Moving bed biomass fractionation system and method

Abstract

Countercurrent extraction of lignocellulosic biomass such as trees, grasses, shrubs, and agricultural residues or waste involves the separation of cellulose fibers from other constituents, for subsequent use in the manufacture of paper, plastics, ethanol, and other industrial chemicals. Systems and methods involve continuous, multiple processing steps that may include chemical reactions with mixing at elevated temperature and / or pressure, efficient reagent or solvent utilization, filtration at elevated temperature and / or pressure, controlled discharge of liquid and solid products, and energy recuperation.

Description

BACKGROUND OF THE INVENTION[0001]Embodiments of the present invention relate to systems and methods for the fractionation of lignocellulosic biomass into its components, including extractives, hemicellulose, lignin, and cellulose.[0002]Natural cellulosic feedstocks typically are referred to as “biomass”. Many types of biomass, including wood, paper, agricultural residues, herbaceous crops, and lignocellulosic municipal and industrial solid wastes have been considered as feedstocks for the manufacture of a wide range of goods. These biomass materials consist primarily of cellulose, hemicellulose, and lignin bound together in a complex gel-like structure along with small quantities of extractives, pectins, proteins, and ash. Due to the complex chemical structure of the biomass material, microorganisms and enzymes cannot effectively attack the cellulose without prior treatment because the cellulose is highly inaccessible to enzymes or bacteria. This inaccessibility is illustrated by th...

AI Technical Summary

Benefits of technology

[0027]Embodiments of the present invention include methods and systems that involve the continuous countercurrent flow of biomass and reactive liquids, and the control of degradation reactions to increase product yields. Design features include elevated temperature and pressure to minimize processing time, and the efficient use of chemical reagents and / or solvents as well as heat energy. Other features provide for the in-situ separation of liquids and solids for discharge, and the optional linking of multiple processing steps.

[0028]Embodiments of the present invention provide ethanol-water mixture techniques that may differ in one or more aspects from known approaches (e.g. Alcell® process of Diebold). For example, in some cases, embodiments include a prehydrolysis step to remove a desired amount of hemicellulose in a two-stage approach, where hemicellulose can be removed in a first stage. Embodiments may also include the use of a regime of high temperature and short residence time during delignification. For example, the residence time may be on the order of minutes, whereas other known approaches may involve a residence time on the order of hours. Embodiments may also provide the ability to produce low-hemicellulose pulp (suitable, for example, in making dissolving pulp) using a two-stage approach, whereas some known approaches may remove about 50% of the hemicellulose. Embodiments may also provide the ability to produce high-yield pulp using a single-stage approach, whereas other known approaches may remove about 50% of the hemicellulose, thereby lowering pulp yield.

[0029]In one aspect, embodiments of the present invention provide a continuous, countercurrent process of one or more stages for the fractionation of a lignocellulosic biomass feedstock. The process includes feeding the biomass feedstock into a first stage of a pressurized reaction vessel, injecting a first wash liquid into the first stage countercurrently to the biomass feedstock, discharging the first wash liquid from the first stage, and discharging a solid biomass product from the reaction vessel in slurry form. The process can also include conveying a first stage biomass product from the first stage to a second stage of the reaction vessel, injecting a second wash liquid into the second stage countercurrently to the first stage biomass product, and discharging the second wash liquid from the second stage. The first wash liquid can include water or a solution of water and a mineral acid for hemicellulose hydrolysis, and the second wash liquid can include water and a sodium or ammonium hydroxide base for lignin hydrolysis. The second wash liquid can include about 40% to about 60% ethanol by weight. The first wash liquid can include a water rinse and a concentrated chemical reagent that mix to form the first wash liquid. In some cases, the first wash liquid provides optimal recovery of oils, proteins, and other extractives. The process can also include maintaining a temperature of at least one of the stages in a range from about 190° C. to about 240° C.

Problems solved by technology

Due to the complex chemical structure of the biomass material, microorganisms and enzymes cannot effectively attack the cellulose without prior treatment because the cellulose is highly inaccessible to enzymes or bacteria.

This inaccessibility is illustrated by the inability of cattle to digest wood with its high lignin content even though they can digest cellulose from such material as grass.

Commercial processes for producing cellulose pulp from wood generally depend on inorganic chemicals as the extracting agent and do not yield lignin as a valuable byproduct.

If a large proportion of white liquor is used in connection with the impregnation, this exposes fibers to the aggressive effect of the white liquor, with carbohydrates degradation and loss of fiber strength.

The separation of cellulose from other biomass constituents is difficult, in part because the chemical structure of lignocellulosic biomass is so complex.

Biomass is widely recognized as a potential raw material for the production of transportation fuel and industrial chemicals, but an economically competitive commercial biorefinery has yet to be devised.

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