EP0078023B1 - Process for treating cellulosic materials with gaseous hydrofluoric acid - Google Patents

Process for treating cellulosic materials with gaseous hydrofluoric acid Download PDF

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Publication number
EP0078023B1
EP0078023B1 EP82109718A EP82109718A EP0078023B1 EP 0078023 B1 EP0078023 B1 EP 0078023B1 EP 82109718 A EP82109718 A EP 82109718A EP 82109718 A EP82109718 A EP 82109718A EP 0078023 B1 EP0078023 B1 EP 0078023B1
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Prior art keywords
desorption
gas
reactor
substrate
sorption
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German (de)
French (fr)
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EP0078023A1 (en
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Rüdiger Dr. Erckel
Raimund Dr. Franz
Rolf Dr. Woernle
Theodor Dr. Riehm
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Hoechst AG
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Hoechst AG
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    • C—CHEMISTRY; METALLURGY
    • C13—SUGAR INDUSTRY
    • C13K—SACCHARIDES OBTAINED FROM NATURAL SOURCES OR BY HYDROLYSIS OF NATURALLY OCCURRING DISACCHARIDES, OLIGOSACCHARIDES OR POLYSACCHARIDES
    • C13K1/00—Glucose; Glucose-containing syrups
    • C13K1/02—Glucose; Glucose-containing syrups obtained by saccharification of cellulosic materials

Definitions

  • cellulosic material such as wood or waste from annual plants
  • mineral acids such as mineral acids.
  • the cellulose contained which is a macromolecular substance, is broken down into glycosidic bonds into water-soluble, smaller molecules down to the monomer units, the glucose molecules.
  • the sugars obtained in this way can be fermented into alcohol or used as a fermentation raw material for the production of proteins.
  • This is the technical meaning of wood saccharification.
  • mineral acids suitable for this purpose dilute sulfuric acid (Scholler process) and concentrated hydrochloric acid (Bergius process) were used on an industrial scale decades ago; see, for example, " Ullmann's Encyclopedia of Technical Chemistry", 3rd ed. Kunststoff-Berlin, 1957, Vol. 8, p. 591 ff.
  • DE-C No. 585318 describes a method and a device for treating wood with gaseous hydrogen fluoride, in which hydrogen fluoride gas, which may be diluted with an inert gas, is reacted with wood in a first zone of a reaction tube with a screw conveyor that this zone is cooled from the outside below the boiling point of the hydrogen fluoride. After the digestion, which may take place in an intermediate zone, the hydrogen fluoride is expelled with an inert gas stream by external heating and / or blowing, in order to be brought back into contact with fresh wood in the cooling zone mentioned.
  • hydrogen fluoride gas which may be diluted with an inert gas
  • gaseous hydrogen fluoride in a mixture with an inert carrier gas can be circulated almost without loss, producing a loading of the substrate required for good yields, without the technically highly disadvantageous cooling below the boiling point of the hydrogen fluoride being necessary.
  • This is achieved by dividing the desorption process into several stages, in which the desorption takes place in cocurrent or countercurrent of HF gas mixtures and reaction material (substrate).
  • HF gas mixtures of different HF concentrations are formed, which act on the substrate at different points in the sorption stage in such a way that low-HF gas mixtures affect unloaded or little loaded HF , Gas mixtures with higher HF concentrations act on already heavily loaded material.
  • the subject of the invention is thus a continuous process for the digestion of cellulose-containing substrate with gaseous hydrogen fluoride by sorption of the HF and subsequent desorption, which is characterized in that the HF is sorbed by the substrate at a temperature above its boiling point in a sorption stage, and after that the The substrate is freed of the sorbed H by heating in n desorption stages, where n is an integer and the stages mentioned are carried out in gas-tight separate reactors, and the substrate is introduced through a gas-tight lock into the sorption reactor, passes through it and then one after the other passes through gas-tight locks into the first, second, ..., nth desorption reactor and is discharged from the last (nth) desorption reactor, and the desorption in each case by the action of one of n heated gas streams in countercurrent to or, preferably, DC with the
  • the substrate is enriched with the respective gas stream with the HF released during the desorption, and the n HF-enriched gas streams, which contain an inert carrier gas in
  • n is an integer, preferably from 2 to 6, in particular from 2 to 4.
  • the reactors separated from one another by gas-tight locks can be of the same or different types: for example, stirred vessels, rotary tubes, flight dryers, slide beds, screw conveyors, vertical countercurrent or fluidized bed reactors are suitable. If necessary, they can be provided with a heating or cooling device.
  • Wood or waste from annual plants e.g. straw or bagasse
  • a pre-hydrolyzate of wood or waste from annual plants or, also preferably, waste paper can be used as cellulose-containing material.
  • This water can either be introduced by being present in the substrate as residual moisture of 0.5 to 20, preferably 1 to 10, in particular 3 to 7,% by weight, or by being contained in the HF / inert gas mixture, or in both.
  • reaction material (substrate), the cellulose-containing material, is transported from one reactor to another, for example, by free fall, via rotary feeders and / or by screw conveyors.
  • the gas is routed in such a way that the gas outlet opening of a sorption reactor via a gas line with an intermediate gas pump (blower) and n-1 branches with the gas inlet openings of n desorption reactors, and the gas outlet openings of these n desorption reactors via gas lines n gas inlet openings of the sorption reactor are connected.
  • a valve and a heat exchanger are interposed in front of the gas inlet openings of the desorption reactors.
  • Heat exchangers can also be arranged in front of the gas inlet openings of the sorption reactor. They may have the task of bringing the gas mixture intended for sorption to the optimum temperature for this. They may also have the task of condensing out any accompanying substances in the feed, such as water, acetic acid, essential oils, which are released during the desorption, while allowing the hydrogen fluoride to pass through in gaseous form.
  • the gas stream leaving the sorption reactor and containing a maximum of 5% by weight HF, preferably almost completely HF-free, is divided by the branches into n partial gas streams, the size of which depends on the respective setting of the valves.
  • These partial gas flows are heated in the heat exchangers to the temperature required for the desorption and are allowed to act on the substrate in the desorption reactors in countercurrent to, or preferably in cocurrent with, the substrate.
  • the n partial gas flows are again enriched with H F by the HF released during the desorption.
  • This enrichment with HF is of different sizes in the individual partial gas streams.
  • a lot of H F is released during the desorption of the substrate, which is introduced here with maximum HF loading.
  • desorption takes place on substrate that has always been freed of HF in the previous desorption stages.
  • the last (nth) desorption reactor only a little HF is released since the substrate is already largely depleted in H F and is introduced into it.
  • the substrate only contains HF traces.
  • n partial gas streams can also take place in such a way that the gas stream leaving the gas outlet opening of the sorption reactor is first fed completely through the pump to the last (nth) desorption reactor - after heating in the upstream heat exchanger - in which it is largely based on HF impoverished. acts substrate. Only after leaving this last (nth) desorption reactor is the gas stream divided into an (nth) partial gas stream which is fed directly to the corresponding gas inlet opening of the sorption reactor and n-1 partial gas streams which are the penultimate ([n-1] th ) to the first desorption reactor, after heating in the respective upstream heat exchanger.
  • the HF concentration in the n-th HF carrier gas stream leaving the last (n-th) desorption reactor is relatively low and increases more and more in the penultimate ([n-1] th) and the previous ones and is in the the first HF carrier gas stream leaving the first desorption reactor is the highest (up to over 95% by weight).
  • the HF carrier gas streams of different HF concentrations are fed through gas lines to the n gas inlet openings of the sorption reactor, in such a way that the nth HF gas flow onto only a substrate loaded with HF and the first HF gas flow onto the substrate with HF ( almost) maximum loaded substrate.
  • the remaining HF gas streams are fed to the substrate at gas inlet openings of the sorption reactor located in between.
  • the maximum HF loading of the cellulose-containing material depends on its type and nature and on the residence time in the sorption stage and is accordingly between 10 and 120, preferably between 30 and 80%, based on the weight of the material used.
  • the substrate loaded with HF after leaving the sorption reactor and before entering the first desorption reactor, can still pass through a dwell reactor which may have a comminution device for coarse reaction material and the temperature of which is expediently kept in a range which is dependent on the temperatures in the last part of the sorption reactor and is trapped in the first desorption reactor.
  • the optimal dwell time i.e. the average length of stay of the substrate in the apparatus from the beginning of the sorption to the end of the desorption depends on the type and nature of the material to be digested and must be tailored to the particular case. Accordingly, it can range from about 30 minutes to about 5 hours.
  • Substrate temperatures in the range from 40 to 120, preferably from 50 to 90 ° C. are selected for the desorption, the temperatures for the individual stages being different, on the other hand, a temperature in the range from 20 to 50, preferably 30 to, for the respectively assigned sorption 45 ° C.
  • the arrangement according to the invention allows the flow rate and temperature of the HF / carrier gas mixture to meet the different requirements in the individual areas of the sorption stage and in the individual desorption stages, depending on the HF loading degree of the substrate adapt.
  • the sorption reactor 1 is connected to the desorption reactor 3a via the gas line 8a, the pump 4, the valve 9a and the heat exchanger 5a, and this is connected to the sorption reactor 1 via the gas line 7a and the heat exchanger 6a. Furthermore, the sorption reactor 1 is connected to the desorption reactors 3b and 3c via the gas line 8a, the pump 4, the gas lines 8b and 8c, the valves 9b and 9c and the heat exchangers 5b and 5c, and these are connected via the gas lines 7b and 3c. 7c and the heat exchangers 6b and 6c connected to the sorption reactor 1.
  • the cellulosic material (substrate) to be digested is introduced into the sorption reactor 1. This process is symbolized by the arrow 12a in FIGS. 1 and 3.
  • HF / inert gas mixtures the HF concentration of which is lowest in the gas line 7a and highest in the gas line 7c, are supplied to the sorption reactor 1 through the gas lines 7a, 7b and 7c. In the sorption reactor 1, they flow against the substrate and emerge from the reactor 1 as an almost completely HF-free total gas stream.
  • the substrate loaded with H F is transported from the sorption reactor 1 to the residence reactor 2 (arrow 12b) and from there successively into the first, second and third desorption reactors 3c, 3b and 3a (arrows 12c, 12d and 12e).
  • the gas stream leaving the sorption reactor 1 is divided into three partial flows after passing through the gas line 8a and the pump 4, in accordance with the respective setting of the valves 9a, 9b and 9c. After heating in the heat exchangers 5a or 5c, these partial gas flows enter the desorption reactors 3a or 3b or 3c and flow through them in countercurrent to or, preferably, in cocurrent with the substrate.
  • H is desorbed by the action of the heated gas streams on the H F-loaded substrate.
  • the first desorption reactor 3c since the substrate with the maximum HF loading is introduced, most HF is released by desorption, a smaller amount is released in the reactor 3b, and in the last desorption reactor 3a, in which the substrate already largely frees from HF, the least amount of HF is released. Accordingly, the HF concentrations in the gas streams leaving the desorption reactors are highest in reactor 3c and lowest in reactor 3a.
  • the HF base stream exiting the reactor 3b has an intermediate HF concentration in between.
  • the HF gas streams of different HF concentrations are fed through the gas lines 7a or 7b or 7c - after passing through the intermediary heat exchangers 6a or 6b or 6c - at different inlet points of the sorption reactor 1.
  • the HF gas flow from the gas line 7a with the lowest HF concentration strikes substrate which is only very slightly loaded with HF.
  • the HF gas stream from the gas line 7c with the highest HF concentration strikes the substrate which (almost) has the maximum HF loading.
  • the HF gas flow from the gas line 7b is allowed to act on the substrate at an intermediate point of the sorption reactor 1, which substrate already has a relatively high HF load.
  • the substrate After desorption has taken place in the reactor 3a, the substrate leaves it in an open form (arrow 12f). It only contains traces of residual hydrogen fluoride and is processed, which is carried out in a manner known per se.
  • a special embodiment is shown schematically in FIG. 2.
  • a three-way valve 10 is interposed in the gas line 7a, which allows a (more or less) part of the HF gas stream emerging from the desorption reactor 3a to be returned to a special circuit via a gas line 11 and between the valve 9a and an intermediate pump 4a into the gas line 8a via a branch.
  • the three-way valve 10 can also be a control valve.
  • the part of the HF / inert gas mixture which is returned in this special circuit is about 10 to about 90, preferably about 50 to about 90%, of the total mixture which leaves the desorption reactor 3a.
  • This particular arrangement which analogously also allows partial recirculation of the HF / inert gas mixtures leaving the desorption reactors 3c or 3b, allows the gas velocities of the HF / inert gas mixtures passing through to be optimized.
  • FIG. 3 shows a further special embodiment of the method according to the invention.
  • the gas line 7a is interposed with a three-way valve 10a, which allows the gas stream leaving the sorption reactor 1 to be divided into partial gas streams only after it has passed the desorption reactor 3a. While a partial stream only passes through the reactor 3a and is fed directly to the sorption reactor 1, the other two partial streams are still passed through a second desorption reactor 3c or 3b before they are fed to the reactor 1 through the gas lines 7c or 7b.
  • This particular embodiment allows the largest possible amount of gas, that is to say the total amount of carrier gas, to act on the substrate in the last desorption stage, as a result of which the desorption is accelerated.
  • the digested material produced by the process according to the invention is a mixture of lignin and oligomeric saccharides. It can be worked up in a manner known per se by extraction with water, expediently in the heat or boiling heat, and by simultaneous or subsequent neutralization with lime. Filtration provides lignin, e.g. can be used as fuel, as well as a small amount of calcium fluoride, which results from the residual fluoride contained in the reaction material. The filtrate, a clear, slightly yellowish sugar solution, can be added to the alcoholic fermentation or fermentation either immediately or after setting an appropriate concentration. The dissolved, oligomeric sugars can also be treated by brief post-treatment, e.g. with highly diluted mineral acid at temperatures above 100 ° C, almost quantitatively converted into glucose.
  • Example 1 was carried out in an apparatus arrangement which is shown schematically in FIG. 1. It consisted of a sorption reactor 1, a residence reactor 2 and three desorption reactors 3a, 3b, 3c, which were connected to one another by pipelines and cellular wheel locks.
  • a vertical tube made of stainless steel with a clear width of 5 cm and a length of 80 cm was used as the sorption reactor, which carried a gas-tight rotary valve with a filling funnel at the upper end and was also provided with a gas-tight rotary valve at the lower end.
  • In the longitudinal axis of the tube was a slowly rotating shaft with narrow wings. At 3 points, which were distributed over the lower two thirds of the pipe length, there were inlets for HF-containing gases.
  • the gas outlet opening was located just below the top rotary valve.
  • the indwelling reactor was a cylindrical vessel of approx. 2 l made of semi-transparent polyethylene.
  • the desorption reactors were made of stainless steel and were designed as heatable rotary tube reactors through which the substrate and the flowing gases could flow in the same direction.
  • the usable volume of the desorption reactors was about 3 I.
  • granular lignocellulose which had been obtained as a residue from a pre-hydrolysis of spruce wood chips and had a water content of about 3% by weight, was continuously conveyed from top to bottom by its own weight.
  • HF / nitrogen mixtures of various concentrations originating from the desorption were introduced through the three gas introductions, specifically at the lowest introduction point with the highest, at the uppermost with the lowest HF concentration.
  • the conveying speed was adjusted so that the reaction mixture emerging from the reactor contained about 60 g HF per 100 g lignocellulose used. From the lower cellular wheel sluice, the substrate passed freely into the dwell reactor 2 and remained there for an average of 30 minutes.
  • First desorption reactor 3c Lignocellulose was loaded from the dwelling reactor 2 by means of a gas-tight cellular wheel sluice in a weight ratio of 60: 100; a substrate with a loading of approx. 35: 100 (weight ratio HF to lignocellulose) was discharged; the desorption temperature was 60 to 70 ° C; the escaping gas mixture contained approx. 65% by weight H F.
  • Second desorption reactor 3b The HF-loaded product from the first desorption reactor 3c was introduced by means of a gas-tight rotary valve; a substrate with a loading of approx. 10: 100 was discharged; the desorption temperature was 70-80 ° C; the exiting gas mixture contained about 25% by weight of HF.
  • Third desorption reactor 3a The product loaded with HF F was entered from the second desorption reactor 3b by means of a gas-tight rotary valve; a substrate with approximately 0.5% by weight HF was discharged; the desorption temperature was approx. 90 ° C; the exiting gas mixture contained about 5% by weight of HF.
  • the three gas mixtures generated in the desorption reactors were passed through the pipes 7a, 7b, 7c and the heat exchangers 6a, 6b, 6c, where they were cooled to 25 to 30 ° C., in the above already described in the sorption reactor 1, so that with continuous delivery of substrate through the apparatus circuits of carrier gas (nitrogen) and HF came about.
  • the digested substrate largely freed of HF, was extracted in the usual way with hot water, the solution thus obtained was neutralized with calcium hydroxide, filtered and evaporated. Wood sugar of light color was obtained in a yield of 90%, based on the cellulose originally present.
  • raw spruce wood shavings were broken down to a residual moisture content of about 5% by weight.
  • wood accompanying substances such as acetic acid were driven off and condensed and separated in the heat exchangers 6c to 6a.
  • wood sugar was obtained in a yield of about 70% by weight, based on the carbohydrates contained in the material used.

