US 2269665 A
Description (OCR text may contain errors)
Patented Jan. 13, 1942 k PREPARATION OF CELLULOSE MEAL Walter Herbst, Danzig-Oliva, Free State of Danzig No Drawing. Application December 24, 1938, Se-
rial No. 247,691.
A principal object of the invention is a process for the production of cellulose meal by extensive or complete destruction of the cellulose fibres, the essential feature of which is that the destruction of the fibres is effected without substantial change of the other properties of the cellulose.
Cellulose meal produced in accordance with the invention is suitable for feeding stock for animals and as a dietetic nutrient or as an addition to such, further as an absorbent and conserving medium for nutrient-rich fluids and for waterrich nutrient and'feeding stock materials (sugar beet molasses, milk, blood, liver, meat, e'tc.), as a carrier and diluent '(excipient) for medicaments,
. pharmaceutical preparations, fiavouring and perfumery substances in tablet or powder form, as a powder and for various technical purposes.
Attempts to reduce cellulose to meal form by mechanical action alone have not led to satisfactory results. But cellulose fibres can easily be more or less destroyed by subjecting the material to an intensive treatment with acids. This possibility has long been known and is utilized In Germany July 23, 1935 technically (carbonization process) to free mixed acids and alkalies, have a reducing action and easily dissolve in hot 1% caustic potash lye. This behaviour clearly shows that hydrocelluloses are not breakdown but reversion products of cellulose.
In addition hydrooellulose in contradistinction to cellulose is very indigestible, it possesses but limited capacity to absorb fluids and in its other physical behaviour is very much like clay; for example it binds very closely together in water and then forms tough layers almost impenetrable to water. i
For all these reasons hydrooellulose is not suitable as a feeding stock or as a dietetic nutrient or as an absorbent or powder.
The technical problem arises therefore to reduce considerably or entirely the fibrous structure of cellulose, which is a hindrance to the stated uses, without substantially changing the material otherwise.
According to the invention this is achieved by acid treatment very strongly reduced in intensity as compared with that necessary for destroying the cellulose fibres, in combination with a suitable mechanical treatment of the material.
Upon contact with acids the cellulose fibres long before their disintegration become crisp and brittle to such a degree that after washing and drying they can in a suitable mill, be ground if not completely to a degree which suffices for many purposes. The meals so obtained are mixtures of hydrooellulose and of cellulose consisting of fragments of fibre and they behave according'ly, that isbetter than hydrooellulose but by no means in the optimum manner in the sense aimed at by the invention.
The complete solution of the problem by the invention consists in the cellulose fibres, after a relatively very short period of acid treatment, for which purpose mineral acids in particular, as for example hydrochloric acid, sulphuric acid, sulphurous acid and nitric acid, come into consideration, being ground in wet condition, in which case they can be practically completely ground.
Inthe optimum case, only 60 seconds immersion of the cellulose in 6% hydrochloric acid at 100? C. suffices to render its fibres capable of being ground in wet, swollen condition. That here not so much a chemical change in the cellulose as aloosening of its physical structure is in question follows from the fact thatquite apart from the short period of treatment necessarythe contact of the cellulose with boiling 6% hydrochloric acid can be reduced from 60 seconds even down to that minimum period (less than 10 seconds) which is necessary to completely soak the material, if the contact is immediately followed by neutralization of the soaked up acid, for example with soda solution. Accordingly the moist condition of the cellulose which makes possible the grinding down of the fibres is increased by the neutralization step.
The cellulose is changed very little physically and practically but not chemicallyby the above stated treatment. In consequence the cellulose meals prepared in accordance with the'invention can be as completely digested, that is broken down to reabsorbable substances, as pure cellulose not treated with acid, for example by agricultural livestock, though the pure untreated cellulose itself practically cannot be be used as a feedingstock owing to the difficulties of feeding occasionally by the fibrous structure, while hydrooellulose though adapted to be fed to animals is-as already stated-t0 a great extent indigestible.
