Process for the digestion of vegetable growths to produce cellulose

Patented Dec. 25, 1934

1,985,609

UNITED STATES PATENT OFFICE

1,985,609

PROCESS FOR THE DIGESTION OF VEGETABLE GROWTHS TO PRODUCE CELLULOSE

Herman B. Kipper, Accord, Mass.

No Drawing. Application September 18, 1933, Serial No. 689,875

Claims.

In my copending applications Serial Numbers 660,649 of March 14th, 1933, 665,957 of April 13th, 1933 and 682,942 of July 31st, 1933 I describe processing for the digestion of wood and other 5 vegetable growths with liberation of cellulose and with or without recovery of resin and other organic constituents.

According to one of the steps evolved in such processing the wood was first steamed and then 10 treated with oxides of nitrogen, nitric acid or nitric acid comingled with carbontetrachloride etc., and subsequently finally digested with an aqueous solution of regularly employed chemicals in the type of digester described in my Patent 15 Number 1,820,276 of August 25, 1931. I have found that the process of steaming the wood and treating with oxides of nitrogen, of from, five to fifteen percent, may be simultaneously carried out and very advantageously in the type of di20 gester or piece of apparatus above referred to, or again the wood may be treated with steam and vaporized nitric acid, about fifty to sixty percent nitric acid, also in the said type of digester. The percentage of nitric acid used on the basis of 25 dry wood was about ten to twenty. The rapidly travelling beater bars or cutting blades tend to disintegrate the wood chips mechanically and to render them more porous so that the action of the steam, nitric oxides or nitric acid are all 30 greatly enhanced.

For instance in the first case noted the wood was steamed for about half an hour in my mechanical type of digester. The bars or blades In this travelled at a peripheral speed of about 35 twenty feet per second. The wood chips are disintegrated and rendered porous so that the steam penetration throughout the chip is rendered even or homogeneous. About ten to twenty percent of steam on weight of dry chips was employed. 40 The steam was admitted through a valve in the bottom of the digester or through a hollow shaft carrying the beater bars. The digester was externally insulated and heated further by steam passing through a coil wound externally around 45 it. The chips were then treated with oxides of nitrogen to from five to fifteen percent. Such treatment must be carried out with sufficient care to prevent overheating of the wood. Cold water was passed through the coil wound externally 50 around the digester to prevent such overheating and also air or nitrogen gas was passed through the digester for reduction of temperature. Such treatments I carried out in from half an hour to a six hour period. As the cooling is increased, M the time of treatment may be reduced. Naturally (Cl. 92—6) those alloys, for instance one of iron, nickel and chromium, practically impervious to the attack of nitric acid, should be employed for the digester construction or the latter should be lined with such alloys, now successfully bonded with steel. 5 I used the straight alloy construction. Subsequently to the above treatment the treated wood was digested with a dilute hot one-fourth to two percent caustic soda solution, or other regularly employed digestion solution, as sodium hydroxide 10 and sodium sulphide, only at very greatly reduced strength from that ordinarily employed.

In carrying out the treatment with steam, nitric oxides, for instance primarily nitrogen dioxide, and simultaneous mechanical beating, the 15 digester was not externally cooled, but air or nitrogen in some of the digestions was circulated through the digester during the said treatment. Also alternate or intermittent steaming and treatments with oxides of nitrogen gave very effl- 20 cient results. Again treatment was carried out in from one half an hour to a six hour period under superatmospheric pressures oi from one to twenty-five pounds and subsequent final digestion was carried out with a dilute caustic soda 25 solution, as already described, and with simultaneous mechanical beating of the digestion mass.

When using a fifty to sixty-five percent nitric acid, fifty to thirty five per cent water vapor the digestion was also carried out as described. I 30 generated the water-nitric acid vapor in a small iron-nickel chromium alloy boiler, connected with the digester with piping also of the same alloy.

