CN108004283A - Use alkaline solution and the preprocessing process of the lignocellulose biomass of vapour explosion - Google Patents

Abstract

The present invention relates to a method of pretreatment of lignocellulosic biomass, said method resulting in a high sugar content obtained from enzymatic digestion of pretreated lignocellulosic biomass, wherein said method comprises the steps of: (a) contacting lignocellulosic biomass with an alkaline solution at ambient temperature; (b) mixing the mixture obtained from step (a) with steam at a temperature of 160° C. to 210° C. in a reactor at a pressure of 5 bar to 20 bar Contact in 30 seconds to 10 minutes; And (c) reduce the pressure and temperature in step (b) to predetermined pressure and temperature, so that lignocellulosic biomass explodes; It is characterized in that, the temperature in step (c) in the range of -10°C to 20°C, and the rate of temperature decrease in step (c) is 5°C/min or more.

Description

Pretreatment process of lignocellulosic biomass using alkaline solution and steam explosion

technical field

Chemistry deals with lignocellulosic biomass technology.

Background technique

Currently, although oil is in high demand according to economic and population growth, because oil resources are limited, attempts are being made to develop biotechnology as a precursor for chemical and fuel production in order to replace oil resources with sustainable energy. In addition, using biomass instead of petroleum resources can reduce the emission of carbon dioxide, which is the main cause of the greenhouse effect that causes global warming.

Generally, lignocellulosic biomass actually has three main components: cellulose, hemicellulose, and lignin. Cellulose is formed by self-association of β-(1-4)-glycosidically linked glucose molecules. Hemicellulose, on the other hand, is a branched polymer composed of hexose sugars (ie, glucose, galactose, and mannose) and pentose sugars (ie, xylose and arabinose). These hemicelluloses are the binders used to cross-link the cellulose and lignin together. Finally, lignin is a complex composed of phenolic compounds. The lignin is arranged like a tube strongly covered with cellulose and hemicellulose. Furthermore, cellulose also has its strongly crystalline arrangement, making it difficult to utilize cellulose and hemicellulose as chemical precursors or in energy sources. Therefore, before lignocellulosic biomass can be used as described above, it is necessary to pretreat lignocellulosic biomass by opening its structure, removing lignin and reducing the crystallization of cellulose in its structure before utilizing it. This lignocellulosic biomass can then be enzymatically digested to more efficiently obtain pentoses and hexoses.

There are several pretreatment methods of lignocellulosic biomass, such as physical pretreatment and chemical or thermal pretreatment, etc. Each method has its advantages and disadvantages depending on the goals and utilization of preprocessing.

Steam explosion is an effective method in the pretreatment of lignocellulosic biomass. The steam explosion method involves the application of high pressure steam followed by a rapid reduction of the pressure in order to cause explosive decomposition of the biomass leading to decomposition of the biomass. The enzymes can then be more exposed to the cellulose, resulting in better breakdown.

There have been studies combining acid and steam explosion in the pretreatment step of lignocellulosic biomass in order to provide more efficient enzymatic digestion. WO2013063478A4 discloses a method for the production of ethanol from biomass. The biomass is soaked in water and then subjected to an acid-catalyzed steam explosion process to obtain a slurry. The slurry is then enzymatically digested and fermented with microorganisms to produce ethanol. However, the methods focus on the production of ethanol which yields sugars of varying quality. Additionally, the use of acid during pretreatment can corrode equipment.

WO2000019004A1 discloses the pretreatment of bagasse in pulp production. Bagasse was soaked in semi-alkaline pulping liquor at 60°C for 20 hours. Then, the liquid is filtered before being subjected to the steam explosion process. The process was found to provide a higher unbleached yield than the soda pulping process together with the use of anthraquinone. However, said document focuses on pulp production. Therefore, the resulting product may not be suitable for sugar production.

