A comparison of batch-wise vs. continuous steam pretreatment of lignocellulosic materials

The pretreatment step is one of the most important operations for production of fuels or chemicals using the sugar platform. The success of the process is to a great extent dependent on the ability to render a material suitable for enzymatic hydrolysis and fermentation. Today, one of the most commonly used pretreatment methods is (acid catalyzed) steam pretreatment, in lab-, demo- and commercial-scale processes. In a lab scale, by far the dominating type of steam pretreatment is batch-wise operation of the equipment, where the pretreatment usually takes place for a few minutes (not including filling and emptying time). However, in a commercial scale it is more likely that some kind of continuous operation will be the main option for steam pretreatment. The resulting materials from batch and continuous pretreatment often have different performance in terms of hydrolysability and fermentability for a material treated at the same severity. For scale-up purposes it is a vital importance to gather data that yield similar results in small-scale and commercial scale operation. In this study pretreatment of spruce and agricultural materials, performed batch-wise in 10-litre scale is compared with steam pretreatment in a 20 kg/h continuous equipment. The study is performed using similar severities and the resulting materials are evaluated in terms of yield after pretreatment, enzymatic hydrolysis efficiencies, generation of inhibitory compounds and the potential for fermentation or SSF.