Waste fibers from papermaking are often rejected due to quality and production issues. Since the rejected fibers also known as 'fines' are discharged as solid waste placing significant strain on landfills, bioconversion into sugars by hydrolysis of their cellulosic content can be very attractive to the paper industry. Earlier experimental investigations studying this hydrolysis have established the roles of the enzyme activity (given in terms of FPU), temperature and pH.
The present work develops a model for the kinetics of the enzymatic hydrolysis of cellulosic pulp fines based on the physico-chemical interactions. The cellulolytic enzymes adsorb to the outer surfaces of the fines after which they diffuse into the interior pores. The fine particles are assumed to be spherical, containing two distinct kinds of pores: one at the macro-scale and another at a micro-scale allowing slow progression of the enzymes into the solid cellulosic matrix. Enzymatic hydrolysis reactions are assumed to occur at the micro-scale within the cellulosic matrix. Convective mass transfer boundary layers reduce the enzyme transport across the external particle surfaces. The main utility of this model is in estimating the optimal reaction conditions and assist in scaling studies of these enzymatic hydrolysis processes.