US2284500A - Hydrolysis of cellulosic materials - Google Patents

Description

Patented May 26, 1942 2,284,500 nrnaou'srs or csnwnosrc MATERIALS Carl Warth, Lowenberg, Germany, assignor to Chemische Fabrik Lowenberg Dr.- Warth 8t Company,-Lowenberg, Silesia, Germany No Drawing.

Application March 20, 1939, Serial No. 263,098. In GermanyMarch 21, 1938 (Cl. 12737) It is already known to hydrolyse cellulose by 11 Claims.

suspending it in an organic liquid (a suspending agent) and then introducing, if necessary under pressure, gaseous hydrogen halide. The process according to the invention relates to improvements in this method of operation.

An important problem when hydrolysing cellulose resides in accelerating the dissolving and to ensure a high yield of solid edible sugar. The applicants have now made the surprising. observation that it is advantageous to first place into hot water and raw material containing cellulose and which has been treated by the process indicated above. After treatment with water it is preferably subjected to a further preliminary treatment with chlorine .and sulphur dioxide.

It was hitherto usual when saccharifying cellulose-containing substances, to use wood which either contained natural moisture or which had been pre-dried. Particular value was also placed takes up more easily the dissolving material, than moist material, and would thus dissolve quickerand more completely. At the most it on the drying as it was considered that dry cellulose-containing material, for example wood,

was considered permissible when using for example forest wood, to use wood containing natural moisture.

It has now been found that the dissolution of cellulose-containing substances, for example wood, for the purpose of sacchari'flcation has a substantially more favourable course when these tracheal elements and the inter-cellular structure of the cellulose-containing substances, for example wood. The air columns located in these narrow and/or capillary hollow spaces oppose.

tracheal elements and the inter-cellular structure and in this manner these points are also exposed to the action of the dissolving liquid. When soaking itis not solely the expulsion of the air enclosures which is important; the imbibition of the wood with water and/or suspending medium or solution also facilitates the penetration of the dissolving liquid to all the necessary points.

This soaking of the cellulose-containing substances, for example wood, before dissolution can be effected by placing this material into water and allowing the water to act for a suitable length of time. The procedure takes place considerably quicker when the natural soaking is supported by constantly maintaining the water hot. For example when soaking wood flour, it is preferable to admix this raw material with water and simultaneously to apply steam. The steaming may however also be effected without previously mashing in water or another liquid.

Instead of water it is also possible to use for example dilute hydrochloric acid. This soaking with dilute hydrochloric acid may also be effected by placing the initial material in the liquid or even by spreading the raw material, in a thin layer, for example on sieves and the like and applying the dilute hydrochloric acid in the form of a fine mist.

The process according to the invention is however not limited in any way to these briefly mentioned liquids.

Soaking agents of all kinds are suitable for the purpose. In many cases the wood used for example as initial material, contains organic resins and the like. when these resins remain in the initial material the subsequent action of the hydrochloric acid on these resins, when hy- 'drolysing the cellulose-containing substances,

leads to decomposition products, such as pinenelike sulistances which stop the hydrolysis. The dissolution of these cellulose-containing substances must not under any circumstances be effected with hydrochloric acid. on the contrary there should be used other hydrogen halides. In all cases however the preliminary treatment of the cellulose-containing substances is equally advantageous.

In order to remove these organic resins there are used, in accordance with the invention, liquids which dissolve these resins and then effect the soaking of the initial material. If necessary the removal of the resins may also be effected in the known manner by means of a suitable chlorine alone is used for this purpose there is formed with the water, subsequently used for soaking, dilute hydrochloric acid. Sulphur dioxide alone is associated with the advantage that it prepares the hydrolysis. When however the initial material is subjected to a preliminary treatment with gaseous chlorine and with gaseous sulphur dioxide, there is formed, during the subsequent soaking in water, sulphuric acid which also effects an acceleration of the soaking and subsequently also causes, in the same way as hydrochloric acid, the hydrolysis of the cellulose in the initial material.

The period of time required for the dissolving can be further reduced when suspending agents are used which possess a low surface tension. If necessary the surface tension can be reduced by the addition of floatation media or even wetting media may be used. It is advantageous to operate with emulsions of suspending media and aqueous halogen hydracid.

