NZ198780A - Obtaining water-soluble saccharides from cellulose-containing material - Google Patents

Abstract

1. A process for obtaining water-soluble saccharides from cellulose-containing material by treating the latter with gaseous hydrogen fluoride, optionally diluted with an inert gas at temperatures between about 20 and 120 degrees C, preferably between about 40 and 80 degrees C, which comprises subjecting cellolignin, a material composed largely of cellulose and lignin and being essentially free of pentosans and hexosans which has been obtained by pre-hydrolysis of natural cellulose-containing material with dilute mineral acid at an elevated temperature and under an elevated pressure, to treatment with hydrogen fluoride.

Description

New Zealand Paient Spedficaiion for Paient Number 1 98780 198780 |Priority Dato{s}: ..

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NEW ZEALAND Patents Act 1953 COMPLETE SPECIFICATION I — "PROCESS FOR OBTAINING WATER-SOLUBLE SACCHARIDES FROM CELLULOSE-CONTAINING MATERIAL." We, HOECHST AKTIENGESELLSCHAFT, a corporation organized under the laws of the Federal Republic of Germany,of D-6230 Frankfurt/Main 80, Federal Republic of Germany, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed,to be particularly described in and by the following statement - 2-- 198780 Cellulose-containing materials occur in nature in large numbers and in great variety. Wood is an example of such a known natural cellulose-containing material. It consists essentially of cellulose (a material mainly "built up from glucose units), hemi-cellulose (a substance mainly built up from pentoses and hexoses) and lignin (a polymeric substance having aromatic rings which are substituted by methoxy groups ) . Wood is utilized in many different ways, for example for the pro-10 duction of heat (burning) and as a building material in the furniture and building industry and the like; utilization of wood by purely chemical means is also possible.

Chemical disaggregation processes, which effect not only the separation of wood into its constituents, hemi-15 cellulose, cellulose and lignin, but also the degradation and modification of the latter, have already been known for a long time. As a rule, chemical processes yield aqueous solutions of monomeric, dimeric and oligomeric saccharides, which may be subjected to subsequent hydrolysis to 20 glucose or can be subjected direct to fermentation to give ethanol, or to concentrating or to evaporation to dryness. Examples of possible fields of use of the products thus obtained are in the sphere of cattle feed additives or, preferably, in that of raw materials for fermentation. 25 In chemical processes for wood saccharification, two principles have been used on a large industrial scale in the past: the disaggregation of wood with concentrated aqueous hydrochloric acid (Bergius-Rheinau-Udic) and disaggregation with dilute sulfuric acid (Scholler-Tornesch- 1 98 Madison); in this context see, for example, Ullmarms Encyclopfldie der technischen Chemie ("Ullmann's Encyclopedia of Industrial Chemistry"), 3rd Edition, Volume 8 (1957), pages 591 et seq.

The disaggregation cf cellulose-containing raw materials with anhydrous hydrofluoric acid has also already been investigated on several occasions. Here, however, none of the processes hitherto disclosed has yet led to a technically satisfactory solution of the problem. / u s Patent Specification 1883676 describes the disagrgre-gationof wood with pure HF, in the form of liquid or vapor, at low temperatures, the HF being recycled by being evaporated or blown off and subsequently condensed. As a continuation of this work, German Patent Specification 585,318 describes a process for the disaggregation of wood with gaseous hydrogen fluoride, which operates in three stages via absorption' of HF on wood at 10°-20°C, disaggregation at 20°-50°C and desorption at 100°-150°C, it being possible to dilute the HF with a stream of inert gas. The out-lay on cooling for condensing the HF has a disadvantageous effect here, as has also.the fact that in the condensation stage initially there is only a very non-uniform distribution of the hydrogen fluoride on the reaction material, a circumstance which can only be counteracted by very long residence times or by greatly increasing the amount of hydrogen fluoride used; otherwise the yields are greatly impaired.

