following parameters were reported (Table 1): • Glucan content in the corresponding biomass (expressed as w/w%). • Theoretical maximum yield of levulinic acid (assuming 100% conversion of glucan, expressed as w/w%) are calculated as: - Mass of glucan/molecular weight of C6 sugar (C6 H12 O6 ) = moles of C6 sugars. - Moles of C6 sugars × molecular weight of LA = mass of levulinic acid (assuming 100% yield). • Yield of levulinic acid based on the biofine process (expressed as w/w%) as 70% of theoretical as claimed by Hayes et al. (2005). • Expected quantity of levulinic acid that could be produced in a year per hectare of land (based on the biofine process) is estimated as: crop yield × biofine LA yield. In this paper we focused on the production of levulinic acid and 2-MeTHF. Any additional information about side/undesired products (chars, combustible material, recycling of sulfuric acid) arising from treatment of biomass, is not within the scope of the analysis. 2. Case study: bio-based 2-MeTHF Three types of lignocellulosic biomass are introduced as a renewable feedstock for the production of 2-methyl tetrahydrofuran (2-MeTHF). The non-edible biomass resources – corn stover, sugarcane bagasse and rice straw – are selected with the consideration that they will not contribute to the social issues of limited food supplies (Lal, 2005). The three top producers of stover, bagasse and rice straw are the U.S. (USDA, 2013; Pikul et al., 2001; Shinners and Binversie, 2007), Brazil (Sun et al., 2013) and China (CNGOIC, 2013) respectively. The high variability of sugars content in the biomass is affected by multiple factors such as location, land fertility, season etc. In our study we based our conclusions on the representative data summarized in Table 1. The next section describes the conversion technology employed to turn sugars into levulinic acid (LA), and subsequently into 2MeTHF. Life cycle assessment (LCA) – introduced in Section 3 – is employed to test the environmental impacts of the whole cradle-to-gate system. LCA investigations are gaining momentum for comparing the sustainability of processes, as well as, for quantifying the environmental impacts of different methods applied in material production (Blengini et al., 2011; Klemeš et al., 2007). To the best of our knowledge, no publications exist in peer reviewed journals on the detailed LCA of 2-MeTHF. 2.1. Synthesis of 2MeTHF from biomass In this work the overall conversion of biomass into 2-MeTHF is considered as part of an ideal process, based on three known industrial sequences described in the literature (Fig. 1) (Farone and Cuzens, 1996; Fitzpatrick, 1997; Elliot and Frye, 1999; Kumar et al., 2009). It is worth noticing that the biofine process could be used for the direct transformation of biomass into levulinic acid in one single efficient process. However, the limited amount of details for such a process (including different types of non-paper biomass), led us to consider three different industrial procedures for the conversion of cellulosic biomass into 2-MeTHF. 175 2.1.1. Step 1: From rice straw to C5 and C6 sugars In the first step (acidic treatment of lignocellulosic material) the biomass is treated with H2 SO4 (sulfuric acid) to furnish C5 (pentoses) and C6 (hexoses) sugars. For this transformation we referred to an industrial process by Farone and Cuzens (1996) in which rice straw is used as biomass and data from such a process were extrapolated (Fig. 2). Further reading on biomass pretreatment can be found in Kumar et al. (2009). Sulfuric acid is used at different stages of the process and its concentration varies along the way, but it is possible to recover it, at least partially. The C5 /C6 sugars are generally obtained as streams (aqueous). Side products of the hydrolysis process are: • Si containing material (which can be either incinerated or processed to produce silica gel). • Combustible residue (which can be used to produce energy for the process). It was found that the energy used in pretreatment was essentially negligible compared with that required for isolation of furfural or levulinic acid. 2.1.2. Step 2: Conversion of C5 sugars to furfural and C6 sugars to levulinic acid The mixture of C5 and C6 sugars can be treated in different ways in order to favour the production of either furfural or levulinic acid (Fitzpatrick, 1997). Some processes targeted furfural as intermediate to 2-MeTHF whereas others preferred levulinic acid as intermediate (Hayes et al., 2005; Rackemann and Doherty, 2011; Parton et al., 