Accelerated pulping process

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United States Patent [19] Prior [54] ACCELERATED PULPING PROCESS [76] Inventor: Eric S. Prior, 830 Signal Way, Coos Bay, Oreg. 97420 [21] Appl. No.: 387,350 [22] Filed: Jun. 11, 1982 Related U.s. Application Data [63] Continuation of Ser. No. 176,182, Aug. 7, 1980, aban doned, and a continuation-in-part of Ser. No. 74,658, Sep. 12, 1979, abandoned, which is a continuation-in part of Ser. No. 20,978, Mar. 16, 1979, abandoned, which is a continuation of Ser. No. 855,754, Nov. 29, 1977, abandoned, which is a continuation-in-part of Ser. No. 699,189, Jun. 23, 1976, abandoned, which is a continuation-in-part of Ser. No. 699,188, Jun. 23, 1976, abandoned. [51] Int. Cl.4 .............................................. .. D21C 3/04 [52] US. Cl. ...................................... .. 162/79; 162/81; 162/ 90 [58] Field of Search ..................... .. 162/4, 7, 8, 10, 11, 162/ 12, 16, 19, 25, 28, 37, 38, 40, 41, 42, 45, 79, 80, 81, 82, 90, 94, 96, 97, 91, 163, 98, 99; 71/23, 25, 64 E, 64 SC; 260/175, 124 R; 106/123 R, 123 LC, 213, 214, 236, 242, 287 SS; 405/263, 264; 426/635, 636, 807; 210/702, 710, 711, 723, 767, 768 [56] References Cited _ U.S. PATENT DOCUMENTS 322,882 7/1885 Young et al. ....................... .. 162/81 1,634,603 7/ 1927 Wood ............. .. 1,716,623 6/1929 Collins et al. ....................... .. 162/11 List Continued on next page. OTHER PUBLICATIONS Sinai et al., “Separation of Sugars & Lignin in Spent Sul?te Liquor by Hydrolysis & Ultra?ltration”, TAPPI, 59(3), 3-1976, pp. 112-114; 162-216. Casey, Pulp & Paper, vol. I, 1960, pp. 370-371, Gp 170. Primary Examiner-Arthur L. Corbin Attorney, Agent, or Firm--Bernard, Rothwell & Brown [11] Patent Number: [45] Date of Patent: 4,652,341 Mar. 24, 1987 ‘[57] > ABSTRACT A process of treating ?brous ligno-cellulose material to form de?bered chemical cellulose pulp suitable, for example, for the manufacture of paper and paperboard and dissolving pulp and to treat de?bered ligno-cel T lulose material to produce basic animal feed or packag ing and- building boards. The process is based on the nitration and dissolving of ' the lignin component of the cellulose material either in an alkaline solution or with a two step operation in which the nitration can be in an acid stage comprising the step of submerging the ?berous ligno-cellulosic material in aqueous nitric acid having an HNO3 concen tration in the range of about 0.125 to 9 weight percent, followed by an alkaline stage to dissolve out the nitrated ; lignin from the ?brous structure. In the production of § chemical pulp or animal feed the lignin containing solu tion (black liquor) is separated from the cellulose mate rial. The time required for nitration is substantially short ened by including in the nitrating solution aluminum , compounds, e.g., aluminum salts of inorganic acids such as aluminum sulfate, aluminum chloride, aluminum phosphate or aluminum nitrate, preferably aluminum sulphate, i.e., papermaker’s alum, in an amount suffi cient to achieve an equivalent aluminum ion concentra tion in the pulping liquor, preferably about 0.065 to 0.105 parts by weight of aluminum sulphate for each 10 parts by weight of nitrate ion in the nitrating solution. The nitrating liquor including wash water, either acid .' or alkaline, can be recycled to nitrating chemical ex haustion. Lignin-containing extraction liquor is recy cled to build up the percentage of lignin solids and, systematically purged. Part or all of the ligneous com , ponent may be recombined with the cellulosic pulp produced with which it acts as a retention agent, binder, water repellant and stiffening agent. In combination with de?bered ligno-cellulosic materials its function is as a binder and hydrophilic material. For grassy, ?brous ligno-cellulosic materials (i.e., straw) nitrate salts such as the alkali salts NaNOg, KNO3, or NH4NO3, which have a relatively lower ionizing factor than nitric acid, can be used in an alka line solution to nitrate and dissolve the ligneous compo nent. The use of nitrates in an alkaline solution for woody ?brous materials (i.e., spruce wood chips) re quires additional pulping time than if an aggressive acid I nitrate source is used for nitration. 21 Claims, 20 Drawing Figures

