US2178266A - Continuous process for the manufacture of semipulp - Google Patents

Description

u. Pomuo Oct. 31 1939.

' commuous PROCESS FOR THE- MANUFACTURE OF SEMIPULP 5 Sheets-Sheet 1 Filed July 16, 1937 +2, INVEN TOR UHBERTQ Pomu Oct. 31, U PQMTLIQ v I v I CONTINUOUS PROCESS FOR. THE MANUFACTURE O sEMIP1Ip P Filed Jul is} 1957 5 spegysfs' aefci- I NVENTO R UMBEIETB Iiimuo m'razusys Oct. 31, 1939. u. POMILIO 2 6 commuous PROCESS FOR THE MANUFACTURE OF SEIMIPULP Filed July 16, 19:57 5 Sheets-Slfei;

l NVEN TOE UMBERFO Fbrnuo fkMM+M HTTOENEYJ Oct. 31,1939.

,u. POMILIO CONTINUQUS PROCESS FOR THE MANUFACTURE OF SEM-IPULP Filed July 16, 1937 l/III/ //II////// I IIIIIII l N V ENTOR UMBERTO Pom/1.10

A TTOEpI s'ys Oct. 31, 1939. u. POMILIO 2.178.266

commuous PROCESS FOR THE MANUFACTURE OF SEMIPULP Filed July 16, 1937 5 Sheets-Sheet 5 mvINToR Mnun'fc Riv/1.10

#TTORNEYS 7 a I Patented Oct. 31 1 939 UNITED STATES;

PATElflI "OFFICE CONTINUOUS PROCESS FOR THE MANU- FACTURE OF SEMIPULP Umberto Pomilio, Rome, Italy, assignor to Poj milio Corporation Limited, London, England Application July 16,1937,-seria1 No. 153,995 In Great Britain Janua y 23. 193'! 1 Claim. (01. 92-13) This invention is for improvements in or relating to processes and apparatus for the extraction of cellulosic fibres from vegetable material such as the straws of wheat, barley, rice, rye and J5 other cereals, the stalks of flax, cotton or hemp, canes such as sugar cane, bagasse, Danube canes, bamboo, grasses such as esparto, sisal, tambucki,

Tatching, elephant grass and other wild grasses, A

V 20 making paper pulp tor fine or white papers aim at substantially complete removal of the noncelluloslc materials and these processes are relatively expensive. There are two well-known methods of produc- 25 ing cheap semipulp. In the Masonite process wood of certain types cut into small pieces is subjected in an autoclave to the action of steam under high pressur'e'which acts both thermally and chemically on the encrustants of the cellu- 30 lose fibres. When the pressure is suddenly released the loosened vegetable material is broken up into filaments. In this process there is no I appreciable removal of the encrustants and the pulp is of a brown colour. It is used for making 35 boards but is unsuitable for making paper since the pulp is not resolved into separate papermakers fibres. I I

Mechanical pulp is made by grinding wood with grinding stones (generally the whiter 40 woods). The wood may be steamed before grinding and again the steaming operation may result in a certain degree of caramelization producing a brown colouration. The power required for the production of mechanical pulp is high, 45 generally of the order of 1000 kilowatt hours -per ton of ground wood or more. Mechanicalpulp contains all the' original encrustants-but the filamentary character of the cellulose is destroyed. It is not normally used alone for 50 the manufacture-of paper. It is employed up to a proportion of about 80% in newsprint (generally in admixture with chemical pulp) and it is employed .in a proportion of 25-40% in many other grades of cheap paper.

.53 In the grinding operation-many of the cellulose fibres are themselves sub-divided and it is practically impossible in the production of mechanical pulp to preserve much of the strength of the original plant filaments. pulp is produced only from wood.

For the manufacture of paper the cellulose Mechanical fibres should, as far as possible, preserve their original length and quality. It is true that in the beating engine certain long fibres, such as cotton fibres, are cut to a shorter length but the cellulose fibres which in nature are short already, such as'those in straws and stalks and wood, should reach the beater, as far as possible, .in their original length.

Speaking broadly, the problem in the present invention lies in utilising a wide variety of fibrous vegetable materials (in each locality thecheapest available), in cutting out or cutting down costly operations or costly materials, and yet producing a semlpulp which can be sent to the beating engine with the confidence that it will produce marketable paper.