Abstract

The continuous process for hydrolyzing cellulose-containing material (substrate) is carried out by sorption of gaseous HF in a sorption reaction (1) and subsequent desorption in n steps, which are carried out in n reactors which are separated from one another in a gas-tight manner. The substrate is introduced via a gas-tight valve into the sorption reactor (1), passes through this and then reaches consecutively, through gas-tight valves, a hold-up reactor (2) and the first (3c), second (3b), . . . nth desporption reactor, from which it is then removed. The desorption is carried out in each case by the action of one of the n inert gas streams on the substrate at different temperatures, the particular inert gas stream being enriched with the HF being liberated during desorption. The gas streams, which are enriched to different extents with HF, are allowed to act on the substrate in the sorption reactor (1) in such a manner that the gas streams of low HF concentration act on a substrate having a zero or low concentration of HF and thereafter the gas streams of higher HF concentration act on substrate having higher HF concentration. The total gas stream (8a) produced from the individual gas streams leaves, after completion of sorption, the sorption reactor (1) largely freed of HF and is either conveyed to the desorption steps after dividing up into individual gas streams or it initially passes through the last desorption step (3a) and is thereafter divided up and passed to the other desorption steps in order, after passing through the latter, to be returned to the sorption reactor (1).

Description

Es ist bekannt, dass man zellulosehaltiges Material, z.B. Holz oder Abfälle von Einjahrespflanzen, mit Mineralsäuren chemisch aufschliessen kann. Hierbei wird die enthaltene Zellulose, die ein makromolekularer Stoff ist, unter Spaltung von glykosidischen Bindungen in wasserlösliche, kleinere Moleküle bis hinunter zu den Monomereinheiten, den Glucosemolekülen, zerlegt. Die so gewonnenen Zucker können u.a. zu Alkohol vergoren oder als Fermentationsrohstoff zur Produktion von Proteinen verwendet werden. Hierin liegt die technische Bedeutung der Holzverzuckerung. Als für diesen Zweck geeignete Mineralsäuren sind verdünnte Schwefelsäure (Scholler-Verfahren) und konzentrierte Salzsäure (Bergius-Verfahren) bereits vor Jahrzehnten grosstechnisch eingesetzt worden; siehe hierzu z.B. "Ullmanns Encyklopädie der technischen Chemie", 3. Aufl. München-Berlin, 1957, Bd. 8, S. 591 ff.It is known that cellulosic material, such as wood or waste from annual plants, can be chemically digested with mineral acids. Here the cellulose contained, which is a macromolecular substance, is broken down into glycosidic bonds into water-soluble, smaller molecules down to the monomer units, the glucose molecules. The sugars obtained in this way can be fermented into alcohol or used as a fermentation raw material for the production of proteins. This is the technical meaning of wood saccharification. As mineral acids suitable for this purpose, dilute sulfuric acid (Scholler process) and concentrated hydrochloric acid (Bergius process) were used on an industrial scale decades ago; see, for example, " Ullmann's Encyclopedia of Technical Chemistry", 3rd ed. Munich-Berlin, 1957, Vol. 8, p. 591 ff.

