DK149782B - PROCEDURE FOR THE PREPARATION OF ETHANOL BY CONTINUOUS PUMPING IN A FERMENTATOR - Google Patents

Description

149782

The present invention relates to a process for the preparation of ethanol by continuous fermentation of a carbohydrate-containing substrate in a fermenter, which is part of a continuous process cycle, thereby maintaining a continuous yeast recycling in the fermenter. In this context, fermenter is preferably meant a single fermentation tank.

In the case of ethanol of a technical type, it is produced mainly by purely synthetic methods from the raw material ethylene, which in turn is obtained from the petroleum raw material or natural gas. Due to the restrictions on the supply of fossil raw materials, research has begun on the possibilities of extracting fuel and chemicals from renewable resources, i.e. based on 15 resources of a vegetable type. In this way, the old technique for producing ethanol from carbohydrates has in the broadest sense been updated again. Ethanol is of interest both as a fuel and as a raw material. It will be recalled that the Swedish organic / chemical industry that emerged; after the Second World War, was based on sulfite spirit, which was transformed into ethylene and on to ethylene oxide, etc. Pen's changing raw material situation has thus updated such synthetic routes. Incorporating gasoline up to 20 µl of anhydrous ethanol improves the octane and only needs to make minor changes on internal combustion engines in order for them to function with such fuel. In many countries where large quantities of cheap sugar or starch-based raw materials are available, intensive care is taken. ongoing development work along these lines. Recent research 30 results make it likely that turning cellulose into digestible sugar could become an economic reality. Cellulose occurs worldwide in seemingly unlimited quantities, and cellulose is a potentially ideal raw material for ethanol production.

149782 2

Most existing plants for the production of ethanol by fermentation are based on batch production, whereby raw materials having a relatively low concentration of fermentable ethanol formed reach a concentration which inhibits fermentation, which in turn results in large quantities of wastewater being obtained. which in the untreated state can give rise to major environmental problems. Increasingly, it is becoming a necessity for the production of ethanol through 10 large-scale fermentation that one has to avoid environmentally harmful emissions when handling residual products from the process in an economically sound manner.

A continuous fermentation method for industrial use is known, which is based on a number of fermentation tanks, which are so-called cascade coupled, in which incrementally increased ethanol concentrations are maintained and incrementally reduced substrate concentrations from tank to tank. This method has not achieved any widespread use, presumably due to infection problems, while still having the same restriction with regard to the concentration of substrate supplied as with the traditional batch method.

Thus, a serious disadvantage of the methods so far used for ethanol production by fermentation can be attributed to the need for some minimal dilution of the substrate, which in turn severely limits the possibility of obtaining a sufficiently concentrated process residual material for economic disposal. Inhibition effects already occur at an ethanol concentration of approx. 7%, which sets the practical limit for the substrate concentration to approx. 16-18% fermentable carbohydrates.

A further limitation of the conventional batch method is the low ethanol productivity relative to the cost of capital. Therefore, with a view to increasing ethanol productivity, various methods have been proposed for maintaining a high yeast cell concentration during fermentation, which for economic reasons also implies that yeast cells must be kept alive and used for ethanol production for a longer period of time. .

U.S. Patent No. 2,440,925 discloses a method of extending a batch fermentation cycle and thus the time during which the same yeast is utilized. The toxic effects on the yeast of ethanol at higher concentration are avoided by removing the ethanol during the batch cycle. In order to remove the ethanol, liquid is removed from the fermentation vessel and stripped under vacuum so that the yeast is not destroyed. From the vacuum vessel, the yeast is recirculated to the fermentation vessel together with the liquid (carrier) in which the yeast is in suspension. However, this unwanted accumulation of fermenters in the fermenter quickly leads to an inhibition of the yeast activity, so that the batch process must be interrupted.

It has also been proposed to keep the fermentor under vacuum and to boil off the alcohol formed at a sufficiently low temperature to maintain the yeast activity. A serious disadvantage of this method is that carbon dioxide formed during fermentation must be removed by the vacuum apparatus, which requires high energy consumption.