The cellulose treated with acid according to the invention is characterized by the feature that if dried without grinding of the moist fibres, it attains a similar condition to the dry untreated raw material, which prevents any extensive destruction of the fibres by mechanical means. Even if the acid treatment of the cellulose is, by stronger concentration of the acid, longer time of treatment, and, it may be, higher temperature, made 30 to 35 times as intensive as is necessary to make the fibres completely grindable in moist condition; for example if the cellulose is boiled at 100 C. with acid 3 times as strong for times as long; grinding of the material in a dry condition in a disc mill still does not yield fibre-free meal.
Accordingly the essential characteristic of the process of the invention is that the acid treatment of the cellulose is notably less intensive than would be necessary to enable su'flicient destruction of the fibres to be efiected by grinding in the dry condition, and that the acid treated material is ground moist if -a completely or at least far-reaching destruction of the fibrous structure of the cellulose is to be achieved.
As above stated, under the action of 6% hydrochloric acid at 100 C., the cellulose fibres become capable of being ground in moist condition after 60 seconds. This optimum is however as a rule only obtained with technically pure that is "soft and bleached sulphite cellulose. To bring less soft or hard" lignin-, or even resin-containing sulphite cellulose, soda cellulose, other celluloses or cellulose-rich materials such as cotton, flax, bast, straw and so forth, into the same condition, the acid treatment must in some circumstances be up to 10 times as intensive, that is instead of for 1 minute, 6% hydrochloric acid at 100 C. must act for up to 10 minutes. Naturally the raw material from which the cellulose was obtained, and finally the condition of subdivision, also have a bearing; thus loose cellulose for example wadding attains a wet grindable condition quicker than thick cellulose pulp sheets.
As in the treatment in accordance with the invention of large masses of cellulose, it is on one hand diflicult to keep the concentration of the acid, the temperature and the time of treatment exactly the same in all parts of the material, and large grinding mills according to experience have not the same efficiency as laboratory mills. On the other hand twoto three-fold increase of the minimum time does not involve any noticeable disadvantages, and use can be made in practical manufacture of this possibility of exceeding the minimum time to obtain a material all parts of azeaees As in the treatment of large masses of cellulose the maintenance of very short reaction times presents technical difliculties, and for practical manufacturing operations a more convenient equivalent of the above described acid treatment may be used. The concentration of the acid or the temperature or both are reduced in order to obtain considerably longer treatment periods which can better be controlled and which can be maintained with smaller percentage errors.
This possibility arises from the following conditions:
The necessary time of acid treatment to bring about the condition of the cellulose according to the invention is inversely proportional,
(a) With constant temperature, to the strength of the acid, whatever the kind of acid, in particular in the case of mineral acids;
(b) With constant strength of acid, to the nth power of a number between 1.10 and 1.15, n being the temperature difference in centigrade degrees, with the proper sign.
Thus, if instead of 6% for example 1% hydrochloric acid is used, the minimum treatment time at 100 C. for the optimum case increases from 1 minute to about 6 minutes. If in addition the treatment temperature is lowered from 100 C. to 75 C. the minimum treatment time is again increased, in this ease up to 1% to 2 hours.
After termination of the appropriate time of treatment the acid is either neutralized or washed out with water, the cellulose then freed from a part of the liquid by draining, pressing or centrifuging, and then with a water content of advantageously about to 75%, mechanically ground for example in disc or cone mills. The swollen, wheat-groats-like product produced in this way can then :be directly, that is in moist condition, used for example? as cattle food or pressed into briquette-like blocks or oil-cake-like plates and if necessary dried, or it can be dried which are properly grindable and at the same time to keep the expenditure of mechanical power necessary for grinding the fibres as low as possible.