Transcript of Accelerated pulping process

Page 1: Accelerated pulping process

United States Patent [19] Prior

[54] ACCELERATED PULPING PROCESS

[76] Inventor: Eric S. Prior, 830 Signal Way, Coos Bay, Oreg. 97420

[21] Appl. No.: 387,350

[22] Filed: Jun. 11, 1982

Related U.s. Application Data [63] Continuation of Ser. No. 176,182, Aug. 7, 1980, aban

doned, and a continuation-in-part of Ser. No. 74,658, Sep. 12, 1979, abandoned, which is a continuation-in part of Ser. No. 20,978, Mar. 16, 1979, abandoned, which is a continuation of Ser. No. 855,754, Nov. 29, 1977, abandoned, which is a continuation-in-part of Ser. No. 699,189, Jun. 23, 1976, abandoned, which is a continuation-in-part of Ser. No. 699,188, Jun. 23, 1976, abandoned. ‘

[51] Int. Cl.4 .............................................. .. D21C 3/04 [52] US. Cl. ...................................... .. 162/79; 162/81;

162/ 90 [58] Field of Search ..................... .. 162/4, 7, 8, 10, 11,

162/ 12, 16, 19, 25, 28, 37, 38, 40, 41, 42, 45, 79, 80, 81, 82, 90, 94, 96, 97, 91, 163, 98, 99; 71/23, 25, 64 E, 64 SC; 260/175, 124 R; 106/123 R, 123 LC, 213, 214, 236, 242, 287 SS; 405/263,

264; 426/635, 636, 807; 210/702, 710, 711, 723, 767, 768

[56] References Cited _ U.S. PATENT DOCUMENTS

322,882 7/1885 Young et al. ....................... .. 162/81 1,634,603 7/ 1927 Wood ............. .. 1,716,623 6/1929 Collins et al. ....................... .. 162/11

List Continued on next page. ’

OTHER PUBLICATIONS

Sinai et al., “Separation of Sugars & Lignin in Spent Sul?te Liquor by Hydrolysis & Ultra?ltration”, TAPPI, 59(3), 3-1976, pp. 112-114; 162-216. Casey, Pulp & Paper, vol. I, 1960, pp. 370-371, Gp 170.

Primary Examiner-Arthur L. Corbin Attorney, Agent, or Firm--Bernard, Rothwell & Brown

[11] Patent Number:

[45] Date of Patent: 4,652,341

Mar. 24, 1987

‘[57] > ABSTRACT

A process of treating ?brous ligno-cellulose material to form de?bered chemical cellulose pulp suitable, for example, for the manufacture of paper and paperboard and dissolving pulp and to treat de?bered ligno-cel

T lulose material to produce basic animal feed or packag ing and- building boards. The process is based on the nitration and dissolving of

' the lignin component of the cellulose material either in an alkaline solution or with a two step operation in which the nitration can be in an acid stage comprising the step of submerging the ?berous ligno-cellulosic material in aqueous nitric acid having an HNO3 concen tration in the range of about 0.125 to 9 weight percent, followed by an alkaline stage to dissolve out the nitrated

; lignin from the ?brous structure. In the production of § chemical pulp or animal feed the lignin containing solu ‘ tion (black liquor) is separated from the cellulose mate

rial. The time required for nitration is substantially short ened by including in the nitrating solution aluminum

, compounds, e.g., aluminum salts of inorganic acids such as aluminum sulfate, aluminum chloride, aluminum phosphate or aluminum nitrate, preferably aluminum sulphate, i.e., papermaker’s alum, in an amount suffi cient to achieve an equivalent aluminum ion concentra tion in the pulping liquor, preferably about 0.065 to 0.105 parts by weight of aluminum sulphate for each 10 parts by weight of nitrate ion in the nitrating solution. The nitrating liquor including wash water, either acid

.' or alkaline, can be recycled to nitrating chemical ex haustion. Lignin-containing extraction liquor is recy cled to build up the percentage of lignin solids and, systematically purged. Part or all of the ligneous com

, ponent may be recombined with the cellulosic pulp produced with which it acts as a retention agent, binder, water repellant and stiffening agent. In combination with de?bered ligno-cellulosic materials its function is as a binder and hydrophilic material.

For grassy, ?brous ligno-cellulosic materials (i.e., straw) nitrate salts such as the alkali salts NaNOg, KNO3, or NH4NO3, which have a relatively lower ionizing factor than nitric acid, can be used in an alka line solution to nitrate and dissolve the ligneous compo nent. The use of nitrates in an alkaline solution for woody ?brous materials (i.e., spruce wood chips) re quires additional pulping time than if an aggressive acid

I nitrate source is used for nitration.