The negative effect on yeast activity when the yeast is exposed to certain concentrations of the constituents contained in the fermentation residue (broth), despite being well known for many years and has discouraged many from the application of broth recirculation, has not been subject to 30 particularly thorough investigation. Some fermentation processes have been practiced in fermentation processes for the production of yeast in order to fully utilize the nutrients in the herb for further propagation of the yeast.

U.S. Patent No. 1,884,272 discloses extracting herb containing yeast from a propagation container to remove the yeast by centrifugation and returning the yeast-free herb to the plant for reuse of an unspecified portion thereof. quantity for further propagation. Since ethanol can also be formed as a by-product, it has also been pointed out the opportunity to occasionally extract some yeast-free herb for extracting ethanol by distillation before returning the herb.

10 In a research report "Biotechnology and Bioengineering, Vol. 19, pages 1125-43 (1977)", mention is made of experiments which indicate that a concentrated substrate containing 33% glucose should be fermented continuously while maintaining a high yeast concentration (4-7%). in a vacuum fermenter. The ethanol is continuously boiled from the fermenter, a drain stream is continuously withdrawn from the fermenter to prevent the accumulation of non-volatile constituents in the fermenter, and the yeast is recycled after being separated from the outlet stream through sedimentation. For industrial applications, it is proposed to replace the sedimentation vessel with a centrifuge. Despite the aforementioned serious disadvantage as a large energy consumption for the compression of carbon dioxide, the report summarizes the vacuum fermentation method, the major advantages and benefits. future opportunities. The reason for this is evidenced by the following quote from this cited paper: "An all-for-profit advantage of the vacuum fermenter is the elimination of the ethanoline ring. This allows fermentation of concentrated sugar solutions at extremely high speeds" (page 1141), as well as "productivity of atmospheric fermentation with cell recirculation was limited by the low glucose concentration needed to be applied in the feed stream to avoid severe ethanol inhibition "(page 1142)". In this relatively new research report, which reports intensive work and attempts to clarify The conditions for continuous fermentation are thus reiterated in the generally accepted view of atmospheric fermentation in a fermentor that inhibition effects of alcohol formed in the fermenter limit the concentration of added fermentable material to the well known limit of about 16-18 wt.%. It should be noted that the report does not comment on the infections cici, which is definitely present by continuous fermentation for a long time in the same fermentation vessel at a temperature favorable for bacterial growth.

The present invention has for its object to provide a process of the kind mentioned in the preamble to which a high carbohydrate concentration substrate can be applied and in which a concentrated effluent stream which can be rendered harmless or utilized on efficient, economical manner.

According to the invention, it is peculiar to a process of the kind mentioned in the preamble that a steady state of the fermentor is maintained through continuous application to such a process cycle of a stream of such substrate having a concentration of fermentable carbohydrates greater than In the molasses of 22 ° Brix, which flow is regulated so as to maintain a concentration of digestible substance in the fermentor not exceeding 2.5% by weight, through the continuous flow of a fermentation liquid from the fermenter, which stream is quantitated so that its content of ethanol is lower than the per se known limit of severe inhibition of the ethanol fermentation in the fermenter, through continuous centrifuge separation of this stream of fermentation liquid to form at least one yeast concentrate stream and one substantially yeast-free stream, return of the yeast concentrate stream to the fermenter, continuous separating ring of the yeast-free stream to an ethanol-enriched stream which is removed and a residual stream, continuous removal of a portion of this residual stream, and recycling 6 149702 of the remaining portion of this residual stream to the fermenter, thereby ensuring that it is returned to the fermentor part of the residual stream is pasteurized by being heated to a temperature higher than 60 ° C.

5 Centrifugal separation is best performed with a centrifugal separator. By returning the yeast concentrate to the fermentation vessel, the yeast is protected from damage by removal of the ethanol. The recycling of yeast also means that a higher concentration of yeast can be maintained in the fermentation vessel, which results in a higher fermentation rate.

