AU463585B2 - Process for manufacturing cellulose pulp - Google Patents

Description

20.4 04 170

The subject of the present irnvention is a process for manufacturing cellulose pulp. The traditional processes for manufacturing cellulose_ pulp from wood usually use salts of alkali metals or of alkaline earth metals, or weak acids, for example sulfuric acid or sulfurous acid, in aqueous solution. These known processes have several disadvantages, in particular they involve digesting the wood for several hours (six to twelve hours), in order to digest the wood completely. To obtain a sufficiently rapid digestion it must be

conducted at temperature of the order of 140 to 150 00, and therefore under a pressure of several atmospheres.

The digestion is usually conducted in rather weak sol-

utions, using a large quantity of water per tonne of wood.

Subsequently the water has to be distilled away from the

rcsulting liquor in order to recover the reagents. The production of 1 tonne of raw pulp results in the

production of 10 m 3 of black liquor.

"~o'sequently the reactors are lerge and complex, and

therefore costly. To produce wood pulp economically a modern pulp mill has to be equipped with digesters and other equipment of enormous size. Furthermore to obtain the necessary. high throughput the-pulp mill has to be builIt In a large forested area. This is particularly difficult in Europe, where there-are few large forested areas. These very large pulp mills are unsuitable for processing the comparatively

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small and highly dispersed stands of timber which are cha-

racteristic of European conditions.

A further disadvantage of the traditional pulping

processes is the emission of large quantities of sulfurous

3ffluent vapours which polute the environment over a radius

of more than 10 kilometres.

The technical literature does describe a number of

processes for removing the lignin from wood, which are

free from some or all of the above disadvantages, but none

of these processes are in use on an industrial scale, for

various reasons, usually because the reagents are too ex-

pensive.

Among these processes Muller describes the extraction 0 of lignin from wood in phenol at 180 C in the presence of

small quantities of hydrochloric acid. Huggland and Urban

use various alcohols, particularly ethylene glycol in the

presence of hydrochloric acid.

In spite of their virtues these processes are not in

use industrially, because the phenol and the alcohols, for

example glycol, combine with the .lignin, under the prevail-

ing operating conditions, to form stable products of the

ether type, and consequently a fraction of the reagents can-

not be regenerated.

The loss of reagents is excessively costly, Several

molecules of alcohol or phenol are lost per molecule of

lignin.

The process according to the present invention overcomes

most of the difficulties mentioned above, and provides the

following advantages:

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-Very little water is consumed. The consumption of water

is limited to the moisture initially present in the wood.

-The digestion produces no malodorous effluent gases, and

therefore is no atmospheric polution.

-No liquid effluents are produced and there is therefore

no polution of rivers.

-The process can handle all types of wood, from coniferous

and deciduous trees.

The reaction is comparatively rapid. The digestion takes only between 30 minutes and 3 hours, depending on the nature of the wood and on the quality of the pulp produced, compared to between 6 and 12 hours by the traditional pro- cesses.

-The digestion is preferably conducted under atmospheric

pressure, whereas in the traditional processes pressures between 4 and 6 kilogrammes per square centimetre have to

be used.

-The lignin can be recovered without it being necessary

to concentrate the black liquor.

-Less solvent is used, compared to the known processes.

-Economical pulp production can be obtained using compara- tively small processing equipment, and consequently less capital investment is required.

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404/70 The present invention resides essentially in an improvement in a process for producing cellulose pulp comprising the step of digesting wood chips at a temperature higher than 100 0 C in contact with a solution of a salt of an alkali metal or alkaline earth metal in a solvent which consists essentially of one or more saturated aliphatic diols or triols until the lignin in the wood has dissolved in the form of a soluble derivative, and the following additional steps: separating the resulting cellulose pulp from the solution; converting the soluble lignin derivative to an insoluble product; separating said insoluble product from the solvent; and recovering said solvent. The improvement in question consists of using as the salt in the above process an alkali metal or alkaline earth metal salt of an organic compound having at least one acidic hydrogen atom bound to an amino nitrogen atom or an alkali metal salt of an organic compound having at least one acidic hydrogen atom bound to a phenolic oxygen atom. The following salts can be used, although this list of salts is not intended to be limiting: sodium phenate and

sodium anilide C6 HNHNa or other anilides of alkali or alkaline earth metals. Preferably there is used as the reactive salt sodium phenate or sodium anilide.