21 Claims, 20 Drawing Figures

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4,652,341 Page 2

US. PATENT DOCUMENTS ' 6 Wm a1 “2/163 X 1,717,199 6/1929 Marr ............................... .. 162 7 x . 3,305,435 2/19 7 15m 9* - ------------- -—

1,829,852 11/1931 Darling n 1622;? x 3,463,699 8/1969 Broadhead et a1. 162/163 2,110,545 3/1938 Dreyfus .. 162/81 3,576,709 4/1971 Menzies .................. .. 162/16 2,269,985 mm mm ____ __ 162,79 3,578,553 11/1971 Godsay 81:81.. 162/81X 2,332,369 10/1943 Burton _____ ,_ __ 16%“ X 3,725,629 4/1973 ‘131361611616 .................... "71/641391v 2,562,898 8/1951 Evans eta]. ..... .. ..162/163x 3,881,986 5/1975 Backlund ........................ ..162/41x 2,615,883 10/1952 Sweeney et a1. 162/81 X 3,929,558 12/1975 Shaw ................ .. .. 162/79X . 2,731,344 1/ 1956 McKee ................................ .. 162/11 4,048,341 9/1977 Lagel'stfom 6'1 a1- ------- 426/636 X

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US. Patent Mar. 24, 1987 Sheet4of13 4,652,341

FIG. 3

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FIG. 5

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US. Patent Mar.24, 1987 Sheet6.of13 4,652,341

FIG. 6

SPRUCE

Nil/Hill

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U. S. Patent Mar. 24, 1987 Sheet7 ofl3 4,652,341

FIG. 8

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U. S. Patent Mar. 24, 1987 Sheet 11 ofl3 4,652,341

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4,652,341 1

ACCELERA'I'ED PULPING PROCESS

This is a continuation of application Ser. No. 176,182 ?led Aug. 7, 1980, which is a continuation-in-part of application Ser. No. 74,658 ?led 'Sept. 12, 1979, which is a continuation-in-part of application Ser. No. 20,978, ?led Mar. 16, 1979, which is a continuation of applica tion Ser. No. 855,754, ?led Nov. 29, 1977, which in turn is a continuation-in-part of application Ser. No. 699,189, ?led June 23, 1976 and application Ser. No. 699,188, ?led June 23, 1976 all now abandoned.

This invention relates to an improved process of breaking the lignin bond of ?brous materials in a form ranging from that of a moderately digested product for animal feed to pulps that can be utilized as chemical or semi-chemical pulp for packaging papers ‘and boards, bleachable pulps for white papers, highly puri?ed pulp for dissolving pulp and to simply develop surface un bonded lignin on ?brous material to act as a binder. The invention relates to a lignin nitration pulping

process in which the nitration can be carried out either in an acid or alkaline solution, and the time for nitration is substantially shortened by the inclusive use of alumi num compounds. ‘

This invention also relates to a pulping process in which the ligneous components extracted from ligno cellulose raw material is recombined with the pulped ?bers to provide added strength characteristics for packaging papers and paperboards or to act as a binder for de?bered ligno-cellulosic material. The use of the inherent ?exibility of the process time,

temperature and chemical ‘concentrations permits con trolled deligni?cation and de?bering to produce animal feed, building board, packaging board and paper, bleached papers and dissolving pulp. The potential use of nitrate ‘containing chemicals,

speci?cally nitric‘ acid, as a speci?c pulping agent for cellulosic structures has been recognized for many years. The processes varied widely in time and acid concentration and were mostly applied to the very easily pulped ?brous structures such as straw or sliv ered wood or hardwoods. The processes depended on partial nitration, ?nal oxidation and subsequent hydro lysis of the lignin structure-the acid consumption was high and the ?ber produced had brittle characteristics. In such a process producing a chemical type pulp, re covery of chemical remains unsolved. So far as I am aware, pulping processes using nitric

acid have never been commercially successful. The following excerpts from patents granted or suggested processes on easily pulped ?brous materials are indica tive of the scope and problems (sometimes hazardous) involved in such processes where high acid concentra tions and usage with lengthy process times make com mercial practice unworkable and uneconomic with no conceivable advantages over present day conventional processes.

Casey-Pulp & Paper, Vol. I

Nitric Acid Pulping of Poplar Wood Patentee

Dreyfuss Miles Solechnik

Acid Concentration (%) 6 8 7 Time of Digestion (hours) 3 9 1.5 Temperature (°C.) 80 100 98

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-continued Nitric Acid Pulping of Wood Wafers

11/100 inch thick! Acid Concentration (%) 42 Acid Temperature (°C.)» 68 Acid Consumption/T on Pulp 15%

Nitric Acid Pulping of Bagasse Acid Concentration (%) 5 Cooking Time (hours) 1.0 Cooking Temperature ('C.) 80 Acid Consumption/T on Pulp 15%

Nitric Acid Pulping of Straw Acid Concentration (%) 24.0 Cooking Time (hours) 4-6.0 Cooking Temperature (°C.) 90

Alternatively Acid Concentration (%) 42.0 Cooking Time (hours) 4.0

In my process chemical concentrations are lower, processing time greatly reduced and nitrating chemical consumption does not exceed 5.5% on pulp yield.

