Pretreatment of lignocellulose using two stage alkali and mechanical refining processes
Disclosed herein are processes for ethanol production from a lignocellulosic feedstock. These processes provide DMR of lignocellulosic biomass comprising two-stage deacetylation followed by mechanical refining so as to increase fermentable sugar yield while reducing hydrolytic enzyme loading requirements.
1. A method for treating lignocellulosic biomass for ethanol production, comprising:
(i) reacting the lignocellulosic biomass with a first alkali to produce a first stage biomass;
(ii) dewatering the first stage biomass to isolate a first stream of first stage solids;
(iii) reacting the first stage solids with a second alkali to produce a second stage biomass;
(iv) dewatering the second stage biomass to isolate a stream of second stage solids; and
(v) mechanically refining the second stage solids, comprising the use of at least one of a single disk mill, a double disk mill, a conical plate mill, a pin mill, a ball mill, a Szego type mill, an attrition mill, an ultrasonics-assisted mill, a stone-wheel grinding mill, or a homogenizer,
wherein the first alkali has a pH of from about 10 to about 12, and the second alkali has a pH of 12 or greater, and
wherein the lignocellulosic biomass comprises a hemicellulose, and wherein less than 4% of the hemicellulose is solubilized in step (i).
2. The method of claim 1 , further comprising:
(vi) dewatering the mechanically refined second stage solids;
(vii) isolating the solids from step (vi), wherein the solids comprise cellulose; and
(viii) enzymatically hydrolyzing the isolated solids from step (vii).
3. The method of claim 1 , wherein the first alkali is selected from at least one of sodium carbonate, potassium carbonate, ammonium hydroxide, magnesium hydroxide, trimethylamine, or methylamine.
4. The method of claim 1 , wherein the second alkali is selected from at least one of sodium hydroxide, potassium hydroxide, barium hydroxide, calcium hydroxide, trisodium phosphate, or tripotassium phosphate.
5. The method of claim 1 , further comprising an additional mechanical refining step after the mechanical refining of the second stage solids of step (v).
6. The method of claim 2 , wherein enzymatically hydrolyzing the isolated solids from step (vii) uses about 10 to about 50 mg of plant cell wall hydrolytic and oxidative enzymes per gram of cellulose in the isolated solids from step (vii).
7. The method of claim 2 , further comprising isolating sugars from the enzymatically hydrolyzed isolated solids from step (viii), wherein the sugars are isolated at greater than about an 80% yield.
8. The method of claim 1 , wherein an amount of lignin in the lignocellulosic biomass is reduced by about 5% to about 15% by steps (i) and (ii), and reduced by about 20% to about 40% by steps (iii) and (iv).