Fibrous vegetable materials are composed broadly speaking, of cellulosic fibres which are embedded or encrusted in non-cellulosic material including lignins, waxes, resins,,pectic and mucic acids, albuminoid matter, starchy matter, sugars (like pentosanes) and inorganic matter.

It is already known that the encrusti'ng materials may be removed from fibrous vegetable matter by treatment with alkali and with chlorine. The alkali interacts with certain encrusting substances of an acid character or saponifiable character, such as waxes and resins and the pectic andmucic acids, whilst chlorine reacts with other encrustants, particularly with the lignins to form chloro-lignins and hydrochloric acid, all of which can then be leached out; According to the present invention, a process for themanufacture from fibrous vegetable mat 40 'ter of semipulp; suitable for paper-makingand cardboard, comprises reacting on 'the' yeg'etable matter successively with alkali and chlorine gas and is characterizedin that the quantities'of the reagents employed are no more than sufiicient to remove a part only' jo the non-cellulosic constituents and in that the 'zalkali reaction 'is carried out with the application of heat at atemperature between 75C.'- jand 100 C. and the chlorine reaction is carried out without the application of heat.

It is found that the more objectionable noncellulosic constituents can be attacked by a more dilute reagent than that required to attack the other constituents. 'I'hus,-in carrying out the thermore, the process may be carried out by so controlling the time over which the reaction takes place that a predetermined quantity of the non-cellulosic constituent is rendered capable of removal while the strength of the reagent may be such as to attack any or all of the noncellulosic constituents.

It has been found that the temperature under which the reactions are carried out also affects the physical characteristics of the resulting fibre in that high temperature conditions tend to damage the fibre, the fibre being increasingly damaged as the temperature rises above 100 C. A still more important consideration is that uniformity of resolution is favoured by carrying out the reactions at low temperature. The reactions with alkali and with chlorine are exothermic and high temperatures are liable to be built up and accordingly it is a feature of the invention that the treatment with alkali and/or with chlorine is not only restricted as regards the extent of removal of non-cellulosic constituents but also is carried out under conditions which ensure that the temperatures built up during a the reactions are sumciently low to diminish damage to the fibre.

A still further feature of the invention consists in that the process comprises a preliminary stage in which the material is treated with a dilute alkali solution, a second stage in which the material is treated with chlorine and a third stage comprising a treatment with a very dilute alkali solution. Since these reactions are exothermic, the temperatures built up are dependent, inter alia, on the velocity at which reactions take place and on the rata-at which theevolved heat is dissipated through the material and through the walls of the reaction vessel and accordinglyit maybe desirable to cool the reaction mass during the chlorination and final alkali treatment.

In a process for treatingflbrous vegetable materials with caustic soda and with chlorine, the cost of the chemicals is a very important item. In the present invention caustic soda may be used in a dilute aqueous solution (a form of alkali readily obtainable by electrolysis 'of common salt solution). A cheap alkali such as soda ash may also be employed. The gaseous chlorine may be used in a moist state diluted with the gases of the air, a form of chlorine which is likewise very readily produced by electrolysis of salt solution. This invention therefore includes a process for the manufacture from fibrous vegetable matter of semi-pulp suitable for paper-marking in which an aqueous solution of common salt is electrolysed to produce a dilute alkali solution and moist gaseous chlorine and in which the moist gaseous chlorine diluted with air is used for the second stage of the process and the caustic soda solution (at the required concentration) is used for the first and third stages of the process.

The process in its preferred form comprises three stages, viz:

a,17a,ace

1. A treatment of the fibrous vegetable matter with a solution of caustic soda of 1% or less for the removal of a substantial proportion of the acid and saponiiiable encrusting constituents;

2. A treatment of the resulting material with moist chlorine gas diluted with air, which treat ment is controlled in the manner set forth above;

3. A treatment of the resulting material with very dilute solution of caustic soda of .2% or less.

As already indicated, the amount of caustic soda used during the first or third treatment and/or the amount of chlorine used during the second treatment can be so controlled that these chemical reagents are completely used up in attacking a predetermined amount of the noncellulosic constituents. It is an important practical feature of this invention that the vegetable matter receives its chemical treatments in a continuous manner (as distinct from batch treatment), the reactions being carried out successively in separate reaction chambers.

