US3762989A - Pyrolysis of spent pulping liquors - Google Patents

Abstract

Disclosed is a process for recovering the organic values in spent pulping liquors by heating aqueous spent pulping liquor in the absence of additive reagents at 490*-700*F under 1,000-3,500 lbs/sq. inch pressure for from 10 minutes to 3 hours to obtain a vapor containing organic valves therein, a solid precipitate containing organic valves therein, and an aqueous effluent.

Description

United States Patent Timpe 1 1 Oct. 2, 1973 [5 PYROLYSIS 0F SPENT PULPING LIQUORS 3,404,063 10/1968 Harding .1 162/16 2,999,044 9/1961 Collins, Jr.... 162/30 [75] Inventor: Wmined G. Timpe, New C1ty, N.Y. 3,111,378 "963 Mugg I I M 23/48 73 Assigneez St. Regis Paper Company, New 3,366,535 1/1968 Cann 162/30 York NY 1,606,338 11/1926 Bradley et al.... 23/49 3,525,666 8/1970 Brannland 162/30 [22] Filed: July 30, 1971 2,750,290 6/1956 Schoeffel 162/36 X 3,244,621 4/1966 Bouthilet 210/39 X 1 1 pp N06 167,871 3,274,104 9/1966 Hamilton 210 39 Related US. Application Data [63] Continuation of Ser. No. 819,817, April 23, 1969, Bashore abandoned, Assistant Examiner-Alfred DAndrea, Jr. AttorneyRaymond J. McElhannon et a1.

[52] US. Cl 162/30, 162/16, 210/71,

' 423/207 57 ABSTRACT [51] Int. Cl. D211: "/12 I 58 Field of Search 162/16, 30, 32, 3s, P PYOFeSS recovirmg the ("game Values 3 49 1n spent pulpmg llqUOl'S heating aqueous spent pulp- 39 423/207 208 ing liquor in the absence of additive reagents at 490-700F under 1,0003,500 lbs/sq. inch pressure [56] References Cited for from 10 minutes to 3 hours to obtain a vapor containing organic valves therein, a solid precipitate con- UNITED STATES PATENTS taining organic valves therein, and an aqueous effluent. 3,607,619 9/1971 Hess et a1. 162/30 3,595,742 7/1971 Hess et a1. 162/30 13 Claims, 3 Drawing Figures W/flTE W000 A/QVUR, fl/-sfga tw 0247025 5446/1 z/qwoe PULP TALL O/L Mfl/(f 0P GHEM/CflLS KCUK E/QJ D/'SOL 1///1/6 Sip/M275 AI/Vp WAS/4 C'AZ/ST/C/ZY/VG L/ME x400 1 Z/QUO/Q L/IWE K/Ul/ SZ/1W6Q, 7? W000 PATENTEUUET 21915 I 3.762.989

INVENTOR.

W/A/Ffl/ED GEORGE 77/14/ 5 /4406 @MMs JW Anna/554$ PYROLYSIS OF SPENT PULPING LIQUORS This application is a continuation of my copending application Ser. No. 8l9,8l7,'filed Apr. 28, l969, now abandoned.

This invention relates generally to the pulping of wood or other lignocellulosic material, and to the treatment of the spent liquor produced in such pulping. More specifically, the invention relates to the conversion of the non-fibrous materials in wood or other pulp source to activated carbon and the use of such carbon for the purification of the water utilized in pulping and paper making operations. The invention relates also to the recovery of valuable organic chemical from the spent liquor and to the regeneration of fresh pulping liquor.

It is a special feature of this invention that it makes possible the operation of a so called closed mill. That is to say, now, for the first time, water taken in from a natural source, such as streams or wells, for use in the various process steps in the mill can be purified and reused without returning all of it to its original source. Thus, once a mill is in operation it is only necessary to supply from the natural water source, the relatively small amounts lost through evaporation and leakage. More importantly, since the water is utilized and con tinuously recirculated, polluted water need not be dumped from the mill and returned to the ground.

An additional and highly significant feature of the invention is that it obviates the use of the recovery boiler which is normally used in the treatment of spent liquor solids. This boiler, as is known, is inefficient as a heat source and is subject to dangerous explosions.

BACKGROUND OF INVENTION For the manufacture of paper, wood or other pulp source such as bagasse, or kenaf is first subjected to a pulping operation to separate the cellulosic fibers which are used in papermaking from the other components of the wood or alternate source. These other components comprise approximately fifty percent of the original solids in the source, and are principally organic chemical values such as hemicelluloses, lignin and derivatives thereof. In the pulping operation these organic chemical values are solubilized by the action of the pulping chemicals. The insoluble pulp is separated by filtration for the manufacture of paper to leave a filtrate which contains a large quantity of dissolved organic chemical values. It is normally referred to as spent liquor, or in the kraft process as black liquor.

The dissolved chemicals, which include both the organic chemical and those inorganic chemicals which are formed in pulping or did not react in the pulping procedure, are referred to as spent or black liquor solids.