2012; Sabesan and Spado, 2013). The main issue in those processes is the separation of C5 sugars from C6 sugars in order to reduce undesired reactions, leading to an extra step to purify/separate materials and eventually a lower yield. However, to the best of our knowledge the biofine process seems to be the only industrially relevant process able to favour the production of either levulinic acid or furfural starting from a mixture of C5 and C6 sugars (Fitzpatrick, 1997). The typical yield claimed for such process is around 50% by mass of C6 sugars into levulinic acid (for example), 20% formic acid and 30% char. This means that if the total sugars input is 0.51 kg (from Step 1), the expected levulinic acid output is 0.17 kg. The remainder mass consist of “solid by-products or chars” and formic acid (from the C6 sugars) which can be easily removed and sold as commodity chemical. The biofine process is described in Fig. 3 (Hayes et al., 2005). 2.1.3. Step 3: Hydrogenation of levulinic acid Finally, levulinic acid can be converted to 2-MeTHF via hydrogenation as explained in the Pacific Northwest Laboratory process (Fig. 4) (Elliot and Frye, 1999). In this process the hydrogen is used in excess (hydrogen/levulinic acid molar ratio = 5.9/1), yielding 2MeTHF (63% by mass). The overall (mass) balance of all inputs and outputs to the process chain can be deduced from Table 1. 3. Method: relative LCA Due to the increasing trend of the transition from a fossilbased to bio-based economy, the importance of carrying out an environmental impact assessment of solvent production from a systems-based perspective is becoming more apparent. LCA provides important additional information that can aid in the selection of a synthesis pathway for a given material (Blengini et al., 2011; Klemeš et al., 2007; Hellweg et al., 2004; Hatti-Kaul et al., 2007). 176 H.H. Khoo et al. / Resources, Conservation and Recycling 95 (2015) 174–182 Table 1 Comparison between different types of biomass (dry mass) to produce levulinic acid. Type of biomass Glucan content (w/w%) Theoretical yield of LA (w/w%) (calculated) Biofine LA yield (w/w%) (reported)g Biomass (kg) required for 1 kg LA (calculated) Potential Productivity of LA from biofine (theoretical) (kg/ha-yr) Bagasse 45.2a 42.9b 29.1 27.7 20.4 19.4 4.90 5.17 4629 4394 Rice straw 33.7c 35.9d 21.8 23.2 15.2 16.2 6.58 6.17 380 405 Corn stover 31.7e 35.9f 20.5 23.2 14.3 16.2 6.99 6.17 501 567 a b c d e f g Yu et al. (2013a). Zhang et al. (2013). Gu et al. (2013). Liu et al. (2013). Yang et al. (2013). Yu et al. (2013b). Hayes et al. (2005). Fig. 1. Summary of the overall process to convert biomass into 2-MeTHF, combining three known processes. Fig. 2. Details of the process to produce C5 /C6 streams of sugars from rice straw. 3.1. Goal and scope each biomass feedstock selection, the system boundary starts with agricultural practices in different locations: corn stover from U.S., sugarcane bagasse from Brazil, and rice straw from China. The entire LCA flow diagram is illustrated in Fig. 5. The functional unit, which ends at the “factory gate”, is defined as 1 kg 2-MeTHF ready for use. In the comparative or relative LCA system, the boundary starts with agriculture activities (farm) where biomass is produced, and next treated for the extraction of usable sugars. The sugars are then sent to the biorefinery where 2-MeTHF is synthesized. For CHO H O HO H H OH H OH OH CH2 OH C6 sugars O O HO H O + COO OH O Hydroxy H meth hylfurfural F) (HMF Le evulinic acid H OH Formic acid CHO H HO O H OH H OH CH2 OH O O O Furfural + H OH O Formic acid a C5 sugars Fig. 3. Biofine process chemical transformation. Deecomposition n products H.H. Khoo et al. / Resources, Conservation and Recycling 95 (2015) 174–182 for stover and rice straw, which are both left on the field after harvest. As for bagasse, mass allocation is made at the mill, where the residual biomass is generated. H2 0.05 Kg H2 0.10 Kg Pacific North hwest P Laboratory y Levulinic acid 1.00 Kg 177 2-MeTHF F 0.63 Kg g 4. Results and discussions 4.1. Feedstock and land area H 2O 0.31 Kg g O 3 H2 COOH H -2 H 2O Lev vulinic acid O 2-Me eTHF Fig. 4. Hydrogenation of levulinic acid yields 2-MeTHF. LCA studies are able to account for the material flows and fluctuations in the value chain of chemical production pathways. Based on the yield of crops per land area (ton/ha-yr), ratio-of-biomass to crop, amount of possible sugars extracted from each biomass feedstock (Table 1), conversion to LA and final synthesis of 2-MeTHF; the amount of