Effects of hydrothermal treatment of cellulosic material and structural interactions of enzymes

Joseph Robert Weil, Purdue University

Abstract

Corn fiber, wood saw dust and newsprint are lignocellulosic materials that can yield potentially fermentable sugars. Aqueous, liquid pretreatments involving high temperatures at saturation vapor pressure were used to promote effective enzymatic conversion of the cellulose to glucose. The pretreatments consisted of mixing wood saw dust, newsprint or white fiber in liquid water while the slurry was heated to temperatures of 220 to 260°C at saturation vapor pressure. The temperature was controlled and the pH monitored in all runs. Small amounts of KOH (2.0 M) were added to the slurry during pretreatment to control the pH. The effectiveness of the pretreatment was gauged by the extent of enzyme hydrolysis of the cellulose to glucose in 48 hours. The highest conversion to glucose was 84% of theoretical for corn fiber, 54% of theoretical for wood saw dust and 38% of theoretical for newsprint. Enzymatic conversion for the untreated materials was 17% of theoretical for the corn fiber, 1% of theoretical for the wood saw dust and 32% of theoretical for the newsprint. Water is both an acid catalyst and a hydrating agent, whose acidity needs to be controlled if pretreatment is going to yield high conversion to glucose. This research developed a modified model based on acid hydrolysis of cellulose at the pretreatment conditions. In this model, acidic organic species, which result when glucose, formed from cellulose and degraded at high temperatures, accelerates the hydrolysis of cellulose. The model fit the compositional changes which occurred during various pretreatment conditions. The model suggests that controlling pH is needed to obtain a high yield of reactive cellulose, both accessible and susceptible to enzyme hydrolysis. Otherwise, a cascade of reactions occurs which causes significant auto-hydrolysis. A limited extent of hydrolysis may be desirable since this may help to disintegrate the substrate into smaller particles and thereby increase surface area available to the enzyme. The model suggests that the most effective conditions for pretreatment are between 200°C and 210°C for corn fiber, between 240°C and 250°C for the wood saw dust and between 200°C and 230°C for the newsprint.

Degree

Ph.D.

Advisors

Ladisch, Purdue University.

Subject Area

Agricultural engineering|Agricultural chemicals

COinS