Spent liquor and its solids content have been the object of intensive study in the paper industry for a number of reasons. One of these is that the liquor is a potent source of pollution of ground water. Another is that it is a possible source of valuable organic chemicals. Still another is that it is wasteful to dispose of the used pulping chemicals without attempting to recover them for reuse.

As a result of intensive efforts through the years a number of pulping procedures have been devised which include the recovery of spent liquor solids and the regeneration of pulping liquor as integral process steps. In all of these procedures the pulp is produced and separated from the source following the general procedures described above. The pulping mixture may be alkaline or acid. Usually it is alkaline, and includes an alkali or alkaline earth 'metal hydroxide as the principal pulping chemical. The most widely employed pulping procedure is the kraft method in which an aqueous mixture of sodium hydroxide and sodium sulfide is utilized. In the polysulfide method the pulping liquor contains sodium hydroxide, sodium sulfide and sodium polysulfide formed from reaction between the sodium sulfide and elemental sulfur. Recently a hydrogen sulfide-alkaline pulping procedure has been described. In this method, wood chips or other lignocellu losic materials are initially treated with hydrogen sulfide in the presence of an aqueous solution containing a mildly alkaline buffer such as sodium carbonate. After this treatment, the chips are subjected to conventional kraft pulping. This procedure is said to afford an increase in yield of about 6 to 7 percent. These pro cesses are generally referred to as alkaline pulping. The process of this invention is applicable to all alkaline pulping procedures.

Sulfite pulping procedures may be carried out under acid, neutral or alkaline conditions. In the acid sulfite process, the aqueous pulping liquor contains calcium or magnesium sulfite and sulfur dioxide. The pH of the mixture is about 2. In neutral sulfite processing the pulping mixture contains sodium bisulfite and a buffer, usually sodium carbonate. Alkaline sulfite pulping is generally employed as a precursor to acid sulfite pulping. The processing liquor contains sodium hydroxide and sodium sulfite. It has been found that by utilizing a pretreatment with an alkaline sulfite liquor, the ordinary acid sulfite treatment can be extended to the use of woods which are not usually susceptible to acid sulfite pulping. The process of this invention is applicable to all types of sulfite pulping for the processing of all types of spent liquors to recover organic chemical values, to regenerate pulping liquor, to purify effluent water and for other purposes.

The invention will now be described in detail as applied to improve a standard kraft pulping system. It will be understood, however, in view of what has been said, that the process is applicable to all pulping procedures and liquors, and that the description herein is applied particurly to the kraft system, as a matterof convenience for the purpose of exemplifying the invention.

THE INVENTION This invention will be better understood by reference to the attached drawings in which:

FIG. I schematically illustrates the conventional kraft process.

FIG. [I schematically illustrates the one embodiment of the invention as the same is applied to black liquor from the kraft process.

FIG. III schematically illustrates a variation of the invention which will be described in more detail hereinafter. a

In the conventional kraft process for the pulping of wood or other lignocellulosic material, the pulping source is initially digested in an aqueous mixture containing, by weight, approximately 9 percent sodium hydroxide, 3 percent sodium sulfide, 0.5 percent sodium sulfate and 2 percent sodium carbonate. The balance is mostly water. The pulping reaction is carried out at a temperature of from about 325F to 375F during a period of from about 1 to 6 hours. During the reaction period the lignin which is principally composed of polymeric phenolic compounds is dissolved leaving the pulp free for separation, usually by filtration. There is some cleavage of phenolic and alkyl groups from the lignin and this gives rise to accumulations of phenol, lower alkyl mercaptans and disulfides such as methyl mercaptan and dimethyl sulfide in the filtrate or black liquor.

From the wood digester the black liquor having a solids content of about 16 percent by weight is brought through an evaporator or series of evaporators of standard design to remove water and increase the solids content to about 23 percent to 27 percent. The evaporators are usually flash or multiple effect evaporators or combinations of these, although other types of evaporators can be employed.

At this point, i.e. 23-27 percent solids content, a mixture of salts, principally sodium salts of fatty and resin acids separates from solution. The mixture of salts, which is called tall oil soap, is recovered and the remaining solution further evaporated, usually in multiple effect evaporators to a solids content of 50 percent to 65 percent by weight.

The solids content comprises, for the most part, sodium sulfide, sodium hydroxide, sodium carbonate formed from the sodium hydroxide during digestion of the wood; sodium sulfate from a source which will be discussed hereinafter; salts of lower organic acids; and salts or lignin, cellulose and hemicellulose; as well as decomposition products of these polymeric materials which are formed during digestion. The object of the kraft recovery procedure is to recover from this mixture as much of the sodium and sulfur values in the form of sodium hydroxide and sodium sulfide as possible so that the same can be used to regenerate pulping liquor or, as it is often called, white liquor.

The concentrated black liquor is then sprayed into a recovery boiler where it is burned. The top section of the recovery boiler is an oxidizing section. In this section the water is evaporated and the oxidizable solids content converted to oxidation products. This is accomplished by burning in the presence of air. A portion of the sodium sulfide is converted to sodium sulfate, or to intermediate oxidation products such as sodium sulfite or thiosulfite. Much of the organic content is converted to carbon dioxide, most of which is ultimately vented to the atmosphere, and some of which reacts with other sodium compounds present to form sodium carbonate. The sodium salts fuse to form a smelt which is principally sodium sulfide and sodium carbonate, but also contains minor amounts of sodium sulfate, sodium sulfite and thiosulfite, together with sodium hydroxide. The smelt is collected from the bottom of the boiler.