SUMMARY OF THE INVENTION

The present invention relates to a process for treating ?brous ligno~cellulose material to form de?bered chem ical cellulose pulp. The process comprises contacting said ligno-cellulose material with an aqueous solution of a nitrate ion source to nitrate the ligneous component of said material, contacting the nitrated material produced in step (a) with an alkaline extraction liquor to extract the nitrated ligneous component to provide softened, partially de?bered cellulosic structures, and completely de?beririg said partially de?bered cellulose material wherein an aluminum compound is added to the solu tion of the nitrate ion source in an amount suf?cient to accelerate the nitration of the lignin and the process is carried out at atmospheric pressure and at temperatures below about 110° C.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram which illustrates a process for converting wood ?akes to pulp. FIG. 1A is a diagram which illustrates a process for

handling waste papers. FIG. 1B is a diagram which illustrates a process for

the pulping of wood ?akes. ' FIGS. 2-17 represent electron micrographs of vari ous cellulosic ?bers produced by the process of the present invention. FIGS. 18 and 19 are diagrams illustrating two possi

ble mechanical installations for pulping that may be used in accordance with the process of the present in

v vention. FIG. 18 illustrates a simple process involving a

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modi?ed hydrapulper for the production of pulp for paper. FIG. 19 illustrates a unit for the production of animal feed and paper pulp.

DETAILED DESCRIPTION OF THE INVENTION

The pulping process of the present invention is based on the nitration of the lignin molecule, which is not soluble in an acid solution, using a variety of chemicals as the nitrating agent, either acid or nitrate salts, and making said nitrated lignin soluble in an alkaline solu tion, either in one or two steps, under conditions of atmospheric pressure and temperatures below 100° C., in times substantially lower than conventional chemical pulp processes.

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Nitrates can be advantageously used in an alkaline solution for pulping straw in one hour at 70° C. using a concentration of 0.0125% nitrate ions in an alkaline solution of pH 13.5 using either NH4NO3 or HNO3 as nitrate sources, modi?ed with aluminum sulphate as previously described. Board made with such process characteristics is equivalent in test and performance values to semi-chemical board made by conventional NSSC pulping processes at high pressures (125 psi) and temperature (175° C.) from wood chips in 15-20 min utes. Nitric acid added as a nitrate source in the deligni ?cation of spruce wood chips in a concentration of 0.025% in an alkaline solution (pH 13.5) produces a chemical type pulp of medium strength in 1.5 hours at atmospheric pressure and at 100° C. The pulp is light in color with a Kappa No. of 125. To reduce the time of processing, and to obtain pulp

of higher purity (i.e., less lignin) and higher strength characteristics, it is advisable to use HNO3 with A11 (SO4)3—l8H2O as an accelerator as a nitrate ion source in an acid step followed by alkaline extraction of the lignin. In this approach the nitrate ion concentration will vary from about 0.125-9 weight percent nitric acid, for example, about 0.15-5 or more and preferably about 0.125 or 0.l5-1.5% for pulping straw and about 2.5%-5 weight percent for pulping wood dependent on species cooked and pulp purity desired.

Spruce chips, for example, can be cooked to a high strength pulp and Kappa No. 75 with a nitrate ion con centration of 3.8 weight percent in the cooking liquor. The nitrate ion used in contacting the dry cellulose

material can usually vary from a minimum of about 0.125 weight percent in the case of straw to a maximum of about 9 but preferably not more than about 5.5

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weight percent, in the case of wood. Actual usage of 35 nitrating chemical with recycling does not usually ex ceed 5.5% and alkali usage—again with recycling of the black liquor-is usually about 4—6%. Together, this total chemical usage compares favorably with the make-up chemicals used in the kraft process where full,

>~ expensive and complicated, chemical recovery is prac ticed.

Since the cooking liquors of this invention are simple solutions of purchased or off-the-shelf chemicals, no complex system of liquor manufacture or control is necessary, and the low concentrations and recycling

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4 capability make for low usage and cost and elimination of a recovery system. Where the black liquor that is purged is desired as a

source of energy rather than be recombined with the pulp, it can of course follow the conventional system in which the recovery boiler uses the heat of combustion of the lignin- to recover chemicals and provide process heat.