A further feature of the invention consists in that the vegetable material is caused to descend under gravity through reaction towers and that the reagents are introduced at zones near the upper ends oi the towers. With this arrangement, the vegetable material becomes progressively consolidated as it descends through the tower and this tends to force the reagents to flow in countercurrent in spite of the fact that in the case of chlorine the gas is heavier than air. By reason of the downward movement of the vegetable matter, a certain amount of the reagents may also be drawn downwardly. In the case of the chlorine, by suitably selecting the point of its introduction into the tower and by controlling its rate of feed and the rate of feed of the vegetable material, the chlorine is prevented from reaching either end of the tower before being completely used up in the reaction. Thus there can be no leakage of chlorine into the atmosphere nor are any sealing means required at the ends of the tower.

The velocity at which the reaction takes place in the alkali treatment is dependent to some extent on the strength of the alkali solution employed. I

For treating straw, should it be required to remove the greater part of the non-ligneous and non-cellulosic material and to remove about half the ligneous non-cellulosic constituents, the strength of the alkali solution in the preliminary stage is of a concentration up to about 1%. when such a solution is employed, the relative proportions of the reacting substances are selected to be 1 part by weight of vegetable material to 3 parts of the solution. The reaction is carried out in an open vessel without pressure for a period of from 1-4 hours according to the strength of the solution. The-temperature of the reaction which is exothermic may vary from 75 C. to 100 C. This treatment would result in a reaction with the greater part of the non-ligneous and non-cellulosic constituents.

The chlorine reaction is also exothermic. Preferably, the chlorine gas is diluted with air and it may be moistened. The reaction mass may also be moistened. The chlorine is used in quantities 01' about 4 to 5 parts by weight to 100 parts of the straw, and this will result in the reaction with about one half of the lignepus noncellulosic constituents. About half of the chlorine reacts to form chloro-lignin whilst the remainder of the chlorine is converted into hydro-,

chloric acid and it is advisable that the time during which the fibres are in contact with the drochloric acid, resulting from thechlorination, should be reduced to a minimum since the cellulosic fibres are liable to be attacked thereby.

An important feature of the invention consists in thatthe chlorination treatment and the final alkali treatment are conducted in the cold. The dilution of the chlorine with air has a dual effect. It reduces the reaction velocity and thus the rate at which heat is evolved, and it also serves toabsorb and conduct away some of the heat; The moistening of the gas and the reaction mass serves byabsorption to reduce concentration within-the fibre of the hydrochloric acid which is there formed and thereby minimises its de1eteri-" ous effect on the fibre. As soon as chlorination iscomplete the reaction mass is immersed in cold water. The proportion of air used with the chlorine is dependent on the nature of the vegetable material being treated and it'may vary from to 1 part by volume of air to one part by volume of chlorine, whilst the moisture content of the chlorine may be up to its saturation point and the moisture content of the mass may be two to five times the weight of the mass itself.

The proportion of chlorine-air mixture to the vegetable material mayvary with the nature of the'material being treated, and may vary from 4 to 5 parts by weight of chlorine to 100 parts of vegetable material. The length '61 chlorination treatment may vary from half-an-hour to three hours by varying the rate .of traverse of the material through the apparatus. The length of the chlorination treatment may vary from half-anhour to three hours.

The compounds formed by these two reactions may not be entirely removed by washing and the third stage, namely, the treatment with a very dilute alkali solution, effects the removal from the material of those compounds affected by the first two treatments but still remaining on the fibres. The strength of the solution employed in this final stage may be about 1%. The quantity of the solution employed is from 5 to 20 parts by weight of solution to, 1 part by weight of the vegetable material and the reaction is carried out in the cold.

The following is a description of one form of apparatus for carrying out the process described above, reference being made to the accompanying, drawings, in which- Figure 1 and Figure 1 taken together represent a side elevation of the plant showing diagrammatically the general arrangement,

Figure 2 is a vertical section on the line 2-2 of Figure 1 showing the alkali towers in elevation,

Figure 3 is a section through a tower on the line 3-3 of Figure 1,

Figure 4 is an enlarged view of one of the mixing devices of Figure 2,

Figure 5 is an enlarged view of'the mechanism for tilting the hopper nozzle as shown in Figure 4. Figure 6 is a side elevation of the device shown inFigure Figure '7 is a plan view of the extractor for the reaction towers.