German Patent Specification 606,009 describes an extraction process using liquid HF, which, however, ■<%$ 1 O 0 7 r, o 1 ^ u / a U requires large quantities of HF and has the disadvantage that large quantities of heat have to be supplied in order to evaporate the hydrogen fluoride from the extract and extraction residue (lignin), and which have to be removed 5 again in the subsequent condensation process. More precise data concerning yields in processes of this kind are to be found in Angew. Chem. 46 (1933) 113/7, where by absorbing HF from the gas phase in an externally cooled vessel at 0°C 32% of sugar is achieved, relative to carlo bohydrates present, at a loading of 50% by weight of HF relative to wood, and 86% of sugar, relative to carbohydrates, is achieved at a loading of 100% by weight. No further information concerning the recycling of the HF is given in this reference.

All these processes suffer from the disadvantage that they consume large quantities of expensive hydrofluoric acid, that the recovery of HF from the reaction products is very expensive and that large losses of HF take place in practice.

A more advanced process is described in Great Britain Patent Specification 471,191, where the existing state of the art is described as follows: "If the reaction is carried out using highly concentrated or anhydrous hydrofluoric acid in a liquid or gaseous state at low 25 temperatures, the degradation of the wood only proceeds in a very non-uniform manner and therefore incompletely. Firstly , at such low temperatures the distribu -tion of the hydrogen fluoride , which is present as a fine mist in the air , is very non-uniform , * • :? r' n r* 1 98780 the more so as the air which is present makes it difficult to achieve a uniform reaction.. On the other hand, it is known that, in the saccharification of wood with concentrated hydrogen fluoride, not only in a liquid 5 but also in a gaseous state , the particles of wood react rapidly at their surface with the concentrated hydrogen "fluoride, form a hard, rather impenetrable skin and shrink whereby the further penetration of the gas into the interior is impeded. In addition, the penetration of the wood 10 particles is already rendered difficult by the air present in the cells. Thus an outer crust which encloses unsaccharified material and prevents further saccharification is formed very rapidly. In order to remove these drawbacks, it has already also been proposed to 15 carry out the disaggregation with concentrated liquid hydrofluoric acid using an extraction process or to prevent the formation of crusts by mixing inert gases into the hydrofluoric acid, in order thereby to achieve a more uniform and more complete disaggregation. However, the extraction pro-20 cess operates with a disproportionately large excess of hydrofluoric acid and the reaction material retains large quantities of hydrofluoric acid without preventing the formation of crusts, with all its disadvantages.

Although dilution with inert gases can somewhat reduce 25 the formation of crusts, it can never eliminate this and it also cannot result in the gas penetrating uniformly into the interior of the wood, since the wood is indeed filled with air. This is because, as is known, wood is only composed to a very small extent of ligneous matter and its 198780 largest component by far is air, which is present between and within the wood cells. A virtually anhydrous wood is composed, for example, of approx. 15% of ligneous matter and approx. 85% of air. Since the wood cells 5 are "extremely small in relation to the size of a piece of wood, however thoroughly it may have been comminuted, the air content plays a predominant part, even in the case of sawdust." Hardening of the surface of wood particles also 10 appears to have been observed in saccharifying wood with aqueous mineral acids, such as aqueous hydrochloric or sulfuric acid, since, for example, in Z. Angew. Chem. ^7 (1924) 221 the substances present in wood, such as lignin, mannan, galactan and the like, are described as "incrus-15 tants" which should be removed, if possible, prior to the actual wood saccharification process, additionally because of interfering degradation products (furfural, acetic acid, formic acid and the like). For their removal it would have been possible - since these "incrustants" ' 1 were known to be hydrolyzable - to consider the use of a kind of "pre-hydrolysis" with dilute mineral acid at elevated temperature and, if appropriate, elevated pressure, also in the case of wood saccharification by means of hydrogen fluoride. However, consideration had not been given 25 to a pre-hydrolysis of this type; instead, it was suggested by Hoch and Bohunek that in order- to avoid the disadvantages described above a vacuum of approx. 30mmHg be employed-for wood saccharification with hydrogen / > fluoride [Great/*Fa tent Specification 476,191, • . • 193780 - 7 - . the Hoch and Bohunek wood saccharification process using hydrogen fluoride is also described in the journal "Holz Roh- und Werkstoff" 1, pages 342-344 (1938)].