Of course I am well aware that wood has been digested with nitric acid but as my processing 35 employs but a small percentage of that ordinarily used as well as a greatly reduced percentage of caustic soda and digestion is brought about in minimum and very noticeably reduced time its commercial advantages are greatly enhanced over 40 the nitric acid processes now known to your applicant. Moreover the use of nitric oxides for the digestion your applicant believes to be fully novel. Finally your applicant may state that without the use of his special type of digester and 45 patented processing methods he was unable to sedure satisfactory complete digestion with the small percentages of oxides of nitrogen or nitric acid used. The rapidly travelling metal bars, beaters or cutting blades cause disintegration of 50 the wood chips, partially brought about by the oxides of nitrogen and greatly enhance the efficient action of the latter. It should be readily understood that as the powerful mechanical action causes disruption or opening up of the wood 55

1,986,600 action of cylindrically rapidly moving metal pieces.

4. In a process for the digestion of vegetable growths to secure cellulose fibre the steps of subjecting the said growths alternately to the action of steam and to the action of oxides of nitrogen and simultaneously to mechanical disintegration produced by cylindrically rapidly moving metal pieces.

5. In a process for the digestion of vegetable growths to secure cellulose fibre the steps of subjecting the said growths alternately to steam and to the action of the oxides of nitrogen and simultaneously to mechanical disintegration produced by the impact action of cylindrically rapidly moving metal pieces and finally the step of disintegrating mechanically the treated vegetable mass, for liberation of cellulose fibre by the impact action of cylindrically rapidly moving metal pieces simultaneously with digestion by chemicals in aqueous solution of the said mass.

6. In a process for the digestion of wood to secure cellulose fibre the steps of subjecting the said wood cut into chips alternately to the action of steam and to the action of the oxides of nitrogen both under superatmospheric pressure and simultaneously to disintegration mechanically produced by the impact action of cylindrically rapidly moving metal pieces, and finally the step of mechanically disintegrating the treated wood 30 mass, for liberation, of cellulose fibre, by the impact action of cylindrically rapidly moving metal pieces simultaneously with digestion by a hot solution of sodium hydroxide of the said mass.

7. In a process for the digestion of wood to se- 35 cure cellulose fibre the steps of subjecting the said wood cut into chips to the action of water and nitric acid vapors and simultaneously to disin-

45.

chips penetration of the oxides of nitrogen or of nitric acid readily occurs, whereas the action of nitric acid in aqueous solution on the wood chips is very slow. In the latter case your applicant has found it necessary to employ some fifty percent of nitric acid on weight of dry wood and some eight to ten percent of sodium hydroxide in about a two percent aqueous solution, whereas by his processing only some ten percent of nitric oxides, or less, were required and two to five percent of sodium hydroxide. Moreover the installation of a plant to produce oxides of nitrogen from ammonia is far less costly than the installation of one for fabrication of nitric acid, all of which features very materially favor the process of your applicant from the commercial standpoint.

I have also used nitric acid and water vapor of about sixty percent concentration of the acid intermittently with oxide treatment. Furthermore I have applied continuous steaming and nitric oxide, diluted with air, treatment in my mechanical digester. The process is the same as that which would be secured by the use of oxides of nitrogen obtained from ammonia oxidation. Cooling of the gases in the latter case would be probably necessary, at least when obtaining a speed of reaction commensurable with commercial practice. Furthermore, after mechanical disintegration in my type of digester; I soaked wood chips in about fifteen percent of nitric acid for from two to forty-eight hours and then brought to boil for about two hours and finally decomposed the treated mass with sodium hydroxide. Such treatment gave a good fibre, far better than one secured by boiling the chips in dilute nitric acid over a protracted period.

These processes in general were also success- ------------- .... . .

fully applied by your applicant in decomposition tegration mechanically produced by the impact । of waste cotton seed hulls for recovery of cellulose action of cylindrically rapidly moving metal _flbre pieces, and finally the step of mechanically dism-