feedstock required can be easily derived from: Feedstock total(kg/ha-yr) = [Yield(crop) in ton/ha-yr × 10−3 ] × ratio(crop-to-residue) × %yield(sugars) For all different biomass to material pathways, similar amounts of sulfuric acid consumption and recovery were assumed. Therefore, there it was not necessary to carry out the LCA of H2 SO4 , nor, compare the environmental impacts due to its consumption. Byproducts (Si, chars, formic acid) are not within the system boundary of the LCA. 3.2. Inventory/data LCA accounts for all input and output flows occurring along the production chains, from planting and harvesting of crops, collection of biomass residues, to the final conversion of levulinic acid from sugars and production of 2-MeTHF. Since for all three cases, the biorefinery (biofine) employed are similar, energy input and emissions from the final stage of production is omitted. Taking into account different scenarios of each location (U.S. and Brazil), the following are included in data collection and analysis: land use for agriculture; CO2 intake and emissions, yield of crop, harvesting and crop-to-lignocellulosic biomass ratio. Details of the data inventory are compiled from corn, sugarcane and rice farms in U.S., Brazil and China respectively. They are presented in Appendix A. Hydrogen supplied to the biorefinery is produced via steam reforming of natural gas. The input-output data for the life cycle of natural gas to hydrogen production is also contained in Appendix A. The input–output inventories are allocated by mass × %conversion(sugars-to-LA) × %conversion(LA-to-2MeTHF) (1) The need to include the viewpoint of competing land use options in the LCAs of green chemicals has been highlighted by Dornburg et al. (2004). Impacts of land use have already been reported LCA investigations. One such example can be found in de Baan et al. (2013), where land use impacts are associated with loss of biodiversity. The land use impacts are also segregated across biogeographic regions and taxonomic groups. In another example, the multi-functionality of land use considering types of biodiversity well as ecosystem services are modelled as environmental impacts (Koellner et al., 2013). In line with the need to measure the sustainability of bio-based products, a different LCA land impact perspective, land footprint (total land area required), is proposed. Land footprint is different from the land use impact reported by Koellner et al. (2013) and de Baan et al. (2013) since biodiversity and various types of ecosystem services are not considered. In addition to that, land use change impacts are directed towards the production of crops rather than its residual biomass (e.g. Davies-Barnard et al., 2014). Hence we can reasonably assume that land use change impact investigations are not applied to biomass residuals. However, since agricultural land is cultivated primarily for growing crops, and the land footprint area is estimated from the amount of crop required as a Fig. 5. Life cycle production stages of biomass cultivation to 2-MeTHF. (a) Amount of biomass feedstock per kg 2-MeTHF (only average values shown). (b) Land footprint (LF) required per kg 2-MeTHF (only average values shown). 178 H.H. Khoo et al. / Resources, Conservation and Recycling 95 (2015) 174–182 Global Warming Potenal per kg 2-MeTHF 16 13.75 14 12.01 kg CO2-eq 12 10 8 6.64 6 5.62 4.95 4 3.05 2 2.57 1.70 1.74 0 stover bagasse rice straw stover Biomass culvaon bagasse rice straw bagasse rice straw stover Conversion/producon Total Fig. 7. Global warming potential results (only average values are shown on graph). Acidificaon Potenal per kg 2-MeTHF 0.05 0.041 0.04 0.039 0.035 kg SO2-eq 0.034 0.03 0.023 0.02 0.015 0.009 0.01 0.006 0.005 0 stover bagasse rice straw Biomass culvaon Fig. 6. (a) Total lignocellulosic feedstock required; (b) corresponding amount of land area required for the production of 1 kg 2-MeTHF. prerequisite stage, before lignocellulosic biomass can be produced. The following equation is introduced: Land footprint(per kg 2-MeTHF) in total ha/yr bagasse rice straw stover bagasse rice straw Conversion/producon Total Fig. 8. Acidification potential results (only average values are shown on graph). eutrophication (Fig. 9) and total energy use (Fig. 10). For all cases, the potential impacts from agriculture are allocated by mass to the biomass residual of stover, bagasse and rice straw. 