Figure 8 is an elevation of the arrangement shown in Figure 7.-

Figure 9 is a cross section on the-line9s9 of Figure 8. i

Assuming stalks or straw of plants, such as are referred to at the commencement of the specification, are to be treated,'these are cut into lengths of a few inches and are loaded into ber l3 open at the top, the lower wall It of which is inclined downwardly from each end to the centre to form a V. A screw-conveyor I5 is horizontally-disposed along the length of'the chamber and has two sets of helical blades arranged end to end, which blades are oppositely pitched to one another, and are driven by a motor 22. Disposed above the chamber and at the centre hoppers Ill arranged at the top of the apparatus.

of the screw-conveyor is a V-shaped deflector I6. The hopper is arranged to deliver the material on to the deflector through a flexible nozother of the V-shaped deflectorthereby adjusting the relative quantities of the material being fed to the two towers. The movement of the nozzle may be effected by a hand wheel is fixed to a worm shaft is in engagement with a rack secured to the nozzle. The worm shaft is mounted in a bracket 2! secured to the chamber i 5. Caustic soda solution is supplied to the chambers through a conduit 23 and a suitable device for maintaining a constant level of the solution in the V-shaped recess in the bottom of the chamber but which level does not. reach the blades of the conveyor. As already indicated, the strengthof the solution may be 1% or less. Each end of the chamber is open and the screwconveyor forces the material mixed with the alkali out through said open ends from which the open end of the reaction (as will be seen from Figure 3), the smaller di-' mension being-about 15 inches and the larger dimension 8 feet. The conveyor I3 is so arranged as to effect a mixture of straw and solution in proportions of one of straw to three of the solution. Steam is introduced through the walls of the tower by a number of pipes 24 in a zone substantially above the horizontal. centre line, e. g.,

'zle I! which may be swung from one side to th 1 one-quarter of the length from the top. The

steam generating plant 25 and main delivery pipe 26 are shown to the left of Figure 1. The mass of material-1 gradually descends under gravity and becomes compacted as it descends, and at the bottom forms a seal 'of interlaced fibres which prevent too rapid an escape of the liquid. The time of descent may vary from one to four hours according to the nature of the material and'the strength of. the caustic solution. Dur ing this time the alkali is almost completely used up to form spent liquor ofav dark colour. The.

tower is provided with inspection windows 9 and sockets 8 for thermometers at different heights. The mass of interlaced fibres is removed from the bottom of the tower by an extractor 21, the

speed of extraction being adjustable; thus, the

. time of treatment may be varied.

As will be seen from Figures 7 to 9 the extractor comprises two parallel shafts 28 each of which carries a number of star-shaped members 29. The two shafts are rotated through gearing 30 in opposite directions so that the arms of the stars draw the material downward and first move towards one another and then away from one an ther. The mountings for shafts ll and the gea g 30 may be so arranged that the distance apart between the shafts may be varied. The gearing may be driven by an electric motor (not-shown) the speed-of which may be controlled thereby controlling the rate of withdrawal oi the material from the bottom of the towers.

- The fibres are separated from the spent liquor by a screening device 3i through which the material is fed by a screw conveyor 32. The screening device is formed in two parts 35, 34 arranged end to end along the length of its conveyor and the part at the outlet end 34 receives a supply of wash water through a pipe 35 which wash liquor is delivered by an outlet pipe 35 to a tank 31. The washed and partly-treated fibres are .dellvered by the conveyor through an outlet conduit 38 to a screw-press 39 where the remainder of the spent liquor is squeezed out of them and delivered to a tank 40 through a pipe 4!. The consolidated mass is then passed through a conduit 42 to an opener 43 having spiked rollers or combs where it is converted into a floccular state. It is then raisedby air blowers 44 through suitable conduits 45 to a receiving chamber 46 arranged above the upper end of a set of chlorinating towers 41. The upper ends of the chlorinating towers are open and the conduits 45 are directed on to a deflecting plate 48 in the collecting chamber 46 whereby the floccular material is caused to fall into the towers.

