1 Environmental implications of biohydrogen based energy production from steam 2 reforming of alcoholic waste 3 4 Antonio Cortésa, Gumersindo Feijooa, Antonio Chicab, Javier Francisco Da Costa- 5 Serrab and Maria Teresa Moreiraa 6 a Department of Chemical Engineering, School of Engineering, University of Santiago de 7 Compostela, Santiago de Compostela 15782, Spain 8 b Instituto de Tecnología Química, Universitat Politècnica de València-Consejo Superior de 9 Investigaciones Científicas, Avd. de los Naranjos s/n, 46022 Valencia (Spain). 10 11 Abstract 12 Nowadays, there is an increasing demand for energy in the world. With an energy system 13 still based on fossil fuels, a paradigm shifts towards clean energy production based on 14 available renewable resources is necessary. Hydrogen is a high-quality energy carrier that 15 can be used with great efficiency and is expected to acquire a great importance in the next 16 generation of fuels. This study aims to analyze the potential environmental impacts 17 associated with the steam reforming of alcoholic waste from distilleries to produce clean 18 electricity by using the Life Cycle Assessment methodology. The main findings from this 19 study reported that the global environmental profile is better than other alternatives more 20 common as sanitary landfill or incineration. In terms of some impact categories as Abiotic 21 and Ozone Depletion, Acidification and Eutrophication, steam reforming of alcoholic 22 waste performed better profiles than other processes that produce hydrogen from diverse 23 feedstocks. 24 Keywords: Alcoholic waste, Environmental profile, LCA, SOFC, Biohydrogen 25 26 1. Introduction 27 Currently, global energy production is based on the use of fossil fuels such as coal, oil 28 and natural gas (Rossetti et al., 2015a) and accounts for approximately 65% of global 29 GHG emissions (Uusitalo et al., 2017). Dependence on the use of fossil fuels as an energy 30 resource has caused environmental problems of global impact, such as air pollution in 31 terms of emission of pollutants and particles, as well as the depletion of natural resources, 32 among others (Hajjaji et al., 2016; Reyes et al., 2015), which leads to adverse 33 consequences for society in terms of human health and damage to the ecosystem (Valente 34 et al., 2019). So much so that the 2030 Agenda and the 17 Sustainable Development Goals 35 (SDGs) set by the United Nations includes ensuring access to affordable, reliable and 36 sustainable energy for all. This objective aims at guaranteeing universal access to energy 37 service, substantially increasing the share of renewable energy in the global energy mix 38 and doubling the rate of improvement in energy efficiency. This is why the paradigm shift 39 towards clean energy production must be based on available renewable resources (Da 40 Costa-Serra and Chica, 2018). 41 In recent years, numerous alternatives to the use of traditional fossil fuels have been 42 proposed, such as the production of biofuels, bioalcohols, hydrogen or any type of 43 renewable energy (Balat, 2011). In particular, biomass is one of the renewable energy 44 sources that has experienced strong growth in recent years, due to its global availability 45 and diversity (Tian et al., 2018; Spiridon et al., 2018). Biofuels derived from biomass 46 offer a number of advantages over their oil-based counterparts according to Demirbas 47 (2008): they can be considered carbon neutral after-combustion by fixing carbon during 48 biomass growth, close to a carbon-neutral balance, so that they contribute to achieving 49 sustainability goals. For this reason, numerous initiatives have been developed in the 50 development of conversion technologies based on resources derived from biomass 51 (Unrean et al., 2018). 52 Focusing on the different types of fuels, hydrogen is a high quality energy vector that 53 can be used with high efficiency (Frolov et al., 2013) and is expected to acquire great 54 importance in next generation fuels (Alipour-Moghadam et al., 2014). This fact, together 55 with declining fossil fuel reserves, steadily rising prices and increasing pollution make 56 hydrogen a very attractive product for meeting global energy demand (Khaodee et al., 57 2011). 58 However, the environmental profile of hydrogen-based energy systems is as "clean" or 59 "dirty" depending on the scheme of conversion (Rabenstein and Hacker, 2008). The 60 traditional schemes producing H2 from natural gas are a major source of CO2, with 61 emissions of approximately 10-12 kg of CO2 per kg of H2 (Spath and Mann, 2001). 62 Traditional plants produce hydrogen by catalytic steam reforming of natural gas, which 63 is a mature technology and is the pathway by which most hydrogen is produced today. 