Disadvantages of these processes are the difficulties of industrial implementation which necessarily occur when operating in vacuo, and also the difficulties caused by the relatively complicated manner in which the reactions are carried out. A drawback from which all the processes 10 suffer is the formation of mixtures of pentoses and hexoses as a result of simultaneous hydrolysis of the hemicelluloses and of the cellulose of the wood.

A further problem is the removal of the acetic acid formed in the hydrolysis of hemicellulose, which -renders 15 difficult 'the circulation of the HF as loss-free as possible, and also the fact that the pentoses are easily decomposed to give furfural.

It has now been found, surprisingly, that the above-described disadvantages of the state of the art 20 can be avoided and that it is possible to saccharify cellulose readily , if the vegetable materials are disaggregated with anhydrous, gaseous HF, not in their natural form, but in the form of "cellolignin" which is obtained after a pre-treatment.

"Cellolignin" is to be understood here as meaning vegetable materials, such as wood, straw, bagasse and similar raw materials having been subjected to a pre-hydroly sis which is in itself known.

This pre-hydrolysis, which is in itself known, of <nr 1987 8 0 wood comprises a relatively short treatment, with very dilute mineral acid,at elevated temperatures and pressures, in which essentially the pentosans and hexosans present in the hemicelluloses are split as far as the 5 monomer units, such as, for example, xylose or mannose. Depending on the reaction conditions, the latter can subsequently be isolated as such or undergo further changes, for example dehydration to give furfural or hydroxymethylfurfural (compare Ullmann, loc. cit., Volume 7 (1957), page 711). In addition to fermentation, the reduction of xylose to xylitol may be mentioned as a further example of the industrial utilization of hemicellulose degradation products. It is thus possible to obtain valuable products from wood by pre-hydrolysis 15 prior to using.the disaggregation process according to the invention.

Cellolignin is also to be understood here as meaning paper material (for example waste, paper) which has a low content of hemicelluloses. In the pre-20 hydrolysis of wood, its structure is largely retained but the cellolignin which can thus be obtained has a much more crumbly and porous nature compared with the natural state, so that HF, including mixtures with air or another inert carrier gas, can penetrate readily without encrus-25 tation of the surface taking place. It is not necessary to operate in vacuo.

A further important advantage of the use of cellolignin instead of native wood is that the reaction material is then appreciably simpler to handle from the 1 98780 point of view of process technology. This is due, on the one hand, to the fact that, compared with wood of the same particle size, cellolignin has an apparent volume which is only approx. half as large and it thus 5 exhibits an appreciably smaller degree of shrinking when disaggregated with hydrogen fluoride gas, which makes matters considerably easier, for example in dimensioning reactors. Secondly, reaction material composed of cellolignin . remains pourable and free-flowing, even when charged 10 with hydrogen fluoride, whilst reaction material composed of native wood has a strong tendency to gum up due to resinous constituents, and also because of cleavage products of the hemicelluloses, and is difficult to convey.

Naturally, such a tendency to gum up also impedes the desorption of hydrogen fluoride, particularly if the latter process step is intended to take place rapidly and as quantitatively as possible. When cellolignin is used as the substrate, however, this is possible without difficulties. 20 Furthermore, in this process it is no longer necessary to separate the mixtures of sugars formed in the hydrolysis of hemicellulose from the oligomeric glucose structural units formed in the hydrolysis of cellulose, or from glucose, which makes it possible to utilize these 25 various sugars more easily in fermentation.

It is also an advantage that no acetic acid and furfural are formed in the disaggregation of cellolignin, so that the HF can be circulated without having to condense these components. Difficulty in 1987 separation and losses of HF are thus avoided.

