(664a) High Yield Biorefining Using Organosolv Processing

Biorefineries capable of processing the relatively recalcitrant lignocellulosic feedstocks can take many forms. A conceptually relatively simple one is the gasification of biomass to create syngas, which can then be converted into a somewhat limited range of organic chemicals by chemical or biological means. Pyrolysis is another thermochemical process that creates a range of gaseous, liquid and solid products. Like gasification, pyrolysis has the advantage of being relatively insensitive to the type of feedstock, but both of these thermochemical processes significantly degrade the complex chemical components in biomass, many of which have potentially high commercial value in their original form. Other biorefinery processes utilize acids, steam or alkali to open up the compact cellular structures in woody biomass, thus exposing the fiber wall polysaccharides, cellulose and hemicellulose, to enzymatic attack. Most of these processes target the production of hexose and pentose sugars derived from the hydrolysis of cellulose and hemicellulose for conversion into fermentation products such as ethanol, butanol, lactic acid, etc. The remaining impure biomass components, such as lignin, rosin and resin extractives, etc. are then mostly used as low value solid fuel to power the process.

Organosolv technology, as used in the ethanol-based Lignol Modified Organosolv Biorefinery Process, allows for the fractionation of lignocellulosic biomass into a series of valuable chemical products, which have a combined commercial value that greatly exceeds the value of a variety of fermentation products made from just the carbohydrate fractions of woody biomass. The advantages of this value-retention strategy are numerous. With greater revenues being obtained from each unit of feedstock, such plants require smaller amounts of resource to be profitable, thus avoiding the need for large harvesting areas and opening up many more suitable locations for biorefineries. This has the added advantage that profitable plants can be smaller, thus requiring a lower total capital investment, which is a considerable advantage for an early stage technology. Furthermore, the revenues of such a plant are less dependent on the potentially-variable market values of any one single product, such as ethanol. The process treats woody biomass, - softwoods, hardwoods, agricultural residues, deliberately grown energy crops, etc. ? with an aqueous ethanol liquor at elevated temperatures. The precise conditions are dictated by the nature of the feedstock, the desired product streams and process energy considerations. The lignin and hemicellulose in the biomass are partially hydrolyzed and dissolve into the liquor, while the hydrophobic ?extractives? also dissolve in the hot organosolv liquor. Some additional chemistry occurs in the process, such as the conversion of some pentose sugars from the hemicellulose into furfural, but generally, most of the fine chemical structures originally in the biomass are preserved. Following the modified organosolv stage, a solid fraction consisting mostly of cellulose with minor amounts of residual lignin and hemicellulose is ready to be converted by enzymatic hydrolysis into a sugars stream useful for various fermentation processes. Because most of the lignin has been removed this cellulose-rich fiber mass is more readily hydrolyzed by enzymes than are equivalent streams from other biorefinery processes. This ?pulp? stream can also be processed further into a number of commercially-useful chemicals and materials, such as cellulose derivatives and powders. The liquor from the organosolv stage is processed to recover separate streams of high-purity lignin (for use in resins and a large number of other applications), as well as furfural, acetic acid from the hemicellulose, wood ?extractives?, pentose and hexose sugars and oligosaccharide products. The ethanol used in the process is recovered by distillation and recycled back to the process. Energy for the process, - steam and electricity only ? can be provided from bark and forestry residuals. No fossil carbon fuel is required for the process. The net water consumption of the process is negligible. The unit processes that make up the Lignol Biorefinery are combinations of well-known processes that currently exist in either the chemicals, biochemicals or pulp and paper industry. Some, but very little new process equipment is required, assuring a high degree of confidence in its operability and performance. A large 70 tonne per day demonstration plant utilizing a substantial portion of this technology has been operated for many years in the past. The multi-product, value-retention approach to biorefining has numerous technical and economic advantages, which will be discussed.