Es ist des weiteren bekannt, dass man zur Holzverzuckerung auch Fluorwasserstoff verwenden kann. Die Lage seines Siedepunktes (19,7 °C) erlaubt es, ihn ohne Wasser als Lösungsmittel mit dem aufzuschliessenden Substrat in Kontakt zu bringen und ihn nach vollzogenem Aufschluss mit vergleichsweise geringem Aufwand wiederzugewinnen. Als Aufschluss-Substrat eignet sich hierbei nicht nur natives Material; vielmehr wurde auch schon vorgeschlagen, stattdessen Altpapier oder Lignozellulose, den Rückstand einer Vorhydrolyse, zu verwenden, der nur noch sehr wenig Hemizlellulosen und andere Holzbegleitstoffe enthält und fast nur noch aus Zellulose und Lignin besteht. Dieser Vorhydrolyse können nicht nur Holz, sondern auch Papier oder Rückstände von Einjahrespflanzen aller Art wie Stroh oder Bagasse unterworfen werden. Sie besteht gemäss dem Stand der Technik aus einer Einwirkung von Wasser oder verdünnter Mineralsäure (ca. 0,5%ig) bei 130 bis 150°C (vgl. z.B. Handbuch "Die Hefen", Bd. 11, Nürnberg, 1962, S. 114 ff.) oder von gesättigtem Wasserdampf bei 160 bis 230 °C (vgl. US-PS Nr. 4160695).It is also known that hydrogen fluoride can also be used for wood saccharification. The location of its boiling point (19.7 ° C) allows it to be brought into contact with the substrate to be digested without water as a solvent and to be recovered with comparatively little effort after the digestion has been completed. Not only native material is suitable as the digestion substrate; on the contrary, it has already been suggested that waste paper or lignocellulose, the residue of a pre-hydrolysis, be used instead, which contains very little hemicelluloses and other wood-related substances and consists almost exclusively of cellulose and lignin. Not only wood, but also paper or residues of annual plants of all kinds such as straw or bagasse can be subjected to this pre-hydrolysis. According to the prior art, it consists of an action of water or dilute mineral acid (approx. 0.5%) at 130 to 150 ° C (see, for example, manual " Die Hefen", vol. 11, Nuremberg, 1962, p. 114 ff.) Or of saturated steam at 160 to 230 ° C (see. US-PS No. 4160695).

Zur Umsetzung von Fluorwasserstoff mit zellulosehaltigem Material sind drei technische Verfahrensprinzipien literaturbekannt:

  • - die Umsetzung mit gasförmigem Fluorwasserstoff, unter Atmosphärendruck,
  • - die Extraktion mit flüssigem Fluorwasserstoff, und schliesslich
  • - die Umsetzung mit gasförmigem Fluorwasserstoff im Vakuum.
Three technical process principles are known from the literature for the implementation of hydrogen fluoride with cellulose-containing material:
  • - reaction with gaseous hydrogen fluoride, under atmospheric pressure,
  • - extraction with liquid hydrogen fluoride, and finally
  • - The reaction with gaseous hydrogen fluoride in a vacuum.

In der DE-C Nr. 585318 wird ein Verfahren und eine Vorrichtung zur Behandlung von Holz mit gasförmigem Fluorwasserstoff beschrieben, bei dem in einer ersten Zone eines Reaktionsrohres mit Förderschnecke Fluorwasserstoffgas, das mit einem Inertgas verdünnt sein kann, mit Holz dadurch zur Umsetzung gebracht wird, dass diese Zone von aussen unter den Siedepunkt des Fluorwasserstoffs gekühlt wird. Nach dem Aufschluss, der sich gegebenenfalls in einer Zwischenzone vollzieht, wird nach diesem Verfahren der Fluorwasserstoff durch äussere Erwärmung und/oder Ausblasen mit einem Inertgasstrom ausgetrieben, um in der erwähnten Kühlzone wieder mit frischem Holz in Berührung gebracht zu werden.DE-C No. 585318 describes a method and a device for treating wood with gaseous hydrogen fluoride, in which hydrogen fluoride gas, which may be diluted with an inert gas, is reacted with wood in a first zone of a reaction tube with a screw conveyor that this zone is cooled from the outside below the boiling point of the hydrogen fluoride. After the digestion, which may take place in an intermediate zone, the hydrogen fluoride is expelled with an inert gas stream by external heating and / or blowing, in order to be brought back into contact with fresh wood in the cooling zone mentioned.

In der Praxis gestaltet sich die Durchführung dieses Verfahrens jedoch schwierig. Beim Kondensieren des Fluorwasserstoffes auf dem Substrat verteilt sich dieser nur ungleichmässig, so dass es zu örtlichen Überhitzungen kommt. Dies gehtz.B. aus der DE-C Nr. 606009 hervor, in der es heisst: "Es hat sich nämlich gezeigt, dass beim blossen Befeuchten der Polysaccharide, z.B. des Holzes, mit Flusssäure bzw. beim Beladen des Holzes u. dgl. mit Flusssäuredämpfen Temperatursteigerungen auftreten können, die zu einer teilweisen Zerstörung der gebildeten Umwandlungsprodukte führen. Eine Abführung dieser Wärme durch Kühlung ist aber infolge der schlechten Wärmeleitfähigkeit des zellulosehaltigen Materials schwierig." Als Abhilfe wird in dieser Patentschrift eine Extraktion mit flüssigem Fluorwasserstoff beschrieben, welche aber grosse Mengen Fluorwasserstoff erfordert und mit dem Nachteil behaftet ist, dass zur Verdampfung des Fluorwasserstoffs aus dem Extrakt und aus dem Extraktionsrückstand (Lignin) grosse Wärmemengen zu- und bei der anschliessenden Kondensation wieder abgeführt werden müssen.In practice, however, this procedure is difficult to carry out. When the hydrogen fluoride condenses on the substrate, it is distributed only unevenly, so that local overheating occurs. This is e.g. from DE-C No. 606009, which states: " It has been shown that when the polysaccharides, for example the wood, are simply moistened with hydrofluoric acid or when the wood and the like are loaded with hydrofluoric acid vapors, temperature increases can occur which lead to a partial destruction of the conversion products formed. However, this heat can be dissipated by cooling because of the poor thermal conductivity of the cellulose-containing material. " As a remedy, extraction with liquid hydrogen fluoride is described in this patent specification, but this requires large amounts of hydrogen fluoride and has the disadvantage that large amounts of heat are added to evaporate the hydrogen fluoride from the extract and from the extraction residue (lignin) and during the subsequent condensation must be removed again.

Die einige Jahre später veröffentlichte AT-A Nr. 147494 setzt sich mit beiden erwähnten Verfahren auseinander. Als Abhilfe gegen den ungleichmässigen und unvollkommenen Abbau des Holzes beim Aufschluss mit hochkonzentrierter oder wasserfreier Flusssäure in flüssigem oder gasförmigem Zustand bei niederen Temperaturen sowie gegen die Nachteile des hohen Flusssäure- überschusses beim Extraktionsverfahren wird in dieser Patentschrift ein technisch aufwendiges Verfahren beschrieben, bei dem das Holz vor der Einwirkung des Fluorwasserstoffes möglichst weitgehend evakuiert wird, und auch die Rückgewinnung des Fluorwasserstoffes sich im Vakuum vollzieht. Das Verfahren ist auch in der Zeitschrift "Holz Roh- und Werkstoff", 1 (1938), 342-344 beschrieben. Der hohe technische Aufwand bei diesem Verfahren ist nicht nur durch die Vakuumtechnik an sich bedingt, sondern auch durch den Umstand, dass der Siedepunkt von Fluorwasserstoff bereits bei 150 mbar den Wert von -20 °C unterschreitet; dies bedeutet, dass ohne Zuhilfenahme aufwendiger Kühlmittel bzw. -aggregate keine Kondensation mehr möglich ist.AT-A No. 147494, published a few years later, deals with both of the methods mentioned. As a remedy for the uneven and imperfect degradation of the wood during digestion with highly concentrated or anhydrous hydrofluoric acid in a liquid or gaseous state at low temperatures and against the disadvantages of the high excess of hydrofluoric acid in the extraction process, this patent describes a technically complex process in which the wood is evacuated as far as possible before the action of the hydrogen fluoride, and also the recovery of the hydrogen fluoride takes place in a vacuum. The process is also described in the journal " Holz Roh- und Werkstoff", 1 (1938), 342-344. The high technical effort involved in this process is not only due to the vacuum technology itself, but also due to the fact that the boiling point of hydrogen fluoride already falls below the value of -20 ° C at 150 mbar; This means that condensation is no longer possible without the use of complex coolants or cooling units.

Der literaturbekannte Stand der Technik des Holzaufschlusses mit Fluorwasserstoff wird durch die beschriebenen drei Verfahren bzw. Vorrichtungen gekennzeichnet. Keine dieser Methoden bzw. Vorrichtungen vereinigt demnach niedrigen Aufwand und gutes Aufschlussergebnis in technisch befriedigender Weise. Die an sich ökonomische Art der Umsetzung von zellulosehaltigem Material mit einem Fluorwasserstoff/Inertgas-Gemisch, das aus der Fluorwasserstoffdesorption stammt, gemäss der oben bereits erwähnten DE-C Nr. 585318, wird nach der später veröffentlichten DE-C Nr. 606009 offenbar durch die Notwendigkeit beeinträchtigt, bei der Absorption unter den Siedepunkt des Fluorwasserstoffes zu kühlen.The literature-known prior art of wood digestion with hydrogen fluoride is characterized by the three methods and devices described. Accordingly, none of these methods or devices combines low expenditure and good digestion results in a technically satisfactory manner. The inherently economical way of reacting cellulose-containing material with a hydrogen fluoride / inert gas mixture, which originates from hydrogen fluoride desorption, according to DE-C No. 585318 already mentioned above, is evidently disclosed by DE-C No. 606009, which was published later Necessary ability to cool during absorption below the boiling point of the hydrogen fluoride.

