טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentAlfassi Gilad
SubjectProcess for Enzymatic Degradation of Cellulose
DepartmentDepartment of Chemical Engineering
Supervisors Professor Yachin Cohen
Dr. Dmitry Rein
Full Thesis textFull thesis text - English Version


Abstract

Cellulose is considered one of the most renewable and abundant materials on earth, yet the production of cellulosic bio-fuels is not fully utilized mainly due to the high costs of conversion. One of the most prominent problems in cellulose hydrolysis is the poor enzymatic accessibility of the cellulose crystals. It thus requires pretreatment that utilizes solvents and their recycle, and necessitates a high enzyme load.  In this research, the accessibility of cellulose was improved in three manners: modifying the surface area of hydrogel particles regenerated from cellulose solutions, by exposing a cellulose coating on emulsified oil droplets and by a novel reaction of slight acetylation which renders cellulose water soluble. Enzymatic hydrolysis of hydrogels was shown to be affected deleteriously by its density, which is directly proportional to the cellulose concentration in the initial solution. High-resolution scanning electron microscopy showed that the hydrogel particles exhibit a porous internal network covered by a dense external surface layer, which limits the hydrolysis rate. Application of shear forces accelerated the hydrolysis rate by up to six-fold by elimination the effect of the external layer. Furthermore, hydrolysis became nearly independent of the initial cellulose solution concentration. These findings allowed usage of lower solvent quantity and enzyme loading. Another aspect investigated was fabrication of emulsified oil droplets coated by cellulose hydrogel. By altering the cellulose/oil ratio the emulsion droplet diameter was controlled in the range of 400nm-10µm, with a corresponding change of the cellulose hydrogel shell thickness. Managing these parameters provides a valuable tool for providing an accessible substrate for enzymatic hydrolysis, that could not be achieved by simple hydrogel manipulations. Finally, a facile cellulose derivatization process was reported using ionic liquids mixed with dichloromethane. The derivatization is done by adding dichloromethane during cellulose dissolution, with control of the degree of substitution (DS, number of acetylated glucose hydroxyls) from 0 to 1.8. At different DS the hydrogel structure and its hydrolysis rate were altered. At a specific range about DS~ 0.6 cellulose was rendered water soluble. At that state an overwhelming increase in hydrolysis rate was achieved.