US1987195A - Process for the digestion of vegetable growths to produce cellulose - Google Patents

Description

Patented Jan. 8, 1935 I a 1,987,195

UNITED STATES PATENT OFFICE PRbCESS FOR THE DIGESTION OF VEGE- iljglgLE GROWTHS TO PRODUCE CELLU- Herman B. Kipper, Accord, Mass.

No Drawing. Application March 3, 1934,

SerialNo. 713,856

6 Claims, (01. 92-9) In my Patent Number 1,820,276 'of August 25, above digester was partially filled with some 1931 I described processing for digestion of vegtwenty pounds of waste cotton seed hulls and a etable growths and more especially wood for hot aqueous solution containing from five to production of cellulose and more especially paper fifteen percent of sodium hydroxide on the 6' pulp. According to the processing described in weight of waste hulls was run into the same until '5 the above patent mechanical disintegration of about three-fourths filled. The heater blades the wood is established simultaneously with traveling at about a speed of twenty feet per secchemical disintegration or digestion by means of nd and nine hundred revolutions per minute bevelled bars or knives which travel with cylinwere then started and oxygen forced into the 10 drical motion within the digester and through bottom of the digester at a rate of about ten cubic 10 the digestion mass at a high rate of speed. Refeet per hour. Digestion was continued for seven ductions in the chemicals required and in the u s. e pulp Was then removed, the digestime and temperature of digestion are thereby estion liquor drawn off from the pulp by means of tablished. In my copending applications Serial a suction filter and the pulp suitably washed. A

' Nos. 660,649 of March 14, 1933, 665,957 of April good pulp high in alpha-cellulose was secured. 15

13, 1933, 682,942 of July '31, 1933 and 689,875 of The spent digestion liquor, of course, can be evap- September 18, 1933, I describe specific improveorated for recovery of chemicals or again it may ments in digestion media as applied to my basic be evaporated t dry A plastic material is method of processing. v secured by the latter step which is adaptable for My present invention embodies a further immoulding purposes. 20

provement over the above processing for diges- I have also employed oxygen at a superatmostion of vegetable growths for recovery of cellu- D o p su e a d p to fifty p d and at lose. Such improvement depends more especially e y-five to O hundred d g Centigrade on a further reduction in the temperature redigestions otherwise similar to that just described.

quired for digestion and hence positive further h di sti p ri d is th y mat ia ly r 25 reduction in the fuel requirement. In order to duced. The same was comp Within about an accomplish this latter result air or oxygen is eu I @1 50 used a r in Place Of Oxygen in a passed into the digester and through the digestion estion practically t Same a those already, liquid or mass. Such air or oxygen may be passed scribed with the exception that about five times into the digester at the bottom of the same, or the V e o a w s d instead of the Oxygen 30 through a perforated hollow shaft bearing the as a ady noted a the pressure was maindisintegration bars or knives, or again in any ned at about o hundred p d The Oxygen other suitable manner, as at the ends of my horia r g t, of-e be circulated through the zontal digester. I have used satisfactorily all digester y a p p Situated externallythree methods mentioned. When employing this Furtherm r f t d s i n agents I have 35 method of digestion I have found it necessary to ed Ca c u hydroxide, ten to fifteen Percent employ only a hot aqueous solution of the dion" the weight of hulls suspended in the digestion gestion chemicals and air or oxygen at atmosmass, and calcium hydroxide in conjunction with pheric or superatmospheric pressure. In other sodium chloride, from one to five per in .0 words, the digestion solution need not be heated so ut on. Calciu hydroxide 18 Of Course, Only 40 above its boiling point. This method of digesvery slightly soluble. Equilibrium between the tion I have found especially advantageous for sodium chloride and calcium hydroxide in soluuse'in the recovery of the cellulose fibre from tion occurs and a small percentage of sodium waste cotton seed hulls. hydroxide is formed. As the latter is quickly In digestion of these waste hulls from their utilized in the digestion process its regeneration 45 cellulose content I'used a small digester two feet with establishment of equilibrium is brought long by sixteen inches internal diameter. A about, so that a small percentage of sodium hyquarter inch pipe coil was wound externally droxide is constantly available for the digestion. around the digester and used for heating the The latter is far more active than the correlatter with steam. For large scale operation such sponding calcium hydroxide, but so-called hy- 50 external heating should be practically unnecesdrated lime is, of course, much the cheaper chemsary as the ratio of -surface'to cubical contents ical so that its use is greatly tobe preferred. in the latter case would be greatly reduced and Without the rapid mechanical mixing or disin- 6 hence surface radiation of heat correspondingly tegrationemployed in my type of digester the'use lessened. Insulation might be required. llhe of such lime, however, is impracticable-and such statement furthermore is very nearly pertinent to the use of oxygen or air for the digestions described. As the percentage of sodium hydroxide present in the solution at any given time, however, is small, the digestion period is considerably increased and six to eight hours were required.

- In order to establish the more rapid digestion of nitrogen, or nitric acid vapor, or soaked in an aqueous solution of ten to twenty percent nitric acid. Subsequent to such treatment, however,

' I have found that I could use hydrated'lime or calcium hydroxide for fibre production also in conjunction with oxygen or air, in place of sodium hydroxide for final fibre liberation. The latter step is of great advantage because of the reduced cost of the calcium hydroxide, or hydrated lime, in comparison with that of the similar sodium salt.

