(406b) Effective Hemicellulose Hydrolysis in a Pilot Scale Continuous Pretreatment Reactor; Improving Reactor Design and Understanding Process Performance

There are many different methods which have been proposed for lignocellulosic biomass pretreatment. A variety of these methods have been shown to exhibit high cellulose and hemicellulose hydrolysis yields in a laboratory scale for pretreatment and the subsequent enzymatic hydrolysis. However, if these methods are going to be used for industrial scale production of cellulosic ethanol, it is necessary to test their performance in scalable, process relevant conditions and equipment. Such tests should be conducted at both a high solids concentration, to increase sugar concentration in resulting fermentation slurries, and in a continuous reactor to determine process performance in an integrated system. We have operated a continuous, horizontal screw reactor for the pretreatment of biomass under acidic conditions and at high solids concentrations. The reactor is capable of pretreating 200 kg per day of dry biomass at elevated temperature and pressures. In this work, we discuss the design of the reactor system as well as the investigation of reactor operating conditions which yield high levels of hemicellulose hydrolysis. Pretreatment experiments using a dilute sulfuric acid pretreatment were carried out to understand the impact of reactor residence time, temperature, and catalyst concentration on the hydrolysis of hemicellulose. Corn stover was pretreated in the reactor under a variety of conditions. Process data indicated significant degradation of hydrolyzed xylan at temperatures above 170°C, and thus lower reaction temperatures were preferred. At reaction temperatures between 150°C and 170°C, more than 80% of the xylan was hydrolyzed with less then 5% of the xylan being degraded to furfural. The hydrolyzed xylan was present as both monomers and oligomers, and an additional hydrolysis step was used to convert the oligomers to monomers. While reaction time, as varied by reactor screw speed, impacted hydrolysis yields, it was difficult to determine an accurate residence time distribution for the system. Overall, the results show that the dilute acid method can be used to effectively pretreat corn stover in a pilot scale continuous reactor and achieve high overall xylan hydrolysis yields.