Enhanced enzymatic conversion of softwood lignocellulose by poly(ethylene glycol) addition

Ethanol production from lignocellulose has great potential and is an important step in changing fuel consumption to a more environmentally friendly alternative. Lignocellulose is a large source of biomass. However, with lignocellulose and softwood lingocellulose in particular, high conversion of cellulose into fermentable sugars requires large amounts of enzymes. Addition of surfactants is known to increase the enzymatic conversion and decrease the amount of enzymes needed. Surfactants and polymers with various amount of ethylene oxide (EO) content were used to study the conversion of steam-pretreated spruce lignocellulose. Increasing conversion was obtained with longer EO chains on the non-ionic surfactants. Similar results were obtained by using only the hydrophilic part of the surfactant, i.e. by addition of ethylene oxide polymers such as poly(ethylene glycol) (PEG) to the hydrolysis mixture. Interactions of enzymes and PEG with substrate was monitored with 14C-labeled PEG 4000 and 3H-labeled Cel7A (CBH I), the dominating cellulase from Trichoderma reesei. Addition of PEG to enzyme hydrolysis of lignocellulose increased the conversion from 42% without addition to 78% in 16 h. Adsorption of Cel7A decreased from 81 to 59%. No effect of PEG was seen on a delignified substrate. By addition of PEG it was possible to perform hydrolysis at 50 °C leading to both high cellulose conversion (80%) and shorter process time (48 h). Two different interactions are proposed in PEG adsorption on lignocellulose, hydrogen bonding and hydrophobic interactions. Our conclusions from experiments on lignocellulose and delignified substrate are that EO containing surfactants and polymers, such as PEG, bind to lignin by hydrophobic interaction and hydrogen bonding and reduce the unproductive binding of enzymes.