EP0041050A1 - Process for treating the waste liquors spent upon the digestion of lignocellulosic materials during paper pulp production according to the sulphite or bisulphite process - Google Patents

Abstract

Methods for separating into an aqueous phase and an organic phase which are not miscible the residual sulphitic or bisulphitic liquor produced by the digestion of ligno-cellulose materials after separation of the cellulose in the production of paper pulp following the so-sold "sulphite" or "bisulphite" methods. The residual liquor is heated within a reactor (6) in the presence of CO and/or pressurized H<u2>u, which transforms the organic materials dissolved within the liquor into a hydrocarbon oil which is then separated from the aqueous phase by decanting or centrifuging. This transformation may take place in one or more stages, the conditions of operation being different stage by stage.

Description

Technical area

The present invention relates to the treatment of used solutions resulting from the manufacture of paper pulps by chemical means, in particular, pulps obtained by the so-called "sulfite" or "bisulfite" processes in neutral or acidic media.

We know that the principle of this manufacture consists in making "digest" cellulosic matters, in particular wood shavings, by an appropriate solution which dissolves the non-cellulosic components of wood (lignin, xylans, extractables, etc ...), this so as to allow isolation, by filtration, of the insoluble cellulose pulp contained in these materials.

As digestion solutions, aqueous solutions of alkali (Na, NH ₄ ) or alkaline earth sulfites (Ca, Mg, etc.) are used, depending on the types of process. The pH of these solutions can vary between approximately 3 and 7 , 5 depending on the amount of dissolved free sulfurous acid (bisulfite) present.

After dissolving the non-cellulosic components in the treatment solution, the cellulose is filtered off and then the spent spent liquor is concentrated, loaded with dissolved organic matter by evaporation of a large part of the water it contains, after which it is burned, which makes it possible to supply energy and to separate the residual mineral materials therefrom. These are either irrecoverable (case of calcium and ammonium), or partially recyclable (case of sodium where it is partially recovered in the form of carbonate which is then retransformed into sulfite by means of S0 ₂ supplied by the combustion of the spent spent liquor). More details on these prior art methods can be found in "Encyclopedia of Chemical Technology" by KIRK & OTHMER and in "The Journal of the Technical Association of the Pulp & Paper Industry 40, 866-72 (1957) 41, 110 -116 (1958); 43, State of the art

These methods of treating spent liquors have the serious drawback of consuming a considerable amount of energy, on the one hand to evaporate part of the water. which they contain at the start and, on the other hand, because the combustion of the concentrated liquor is accompanied by the complete vaporization of the remaining water with loss of the heat consumed by this vaporization. In addition, these processes lead to a complete destruction of the organic materials of the sulfite detergents, materials which it may be advantageous to recover for other purposes.

The present invention avoids these defects and relates to a process for treating spent liquors for digestion of lignocellulosic materials under hot conditions and under pressure of carbon monoxide and / or hydrogen, which leads to the transformation of dissolved organic materials into gas. and / or organic liquid easily separable from the aqueous phase by the usual means.

• Le brevet FR 1.319.466 a pour objet un procédé pour le traitement de solutions résiduelles provenant des traitements de fabrication de la cellulose. Suivant cette référence, on pulvérise la solution à traiter dans un courant de 'gaz chaud tel que de la vapeur d'eau, du C0₂, du CO, de l'hydrogène, de l'azote ou des mélanges de ces gaz, de manière que les composants gazeux de cette solution se séparent des composés minéraux résiduels. La chaleur nécessaire à chauffer ces gaz est fournie par la combustion de combustibles solides (charbon), liquides (mazout) ou gazeux (les gaz combustibles qui se séparent lors de la pyrolyse de la solution de traitement). Il n'est pas fait mention, dans cette référence, de la récupération, sous forme liquide, de la matière organique contenue dans ces liqueurs résiduelles.

Before describing the present invention more precisely, we will indicate the existence of the references below, the subject of which is more or less related to it:

• Patent FR 1,319,466 relates to a process for the treatment of residual solutions originating from the treatments for manufacturing cellulose. According to this reference, the solution to be treated is sprayed into a stream of hot gas such as water vapor, C0 ₂ , CO, hydrogen, nitrogen or mixtures of these gases, so that the gaseous components of this solution separate from the residual mineral compounds. The heat necessary to heat these gases is provided by the combustion of solid (coal), liquid (oil) or gaseous fuels (the combustible gases which separate during the pyrolysis of the treatment solution). No reference is made in this reference to the recovery, in liquid form, of the organic matter contained in these residual liquors.

