The Study On The Separation Technology Of Major Compoments Of Rice Straw

Straw had a full use as raw materials in pulp and paper-making in China. But because of its structure characteristics, there were many disadvantages of the traditional straw cooking. For example, more hemicelluloses and ash of straw make black liquid have high viscosity, as well as making alkali recover difficulty. It not only brought trouble in straw cooking, but also made hemicelluloses,lignin and inorganic materials not be fully utilized, resulting in waste of resources. This subject added a pre-extraction process before rice straw alkali pulping to extract hemicelluloses, lignin and ash. This will reduce the pressure on the follow alkali recovery, and make hemicelluloses and lignin a full use, because milder pre-extraction conditions and the step by step of pre-extraction made the component of pre-extraction solution have a better extraction.In this study, the way of multi-level pre-extraction was investigated. The multi-level pre-extraction can dissolute each component step by step. By this way, the component of pre-extraction solution can be better recovered. After researching, the two appropriate pre-extraction path:"Hot water pre-extractionâ†'Alkaline pre-extraction" and "Hot water pre-extractionâ†'Enzyme pre-extractionâ†'Alkaline pre-extraction".1. "Hot water pre-extractionâ†'Alkaline pre-extraction" pathStraw was pre-extracted by Hot water first, and then was pre-extracted by Alkaline. The appropriate conditions for pre-extraction were as follows: The appropriate conditions for Hot water pre-extraction in this pre-extraction path were obtained as follows:liquid-to-solid ratio was 1:20, pre-extraction time was 120min, pre-extraction temperature was 80℃; The appropriate conditions for Alkaline pre-extraction in this pre-extraction path were obtained as follows:liquid-to-solid ratio 1:20, pre-extraction time 4h, pre-extraction temperature 65℃, alkaline charge 0.65%.2. "Hot water pre-extractionâ†'Enzyme pre-extractionâ†'Alkaline pre-extraction" pathStraw was pre-extracted by Hot water first, then was pre-extracted by enzyme, and was pre-extracted by alkaline in final. Xylanase was used in enzyme pre-extraction. The appropriate conditions for pre-extraction were as follows:The appropriate conditions for Hot water pre-extraction in this pre-extraction path as same as first pre-extraction:liquid-to-solid ratio was 1:20, pre-extraction time was 2.5h, pre-extraction temperature was 80℃; The appropriate conditions for Enzyme pre-extraction in this pre-extraction path were obtained as follows:liquid-to-solid ratio was 1:20, pre-extraction time was 2.5h, pre-extraction temperature was 50℃. pre-extraction pH was 7, enzyme charge was 80IU/g; The appropriate conditions for Alkaline pre-extraction in this pre-extraction path were obtained as follows:liquid-to-solid ratio 1:20, pre-extraction time 4h, pre-extraction temperature 65℃, alkaline charge 0.45%. We can saw alkaline charge in alkaline pre-extraction can reduce 0.65% to 0.45% after added enzyme pre-extraction. It means we can saving 30% alkaline charge.3. The effect of pre-extraction on the structure of dissolved lignin and hemicellulosesFrom the fomer, we could get two pre-extraction path in which there were four kinds of pre-extraction methods. That were hot water pre-extraction, enzyme pre-extraction, alkaline pre-extraction (alkaline charge was 0.45%) and alkaline pre-extraction (alkaline charge 0.65%).The dissolved lignin and hemicellulose of pre-extraction were detected and analyzed by the method of FT-IR. The four pre-extraction methods had little damage on the basic structure of dissolved lignin and dissolved hemicellulose. Four lines of dissolved lignin appeared more strong absorption peaks near the characteristic peaks of lignin at 1510cm-1, indicating that the skeleton of benzene ring of dissolved lignin had been preserved. Similarly, four lines of dissolved hemicellulose appeared more strong absorption peaks near the characteristic peaks of hemicellulose at 3416cm-1 and 1046cm-1, which were the hydroxyl and ether adsorption peaks in hydroxyl unit, indicating that the six-membered ring structure of hydroxyl unit of dissolved hemicellulose hasd been preserved. At the same time, the peaks near 1169cm-1 and 1735cm-1 also showed that the side chain of xylan had been preserved.