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COMPLEX USAGE OF THE SUBSTRATE IN THE BLEACHED KRAFT PULP ENZYMATIC HYDROLYSIS

Evgenii Novozhilov

Abstract

Enzymatic conversion of lignocellulosic substrates into sugars is an upcoming sphere of biotechnology. Most of the ways, aimed on hydrolysis process improvement are focused at maximizing of raw materials conversion into monosaccharides. Thus, process improvement usually focuses on substrates pretreatment, choosing of the most effective enzyme complexes and control of the hydrolysis process parameters such as increasing the process duration and enzyme dosage, substrate concentration reduction. Kraft woody pulp enzymatic hydrolysis is much more promising approach of plant raw materials conversion process comparing to wood. Bleached pulp is less structured so it has more accessible to hydrolysis structure; it also contains almost no inhibitors of enzymatic activity. However, it should be noticed that reaching of high conversion degrees is not always necessary, since it does not compensate all process costs. Thus, determination of optimal substrates conversion degree values and rational use of non-hydrolysable residue is crucially important. The aim of this work was to develop a new approach of bleached kraft pulp enzymatic hydrolysis with Penicillium verruculosum enzymes for two main products production: sugars and cellulose powder. A comparative evaluation of different morphological features limiting effect of hardwood and softwood substrates on hydrolysis process was studied. The positive effect of fibers shortening during the early stages of enzymatic hydrolysis on high substrate concentration process (10...15 %) efficiency has been established. As a result hydrolysates with a sugar concentration of 60-108 g/l were obtained with acceptable enzyme consumption of 10 FPU/g. Hardly hydrolysable bleached kraft pulp fraction was isolated after sedimentation of non-hydrolysed residue. It consisted of fibers? primary cell wall fragments and hardwood vessels. Non-hydrolysable residues were treated for cellulose powder production. Cellulose powder samples were evaluated for the following parameters: crystallinity degree, adsorption activity and gel-forming capability. Based on the obtained data a complex approach for bleached kraft pulp high-concentration enzymatic hydrolysis was proposed. The possibility of achieving hydrolysates with more than 50 g/l sugar concentration and high crystallinity degree cellulose powder was performed.

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