For many purposes of use of cellulose meal the minimum treatment time can even be exceeded 4 to 10 fold,-for example if the final product is to be relatively dense and to have relatively small capacity for absorbing fluids. But even with such prolonged reaction times a product which will yielda fibre-free meal if ground dry, is not obtained, because-as already mentioned-times of treatment would be necessary which correspond to even more than 30 to 35 times the minimum period.
But under given conditions (nature of the raw material, concentration of acid, temperature oi treatment, desired qualities of the final product), the optimum reaction times determined by preliminary tests will be maintained as closely as in the groats form and then used, or after drying be further ground to a fine powder for example in mills having beaters.
If for certain special purposes, cellulose meal is to be obtained which still shows a certain fibrous structure, that is consisting partly or mainly of fibrous fragments, this can be obtained by carrying out the wet grinding of the cellulose treated according to the invention with acid and then de-acidified, with only weakly pressed grinding mill discs when the fibres ar only partially ground, or by grinding the material only after first drying it.
Cellulose preparations prepared in accordance with .the above description from cellulose contaniinated with resins or similar substances, have the property which is for many purposes a fault, of taking up water very imperfectly after drying at higher temperature, and of not being able to be brought again into a broth like or suspended condition, as they could before drying, with water after soaking for days and even boiling.
This behaviour can according to the invention be prevented or overcome by freeing the material of the impurities by washing before or after the acid treatment with alkali solution for example dilute, preferably hot caustic soda lye, soda solution, or with other resin-dissolving agents, or.(and) by carrying out the final drying following the wet grinding at temperatines below 75 to C.
The described property of only absorbing water imperfectly and not becoming properly soaked after drying is also true of any cellulose the fibres of which have become capable of being ground in the wet condition, by the action of sulphur-containing acidssuch as sulphuric acid or sulphurous acid, for example in the sulphite boiling process in the presence of free sulphurous acid. The insuiiicient absorbing and soaking capacity of such a cellulose is, apart from any contamination by resinous substances, caused by the presence of sulphur-containing organic'compounds.
Such cellulose preparations can according to will depend on the properties of the material under treatment in any particular case, on the quantity of sulphur-containing compounds contained therein, whether in addition to these resins or similar impurities are present.
In all cases in which a steeping treatment of the moist material in dilute, preferably hot alkali solution does not suffice to obtain cellulose products which after drying are easily soakable again, the combination of the alkali treatment with the prior intermediate drying set forth under 1. leads to success, the action being best if the dried material is exposed for some time to an elevated temperature up to above 100 C. In that case cellulose products are obtained in which the final drying under 4. can be completed at high temperature without damage, whereas material treated with alkali solution without revious drying and dried at ordinary temperature only yields a final product which can be satisfactorily soaked if the final drying is effected at a low temperature. Nevertheless if the final drying is effected below '75 to 80 C. the effect of the described after-treatment is in any case improved.
With celluloses that contain resins and similar impurities or sulphur-containing organic compounds, the treatment with alkalies can be dispensed with if the 'ability again to absorb and Example 1- Ordinary commercial bleached sulphite cellulose, still containing however small quantities of resin and the like, is boiled in 1% hydrochloric acid for to 60 minutes at 100 C., freed of acid by washing with water, then boiled with 0.5% soda solution for say 15 minutes, again washed with water, partially dewatered by the aid of a Worm press, ground down with a water content of about 50 to 75% in a disc mill until the fibrous structure of the cellulose has been completely destroyed, dried in the usual way at 100 to-110" C. and finally for example in a beater mill further ground to a fine fibre-free powder.
. Example 2 After the treatment with acid as in Example 1 and after washing or neutralization thereof, the
material is dried and then ground either first in a disc mill and then in a beater mill or straight away in a beater mill, whereby a meal consisting mainly of short fragments of fibre and tending to fiocculate is obtained.
Example 3 Cellulose boiled down in the usual sulphite boiling process in the presence of free sulphurous acid, to the condition according to the invention enabling the fibres to be ground by moist grinding, is, after washing out the cooking liquid,
partially dewatered by the aid of a centrifuge then according to Example 1 wet ground, dried at110 to 120 C. and after drying held at this temperature for about 15 to minutes longer, then boiled for about 15 minutes in 0.5% caustic soda lye and after washing out the lye dried again.