These. towers may also be about 30 feet in height although those shown in the drawing are shorter. They are of a flattened oval shape in cross-section, the general dimensions being the same as those of the alkali towers. Chlorine is introduced into the fibrous mass at a zone about 10 feet from the top of each tower. As already indicated the top of each tower is open but the 10 foot column of fibrous material above the zone is suillcient completely to absorb the chlorine and prevent leakage, and the sealing action is enhanced by the fact that the material is descending. The chlorine is introduced into the zone by pipes 49 which extend from a header pipe 50 through the walls of the tower and stop flush with the inside face, and also by means of a set of pipes 5! which extend downwardly from a header pipe 52. From practical considerations the width between the side walls of the tower cannot be made much less than 15 inches and since chlorine cannot readily penetrate the fibrous material to that extent, the additional vertical delivery pipes are provided. Thus a comparatively small penetration is required without the necessity of applying substantial pressure to the chlorine.

Chlorine with the required degree of moisture,

may be prepared in an electrolytic plant 53 from which it passes through a delivery conduit 54 to.

a blower 55 driven by a motor 56. The inlet or suction side of the blower communicates with the atmosphere through a valve 51 and air pipe 58. By adjusting the valve 51 a desired quantity of air may be mixed with the chlorine. The chlorine air mixture is delivered by a pipe 59, to the aforesaid header pipes 49 and 52 through suitable valves 53 and 54. The fibrous material gradually sinks through the tower and is removed from the bottom of the tower by an extractor 55, similar to the aforesaid extractor 21 the speed of extraction being adjustable as in the case of the alkali tower. .As in the alkali tower inspection windows 9 and sockets for thermometers are provided.

The material is then delivered by the extractor into a tank having rotating stirrers 5| therein through which tank cold water is circulated. The material passes thence along a trough 82 to a rotating conical sieve N, the axis of which is horizontal and the angle of inclination of the walls of which is such as to feed the material from the smaller end of the sieve to the larger end. The diluted hydrochloric acid percolates out through the sieve walls into a tank 54 and the fibrous material thus partially freed of acid is passed through screw-presses 85 where it is consolidated. The fibrous material is then passed through a mixingvat ll' containing a weak solution of caustic soda, e. g., a soda solution of .2% concentration or less. The material is treated in this vat for afra'ction of an hour and this results in the-removal oi the chloro-lignin compounds and/or other non-cellulose soluble matter. Also, any remaining hydrochloric acid or chlorine combines with the caustic soda. Thereafter the fibres are passed through the usual washing and sorting apparatus where knots are removed.

As already indicated the towers both for the alkali and'chlorine treatments are provided with thermometers so that the predetermined temperatures of the reactions may be maintained, for example, by controlling the rate of extraction of the material from the bottom of the towers. Furthermore, means are provided for periodically testing the air and moisture content of the chlorine mixture.

The starting material may be considered to contain roughly 50% cellulosic constituents and 50% non-cellulosic constituents. The three-stage treatment, namely, the first alkali treatment and the chlorine treatment and the final stage, removes the required amount of the readily removable constituents and at the same time leaves behind on the fibres a substantial part of the more desirable non-cellulosic constituents, especially the ligneous constituents. If the control of the chemical treatment is such that only half the non-ceilulosicmaterial is removed, the total yield of solids in the pulp would be about 75% of the original weight of vegetable matter. By operating in this manner it will be appreciated that not only is the time of treatment very considerably reduced but also the consumption of chemicals is very much less than where the treatment is carried out to remove the whole of the encrusting materials from the cellulosic fibres. The semipulp which is obtained by the process herein described if desired is capable of being satisfactorily bleached, satisfactorily treated in the beating engine and may be easily felted to form a good grade of paper. The process, therefore, may be very cheaply operated to produce high-grade semipulp.

I claim:

A continuous process for the manufacture of semipulp from straw which consists in mixing the straw with an alkali solution of 1% strength and in proportions of 1 part by weight of straw to 3 parts by weight of the solution, traversing the mixture through a reaction tower raised to a temperature between 75 C. and C. at such a rate that the material remains in the tower from 1 to 4 hours, transferring the material to a vessel where it is washed with water, dewatering the material and introducing it with chlorine gas diluted with air in proportions of .5 to 1 part by volume of air to 1 part by volume of chlorine and in quantities such that there are 4 to 5 parts by weight of chlorine introduced to 100 parts by in a cold water bath, transferring the' material POMILIQ. 5

weight of straw, traversing the material at such it with analkali solution of a strength of .1% and a rate that it remains in the reaction vessel from in quantities from 5 to 20 parts by weight of half an hourto three hours, immersing the matesolution to 1 part by weight of the vegetable rial, immediately after leaving the last said vessel, material. I

from said bath to another vessel and treating

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