Conventional pulp mills require large capital invest ment due to the minimum size that is economic (250 tons of pulp per day), to the high temperatures and pressures involved and the absolute need to recover and mix the complex cooking chemicals. Further, substan tial investment is required for both air and water pollu tion control. The process of this invention uses simple chemicals, does not require either vacuum or superat mospheric pressure or temperatures over 100° C., offers minimal and easily avoidable problems of air and water pollution and offers high value usability of the ligneous products of pulping, normally disposed of by burning or wasted by dumping.

I have now also discovered that in the chemical pulp ing process involving nitration of particulate, ?brous ligno-cellulose raw material with various sources of nitrate ions, which may be coincidental with or fol lowed by an alkaline extraction from the material of the nitrated lignin, leaving softened, partially de?bered cellulosic structures which can further be completely defibered by normal mechanical means, the total time required for nitration/extraction can be substantially shortened by including a proportionate amount of alu minum compounds in the nitrating solution. While the precise time required for the nitration/extraction pro cess, either simultaneous or sequential, is dependent upon the variables of particle thickness, temperature and reagent concentration, it can be said for the process of the present invention that total process time is greatly reduced. For example, for chemical type high yield wood pulps from coniferous wood chips, the total pro cess time is 90 minutes using atmospheric pressure and temperatures not exceeding 100' C. This time is to be compared with conventional sulphite process time of 6-7.50 hours and the sulphate kraft process of 2.5-5.0 hours at high pressure and temperatures as set forth in the following Table 1:

TABLE 1 PULPING PROCESSES COMPARED

Liquor Concen- Total Cooking Temperature Pressure Fiber tration wt. % Time ‘C. P.S.I.G. Species

1. Casey, "Pulp and Paper", Vol. 1 p. 169 Sulphite - Bleach Grade

Calcium Base 6.0 6.25 Hrs. 140 80 Western Amonia Base 6.0 7.50 Hrs. 146 80 Conifer

2. Casey, pp. 230-264 Sulphate - High Yield 18.5 2.50 Hrs. (1) 170 140 U.S. Sulphate - Bleachable 22.0 5.00 Hrs. (l) 160 100 Southern (1) includes time to bring to temperature Pine

3. TAPPI CA Report, 52, pp. 17-19 Bagasse - Soda Process 6.5 26.50 Min. (2) 170 114 Bagasse (2) includes cooking time in blow tank

4. TAPPI CA Report 52, PP- 26-27 Bamboo - Kraft Process 17-19 1.25 Hrs. 150 85 Bamboo

5. Accelerated Pulping - Se?uential Process

Examples (Invention) HN03 NaOH High Yield Pulp 5.5/0.3 90 Min. 85-100 None U.S. Pine Sugar Cane (bleachable) 2.0/0.2 45 Min. 85-100 None Bagasse Bamboo (bleachable) 3.0/0.2 45 Min 85-100 None Bamboo Wheat Straw (bleachable) 1.0/0.2 45 Min. 85-100 None Straw Linerboard Pulp 4.0/0.2 90 Min. 85-100 None Spruce Rice Straw 0.5/0.2 45 Min. 85-100 None Straw

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TABLE l-continued PULPING PROCESSES COMPARED

6. Casey, "Pulp & Paper“ Vol. 1, p. 406 Soda

1.5

It is of course to be understood that the shortening of the pulping time in itself is not enough since pulp quality or the ?ber strength characteristics must be maintained at normal levels for commercial purposes. The use of alum (aluminum sulphate) as an accelerant is employed in this vein and its being widely recognized and used in the paper industry as a safe, inexpensive, responsive chemical makes it application in the instant process easily acceptable by industry. However, other alumi num compounds can be used such as aluminum nitrate, aluminum chloride hydrate, aluminum oxide, etc., the use of which will be dictated by cost, ready availability and safety factors. The aluminum compounds are used in the ratio of nitrate ion equivalent to the relative con centration of active available aluminum ions. The ability of the present process to be conducted at

2.00 Hrs.

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atmospheric pressure eliminates the explosive release of - pressure that is normally used in conventional systems to empty the digester. This pressure release additionally de?bers at least-partially the natural ?ber structure. The basic preservation of the ?brous structure permitted by the non-pressure system permits reduced chemical usage by easy drainage of cooking liquor and washing off of the residual cooking and black liquor leaving the ?brous structure still substantially intact. De?berization can be closely controlled to preserve long thin ?ber bundles from ?brous structures made up of very short (under 0.5 mm) ?bers vthus improving strength and maintaining good drainage characteristics even through

i the bleaching process where repeated washings present a major problem if drainage is poor.

