This project is aimed at developing the pretreatment, hydrolysis, and post-treatment/detoxification technologies required for converting waste biomass into feedstock for microbial fermentation processes.
Lignocellulosic biomass is essentially structured with a sheath of lignin and hemicellulose surrounding a core of cellulose. The lignin and hemicellulose protect cellulose from chemical and/or biological hydrolysis. Some direct hydrolysis technologies, such as those using concentrated acid or dilute acid at high temperature, have had long industrial histories. These “harsh” procedures tend to destroy significant portions of sugar content in the original biomass. In addition, they generate appreciable amounts of toxic or inhibitory compounds, such as acetic acid, furfural and hydroxymethayl furfural, which need to be removed (detoxified) for usage in bioprocesses.
It is currently believed that the technology combining a mild pretreatment and a subsequent enzymatic hydrolysis has the highest potential for reducing the cost of producing fuel ethanol and enabling biorefinery development. Less stringent detoxification requirements may be involved with such a technology.
Supercritical CO2 based pretreatment has the following attractive features: gentle on treated materials, good operation controllability, easy product separation, and friendly to the environment. In addition, our study using supercritical CO2 (and a small amount of H2O), have confirmed that the method preserves almost all the hemicellulose (unlike acid hydrolysis and other pretreatment methods that destroy hemicellulose) and loosens the biomass structure for easy enzymatic hydrolysis (with similar glucose yield and higher total sugar yield compared to those of dilute acid-pretreated biomass). Although the economic viability of using the supercritical method for the sole purpose of biomass pretreatment is uncertain, the method will be very beneficial when applied to plants that are or can be supercritically extracted or processed to produce a range of products. Moreover, the integrated process developed in this project will produce hydrolysate with high sugar yield and no/low inhibition to microorganisms. Such hydrolysate can be readily used in other fermentations for producing numerous biobased products.
Statistical optimization of operating conditions for supercritical carbon dioxide-based pretreatment of guayule bagasse. (N. Srinivasan and L.-K. Ju) Biomass and Bioenergy. DOI Link
Pretreatment of guayule biomass using supercritical carbon dioxide-based method. (N. Srinivasan and L.-K. Ju). Bioresource Technology 101(24), 9785-9791 (2010). DOI Link