The stream of fermentation liquid can also be divided into three streams, namely in addition to the so-called sludge stream containing contaminants. This can be accomplished with a centrifugal separator which divides the incoming stream of fermentation liquid into a continuous yeast concentrate stream and a continuous yeast-free stream, and partly into an intermittent stream of sludge. This implies that sludge is collected in the rotor periphery of the centrifugal separator and discharged intermittently therefrom. This prevents contamination from accumulating in the system. In a suitable design of such a centrifugal separator, the yeast concentrate stream is supplied by means of a distribution tube and the yeast-free stream with a distribution disc.

In conventional ethanol fermentation technique, one is used. such substrate concentration that the ethanol content after completion of fermentation reaches approx. 7% by weight. If molasses is used as a substrate, the initial molasses concentration is about 22 ° Brix. Such a substrate can be completely fermented. Higher molasses concentrations cannot be completely fermented, as this would result in higher e-30 thanol concentrations than 7 wt% which inhibit fermentation reactions. According to the present invention, molasses with the highest concentrations in the sugar industry of 50-60 ° Brix can be fermented by preventing the ethanol concentration from reaching above approx. 5% by weight of continuous removal of ethanol from the fermentation liquid circulation cycle.

149762 7

In one embodiment of the process according to the invention, the yeast-free substrate stream obtained from the centrifugal separation is partitioned by distillation in a stream enriched with ethanol and in a residual stream, part of which is returned to the fermentation vessel, while the remaining partial stream is removed from the circulation cycle. in the form of a carrying case. In the process of the present invention, this broth achieves significantly higher concentration than is the case with the previously used distillation methods 10 in connection with ethanol fermentation. A major advantage of the process of the present invention is that the distillation curve of ethanol is significantly improved at the high substrate concentrations used, which, in combination with the maintenance of a large recycle ratio, causes the content of soluble non-digestible substance in the stream through the distillation step becomes significant.

Alternatively, the distillative methods for separating ethanol from the circulating fermentation liquid can be reduced to -20 extraction methods, i.e. take up the ethanol in a circulation circuit of some suitable solvent having affinity for the compound in question but less affinity for the water. An example of such a solvent is octanol. The ethanol is then recovered from the octanol solution 25 by fractionation. Such an extraction process exhibits good heat economy.

The distillative or extractive separation of the ethanol is conveniently carried out essentially at atmospheric pressure. Thermal separation under vacuum has the advantage of keeping the temperature lower, but the operating costs of maintaining a vacuum involve a disadvantage.

8 149782

In the process of the invention, the residual stream coming from the distillative or extractive separation is pasteurized at a temperature of 60-100 ° C before returning the stream to the fermentation vessel.

A major advantage of the process is that, independently of the manner in which the ethanol is extracted, a high concentration of substance flow stream which can be treated in an economically sound manner is obtained. Thus, a carrier is obtained which is 4-6 times more concentrated than conventional ethanol distillation boilers, and which has a positive combustion heat value, which contributes to a good operating economy in the process. Due to the high organic matter content of the carrier, it may be used as a raw material for the production of products such as furfurol, etc.

The method according to the invention will now be described in more detail with reference to the accompanying drawings, in which: FIG. 1 is a schematic flow diagram of the method 20 according to the invention; FIG. Figure 2 is a flow chart of the process of distillative separation of the ethanol; Figure 3 shows a scheme for the process of extractive ethanol extraction.

25 In FIG. 1, a fermentation vessel is denoted by F, a centrifugal separator with C, a unit for removing ethanol with RU and a mixer with M. These units are connected by means of lines 1, 2, 3 and 4 to form a circulation circuit. The centrifugal separator C is further directly connected to the mixer M by means of a conduit 5.

9 149782

A supply line 6 for the circulation circuit is connected to the mixer M. The fermenter F is additionally provided with a gas outlet 7, the centrifugal separator C with a sludge outlet 8, the unit RU with an outlet 9 for a stream enriched with 5 ethanol, while the line 3 is provided. with a branch 10 for tapping away from the circulation circuit. The centrifugal separator C is of a type which divides an incoming stream into two continuous liquid streams and an intermittent sludge stream.