Überraschenderweise wurde nun gefunden, dass man gasförmigen Fluorwasserstoff im Gemisch mit einem inerten Trägergas unter Erzeugung einer für gute Ausbeuten erforderlichen Beladung des Substrates nahezu verlustfrei im Kreis führen kann, ohne dass die technisch stark nachteilige Kühlung unter den Siedepunkt des Fluorwasserstoffes dabei notwendig wird. Dies gelingt durch Teilung des Desorptionvorganges in mehrere Stufen, in denen die Desorption im Gleichstrom oder Gegenstrom von HF-Gasgemischen und Reaktionsgut (Substrat) erfolgt. Entsprechend der unterschiedlichen HF-Beladung des Substrates beim Eintritt in die einzelnen Desorptionsstufen werden HF-Gasgemische unterschiedlicher H F-Konzentrationen gebildet, die an verschiedenen Stellen der Sorptionsstufe derart auf das Substrat einwirken, dass HF-arme Gasgemische auf unbeladenes oder wenig mit HF beladenes Material, Gasgemische mit höheren HF-Konzentrationen auf bereits stärker beladenes Material einwirken.Surprisingly, it has now been found that gaseous hydrogen fluoride in a mixture with an inert carrier gas can be circulated almost without loss, producing a loading of the substrate required for good yields, without the technically highly disadvantageous cooling below the boiling point of the hydrogen fluoride being necessary. This is achieved by dividing the desorption process into several stages, in which the desorption takes place in cocurrent or countercurrent of HF gas mixtures and reaction material (substrate). Corresponding to the different HF loading of the substrate when entering the individual desorption stages, HF gas mixtures of different HF concentrations are formed, which act on the substrate at different points in the sorption stage in such a way that low-HF gas mixtures affect unloaded or little loaded HF , Gas mixtures with higher HF concentrations act on already heavily loaded material.

Diese Massnahme war nicht naheliegend. Angaben in der Literatur lassen vielmehr den Schluss zu, dass eine ausreichende Beladung von Holzmaterial auch mit unverdünntem Fluorwasserstoff oberhalb seines Siedepunktes nicht möglich ist. In einer Arbeit von Fredenhagen und Cadenbach, "Angew. Chem.", 46 (1933), 113/7 heisst es (S. 115 rechts unten bis S. 116 links oben): "Wenn man gasförmigen HF bei Zimmertemperatur auf Holz einwirken lässt, so wird HF absorbiert und infolge dessen steigt die Temperatur. Dies bewirkt aber, dass keine weiteren HF-Mengen absorbiert werden, so dass die Reaktion zum Stillstand kommt und keine weitere Temperaturerhöhung eintritt." Um so überraschender war nun der Befund, dass die Fluorwasserstoffsorption von der Wärmetönung der Reaktion, die sich nur bis zu relativ niedrigen Beladungen bemerkbar macht, weitgehend unabhängig ist, vielmehr bei gegebener Temperatur nur von der HF-Konzentration im einwirkenden Gasgemisch abhängt. d.h. also auch bei Temperaturen oberhalb des Siedepunktes von Fluorwasserstoff bis zu den für gute Ausbeuten erforderlichen Beladungshöhen durch stufenweise Erzeugung und Verwendung von Strömen unterschiedlicher HF-Konzentration geführt werden kann.This measure was not obvious. Rather, data in the literature allow the conclusion that an adequate loading of wood material even with undiluted hydrogen fluoride above its boiling point is not possible. In a work by Fredenhagen and Cadenbach, " Angew. Chem.", 46 (1933), 113/7 it says (p. 115 bottom right to p. 116 top left): " If you let gaseous HF act on wood at room temperature , HF is absorbed and the temperature rises as a result. However, this means that no further HF quantities are absorbed, so that the reaction comes to a standstill and no further temperature increase occurs. " It was therefore all the more surprising to find that the hydrogen fluoride sorption is largely independent of the heat of the reaction, which is only noticeable up to relatively low loads, but rather depends only on the HF concentration in the gas mixture at a given temperature. that is, even at temperatures above the boiling point of hydrogen fluoride up to the loading heights required for good yields can be carried out by stepwise generation and use of streams of different HF concentrations.

Erfindungsgegenstand ist somit ein kontinuierliches Verfahren zum Aufschluss von zellulosehaltigem Substrat mit gasförmigem Fluorwasserstoff durch Sorption des HF und anschliessende Desorption, das dadurch gekennzeichnet ist, dass die Sorption des H F durch das Substrat bei einer Temperatur oberhalb seines Siedepunktes in einer Sorptionsstufe erfolgt, und dass danach das Substrat durch Erwärmen in n Desorptionsstufen von dem sorbierten H befreit wird, wobei n eine ganze Zahl und wobei die genannten Stufen in jeweils gasdicht voneinander getrennten Reaktoren ablaufen, und wobei das Substrat durch eine gasdichte Schleuse in den Sorptionsreaktor eingebracht wird, diesen durchläuft und dann nacheinander durch gasdichte Schleusen in den ersten, zweiten,..., n-ten Desorptionsreaktor gelangt und aus dem letzten (n-ten) Desorptionsreaktor ausgetragen wird, und wobei die Desorption jeweils durch Einwirken eines von n erhitzten Gasströmen im Gegenstrom zum oder, vorzugsweise, Gleichstrom mit dem Substrat unter Anreicherung des jeweiligen Gasstroms mit dem bei der Desorption freiwerdenden HF erfolgt, und wobei die n HF-angereicherten Gasströme, die neben dem H ein inertes Trägergas enthalten, im Gegenstrom zum Substrat im Sorptionsreaktor auf dieses derart einwirken, dass Gasströme niedriger HF-Konzentration auf unbeladenes oder noch wenig mit HF beladenes Substrat und Gasströme hoher HF-Konzentration auf stärker mit HF beladenes Substrat einwirken, und wobei der aus den einzelnen Gasströmen entstandene Gesamtgasstrom nach erfolgter Sorption den Sorptionsreaktor, weitgehend an HF verarmt, verlässt und entweder nach Aufteilung in Einzelgasströme im Kreislauf den Desorptionsstufen zugeführt wird oder zunächst die letzte Desorptionsstufe durchläuft und danach aufgeteilt und den anderen Desorptionsstufen und dem Sorptionsreaktor zugeführt wird.The subject of the invention is thus a continuous process for the digestion of cellulose-containing substrate with gaseous hydrogen fluoride by sorption of the HF and subsequent desorption, which is characterized in that the HF is sorbed by the substrate at a temperature above its boiling point in a sorption stage, and after that the The substrate is freed of the sorbed H by heating in n desorption stages, where n is an integer and the stages mentioned are carried out in gas-tight separate reactors, and the substrate is introduced through a gas-tight lock into the sorption reactor, passes through it and then one after the other passes through gas-tight locks into the first, second, ..., nth desorption reactor and is discharged from the last (nth) desorption reactor, and the desorption in each case by the action of one of n heated gas streams in countercurrent to or, preferably, DC with the The substrate is enriched with the respective gas stream with the HF released during the desorption, and the n HF-enriched gas streams, which contain an inert carrier gas in addition to the H, act in countercurrent to the substrate in the sorption reactor in such a way that gas streams of low HF concentration act on an unloaded or HF-loaded substrate and gas streams with a high HF concentration on a substrate heavily loaded with HF, and the total gas stream resulting from the individual gas streams leaves the sorption reactor, largely depleted in HF, after sorption, and either after division into individual gas streams is supplied to the desorption stages in the circuit or first passes through the last desorption stage and then divided and fed to the other desorption stages and the sorption reactor.

n ist eine ganze Zahl, vorzugsweise von 2 bis 6, insbesondere von 2 bis 4.n is an integer, preferably from 2 to 6, in particular from 2 to 4.

Die durch gasdichte Schleusen voneinander getrennten Reaktoren können gleichen oder verschiedenen Typs sein: beispielsweise eignen sich Rührgefässe, Drehrohre, Flugtrockner, Rutschbetten, Schneckenförderer, vertikale Gegenstrom-oder Fliessbettreaktoren. Sie können gegebenenfalls mit einer Heiz- oder Kühlvorrichtung versehen sein.The reactors separated from one another by gas-tight locks can be of the same or different types: for example, stirred vessels, rotary tubes, flight dryers, slide beds, screw conveyors, vertical countercurrent or fluidized bed reactors are suitable. If necessary, they can be provided with a heating or cooling device.

AIs zellulosehaltiges Material eingesetzt werden können Holz oder Abfälle von Einjahrespflanzen (z.B. Stroh oder Bagasse) oder, vorzugsweise, ein Vorhydrolysat von Holz oder Abfällen von Einjahrespflanzen oder, ebenfalls vorzugsweise, Altpapier.Wood or waste from annual plants (e.g. straw or bagasse) or, preferably, a pre-hydrolyzate of wood or waste from annual plants or, also preferably, waste paper can be used as cellulose-containing material.

Bekanntlich ist zum Aufschluss der Zellulosen, der ja eine hydrolytische Spaltung darstellt, die Anwesenheit einer bestimmten Menge von Wasser erforderlich. Dieses Wasser kann entweder dadurch eingebracht werden, dass es im Substrat als Restfeuchte von 0,5 bis 20, vorzugsweise 1 bis 10, insbesondere 3 bis 7, Gew.-% vorhanden ist, oder dass es im HF/Inertgas-Gemisch enthalten ist, oder in beiden.It is known that the presence of a certain amount of water is necessary for the digestion of the cellulose, which is a hydrolytic cleavage. This water can either be introduced by being present in the substrate as residual moisture of 0.5 to 20, preferably 1 to 10, in particular 3 to 7,% by weight, or by being contained in the HF / inert gas mixture, or in both.

Der Transport des Reaktionsgutes (Substrats), des zellulosehaltigen Materials, von einem Reaktor zum anderen erfolgt beispielsweise durch freien Fall, über Zellenradschleusen und/oder durch Förderschnecken.The reaction material (substrate), the cellulose-containing material, is transported from one reactor to another, for example, by free fall, via rotary feeders and / or by screw conveyors.

