Abstract
This study assessed the breakdown of lignocellulosic biomass (LB) with the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([Emim][Ac]) as a pretreatment to increase the methane yield. The pretreatment was conducted for wheat straw (WS), barley straw (BS), and grape stem (GS) at 120 °C for 120 min, using several LB to [Emim][Ac] ratios (1:1, 1:3, and 1:5 w/w). Pretreatment significantly disrupted the lignocellulose matrix of each biomass into soluble sugars. GS showed the highest sugar yield, which was followed by WS, while BS was slightly hydrolyzed (175.3 ± 2.3, 158.2 ± 5.2, and 51.1 ± 3.1 mg glucose g–1 biomass, respectively). Likewise, the pretreatment significantly reduced the cellulose crystallinity index (CrI) of the resulting solid fractions of GS and WS by 15% and 9%, respectively, but slightly affected the CrI of BS (5%). Thus, BMP tests were only carried out for raw and hydrothermally and [Emim][Ac] (1:5) pretreated GS and WS. The untreated GS and WS showed similar methane yields to those achieved for the solid fraction obtained after pretreatment with an LB to [Emim][Ac] ratio of 1:5 (219 ± 10 and 368 ± 1 mL CH4 g–1 VS, respectively). The methane production of the solid plus liquid fraction obtained after IL pretreatment increased by 1.61- and 1.34-fold compared to the raw GS and WS, respectively.
Highlights
The European Union (EU) is at the forefront of renewable energy transition and efforts to tackle climate change
By 2017, the EU greenhouse gas (GHG) emissions had fallen to 78.3% of the 1990 levels, exceeding the target of a 20% cut outlined by the Paris Agreement by 2020 [1]
We studied the energy recovery by mesophilic anaerobic digestion of pretreated samples of wheat straw, barley straw, and grape stem with [Emim][Ac] at different mixing ratios (1:1, 1:3, and 1:5 w/w biomass to [Emim][Ac])
Summary
The European Union (EU) is at the forefront of renewable energy transition and efforts to tackle climate change. Over the ten years, the EU plans to reduce the heating bill to achieve at least a 40% cut in GHG, as space heating and hot water alone account for 79% of the current energy usage (192.5 Mtoe) in households and 70.6% of the energy consumption (193.6 Mtoe) of industry [2]. A mixture of approximately 60% methane and 40% carbon dioxide, produced from the anaerobic digestion (AD) of biomass, has long been rolled out in Europe as a renewable fuel for combined heat and power systems, turbines, and boilers [3]. Biomethane (upgraded biogas: approximately 96% methane and 4% propane) is fed into the gas grid to reduce the housing and industry carbon footprints from heating, or it is compressed to fuel natural gas vehicles [4]
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