In patent DE 325,756, the treatment of residual liquors from the calcium bisulfite process is described with, successively, CO, C0 ₂ and oxygen in order to separate the sulfur impurities from the calcium and the woody residues which can then be directly subjected to fermentation. This reference does not, however, deal with the conversion of such residual liquors to hydrocarbons.

However, it is already known that organic materials can be treated with CO and / or H ₂ so as to convert them into liquid or pasty hydrocarbons. Thus, US Pat. No. 3,733,255 describes the treatment of municipal waste under CO pressure in the presence of water so as to obtain heavy oils or bitumens. The same kind of treatment is known with regard to lignins (see DRP No 382 367). Furthermore, under such conditions, the cellulose can itself be transformed into hydrocarbon oil (see patent USP 3,864,096), as can the lignin and the hemicellulose separated by precipitation with H ₂ SO ₄ from black liquors from the manufacture of cartons and other cellulosic products by the KRAFT process (see J. Appl. Chem. Biotechnol. 27, 443-63 (1977). Furthermore, in the following reference: Abstract Bulletin of the Institute of Paper Chemistry, 47 (1977) page 979, abstract 9473, we mention the possibility of converting organic waste into hydrocarbons by heating in the presence of CO and H ₂ 0. In this reference, we are talking about wood waste and in particular, lignin, but no residual liquors from the digestion of wood in sulphite or other media. In addition, this reference does not provide any details on the yields, the possible catalysts and the working conditions. prior art seem to have the following shortcomings: either they have a very low yield (generally not exceeding 25 to 30%), or they are relatively complicated, not very economical and require the aid of basic catalysts to increase the conversion yield.

Now, it has now been discovered with astonishment in the context of the present invention that the spent sulfitic or bisulfitic liquor can be directly heated under pressure with carbon monoxide and / or hydrogen, which leads to the formation of a oily phase insoluble in the aqueous phase and which can be easily separated by decantation or the like. In this process, most of the organic matter in the spent laundry is transferred as an organic liquid, a small part of it is carbonated and the small amount which may remain in the aqueous phase is negligible and does not interfere with the possible subsequent recovery of the mineral materials thereof.

Description of the invention

Thus, the process of the invention is characterized in that the sulfitic or bisulfitic solution is heated coming directly from the digester after separation of the cellulose pulp, this detergent having been, or not, previously concentrated by evaporation, in the presence of CO and / or hydrogen under pressure until its organic constituents are almost completely transformed into liquid and gaseous products, said liquid part separating in the form of an insoluble oil from the aqueous phase. In this process, the preliminary concentration of the sulfitic or bisulfitic solution by evaporation is no longer necessary; it can however be carried out, if desired, in the evaporators usually provided for this purpose.

This invention gives particularly interesting and unexpected results, in particular as regards the yields which are practically quantitative even in the absence of catalysts and even with acid solutions. Such efficiency is perhaps due to the presence of mineral and / or organic compounds in the spent solution, this point, however, having not been clarified.

Best conditions for implementing the invention

The conditions which are preferred to use to carry out the process of the invention are the following: pressure 100-300 bars; temperature 200-350 ° C. Below 200 ° C, the reaction becomes slow and above 350 °, the resulting increase in pressure hardly increases the yields and it becomes dangerous for the installation. The concentration of solids in the solution does not play a critical role and can be, for example, from 100 to 500 g / l of organic matter and from 50 to 200 g / l of mineral compounds. In practice, all kinds of sulfite and bisulfide solutions ticks which are formed by treatment of woods for the manufacture of cellulosic products by so-called neutral or acidic "sulfite" or "bisulfite" processes can be treated according to the invention. In addition, the models of reactors suitable for this reaction of conversion of organic materials dispersed or dissolved in water into non-water-soluble organic liquids are numerous and most of the usual reactors making it possible to subject liquids to heat and to pressure agree. Thus, it is just as possible to work in a 1 liter laboratory autoclave as, on a large scale, in an industrial reactor.

