FI65786C - FARING EQUIPMENT FOR CELLULOSE AND CELLULOSIC MATERIAL - Google Patents

Description

65786

A method for recovering cellulose from cellulosic materials

This invention relates to a process for recovering cellulose from cellulosic materials, wherein the cellulosic material is hydrolyzed with a dilute acid at about 121 ° C and the hemicellulose is removed.

10 The utilization of cellulosic waste materials, such as corn stalks, sawdust, straw and bagasse, has recently been of great interest, especially for the utilization of these waste materials for the production of fuels, nutrients, chemicals and other useful products.

Cellulosic materials contain 3 main constituents, namely cellulose, hemicellulose and lignin. Methods for extracting hemicellulose have been previously proposed and / or used, and this known hemicellulose 20 can be utilized in a variety of currently used methods, such as hydrolysis, fermentation, and pyrolysis.

Lignin has also been isolated from cellulosic materials. Because lignin has a higher hydrogen and carbon content and a lower oxygen content than cellulose or hemicellulose, its fuel value is the higher of the three. The separated lignin can be combusted to generate water vapor and electricity and can also be used to make a number of useful products, such as vanillin, dimethyl sulfoxide, dimethyl sulfide, methyl mercaptan, and ka-30.

The recovery and utilization of cellulose, for example by hydrolysis to glucose, has hitherto been difficult due to the crystalline structure of the cellulose and the lignin contained in the substance.

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Attempts have been made to hydrolyze cellulose using acids and enzymes, but these efforts have not been successful.

The use of acids such as sulfuric acid in the hydrolysis of cellulosic materials to form glucose has been known for several decades. In general, all of the previously described methods for hydrolyzing cellulose using sulfuric acid can be divided into two major groups; those using dilute sulfuric acid and those using concentrated sulfuric acid. In dilute acid processes, the sulfuric acid solution usually contains about 5 to 50 g of sulfuric acid / kg of aqueous solution. At temperatures of 150 to 350 ° C, cellulosic materials such as wood chips, when suspended in dilute acid, hydrolyze to form glucose from cellulose and sugars containing 5 carbon atoms from hemicellulose. Since the reaction temperature is usually above the boiling point of the dilute acid, the hydrolysis reaction must be carried out in a pressure reactor. At high temperatures, glucose and sugar containing 5 carbon atoms decompose under the influence of acid to form furfural and its derivatives, which often continue to react to form harmful by-products. Thus, a process using a dilute acid is generally not successful in obtaining glucose from cellulose in high yields at low cost. Usually, the process using 25 dilute acids gives a yield of about 50% or less, based on the available cellulose and contaminated with unusable by-products. Methods using dilute acid are well known and have been extensively studied by several researchers.

There are also numerous publications on cellulose hydrolysis processes using concentrated sulfuric acid. Examples include a relatively new publication,

Bose et al., (See Bharati Bose, T. R. Ingle, and J. L. Bose, "Saccharification of Groundnut Shell Pulp with Sulfuric Acid," 35 Indian Journal of Technology, Vol. II, September 1973, p.

391-393) and earlier publication 3 65786 by Dunning and Lathropo (see GW Dunning and EC Lathrop, "The Saccharification of Agricultural Residues", Industrial and Engineering Chemistry, Vol. 37, 1945, pp. 24-29). . Generally, concentrated sulfuric acid (e.g., 750 g sulfuric acid / kg acid) is added to the 5 finely divided cellulosic materials. After absorption and thorough mixing, 8-10 volumes of water are added to dilute the acid. The mixture is then refluxed with cooling for a few hours at normal pressure to form glucose. Typically, 90-93% of the available cellulose can be converted to glucose by this method and no significant by-products are formed. However, the disadvantage of the known methods is that large amounts of acid have to be used. Upon completion of the hydrolysis, both the acid and glucose are dissolved in the same aqueous solution. An equal amount of base (usually lime) must be used to neutralize the acid before sugars can be utilized, for example, as a carbon source for yeast fermentation. These methods have the difficulty of disposing of large amounts of calcium sulfate as a by-product, as well as the high acquisition costs of both acid and base.

A new method for recovering cellulose from cellulosic materials has now been invented, in which the cellulosic material is hydrolyzed with a dilute acid at about 121 ° C and the hemicellulose is removed. The process according to the invention is characterized in that concentrated acid is added to the hydrolysis residue to dissolve the cellulose therefrom at room temperature, the mixture of the hydrolysis residue and the concentrated acid is thoroughly mixed and the cellulose is precipitated by diluting said acidic mixture as a selected solvent.

A suitable solvent is water or an organic solvent such as methanol. The acid used is preferably sulfuric acid, which can be easily recovered in large quantities, and the recovered cellulose is hydrolyzed by either cellulase-35 enzymes or a dilute acid or a combination of enzymes and acids to obtain glucose in high yields.

Because most of the acid is recovered for reuse, the chemical cost is low. A high yield of glucose is recovered from the cellulose by hydrolyzing 5 cellulose with cellulase enzymes and / or dilute acids.

In the process of this invention, a cellulosic raw material, such as corn stalks, is first hydrolyzed with either fresh or reusable dilute sulfuric acid under mild conditions to remove hemicellulose. At this stage, well-known reaction conditions are used (typically 1.9% sulfuric acid at 121 ° C for 50 minutes). After neutralization, the liquid hemicellulose hydrolyzate can be used as a fermentation medium with lime. Said first step is typically shown below.

