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

• US 7,666,637 B2
• Filed: 02/01/2007
• Issued: 02/23/2010
• Est. Priority Date: 09/05/2006
• Status: Expired due to Fees

• Current Assignee: Xuan Nghinh Nguyen
• Original Assignee: Xuan Nghinh Nguyen
• Inventors: Nguyen, Xuan Nghinh
• Primary Examiner(s): Tate; Christopher R
• Assistant Examiner(s): Kosar; Aaron J
• Application Number:
  US11/700,718
• Publication Number:
  US 20080057555A1
• Time in Patent Office: 1,118 Days
• Field of Search: None
• 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

The invented process separates main components in lignocellulosic biomass, specifically hardwoods, softwoods into lignin and fractions of high purity sugars which are used for ethanol production. The invented process comprises of treatment stages at high temperature and high pressure with hydrochloric acid or sulfuric acid. Residual lignin and extractives in the cellulosic solid fraction are selectively removed by chemical treatments of sodium chlorite, anhydrous acetic acid, chlorine and chlorine dioxide to enhance the purity and biological conversion of cellulose to ethanol. The pre-hydrolysate generated from the acid treatment stage, containing xylose, arabinose, galactose, glucose and the purified cellulosic fraction are enzymatically hydrolyzed and fermented to produce ethanol. Significant amount of lignin from the process is recovered as a by-product.

Claims

1. A process of treating and fractionating a lignocellulosic feedstock into high-purity fermentable sugars and lignin to produce ethanol, wherein the feedstock is selected from the group consisting of a softwood and a hardwood, the process comprising:

(a) obtaining logs and separating said logs into hardwood and softwood logs;

(b) chipping the separated logs of step (a) into wood chips having a length or width of approximately ¼

inch to 1 inch and a thickness of ¼

inch;

(c) pre-hydrolyzing, said pre-hydrolyzing comprising;

(i) charging into a pre-soak tank;

(a′

) the wood chips obtained from step (b), wherein said wood chips have their natural moisture content; and

(b′

) saw dust, fines, and over-size chips resulting from the chipping of step (b); and

(ii) acid pre-soaking by contacting said charged wood chips of step (a′

) and said over-sized wood chips, saw dust, and fines of step (b′

) with an acid selected from the group consisting of sulfuric acid, nitric acid, and hydrochloric acid;

wherein said acid is present in an amount of up to 5% acid by weight of the dry-weight of the charged wood chips obtained from step (a′

);

wherein said acid provides a pH in said pre-soak tank of between pH 2 and 3; and

wherein said contacting comprises contacting for a time of up to 5 hours;

(d) centrifuging and draining the acid-presoaked wood chips obtained from step (c) to consistency of approximately 30% solids;

(e) preheating the centrifuged-and-drained material obtained from step (d) in a series of steam mixers;

(f) screw-feeding the preheated material into a pressurized reactor, wherein the reactor is pressurized to a reactor pressure of 150 psi to 1000 psi and heated to a reactor temperature of 150°

C. to 300°

C. by injecting into the reactor direct live steam and a gas selected from the group consisting of nitrogen, carbon dioxide, oxygen, and air; and

then maintaining the screw-fed material in the pressurized reactor at said temperature and said pressure for a period of time of 1 minute to 30 minutes;

(g) blowing the steam-pressure-treated material obtained from step (f) into a series of blow tanks or flash tanks, thereby disintegrating the material into lignocellulosic solids comprising impregnable fibers and fiber bundles, wherein steam is recovered from the blow tanks and recycled into the steam mixers of step (e);

(h) pressing the lignocellulosic solids containing the impregnable fibers and fiber bundles thereby separating a pre-hydrolysate liquor from the solids, wherein said pressing further comprises recovering from the impregnable fibers and fiber bundles of said solids trapped hemicellulosic xylose, arabinose, galactose, mannose, and glucose by washing the solids in a series of counter-current washers;

(i) neutralizing the pre-hydrolysate liquor and a filtrate obtained from the counter-current washers obtained from step (h) by treating the liquor and the filtrate with lime at a pH of 8 to 10, at a temperature of 40°