The conversion operation can be carried out in one or more stages. When operating, for example, in two stages, the pressure heating of CO and / or H ₂ is interrupted at a given moment and some or all of the CO ₂ which has already been released from the reactor trained in this first step. This can moreover be done without stopping heating or, better, the autoclave is allowed to cool somewhat, and even down to room temperature, the pressure is released and it is refilled with the desired amount of gas or mixture of reducing gases. This procedure has two advantages: a) it improves the conversion yield by around 10% compared to the same reaction carried out in one step; b) it makes it possible to work in more moderate overall conditions. Thus, for example, according to an advantageous operational sequence, the initial conditions of step 1 include a relatively high pressure (approximately 50-80 bar of reducing gas at room temperature) and a relatively low temperature (approximately 200-220 ° C) ; then, in the second step, the pressure is adjusted to a lower value (about 30-40 bar) and then heated higher (around 300-350 ° C). Consequently, the mechanical stresses to which the machinery is generally subjected are kept between less extreme limits, this being without having to reduce the yield of composition of liquid hydrocarbons.

The invention will now be described with reference to the appended drawing which schematically represents an installation working according to the calcium or sodium bisulfite method and in which the method of the invention is incorporated.

The installation shown in the drawing first includes a diges tor 1 wherein introducing wood chips to be disintegrated as well as the aqueous solution containing CaS0 ₃ (or Na ₂ S0 ₃₎ + H ₂ SO ₃ ^g r ^â- that the means schematically represented by the arrows 2 and 3. Digestion takes place in a few hours at 100-140 ° C and, once it is finished, the pulp is removed from the reactor at its lower part (see arrow 4) and the resulting spent liquor is sent to an evaporator 5 where a concentration takes place (it will be noted however that the evaporator is purely optional in the case of the invention). Then the solution enters an autoclave 6 comprising a heating means represented schematically by a winding 7. By means of the compressor 8, carbon monoxide and / or hydrogen is sent under pressure to the reactor 6 where the solution stays hot and under pressure until its organic constituents are almost completely transformed into gas and oily liquid insoluble in water. Then, the gas, the oil and the aqueous phase are introduced into a decanter 9 from which the gas escapes and is collected as indicated by arrow 10 and the organic and aqueous phases are separated by decantation or centrifugation. The oil that is collected passes through a heat exchanger 11 where it cools, the recovered heat can be used elsewhere in the factory, while the aqueous phase which now contains only insignificant quantities of organic matter is sent to a reservoir 12 where the separation of the mineral components takes place, that is to say of insoluble CaSO ₄ or, in the case of sodium, of Na ₂ SO ₃ formed in the aqueous phase during liquefaction. Such separation is carried out by the usual means, for example by evaporation (if necessary) and filtration. Calcium sulfate is not reused. On the other hand, if sodium sulfite is used, the latter can be recycled as indicated by the dotted lines in arrow 20.

It will be noted that the oil supplied by the generator 6 can be used as fuel or it can be distilled and refined according to the usual means.

Experimental part and industrial exploitation

The following examples illustrate the invention.

Example 1

300 g of a used sulphite lye from a paper pulp factory (this lye contains, by weight, 48% of solids, pH 7.4, and 180 ml of water) are placed in a one-liter autoclave. The autoclave was connected to a source of CO and, by means of this gas, a pressure of 70 bar was established. It was then heated for 1 hour at 300 ° C., the pressure rising under these conditions, at ~ 190 bar.

After cooling to room temperature, the autoclave was opened and the liquid organic phase floating above the now clear and transparent aqueous phase was separated by decantation. This viscous phase amounted to 75 g, which corresponds to a liquefaction rate of the original organic materials exceeding 90%. By analysis, it was found that the residual level of organic matter in the aqueous phase was negligible; the elementary analysis of the oil thus obtained was as follows: C 65%; H 6.2%; 0 16.2%; H2O 8.7%; S 2.7%; total ash 3.9%.

Example 2

The procedure was as in Example 1 using the following ingredients: calcium bisulfite lye at pH 4.7 containing 48% dissolved solids 300 g, H ₂ 0 180 ml. Initial pressure 70 bar of CO, temperature 300 ° C corresponding to an operational pressure of 220 bar. Reaction time 1 hour. Yield 84 g of liquid organic product; analysis, found: C 64.6%; H 6%; 016.8%; S 3%; ash 5%; H ₂ 0 7.1%. The transparent and colorless aqueous phase after removal of the gypsum by sedimentation contained only an insignificant amount of organic matter.