An embodiment of the process by which ethanol is separated from the circulation circuit by distillation, either in the form of a simple evaporation or through fractionation, is depicted in FIG. 2. In this figure, the same designations as in FIG. 1 for corresponding ap-15 prepared devices and wires. The unit Ru in FIG. 1 has been replaced by a distillation unit D. The conduit 2 of the distillation unit and the conduit 3 from the same are in a heat exchanger connection through a heat exchanger HE i. The conduit 3 passes through a cooler HE il before connection to the mixer M.

In preparing ethanol in a plant of the kind shown in FIG. 2, concentrate clarified substrate is supplied by the inlet line 6 and mixes M to the fermentation vessel F. The feed is thereby mixed partly with the yeast-free stream coming from the centrifugal separator and partly from the yeast-free stream coming from the distillation unit, i.e.. the carrying case. In the centrifugal separator, intermittent contaminant sludge is excreted, which would otherwise accumulate in the plant. Ethanol is stripped from the yeast-free stream in the distillation unit D, whereby the required heat is supplied either by indirect heating or by direct vapor supply. In the latter case, the dilution is compensated by an increase in the concentration of the applied substrate. The advantage of the direct steam supply is that avoiding coatings on heat transfer surfaces. Ethanol is taken out at outlet 9, and the carrier emits almost all of its available heat content to the stream entering the distillation unit by means of the heat exchanger.

A smaller portion of the carrier current is derived from the circulation circuit by means of the outlet 10, and it is so concentrated here that it can be handled economically. The remainder 5 of the carrier stream is cooled by means of the heat exchanger HE ll and then supplied via the mixer M to the fermentation vessel F. The gas formed during the fermentation, i.e., mainly carbon dioxide, is discharged through the outlet 7. The process is carried out in such a way that the ethanol content of the fermentation vessel is kept at a low level, in the order of 4 wt.%, in the fermentation vessel, whereby the substrate is fermented to almost 100% extent under the process conditions thus chosen. The e-thanol content of the distillation-derived carriers is very low. .

As an alternative to distillative separation of the ethanol from the circulation circuit, extractive techniques can be used. In FIG. 3 outlines a plant equipped for such a process. The plant contains, in addition to the units known from Figures 2 and 3, an extraction unit E, for example 20 in the form of a countercurrent extraction column, and a distillation unit FR, for example a fractionation column. In this case, the conduit 2 from the centrifugal separator is connected to the extraction unit E, to which a solvent stream is also passed through an inlet 15. This solvent stream flows through the extraction unit E, thereby receiving ethanol, and then flows through a conduit 16 to the distillation unit FR, from which the ethanol passes through an outlet 17. The bottom stream of solvent from the distillation unit FR flows through a conduit 18 to the inlet 15, which is also supplied to solvent through an inlet 19. A portion of the stream extracted from the extraction unit E which is poor on ethanol is drained from The distillation unit is conveniently heated by indirect heating 21.

EXAMPLE 1 11 149782

As an example of carrying out a method according to the invention, a continuous fermentation of molasses in a plant of the type shown in FIG. 2nd

5 To begin the process, 10 kg of press yeast in 100 liters of molasses with 20 ° Brix was placed in a fermenter fitted with a stirrer. In the circulation circuit is placed a cooler. The fermentation temperature was adjusted to 32 ° C and the fermentable sugar was converted to ethanol within 90% 10 within approx. 3 hours. During the last part of the fermentation process, ethanol had to be continuously removed from the substrate in order to maintain an alcohol content of approx. 4% by weight. Therefore, fermentation liquid had to circulate through a centrifugal separator C, whereby a stream of yeast concentrate could be funneled back to the fermentation vessel, while a yeast-free stream was fed to a simple distillation unit D where the ethanol was evaporated under atmospheric pressure. When the fermentation of the original charge was complete, 20 to 13.7 kg / h of molasses clarified molasses with continuous 40 ° continuously was added continuously.

Brix. A fermentation volume of 100 liters was maintained in the fermentation vessel. The fermentation took place for a week and during this time an ethanol stream with an ethanol content of 25-35% by weight was removed, keeping the ethanol content of the fermentation vessel at approx. 4% by weight. A small stream of 25-30 wt.% Solids content stream was withdrawn from the circulation circuit.

