Integrated process for separation of lignocellulosic components to fermentable sugars for production of ethanol and chemicals

• US 20080057555A1
• Filed: 02/01/2007
• Published: 03/06/2008
• Est. Priority Date: 09/05/2006
• Status: Active Grant

• Current Assignee: Xuan Nghinh Nguyen
• Original Assignee: Xuan Nghinh Nguyen
• Inventors: Nguyen, Xuan Nghinh
• Granted Patent: US 7,666,637 B2
• Time in Patent Office: Days
• US Class Current: 435/165
• CPC Class Codes: C12P 7/10 substrate containing cellulosic material
• CPC Class Codes: Y02E 50/10 Biofuels, e.g. bio-diesel
• CPC Class Codes: Y02P 20/10 Process efficiency

Abstract

A continuous and modular process converts lignocellulosic materials for the production of ethanol principally and/or chemicals such as methanol, butanediol, propanediol, hydrocarbon fuel, etc. Renewable lignocellulosic biomass such as but not all inclusive hardwoods (gum, beech, oak, sweet gum, poplar, eucalyptus, etc.), soft woods (pines, firs, spruce, etc.), corn stovers, straws, grasses, recycled papers, waste products from pulp and paper mills, etc can be used as feedstock. The process is designed to be modular and the feed entry point can be selected to adapt to different biomass feedstock. Lignocellulosic biomass such as hardwood and softwood are subjected to chemical/pressure treatment stages using potent and selective chemicals such as sodium chlorite/acetic acid (anhydrous) and chlorine/chlorine dioxide to separate the main components—lignin, cellulose (glucose) and hemicelluloses (xylose, arabinose, galactose)—into three process streams. The separated carbohydrates are further subjected to washing, cleaning, neutralization, and/or mild hydrolysis and subsequently fermented to produce ethanol. Residual lignin and extractives remained with the cellulose are removed by chemical treatment steps to enhance the fermentations of cellulose. Pre-hydrolysate after neutralization to neutralize and remove toxic components such as acetic acid, furfural, phenolics, etc. containing (xylose, arabinose, galactose) and hexoses (glucose) can be either separately or together with the purified cellulosic fraction fermented to produce ethanol. Approximately 100 gallons of ethanol, suitable to be used as a fuel, can be produced from one dried ton of wood. Significant amount of lignin are separated as a by-product and can be converted to hydrocarbon fuel, surfactant, drilling aid, or can be incinerated for generation of power and steam.

Claims

1. A process for the conversion of biomass containing lignin, cellulose, hemicelluloses, starch and minor components such as extractives, including hardwoods, softwoods, grasses, waste papers, sugar cane, corn stover, grass, recycled papers, pulp and paper mill primary waste products, etc. to produce ethanol, a biofuel, wherein manufacturing operating conditions for the claimed process comprising of treatment steps described below to convert wood biomass into fermentable sugars and remove residual lignin and extractives can be optimized for agricultural residues (corn stover, corn stalk, grasses, etc.) and could be simplified for feedstocks already processed in a paper mill, such as primary clarifier sludge, white bond recycled paper, etc. and entry point to the claimed process could be determined when compositions of these feedstocks are known.

2. This integrated continuous process, robust and modular in nature, consists essentially of the following sequential steps for hardwoods and softwoods, since wood is the most abundant, least expensive and more difficult to convert to fermentable sugars than other lignocellulosic biomass:

a. (Wood preparation);

obtaining hardwood, mixture of hardwood, mixture of softwood (although mixtures of softwood and hardwood can be used, separation into similar type, based on compositions can enhance process efficiency and operating costs);

b. converting wood into wood chips of ¼

″

to 1 inch with thickness of approximately ¼

″

, similar to wood chips used in the pulp and paper industry;

saw dust, fines, over sizes, and over thick chips from chipping operation can be used in the process as well;

c. (Pre-hydrolysis);

charging wood chips, at their natural moisture content (about 40-50%), and up to 5% (on oven-dried weight basis of biomass) acid (sulfuric acid, nitric acid, hydrochloric) into a pre-soak tank or acid impregnator to achieve a pH value of about 2-3;

