Pretreatment Of Miscanthus Straw By Different Alkaline Catalysts

Pretreatment is an essential element in the bio-conversion of lignocellulosic substrates. Nowadays, most of the pretreatment methods have many disadvantages, such as their energy consumption is high, they are strict in equipment, they cause serious environmental pollution, and the catalysts cannot be recycled, etc. This study was based on Miscanthus, one kind of energy crop, as the research object, with organic alkaline guanidine and aminoguanidine, inorganic alkali calcium hydroxide as catalysts to pretreat the Miscanthus. The effect of different pretreatment conditions on the saccharification has been investigated. The structure and properties of native and pretreated Miscanthus have been characterized, using a variety of advanced means. The relationship between the structure of pretreated Miscanthus and the crack of lignocellulose degradation resistance barrier has been discussed. The major results of this paper were summarized as follows:1. Miscanthus straw was pretreated with guanidine, guanidine and hydrochloride, respectively. The effect of the catalysts’dosage, the pretreatment temperature and the reaction time on the enzymatic saccharification has been studied. The pretreated samples have been characterized via XRD, FTIR, TG and SEM. Results showed that the main factors influencing the effect of pretreatment were the catalysts’dosage and the pretreatment temperature. The SEM images showed that the surface of the pretreated samples were porous and corrosion; the XRD showed that relative crystallinity index of cellulose increased slightly; FT-IR spectra confirmed that guanidine and aminoguanidine can effectively get rid of the hydrogen bonding of lignin and cellulose; TG showed that the cellulose had sharply weightlessness when pretreated with guanidine.2. Miscanthus was also pretreated by calcium hydroxide without heating, vibration and energy consumption, just for stewing. The effect of the catalysts’dosage and the days for soaking on the saccharification has been investigated. The pretreated samples have been characterized via XRD, FTIR, TG and SEM. The time and temperature was set at 30 days and room temperature (28℃), respectively. At the same time, we chose the pretreatment of heating and oscillation for 12 h as comparison. Results showed that the change trend of soluble C5 sugar and C6 sugar in blank samples without calcium hydroxide were different from the samples added with calcium hydroxide. With the preatreatment time increasing, the content of sugar in blank sample gradually reduced. The catalysts’dosage is the key factor which affects enzymatic saccharification on the low catalysts’dosage. When the dosage of calcium hydroxide was greater than 0.10 g/g dry biomass, there has not obvious improvement on the efficiency of the pretreatment. The highest yield of C5 sugar was 148 mg/g dry biomass, obtained via pretreatment for 10 days, and the the highest yield of C6 sugar was 268 mg/g dry biomass, obtained via pretreatment for 4 days. As the pretreatment time increasing, the content of insoluble lignin was increased. The SEM images showed that surface of the pretreated sample was loose and porous; the XRD diffraction showed that the degree of crystallinity in cellulose was increased; the FT-IR spectra confirmed that the lignin can be effectively removed and the hydrogen bonds in cellulose was degraded through calcium hydroxide.3. By comparing different pretreatment methods, we found that pretreatment without energy consumption can reach the same purpose compared to the energy consumption, just slightly different in terms of pretreatment time. We further found that calcium hydroxide pretreatment has a good application prospect compared with organic guanidine pretreatment, because it is cheaper and more eco-friendly.