All ‘forms of ligno-cellulosic materials can be sub jected to the pulping process of the present invention. That includes, without limitation, woody materials such as US. Southern pine, spruce, beech, and bamboo, as well as grassy materials which?ndusage such as

' straws, bagasse, and kenaf. In addition to these normally used sources of papermaking ?bers, other, now wasted, ?brous plants,‘ such as rape seed straw, and rice husks, which resist conventional pulping methods, can be re duced to commercially useful ?ber by this process. High yield shrub growth, such as coppice willow, or agricultural waste, such as cotton stalks, presently un used, produces, including its bark, an acceptable, eco nomically useful ?brous material with my process. He sides such virgin materials, the process of the present invention can be used to delignify and further de?ber paper wastes, such as waste newsprint made from me chanical (groundwood) pulp or waste corrugated boxes containing semichemical board. Additionally, using the instant invention, it is practical to economically pulp accumulations of.‘ chipped wood slab' waste and also sawdust, which is generally discarded. The raw material should be in a uniformly sized par

ticulate form before being submitted to the nitration step. Virgin plant material, for example, can be chopped, crushed, chipped, ?aked or de?bered, de pending on the initial ?brous form to be processed. Paper wastes should be mechanically pulped in water to the de?ber state, for example, to obtain a slurry contain ing about 5 to 9 weight percent preferably about 7 to 9 weight percent cellulose. Paper wastes are readily im pregnated and reacted with the nitrating agent. In the

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process, mechanical and semi~mechanical pulps can be effectively upgraded through de?bration of uncooked ?ber bundles by deligni?cation. My pulping process also permits the simultaneous removal of waste paper contaminants such as ink, plastics and wax, due to the temperatures used and the open vessel processing which permit separation of the contaminants. At the temperatures required for the pulping process and the low consistency during which reaction takes place these contaminants are released, rise to the surface, and can be aspirated easily from the vortex center of a second hydrapulper where they concentrate. Such contami nants which can represent l-,-2% of the waste ?ber furnish can be dumped along with the wire, rope and other extraneous contents found with waste paper. The process for handling waste papers is illustrated

by FIG. 10 wherein the baled waste is pulped in a nor mal way in a hydrapulper and the wire, rope, wood, sheet, or ?lm plastic removed by the conventional rag ger. The suspension of waste ?ber is then pumped to a

second hydrapulper where it is nitrated at 80°-90° C. with only moderate turbulence to permit the aspiration from the vortex of the wax, ink, styrofoam and plastic residues that will accumulate there. The nitrated, cleaned material can then be passed

through a high density press to remove excess alkali and lignin, then passed over a washer to remove excess alkali and lignin.

After de?bering, conventional paper machine prac~ tice is followed. The black liquor derived from the press 22 can be

recycled to the extraction step 21 to fully utilize any unexpended alkali or partly diverted to the paper ma chine 31 where it can be precipitated on the ?bers or to a settling basin where it can be precipitated and concen trated. _

The nitration of the ligno-cellulosic raw material is accomplished by submerging or wetting with recycled nitrating agent the material in a suf?cient amount of aqueous nitrating agent at elevated temperature, prefer ably about 75° or 85° to about 100° C., to accelerate penetration of the ?brous structure and react with the lignin. In order to permit the use of a non-pressure, open vessel for the nitration step with minimum emission of harmful nitrogen oxide vapors when using nitric acid as the nitrating agent, it is preferred to use as dilute a ni trating agent as possible with the limiting factors of time and pulp quality factors considered, say having a nitrat~ ing agent concentration ranging from 0.05 or 0.3 to about 7.0 to 7.5 weight percent, preferably less than about 4.5 or 5 weight percent. The exact percentage used will be dependent on the type of ?brous structure being pulped, the required level of deligni?cation, time limitations and pulp quality desired. The ligno-cellulosic raw material may be subjected to

steaming and/or impregnation step before the cooking nitration step. The impregnation is done ‘with a dilute concentration of the cooking liquor at low temperatures (e.g., about 70° C. or below, e.g., about 50“ C. or below) and serves three purposes:

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(a) utilization of drained concentrated liquor after the cooking process together with the dilute cooking liquor from the washing process,

(b) conservation of heat and chemicals by recycling liquor, and

(c) even moisture distribution throughout the ?brous structure before cooking.

In the process of the present invention where nitric acid is used as the nitrating agent it is augmented with a nitration accelerating amount of aluminum sulfate, pref- 10 erably about 0.8 to 1.3 parts thereof per each 10 parts by weight of HNO3. As stated above, the presence of the aluminum sulfate in the nitrating treatment serves to shorten the time necessary to convert the lignin compo nent of the raw material to lignin nitrate, while holding 15 quality levels of the resultant pulp at acceptable levels of strength. Normal usage is about 1 part of the alumi num sulfate (Al2(SO4)3>< 181120) per each 10 parts by weight of HNO3 (100%).