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The process according to the invention can be conducted

by either of two methods:

Liquid phase process

The wood chips are suspended in an excess of the sol-

vent containing in solution one or more of the reagents

mentioned above.

The whole is heated to a temperature above 100°C, if

desired as high as 200 C, for as long as is necessary for

completing the lignin removal, the time depending on the

type of wood. In general the digestion time can be any-

thing between 30 minutes and 3 hours.

In the liquid phase process the vapours escaping from

the tops of the reaction vessels during the digestion are

recovered, either by condensation or by compression. The resulting condensates are recycled.

After this liquid phase digestion, the cellulose pulp

is separated from the black liquor by filtration.

To the black liquor there is added an aqueous solution

of calcium hydroxide, producing a precipitate of calcium

lignate, which is separated from the glycol by filtration.

Alternatively the lignin can be precipitated by adding

to the black liquor a strong acid, for example hydrochloric

acid, producing a precipitate of insoluble lignin-sulfonic

acid.

The recovered lignin can if desired be used directly

as a fuel, in the manner known to the pulp industry.

The recovered solvent, after readjustment of the

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20.4 04/70 concentrations of reagents s reused for digesting a fuher batch of wood chips.

The raw pulp produced in this way is ashed and can then be subjected to the way is washed and can e e e customary treatment. The raw cellulose pulp can be bleached, for example, by the electrolytic bleaching process. y t

The drawing represents diagrammatically example, one installation for operatin the as an rocess according to the invention. p r o ce s s

Figure 1 shows a first installation.

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There will now be described, on the basis of figure I, a plant for the semi-continuous production of cellulose pulp by digestion of wood chips suspended in a glycolic solution. The output is 15 tonnes of cellulose pulp per day. The wood chips are charged into a digester 50. To the wood chips in the digester 50 there is added 10 m 3 of ethylene glycol containing in solution 10% by weight of sodium phenate, as the reagent. This solution reaches the digester 50 from a storage tank 52 through a pipe 53 equipped with a valve 54. When the digester 50 has been charged, the liquid phase is circulated around in a closed circuit, the stream of liquid flowing through the mass of wood chips, out through the bottom of the digester and around the closed circuit marked a in the drawing, the liquid passing through the valves 55, 56, 57, 58, and through a heater 59, which heats the liquid to a tempera- ture between 160 and 190 0°C and maintains this temperature during the duration of the digestion. The liquid is circu- lated by a pump which is not shown in the drawing. When the digestion has been completed, the temperature of the material in the digester 50 is lowered to80 to 900 C. To lower the temperature the valves are actuated so that the circulating liquid no longer passes through the heater 59, that is to say the vales 55, 58, 60, 61 are actuated so that the liquid, which is an organic alkali-lignin solu- tion, now circulates through the closed circuit b, pass- ing through a heat exchanger 62. As soon as the contents of the digester 50 have been cooled sufficiently, a valve 63 is actuated, allowing the lignous solution to flow

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through a pipe 64 into a mixer 65. To the lignous liquid in the mixer 65 there is added a quantity of calcium hydroxide, with the result that the lignin is precipitated in the form of calcium lignate, with regeneration of reagent alkali. The contents of the mixer 65 are subsequently discharg- ed through a pipe 66 into a centrifugal filter 67. The calcium lignate is retained on the filter. The filtrate containing alkali regenerated by the calcium reaction, pas- ses through a pipe 68 into the storage tank 52. After the concentration of sodium phenate in the ethy- lene glycol has been readjusted, the reagent liquid in the storage tank 52 is used to digest a fu"ther batch of wood chips, the reagent liquid flowing through the pipe 53 and, this time, through a valve 54 into the second digester which by now contains a further charge of wood chips. Dur- ing this digestion in the digester 50', the digested cellu- lose pulp which has been retained on the screen 51 in the first digester 50 is washed as follows. Hot water from a hot water storage tank 69 flows through the pipe 70 and through a valve 71 into the digester 50, washing the cel- lulose pulp. The effluent wash water leaves the digester through the valve 63 and, ryssing through the pipe 64 reaches the mixer 65. This effluent wash water contains alkali lignin and residual organic solvent. In the mixer calcium.hydroxide is

