EP0081678B1 - Process and apparatus for the hydrolysis of cellulose - Google Patents

Abstract

A method for acid-catalyzed hydrolytic splitting of cellulose to give a high yield in sugar with a minimal expenditure in energy, in particular, with the smallest possible charge of live steam. Admission of steam is performed in a plurality of successive, discrete reaction stages having in each case defined temperature and pressure values in such a manner that the temperature rises from one stage to the next while the reaction time decreases and a rapid expansion takes place subsequently to the last reaction stage. A high pressure poured bed reactor is used for performing this method.

Description

The invention relates to a method according to the preamble of claim 1 and an apparatus for performing this method.

In the course of the overall development of the energy industry, alcohol is becoming increasingly important as a fuel or as a fuel additive. Alcohol for such purposes can be produced from cellulose or cellulose-containing biomass in two stages by first hydrolyzing cellulose to sugar and then fermenting it to ethanol. While the fermentation of sugar to ethanol is technically well mastered, the hydrolysis of cellulose remains the critical process step that decides on the overall economy of the process.

In the known, essentially based on Bergius and Scholler (DE-C-577 850) processes of acid-catalyzed hydrolysis of cellulose, shortcomings lie primarily in the fact that the energy content of the alcohol produced is often lower than the energy required to operate the overall system, the especially in the form of heating steam and electric current.

So z. B. from DE-A-1567350 and 1567335 percolator fixed bed reactors for a semi-continuous hydrolysis, where batches of dilute sulfuric acid trickle over a fixed bed of wood chips, and at a hydrolysis temperature of 120 to 145 ° C and a residence time of 15 to 60 minutes Cellulose is converted to glucose with a yield of approximately 50%. In addition to the relatively unfavorable glucose yield, a high specific energy input is required.

A major theoretical approach to improvement results from the publication by Hans E. Grethlein in the journal "Biotechnology and Bioengineering •, Vol. 11 (1978), pages 503 to 525" Comparison of the Economics of Acid and Enzymatic Hydrolysis of Newsprint •. There it was postulated that a high yield of glucose, based on the ALPHA cellulose used, is achieved if the hydrolysis temperatures are raised above 250 ° C. to 300 ° C. at pressures of 40 to 90 bar, and if dilute sulfuric acid is used at a concentration of up to 2.0% used and the hydrolysis time is extremely short.

Based on this situation, the object of the invention is to create a method and a device by means of which high yields of fermentable sugar, based on the cellulose used, of over 60% are achieved, by means of which the energy requirement is as low as possible, in particular below 0.5 kg of steam per kg of dry matter and less than 0.01 kWh of drive energy per kg of dry matter is kept, by means of which the investment costs remain within a reasonable range and ultimately an environmental friendliness of the process itself and of the by-products to be eliminated is guaranteed.

The starting point for the solution according to the invention were experimental studies of the kinetics of hydrolysis, by means of which the theoretical foundations were supplemented and completed for a technical application. The experiments showed that the yield of fermentable sugar, depending on the reaction time, runs through a maximum, that as the temperature rises, it becomes higher and narrower, and with short residence times. The selectivity to fermentable sugar drops more slowly at higher temperatures with increasing sales. These results, which are described in more detail below in connection with an exemplary embodiment, lead to the knowledge on which the invention is based that the desired maximum yield to sugar can be achieved in a particularly advantageous manner by means of a cyclical temperature control.

Accordingly, the object of the invention is achieved in a method of the generic type by the characterizing features of claim 1. By coordinating the reaction time to the respective temperature level in such a way that the respective maximum of the yield is recorded, so that overall the greatest possible yield can be achieved. In principle, the temperature parameter can be freely selected over a wide range if only the corresponding decrease in the reaction time with increasing temperature is ensured. The number of reaction stages is dimensioned such that the ratio of the data characteristic of the respective stage to the reaction time of this stage is sufficiently high and remains sufficiently manageable within the framework of an industrial process. By working with different reaction stages, it is also possible that the heating steam supply does not have to be continuous or in one go, but can take place according to the individual reaction stages, which in principle allows a very favorable utilization of the total amount of steam used.

A very advantageous possibility of quantitative measurement of the individual reaction stages is made possible by the procedure according to claim 2. The relationship between the reaction temperature and duration given there also makes it possible to set the temperature stages in such a way that reaction times which are technically manageable result.