Als inertes Trägergas eignen sich Luft, Stickstoff, Kohlendioxid oder eines der Edelgase, vorzugsweise Luft oder Stickstoff.Air, nitrogen, carbon dioxide or one of the noble gases, preferably air or nitrogen, are suitable as the inert carrier gas.

Die Gasführung erfolgt erfindungsgemäss so, dass die Gasaustrittsöffnung eines Sorptionsreaktors über eine Gasleitung mit zwischengeschalteter Gaspumpe (Gebläse) und n-1 Abzweigungen mit den Gaseintrittsöffnungen von n Desorptionsreaktoren, und die Gasaustrittsöffnungen dieser n Desorptionsreaktoren über Gasleitungen mit n Gaseintrittsöffnungen des Sorptionsreaktors verbunden sind. Vor den Gaseintrittsöffnungen der Desorptionsreaktoren sind noch jeweils ein Ventil und ein Wärmetauscher zwischengeschaltet.According to the invention, the gas is routed in such a way that the gas outlet opening of a sorption reactor via a gas line with an intermediate gas pump (blower) and n-1 branches with the gas inlet openings of n desorption reactors, and the gas outlet openings of these n desorption reactors via gas lines n gas inlet openings of the sorption reactor are connected. In front of the gas inlet openings of the desorption reactors, a valve and a heat exchanger are interposed.

Auch vor den Gaseintrittsöffnungen des Sorptionsreaktors können gegebenenfalls Wärmeaustauscher angeordnet sein. Sie haben gegebenenfalls die Aufgabe, jeweils das zur Sorption bestimmte Gasgemisch auf die hierfür optimale Temperatur zu bringen. Sie haben unter Umständen des weiteren die Aufgabe, bei der Desorption eventuell freigewordene Begleitstoffe des Einsatzmaterials, wie Wasser, Essigsäure, ätherische Öle, auszukondensieren, den Fluorwasserstoff hingegen gasförmig passieren zu lassen.Heat exchangers can also be arranged in front of the gas inlet openings of the sorption reactor. They may have the task of bringing the gas mixture intended for sorption to the optimum temperature for this. They may also have the task of condensing out any accompanying substances in the feed, such as water, acetic acid, essential oils, which are released during the desorption, while allowing the hydrogen fluoride to pass through in gaseous form.

Der den Sorptionsreaktor verlassende, maximal 5 Gew.-% HF enthaltende, vorzugsweise fast vollständig HF-freie Gastrom wird durch die Abzweigungen in n Teilgasströme aufgeteilt, deren Grösse von der jeweiligen Einstellung der Ventile abhängt. Diese Teilgasströme werden in den Wärmetauschern auf die für die Desorption jeweils erforderliche Temperatur aufgeheizt und in den Desorptionsreaktoren im Gegenstrom zum oder, vorzugsweise, im Gleichstrom mit dem Substrat auf dieses einwirken gelassen. Dabei werden die n Teilgasströme durch die bei der Desorption abgegebene HF wieder mit H F angereichert.The gas stream leaving the sorption reactor and containing a maximum of 5% by weight HF, preferably almost completely HF-free, is divided by the branches into n partial gas streams, the size of which depends on the respective setting of the valves. These partial gas flows are heated in the heat exchangers to the temperature required for the desorption and are allowed to act on the substrate in the desorption reactors in countercurrent to, or preferably in cocurrent with, the substrate. The n partial gas flows are again enriched with H F by the HF released during the desorption.

Diese Anreicherung mit HF ist in den einzelnen Teilgasströmen verschieden gross. Im ersten Desorptionsreaktorwird bei der Desorption des Substrats, das hier mit maximaler HF-Beladung eingebracht wird, viel H F frei. In den folgenden Desorptionsreaktoren erfolgt die Desorption bei Substrat, das in den vorangegangenen Desorptionsstufen bereits jeweils immer weiter von HF befreit worden ist. Im letzten (n-ten) Desorptionsreaktor wird nur noch wenig HF frei, da das Substrat bereits weitgehend an H F verarmt in diesen eingebracht wird. Beim Verlassen dieses letzten Desorptionsreaktors enthält das Substrat nur noch HF-Spuren.This enrichment with HF is of different sizes in the individual partial gas streams. In the first desorption reactor, a lot of H F is released during the desorption of the substrate, which is introduced here with maximum HF loading. In the following desorption reactors, desorption takes place on substrate that has always been freed of HF in the previous desorption stages. In the last (nth) desorption reactor only a little HF is released since the substrate is already largely depleted in H F and is introduced into it. When leaving this last desorption reactor, the substrate only contains HF traces.

Die Aufteilung in n Teilgasströme kann auch so erfolgen, dass der die Gasaustrittsöffnung des Sorptionsreaktors verlassende Gasstrom zunächst vollständig durch die Pumpe dem letzten (n-ten) Desorptionsreaktor - nach Aufheizen in dem vorgeschalteten Wärmetauscher - zugeführt wird, worin er auf das bereits weitgehend an H F verarm-. te Substrat einwirkt. Erst nach Verlassen dieses letzten (n-ten) Desorptionsreaktors wird der Gasstrom aufgeteilt in einen (n-ten) Teilgasstrom, der direkt der entsprechenden Gaseintrittsöffnung des Sorptionsreaktorszugeführtwird, und in n-1 Teilgasströme, die dem vorletzten ( [n-1 ] -ten) bis ersten Desorptionsreaktor, nach Aufheizung im jeweiligen vorgeschalteten Wärmetauscher, zugeführt werden.The division into n partial gas streams can also take place in such a way that the gas stream leaving the gas outlet opening of the sorption reactor is first fed completely through the pump to the last (nth) desorption reactor - after heating in the upstream heat exchanger - in which it is largely based on HF impoverished. acts substrate. Only after leaving this last (nth) desorption reactor is the gas stream divided into an (nth) partial gas stream which is fed directly to the corresponding gas inlet opening of the sorption reactor and n-1 partial gas streams which are the penultimate ([n-1] th ) to the first desorption reactor, after heating in the respective upstream heat exchanger.

Die HF-Konzentration im n-ten HF-Trägergas-Strom, der den letzten (n-ten) Desorptionsreaktor verlässt, ist relativ niedrig und nimmt im vorletzten ([n-1]-ten) und den vorhergehenden immer mehr zu und ist im ersten H F-Trägergas-Strom, der den ersten Desorptionsreaktor verlässt, am höchsten (bis über 95 Gew.-%).The HF concentration in the n-th HF carrier gas stream leaving the last (n-th) desorption reactor is relatively low and increases more and more in the penultimate ([n-1] th) and the previous ones and is in the the first HF carrier gas stream leaving the first desorption reactor is the highest (up to over 95% by weight).

Die HF-Trägergas-Ströme unterschiedlicher HF-Konzentration werden durch Gasleitungen den n Gaseintrittsöffnungen des Sorptionsreaktors zugeführt, und zwar so, dass der n-te HF-Gasstrom auf nur wenig mit HF beladenes Substrat und der erste HF-Gasstrom auf das mit HF (nahezu) maximal beladene Substrat trifft. Die übrigen HF-Gasströme werden an dazwischenliegenden Gaseintrittsöffnungen des Sorptionsreaktors dem Substrat zugeführt.The HF carrier gas streams of different HF concentrations are fed through gas lines to the n gas inlet openings of the sorption reactor, in such a way that the nth HF gas flow onto only a substrate loaded with HF and the first HF gas flow onto the substrate with HF ( almost) maximum loaded substrate. The remaining HF gas streams are fed to the substrate at gas inlet openings of the sorption reactor located in between.

Die maximale HF-Beladung des zellulosehaltigen Materials richtet sich nach dessen Art und Beschaffenheit sowie nach der Verweilzeit in der Sorptionsstufe und liegt demgemäss zwischen 10 und 120, bevorzugt zwischen 30 und 80%, bezogen auf das Gewicht des eingesetzten Materials.The maximum HF loading of the cellulose-containing material depends on its type and nature and on the residence time in the sorption stage and is accordingly between 10 and 120, preferably between 30 and 80%, based on the weight of the material used.

Gegebenenfalls kann das mit HF beladene Substrat nach Verlassen des Sorptionsreaktors und vor Eintritt in den ersten Desorptionsreaktor noch einen Verweilreaktor durchlaufen, der gegebenenfalls eine Zerkleinerungsvorrichtung für grobstükkiges Reaktionsgut aufweist und dessen Temperatur zweckmässig in einem Bereich gehalten wird, der von den Temperaturen im letzten Teil des Sorptionsreaktors und im ersten Desorptionsreaktor eingeschlossen wird.If necessary, the substrate loaded with HF, after leaving the sorption reactor and before entering the first desorption reactor, can still pass through a dwell reactor which may have a comminution device for coarse reaction material and the temperature of which is expediently kept in a range which is dependent on the temperatures in the last part of the sorption reactor and is trapped in the first desorption reactor.

Die optimale Verweilzeit, d.h. die durchschnittliche Aufenthaltsdauer des Substrats in der Apparatur vom Anfang der Sorption bis zum Ende der Desorption hängt von Art und Beschaffenheit des aufzuschliessenden Materials ab und mussauf den jeweiligen Fall abgestimmt werden. Sie kann demgemäss im Bereich von etwa 30 min bis etwa 5 h liegen.The optimal dwell time, i.e. the average length of stay of the substrate in the apparatus from the beginning of the sorption to the end of the desorption depends on the type and nature of the material to be digested and must be tailored to the particular case. Accordingly, it can range from about 30 minutes to about 5 hours.

Für die Desorption wählt man Substrattemperaturen im Bereich von 40 bis 120, vorzugsweise von 50 bis 90 °C, wobei die Temperaturen für die einzelnen Stufen verschieden sein können, hingegen für die jeweils zugeordnete Sorption eine Temperatur im Bereich von 20 bis 50, vorzugsweise 30 bis 45°C.Substrate temperatures in the range from 40 to 120, preferably from 50 to 90 ° C. are selected for the desorption, the temperatures for the individual stages being different, on the other hand, a temperature in the range from 20 to 50, preferably 30 to, for the respectively assigned sorption 45 ° C.