The heat from the recovery boiler is utilized to make some of the steam which is required for various purposes in the mill. The recovery of heat values from the burning of the solids in the recovery boiler is only about 65 percent. The principal reason for this is that much of the heat is used to convert the water content of the concentrated black liquor to steam which escapes in the stack gas from the boiler.

The stack gas also contains appreciable amounts of sulfur in the form of hydrogen sulfide, sulfur dioxide, and methyl mercaptan or other lower alkyl sulfur compounds. These sulfur compounds have a very offensive odor so that their venting to the atmosphere is most objectionable and a source of atmospheric pollution. Ad-

ditionally, they represent a considerable loss of the sulfur values present in the original pulping liquor.

The losses of sulfur through the stack gas are normally replaced in the standard kraft process by adding make-up chemicals, principally sodium sulfate to the concentrated black liquor before it enters the recovery boiler. Most of the sulfur in the make-up chemicals appears as sodium sulfide in the smelt. A small amount remains unconverted and it is this sodium sulfate, which continues to circulate through the whole recovery system. lt appears in the solids content of the black liquor from the digestion and the evaporating system.

The smelt from the recovery boiler goes to a dissolving tank where it is dissolved in water to provide a solution containing principally sodium carbonate and sodium sulfide. This solution, called green liquor, next goes to a causticizing tank where it is contacted with calcium hydroxide to produce a solution of sodium sulfide and sodium hydroxide. This solution is useful as a pulping liquor or can be enriched or diluted to form a pulping liquor.

The reaction for the formation of sodium hydroxide results in the precipitation of calcium carbonate. The precipitant is washed and then heated in a lime kiln to form carbon dioxide and calcium oxide. The former exits the kiln as stack gas and the latter is slaked with water to regenerate calcium hydroxide.

The various alkaline and sulfite systems, especially the kraft system, are widely employed in the production of pulp and paper. The kraft system is utilized in the production of hundreds of thousands of tons of pulp and paper each year in the United States alone. There are, however, many problems associated with the usage of the various systems. For example, even with the most careful control, large amounts of relatively impure water are returned to the stream or other source of water. Additionally, as pointed out above, the burning of the concentrated black liquor in the recovery boiler is not an efficient method for the conversion of the potential heat energy present in the organic chemical values of the spent liquor solids. Furthermore, and this is a very significant factor in those mills operating on the kraft system, certain of the reactions in the recovery boilers may take place with explosive violence. Accordingly, considerable effort has been expended to make it possible to purify effluent water from the mill, to recover organic chemical values from the solids content of the spent liquor, to avoid the use of the recovery boiler and to generally attain increased efficiency in heat production and use. Despite these massive efforts, no wholly satisfactory procedure has yet been discovered.

A simple and efficient process has now been discovered according to this invention which makes possible the elimination of the recovery boiler from pulping liquor regeneration systems. By the use of the process it is possible to recover organic chemical values from the spent pulping liquor, to burn these organic values more efficiently to produce heat energy, and, if desired, produce a sufficient amount of activated carbon to purify all of the water produced in the various operations in a pulp and paper mill, including pulp making, pulp bleaching and paper making so that the same water can be used over and over again without a constant requirement for huge quantities of fresh water.

What has been discovered is that the major portion of the original organic chemical values in spent pulping liquor solids can be converted to a water insoluble fraction by heating under pressure. FIG. ll illustrates the operation of one embodiment of the process including the important step of hydropyrolysis to separate organic chemical values. The process is applicable to the black liquor as it comes from the kraft digestor at a solids content of 16 percent, by weight, or even lower, or indeed at any solids content up to, for example, 65 percent by weight, or even higher. Preferably, however, the hydropyrolysis step will be introduced into the white liquor regeneration and recovery system when the solids content of the black liquor is about 23 percent to 27 percent, by weight, after removal of the tall oil salts.

in the process, the black liquor to be treated is heated under a pressure, usually autogenous, of from about L000 to 3,500 pounds per square inch during a period of from about minutes to 3 hours. The temperature of the hydropyrolysis step is from about 490F. to about 700F.

The preferred conditions for purposes of economy and efficiency are 550F. to 650F., 1,300 to 2,700 pounds per square inch pressure for a period of from minutes to 1 hour.

During hydropyrolysis, the major portion of the organic chemical values separate as a water insoluble precipitate. The inorganic constituents of the precipitate are principally sodium carbonate with minor amounts of sodium sulfate, sodium sulfide and sodium bicarbonate also present.