By proceeding according to claim 3, the desired maximum utilization of the steam used is largely achieved. It is assumed that the process according to the invention is carried out quasi-continuously, that is to say that a large number of reaction stage runs are carried out on one another closes. In this way, the advantages of a continuous operation are combined with the favorable situation with regard to the yield in batch processes.

A measure that also goes in the direction of minimizing the required superheated steam is proposed by claim 4.

A device according to claim 5 is used to carry out the method described above. A fluidized bed reactor provided thereafter creates the conditions for the short to very short reaction times desired according to the invention, since the reaction times of the stage can be set very quickly there. The preheating chamber, which is also provided, allows the waste heat to be used advantageously, and its assignment to the actual reaction vessel results in very short transport routes for the products to be subjected to hydrolysis, the plunger representing a type of feed of the starting material, which in particular also enables quasi-continuous operation .

Due to the design of the reactor vessel according to claim 6, good product fluidization is achieved in the steam supply and favorable product / steam separation is achieved in the steam relaxation. The sealing forces for the inlet and outlet valve are applied by the excess pressure inside the reactor vessel, so that the hydraulic or pneumatic actuating devices can work with only slight forces.

The stripping devices provided according to claim 7 eliminate cellulose residues which stick to the actuating rod in the preheating chamber during the preheating process. In addition, water showers can be provided for cleaning the valve closing part.

An embodiment according to claim 8 also ensures that the material to be hydrolyzed is fluidized in the reactor vessel and is surrounded on all sides by condensing water vapor. This avoids the formation of lumps, which would increase the heating times.

By arranging the ring nozzle channel according to claim 9, the rapid relaxation important for kinetic reasons is also promoted at the end of each cycle stage. The rate of expansion may at most be such that no hydrolysis product or remaining starting material escapes from the reactor vessel through the steam discharge line.

The embodiment according to claim 10 enables in particular the implementation of the live steam-saving method step according to claim 3, which applies accordingly to the measure of claim 11 with regard to the procedural procedure according to claim 4.

• Figur 1 eine schematische Darstellung einer erfindungsgemäßen Vorrichtung mit einem Schnitt durch das Reaktorgefäß ;
• Figur 2 ein die einzelnen Reaktionsstufen veranschaulichendes Diagramm ;
• Figur 3 eine grafische Darstellung der experimentell gewonnenen Ergebnisse für die Abhängigkeit von Selektivität und Umsatz von Cellulose und Ausbeute von Zucker in Abhängigkeit von der Reaktionszeit;
• Figur 4 eine grafische Darstellung der Abhängigkeit der Selektivität zu Zucker vom Umsatz von Cellulose und
• Figur 5 die Abhängigkeit des spezifischen Dampfverbrauchs von der Zahl der Hydrolysestufen bzw. der Dampfspeicher.

Further features, advantages and details of the invention result from the following description of a preferred embodiment with reference to the drawing. Show:

• Figure 1 is a schematic representation of a device according to the invention with a section through the reactor vessel;
• FIG. 2 shows a diagram illustrating the individual reaction stages;
• FIG. 3 shows a graphic representation of the experimentally obtained results for the dependence on selectivity and conversion of cellulose and yield of sugar as a function of the reaction time;
• Figure 4 is a graphic representation of the dependence of the selectivity to sugar on the conversion of cellulose and
• Figure 5 shows the dependence of the specific steam consumption on the number of hydrolysis stages or the steam store.

• Wie in Fig. 3 dargestellt, durchläuft die Ausbeute A an vergärbarem Zucker, d. h. die Menge an Zucker bezogen auf die eingesetzte Alpha-Cellulose, in Abhängigkeit von der Reaktionszeit ein Maximum, das bei steigenden Temperaturen höher und schmaler wird und bei kürzeren Verweilzeiten liegt. In Fig. 3 sind für drei Temperaturbereiche drei entsprechende Maxima dargestellt. Der Umsatz U an Cellulose verläuft nach einer Exponentialfunktion von 0 % bei einer Verweilzeit 0 gegen 100 % bei sehr langen Verweilzelten (vgl. ebenfalls Fig. 3). Die zusätzliche Bestimmung der Selektivität S zu vergärbarem Zucker, d. h. die Menge an Zucker bezogen auf die umgesetzte Menge an Alpha-Cellulose, ergibt. wie in Fig. 4 dargestellt, daß die Selektivitat S bei einer Temperatur von 175 °C bei einem Umsatz von 0 % bei ca. 100 % beginnt und dann bei höheren Umsätzen rasch abfällt. Dagegen beginnt die Selektivität S bei einem Umsatz von 0 '. bei der Temperatur 225 °C bei 95 %, bei 260 C sogar erst bei 90 %, und der Abfall erfolgt dabei jeweils bei steigendem Umsatz langsamer Diese Erscheinung ist durch eine konkurrierende Reaktion bei höheren Temperaturen zu erklaren