Biotechnology and Bioengineering, Vol. 26, 1984, pp. 426-433 discloses the use of an alkaline solution, ie sodium hydroxide, calcium hydroxide or ammonia, in the pretreatment of bagasse at 20°C for at least 18 hours. It was then subjected to steam explosion at 200° C. for 5 minutes at a pressure of 6.9 MPa (69 bar). This pretreatment yielded an organic matter digestibility of about 700 grams per kilogram of starting biomass. More than half the amount of hemicellulose dissolved in the system. However, the method preprocessing takes too long.

Process Biochemistry, Vol. 41, 2006, pp. 423-429 discloses the pretreatment of olive trees by steam explosion at 190°C to 240°C for 5 minutes. The insoluble fiber is then extracted with alkaline peroxide to further remove the lignin, thereby enhancing the effectiveness of the enzymatic digestion. The process yielded about 288 grams of sugar per kilogram of starting biomass. However, the use of peroxide compounds may result in the loss of cellulose and hemicellulose in the form of unwanted by-products and may negatively affect the next pretreatment step.

Biotechnology for Biofuels, 2010, discloses an ammonia fiber expansion (APEX) pretreatment process by adding ammonium to switchgrass biomass at a pressure of 0.6 MPa to 3 MPa and a temperature of about 70°C to 200°C. Then, the pressure drops rapidly. The process yields a sugar content of 400-500 g/kg starting biomass.

However, the above invention produces a sugar content that is not too high compared to the weight of the starting biomass. Therefore, further research is necessary in order to invent production methods of sugars with higher yields, especially for glucose.

In summary, the object of the present invention is to develop a method for the pretreatment of lignocellulosic biomass using alkaline solutions and steam explosion, which applies less extreme conditions, employs fewer chemicals and has low energy consumption in the pretreatment. The biomass obtained from this pretreatment can be subjected to enzymatic digestion to efficiently produce sugars. Economically, this will make it possible to use biomass as a precursor for the production of basic chemicals and alternative energy sources.

Contents of the invention

The object of the present invention is to develop a method for the pretreatment of lignocellulosic biomass, wherein said method comprises the following steps:

(a) contacting the lignocellulosic biomass with an alkaline solution at ambient temperature;

(b) contacting the mixture obtained from step (a) with steam at a temperature of 160° C. to 210° C. in a reactor for 30 seconds to 10 minutes at a pressure of 5 bar to 20 bar; and

(c) reducing the pressure and temperature in step (b) to a predetermined pressure and temperature to detonate the lignocellulosic biomass;

It is characterized in that the temperature in step (c) is in the range of -10°C to 20°C, and the rate of temperature decrease in step (c) is 5°C/min or above.

Detailed ways

definition

Unless otherwise specified, technical or scientific terms used herein have definitions as understood by those of ordinary skill in the art.

Any tool, device, method or chemical mentioned herein means a tool, device, method or chemical commonly operated or used by those skilled in the art, unless it is indicated that they are specific tools, devices, methods only in the present invention or chemicals.

Use of a singular noun or singular pronoun with "comprising" in the claims or specification means "one", as well as "one or more", "at least one", "and one or more".

FPU (Filter Paper Cellulase Units) is meant to include the digestibility or activity of cellulase, where 1 unit of FPU means the amount of enzyme catalyzed in digesting Whatman no. 1 filter paper into 1 micromole of glucose in 1 minute .

The following details describe the specification of the invention and are not intended to limit the scope of the invention in any way.

The present invention relates to the pretreatment method of lignocellulosic biomass, comprising the following steps:

(a) contacting the lignocellulosic biomass with an alkaline solution at ambient temperature;

(b) contacting the mixture obtained from step (a) with steam at a temperature of 160° C. to 210° C. in a reactor for 30 seconds to 10 minutes at a pressure of 5 bar to 20 bar; and

(c) reducing the pressure and temperature in step (b) to a predetermined pressure and temperature to detonate the lignocellulosic biomass;

It is characterized in that the temperature in step (c) is in the range of -10°C to 20°C, and the rate of temperature decrease in step (c) is 5°C/min or above.

Preferably, the temperature in step (c) is in the range of about -5°C to 10°C.

Preferably, the rate of temperature decrease in step (c) is in the range of about 5°C/min to 20°C/min.

