The conversion process of lignocellulose to chemicals, such as, ethanol, lactic acid or oleochemicals, consists of four main steps, i.e., pretreatment, hydrolysis, fermentation and downstream processing, often performed in simultaneous processes which decreases the process time and product inhibition.
In the present research, poplar wood was pretreated by steam explosion and two fractions were obtained, i.e., the solid glucose rich fraction and the liquid xylose rich fraction. Both fractions also contain phenolic degradation products of lignin which have an inhibitory effect on the hydrolyzing enzymes and the fermenting microorganisms. During the hydrolysis, the polysaccharides are cut to monosaccharides. Due to inhibition by lignin, the yield is lower and less sugar can be obtained from a certain amount of biomass. Therefore, it was first investigated how commercial laccase enzymes may positively affect the enzymatic hydrolysis reaction of polysaccharides to monosaccharides, by oxidizing the lignin-derived phenolics. After this, so-called, laccase detoxification, hydrolysis was performed and it was investigated whether it gave a better result. The experiments showed that the presence of solids significantly altered the reaction performance of the laccase enzyme and that, dependent on the applied enzyme, laccase reaction was improving hydrolysis or decreasing its efficiency.
As enzyme cost is considered to be one of the main factors that define the process costs, enzyme immobilization and recycling was researched. However, the solid particles present in a simultaneous saccharification and fermentation process (SSF) will prevent recovery of the enzymes by centrifugation or filtration. Moreover, solid particles are preferably in high concentrations which further increases the problem. Therefore, the use of magnetic immobilized enzymes (m-CLEAs) was investigated experimentally and from liquid medium, 99.5 m/m% of m-CLEAs could be recovered by a magnet in one step, while 88 m/m% could still be recovered from the high-solids SSF fermentation broth.
In the presentation, the reactor set-up in high-solids conditions, the enzyme recuperation and the enzyme costs will be discussed.