Optimization of microwave pretreatment on wheat straw for ethanol production
Highlight
► An orthogonal design was used to optimize the microwave pretreatment on wheat straw for ethanol production. ► Four factors with three different levels were investigated. ► An optimal condition was achieved based on the orthogonal analysis. ► Ethanol yield from microwave-treated wheat straw was 5 times than that from the untreated.
Introduction
In order to make the lignocellulose easily hydrolyzed by cellulase and further converted to ethanol, pretreatment is necessary to break down the recalcitrant structure of the raw materials [1], [2]. A lot of attempts have been done in this area including physical, biological and chemical technologies [3], [4], [5], [6], [7], [8], [9].
Among all the technologies, microwave has been one of those which have a long history in pretreating biomass. It was first introduced in 1984 by Ooshima to pretreat different hardwoods and softwoods [10]. But there was almost no development in 1990s due to the maturity of the dilute acid pretreatment [11], [12], [13], [14], [15], [16], [17]. Until recently, microwave pretreatment was re-used by several investigations [18], [19], [20]. But most of them were mainly focused on enhancing enzymatic digestibility of the biomass pretreated by microwave.
In the present study, the microwave pretreatment condition was optimized for ethanol production.
Section snippets
Raw material
Wheat straw (Hattrick) was grown in Denmark. It was harvested by reaper in September, 2007 and the wheat straw (without chaff) was then pressed to big bales. After the ear of the wheat were removed, chopped corn stover was baled by the windrow binder. After being sent to the pilot plant at Risø-DTU, the wheat straw was milled to a particle size ≤2 mm for the pretreatment experiments with Wiley mill, standard Model No. 3. The dry matter (DM) content was 92.25%. Cellulose, Hemicellulose (the sum
Effect of different factors/levels on the chemical composition of wheat straw after pretreatment
The four factors, A (Ratio of raw material to NaOH solution), B (Pretreatment time), C (Microwave Power), and D (Concentration of NaOH solution) with 3 levels for each one had different influence on the Cellulose, Hemicellulose and Lignin content after pretreatment. The orthogonal analysis is shown in Fig. 1 and the R values are listed in Table 3.
Compared with raw wheat straw, the cellulose content in the pretreated wheat straw was increased for all the factors at different levels. Both the
Acknowledgments
The work was financially supported by HTF project (10077-1). We like to thank Tomas Fernqvist, Ingelis Larsen, and Annette Eva Jensen in Risø-DTU for the technical assistance.
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