A further advantage is that it is possible to absorb HF onto cellolignin above the boiling point of HF, so that external cooling is no longer necessary. It 5 was also surprising, that yields of >90% of glucose or oligomeric glucose, relative to the cellulose employed in the cellolignin, are achieved in a simple manner in the process according to the invention, the sugars produced being high-grade in quality, that is to say almost 10 colorless.

The invention therefore relates to a process for obtaining water-soluble saccharides (glucose or oligomeric glucose) from cellulose-containing material by treating the latter with gaseous hydrogen fluoride -15 optionally diluted with an inert gas - at temperatures between about 20 and 120°C, preferably between about 40 and 80°C; the process comprises subjecting cellolignin to a treatment with hydrogen fluoride.

Cellolignin is to be understood here, as defined 20 above, as a material composed largely of cellulose and lignin.

In view of the state of the art, in which the most recent process to be developed to a major extent (Hoch and Bohunek, loc. cit.) attempts to remove the dis-25 advantages associated with the non- uniform disaggregation and with the formation of encrustations , by using the expensive vacuum method - although the fact that hemicelluloses can be hydrolyzed readily was known (Oesterr. Chem.-Zeitg. 40, 5 et seq. (1937)) the use of pre-hydrolyzed material was 1 987 80 in no way obvious. It was, therefore, rather surprising that this measure, which lies in the opposite direction to that suggested by the state of the art, permits uniform and problem-free saccharification of 5 wood and materials similar to wood.

The cellolignin which, in accordance with the invention, is particularly suitable for degradation to give water-soluble- sugars is obtained by pre-hydrolysis of natural, cellulose-containing material (wood, straw, 10 bagasse and the like) with dilute aqueous mineral acid, preferably dilute hydrochloric or sulfuric acid. As already pointed out in describing the state of the art, the process of pre-hydrolysis is known in wood saccharification and is also to be found in fairly recent literature, 15 such as Ullmanns Encyclop&die der technischen Chemie ("Ullmann1s.Encyclopedia of Industrial Chemistry"), 3rd Edition, Volume 8 (1957), pages 591-595, and also in the book by ¥. Sandermann, "Chemische Holzverwertung" ("The Chemical Utilization of Wood"), Bayrischer 20 Landwirtschaftverlag, Munich 1963, page 253.

It comprises a relatively brief treatment of the natural starting material with a very dilute mineral acid at an elevated temperature (preferably between about • 100 and 160°C) and under an elevated pressure (preferably up 25 to about 10 atmospheres), in the course of which essentially the pentosans and hexosans present in the hemicelluloses are split as far as the monomeric units (xylose, arabinose, mannose and the like). Depending on the reaction conditions, the latter can then be isolated 1 9878 0 as such or undergo further changes, for example to give furfural and the like by dehydration.

They are preferably employed as raw materials for fermentation or for the production of xylitol.

Waste paper of low hemicellulose content is also very suitable for use as the starting material in the process of the invention.

The disaggregation process according to the invention can, for example, be effected either by bringing the pre- treated material (cellolignin or, for example, paper shredder material) which has been dried to a moisture content of 0 to about 20%, preferably about 2-5%, and has been comminuted-if required, into contact with HF gas, optionally mixed with air or another inert carrier gas discontinuously in a suitable stirred vessel made of a material resistant to hydrogen fluoride, or by passing a gas mixture containing HF, advantageously in a conveying equipment, in countercurrent to a continuous stream of the substrate to be disaggregated.

As a result of the heat of reaction, which is liber-20 ated spontaneously, the temperature rises and can be kept within the desired range between about 20 and 120°C, preferably between 40 and 80°C, by carrying out the reaction in a suitable manner., such as, for example, by diluting with inert gases.

The contact of the substrate with hydrogen fluoride gas is maintained until one part by weight of the material has taken up about 0.2 to 3.0, preferably about 0.4 to 0.8, parts by weight of hydrogen fluoride.