The wood chips were first steamed to about a twenty percent moisture content andthen treated for two to three hours with air at about fifteen pounds super-atmospheric pressure andwith five to fifteen percent of the oxide of nitrogen and under constant mechanical beating as induced in my patented type of digester. The air supply was renewed continuously so that about ten to twenty percent of oxygen on the weight of wood was employed. Hot water containing ten to twenty percent, on the weight of wood, of calcium hydroxide in suspension was then run into the digester and beating continued for from one to two hours also under super-atmospheric pressure produced by air. In the latter case I used about fifty pounds pressure. It will be understood that the rapidly moving digestion mass is mechanically sprayed through the compressed air situated above it and hence forced penetration of the mass by oxygen continuously established. It

.' steamed into the digester. I Otherwise the processing was practically that described.

When pretreating the wood with nitric acid about fifteen to twenty percent of the latter diluted with water was used, and the wood allowed to soak for some twenty-four to forty-eight hours depending on the size of the wood chips. It was then treated with air at about fifteen pounds superatmospheric pressure in my type of digester for an hour or two at fifty to one hundred degrees centigrade. The processing subsequently used was that already described. In the soaking process the percentage of nitric acid required is about double that needed in the first two mentioned methods so that the latter process is not relatively as efllcient. I have used also a calcined dolomite stone in place of limestone, or a hydrate secured from the former.

The pulpin such case is somewhat lighter in color. I have further used sodium hydroxide in conjunction with calcium and magnesium hydroxide. Y

A limitless number of combinations of different chemicals in alkaline digestion'liquors, in place of those described, might of course be employed. I used'sodium nitrate and nitrite as well as sodium sulphite, and a combination of sodium nitrate and sodium sulphite in this connection,

but without any very distinct advantages. Also other oxidizing agents as potassium permanganate andpotassium dichromate were not found of sufficient added advantage to warrant the additional costs involved in their use. I have used only hot aqueous solutions of the digestion chemicals, as such were found entirely satisfactory, but, of course, higher temperatures and superatmospheric steam pressures might be employed with consequent reduction in thedigestion periods. On the other hand if colder digestion liquors are used we should expect to have to employ longer digestion periods. Although I have not used cold liquors I have employed the same heated only to fifty degrees centigrade and found such use as positive.

. In freeing the cellulose from cotton seed hulls I have also used hydrated lime, or calcium hydroxide, in place of sodium hydroxide, or mixtures of these two chemicals, in conjunction with oxygen or air. For the latter step I employed about eighty per cent of lime, or the full equivalent of lime required and twenty per cent of sodium carbonate. Again I have brought about the digestion with sodium hydroxide, and after separation of the cellulose fibre from the spent hot digestion liquor I have treated the latter under stirring. The partially oxidized hull material is thereby precipitated as the calcium salt and the sodium hydroxide solution is regenerated for digestion purposes. The calcium salt of the oxidized hull material after drying, and while hot, isplastic and under pressure can be molded.

I have also used sodium andcalcium hydroxides for wood digestion, but without oxygen, but

even in my type of digester seventy five to one hundred pounds steam I claim: v 1. In a process for the digestion of vegetable growths to produce cellulose fibre and of disintegrating the said vegetable material mechanically by the action of cylindrically rapidly moving pressure are required.

metal pieces which travel through the digestion mass simultaneously with the process of digestion by chemicals in aqueous solution the step of forcing oxygen (air) through the digestion mass simultaneously to the period of chemical digestion.

2. In a process for the digestion of vegetable growths to produce cellulose fibre and of disintegrating the said vegetable material mechanically by the action of cylindrically rapidly moving metal pieces which travel through the digestion mass simultaneously with the process of digestion by chemicals in aqueous solution the step of forcing oxygen (air) at superatmospheric pressure through the digestion mass simultaneously to the sure through the digestion mass simultaneously to the period of chemical digestion.

4. In a process for the digestion of vegetable growths to produce cellulose fibre. and of disintegrating the said vegetable material mechanically by the action of cylindrieally rapidly moving metal bars which travel through the digestion mass simultaneously to the said digestion process the step of digesting the vegetable matter by a hot aqueous solution of sodium hydroxide produced from sodium carbonate in thesaid solution and of calcium hydroxide suspended in the digestion mass and the step of forcing oxygen (air) at superatmospheric pressurethrough the digestion mass simultaneously to the period of chemical digestion.

5. In a process for the digestion of vegetable growths to produce cellulose fibre and of disin-' tegrating the said vegetable material mechanically by the action of cylindrically rapidly moving metal bars which travel through the digestion mass simultaneously to the said digestion process the step of pretreating the vegetable matter with steam, oiwgen, (air) and nitric oxides (nitric acid) and the step of digesting the said matter with calcium hydroxide suspended in hot water and added to the digestion mass and finally the step of'forcing oxygen (air) through the digestion mass simultaneously to theperiod. of chemical digestion and by-means oi the rapidly traveling beater elements and with or without exterior circulation of the gas.

6. In a process for the digestion of vegetable growths to produce cellulose fibre and of disintegrating the said vegetable material mechanically by the action of cylindrically rapidly moving metal bars which travel through the digestion mass simultaneously to the said digestion process the step of pre-treating wood chips with steam, oxygen (air) and nitric oxides (nitric acid) at superatmospheric pressure and the step of digesting the said treated wood chips with calcium hydroxide suspended in hot water and added to the digestion mass and finally the step of forcing oxygen (air) at superatmospheric pressure through the digestion mass simultaneously to the period of chemical digestion and by means of the rapidly traveling beater elements and with or without exterior circulation.

HERMAN B. KIPPER.