Further it is important that the liquids or solutions used possess a suitable specific gravity. This specific gravity must be-so high that the cellulose-containing substances to be dissolved are suspended therein, For example the specific gravity when treating wood, may amount to from 1.15 to about 1.10.

These organicliquids or solutions must further not take up hydrogen halides, further they must not dissolve any sugar, take up water and further must not attack cellulose.

These liquids or solutions must therefore only moisten the material to be hydrolysed. Y

- No permanent emulsions must be formed with water but it may be found of advantage to produce emulsionsjtemporarily. In the production of a suitable liquid theprocedure is therefore such that'for example benzene hydrocarbon is mixed with liquids having a higher boiling point and which also have a higher specific gravity, as for example tetra hydro naphthalene and/or deca hydro naphthalene and carbon tetrachloride and one of the known wetting agents is added to this mixture, as used for example in the textile industry, for example methyl hexalene. This addition, which considerably increases the wetting capacity of the liquid, is also for the purpose of adapting the specific gravity of the liquid to that of the cellulose-containingv substances to be dissolved. Modifications in the specific gravity are effected during the course of the process by further additions whlchincrease or reduce the specific gravity.

There is then formed with the halogen hydracid, which effects the dissolution, an emulsion with these suspending media. When the cellulose-containing material to be dissolved is introduced into this emulsion, the emulsion is decomposed. Further it is preferable to introduce into this temporarily formed emulsion, concentrated hydrogen halide either in the gaseous form or as liquid.

It is further necessary to separate the products produced by the process above described in a simple manner. For this purpose there is preferably utilised the emulsion formation. Before initiating the hydrolysis there is produced an emulsion of two liquids which during the course of the process decomposes automatically and by the formation of layers effects a separation of the solid substances from the sugar solution. In one layer there is then contained the total amount of sugar, in the other layer lignin which can be separated easily from the suspending medium by filtration or in any other suitable manner.

According to the invention there is used a plurality of liquids which are capable of eifecting a selective separation of the products produced during the course of the process. The procedure is such that to these liquids there is added an emulsifying agent and an emulsion is formed by means of an aqueous halogen hydracid. Into this emulsion there is introduced cellulose-containing material which if necessary is first dried. This material has a water extracting action and therefore destroys the existing emulsion which is then decomposed into two phases. As aqueous acid, which is used for the production of this emulsion, there is used the product which is obtained when drying the washed sugar solution in suitable drying apparatus, as a gaseous phase. This .vapor is liquified by condensation and this condensate is used for the production of the emulsion. The liquid, within which the dissolution is effected, may for example be produced in such a manner that an emulsion of water and hydrogen halide forms non-dissolving organic substances, and gaseous hydrogen halide is introduced into this emulsion. This emulsion is at first stable and decomposes when introducing emulsion destroying media, which for example may be the celluiose-cohtaining substance, for example wood, to be dissolved.

As suspending medium there may be mentioned for example carbon tetrachloride or benzene. It is also possible to mix the two said liquids preferably in a proportion of 125 parts of carbon tetrachloride to parts of benzene.

Deca hydro naphthalene is also suitable as a suspending medium. As the second phase there is used 30% hydrochloric acid which is emulsifled with the'suspendingmedia. The formation of the emulsion is promoted when about 1% of hexa hydro phenol is added to the mixture and the wetting action can be increased by an addition of l to 1.5% of hexa hydro methoxy benzene.

The separation of the reaction products can be avoided by initially selecting initial substances free from iignin. When starting for example with pine wood flour there is obtained as final product a mixture of lignin, sugar and suspending medium. From this solid mixture the sugar and/or glucose can be dissolved in the known manner, The magnitude of the quantities to be extracted in this case depends on the fact that for example pine wood, which is frequently used for sugar extraction, contains 30% lignin substance.

It has now been found that in many cases it and more erally burnt on the fields and of which the ashes produced, contained solely small quantities of inorganic salts suitable for ground fertilisation.

According to prudent estimation, the waste in potato tops suitable for sugar extraction amounts in Germany annually to about one million tons of dry material. By the processaccording to the invention this quantity can thus beused for the recovery of valuable substances.

The process according to the invention is however not restricted solely to these potato tops. It is also possible for example to use waste from cotton spinning which is also suitable for sac charification.