The insoluble precipitate is separated by filtration or analogous process and the solution containing the dissolved inorganics is brought directly to the causticizing tank where the sodium carbonate is converted to sodium hydroxide by the process described above. The aqueous solution from the causticizing tank contains mostly sodium hydroxide. Reaction of the alkaline solution with hydrogen sulfide (preferably from a source hereinafter described) converts a sufficient quantity of sodium hydroxide tosodium sulfide to make a solution useful for pulping liquor.

As indicated above, hydropyrolysis is effected at a pressure of from about 1,000 to 3,500 pounds per square inch at a temperature of from about 490F. to about 700F. The vessel in which hydropyrolysis takes place is vented to a condenser to condense water and the less volatile components of the hydropyrolysis vapor fraction of the organic chemical values originally present in the black liquor solids. These include hydroxylated, monocyclic aromatic compounds, principally phenol and cresols. These may be separated and recovered using standard techinques. One fraction of the total organic chemical values in the black liquor solids is thus recovered by hydropyrolysis followed by condensation of the vapor.

The uncondensed fraction of the gas or vapor stream generated during hydropyrolysis contains principally methyl mercaptan and dimethyl sulfide together with appreciable quantities of carbon dioxide, hydrogen sulfide, hydrogen, methane and other hydrocarbons containing up to three or more carbon atoms as well as other sulfur containing organic compounds. This stream is subjected to any of the well known thermal cracking or hydrodesulfurization processes widely employed in the petroleum industry for removing sulfur from a hydrocarbon stream and converting it to hydrogen sulfide. The products resulting from this treatment will include principally hydrogen sulfide, but there will be some hydrogen, oxides of carbon, and hydrocarbons. All of these compounds can be separately recovered if desired. Normally the hydrogen sulfide will be separated by passing the stream through water and the balance of the stream will be employed as fuel for the power boiler. In the kraft system as described herein, the hydrogen sulfide is utilized in a hydrogen sulfide absorption tank to converta part of the sodium hydroxide from the causticizer to sodium sulfide.

As mentioned above, the major fraction of the organic chemical values in the black liquor solids is insolubilized during hydropyrolysis. The water insoluble fraction is separated, for example, by filtration, and, in accordance with the invention, is next converted to activated carbon for use in purifying the water used in the plant. After its use for purification purposes, the carbon with the absorbed impurities from the water is available as a fuel for the plant power boiler, or may be reactivated for reuse. Of course, the precipitated solids need not be converted to activated charcoal. They may instead be conveyed directly to the power boiler for burning. If the solids are utilized directly in the power boiler, they will ordinarily be water washed to remove any water soluble inorganic materials which coprecipitate with organic chemical values, and then dried before burning.

Any of a wide variety of the well known thermal cracking procedures can be used to convert the sulfur containing organic compounds to hydrogen sulfidejln these procedures the gas stream containing the compounds to be converted are contacted at an elevated temperature with an appropriate catalyst either in a fixed or fluid bed. Often the reaction is carried out under elevated pressure. Typical catalysts which have been employed include metallic sulfides and oxides particularly cadmium or nickel sulfides and mixed cobalt-molybdenum-nickel oxides or cobaltmolybdenum-aluminum oxides. The temperature of the reaction may vary within wide limits, and temperatures in the range of from about 550F. to l,200F. are not unusual. Pressures up to 200 atmospheres are often employed.

The solids are washed and activated in the usual way. They may be carbonized initially by heating at about 800F. to 1,200F. for 5 to 30 minutes in a conventional carbonizing atmosphere. It is not necessary to carbonize. The solids may be activated directly by heating at an elevated temperature of at least l,400F., but preferably at a higher temperature, for example, from about 1,600F. to about l,800F. during a period of from about 15 to 45 minutes in a conventional carbonizing and activating atmosphere. A suitable atmosphere for carbonizing and activating will contain carbon monoxide, carbon dioxide, steam and nitrogen. Other reducing atmospheres are known arid can be utilized.

The activated carbon produced in this manner canbe water grade, decolorizing grade, or gas purification grade depending upon the conditions employed.

It may be advantageous to mix the precipitated solids or char with a binding agent before they are treatedin the activating furnace. This permits easier handling of the char. Preferably the binder is a material which is itself converted to activated carbon by treatment in the furnace. A convenient binding agent which is often available in many pulp and paper mills is tall oil pitch.

This material is the tarry bottoms which are collected during the purification of tall oil by distillation.

A special feature of this invention is that the bark. sawdust, fly ash, and other carbonizable wood wastes which accumulate in large quantities in a pulp mill may be usefully incorporated in the recovery stream. They may, for example, be mixed with the char before it is converted to activated carbon. Preferably, the wood wastes are mixed with the concentrated black liquor before hydropyrolysis where their presence helps to keep the precipitating solids from collecting on the walls of the hydropyrolysis vessel. Additionally, the heat treatment which the wood wastes receive in the black liquor results in their more facile conversion to carbon. The ratio of the spent liquor solids, or of the char, to wood wastes may vary on a parts by weight basis of from about 1:1 to 10:1 or even higher. The process is most efficient and economical when the ratio is from 6:1 to 3:1.