Alternatively other aluminum compounds can be 20 used in the pulping process, e.g., aluminum salts of inorganic acids such as aluminum chloride, aluminum phosphates and aluminum nitrate, and aluminum oxides such as AIZOQHZO. The aluminum compounds should be soluble in the aqueous nitric acid used in the pulping 25 process. The aluminum compounds should be used in amounts

to achieve a sufficient aluminum ion concentration in the pulping liquor, often at least about 0.01 part, prefer ably about 0.065 to 0.105 part, by weight of aluminum 30 ions per each 10 parts of HNO3 (100%).

It has been found, however, that with exceeding a certain aluminum level no further advantage as to time reduction is obtained so that higher amounts are not desirable for both economic and environmental pollu- 35 tion reasons. The preferred range is approximately 0.065 to 0.105 part by weight of aluminum ions per each 10 parts by weight of HNO3, a value of about 0.08 per 10 parts giving desirable results in the practice of the process of the instant invention. 40 The amount of nitrating agent used in the nitration

step should be suf?cient to completely submerge or contact by recirculation the particulate ligno-cellulosic material and adequate, on a stoichiometric basis, to nitrate substantially all of the readily accessible lignin 45 content of the raw material. This will usually mean, for example, formation of a mixture of about 5 parts of liquid nitrating agent to about 1 part of dry wood to about 10 parts of liquid nitrating agent for 1 part of dry grass ?ber (straw). Where the nitration liquor can be 50 circulated and heated indirectly, lower ratios can be used. Additionally, the nitrating agent, either acid or nitrate salt, may be sprayed or it may be foamed in low concentration where minimum quantities but overall intimate contact may be needed. 55 The temperature at which the nitrating cooking step

is performed should be adequate to effect nitration of

8 the lignin, but is preferably not so high (over 100° C.) as to cause degradation of the cellulosic ?bers or so low-below 75°—to take excessive reaction time. Tem peratures in the range of about 75° or 85° to 100° C., in particular about 85° to 95° or 100° C., are preferred. The nitration-extraction process of the present inven

tion can be performed in a short period of time, under atmospheric pressure conditions, although above atmo spheric pressures, e.g., up to about 10, 15 or 35 p.s.i.g., can be used if it is desired to shorten further the time, but can be used chie?y to provide ease of production on a continuous basis. The pressure may be up to about 150 p.s.i. g. and such may be particularly advisable in certain situations as noted below. The improvement provided by the present invention is independent of whether the process is conducted under atmospheric pressure or at elevated pressures. The introduction of a non-pressure system is designed speci?cally for use in new and rela tively small pulping installations (l0~50 tons per day) throughout the world. However, it is recognized that the requirement for larger production units can be met by larger or multiple units and that in many instances existing pulp mill equipment could be utilized to reduce further investment costs while minimizing present pol lution problems.

All present commercial systems employ high pres sures and temperatures coupled with long cooking peri ods for pulping woody ?bers to chemical grade pulps. It has been found that by cooking with light pressures (e.g., up to about 15 to 35 p.s.i.g.) while holding temper atures certainly below 110° C. and preferably below about 100° C., the nitration period can be shortened to about 5 to 7 or 10 minutes for wood ?akes, straw, etc. Conventional sized wood chips, 6-20, but generally 10-20 mm., thick are usually too irregular in size for cooking by the instant process and must be made uni form and generally smaller in size to achieve uniformly cooked and de?berable pulp of normal quality levels in one hour’s time. Using light pressures with either wood ?akes or chips

makes practical the conversion of existing sulphite pulp mills to the process of this invention. However, the use of pressure for pulping any ?brous structure or wood ?akes or chips is not necessary and is recommended only to ?ll the utilization possibilities of existing installa tions.

Pulping systems, such as the “Kamyr" or "Pandia”, which are continuous, operate at high pressure, about 150 to 175 p.s.i.g. These units are also adaptable for processing wood chips in one stage in accordance with the present invention to produce a semi-chemical type product or full chemical pulping.

Typical times and conditions at these different pres sures for treating several ligno-cellulosic materials and where an alkali deligni?cation state is being used, are in Table 2a.

TABLE 2a COMPARATIVE HNO3 PRESSURIZED NITRATION CYCLES CHEMICAL OR DELIGNIFIED PULP WITH ALKALl STAGE

A. Non-Pressure System - Wood Flakes or Equivalent

Pine Spruce Beech Straw Cooking Time Minutes 15 15 l5 15 Temperature '‘C. 85-100 85-100 85-100 85-100 Liquor Concentration % Acid 5.5 5.0 4.0 1.0

B. Pressure 15-35 P.S.I.G. - Wood Flakes or Equivalent

Pine Beech Straw Bamboo Cooking Time Minutes 7 7 5 7

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4,652, 34 1 9 .