I declare that what I claim is: 1. A process for the production of cellulose meal which includes the preparatory step of treating cellulose with approximately 1 to 6% acid for 1 to minutes, in particular mineral acid, until the treated cellulose can in its wet swollen condition be ground until it loses its fibrous structure and terminating such treatment 1 while the cellulose is still in a condition in which dry grinding yields a meal which consists mainly of fragments of fibre.
2. A process as set forth in claim 1 also including the steps of -de-acidifying the treated cellulose and then grinding it in wet condition.
3. A process as set forth in claim 1 also including the steps of washing the treated cellulose to remove acid and then grinding it in wet condition.
4..A process as set forth in claim 1 also including the preparatory steps of deacidifying the treated cellulose, grinding it in the wet condition, drying it, and then grinding it still finer in dry condition.
5. A process for the production of cellulose meal which includes the steps of subjecting technically pure sulphite cellulose to heating with 1% aqueous hydrochloric acid solution for 15 to 60 minutes at C. and subjecting the material to Wet grinding. I
6. A process for the production of cellulose meal which includes the preparatory step of subjecting technically pure sulphite cellulose to heating with dilute mineral acid for a time which for a given temperature is inversely proportional to the strength of the acid and for a given' strength of acid is inversely proportional to the nth power of a number between' 1.10 and 1.15, n being the temperature difference in centigrade degrees from a given temperature with the proper sign, the time for 1% aqueous hydrochloric acid solution at 100 being from 15 to 60 minutes, and subjecting the material to wet grinding.
"7. A process for the production of cellulose meal which includes the preparatory step of subjecting a mainly cellulose-containing raw material such as sulphite-cellulose containing lignin, resin and the like impurities; caustic soda cellulose, cotton, flax, bast and straw, to heating with 1% aqueous hydrochloric acid solution up to hours at 100 C., and subjecting the material to wet grinding.
8. A process for the production of cellulose meal which includes the preparatory step of subjecting a mainly cellulose-containing raw material such as sulphite-cellulose containing lignin, resin and the like impurities, caustic soda. cellulose, cotton, flax, bast, and straw to heating with dilute mineral acid for a time which for a given temperature is inversely proportional to the strength of the acid and for a given strength of acid is inversely proportional to the nth power of a number between 1.10 and 1.15, n being the temperature difference in centigrade degrees from a given temperature with the proper sign, the time for 1% aqueous hydrochloric acid solution at 100 C. being from 1 up to 10 hours, and subjecting the material to wet grinding.
9. A process for the production of cellulose meal which includes two preparatory steps applied to cellulose containing impurities, one of which steps consists in treating the material with' approximately 1 to 6% acid for 1 to minutes, in particular mineral acid, until the treated material can in its wet swollen condition be ground until it loses its fibrous structure and terminating such treatment while the material is still in a condition in which dry grinding yields a meal which consists mainly of fragments of fibre, and the other of which steps consists in immersion of the material for a period in alkali such as diluted preferably hot caustic soda or soda solution.
10. A process as set forth in claim 9 wherein the alkali treatment succeeds the acid treatment, and including the further steps of deacidifying, drying and heating the cellulose for a period up to above 100 C. between the acid and alkali treatments. 1
11. A process as set forth in claim 6 including the further steps of wet grinding the cellulose and then drying the cellulose at a temperature below about to C.
12. A process as set forth in claim 9 including the further step of grinding the treated cellulose in wet condition between the acid and alkali treatment.
13. A process as set forth in claim 9 wherein the acid treatment is effected first, the cellulose deacidified, ground in wet condition, dried at 111 to C., held at such temperature for a period, subjected to the alkali treatment, washed and dried at a temperature below about 75 to 80 C.