The process is not only based on the utilisation of waste hitherto not used but it is possible therewith to effect in a far simpler manner saccharification and thus to obtain the desired final products more economically. As stated the process is particularly suitable in those cases in which there is desired a waste containing only small quantities of lignin substance.

An eflicient separation of the reaction. products' can be obtained by treating them with a solvent as long as they are still distributed in thesuspending media. During hydro'lysisthere occasionally occurred a dimculty in separating the sugar produced from the suspending inedium as comparatively stable emulsions and/or suspensions are formed. It may however be mentioned that in this respect they are not emulsions or suspensions in the ordinary sense. On the contrary it was ascertained that the separate particles of the cellulose-containing sub- Stancessubjected to hydrolysis, had the following constitution; in the interior, of the separate particles there is located unchanged lignin, and around this lignin core there is located a wall of sugar formed by the hydrolysis. To this sugar wall there clings, by adsorption and/or absorption, a layer of the suspending medium. when it is desired to separate from the mixture the sugar formed by the hydrolysis, it is neces sary to remove the adsorbed and/or absorbed suepending medium from the separate particles so as to release the sugar and thus render it also possible to effect a separation of the lignin.

According to the inventionv the decomposition of these emulsions and suspensions and the separation of the sugar produced by the hydrolysis, associated therewith, is effected in such a manner that a washing medium, as for example water, is allowed to act on the mixture to be decomposed. These washing media may be cold or hot and may for example'also be acid liquids.

The washing medium used separates the suspensions and it must therefore'be of such a constitution that it is capable of dissolving the sugar and also the acid used for the hydrolysis.

The quantities of washing medium used and the temperature thereof depends upon the con stitution of the suspension to be decomposed and the manner in which the solutions, produced by the separation are to be further treated.

When for example water is used as the washing medium it is necessary, as regards the quantity thereof used, to bear in mind whether the sugar produced by the hydrolysis is to be obtained in a dry form or as a nourishing solution for micro-organisms. when solid sugar is to be produced there are onLv used predetermined quantities of water; when however it is desired to produce a nourishing solution the quantity of water may naturally be substantially larger. It will be understood that also the temperature of the washing medium. for example of the water, which is used is dependent on these different quantities.

At temperatures above 40 C. the sugar is at- 5 tacked in the presence of acid. When the quantity of washing medium is small its temperature must be below this limiting temperature. When however using large quantities of washing media it is not essential to avoid high temperatures as It) by reason of the considerable dilution which occurs a decomposition no longer takes place.

An efiicient decomposition of the suspension is also necessary because the absence of acid is particularly important when the sugar is to be produced in solid form. If for example the sugar is dried at high temperatures in the presence of acid caramelisation becomes unavoidably noticeable. The product obtained is then partly decomposed and coloured black.

separation is however not necessary when this drying is to be carried out at such temperatures which are located below this decomposing temperature of the sugar. .This, for example is the case when the solution is evaporated by the use of a hot air stream moving at a high velocity, as is the case amongst others in the Krause dryer and the like. By the rapid evaporation in these devices the temperature is considerably reduced and is therefore well below the said decomposing a temperature.

The addition of the washing medium to the emulsions and suspensions to be decomposed can be effected according to the invention for 5 example by passing the washing medium and the mixture to be decomposed through one another on the counter current principle. The direction of these two streams depend upon the specific gravities of the mixture and of the washing medium. By reason of the decomposition thus produced the layer of suspending material, forming thesheath of the particles is removed and the sugar dissolved. The decomposition in this case takes place on the basis of the difference of the specific gravity.

The separation may be made more eifective by passing the mixture thus decomposed through a drying device, as for example, a fine-mesh sieve and/or a fiber cloth or a suction filter. In this case subsequent washing may then be carried out if necessary with increasing quantities of washing media. The residues of the hydrolysed cellulose-containing substances are then retained. Instead of a filter it is also possible to use a centriiuge through which the decomposed mixture passes and in which the residues of the hydrolysed cellulose-containing substances are separated in the known manner from the sugar solution completely free from suspended particles.

Finally the sugar solution must then be advantageously fermented as far as possible. vFor this purpose the pH value must be adjusted. whilst simultaneously diluting, to 3-6 by introducing ammonia as solution or in the form of gas.