It is then advantageous to continue the reaction 1 98780 by choosing, depending on the nature of the substrate and on the conditions of HF absorption, a residence time which is adequate to achieve a high yield. Longer residence times are not disadvantageous, but have no advan-5 tage either. The reaction times can be between 15 minutes and several hours. Preferred reaction con ditions are those in which a residence time of about 1 hour is not exceeded.

The subsequent HF desorption can be carried out in 10 accordance with the state of the art by warming the reaction material and/or by evacuation or by treatment v/ith a stream of an inert gas (for example nitrogen, air, C02 or a rare gas) of suitable strength, again with or without simultaneous warming*and/or evacuating. The hydro-15 gen fluoride thus recovered can be isolated by condensation or can be reacted directly with fresh substrate so as to produce a circulation of gaseous hydrogen fluoride. The further processing of the material which has now been disaggregated ("saccharified") can also be carried out in a 20 manner which is in itself known, as described, for example, by K. Fredenhagen and G. Cadenbach, Angewandte Chemie 46 (1933), pages 113 to 117. That is to say, for example, the material is extracted with hot water, insoluble lignin is filtered off, the small quantity of hydrogen fluoride 25 adhering is neutralized in the filtrate with calcium carbonate or calcium hydroxide and the mixture is concentrated .

In the procedure according to the invention, the quantity of "wood sugar" (or "straw sugar" and the like) I 987 80 obtained after drying the residue from evaporation is in all cases mors than about 90% of the cellulose present in the substrate (calculated on dry substance).

Because of the high "sugar" yield,the exceptionally simple and smooth performance of the process (increased porosity of the substrate and thus easier penetration of HF) and also the energy-saving absorption of hydrogen fluoride (no cooling or vacuum required), the invention constitutes a not inconsiderable advance in this field.

The oligomeric glucose structural units can be employed for further utilization (fermentation to give ethanol, concentrating or evaporation and use as cattle feed additives or as raw materials for fermentation and the like) in the form in which they are produced or they can also be subjected in a manner which is in itself known to further hydrolysis to give monomeric glucose.

The invention will now be illustrated in greater detail by means of the following examples: Example 1 500 g of spruce cellolignin (59% of cellulose + 41% of lignin) of particle size approx. 2 mm were placed in a cylindrical~ 2 1 vessel made of transparent polyethylene, fitted with a stirrer, a thermometer and a gas inlet, and were treated with a mixture of air and hydrogen fluoride gas, which is prepared by passing air over liquid hydrogen fluoride at 20°C (waterbath). In the course of this treatment, the material was stirred slowly and it turned dark brown. The air stream and the vaporization of HF were regulated in such a way that the internal temperature did not exceed 70°C.

J 987 After 500 g of hydrogen fluoride had been absorbed, care was taken to maintain an internal temperature of 50°C for 30 minutes. The hydrogen fluoride was then expelled by passing in warm air, with continued 5 stirring. In so doing, part of the heat of desorption required was also supplied by external heating. The desorption was continued with a continually increasing temperature until a hydrogen fluoride content of about 5% in the substrate had been reached. The material was 10 then transferred to a fluid bed dryer and hydrogen fluoride was blown off until a residual quantity of approx. 0.5% had been reached. The HF/air mixtures thus produced could be used directly for further batches.

