Abstract
The effects of microwave-assisted alkali pre-treatment on pellets’ characteristics and enzymatic saccharification for bioethanol production using lignocellulosic biomass of canola straw and oat hull were investigated. The ground canola straw and oat hull were immersed in distilled water, sodium hydroxide and potassium hydroxide solutions at two concentrations (0.75% and 1.5% w/v) and exposed to microwave radiation at power level 713 W and three residence times (6, 12 and 18 min). Bulk and particle densities of ground biomass samples were determined. Alkaline-microwave pre-treated and untreated samples were subjected to single pelleting test in an Instron universal machine, pre-set to a load of 4000 N. The measured parameters, pellet density, tensile strength and dimensional stability were evaluated and the results showed that the microwave-assisted alkali pre-treated pellets had a significantly higher density and tensile strength compared to samples that were untreated or pre-treated by microwave alone. The chemical composition analysis showed that microwave-assisted alkali pre-treatment was able to disrupt and break down the lignocellulosic structure of the samples, creating an area of cellulose accessible to cellulase reactivity. The best enzymatic saccharification results gave a high glucose yield of 110.05 mg/g dry sample for canola straw ground in a 1.6 mm screen hammer mill and pre-treated with 1.5% NaOH for 18 min, and a 99.10 mg/g dry sample for oat hull ground in a 1.6 mm screen hammer mill and pre-treated with 0.75% NaOH for 18 min microwave-assisted alkali pre-treatments. The effects of pre-treatment results were supported by SEM analysis. Overall, it was found that microwave-assisted alkali pre-treatment of canola straw and oat hull at a short residence time enhanced glucose yield.
Highlights
The world relies on fossil fuels for its energy usage and the sources of these fossil fuels are coal, oil and natural gas
The following conclusions can be drawn from this investigation: 1. Microwave-assisted alkali pre-treatment of canola straw and oat hull resulted in better physical quality and improved the enzymatic digestibility of these substrates
Canola straw and oat hull samples hammer milled with 1.6 mm screen size resulted in pellets with better physical quality compared to samples hammer milled with 3.2 mm screen size
Summary
The world relies on fossil fuels for its energy usage and the sources of these fossil fuels are coal, oil and natural gas. The negative impact of fossil fuels on the environment is the increasing problem of greenhouse gas emissions. These emissions have attracted global interest in the search for alternative, non-petroleum-based sources of energy [1,2]. These renewable energy sources include solar energy, biomass, wind, hydroelectric and other sources that are more environmentally friendly [3]. In the USA, 10% of total gasoline consumption by 2020 have been targeted and the production of 136 billion litres of biofuel is targeted [5]
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