C. to 80°

C., and for a period of time of about 30 minutes to about 180 minutes, thereby precipitating compounds which are toxic to fermentation, the precipitated compounds selected from the group consisting of furfural, a phenol-containing compound, and acetic acid;

(j) delignifying and deresinating the washed solids obtained from step (h) wherein said washed solids further comprise lignin, cellulose, and extractives, said delignifying and deresinating comprising either;

(ia) charging the washed solids from step (h) into a four-stage, continuous, co-current delignification and deresination reactor; and

mixing with a stock mixer in each stage in the four-stage reactor, the charged solids with a 1% to 10% solution based on the weight of the charged washed solids,

(a′

) wherein the solution comprises (i′

) a delignifying oxidant selected from the group consisting of sodium chlorite, sodium hypochlorite, acidic hydrogen peroxide, a solution of chlorine-and-chlorine dioxide, and a combination thereof, and (ii′

) an acid selected from the group consisting of anhydrous acetic acid, acetic acid, peracetic acid, and sulfuric acid and wherein the ratio in said solution of said oxidant to said acid is from 3;

1 to 6;

1;

(b′

) wherein each reactor stage comprises a residence time period between 3 hours and 4 hours and a reactor temperature between 120°

F. and 180°

F.;

(c′

) wherein the four-stage total amount of delignifying oxidant relative to the amount of lignin and extractives in the solids of step (h), is an amount having a oxidant-to-lignin ratio of between 1;

1 and 1.5;

1;

(d′

) wherein the total solution is distributed to each stage of the four-stage reactor the distributing consisting of distributing 40% to the first stage, 30% to the second stage, 20% to the third stage, and 10% to the fourth stage; and

(ib) obtaining from the four-stage reactor solids and liquids exiting from each stage of the reactor and then washing the obtained solids and liquids by vacuum filtering the obtained solids and liquids, thereby producing a purified cellulose solid product and wherein said vacuum filtering further comprises combining the filtered liquid into a filtrate tank, thereby obtaining a lignin-containing liquid filtrate for lignin recovery;

or;

(ii) extracting the washed solids from step (h) with caustic at a temperature between 80°

F. and 150°

F. and for a period of time between 1 and 3 hours, then washing the caustic-extracted solids by vacuum filtering;

(k) further delignifying and purifying the purified cellulose solid material obtained from step (j)(ib) or the extracted-and-washed solid obtained from step (j)(ii) by mixing therewith a solution selected from the group consisting of chlorine-and-chlorine dioxide having a chlorine dioxide amount of 30% to 50% of the total chlorine in the solution or sodium chlorite-and-anhydrous acetic acid, wherein when a chlorine-and-chlorine dioxide solution or the sodium chlorite-and-anhydrous acetic acid solution is mixed at 120°

F. and for a period of time of 3 hours, thereby providing a solids consistency of 3% to 10% solids and producing a cellulose solid product;

(l) washing the cellulose solid product of step (k) in a three-stage counter-current washer train to produce a purified cellulose solid product and a lignin-containing liquid filtrate;

(m) evaporating the lignin-containing liquid filtrate obtained from step (j)(ib) or step (l) by multiple-effect evaporators to 50% to 70% solids content, thereby recovering said lignin;

(n) enzymatically saccharifying or acid-hydrolyzing the purified cellulosic solids of step (l), thereby converting the purified cellulosic solids into a fermentable glucose; and

(o) fermenting the glucose obtained from step (n) and the xylose and arabinose from step (h) with a yeast or a bacterium, thereby producing said ethanol.

2. The process of claim 1, wherein:

the concentration of acid having up to 5% acid by weight in step (c)(ii) is in the range of 0.1% to 8% by volume;

wherein the recovered steam in step (g) is a saturated steam and is directly added to the steam mixers of step (e) and to the pressurized reactor of step (f);

wherein in step (j)(ia)(a′

) a combination of the oxidants and the acids are added to selectively delignify the solids obtained from step (h);

wherein in step (k) the solution is a chlorine-and-chlorine dioxide solution which is added to improve biological conversion and production of the ethanol; and

wherein in step (m) the recovering lignin further comprises recovering the lignin as a lignin-containing liquor for incinerating in steam and power generation or for forming lignin-containing chemicals selected from the group consisting of drilling fluid aids and hydrocarbons feedstocks.