64 Because of this, reducing CO2 emissions associated with hydrogen production would 65 result in a considerable reduction of pollution (Salkuyeh et al., 2018). 66 In this sense, fuel cells technology and the use of hydrogen are proposed as one of the 67 most promising environmental solutions in relation to the reduction of global emissions 2 68 (Díaz-Alvarado & Gracia, 2012). Fuel cells are devices that electrochemically convert 69 chemical energy from fuels into electricity (Morales et al., 2010). Among the different 70 types of fuel cells, the Solid Oxide Fuel Cell (SOFC) is the most efficient, due to its high 71 operating temperatures and the fact that it is not poisoned with CO (Hernández and 72 Kafarov, 2009). When this type of battery is used, an efficiency around 50% can be 73 obtained (Strazza et al., 2015); in addition, an efficiency of 70% can be achieved if 74 cogeneration system is used (Strazza et al., 2010). 75 Hydrogen production from renewable sources such as poplar (Susmozas et al., 2016) 76 or willow wood (González-García et al., 2012), sugar cane (Halleux et al., 2008), sweet 77 potato (Costa et al., 2018), sorghum (Aguilar-Sánchez et al., 2018) or sugar beet (Luo et 78 al., 2009) have been investigated as the first actions to achieve a significant reduction of 79 environmental impacts (Salkuyeh et al., 2018). Hydrogen can be obtained from different 80 feedstocks through steam reforming (Braga et al., 2016; López et al., 2019; Zheng et al., 81 2019), autothermal reforming (Khila et al., 2017; Spallina et al., 2018; Xue et al., 2017) 82 and aqueous phase reforming (Coronado et al., 2018; Esteve-Adell et al., 2017; García et 83 al., 2018), among them, steam reforming is the most common and has the highest 84 conversion efficiency (Haryanto et al., 2005). 85 Steam reforming of natural gas is the most popular method for producing commercial 86 hydrogen that currently produces about 50% of global hydrogen demand (Anzelmo et al., 87 2018) and is sometimes referred to as steam methane reforming (SMR). Steam reforming 88 is an endothermic process based on the reaction of gas with steam at high temperature 89 and moderate pressure. In this way, the chemical reaction taking place leads to hydrogen 90 and carbon dioxide (Reaction 1): 91 CH CH OH + 3H O 2CO + 6H (1) 3 2 2 → 2 2 92 However, depending on the reaction mixture and operating conditions in the reactor, 93 another route can be followed, producing undesirable products (Ni et al., 2007), such as 94 carbon monoxide (Reaction 2), methane (Reaction 3) or ethylene (Reaction 4): 95 CH CH OH + H O 2CO + 4H (2) 3 2 2 → 2 96 CH CH OH CO + CH + H (3) 3 2 → 4 2 97 CH CH OH C H + H O (4) 3 2 → 2 4 2 3 98 Once the process is complete, the output stream must undergo purification treatment to 99 avoid the presence of by-products such as methane and carbon monoxide. The removal 100 of CO is an important step because it normally poisons the catalyst in fuel cells, which is 101 why CO is removed first by the Water Gas Shift (WGS) reaction (Reaction 5). WGS is 102 an exothermic and reversible reaction usually used in industry to produce high purity 103 hydrogen (Alamolhoda et al., 2019). Normally, 90% of the CO outflowing from the 104 steam reforming reactor can be converted to CO2 (Rossetti et al., 2015b). 105 CO + H O H + CO (5) 2 → 2 2 106 Following this stage, the Pressure Swing Adsorption (PSA) process separates hydrogen 107 from the rest of the components of the gas stream with 85% efficiency, obtaining H2 with 108 99% purity (Susmozas et al., 2013), and whose energy content is usually higher than that 109 of the natural gas used for reforming. 110 The implementation of other alternatives of hydrogen production can be considered 111 from alternative raw materials, such as alcohols (Rossetti et al., 2015a). In addition to 112 steam reforming of ethanol, studies have been published on steam reforming of different 113 types of alcohol with the aim of producing hydrogen. Some of these alcohols are butanol 114 (Kumar et al., 2018), propanol (Wang et al., 2015), methanol (Tian et al., 2017) or 115 glycerol (Menezes et al., 2018) but, even so, the use of ethanol for this purpose offers the 116 best opportunity to produce hydrogen from renewable sources (Ramírez and Homs, 117 2008), especially if this ethanol is derived as residue from other processes. Specifically, 118 the alcoholic wastes from the wine industry results an attractive raw material due to 65% 119 of world wine production is managed by European winegrowers [European Wine: a solid 120 pillar of the European Union economy. In: Vins– CCEdE, editor. 121 http://www.ceev.eu/about-the-eu-wine-sector2016], mostly small and medium-sized 122 wineries. Wine production generates large amounts of solid and liquid wastes, with a 123 serious impact on the environment when they are not adequately treated.