The basis for the procedure according to the invention is formed by the experiments carried out in connection with the invention, the results of which can be summarized as follows:

• As shown in FIG. 3, the yield A of fermentable sugar, ie the amount of sugar based on the alpha-cellulose used, runs through a maximum as a function of the reaction time, which becomes higher and narrower with increasing temperatures and with shorter residence times. 3 shows three corresponding maxima for three temperature ranges. The conversion U of cellulose follows an exponential function of 0% with a dwell time of 0 against 100% in the case of very long dwellings (cf. also FIG. 3). The additional determination of the selectivity S for fermentable sugar, ie the amount of sugar based on the amount of converted alpha-cellulose, results. as shown in Fig. 4, that the selectivity S begins at a temperature of 175 ° C with a conversion of 0% at about 100% and then drops rapidly with higher conversions. In contrast, the selectivity S begins with a conversion of 0 '. at the temperature 225 ° C at 95%, at 260 C even at 90%, and the drop occurs more slowly with increasing sales. This phenomenon can be explained by a competing reaction at higher temperatures

From these experimental results, the basic idea according to the invention results that a maximum yield of sugar can be obtained in a particularly favorable manner by a cyclical temperature increase. On the basis of the test results shown in FIGS. 3 and 4, an advantageous possibility for carrying out the method according to the invention is a reaction stage run. as illustrated in Fig. 2.

Accordingly, the material to be hydrolyzed, e.g. B. waste paper, residual wood, straw and. Like., First crushed in a conventional manner. then impregnated in a dilute sulfuric acid or other suitable acid solution of 0.5 to 10%, then mechanically dewatered to 10 to 80% by weight of moisture and then loosely poured into a preheating chamber of a reactor vessel in a comminuted form again. In the preheating chamber, the starting material is heated from room temperature to 100 ° C. by condensation of the steam by means of steam from a previous reaction stage pass. The material is then passed from the preheating chamber into the actual reactor vessel.

In a first reaction stage 1, the cellulose conversion is allowed to rise from 0 to 4% at a temperature of 175 ° C. for a reaction time of 40 seconds. In the following stage II, the conversion at a temperature of 225 ° C. during a reaction time of 4.5 seconds is increased from 4% to 30%, and finally the conversion in stage III at a temperature of 260 ° C. during a reaction time increased from 30% to 85% from 1.3 sec. After the reaction time of the last stage 111 has expired, the temperature is rapidly lowered by releasing the steam in the reaction vessel in order to prevent a further reaction which would preferably decompose the sugar formed.

Against the background of the experimental results, it can be seen that this mode of operation gives a higher yield of fermented sugars than if the reaction temperature were suddenly raised to 260 ° C. and the reaction was allowed to proceed from conversion 0 to 85%.

• Die zur Materialaufwärmung zum Zustand a (auf 100 °C vorgewärmtes Material) auf Zustand b (Reaktionsstufe I) und zur Druckbeaufschlagung des Reaktionsgefäßes vom Druck _P1 auf _P2 erforderliche Dampfmenge ist gleich derjenigen, die bei einer stufenweisen Entspannung vom Zustand c (Reaktionsstufe II) in den Zustand b frei wird. Ein Dampfspeicher im Zustand b ist daher in der Lage, aus dem eingespeisten Entspannungsdampf aus der Zustandsänderung c-b den erforderlichen Heizdampf für die Zustandsänderung a-b zu liefern.