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added to the effluent wash water, precipitating the lignin as calcium lignate. The contents of the mixer 65 are subsequently discharged through the pipe 66 into the centri- fugal filter 67. In the centrifugal filter 67 the residual lignin in the wash water is removed in the form of calcium lignate, which remains on the filter. The filtrate, which is purified

wash water is sent through a pipe 72 into the heat exchanger 62, where it acts as a coolant for cooling the alkali lignin organic solution produced during the digestion. Phenol-containing vapours produced during the digestion pass from the top of the digester into line 75, provided with valve 74, and thus to the heat exchanger 62.

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After paZsing through the heat exchanger 62 the purifi- ed wash water, partly in the form of vapour, is fed to a fractionating column 75, which perform the following se-

paration: From the head of fractionating column 75 distilled water is returned through a pipe 76 to the storage tank 69. From the tail of fractionating column 75 ethylene glycol is returned through a pipe 77 and a valve 78 into the storage tank 52. After the cellulose pulp has been washed on the screen 51 in the digester 50, it is removed through an outlet 79, after which it can be bleached in the known way. The

digester 50 is now empty and can be used for digesting a further batch of wood chips. During the digestion of this further batch in the digester 50, the cellulose pulp is being washed in the digester 50', and so on, the cycle being repeated. Although figure 3 shows only two digesters 50, 50', the system can of course if desired contain more than two digesters. The same quantity of reagent, organic solvent and wash water is reused again and again, apart from inevitable losses. It should be observed that a part of the sodium phenate is recovered in the distillate leaving the digester during each digestion. Another part of the sodium phenate is converted into calcium phenate mixed with the calcium lignate. The phenol can be recovered from this by reacting the calcium phenate with CO2 (by means not shown in the drawing), the phenol being recovered by entrainment in steam.

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The plant can be operated at an average throughput of approximately 1 digester charge every 3 hours, the plant plant producing approximately 15 tonnes per'day of dry cellulose pulp. The sane quantity of solvent is reused constantly, passing from one digester to the other. To summarise, using only 10 m 3 of solvent, a production of 15 tonnes of dry cellulose pulp is obtainable per 24 hours. This excellent result is due essentially to the following facts: -The digestion period proper is only 3 hours. -The same body of solvent is used again and again, the solvent being passed repeatedly from the one digester to the other. The water also circulates repeatedly around a closed circuit, the water also being passed repeatedly from the one digester to the other.

The number of batches digested per day is:

24 Duration of digestion, hours. To keep the plant in operation continuously, the

digestions following each other without interruption, the

number of digester required is: Duration of'one complete cycle of operations Duration of digestion. For example: Let it be assumed that one complete cycle of operations

occupies 9 hours, and that the digestion period is 3 hours,

The number of digesters required is;

S3 3

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These considerations are of fundamental importance in

regard to the technology of the installation, in view of

the fact that to produce 15 tonnes per day of cellulose

pulp in a conventional installation, using only a single 3 digester, involves the consumption of 150 m of water.

The process according to the invention will now be

illustrated by means of the following non-limiting examples:

Example 1

Into a flask equipped with a reflux condenser there

were charged 10 g of pine chips, 6 g of sodium phenate and

100 ml of ethylene glycol, and the whole was heated to 185 C

for 1 hour at atmospheric pressure. After the digestion

the contents were removed from the flask and the cellulose

pulp separated from the black liquor. The raw pulp was washed, dried and weighed. The yield was 4.8 g of crude

cellulose pulp, which was easy to bleach.

A quantity of calcium hydroxide was added to the back

liquor, precipitating calcium lignate, which was separated by filtration. There were recovered 86 ml of glycol.

Example 2 Proceeding as described for example 1, a mixture consist-

ing of 10 g of birch chips, 6 g of sodium phenate and 100ml 0 of glycerol was heated at a temperature of 180 to 190 C for minutes. After treating the digested material as describ-

ed for example 1, the yield obtained was 4.6 g of dry

cellulose pulp with very little colouration, and 80 ml of solvent.