Preparation of lignocellulose 10 g of maize waste (mesh number greater than 40) are mixed with 500 ml of 65-70% sulfuric acid. The mixture is heated to 20 ° in a cooking vessel equipped with a 2-liter condenser and boiled gently for one hour. The mixture is filtered and washed with 1: 1 hot water in a glass filter and then with acetone until the color has completely disappeared. The mixture is then transferred to an aluminum foil and can be air dried overnight if desired.

The solid residue containing mainly cellulose and lignin is filtered or centrifuged to remove hemicellulose hydrolyzate.

Concentrated sulfuric acid is then added, the strength of the acid 30 being preferably 60 to 90% (60% acid contains 600 g sulfuric acid / kg acid). At this acid strength, the cellulose can be dissolved in an acid solution. This step is shown in Examples 1-3.

The moist mixture is then mixed with concentrated sulfuric acid 35 (during this mixing, most of the cellulose dissolves in concentrated sulfuric acid), whereby the reaction conditions, temperature, time, acid strength, and acid to solid ratio are carefully monitored. The cellulose is then reprecipitated by diluting the acid at the end of the mixing with 2-5 volumes of water or an organic solvent such as methanol.

Careful control of the reaction conditions is important and the key is the successful recovery of sulfuric acid and the efficient hydrolysis of the reprecipitated cellulose to obtain glucose. For example, if the reaction time is too long, the cellulose may be too hydrolyzed and much of it soluble because cellodextrins having a degree of polymerization of less than 7 are soluble in water. When this happens, that part of the carbohydrates is lost because there is no cheap way to separate the dissolved sugars from the sulfuric acid. It is assumed that this is the main reason for rendering known methods using concentrated sulfuric acid unusable due to the high cost of the acid and the base required to neutralize it in order to utilize dissolved sugars.

When the reaction conditions are monitored according to the invention when mixing the cellulose-lignin mixture with concentrated sulfuric acid, approximately 97% by weight of the original cellulose is in solid form after the addition of 2-5 volumes of water to the mixture at the end of the mixing. If an organic solvent such as methanol is added instead of water, an even larger portion (i.e., more than 97%) of the original cellulose is reprecipitated. By filtering or centrifuging the mixture immediately after the addition of water or an organic solvent such as methanol, about 90% of the sulfuric acid is recovered, which dilute sulfuric acid can be concentrated in an evaporator to remove excess water or added methanol before being returned to the process. The cellulose obtained by filtration or centrifugation is then washed with water to form a dilute acid which can be returned to the initial stage of the process to hydrolyze the hemicellulose.

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The resulting cellulose in solid form is partially hydrolyzed to a lower degree of polymerization than the original, and its internal structure and lignin seams are completely broken, and can thus be easily and completely hydrolyzed to glucose by dilute acid and / or cellulase enzymes after pH adjustment.

As can be seen from the above, the process of the present invention takes advantage of the fact that prior to solubilizing hydrolysis, cellulose can be precipitated from a concentrated sulfuric acid solution by diluting it with water or an organic solvent such as methanol. The cellulose thus precipitated can be easily and completely hydrolyzed to glucose by enzymes and / or dilute acids. Precipitation allows the separation and recovery of the acid, i.e. the efficient recycling of the acid, which significantly reduces chemical costs.

Example 1 1 ml of 70- * sulfuric acid is periodically mixed with 0.4 g of Avicel (microcrystalline cellulose, manufactured by FMC Corporation, type PH101) for half an hour at room temperature and then diluted with 3 ml of methanol (99%, reagent-tartrate AR). The mixture is filtered to give a sugar loss in the filtrate of 0.3% (determined by the Anthrone method). The mixture 25 is then washed with water until it is only slightly acidic.

3.6 mg of this pretreated amorphous cellulose are added to 0.4 ml of sodium acetate buffer solution, pH 5, and 0.04 ml of cellulase enzyme is added, achieving a 90% conversion of cellulose to glucose in 3 hours.

30 Example 2

The procedure and reagents are the same as in Example 1, except that 4 ml of water is used to dilute the acid mixture instead of 3 ml of methanol. The sugar loss in the filtrate is 7.8% and the effect of the enzyme on the solid residue is the same as in Example 1.

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Example 3 0.6 ml of 65% sulfuric acid is mixed with 0.1 g of lignocellulose (prepared according to the above pretreatment) and the mixture is subjected to the treatment of Example 1, except that the dilution is made with 2 ml of methanol, whereby the sugar loss in the filtrate is 1 .3%, and a 90% cellulose change is achieved in 10 hours.

Claims (5)

8 65786 A process for recovering cellulose from cellulosic materials, wherein the cellulosic material is hydrolyzed with a dilute acid at about 121 ° C and the hemicellulose is removed, characterized in that concentrated acid is added to the hydrolysis residue to dissolve the cellulose at room temperature. mixing the cellulose by diluting said acidic mixture with water or methanol. A method according to claim 1, characterized in that said dilute acid and said concentrated acid are sulfuric acid. Process according to claim 2, characterized in that the concentration of said concentrated sulfuric acid is about 60 to 90%. Process according to Claim 2, characterized in that the solvent is water and in that about 2 to 5 parts by volume of water are added to the mixture of hydrolysis residue and sulfuric acid to precipitate cellulose. Process according to any one of the preceding claims, characterized in that said concentrated acid is recovered after the addition of said solvent and reconcentrated.