Im Gegensatz zum normalen Gegenstromprinzip gemäss dem Stand der Technik erlaubt es die erfindungsgemässe Anordnung, die Strömungsgeschwindigkeit und Temperatur des HF/Trägergas-Gemisches an die in den einzelnen Bereichen der Sorptionsstufe und in den einzelnen Desorptionsstufen jeweils unterschiedlichen, vom HF-Beladungsgrad des Substrats abhängigen Erfordernisse anzupassen.In contrast to the normal countercurrent principle according to the prior art, the arrangement according to the invention allows the flow rate and temperature of the HF / carrier gas mixture to meet the different requirements in the individual areas of the sorption stage and in the individual desorption stages, depending on the HF loading degree of the substrate adapt.

Die Erfindung soll anhand der Fig. 1 bis 3 näher erläutert werden.

  • Fig. 1 stellt das Fliessbild eines erfindungsgemässen Reaktionsablaufs in einem Sorptions- und drei Desorptionsreaktoren dar.
  • Fig. 2 stellt einen Ausschnitt aus dem Gesamtfliessbild von Fig. 1 dar mit einer weiteren Unterteilung eines der Gaskreisläufe mit teilweiser Rückführung.
  • Fig. 3 stellt das Fliessbild einer weiteren erfindungsgemässen Möglichkeit des Reaktionsablaufs in einem Sorptions- und drei Desorptionsreaktor dar.
The invention will be explained in more detail with reference to FIGS. 1 to 3.
  • 1 shows the flow diagram of a reaction sequence according to the invention in one sorption and three desorption reactors.
  • FIG. 2 shows a section of the overall flow diagram of FIG. 1 with a further subdivision of one of the gas circuits with partial recirculation.
  • 3 shows the flow diagram of a further possibility according to the invention for the course of the reaction in one sorption and three desorption reactor.

In diesen Figuren stellen dar:

  • 1 Sorptionsreaktor
  • 2 Verweilreaktor
  • 3a, b, c Desorptionsreaktoren
  • 4, 4a Gaspumpen (Gebläse) ,
  • 5a, b, c Wärmetauscher
  • 6a, b, c Wärmetauscher
  • 7a, b, c Gasleitungen von Desorptionsreaktoren 3a, b, c zum Sorptionsreaktor 1 (über die Wärmetauscher 6a, b, c)
  • 8a Gasleitung vom Sorptionsreaktor 1 zum Desorptionsreaktor 3a über die Gaspumpe 4, das Ventil 9a und den Wärmetauscher 5a
  • 8b, c Gasleitungen abzweigend von der Gasleitung 8a zu den Desorptionsreaktoren 3b, c über die Ventile 9b, c und die Wärmetauscher 5b, c 9a, b, c Ventile (Hähne)
  • 10, 10a Dreiwegeventile (Dreiwegehähne)
  • 11 Gasleitung vom Dreiwegehahn 10 zur Gasleitung 8a
  • 11 c Gasleitung vom Dreiwegeventil 10a über das Ventil 9c und den Wärmetauscher 5c zum Desorptionsreaktor 3c
  • 11 b Gasleitung, abzweigend von der Gasleitung 11 c über das Ventil 9b und den Wärmetauscher 5b zum Desorptionsreaktor 3b
  • 12 a-f diese Pfeile symbolisieren den Materialfluss
In these figures:
  • 1 sorption reactor
  • 2 indwelling reactor
  • 3a, b, c desorption reactors
  • 4, 4a gas pumps (blowers),
  • 5a, b, c heat exchanger
  • 6a, b, c heat exchanger
  • 7a, b, c gas lines from desorption reactors 3a, b, c to sorption reactor 1 (via heat exchangers 6a, b, c)
  • 8a gas line from the sorption reactor 1 to the desorption reactor 3a via the gas pump 4, the valve 9a and the heat exchanger 5a
  • 8b, c gas lines branching from the gas line 8a to the desorption reactors 3b, c via the valves 9b, c and the heat exchangers 5b, c 9a, b, c valves (taps)
  • 10, 10a three-way valves (three-way valves)
  • 11 Gas line from three-way valve 10 to gas line 8a
  • 11 c gas line from the three-way valve 10a via the valve 9c and the heat exchanger 5c to the desorption reactor 3c
  • 11 b gas line branching from the gas line 11 c via the valve 9b and the heat exchanger 5b to the desorption reactor 3b
  • 12 These arrows symbolize the material flow

Der Sorptionsreaktor 1 ist über die Gasleitung 8a, die Pumpe 4, das Ventil 9a und den Wärmetauscher 5a mit dem Desorptionsreaktor 3a, und dieser über die Gasleitung 7a und den Wärmetauscher 6a mit dem Sorptionsreaktor 1 verbunden. Ferner ist der Sorptionsreaktor 1 über die Gasleitung 8a, die Pumpe 4, die Gasleitungen 8b bzw. 8c, die Ventile 9b bzw. 9c und die Wärmetauscher 5b bzw. 5c mit den Desorptionsreaktoren 3b bzw. 3c, und diese über die Gasleitungen 7b bzw. 7c und die Wärmetauscher 6b bzw. 6c mit dem Sorptionsreaktor 1 verbunden.The sorption reactor 1 is connected to the desorption reactor 3a via the gas line 8a, the pump 4, the valve 9a and the heat exchanger 5a, and this is connected to the sorption reactor 1 via the gas line 7a and the heat exchanger 6a. Furthermore, the sorption reactor 1 is connected to the desorption reactors 3b and 3c via the gas line 8a, the pump 4, the gas lines 8b and 8c, the valves 9b and 9c and the heat exchangers 5b and 5c, and these are connected via the gas lines 7b and 3c. 7c and the heat exchangers 6b and 6c connected to the sorption reactor 1.

Das aufzuschliessende zellulosehaltige Material (Substrat) wird in den Sorptionsreaktor 1 eingebracht. In den Figuren 1 und 3 wird dieser Vorgang durch den Pfeil 12a symbolisiert.The cellulosic material (substrate) to be digested is introduced into the sorption reactor 1. This process is symbolized by the arrow 12a in FIGS. 1 and 3.

Durch die Gasleitungen 7a, 7b und 7c werden dem Sorptionsreaktor 1 HF/Inertgas-Gemische, deren HF-Konzentration in der Gasleitung 7a am niedrigsten und in der Gasleitung 7c am höchsten ist, zugeführt. Im Sorptionsreaktor 1 strömen diese dem Substrat entgegen und treten als fast vollständig HF-freier Gesamtgasstrom aus dem Reaktor 1 aus.HF / inert gas mixtures, the HF concentration of which is lowest in the gas line 7a and highest in the gas line 7c, are supplied to the sorption reactor 1 through the gas lines 7a, 7b and 7c. In the sorption reactor 1, they flow against the substrate and emerge from the reactor 1 as an almost completely HF-free total gas stream.

Vom Sorptionsreaktor 1 wird das mit H F beladene Substrat in den Verweilreaktor 2 transportiert (Pfeil 12b) und von dort nacheinander in den ersten, zweiten und dritten Desorptionsreaktor 3c, 3b und 3a (Pfeile 12c, 12d und 12e).The substrate loaded with H F is transported from the sorption reactor 1 to the residence reactor 2 (arrow 12b) and from there successively into the first, second and third desorption reactors 3c, 3b and 3a (arrows 12c, 12d and 12e).

Der den Sorptionsreaktor 1 verlassende Gasstrom wird nach Passieren der Gasleitung 8a und der Pumpe 4 in drei Teilströme, entsprechend der jeweiligen Einstellung der Ventile 9a, 9b und 9c aufgeteilt. Nach Erwärmung in den Wärmetauschern 5a bzw. 5c treten diese Teilgasströme in die Desorptionsreaktoren 3a bzw. 3b bzw. 3c ein und durchströmen diese im Gegenstrom zum oder, vorzugsweise, im Gleichstrom mit dem Substrat.The gas stream leaving the sorption reactor 1 is divided into three partial flows after passing through the gas line 8a and the pump 4, in accordance with the respective setting of the valves 9a, 9b and 9c. After heating in the heat exchangers 5a or 5c, these partial gas flows enter the desorption reactors 3a or 3b or 3c and flow through them in countercurrent to or, preferably, in cocurrent with the substrate.

Durch die Einwirkung der erwärmten Gasströme auf das H F-beladene Substrat wird H desorbiert. Im ersten Desorptionsreaktor 3c wird, da hier das Substrat mit maximaler H F- Beladung eingebracht wird, am meisten HF durch Desorption frei, im Reaktor 3b eine geringere Menge, und im letzten Desorptionsreaktor 3a, in den das Substrat bereits grösstenteils von HF befreit eintritt, wird die geringste H F-Menge frei. Enstprechend sind die HF-Konzentrationen im den die Desorptionsreaktoren verlassenden Gasströmen beim Reaktor 3c am höchsten und beim Reaktor 3a am geringsten. Der H F- Basstrom, der aus dem Reaktor 3b austritt, hat eine dazwischenliegende mittlere HF-Konzentration.H is desorbed by the action of the heated gas streams on the H F-loaded substrate. In the first desorption reactor 3c, since the substrate with the maximum HF loading is introduced, most HF is released by desorption, a smaller amount is released in the reactor 3b, and in the last desorption reactor 3a, in which the substrate already largely frees from HF, the least amount of HF is released. Accordingly, the HF concentrations in the gas streams leaving the desorption reactors are highest in reactor 3c and lowest in reactor 3a. The HF base stream exiting the reactor 3b has an intermediate HF concentration in between.