By the addition of ammonia and by neutralising the acid there is formed the corresponding halogen-ammonium compound. For example this is sal ammoniac when hydrochloric acid was used for dissolving, or ammonium fluoridewhen the dissolution was effected by means of hydrofluoric acid. The halogen-ammonium compound forms the inorganic nitrogen source for the development of the micro-organisms. As microorganisms for the utilisation of the said solution,

there may be mentioned in the first instance so- A complete elimination of the acid before the called wild yeast, torula types, which with a pH value of 3-6 have an optimum yield in these solutions. Further it is also possible to obtain excellent results with butyl alcohol fermentation promoters. These anerobic bacteria produce for example also acetone. Finally there may also be used aspergillaceae which for example produce citric acid.

It has already been proposed, for the extraction of yeast from a sugar solution of another type, to operate in the presence of ammonium compounds as nitrogen source but according to the earlier process it was necessary to follow a round-about way through an alkaline reaction, a step which is foreign to the present process.

The term "soaking agents" in the specification and claims is used to define those agents which remove the air present in the cellulosic substances and promote the penetration of the hydrolyzing compound, for example, water, dilute hydrochloric acid, etc.

I'claim:

l. A process for hydrolyzing cellulose-containing substances that comprises soaking said substance with an aqueous agent to cause substantially complete penetration of said substance with said agent but substantially no hydrolysis, suspending the treated substance in an inert organic suspension medium and hydrolyzing the same while in suspension with a hydrogen halide.

2. A process for hydrolyzing cellulose-containing substances that comprises soaking said substance in a hot aqueous solution to cause substantially complete penetration of said substance with said agent but substantially-no hydrolysis, adding a reagent from the group consisting of chlorine,

sulfur dioxide and mixtures thereof, suspending the treated substance in an inert organic suspension medium and hydrolyzing. the same with a hydrogen halide while in suspension.

3. A process for hydrolyzing cellulose-containing substances that comprises soaking said substance in a hot aqueous solution to cause substantially complete penetration of said substance with said agent but substantially no hydrolysis,

adding thereto areagent from the group con-.

ing substances that comprises soaking said substance-with water and sulfur dioxide to cause substantially complete penetration of said substance with said agent but substantially no hydrolysis,

suspending the treated substance in an inert organicsuspension medium and hydrolyzing the lose-containing substances that comprises soaking said substance with water and a reagent from the group consisting of chlorine, sulfur dioxide and mixtures thereof to cause substantially complete penetration of said substance with said agent but substantially no hydrolysis, suspending the treated substance in a temporary stable aqueous emulsion of an inert organic suspension medium and hydrolyzing the suspended cellulosic substance, said aqueous emulsion separating upon an inert organic hydrolysis into its corresponding phasesand af-. fecting the separation of the hydrolyzed product from the residual components of the raw material by selective solubility in the two phases.

8. A process for the saccharification of cellulose-containing substances that comprises soaking said substance with water and a reagent from the group consisting of chlorine, sulfur dioxide and mixtures thereof to cause substantially complete penetration of said substance with said agent but substantially no hydrolysis, suspending the treated substance in an inert organic suspension medium, hydrolyzing the said cellulosic substance while in suspension with a hydrogen halide and washing the reaction product with an aqueous washing solution capable of solubilizing the hydrolyzed product and the hydrolyzing agent.

9. A process according to claim 8 in which the washing solution is water at a temperature below 40 C.

10. A process for the saccharification of cellulose-containing substances that comprises soaking said substance with water and a reagent from the group consisting of chlorine, sulfur dioxide and mixtures thereof to cause substantially complete penetration of said substance with said agent but substantially no hydrolysis, forming an emulsion with a benzene hydrocarbon and a hydrogen halide, adding to this emulsion a wetting agent, introducing into said emulsion the pretreated cellulosic substance, hydrolyzing the suspended substance by means of a hydrogen halide, separating said emulsion to its component phases, segregating the hydrolyzed product from the residue of the raw material'by means of a washing solution and purifying the resultant sugar solution.

11. A process according to claim' 10,wherein the resultant sugar solution is separated from the products of hydrolysis by filtration or centrifugation and purified by spray evaporation.

CARL WAR'TH.