It should be noted to return to the installation shown in the drawing, that one could operate using, instead of a single reactor 6, a succession of two or more reactors 6 ', 6 ", etc. (not shown in the drawing), placed in series, this in order to be able to vary, while going from one reactor to another, the working conditions (temperature and pressure). Indeed, it can be advantageous to operate, according to a first stage, at relative temperature This is very low and at high pressure of CO and / or dtH2 and, in a subsequent step, at higher temperature and at relatively low pressure, this in order to improve the yields and the working energy conditions (energy saving). In addition, between the stages, provision may be made to eliminate all or part of the C0 ₂ which has already formed, this, for example, by temporary lowering of the temperature and total or partial relaxation of the pressure.

Example 3

240 g of sulfite liquor similar to that of Example 1 and 150 ml of water were placed in an autoclave and, after having introduced hydrogen under an initial pressure (at room temperature) of 70 bar, it was heated 1 h at 220 ° C. Then allowed to cool, the gases were removed from the autoclave and again filled with hydrogen under a pressure of 30 bar. After 1 h of heating at 310 ° C., the mixture was allowed to cool, the autoclave was emptied and, by decantation, 63 g of oily liquid with a composition similar to that of the products of the preceding Examples were collected.

Example 4

300 g of spent bisulphite liquor (pH 5) were placed in an autoclave as in Example 1 and, after having introduced a mixture (1: 1) of CO and H ₂ at 75 bar, 1.5 was heated h at 220 ° C. Then, after cooling, removing the gases from the autoclave and refilling it with the same mixture of gases under a pressure, under ordinary conditions, of 35 bar, the mixture was heated for another hour at 280 °. After cooling, 72 g of oily liquid were obtained after separation. The aqueous phase, which now contained only insignificant amounts of organic matter, was evaporated and the mineral residue thereof, a slightly colored product, could be collected.

Claims (7)

1. Process for treating the sulphite or bisulphite lye produced during the manufacture of wood pulp by means of the so-called "sulphite" and "bisulphite" methods of Ca, M ₃ , Na or NH ₄ to separate them organic constituents without having to vaporize the water in its aqueous phase, characterized in that this residual detergent is heated in the presence of carbon monoxide and / or hydrogen under pressure until substantially complete transformation of said organic constituents into liquid products and gaseous, said liquid part consisting of an oily phase insoluble in the aqueous phase and capable of being easily separated therefrom. 2. Method according to claim 1, characterized in that the oily phase is separated from the aqueous phase by the usual means, for example by decantation or centrifugation. 3. Method of manufacturing wood pulp usable in the paper and cellulosic products industry according to which a) a lignocellulosic material is digested with a sulphite or bisulphite solution of Ca, Mg, Na or NH ₄ containing, or not, an excess of H ₂ S0 ₃ and whose pH is acidic or neutral, so as to obtain cellulosic pulp and residual sulfite lye, b) the pulp is separated from this spent detergent, c) this spent lye is treated in order to separate its organic constituents from its aqueous phase, d) the mineral constituents of said aqueous phase are separated,
characterized in that in step c) the spent detergent is heated in the presence of carbon monoxide and / or hydrogen under pressure until the organic constituents are almost completely transformed into liquid and gaseous organic products, said liquid part consisting of an organic phase insoluble in water and easily separable from the aqueous phase by decantation or centrifugation. 4. Method according to claim 1, characterized in that the process is divided into two or more stages, the temperatures and pressures being modified from one stage to another and one part or all of the C0 ₂ formed during a step being eliminated during the passage from this step to the next. 5. Method according to claim 4, characterized in that during the first step the temperature is relatively moderate and the pressure relatively high while the temperature is relatively high and the pressure relatively low in the second step and that, between these steps , the reaction mixture is somewhat cooled and the pressure is released in order to expel the C0 ₂ formed during the first step. 6. Method according to claim 3 and in accordance with the content of the characterizing part of claim 4. 7. Method according to claim 6, characterized in that the conversion of the organic materials of the residual solution into organic liquid is carried out in two or more independent reactors and that, during the passage of the reaction mixture from one reactor to another , eliminating the C0 ₂ already formed by cooling the said mixture somewhat and releasing the pressure partially or completely.

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