Operating data were recorded for both feed rates, as shown in the following table: 12 149782

Supply rate F ^ / Fg Equilibrium for- Ethanol resistance 40 ° fermentable sugar diactivity

Brix molasses in fermentation (100%) kg / h container in kg / 100 l / h wt% 7.0 10.0 1.0 1.0 13.0 5.5 2.5 1.7

The term F ^ / Fg denotes the ratio of the volume currents in lines 3 and 6 of FIG. 2. The table shows that the productivity of ethanol was increased with increased raw material addition, but at the expense of utilization of the added sugar, since more of this remained unused in the latter cases. It is clear that the optimization of the feed rate is determined by the ratio of the raw material costs and the capital and operating costs respectively.

It should be noted that the raw material was not sterilized at the fermentation described. Despite this, there was no accumulation of bacteria in the system, which clearly caused the flow to be sterilized in the distillation unit.

EXAMPLE 2 Continuous fermentation of cane sugar molasses was carried out in a fermentor which was kept under stable conditions by means of the one shown in FIG. 2. The fermentor was kept under atmospheric pressure, the fermentation pH and temperature were adjusted to approx. 4.5 and 32 ° C, respectively.

20 Yeast growth was regulated through air supply. As a yeast, the Schizosaccharomyces pump was used.

Process cycles were added using 6: 13 149782 kq / h wt%

Digestible substance 56 23

Non-digestible, soluble substance 22 9

Non-digestible solid 2 1

Water (total) 163 67 243 100

The substantially yeast-free stream 2 introduced from the separator into the distillation column Df was 580 kg / h, and the carrier flow recirculated to the fermentor F (stream 3 '- stream 10) was 363 kg / h and had a 5 ethanol concentration. of approx. 0%. From the distillation column D, 65 kg / h of steam containing 68% ethanol was extracted, and 26 kg / h of carbon dioxide was extracted from the fermentor.

In the fermentor F, the following stable conditions were maintained: Yeast 5 x 10 6 cells / ml

Air 0.1 ppm

Ethanol 4.3% Solids content (in addition to yeast) 15%

Fermentable sugar 0.2% 10 A load stream 10 of 152 kg / h with a solids content of 17% by weight was taken continuously.

EXAMPLE 3

Wheat (87% dry matter) was used as feedstock for the continuous ethanol fermentation. The example is in accordance with that of FIG. 2, with the addition of a suction step which the feed ice stream 6 passes before reaching the mixer M. The fermentor was kept under atmospheric pressure, the pH of the fermentor was adjusted to approx. 4.5, and the temperature of the fermentor was maintained at 32 ° C. In order to avoid large particles in the fermentation fluid stream 1 from the fermenter passing the separator C, a centrifugalsi with mesh openings of 200 µm were inserted into the line 1 before the separator, whereby the retained material was brought together with the yeast-free stream 2 before introduction to the distillation column D. A similar strainer was placed in the carrier stream 3 from the distillation column to dispose of coarser particles and remove them with this removed carrier stream 10. The yeast used was Saccharomyces cerevisiæ.

10 The following quantities of wheat raw material were continuously fed through the sugaring stage and the feed stream 6: kg / h wt.%

Digestible Substance 62 30.6

Non-digestible soluble substance 10 4.9

Non-fermentable solid 15 7.4

Total water 116 57.1 203 100.0

The stream 2 supplied to the distillation column D, which contained both the yeast-free stream separated in the separator C and the intended retained material from stream 1, 15 was 530 kg / h, and the carrier stream recirculated (stream 3 - stream 10) was at 360 kg / h (ethanol concentration about 0). From the distillation column D, 69 kg / h of vapor containing 42% by weight of ethanol was extracted and from the fermentor 33 kg / h of carbon dioxide was extracted.

In the fermentor F, the following stable conditions were maintained: Yeast 5 x 10 8 cells / ml

Air 0.015 ppm

Ethanol 5.5%

Total dry matter (excluding yeast) 16%

Fermentable sugar 0.05% 1A 97 8 2 15

The carrier current removed via 10 continuously, which also contained the material retained on stream 3, was 101 kg / h and its total dry matter content was 26% by weight.