The process of this invention has a number of advantages, as will be seen from the above. It permits the omission of the recovery boiler in the kraft system so that those organics which are burned for their heat value are burned in a power boiler, not a recovery boiler. There is little or no water present during the burning so that heat values are preserved. Additionally, the chemical values in the spent liquor solids are utilized as a source of activated carbon for purifying the water utilized in the mill so that it can be repeatedly reused.

A most surprising aspect of the hydropyrolysis reaction is that during the treatment some of the sodium sulfate present in the concentrated spent liquor is reduced to sodium sulfide. This is a most important feature of the invention since it means that the same sulfur make-up chemicals used in the kraft process, comprising principally sodium sulfate, can be used for the new improved process. The reduction is enhanced by increasing the amount of vapor which is vented from the hydropyrolysis vessel. The efficiency of the process of this invention is at such a high level that only relatively small amounts of make up chemicals need to be added. This means that the reduction can be controlled by venting the vapor in the most economical manner in respect of energy utilized, hydrogen sulfide produced and other factors.

It will be understood that the water purification referred to herein need not be the only purification treatment that the water from the mill will receive before reuse, or before return to ground. This treatment normally will be in addition to the usual primary or primary plus secondary purification treatments ordinarily employed to purify used water before returning it to ground. Primary and secondary treatments usually comprise removal of floating solids reoxygenation and microbiological treatment. They provide water at a purity level which is acceptable for return to ground but not for reuse in the mill. The purification procedure contemplated here is a tertiary treatment in which the water which has already been subjected to primary and secondary treatments is further purified by contact with activated carbon to make it reusable in the mill, or to further increase its purity before return to ground.

From an economic point of view, perhaps the most significant aspect of this invention is that it reduces the cost of producing activated carbon by more than one hundred percent over ordinary industrial methods. The

importance of this point is that at the new cost level, which was not possible heretofore, it is economically practical to operate a closed mill, that is one in which there is substantially no return of used water to ground.

FIG. III schematically illustrates an improved aspect of this invention in which the black liquor with a solids content of about 23-27 percent is first contacted or stripped by passage of a stream of carbon dioxide through it. An excellent source of the carbon dioxide is the carbon dioxide-steam mixture in the flue gas exiting the lime kiln, and the presence of steam and nitrogen in the flue gas will not be harmful.

When the black liquor is exposed to carbon dioxide the following reactions take place:

Na S co H2O Na CO H28 Na CO c0 H2O ZNaHCO ZNaOH co Na CO H2O One result of this series of reactions is that the hydrogen ion concentration of the black liquor concentrate increases from a pH of about 13.5 to a pH of about 8.9. This causes certain of the organic constituents of the black liquor solids to convert from the water soluble salt form to insoluble, neutral or acid forms. These constituents are principally lignin or lignin derivatives produced or liberated during digestion of the wood with the pulping liquor. Lignin is a polymeric substance containing relatively large numbers of phenolic hydroxyl groups which are converted to the sodium phenolate form during digestion. This has the effect of solubilizing the lignin or any of its phenolic group containing decomposition products. When the hydrogen ion concentration increases these salts are neutralized and the organics precipitate.

If desired the precipitate can be further treated to isolate pure organic compounds such as lignin itself. Normally, however, it will be carbonized and converted to activated carbon by the procedure described above.

The precipitate is separated from the stripped black liquor, for example, by filtration. The filtrate is then subjected to hyrdropyrolysis using the same procedure described above.

The stripping process is preferably carried out at a temperature of from about 140F. to 205F. in the presence of at least the stoichiometric amount of carbon dioxide. To insure as complete a reaction as possible it is preferred to use an excess, for example, a 20 percent to percent excess of carbon dioxide.

The gas stream leaving the stripping vessel contains principally carbon dioxide and hydrogen sulfide. The two gases can be separated by any convenient method, for example, by preferential absorption of the hydrogen sulfide on a resin, followed by desorption. The hydrogen sulfide can be used to convert the sodium hydroxide from the causticizing tank to sodium sulfide.

There are many advantages to using hydrogen sulfide stripping in association with the overall process of this invention. One advantage is that there is a greater overall recovery of organic chemical values both as condensed liquids and as precipitated solids. Another is that the solids which precipitate during hydropyrolysis after hydrogen sulfide-stripping tend to be less viscous and adhesive and therefore easier to handle than when hydropyrolysis alone is used. Still another is that the gas stream which is subjected to thermal cracking is decreased in volume by the amount of hydrogen sulfide removed by stripping. This appreciably reduces the cost of the thermal cracking appratus and procedure.

The following non-limiting example illustrates the process of this invention.

Example 1 Ten thousand gallons of black liquor from a kraft pulping recovery operation is concentrated to a solids content of about 25 percent by weight and the tall oil soap removed. It is heated for about 30 minutes at a temperature of 600F. and a pressure of 2,000 pounds per square inch in a hydropyrolysis reactor equipped with an agitator and a condensor. During the heating period a charry, black precipitate forms, and it is separated by filtration and washed with water. The washings and filtrate are combined. The precipitate which weighs approximately 6,000 pounds on a dry basis is separated into two equal fractions. One fraction is found to be an excellent fuel for the power boiler.