In one embodiment, the lignocellulosic biomass is selected from rice straw, bagasse, corn cobs, corn fiber, pineapple peel, bamboo, or mixtures thereof.

In one embodiment, the alkaline solution is selected from sodium hydroxide solution, ammonia solution or mixtures thereof. Preferably, the alkaline solution is sodium hydroxide solution.

Preferably, the concentration of the alkaline solution is in the range of about 2 g/L to 6 g/L.

In one embodiment, the mass/volume ratio of lignocellulosic biomass to alkaline solution is in the range of about 250 g/L to 600 g/L.

In one embodiment, the temperature of the steam in step (b) is in the range of about 160°C to 180°C.

In one embodiment, the pressure in step (c) may be between atmospheric pressure and about 2 bar, preferably about atmospheric pressure. The following are embodiments of the present invention without any purpose of limiting any scope of the present invention.

Prior to the lignocellulosic biomass pretreatment process, the lignocellulosic biomass (e.g. bagasse) was subjected to size reduction by physical means using a cutter and size sorted using a 0.85 mm screen, and then subjected to dry.

The bagasse obtained from the process contains about 35.8% by weight of cellulose, about 21.5% by weight of hemicellulose and about 23.71% by weight of lignin.

Comparative sample A

500 g of bagasse was added to an approximately 10 L high-pressure stainless steel reactor connected to steam injection, and an internal thermometer was installed inside the reactor. Then, steam at a temperature of about 200°C is injected into the reactor until a target temperature of about 200°C is reached. The internal pressure of the reactor was about 14.5 bar. Calculate operation time. After about 5 minutes, the biomass was fed into the receiving chamber at a temperature of about 30°C, and the temperature and pressure were rapidly reduced to 30°C and a pressure of about 1 bar. The rate of temperature decrease was about 2°C/min to 4°C/min.

Then, the pulp yield is filtered from the liquid. The solid portion was washed in water until the pH was about 5-8. It is then subjected to drying at a temperature of about 50°C to 100°C until the weight stabilizes. The resulting solid is called pretreated bagasse.

By adding about 10 FRU/g of cellulase ( CTec2) to digest the pretreated bagasse and aged at about 50°C for about 72 hours. The centrifugation speed of the mixture is about 200 rpm. Then, test the glucose content of the liquid sample obtained from the centrifugation.

Comparative sample B

Comparative Sample B was prepared by the method described in Comparative Sample A, wherein the temperature of the receiving chamber was about 5°C. Rapid decrease in temperature and pressure at a rate of decrease in temperature of approximately 6°C/min to 10°C/min to a temperature of approximately 5°C and a pressure of approximately 1 bar, which may be achieved by exposing the receiving chamber with ice or any other coolant .

Comparative sample C

Comparative Sample C was prepared by the method described in Comparative Sample B by adding a mixture of about 500 g of bagasse and about 1,500 mL of water to the reactor.

Samples according to the invention

By the method described in Comparative Sample B, by adding to the reactor a mixture of about 500 g of bagasse and about 1,500 mL of sodium hydroxide solution (which has the concentrations described in Table 1 for each sample), Samples of the invention. Steam having the temperature and pressure described in Table 1 was injected into the reactor.

Table 1: Process conditions for pretreatment of lignocellulosic biomass for comparative samples and samples according to the invention

preprocessing Steam temperature(℃) Reactor pressure (bar) NaOH concentration Comparative sample A 200 14.5 - Comparative sample B 200 14.5 - Comparative sample C 200 14.5 - Sample 1 according to the invention 200 14.5 3 Sample 2 according to the invention 170 6.9 5 Sample 3 according to the invention 200 14.5 5 Sample 4 according to the invention 206 16.9 5

The following is an example of the analysis of the sugar content resulting from the digestion of lignocellulosic biomass obtained from the pretreatment process, where the methods and equipment are those commonly used unless otherwise stated and are not intended to limit the scope of the invention .

Using HPLC Watere2695 (Water, USA) equipped with a differential refractometer detector and Aminex HPX-87H column (Bio-Rad, USA), by high-performance liquid chromatography, according to NREL (National Renewable Energy Laboratory) using bio Determination of carbohydrates and lignin in substances to analyze glucose and lignin.