The steam control described below by way of example also achieves minimal fresh steam consumption in addition to a high yield. Assuming balanced steam and energy balances in a reactor vessel at each reaction stage, the procedure for a freely selected number of 3 stages is as follows:

• The amount of steam required to warm up the material to state a (material preheated to 100 ° C) to state b (reaction stage I) and to pressurize the reaction vessel from pressure _P1 to _P2 is the same as that in a gradual relaxation from state c (reaction stage II) in the state b becomes free. A steam accumulator in state b is therefore able to supply the heating steam required for the state change from the expansion steam fed in from the state change cb.

The amount of steam required to heat the material from state b to c and to pressurize the reactor to pressure _P3 is the same as that which is released during the expansion from state d to state c. A second steam accumulator in state c is therefore able to supply the heating steam required for the state change bd from the expansion steam fed in from the state change dc.

The amount of steam required to heat the material from state c to d and to pressurize the reactor vessel to pressure _P4 must be supplied by a steam generator. Its pressure _Ps is expediently chosen to be very high, e.g. B. 100 bar, so that the heating time from state c to d is very short compared to the reaction time.

The exhaust steam from the last expansion stage, the change in state from b to a, is used to preheat the material impregnated with acid in the preheating chamber. After warming up, a new full reaction stage run can begin.

5 shows that the specific amount of steam d _F required for the last heating step decreases with increasing number of stages or number of steam stores and with decreasing water content of the impregnated cellulose-containing material used.

A device shown in FIG. 1 is used to carry out the method according to the invention. This comprises a section of concave reactor vessel 1. This is designed as a high pressure vessel. The inside of the vessel 1 is coated with an acid-resistant, poorly heat-conducting material, such as ceramic, in order to avoid the condensation of water vapor and the resulting losses as far as possible. In addition, thermal insulation, not shown in the drawing, is provided.

A preheating chamber 2 is arranged above the reactor vessel 1. This is connected to the reactor vessel 1 via an inlet opening 3. The inlet opening 3 is closed by a movable valve closing part 4, which is shown in dashed lines in its open position. This forms, together with an actuating rod 5 passing through the preheating chamber 2 and hydraulic or pneumatic actuating devices 6, an inlet valve 7. Around the actuating rod 5, stripping devices 8 are provided for stripping residues of the starting material which are adhered there and which are actuated via hydraulic or pneumatic drive devices 9.

At the bottom of the reactor vessel 1, an outlet opening 10 is provided, which is closed by a valve closing part 11, the open position of which is also shown in dashed lines. The valve closing part 11 is connected via an actuating rod 12 to a hydraulic or pneumatic actuating device 13, the actuating rod 12 passing through a product outlet channel 14 ′ adjoining the outlet opening 10. Valve closing part 11, actuating rod 12 and actuating device 13 together form an outlet valve 14.

The preheating chamber 2 has a feed opening 15 on the side, to which a horizontal channel 16 with a plunger 17 which is longitudinally movable and sealingly guided is connected. A funnel-shaped lower part 18 of a material storage container 19 opens into the channel 16 from above.

On the reactor vessel 1 is a ring nozzle below the closing part 4 of the inlet valve 7 vertical channel 20 is provided with a plurality of steam inlet nozzles 21. The ring nozzle channel 20 is connected to a steam outlet 22 and a steam outlet line 23. A line 24 leads from the steam outlet line 23 via a shut-off device 25 to the preheating chamber 2, while the steam outlet line 23 is in turn connected to steam pressure storage devices 26 and 27. Shut-off devices 28 and 29 are assigned to the steam pressure storage devices 26 and 27.

A second ring nozzle channel 30 is located in the reactor vessel 1 above the closing part 11 of the outlet valve 14 and is connected to a steam inlet opening 31 and a steam inlet line 32. The steam inlet line 32 is connected via shut-off devices 33 and 34 and 35 on the one hand to a live steam source (not shown) and on the other hand to the steam pressure storage devices 26 and 27.

The device according to the invention is operated such that the material pre-impregnated, dewatered and shredded cellulose-containing material is filled into the material storage container 19. The funnel-shaped lower part 18 acts together with the channel 16 as a metering trough, which is delimited by the plunger 17 in FIG. 1 in the starting position on the right. The material is pushed into the preheating chamber 2 by a longitudinal movement of the tappet 17, the inlet valve 7 being in the closed position. In the end position, the plunger 17 closes the feed opening 15. No special requirements need be made of the quality of this seal.