residence time can be as long as 4-5 hours or shorter;

d. draining the acid-presoaked chips by centrifuging to remove excess acid and effect a solids consistency of about 30-35%;

the chips are conveyed and heated in a series of steam/gas mixers with flash steam from the blow tanks and screw fed into a pressurized reactor;

direct live steam with or without inert gas (such as carbon dioxide, air, nitrogen, oxygen) can be added to raise the reactor temperature and pressure;

the reaction time is 1 minute to 30 minutes at 150 C(entigrade) to 300 C and 150-1000 psig pressure;

e. blowing (releasing) wood chips from the high pressure reactor under high pressure into a series of blow tanks or flash tanks with some capacity for holding time disintegrates them into more impregnable lignocellulosic solids for subsequent treatment stages;

flash steam are recycled to the pre-heat steam mixers;

f. pressing the solids product from the blow tank to separate the liquor and solids;

the solids can be further washed in a series of countercurrent washers to recover the hydrolyzed (hemicellulosic) sugars;

the filtrates from the washer contain high concentration of pentose sugars such as xylose, arabinose, galactose, etc;

g. adding lime to neutralize the pre-hydrolysates to a pH 8-10, if necessary;

in this treatment, temperature is raised to 40-80 C with about 30 minutes to 180 minutes residence time;

lime precipitates compounds which could be toxic to fermentation;

after liming the pre-hydrolysate containing essentially sugars from hemicelluloses is sent to a prehydrolysate storage tank ready for fermentation;

h. (Delignification/Deresination);

the washed solids from the pressurized pre-hydrolysis stage now containing primarily lignin, cellulose and extractives;

lignin from some wood species could be highly condensed and difficult to remove;

hence, there are two (2) process options for extracting/delignifying the lignocellulosic solids and purify the cellulosic fraction;

the first option to treat the highly condensed lignin product (typically resulting from softwood feedstock) is as follows;

i. charging washed lignocellulosic solids into a series of two to four-stage continuous co-current delignification/deresination reactors;

in each stage, a 1% to a maximum 10% chemical charge (based on solids) of solution of sodium chlorite/acetic acid anhydrous (may substitute acetic acid anhydrous for peracetic acid, acetic acid, or sulfuric, or nitric acid), or of solution of chemicals such as chlorine/chlorine dioxide, or sodium hypochlorite, or acidic hydrogen peroxide, or a combination of these highly selective delignifying oxidants, are mixed with the incoming lignocellulosic solids in a stock mixer before the reactor;

the temperature of the reactor is in the range of 120-180 F(arenheit);

the residence time of the reactor is 3-4 hours;

j. after exiting from the first stage reactor, the solids are separated from the filtrate without washing;

the solids are sent to subsequent stages, where fresh solutions of sodium chlorite/glacial acetic acid (anhydrous) are added at the beginning of each stage;

process conditions such as temperature, pressure, and residence time in these subsequent stages are similar to the first stage;

alternatively, as mentioned earlier other chemicals such as acidic hydrogen peroxide or chlorine dioxide/chlorine, could be used in place of sodium chlorite/acetic acid anhydrous;

the total amount of (oxidant) chemical charges are based on the amount of lignin and extractives, typically from 1/1 to 1.5/1 chemical/lignin ratio, ratio of sodium chlorite to acetic acid anhydrous are 3/1 to 6/1, and the chemicals can be equally distributed or staggered with most being applied toward the front end, for example, for a four-stage reaction, a 40% of total chemicals in the first stage reactor, 30% in second, 20% in third, and 10% in the last stage;

k. for the second process option with the less condensed and more easily extracted lignin;

the lignocellulosic solids are first extracted with caustic at moderate temperature;

typical ranges of operating conditions are caustic charge 2%-12% on solids, temperature 80 F-150 F, residence time 1-3 hours;

l. after caustic extraction, the solids are washed;

chlorine/chlorine dioxide (or sodium chlorite/acetic acid anhydrous) are charged (based on the lignin content remained) to delignify/de-resinate and purify the cellulosic solid;

chlorine dioxide charge should be 30-50% of the total equivalent chlorine charge;