Glucose produced = glucose content (mg) / pretreated bagasse content (g)

Lignin removal percentage = ((lignin content (g) in the initial bagasse - lignin content (g) in the pretreated bagasse) / lignin content (g) in the initial bagasse) × 100

The temperature of the receiving chamber and the rate of temperature reduction during pretreatment using steam explosion have an effect on the pretreated biomass The influence of main components, lignin removal percentage and glucose content produced

As can be seen from Table 2, when comparing Comparative Sample A and Comparative Sample B, it was found that Comparative Sample B, which had a higher rate of temperature decrease in order to detonate the lignocellulosic biomass, produced Higher lignin removal percentage and glucose content produced. Furthermore, the rapid temperature decrease in comparative sample B provided a better breakdown of the lignocellulosic structure and also reduced the crystallinity of the cellulose. These lead to good digestion of amorphous cellulose.

The effect of sodium hydroxide concentration on the main components of pretreated biomass, lignin The effect of the percentage of protein removal and the content of glucose produced

As can be seen from Table 2, when comparing Comparative Sample B and Comparative Sample C, it was found that the addition of water to Comparative Sample C together with steam explosion had no significant effect on the main components of the pretreated bagasse and the resulting glucose content.

Furthermore, when comparing comparative sample C with added water together with steam explosion with samples 1 and 3 according to the invention with sodium hydroxide solution together with steam explosion (under the same temperature and pressure conditions), it was found that using sodium hydroxide solution The combination with steam explosion caused a greater reduction in the lignin content than the method without alkaline solution and resulted in a higher glucose content.

Effect of steam temperature on the main component of pretreated biomass, lignin, during pretreatment using steam explosion Effect of Percent Removal and Glucose Content Produced

As can be seen in Table 2, when comparing the samples of samples 2, 3 and 4 according to the invention pretreated with steam temperatures of about 170°C, 200°C and 206°C, respectively, it was found that pretreatment with a steam temperature of about 170°C Sample 2 according to the invention produced the highest percentage of cellulose and the highest produced glucose content of about 701.4 mg/g.

Table 2: Main component content, lignin removal percentage and glucose content produced of pretreated biomass from enzymatic digestion of pretreated bagasse

BEST MODE OF THE INVENTION

The best mode of the present invention is provided in the description of the present invention.

Claims (10)

1. A pretreatment method for lignocellulosic biomass, comprising the following steps: (a) contacting the lignocellulosic biomass with an alkaline solution at ambient temperature; (b) contacting the mixture obtained from step (a) with steam at a temperature of 160° C. to 210° C. in a reactor for 30 seconds to 10 minutes at a pressure of 5 bar to 20 bar; and (c) reducing the pressure and temperature in step (b) to a predetermined pressure and temperature to detonate the lignocellulosic biomass; It is characterized in that the temperature in step (c) is in the range of -10°C to 20°C, and the rate of temperature decrease in step (c) is 5°C/min or above. 2. The method according to claim 1, wherein the temperature in step (c) is in the range of -5°C to 10°C. 3. The method of claim 1, wherein the rate of temperature decrease in step (c) is in the range of 5°C/min to 20°C/min. 4. The method of claim 1, wherein the lignocellulosic biomass is selected from rice straw, bagasse, corn cobs, corn fiber, pineapple peel, bamboo or mixtures thereof. 5. The method according to claim 1, wherein the alkaline solution is selected from sodium hydroxide solution, ammonia solution or a mixture thereof. 6. The method of claim 5, wherein the alkaline solution is a sodium hydroxide solution. 7. The method according to claim 1, wherein the concentration of the alkaline solution is in the range of 2 g/L to 6 g/L. 8. The method of claim 1, wherein the mass/volume ratio of the lignocellulosic biomass to the alkaline solution is in the range of 250 g/L to 600 g/L. 9. The method of claim 1, wherein the temperature of the steam in step (b) is in the range of 160°C to 180°C. 10. The method of claim 1, wherein the pressure in step (c) is atmospheric pressure.