Now, in the preheating chamber 2 with the shut-off device 25 open, exhaust steam from the last expansion stage of the previous reaction stage run is admitted via line 24. The heat of condensation of the exhaust steam heats the material from room temperature to approx. 100 ° C. Then the inlet valve 7 opens, so that the material from the preheating chamber 2 can easily fall into the reaction vessel 1 when the outlet valve 14 is closed. By actuating the stripping device 8 it is prevented that material residues remaining form undesired bridges. When closing the inlet valve 7, the sealing surface can be cleaned by a steam jet. The stripping device 8 and the plunger 17 likewise move back into their starting position and are thus ready to repeat the loading process.

In the reaction vessel 1, the reaction stages now take place in the manner described above, in that steam is fed in succession from the steam pressure storage devices 26 and 27 via the inlet line 32 and finally live steam by opening the shut-off device 33. The steam added in each case flows in via the ring nozzle channel 30, so that the material to be hydrolyzed is fluidized in the reaction vessel.

During the gradual expansion after the end of the reaction stage, steam is drawn off via the upper ring nozzle channel 20 and the line 23 and, depending on the reaction stage, is fed to the steam pressure storage devices 26 or 27. The exhaust steam from the last expansion stage is fed to the preheating chamber 2 via the shut-off device 25. The device is then ready to go through a new reaction cycle in quasi-continuous operation.

Claims (11)

1. Method for the hydrolytic separation of cellulose comprising acid treatment and dehydration treatment of the comminuted raw cellulose material and the subsequent reaction of water vapour with an increased pressure and increased temperature in a reactor vessel, characterised in that water vapour is admitted in several successive discrete reaction stages, each having definite temperature and pressure values, in such a manner that the temperature rises from one stage to the next and the reaction time decreases and, following the last reaction stage, rapid expansion takes place.

2. Method according to Claim 1, characterised in that the reaction time of successive reaction stages is calculated to decrease approximately exponentially depending on the increasing reaction temperature.

3. Method according to Claim 1 or 2, characterised in that, after the last reaction stage is reached, a rapid stepwise expansion corresponding to the reaction stages passed is effected, vapour from several expansion stages is fed to separate pressure accumulators and the waste steam of an n + 1-th reaction stage is used in a quasicontinuous operation to set the reaction conditions of an n-th reaction stage of each following complete reaction stage process.

4. Method according to any one of Claims 1 to 3, characterised in that the waste steam of the last expansion stage is used to preheat the raw cellulose material.

5. Apparatus for carrying out the method according to any one of Claims 1 to 4, characterised in that it comprises a high-pressure packed bed reactor and a preheating chamber (2) which is arranged above the actual reactor vessel (1) of the packed bed reactor and which is connected thereto, there being provided an approximately horizontal channel (16) leading to the preheating chamber (2) and having a slide (17) which is guided in the channel to create a seal and which is longitudinally displaceable in the channel (16), there being arranged above the channel (16) a material storage tank (19) which leads into this channel and the slide (17), when in its end position, sealing the material storage tank (19) and the preheating chamber (2).

6. Apparatus according to Claim 5, characterised in that the reactor vessel (1) is defined at the top and bottom by inlet and product outlet valves (7 and 14, respectively) and is designed conically at least in sections.

7. Apparatus according to any one of Claims 5 or 6, characterised in that the product inlet valve (7) can be actuated by a rod (5) which passes through the preheating chamber (2), stripping-off devices (8) being provided around the rod (5).

8. Apparatus according to any one of Claims 5 to 7, characterised by an annular nozzle channel (30) which is connected to the steam inlet pipe (32) in the area of the underside of the reactor vessel (1).

9. Apparatus according to any one of Claims 5 to 8, characterised by an annular nozzle channel (21) which is connected to the steam outlet pipe (23) in the area of the upper side of the reactor vessel (1).

10. Apparatus according to any one of Claims 5 to 9, characterised by at least one vapour pressure accumulator (26 or 27) which is connected to the steam inlet and outlet pipes (32 and 23, respectively) in .such a manner that it can be shut off.

11. Apparatus according to any one of Claims 5 to 10, characterised by a line (24) which is connected to the steam outlet pipe (23) in such a manner that it can be shut off and which leads to the preheating chamber (2).

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