Die HF-Gasströme unterschiedlicher HF-Konzentration werden durch die Gasleitungen 7a bzw. 7b bzw. 7c- nach Passieren derzwischengeschalteten Wärmetauscher 6a bzw. 6b bzw. 6c - an verschiedenen Einlassstellen des Sorptionsreaktors 1 in diesen eingespeist. Dabei trifft der HF-Gasstrom aus der Gasleitung 7a mit der geringsten HF-Konzentration auf Substrat, das erst ganz wenig mit HF beladen ist. Der HF-Gasstrom aus der Gasleitung 7c mit der höchsten HF-Konzentration trifft auf Substrat, das (nahezu) die maximale HF-Beladung aufweist. Der HF-Gasstrom aus der Gasleitung 7b wird an einer dazwischen liegenden Stelle des Sorptionsreaktors 1 auf Substrat einwirken gelassen, das bereits eine relativ hohe HF-Beladung aufweist.The HF gas streams of different HF concentrations are fed through the gas lines 7a or 7b or 7c - after passing through the intermediary heat exchangers 6a or 6b or 6c - at different inlet points of the sorption reactor 1. The HF gas flow from the gas line 7a with the lowest HF concentration strikes substrate which is only very slightly loaded with HF. The HF gas stream from the gas line 7c with the highest HF concentration strikes the substrate which (almost) has the maximum HF loading. The HF gas flow from the gas line 7b is allowed to act on the substrate at an intermediate point of the sorption reactor 1, which substrate already has a relatively high HF load.

Nach erfolgter Desorption im Reaktor 3a verlässt das Substrat diesen in nunmehr aufgeschlossener Form (Pfeil 12f). Es enthält nur noch Spuren von Rest-Fluorwasserstoff und wird der Aufarbeitung zugeführt, die in an sich bekannter Weise erfolgt.After desorption has taken place in the reactor 3a, the substrate leaves it in an open form (arrow 12f). It only contains traces of residual hydrogen fluoride and is processed, which is carried out in a manner known per se.

Eine besondere Ausführungsform wird schematisch in Fig. 2 dargestellt. In die Gasleitung 7a wird ein Dreiwegeventil 10 zwischengeschaltet, das es erlaubt, einen (mehr oder weniger grossen) Teil des aus dem Desorptionsreaktor 3a austretenden HF-Gasstroms über eine Gasleitung 11 in einen speziellen Kreislauf wieder zurückzuführen und zwischen dem Ventil 9a und einer zwischengeschalteten Pumpe 4a in die Gasleitung 8a über eine Verzweigung einzuleiten. Das Dreiwegeventil 10 kann auch ein Steuerventil sein. Der in diesem speziellen Kreislauf zurückgeführte Teil des HF/Inertgas-Gemisches beträgt etwa 10 bis etwa 90, vorzugsweise etwa 50 bis etwa 90%, des Gesamtgemisches, das den Desorptionsreaktor 3a verlässt. Selbstverständlich kann man das Dreiwegeventil 10 durch ein T-Stück ersetzen und in die Gasleitung 11 ein (Steuer)ventil einbauen.A special embodiment is shown schematically in FIG. 2. A three-way valve 10 is interposed in the gas line 7a, which allows a (more or less) part of the HF gas stream emerging from the desorption reactor 3a to be returned to a special circuit via a gas line 11 and between the valve 9a and an intermediate pump 4a into the gas line 8a via a branch. The three-way valve 10 can also be a control valve. The part of the HF / inert gas mixture which is returned in this special circuit is about 10 to about 90, preferably about 50 to about 90%, of the total mixture which leaves the desorption reactor 3a. Of course, you can replace the three-way valve 10 with a T-piece and install a (control) valve in the gas line 11.

Diese besondere Anordnung, die analog auch eine teilweise Rückführung der die Desorptionsreaktoren 3c bzw. 3b verlassenden HF/Inertgas-Gemische ermöglicht, erlaubt es, die Gasgeschwindigkeiten der durchlaufenden HF/Inertgas-Gemische zu optimieren.This particular arrangement, which analogously also allows partial recirculation of the HF / inert gas mixtures leaving the desorption reactors 3c or 3b, allows the gas velocities of the HF / inert gas mixtures passing through to be optimized.

Fig. 3 zeigt eine weitere besondere Ausführungsform des erfindungsgemässen Verfahrens. In die Gasleitung 7a wird ein Dreiwegeventil 10a zwischengeschaltet, das es erlaubt, die Aufteilung des den Sorptionsreaktor 1 verlassenden Gasstroms in Teilgasströme erst nach Passieren des Desorptionsreaktors 3a vorzunehmen. Während ein Teilstrom nur den Reaktor 3a passiert und direkt dem Sorptionsreaktor 1 zugeführt wird, werden die beiden anderen Teilströme noch durch einen zweiten Desorptionsreaktor 3c bzw. 3b geleitet, bevor sie durch die Gasleitungen 7c bzw. 7b dem Reaktor 1 zugeführt werden.3 shows a further special embodiment of the method according to the invention. In the gas line 7a is interposed with a three-way valve 10a, which allows the gas stream leaving the sorption reactor 1 to be divided into partial gas streams only after it has passed the desorption reactor 3a. While a partial stream only passes through the reactor 3a and is fed directly to the sorption reactor 1, the other two partial streams are still passed through a second desorption reactor 3c or 3b before they are fed to the reactor 1 through the gas lines 7c or 7b.

Diese besondere Ausführungsform erlaubt in der letzten Desorptionsstufe das Einwirken einer möglichst grossen Gasmenge, das heisst der gesamten Trägergasmenge, auf das Substrat, wodurch die Desorption beschleunigt wird.This particular embodiment allows the largest possible amount of gas, that is to say the total amount of carrier gas, to act on the substrate in the last desorption stage, as a result of which the desorption is accelerated.

Es ist vorteilhaft, eventuell im den Sorptionsreaktor verlassenden Gasstrom noch enthaltenes H F zur Sorption auszunutzen, indem man diesen Gasstrom durch den Substrat-Vorratssilo leitet, bevor er über die Gasleitung 8a der Pumpe 4 zugeführt wird.It is advantageous to use any H F still present in the gas stream leaving the sorption reactor for sorption by passing this gas stream through the substrate storage silo before it is fed to the pump 4 via the gas line 8a.

Das nach dem erfindungsgemässen Verfahren hergestellte, aufgeschlossene Material stellt ein Gemisch aus Lignin und oligomeren Sacchariden dar. Es kann in an sich bekannter Weise durch Extraktion mit Wasser, zweckmässig in der Wärme oder Siedehitze, und durch gleichzeitiges oder anschliessendes Neutralisieren mit Kalk aufgearbeitet werden. Eine Filtration liefert Lignin, das z.B. als Brennmaterial Verwendung finden kann, sowie eine geringe Menge Calciumfluorid, das von dem im Reaktionsgut enthaltenen Restfluorwasserstoff herrührt. Das Filtrat, eine klare, schwach gelbliche Zuckerlösung, kann entweder unmittelbar oder nach Einstellen einer zweckmässigen Konzentration der alkoholischen Gärung bzw. Fermentierung zugeführt werden. Die gelösten, oligomeren Zucker können auch durch kurze Nachbehandlung, z.B. mit stark verdünnter Mineralsäure bei Temperaturen oberhalb 100 °C, nahezu quantitativ in Glucose überführt werden.The digested material produced by the process according to the invention is a mixture of lignin and oligomeric saccharides. It can be worked up in a manner known per se by extraction with water, expediently in the heat or boiling heat, and by simultaneous or subsequent neutralization with lime. Filtration provides lignin, e.g. can be used as fuel, as well as a small amount of calcium fluoride, which results from the residual fluoride contained in the reaction material. The filtrate, a clear, slightly yellowish sugar solution, can be added to the alcoholic fermentation or fermentation either immediately or after setting an appropriate concentration. The dissolved, oligomeric sugars can also be treated by brief post-treatment, e.g. with highly diluted mineral acid at temperatures above 100 ° C, almost quantitatively converted into glucose.

Beispiel 1example 1

Beispiel 1 wurde in einer apparativen Anordnung durchgeführt, die schematisch in Fig. 1 dargestellt ist. Sie bestand aus einem Sorptionsreaktor 1, einem Verweilreaktor 2 und drei Desorptionsreaktoren 3a, 3b, 3c, die miteinander durch Rohrleitungen und Zellenradschleusen verbunden waren. Als Sorptionsreaktor diente ein senkrecht stehendes Rohr aus nichtrostendem Stahl von 5 cm lichter Weite und 80 cm Länge, das am oberen Ende eine gasdichte Zellenradschleuse mit Einfülltrichter trug und am unteren Ende ebenfalls mit einer gasdichten Zellenradschleuse versehen war. In der Längsachse des Rohres war eine langsam rotierende, mit schmalen Flügeln versehene Welle angebracht. An 3 Stellen, die über die unteren zwei Drittel der Rohrlänge verteilt waren, befanden sich Einleitungen für HF-haltige Gase. Die Gasaustrittsöffnung befand sich kurz unterhalb der oberen Zellenradschleuse. Der Verweilreaktor war ein zylindrisches Gefäss von ca. 2 I Inhalt aus halbtransparentem Polyethylen. Die Desorptionsreaktoren bestanden aus nichtrostendem Stahl und waren als heizbare Drehrohrreaktoren ausgebildet, die vom Substrat und von den strömenden Gasen gleichsinnig durchflossen werden konnten. Das nutzbare Volumen der Desorptionsreaktoren betrug jeweils etwa 3 I.Example 1 was carried out in an apparatus arrangement which is shown schematically in FIG. 1. It consisted of a sorption reactor 1, a residence reactor 2 and three desorption reactors 3a, 3b, 3c, which were connected to one another by pipelines and cellular wheel locks. A vertical tube made of stainless steel with a clear width of 5 cm and a length of 80 cm was used as the sorption reactor, which carried a gas-tight rotary valve with a filling funnel at the upper end and was also provided with a gas-tight rotary valve at the lower end. In the longitudinal axis of the tube was a slowly rotating shaft with narrow wings. At 3 points, which were distributed over the lower two thirds of the pipe length, there were inlets for HF-containing gases. The gas outlet opening was located just below the top rotary valve. The indwelling reactor was a cylindrical vessel of approx. 2 l made of semi-transparent polyethylene. The desorption reactors were made of stainless steel and were designed as heatable rotary tube reactors through which the substrate and the flowing gases could flow in the same direction. The usable volume of the desorption reactors was about 3 I.