The second fraction is heated in a Herreshoff furnace at 1,675F. for 30 minutes in an atmosphere of carbon monoxide, carbon dioxide, steam and nitrogen to produce approximately 1,000 pounds of water grade activated carbon.

A mixture of 100,000 gallons of combined effluent from a kraft pulp and paper mill including liquors ob tained from the pulping and bleaching operations together with water used in the paper making is subjected to primary and secondary purification in the usual manner and then contacted with 200 pounds of the activated carbon produced as described above by stirring the carbon in the effluent water at ambient temperature for 30 minutes. The water is tested and found to be of suitably high purity for reuse in a mill for pulp and paper making purposes. The carbon is recovered by filtration and found to be an excellent fuel for the mill power boiler.

The vapor from the hydropyrolysis reaction is condensed with running tap water to recover a condensate from which water, phenol and cresols are separated. The uncondensed fraction of the vapor is passed over a bed of powdered cadmium sulfide catalyst in a tube reactor at a temperature of 1,000F. to convert the major portion of the sulfur containing organic compounds in the gas stream to a mixture containing ethylene, methane and hydrogen together with approximately 600 pounds of hydrogen sulfide.

The combined filtrate and washings from the hydropyrolysis reaction are causticized with calcium hydroxide in the usual manner to produce an aqueous solution containing a large amount of dissolved sodium hydroxide together with a lesser amount of sodium sulfide and sodium sulfate. The gas stream from the thermal cracking operation is passed through this solution to increase the concentration of sodium sulfide. The insoluble components in the gas stream pass through the solution and are useful as fuel in the power boiler. The hydrogen sulfide treated solution is suitable for use in the pulping process.

The process is repeated, except that before hy dropyrolysis a stream of carbon dioxide and steam is passed through the concentrated black liquor until the pH is reduced to 9. The precipitate which forms is separated by filtration and washed with water. The washings are combined with the filtrate from the hydropyrolysis step. The precipitate is carbonized by heating at 900F.

for 20 minutes and then converted! to activated carbon as described above.

I claim:

1. A method for the separation of lignin and derivatives thereof from an aqueous spent liquor solution formed by reaction in aqueous medium at elevated temperature of a lignocellulosic material with an alkaline pulping liquor which reacts with said material to form fatty and resin acid tall oil soap, which method comprises: separating the aqueous spent liquor solution from said pulp and concentrating until the tall oil soap content separates out, removing the tall oil soap from said liquor and passing a stream of carbon dioxide and steam through the remaining aqueous spent liquor solution thereby to cause lignin and derivatives thereof to form a first insoluble precipitate, separating said precipitate by filtration from the remaining aqueous solution and subjecting the remaining solution to heating in the absence of additive reagents at a temperature of from about 490F. to about 700F. under a pressure of from about 1,000 to about 3,500 lbs/sq. inch for a pe riod of from about 10 minutes to 3 hours whereby an additional portion of said organic chemical values separates from said aqueous solution as a second solid precipitate and a further portion is evolved as a vapor.

2. A method as in claim 1 wherein said heating is effected at a temperature of from 550F. to 650F. and under a pressure of from 1,300 to about 2,700 lbs/sq. inch for a period of from about 20 minutes to l hour.

3. A method as in claim 1 wherein said second precipitate is separated by filtration from the remaining aqueous solution.

4. A process as in claim 1 including the further steps of cooling said vapor portion to form a condensed fraction comprising hydroxylated, monocyclic aromatic compounds and an uncondensed fraction comprising methyl mercaptan and dimethyl sulfide.

5. A method as in claim 4 including the additional step of thermally cracking the uncondensed fraction to produce hydrogen sulfide.

6. A method as in claim 5 including the further step of purifying the effluent water produced in the pulping operation by contacting it with at least a portion of the activated carbon produced.

7. A method for the separation of organic chemical values present in an aqueous spent liquor solution resulting from reaction in aqueous medium at elevated temperature of a lignocellulosic material with a sodium and sulphur containing pulping agent and removal of the pulp, which comprises: heating the aqueous spent liquor solution in the absence of additive reagents at a temperature of from about 490F. to about 700F. and under a pressure of from about 11,000 to about 3,500 lbs/sq. inch for a period of from about l0 minutes to 3 hours to evolve a first portion of said organic chemical values as a vapor containing organic chemical compounds and sulphides and to precipitate a second portion of said values from the remaining aqueous solution containing sodium compounds, separating said precipitate from said solution for separately recovering said precipitate and sodium values, cooling said vapor to condense and separate organic values therein, and recovering sulphur values from the uncondensed vapor as hydrogen sulphide.

8. A method for the separation of organic chemical values present in an aqueous spent liquor solution re sulting from reaction in aqueous medium at elevated temperature ofa lignocellulosic material with a pulping agent containing sodium and sulphur compounds, which comprises: heating the aqueous spent liquor solution in the absence of additive reagents at a temperature of from about 490F. to about 700F. and under a pressure of from about 1,000 to about 3,500 lbs/sq. inch for a period of from about minutes to 3 hours to evolve a first portion of said organic chemical values as a vapor containing organic chemical compounds and sulphides and to precipitate a second portion of said values from the remaining aqueous solution containing sodium compounds, separating said precipitate from said solution, cooling said vapor to condense organic values, and recovering sulphur values from the uncondensed vapor as hydrogen sulphide.

