Separation of Solid Residues after SSF and SHF in Fuel Ethanol Production from Spruce

Production of fuel grade ethanol from various lignocellulosic materials using enzymatic hydrolysis has been under development for some time now. Some of the individual steps such as pretreatment, hydrolysis and fermentation have been improved to a great extent. Much effort has also been put into making the process as such more efficient. This includes studies on the effect of recirculation of process streams to minimise fresh water consumption and effluent streams. However, one major technical obstacle is still to be met, especially in the SSF (simultaneous saccharification and fermentation) process: the separation of the solid residue from the liquid. This residue, which consists mainly of lignin and non-hydrolysed cellulose, tends to be extremely difficult to separate into a solid and a liquid fraction, since it is very sticky. In SSF yeast cells are also present, which complicates the separation. Common separation methods of these residues often result in a slow filtration rate. When a filter press is utilised an extremely compact filter cake is rapidly formed. Employment of a decanter centrifuge, on the other hand, is rapid but yields a solid phase having a low dry matter content. In this work, a rather new technology has also been studied. A vibrating membrane separation unit (VSEP) was used to separate material from SSF or SHF. Due to high shear forces the membrane surface is not easily fouled, but the liquid flux through the membrane is maintained at a high level. Results from this study are presented.