The contents of the reactor were then digested for 15 15 minutes with approx. 2 1 of hot water, were suction-fetrained rinsed with a little water. The dark brown filter residue weighed about 250 g after drying and was thus composed of 82% of lignin and 18% of still not disaggregated cellulose. The filtrate was rendered alkaline, while still 20 hot, with technical calcium hydroxide, the excess of hydroxyl ions was neutralized with carbon dioxide,and calcium fluoride and calcium carbonate were filtered off, if necessary by means of a filtration aid. The clear, slightly yellow, neutral solution was evaporated to dry-25 ness in vacuo. This gave approx. 250 g of slightly yellowish wood sugar, corresponding to 85% of the theoretical yield. The product gave a clear solution in water and contained between 2 and 10% of monomeric glucose, the remainder being composed of oligomeric glucose. 1937 8 Examples 2-13 A jacketed tube, resistant to hydrogen fluoride, of length 30 cm and internal width 4 cm in a horizontal position was filled about half full with 30 g of cello-5 lignin of particle size 1-2 mm, and was closed at both ' ends with bored rubber stoppers. One of two-thin steel tube, perforated over their entire length, was placed in the layer of cellolignin and the other in the free space above the latter. These tubes led to the exterior on both 10 sides through holes in the sealing stoppers and were used for the introduction or removal of HF/air mixture, respectively. This made it possible to treat the cellolignin with gas at right angles to the surface of the bed. The material was allowed to absorb hydrogen fluoride and appropriate 15 heating was used to ensure an internal temperature of 50°C during the subsequent residence time. Hot air, instead of the HF/air mixture, was then blown through the bed for 15 minutes,and the reaction material thus obtained, which had been freed from the bulk of the hydrogen fluoride, was 20 worked up as described in Example 1.

The yields corresponding to different quantities of HF absorbed and residence time are shown in the following table. 198780 Example HF absorbed Residence time Yield of wood No. [g] [minutes] sugar [ gj # of theor. value 2 9 120 4 24 3 11 120 6 4 120 9.5 56 16 120 11 65 6 17 120 12 71 7 19 120 88 8 120 16 94 9 19 11 65 19 13 77 11 19 14 82 12 19 88 13 19 60 88 Example 14 In a long, horizontal tube made of material resistant to hydrogen fluoride in which a free-flowing solid can be propelled continuously by means of a screw conveyor, a hydrogen fluoride/carrier gas mixture was passed in counter-current to a continuous charge of. cellolignin at such aerate that the -material at the HF inlet end of the tube had a content of approx. 60% of HF, relative to cellolignin,whilst only pure carrier gas flowed out at the cellolignin inlet end. The material was continuously discharged at the HF inlet end, while fresh cellolignin was recharged at the opposite end. After having passed a residence time section for half an hour , the material discharged was freed from hydrogen fluoride by blowing the latter off, and the HF-rich gas mixture thus obtained was fed back 19 8780 into the reaction tube. The disaggregated cellolignin was worked up in the manner described in Example 1. The yield of wood sugar amounted to approx. 85% of the theoretical value.

Example 15 150 g of shredded newspaper material were treated with a hydrogen fluoride/air mixture in the manner described in greater detail in Example 1. After a residence time of one hour at 50°C the reaction mixture 10 was freed from the hydrogen fluoride, down to a residual content of 2%, by passing in a stream of warm air, and ■the daik-colored residue was digested with hot water.

After filtering and drying, this gave 50 g of insoluble material, mainly composed of lignin. The filtrate was neutralized with calcium hydroxide and the calcium fluoride was filtered off with suction. The residue from the evaporation of the filtrate weighed 80 g and contained approx. 10% of monomeric glucose (remainder: oligomeric glucose). 19878

Claims (5)

WHAT WE CLAIM IS:

1. A process for obtaining water-soluble saccharides from cellulose-containing material by treating the latter with gaseous hydrogen fluoride, optionally diluted with an inert gas at temperatures between substantially 20 and 120°C, which comprises subjecting cellolignin to treatment with hydrogen fluoride.

2. A process according to claim 1 wherein the temperature range is between substantially 40 and 80°C.

3. A process as claimed in claim 1, wherein the cellolignin used is a material obtained by pre-hydrolysis of natural cellulose-containing material with dilute mineral acid at an elevated temperature and under an elevated pressure

4. A process as claimed in claim 1, wherein the cellolignin used is waste paper.

5. A process according to claim 1 substantially as hereinbefore described with reference to the examples. HOECHST AKTIENGESELLSCHAFT By Their Attorneys