9. A method for the separation of organic chemical values present in an aqueous spent liquor solution resulting from reaction in aqueous medium at elevated temperature of a lignocellulosic material with a sodium and sulphur containing pulping agent and removal of the pulp, which comprises: heating the aqueous spent liquor solution in the absence of additive reagents at a temperature of from about 490F. to about 700F. and under a pressure of from about 1,000 to about 3,500 lbs./sq. inch for a period of from about 10 minutes to 3 hours to evolve a first portion of said organic chemical values as a vapor containing organic chemical compounds and sulphides and to precipitate a second portion of said values from the remaining aqueous solution containing sodium compounds, separating said precipitate and lime causticizing said solution for converting sodium values to NaOH, cooling said vapor to condense and separate organic values, recovering sulphur values from the uncondensed vapor as H 8, and contacting said causticized solution therewith to produce Na S therein.

10. A method for the separation of organic chemical values present in an aqueous spent liquor solution resulting from reaction in aqueous medium at elevated temperature ofa lignocellulosic material with an NaOH and H 8 containing pulping agent and removal of the pulp, which comprises: heating the aqueous spent liquor solution in the absence of additive reagents at a temperature of from about 490F. to about 700F. and under a pressure of from about 1,000 to about 3,500 lbs/sq. inch for a period of from about 10 minutes to 3 hours to evolve a first portion of said organic chemical values as a vapor containing organic chemical compounds and sulphides and to precipitate a second portion of said values from the remaining aqueous solution containing sodium compound, lime causticizing said solution for converting sodium values to NaOH, cooling said vapor to condense organic values, recovering sulphur values from the uncondensed vapor as H 8 and contacting said causticized solution therewith to produce Na S therein, and recycling said solution to said pulping stage.

11. A method for the separation of organic chemical values present in an aqueous spent liquor solution resulting from reaction in aqueous medium at elevated temperature of a lignocellulosic material with a pulping agent and removal of the pulp, which comprises: heating the aqueous spent liquor solution in the absence of additive reagents, at a temperature of from about 490F. to about 700F. and under a pressure of from about 1,000 to about 3,500 lbs/sq. inch for a period of from about 10 minutes to 3 hours whereby a first portion of said organic chemical values is evolved as a vapor from said solution, and a second portion separates as a solid precipitate from the remaining aqueous solution, wherein the lignocellulosic material is wood and said pulping agent reacts with said lignocellulosic material to form tall oil soap containing fatty and resin acids, and wherein the spent liquor is concentrated by evaporation prior to said heating under said pressure, to a total solids content of from about 23 to about 27 percent, by weight, based on the total weight, thereby to cause the separation from said liquor of the tall oil soap content thereof, and the tall oil soap is removed prior to said heating under said pressure.

12. A method for the separation of organic chemical values present in an aqueous spent liquor solution resulting from reaction in aqueous medium at elevated temperature of a lignocellulosic material with a pulping agent and removal of the pulp, which comprises: heating the aqueous spent liquor solution in the absence of additive reagents, at a temperature of from about 490F. to about 700F. and under a pressure of from about 1,000 to about 3,500 lbs/sq. inch for a period of from about 10 minutes to 3 hours whereby a first portion of said organic chemical values is evolved as a vapor from said solution, and a second portion separates as a solid precipitate from the remaining aqueous solution, cooling the evolved vapor to form a condensed fraction comprising hydroxylated, monocyclic and other aromatic compounds, and an uncondensed fraction comprising fractions consisting principally of methyl mercaptan, dimethyl sulfide, H 8, CO and hydrocarbons.

13. A process as in claim 12 which includes the additional step of thermally cracking said uncondensed fraction to evolve hydrogen sulfide.

Claims (12)