the sequence of chemical application is chlorine dioxide and then chlorine to achieve maximum effect of oxidation;

temperature is 80-120 F, residence time is 1 hr-3 hr, solids consistency is 3-10%;

m. after chlorine dioxide/chlorine delignification stage, the solids are washed in a counter-current washer train;

n. the washed solids from the delignification/deresination stage contain primarily cellulose and the washer filtrates contain primarily lignin;

the filtrates can be combined with other filtrates containing lignin and other degradation products for evaporation and recovery;

o. (Fermentation and Saccharification);

the cellulose can be converted to glucose by cellulose enzymatic hydrolysis;

or it can be converted directly to ethanol by adding cellulase and yeast or bacteria together;

p. alternatively, a dilute acid hydrolysis stage under moderate temperature can be used to hydrolyze cellulose into fermentable glucose;

conversion yield to glucose above 90% is typical with pure cellulose solids;

q. the two process hydrolysates containing primarily glucose (main hydrolysate) and xylose/arabinose (prehydrolysate) can also be combined and fermented (for example, with Z. Mobilis, or Schizosaccharomyces Pombe, cellulase, beta-glucosidase, and xylose isomerase) to produce ethanol;

or alternatively, these two process streams containing glucose and hemicelluloses sugars can be fermented separately (for higher conversion efficiencies);

r. as an alternative to ethanol, a biofuel, the main product from hemicelluloses and cellulose, the prehydrolysate containing primarily xylose can be converted to furfural or xylytol, etc. and the cellulose can be used as such;

s. process stream containing lignin, can be concentrated and used as a by-product like drilling mud additive, to produce phenolic chemicals or burn to generate power and steam;

t. steam and gas from blow tank can be flashed in two or three stages, and flash steam/gases are recycled to preheat the pre-soaked feed into the pressurized reactor.

3. A process as defined in claim 2c wherein the acid (nitric acid, sulfuric acid) is used;

as defined in claim 2c wherein the dilute hydrolyzing acid has concentration of about 0.1% to about 8% acid by volume;

as defined in claim 2c wherein the lignocellulosic feedstock after pre-soaking with dilute acid would be pressed to approximately 25%-40% consistency (solids concentration) prior to a series of steam mixers and high pressure reactor;

as defined in claim 2d wherein saturated and/or unsaturated steam recovered from high pressure high temperature reactor are directly added to the steam mixers and to the pressurized reactor to achieve the high pressure;

as defined in claims 2h to 2j is for very difficult to delignify feedstock such as dense hardwoods, softwoods with significant amount of resins, extractives and lignin remained;

as defined in claims 2k to 2m is for materials with less condensed and more soluble lignin and the amount of lignin remained are not substantial;

as defined in claim 2p wherein during the hydrolyzing step the cellulosic material is hydrolyzed with dilute acid (sulfuric or nitric acid) at 0.5% to 2% concentration, at a temperature range of about 150 F to about 350 F at a pressure from about 60 psi to about 200 psi for a period of about 10 minutes to about 90 minutes;

as defined in claims 2i-2j wherein a combination of chemical agents such as chlorine/chlorine dioxide, or sodium chlorite/glacial acetic acid, or hypochlorite are used to selectively remove the lignin from the pre-hydrolyzed solids;

as defined in claims 2k-2m wherein mixture of chemicals such as chlorine and chlorine dioxide are used to de-lignify and de-resinate the prehydrolyzed solids to improve fermentability of the cellulosic residue;

as defined in claim 2 wherein fermentable sugars such as xylose, arabinose, galactose, glucose are produced from renewable lignocellulosic biomass including hardwoods and softwoods and lime can be added to neutralize and adjust pH prior to saccharification and/or fermentation of the sugars;

as defined in claimed 2 wherein all filtrates from counter-current washers containing lignin, extractives, excess chemicals used in reaction steps are combined and evaporated to 50%-70% solids in a multiple effect evaporator train;

the high solids lignin could be directly incinerated to generate heat, steam, power and/or used as by-product chemicals such as drilling fluid aids, hydrocarbon feedstock for hydrogenation, etc.