4.2. Global warming potential (2) The results are displayed in Fig. 6a and b respectively. From Fig. 6(a) the widest range of biomass feedstock amount required seems to be stover, which is an indication of the potential amount of sugars that can be extracted from stover (refer to Table 1); from these amount of feedstock consumed, the associated land footprint per product can be estimated. In terms of land footprint (LF) per product (Fig. 6(b)), the order of preference is sugarcane-bagasse, next rice straw and last of all, corn stover. The most efficient crop (per land area utilized) is sugarcane, where yields in the range of 60.11 ton/ha-yr to as high as 112.4 ton/ha-yr have been reported (de Figuiredo and La Scala, 2011; Sun et al., 2013). Comparatively, the highest recorded yields for the other two crops are about 10 ton/ha-yr for both corn (Kim et al., 2009; USDA, 2013) and rice (Xia and Yan, 2011; CNGOIC, 2013). This gives sugarcane-bagasse a competitive edge as a choice of feedstock for producing various types of biomass products. However, it should be highlighted that the widespread promotion of bio-materials made from sugarcane and its by-products come with an additional environmental burden – the demand for sugarcane-bagasse has led to the clearing of forest areas for the expansion of sugarcane plantations in Brazil. It was reported that during the years 1996–2006 land conversions to grow more sugarcane led to more greenhouse gas emissions due to deforestation (Sparovek et al., 2009). The next sets of environmental impacts, from cradle-togate, are global warming potential (Fig. 7), acidification (Fig. 8), As shown in Fig. 7, a significant portion of GWP results are from agriculture, most notably from rice straw. China, the world’s major rice producer, is a large contributor of nitrous oxide (N2 O) and methane (CH4 ) – two significant greenhouse gases that are released from rice paddy fields (Ahmad et al., 2009). The amount of CH4 generation is known to be affected by different farming practices including fertilizer practices (Li et al., 2011) and tillage management (Cruvinel et al., 2011). Nitrogen related emissions are due to N-fertilizer usage in the fields. The GWP result shown for bagasse, which is slightly higher than stover, is due to the emissions related to the transportation of sugarcane to the mill, where bagasse is generated as a by-product Eutrophicaon per kg 2-MeTHF 0.008 0.007 0.007 0.007 0.007 0.006 kg phosphate-eq = Feedstock total(kg/ha-yr) × [1/ratio(crop-to-residue) ] × [1/Yield(crop) in ton/ha-yr × 10−3 ] stover 0.004 0.004 0.003 0.002 0.001 6.45E-05 6.40E-05 0 stover bagasse rice straw Biomass culvaon stover bagasse rice straw Conversion/producon stover bagasse rice straw Total Fig. 9. Aquatic eutrophication results (only average values are shown on graph). H.H. Khoo et al. / Resources, Conservation and Recycling 95 (2015) 174–182 Total Energy consumpon per kg 2-MeTHF 20 19.45 19.65 18 16 179 Compared with agricultural stages of the LCA, other upstream processes do not have any significant energy demands. According to Hayes et al. (2005), the chars generated from the biofine process can provide sufficient energy input for the biorefinery. total MJ 14 12 11.48 11.28 10 8 5. Concluding remarks 9.22 9.02 6 4 2 0.20 0 stover bagasse rice straw Biomass culvaon stover 0.20 0.20 bagasse rice straw Conversion/producon stover bagasse rice straw Total Fig. 10. Energy use (only average values are shown on graph). after sugarcane milling. Overall, in order to produce 1 kg 2-MeTHF, rice straw resulted in about 52% and 60% higher global warming potential results, compared to bagasse and stover respectively. 4.3. Acidification potential and eutrophication Both stover and rice straw score about 41–44% higher than bagasse in acidification and eutrophication impacts. Emissions of NOx and NH3 are the consequences of N-fertilizer applications in agricultural lands. Measured in LCA environmental impact models as acidification potential (Fig. 8) and eutrophication (Fig. 9), these emissions are released from soil to atmosphere after fertilizations, during the growing season, before and after harvesting (Yang et al., 2010). Both results show that the weights of these environmental burdens fall mostly on the agriculture stages of the production chain, with little contribution from the processes employed to produce chemicals. Out of eight corn and stover production areas in the U.S. Corn Belt, Kim et al. (2009) reported that nitrogen-related emissions from soil are major contributors to the environment since large quantities of N-fertilizers are applied. The environmental impacts of anthropogenic reactive nitrogen-related emissions (NOx , NH3 ) are also evident from rice fields in China (Yang et al., 2010; Xia and Yan, 2011). Studies have been undergoing to control the use of N-fertilizers which can result in tradeoffs with respect to eutrophication. Improvements can be made by a combination of three farming strategies: tillage, fertilizer practices and the use of buffer strips to sequester nutrients (Xue et al., 2014). 