1. 2. A method as in claim 1 wherein said heating is effected at a temperature of from 550*F. to 650*F. and under a pressure of from 1,300 to about 2,700 lbs./sq. inch for a period of from about 20 minutes to 1 hour.
2. 3. A method as in claim 1 wherein said second precipitate is separated by filtration from the remaining aqueous solution.
3. 4. A process as in claim 1 including the further steps of cooling said vapor portion to form a condensed fraction comprising hydroxylated, monocyclic aromatic compounds and an uncondensed fraction comprising methyl mercaptan and dimethyl sulfide.
4. 5. A method as in claim 4 including the additional step of thermally cracking the uncondensed fraction to produce hydrogen sulfide.
5. 6. A method as in claim 5 including the further step of purifying the effluent water produced in the pulping operation by contacting it with at least a portion of the activated carbon produced.
6. 7. A method for the separation of organic chemical values present in an aqueous spent liquor solution resulting from reaction in aqueous medium at elevated temperature of a lignocellulosic material with a sodium and sulphur containing pulping agent and removal of the pulp, which comprises: heating the aqueous spent liquor solution in the absence of additive reagents at a temperature of from about 490*F. to about 700*F. and under a pressure of from about 1,000 to about 3,500 lbs./sq. inch for a period of from about 10 minutes to 3 hours to evolve a first portion of said organic chemical values as a vapor containing organic chemical compounds and sulphides and to precipitate a second portion of said values from the remaining aqueous solution containing sodium compoundS, separating said precipitate from said solution for separately recovering said precipitate and sodium values, cooling said vapor to condense and separate organic values therein, and recovering sulphur values from the uncondensed vapor as hydrogen sulphide.
7. 8. A method for the separation of organic chemical values present in an aqueous spent liquor solution resulting from reaction in aqueous medium at elevated temperature of a lignocellulosic material with a pulping agent containing sodium and sulphur compounds, which comprises: heating the aqueous spent liquor solution in the absence of additive reagents at a temperature of from about 490*F. to about 700*F. and under a pressure of from about 1,000 to about 3,500 lbs./sq. inch for a period of from about 10 minutes to 3 hours to evolve a first portion of said organic chemical values as a vapor containing organic chemical compounds and sulphides and to precipitate a second portion of said values from the remaining aqueous solution containing sodium compounds, separating said precipitate from said solution, cooling said vapor to condense organic values, and recovering sulphur values from the uncondensed vapor as hydrogen sulphide.
8. 9. A method for the separation of organic chemical values present in an aqueous spent liquor solution resulting from reaction in aqueous medium at elevated temperature of a lignocellulosic material with a sodium and sulphur containing pulping agent and removal of the pulp, which comprises: heating the aqueous spent liquor solution in the absence of additive reagents at a temperature of from about 490*F. to about 700*F. and under a pressure of from about 1,000 to about 3,500 lbs./sq. inch for a period of from about 10 minutes to 3 hours to evolve a first portion of said organic chemical values as a vapor containing organic chemical compounds and sulphides and to precipitate a second portion of said values from the remaining aqueous solution containing sodium compounds, separating said precipitate and lime causticizing said solution for converting sodium values to NaOH, cooling said vapor to condense and separate organic values, recovering sulphur values from the uncondensed vapor as H2S, and contacting said causticized solution therewith to produce Na2S therein.
9. 10. A method for the separation of organic chemical values present in an aqueous spent liquor solution resulting from reaction in aqueous medium at elevated temperature of a lignocellulosic material with an NaOH and H2S containing pulping agent and removal of the pulp, which comprises: heating the aqueous spent liquor solution in the absence of additive reagents at a temperature of from about 490*F. to about 700*F. and under a pressure of from about 1,000 to about 3,500 lbs./sq. inch for a period of from about 10 minutes to 3 hours to evolve a first portion of said organic chemical values as a vapor containing organic chemical compounds and sulphides and to precipitate a second portion of said values from the remaining aqueous solution containing sodium compound, lime causticizing said solution for converting sodium values to NaOH, cooling said vapor to condense organic values, recovering sulphur values from the uncondensed vapor as H2S and contacting said causticized solution therewith to produce Na2S therein, and recycling said solution to said pulping stage.
10. 11. A method for the separation of organic chemical values present in an aqueous spent liquor solution resulting from reaction in aqueous medium at elevated temperature of a lignocellulosic material with a pulping agent and removal of the pulp, which comprises: heating the aqueous spent liquor solution in the absence of additive reagents, at a temperature of from about 490*F. to about 700*F. and under a pressure of from about 1,000 to about 3,500 LBS./SQ. inch for a period of from about 10 minutes to 3 hours whereby a first portion of said organic chemical values is evolved as a vapor from said solution, and a second portion separates as a solid precipitate from the remaining aqueous solution, wherein the lignocellulosic material is wood and said pulping agent reacts with said lignocellulosic material to form tall oil soap containing fatty and resin acids, and wherein the spent liquor is concentrated by evaporation prior to said heating under said pressure, to a total solids content of from about 23 to about 27 percent, by weight, based on the total weight, thereby to cause the separation from said liquor of the tall oil soap content thereof, and the tall oil soap is removed prior to said heating under said pressure.
11. 12. A method for the separation of organic chemical values present in an aqueous spent liquor solution resulting from reaction in aqueous medium at elevated temperature of a lignocellulosic material with a pulping agent and removal of the pulp, which comprises: heating the aqueous spent liquor solution in the absence of additive reagents, at a temperature of from about 490*F. to about 700*F. and under a pressure of from about 1,000 to about 3,500 lbs./sq. inch for a period of from about 10 minutes to 3 hours whereby a first portion of said organic chemical values is evolved as a vapor from said solution, and a second portion separates as a solid precipitate from the remaining aqueous solution, cooling the evolved vapor to form a condensed fraction comprising hydroxylated, monocyclic and other aromatic compounds, and an uncondensed fraction comprising fractions consisting principally of methyl mercaptan, dimethyl sulfide, H2S, CO2 and hydrocarbons.
12. 13. A process as in claim 12 which includes the additional step of thermally cracking said uncondensed fraction to evolve hydrogen sulfide.

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