Pretreatment is an integral part of the conversion process of cellulosic feedstocks to biofuels via biochemical process routes. However, it is also one of the most costly and energy intensive steps of the process. Many pretreatments have been demonstrated effectively in the laboratory under conditions which would not be feasible at commercial scale. It is therefore important to demonstrate scaling of pretreatment processes as part of a rigorous evaluation and demonstration of their commercial potential. High dry matter (DM) content is an important factor in large scale pretreatment, but can present significant issues in scale up and process performance.

One of the key process parameters for some catalyst based pretreatments is the handling of biomass before pretreatment and the impregnation of the biomass with the catalyst. Especially when operating at high solids concentrations, catalyst impregnation can greatly impact the efficacy of a given pretreatment. In this study we evaluated a wide range of process parameters related to catalyst impregnation thought to impact pretreatment results of dilute sulfuric acid pretreatment. Corn stover was impregnated under various preprocessing scenarios and pretreated in a steam digester under low and high pretreatment severity conditions. This was carried out using a Placket-Burman experimental design meant to screen many processing scenarios and factors for significance. Factors investigated included impregnation time and temperature, spraying versus soaking impregnation methods, particle size, vacuum application and passage through a compression screw feeder. All samples were pretreated at an initial dry matter content of 45% in a batch steam digester. Initial results pointed to the method of catalyst impregnation as the most significant factor, along with catalyst loading during impregnation. A follow up study was carried out to investigate the amount of excess acidified liquid necessary to apply to the biomass to maximize xylose yields, by varying the impregnation solids concentration and sulfuric acid loading. Results show the impacts of these process variations on xylose yield and enzymatic digestibility, while providing information on optimal regions for the operation of catalyst impregnation processes. The impact of these results on industrial scale impregnation scenarios will be discussed along with their implications for future processing scenarios for continuous reactors.