4.4. Energy use Of all three lignocellulosic biomass resources, bagasse has to be collected after the processing of sugarcane at the sugar refinery. On the contrary, stover and rice straw are collected directly from fields after harvesting. The additional steps for bagasse include transportation from sugarcane plantations to the sugar mill, plus power consumption during the processing sugarcane at the mills, resulted in 53% and 42% more energy consumed than stover and rice straw respectively (per 1 kg 2-MeTHF produced). If bagasse – typically a by-product from sugarcane mills – is not used for making bio-based materials, the by-product will be burned on-site to power the mill itself. Assuming a traditional cogeneration system employed in Brazilian sugarcane mills which operates on Rankine Cycle processes (with overall efficiency 50%), along with a heating value of bagasse as 7.5 MJ kg, about 3.75 MJ worth of steam can be generated from 1 kg bagasse (Dias et al., 2011). Since about 8 kg of bagasse is required per kg 2-MeTHF (Fig. 6(a)), a total 30 MJ would be made available to the sugar mills if bagasse is not utilized to make other materials or chemicals. Efforts to shift from fossil-based resource to renewable ones have recently gained momentum. As fossil fuel depletion continues to be a global concern, various industries are exploring ways to produce bio-based materials and chemicals. Three types of lignocellulosic biomass (stover, bagasse and rice straw) are introduced as a renewable feedstock for the production of 2-methyl tetrahydrofuran (2-MeTHF). Life cycle assessment or LCA is applied for each biomass feedstock selection, from their respective agricultural production systems to biomass collection, sugars (C5 /C6 ) extraction, a biorefinery and ends at the “factory gate”, to produce 1 kg 2-MeTHF ready for use. The inventory data to support the LCA for biomass cultivation for corn-stover, sugarcane-bagasse and rice straw were extracted from the U.S., Brazil and China respectively. However, the sugars content in all three biomass resources are derived from various reports (summarized in Table 1). The biofine process was employed as a model for the production of levulinic acid from a mixture of C5 and C6 sugars before the final synthesis of 2-MeTHF. This work highlighted that alternative biomass resources should be carefully selected based on their availability, sustainability and the available technologies that can effectively convert them into useful products. The LCA results demonstrated that bio-based chemicals may not automatically be synonymous with “green”. Such efforts to create more informed quantitative environmental performance of bio-products have also been reported in other case studies (e.g., Blengini et al., 2011). Apart from GWP, acidification, eutrophication, energy use, a new LCA impact, land footprint (total land area required), was proposed. The order of preference for the results shown for land footprint (LF) per kg 2-MeTHF is sugarcane-bagasse, followed by rice straw and last of all, corn stover. All agriculture stages score significantly higher in global warming potential, acidification, eutrophication and energy use, compared to the impacts from the stages of processing biomass to 2-MeTHF. Rice straw resulted in about 52% and 60% higher global warming potential results compared to bagasse and stover respectively. Both stover and rice straw score about 41–44% higher than bagasse in acidification and eutrophication impacts. Bagasse contributed the most to energy utilization, 53% higher than stover and 42% higher than rice straw. This is due to the extra stages of transportation from sugarcane plantations to the sugar mill, and power consumption during the processing of sugarcane at the mills. However, the overall observed environmental impact of bagasse was much lower than those of stover and rice straw. Besides being a valuable source of providing energy for (when burned) sugar mills, bagasse seemed to be the most suitable candidate for producing bio-based chemicals. Apart from being the most efficient crop per land footprint, a relatively higher glucan content (up to 45 w/w%) provides a higher potential for levulinic acid production. Acknowledgement The team would like to thank the GSK-Singapore Partnership for Green and Sustainable Manufacturing for funding and supporting our work on A Multi-Disciplinary Assessment of Sustainable Solvents. 