TABLE Za-continued COMPARATIVE l-1NO3 PRESSURIZED NlTRATION CYCLES CHEMICAL OR DELlGNlFlED PULP WITH ALKALI STAGE

10

_ and extending the time of reaction slightly, e.g.,

Temperature °C. 100-1 10 100-110 l00-110 100-110 Liquor Concentration % Acid 5.5 3.5 0.5 2.5

C. Non-Pressure System - Wood Chips Spruce Beech

Cooking Time Minutes 60 40 Temperature °C. 95-100 95-100 Liquor Concentration % Acid 4.0 3.5

D. Pressure 15-120 P.S.l.G. - Wood Chips

' Beech

Spruce Beech Semi-Chemical Cooking Time Minutes 45 30 15 Temperature °C. 100-110 100-110 110 Liquor Concentration % Acid 4.0 3.5 3.0

Additionally, it has been found that the use of pres sure permits full de?bering of wood ?brous structures in the acid nitration stage, and a lignin alkali extraction stage may thus be avoided since the lignin component is hydrolyzed by this stage. This can be accomplished when nitric acid is the nitrating agent by raising, depen dent on ?brous structure processed, the HNO3 liquor concentration by about 2.5 to 3.5% over that employed for the normal nitration-alkali deligni?cation sequence,

by about 3-5 or more minutes. ‘

Thus, without usingpressure, i.e., when conducting

20

25

false pressure is created, permitting the keeping of oper ating temperatures below 110° C. thus avoiding cellu lose degradation. The degree of false pressure created is dependant on nitrating agent concentration.

Typical times and conditions at different elevated pressures for treating several ligno-cellulosic materials without there being an alkali deligni?cation state, are in Table 2b. Where additional pressure is needed, as in the “Kamyr” pulping process, it can easily and economi cally be obtained with air injections. The low tempera tures involved reduce the chronic problems of scaling and maintenance to a minimum.

TABLE 2b Comparative HN03 Pressurized Nitration Cycles, Alkali Delignifaction Stage Eliminated

A. Pressure 15-35 p.s.i.g. - Wood Flakes or Eguivalent

Chemical Pulp Pine Beech Straw Bamboo

Cooking Time Minutes l0 l0 6 10 Temperature °C. 100-1 10 l 10 l 10 1 10 Liquor Concentration % 9.0 5.5 1.5 5.0

B. Pressure 100-150 p.s.i.g. - Wood Chips

Chemical Pulp M

Cooking Time ' Minutes 45 45 Temperature °C. 100-110 110 Liquor Concentration % 8.0 5.5

C. Pressure 35-150 p.s.g.i. - Wood Chips

Semi-Chemical Pulp Mixed Hardwoods - Beech

Cooking Time Minutes 10 Temperature °C. 100 Liquor Concentration % 4.0

the process under approximately atmospheric pressure conditions, the HNO3 liquor concentration may be up to about 5.5 weight percent, preferably up to about 5 weight percent. When employing elevated pressures, the HN03 concentration may be no more than about 7 to 7.5 weight percent, and thelower concentrations as stated for the non-pressurized nitration step can be ad vantageously used. '

For grassy ?brous structures pressure is not necessary and only a 0.5-l% additional acid concentration is re quired. ' ’

This embodiment of the present invention without an alkali stage produces a ?ber with different strength characteristics from that obtained when deligni?cation is accomplished by alkali ‘extraction. The ?ber is, how ever, of very light colour, high yield and can be easily bleached.

Regardless of the pressure employed, it is not neces sary to vent any gases, in fact it is preferable, since with the gases contained and retained in the treating vessel, a

50

55

65

The ability to conduct the nitration step at atmo spheric pressure means that non-pressure vessels can be employed, providing a substantial savings in equipment and operating cost compared to conventional high-pres sure pulping processes. Although a non-pressure vessel is employed for the nitration step, it is preferred to maintain closure with recycling of any vapors to pre vent heat loss and possible emissions. Present environ mental laws in the USA. permit a maximum nitrogen oxide emission level of only 185 ppm. The precise tem perature at which nitrogen oxide or other gases can be released from the slurry in the nitration step will depend upon the concentration and form of the nitrating agent, since the higher the concentration, the lower will be the temperature at which vapor emissions will occur. By way of further explanation, nitric acid decom

poses at about 86° C. into water and nitrogen oxide gas, which is potentially lethal and can be explosive when in highly concentrated form. Where an impregnation step

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