Example 3 Proceeding as described for example 1, 10 g of

pine chips, 10 g of sodium 13 463585

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anilide and 10 ml of ethylene glycol were heae-d at 185 to 190 C for 1 hour. After treating the digested mass as -described for example 1, there were obtained 4.7 g of crude dry cellulose pulp easy to bleach, and 80 ml of recovered solvent. In order to provide a basis for comparisons, the experi- ment was repeated using 10 g of aniline instead of the sodium arilide. The yield was 7.4 g of dry crude cellulose pulp, instead of the 4.7 g previously obtained, indicating incom- plete removal of lignin. Example 4 Proceeding as described for example 1, 10 g of fir chips, 2 g of sodium hydroxide pellets and 4.6 g of aniline in 100 ml of glycerol were heated. In this example the aniline reacts with the sodium hydroxide in situ, forming sodium anilide. After treating the reacted mass as described for example 1, there were finally obtained 4.8 g of crude cellulose pulp, easy to bleach.

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Example

Proceeding as described for Example 1, a mixture consisting of 10 g of fir chips, 1 g of sodium hydroxide pellets, 3 g of sodium phenate and 100 ml of ethylene glycol 0 was heated at 180 to 190 C for 80 minutes. After treating the digested mixture as described for Example 1 there was finally obtained a yield of 4.8 g of dry raw cellulose pulp, very easy to bleach.

Example 6

Proceeding as in Example 1, a mixture consisting of g of oak chips, 6 g of sodium phenate; 30 ml of lauric

alcohol and 70 ml of ethylene glycol was heated at 1800 to 190 0 C for 2 hours. After treating the digested mixture as in Example 1 the yield was 3.6 g of dry pulp, easy to bleach.

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Claims (1)

1. 20.404/70

   THE CLAIM DEFINING THE INVENTION ARE AS FOLLOWS:

   1. In a process for producing cellulose pulp by ,_Agesting wood chips at a temperature higher than 1000 C in contact with a solution of a salt of an alkali metal or alkaline earth metal in a solvent selected from the group consisting essentially of at least one saturated aliphatic diol or triol until the lignin has dissolved in the form of a soluble derivative, separating the resulting cellulose pulp from said solution, converting said soluble lignin derivative to an inso luble product, separating said insoluble product from the solvent, and recovering said solvent; the improvement consisting of using as said salt an alkali metal or alkaline earth metal salt of an organic compound having at least one acidic hydrogen atom bound to an amino nitrogen atom or an alkali metal salt of an organic compound having at least one acidic hydrogen atom bound to a phenolic oxygen atom.

   2. Process as claimed in claim 1, characterized in that the digestion is conducted under atmospheric pressure.

   3. Process as claimed in claim 1, wherein said solvent is selected from the group consisting of ethylene glycol and glycerol.

   4. Pocessas claimed in claim 2, characterized in that the solvent used is ethylene glycol.

   Process as claimed in claim 1, characterized in that the salt is selected from the group consisting of sodium phenate and sodium anilide.

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   6. Process as claimed in claim 5, characterized in that the salt is sodium phenate.

   7. Process as claimed in claim 5, characterized in that the salt is sodium anilide.

   8. Process as claimed in claim 1, characterized in that the solution is maintained substantially anhydrous during the digestion.

   9. Process as claimed in claim 1, characterized in that the wood chips are digested while suspended in said solution..

   Process as claimed in claim 1, wherein the recovered solvent is recycled for processing a further batch of chips.

   11. Process as claimed in claim 1, characterized in that the dissolved lignin is precipitated by adding a strong acid to the solution.