180 H.H. Khoo et al. / Resources, Conservation and Recycling 95 (2015) 174–182 Table 4.A Input and output data for rice production in China [12]. Appendix A. The yields of crops are extracted from various country and national reports from U.S., Brazil and China [1–8]. They are compiled in Table 1.A. The input–output datasets pertaining to various agricultural practices within each country are also extracted from literature [9–13]. Fertilizer use and other inputs, as well as the associated emissions, are reported for sugarcane, corn and rice in Tables 2.A, 3.A and 4.A respectively. H2 gas is produced from steam reforming of natural gas. In the process, the hydrocarbons are catalytically split in the presence of steam at temperatures of 800–900 ◦ C [14]. During the Table 1.A Yield of crops [1–8]. Yield Range in ton/ha-yr Sugarcane Corn Rice 60.11–112.4 5.75–10.16 3.6–10.0 Component Amount Comments Input per 1 kg rice crop production 0.944 m3 Water Energy used 0.78 MJ Nitrogen fertilizer 1.71 × 10−3 kg Phosphate fertilizer 4.73 × 10−3 kg 3.79 × 10−3 kg Potassium fertilizer 3.53 × 10−5 kg Pesticides Substances Amount For pest prevention Allocated to RS in field Output/emissions per 1 kg rice production CO2 1.28 × 10−3 kg 8.96 × 10−2 kg 4.07 × 10−2 kg 2.85 × 10−2 kg CH4 5.98 × 10−4 kg 4.19 × 10−4 kg N2 O 6.42 × 10−7 kg 4.49 × 10−7 kg NOx a NH3 1.28 × 10−3 kg 8.96 × 10−2 kg 0.7 kg Rice straw a For irrigation For traction Fertilizers used in field Comments GHG emissions from rice field From N-fertilizers Residual biomass left on field after rice harvest Extracted from EcoInvent [13]. Table 2.A Input and output data for sugarcane production in Brazil [9]. Component Amount Comments Input per 1 kg sugarcane production 0.043 m3 Water 0.103 MJ Energy used 1.184 × 10−3 kg Nitrogen fertilizer 9.686 × 10−4 kg Phosphate fertilizer 3.239 × 10−3 kg Potassium fertilizer Lime 0.005 kg For irrigation For traction Fertilizers used in field For soil treatment/condition enhancer For pest prevention 4.892 × 10−5 kg Pesticides Output/emissions per 1 kg sugarcane production a −1173 kg/ha-yr CO2 -eq Carbon sequestration due to application of green harvest From manual harvesting which involves traditional burning before harvest From fertilizer application 950 kg/ha-yr 1.560 × 10−5 kg 4.42 × 10−6 2.49 × 10−4 N2 O NOx NH3 Input per 1 kg bagasse production (at sugarcane mill) Residual biomass 3.78 kg (26.4% bagasse Sugarcane per kg sugarcane) 0.567 kWh Energy input a Extracted from De Figueiredo and La Scala [10]. Table 3.A Input and output data for corn production in U.S. from seven corn producing states in U.S. Corn Belt [11]. Component Amount Input per 1 kg whole corn production 0.5 MJ Energy used 0.02 kg Nitrogen fertilizer Phosphate fertilizer 8.27 × 10−3 kg 8.18 × 10−2 kg Potassium fertilizer 2.83 × 10−4 kg Herbicides/insecticides Substances Amount Allocated to stover in field Comments For field operations Fertilizers used in field For pest prevention Table 5.A Input and output data for Hydrogen production from natural gas [15]. Component Input per 1 kg H2 production Natural gas Energy used Amount 4 kg 1.15 MJ Output/emissions per 1 kg H2 production 9.155 kg CO2 CO 0.04 g N2 O 0.023 g 0.9 g NOx Comments Steam reforming process Water-gas shift reactor Based on the production capacity of the hydrogen plant of 1.5 million Nm3/day (57 million scfd) Table 6.A Input and output data for hydrogen production from natural gas [16–17]. Component Amount Input per 1 kg natural gas production Oil 0.042 MJ Natural gas 0.16 kg Output/emissions per 1 kg natural gas production 70.9 g CO2 0.25 g CO 14.17 g CH4 0.46 g NOx 0.28 g SOx Comments Process details from Cetinkaya et al. [17], page 3, Table 2 Gas losses due to piping negligible catalytic split, syngas is produced that mainly consists of H2 and CO: Cn Hm + nH2 O → nCO + (n + m/2)H2 . From there, CO from syngas is converted into CO2 and H2 : CO + H2 O → CO2 + H2 . The input–output data for H2 production is extracted from Spath and Mann [15], and is compiled in Table 5.A. The inventory for natural gas production (Table 6.A) is compiled from Spath and Mann [16]; and verified with process details from Cetinkaya et al. [17]. 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