Im Sorptionsreaktor 1 wurde gekörnte Lignocellulose, die als Rückstand bei einer Vorhydrolyse von Fichtenholzspänen erhalten worden war und einen Wassergehalt von etwa 3 Gew.-% aufwies, kontinuierlich durch ihr Eigengewicht von oben nach unten gefördert. Durch die drei Gaseinleitungen wurden aus der Desorption stammende HF/ Stickstoff-Gemische verschiedener Konzentration eingeleitet, und zwar an der untersten Einleitungsstelle mit der höchsten, an der obersten mit der niedrigsten HF-Konzentration. Mit Hilfe von am unteren Zellenrad entnommenen Proben wurde die Fördergeschwindigkeit so einreguliert, dass das aus dem Reaktor austretende Reaktionsgemisch etwa 60 g HF auf 100 g eingesetzte Lignocellulose enthielt. Aus der unteren Zellenradschleuse gelangte das Substrat durch freien Fall in den Verweilreaktor 2 und verblieb dort durchschnittlich 30 min. Durch Anblasen des Gefässes mit warmer Luft wurde im Inneren eine Temperatur von 50 °C aufrechterhalten. Der den Sorptionsreaktor 1 oben verlassende, nahezu HF-freie Stickstoff wurde durch eine Gasleitung 8a über eine Gaspumpe 4 und die abzweigenden Gasleitungen 8b, 8c auf die drei Desorptionsreaktoren 3a, 3b, 3c verteilt. Mit Hilfe der Drosselventile 9a, 9b, 9c und der Gaserhitzer 5a, 5b, 5c wurde der in den jeweiligen Desorptionsreaktor eingeleitete Stickstoff so einreguliert, dass unter Mitwirkung der am Reaktor selbst vorhandenen Heizung die folgenden Gasgemische und Desorptionsgrade erhalten wurden.In the sorption reactor 1, granular lignocellulose, which had been obtained as a residue from a pre-hydrolysis of spruce wood chips and had a water content of about 3% by weight, was continuously conveyed from top to bottom by its own weight. HF / nitrogen mixtures of various concentrations originating from the desorption were introduced through the three gas introductions, specifically at the lowest introduction point with the highest, at the uppermost with the lowest HF concentration. With the aid of samples taken from the lower cellular wheel, the conveying speed was adjusted so that the reaction mixture emerging from the reactor contained about 60 g HF per 100 g lignocellulose used. From the lower cellular wheel sluice, the substrate passed freely into the dwell reactor 2 and remained there for an average of 30 minutes. By blowing the vessel with warm air, a temperature of 50 ° C was maintained inside. The almost HF-free nitrogen leaving the sorption reactor 1 above was distributed to the three desorption reactors 3a, 3b, 3c through a gas line 8a via a gas pump 4 and the branching gas lines 8b, 8c. With the help of the throttle valves 9a, 9b, 9c and the gas heaters 5a, 5b, 5c, the nitrogen introduced into the respective desorption reactor was regulated in such a way that the following gas mixtures and degrees of desorption were obtained with the help of the heating provided on the reactor itself.

Erster Desorptionsreaktor 3c: Eingetragen wurde aus dem Verweilreaktor 2 mittels gasdichter Zellenradschleuse im Gewichtsverhältnis 60: 100 mit HF beladene Lignocellulose; ausgetragen wurde ein Substrat mit einer Beladung von ca. 35: 100 (Gew.-Verhältnis HF zu Lignocellulose); die Desorptionstemperatur lag bei 60 bis 70 °C; das austretende Gasgemisch enthielt ca. 65 Gew.-% H F.First desorption reactor 3c: Lignocellulose was loaded from the dwelling reactor 2 by means of a gas-tight cellular wheel sluice in a weight ratio of 60: 100; a substrate with a loading of approx. 35: 100 (weight ratio HF to lignocellulose) was discharged; the desorption temperature was 60 to 70 ° C; the escaping gas mixture contained approx. 65% by weight H F.

Zweiter Desorptionsreaktor 3b: Eingetragen wurde das mit HF beladene Produkt aus dem ersten Desorptionsreaktor 3c mittels gasdichter Zellenradschleuse; ausgetragen wurde ein Substrat mit einer Beladung von ca. 10:100; die Desorptionstemperatur lag bei 70-80 °C; das austretende Gasgemisch enthielt ca. 25 Gew.-% HF.Second desorption reactor 3b: The HF-loaded product from the first desorption reactor 3c was introduced by means of a gas-tight rotary valve; a substrate with a loading of approx. 10: 100 was discharged; the desorption temperature was 70-80 ° C; the exiting gas mixture contained about 25% by weight of HF.

Dritter Desorptionsreaktor 3a: Eingetragen wurde das mit HF F beladene Produkt aus dem zweiten Desorptionsreaktor 3b mittels gasdichter Zellenradschleuse; ausgetragen wurde ein Substrat mit ca. 0,5 Gew.-% HF; die Desorptionstemperatur lag bei ca. 90 °C; das austretende Gasgemisch enthielt ca. 5 Gew.-% HF.Third desorption reactor 3a: The product loaded with HF F was entered from the second desorption reactor 3b by means of a gas-tight rotary valve; a substrate with approximately 0.5% by weight HF was discharged; the desorption temperature was approx. 90 ° C; the exiting gas mixture contained about 5% by weight of HF.

Die in den Desorptionsreaktoren erzeugten drei Gasgemische wurden durch die Rohrleitungen 7a, 7b, 7c und die Wärmetauscher 6a, 6b, 6c, wo sie auf 25 bis 30 °C abgekühlt wurden, in der oben bereits beschriebenen Weise in den Sorptionsreaktor 1 geleitet, so dass unter kontinuierlicher Förderung von Substrat durch die Apparatur Kreisläufe von Trägergas (Stickstoff) und H F zustande kamen.The three gas mixtures generated in the desorption reactors were passed through the pipes 7a, 7b, 7c and the heat exchangers 6a, 6b, 6c, where they were cooled to 25 to 30 ° C., in the above already described in the sorption reactor 1, so that with continuous delivery of substrate through the apparatus circuits of carrier gas (nitrogen) and HF came about.

Das aufgeschlossene, von HF weitgehend befreite Substrat wurde in üblicher Weise mit heissem Wasser extrahiert, die so erhaltene Lösung mit Calciumhydroxid neutralisiert, filtriert und eingedampft. Es wurde so Holzzucker von heller Farbe in einer Ausbeute von 90%, bezogen auf die ursprünglich vorhandene Cellulose, erhalten.The digested substrate, largely freed of HF, was extracted in the usual way with hot water, the solution thus obtained was neutralized with calcium hydroxide, filtered and evaporated. Wood sugar of light color was obtained in a yield of 90%, based on the cellulose originally present.

Beispiel 2Example 2

In der in Beispiel 1 beschriebenen Apparatur und nach dem dort ausführlich beschriebenen Verfahren wurden rohe, bis auf eine Restfeuchte von etwa 5 Gew.-% getrocknete Fichtenholz-Hobelspäne aufgeschlossen. Bei der Desorption in den Reaktoren 3c bis 3a wurden Holzbegleitstoffe wie Essigsäure mit ausgetrieben und in den Wärmetauschern 6c bis 6a auskondensiert und abgetrennt. Nach üblicher Aufarbeitung, wie in Beispiel 1 beschrieben, wurde Holzzucker in einer Ausbeute von etwa 70 Gew.-%, bezogen auf die im eingesetzten Material enthaltenen Kohlenhydrate, erhalten.In the apparatus described in Example 1 and according to the process described in detail there, raw spruce wood shavings were broken down to a residual moisture content of about 5% by weight. During the desorption in the reactors 3c to 3a, wood accompanying substances such as acetic acid were driven off and condensed and separated in the heat exchangers 6c to 6a. After the usual work-up, as described in Example 1, wood sugar was obtained in a yield of about 70% by weight, based on the carbohydrates contained in the material used.

Claims (5)

1. A continuous process for digesting cellulose-containing substrate with gaseous hydrogen fluoride by sorption of the HF and subsequent desorption, which comprises carrying out the sorption of the HF by the substrate at a temperature above its boiling point in a sorption step, and then the sorbed H F is removed from the substrate by heating in n desorption steps, wherein n is a whole number and wherein the steps mentioned are carried out in reactors which are each separated from one another in a gas-tight manner, and wherein the substrate is introduced through a gas-tight valve into the sorption reactor, passes through this and then consecutively reaches, through gas-tight valves, the first, second, ..., nth desorption reactor and is removed from the last (nth) desorption reactor, and wherein the desorption is carried out in each case by action of one of n heated gas streams, counter-currently or, preferably, cocurrently with the substrate, with enrichment of the particular gas stream with the H being liberated during desorption, and wherein the n enriched HF gas streams, which contain an inert carrier gas in addition to H F, act on the substrate in the sorption reactor, counter-currently thereto, in such a manner that gas streams of low HF concentration act on substrate which has zero or only a low concentration of H F and gas streams of high HF concentration act on substrate which has a higher HF concentration, and wherein the total gas stream being produced from the individual gas streams leaves, after completion of sorption, the sorption reactor, being largely freed of HF, and is either conveyed, after division into individual gas streams, in the circulation to the desorption steps, or initially passes through the last desorption step and thereafter is divided up and conveyed to the other desorption steps and the sorption reactor.
2. The process as claimed in Claim 1, wherein n is a whole number from 1 to 6, in particular from 2 to 4.
3. The process as claimed in one of Claims 1 or 2, wherein a preliminary hydrolyzate of wood, waste from annual plants or waste paper is employed as the substrate.
4. The process as claimed in any of Claims 1 to 3, wherein air or nitrogen is used as the inert carrier gas.
5. The process as claimed in any of Claims 1 to 4, wherein an HF gas stream or several HF gas streams is (are) divided up after leaving the desorption reactor(s) and one part is directly returned to the inlet of the desorption reactor(s).
EP82109718A 1981-10-24 1982-10-21 Process for treating cellulosic materials with gaseous hydrofluoric acid Expired EP0078023B1 (en)

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US4556432A (en) 1985-12-03
ATE12258T1 (en) 1985-04-15
CA1192706A (en) 1985-09-03
EP0078023A1 (en) 1983-05-04

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