   12. Process as claimed in claim 11, characterized in that the strong acid is hydrochloric acid.

   13. Process as claimed in claim 1, wherein said insoluble product is a lignin salt.

   14. Process as claimed in claim 9, characterized in that the following operations are conducted in the form of a continuous manufacturing process: wood chips are charged, with the above solution, into a digester; the mixture is digested at a temperature which is maintained above 100°C; the digested mixture, consisting of a suspension of cellulose pulp in a solution containing lignin, is removed from the digester and filtered; the yield of cellulose pulp is washed

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   on the filter with water; the effluent wash waters from the filter are distilled; to the distilled water there is added

   at least a part of the water obtained by condensing the

   vapours leaving the digester; the combined waters are

   recycled as the water used for washing the yield of cellulose

   pulp; the tail fraction from the distillation is combined

   with the filtrate from the filter; to the combined liquids

   there is added calcium hydroxide, which precipitates the

   lignin in the form of a suspension of calcium lignate; the resulting mixture is filtered; the yield of calcium lignate

   is washed with water on the filter; the effluent wash waters

   from the filter are distilled; the resulting distilled water is the water used for washing the calcium lignate; the tail fraction from the distillation is combined with the filtrate;

   and the combined liquid is recycled and used as the solvent

   in the digester.

   Process as claimed in claim 1, characterized in that the process is conducted as a batch-continuous process using

   several digesters which operate in alternating sequence,

   each batch being processed by the following sequence of

   operations: a charge of wood chips is introduced, together with said solvent containing said salt, into a digester;

   the solution is circulated in a closed circuit containing a heater, which heats the solution up to the reaction

   temperature and maintains this temperature throughout the

   digestion; the circuit is changed so that the solution flows

   through a heat exchanger instead of through the heater;

   after cooling sufficiently, the solution is drained out of

   the digester; the cullulose pulp is washed in the digester,

   from which it is then removed; the lignin in the solvent is

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   precipitated as calcium lignate, which is removed from the solvent and washed; the lignin in the wash waters is also precipitated and recovered as calcium lignate; and the purified wash waters are distilled, giving distilled water and a tail fraction, which is combined with the recovered solvent, the wash waters before distillation passing through the-heat exchanger for cooling the solution in the digester during the digestion.

   16. Process as claimed in claim 1, characterized in that the following operations are performed: a charge of wood chips is digested in a first digester in a solution which is circulated through a closed circuit containing a heater which heats the solution up to the reaction temperature and maintains this temperature throughout the digestion whereupon, after the digestion has been completed, the solution is circulated through a heat exchanger which cools it down; the solution is removed from the digester and the dissolved lignin is precipitated as calcium lignate, which is recover- ed; the purified solution, after removal of the lignin, is used for digesting a second batch of chips in a second digester, repeating operations and above; during operation in the second digester the cellulose pulp in the first digester is washed with water, the lignin in the wash waters is precipitated as calcium lignate, which is recovered, the purified wash waters are distilled, the so>. -nt being recovered as the tail fraction, the wash waters be-i;, used, before distillation, as the coolant in the heat exchanger which cools the solution during the digestion; the washed cellulose pulp is removed from the first

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   digester and a third batch of chips is charged to the

   first digester, during which time operation is repeated

   on the solution which has been circulating through the

   second digester; operations and are repeated

   in the second digester while operation is being repeated

   in the first digester, and so on, the digesters being operated

   in -alternation.

   17. Process as claimed in claim 15, characterized in that the salt used is sodium phenate, and in that the phenol

   vapourised during the digestion is recovered by combining it

   with the purified wash waters from which the lignin has been

   removed, the phenol beingabsorbed into these waters before

   their distillation.

   18. Process as claimed in claim 16, characterized in that

   the salt used is sodium phenate, and in that the phenol

   vaporized during the digestion is recovered by combining it

   with the purified wash waters from which the lignin has been

   removed, the phenol being absorbed into these waters before

   their distillation.

   19. Process as claimed in claim 17 or 18, characterized

   in that the calcium lignate, which contains some calcium

   phenate, is reacted with CO 2 followed by steam, in order to

   recover the phenol.

   Process as claimed in claim 16, 17 or 18 character-

   ized in that the number of digesters operated in alternating

   succession is equal to the ratio of the total duration of

   463.585 oz~erations and to the duration of operatioA (a) in each digester.

   DATED this 7th day 6f July~,

   -SOCIETE GENERALE DE BREVETS INDUSTRIELS ET CHIMIQUES

   EDWD. WATERS SONS PATENT ATTORNEYS QUEEN STREET M4ELBOURNE VICTORIA AUSTRALIA.

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   2< .501

   51

   p

   Fig. I

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