DE3409138A1 - METHOD FOR PRODUCING PROTEIN-CONTAINING MATERIALS - Google Patents

Description

LINDE AKTIENGESELLSCHAFT

(H 1482) H 84/31

Hm / fl 12.3.1984

Process for the production of proteinaceous materials

The invention relates to a method for producing protein-containing Materials based on growing microorganisms in a culture medium under aerobic conditions of methanol, which is produced by synthesis from a synthesis gas which contains hydrogen in excess, the cultivated biomass being separated and as a single-cell protein is won.

There are a number of methods for making single-cell protein. They differ from each other in essential through the use of different carbon sources, different microorganisms and different

as
Fumigation systems. Carbon sources are used, for example, sulphite waste liquors, solutions containing sugar, in particular molasses, substances containing hydrocarbons, in particular paraffins, and alcohols, in particular ethanol and methanol. The main microorganisms used are bacteria, yeasts, fungi and algae. The culture medium can be gassed with air, oxygen or oxygen-enriched air.

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It is already known to use single-cell protein, directly from natural gas Attract bacteria. The disadvantage here is that the carbon source from the bacteria is very poor is exploited. These processes have therefore not caught on because they are the main cost factor in industrial Production of single cell protein is usually the consumption of the carbon source. The starting material is insofar of great importance.

Processes based on alcohols, in particular methanol, have been of particular interest recently. Because alcohols are not agricultural products, but industrial products and are therefore not only seasonal are available, can be mixed well with water and are available in large quantities and pure.

It is known to cultivate bacteria on the basis of methanol in a culture medium which is gassed with air.

The invention is based on the object of specifying a method of the type described at the outset which is characterized by a particularly good utilization of the carbon source.

This object is achieved according to the invention in that Carbon dioxide from the exhaust gas formed during the cultivation of the microorganisms in the synthesis gas or in the synthesis gas recovery stage is returned.

According to the invention, the carbon source used is hydrocarbons, for example natural gas, which are preferably converted by steam reforming into a synthesis gas which is suitable for methanol synthesis and essentially consists of carbon monoxide and hydrogen, without the carbon form. 5729 7.78

dioxide return has an excess of hydrogen, the is discharged from the methanol system via the purge gas together with the inert components (nitrogen, methane). By the carbon dioxide recycling according to the invention can this excess hydrogen together with the carbon dioxide in the Synthesis can be converted in addition to methanol. Specifically, an optimal methanol synthesis is only possible if the following Condition is met:

H ₀ - CO ₀

CO + CO ₂

It follows that some of the carbon dioxide comes from fermentation

sensible between the synthesis gas generation and the methanol can / Synthesis are fed into the synthesis gas stream instead of or in addition to the addition of carbon dioxide to the raw gas for synthesis gas generation. Methanol produced in this way is used to cultivate the microorganisms in a Fermenter passed in which this in an aqueous culture medium containing nutrient salts in the presence of oxygen to be cultivated. During the cultivation of the microorganisms, carbon dioxide-containing exhaust gases are produced. According to the invention the carbon dioxide of this exhaust gas is returned to a steam reforming stage, for example. Caused at this stage the carbon dioxide that the formation of carbon dioxide from the hydrocarbons and water is reduced.

By recycling carbon dioxide in the steam reforming. The hydrocarbon feed can be reduced at the 1st stage. Thus, in the process according to the invention, the overall yield of the hydrocarbon used for the production of methanol is elevated. At the same time, the energy balance of the overall system improves, so that less heating medium is required

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will. This amount of energy can advantageously be used, for example, to dry the separated biomass. In addition, the investment costs for a plant for the synthesis of methanol from hydrocarbons are under recycling of carbon dioxide is lower than for a corresponding system without carbon dioxide recycling.

With particular advantage, according to a feature of the invention, yeasts are used as microorganisms, i.e. carbon dioxide of the exhaust gas formed during the cultivation of yeasts in the synthesis gas or in the synthesis gas generation stage returned:

Compared to bacteria, for example, yeasts have fundamental Advantages: Yeast cultivation systems can be operated non-sterile. Because of the low risk of contamination if the operational readiness of the system is increased significantly, the demands on skill are increased and the training of the operating personnel is reduced and the profitability is reduced because of the lower Improved raw material and nutrient preparation costs. In addition, there is less suspicion of Harmful to health than bacteria since yeast has long been in use for human consumption.

When used in animal feed, yeast protein is often superior to bacterial protein, as in the literature is reported (e.g. G. Cardini, SCP-products from methanolgrown yeasts, Dechema-Monographie, Vol. 83, 1979, pages 219-225). After all, yeasts are much easier to separate from the fermenter broth than bacteria.

The main disadvantage of yeasts is that they breathe a higher proportion of the carbon source into carbon dioxide than bacteria. The greater the specific carbon dioxide release is, the lower the utilization of the

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Sources of carbon and the higher and more expensive theirs Consumption or use. Bacteria have the highest protein content and a relatively low one Carbon dioxide release. This means that bacteria are making the best use of carbon sources. As before mentioned, the carbon source accounts for the major part represents the cost of the end product, were in previous processes because of the better utilization of the carbon source Bacteria used as microorganisms. In doing so, they became aware of the disadvantages of bacteria, especially the necessity sterile operating conditions accepted.

With the method according to the invention it is now possible to improve the utilization of the carbon source in the use of yeast so that that in previous processes given difference in the utilization of the carbon source between bacteria and yeasts practically balanced will. At the same time, the advantages that yeast offer compared to bacteria are retained.

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Example ;

The exploitation of the carbon source by bacteria amounts to According to the literature, 0.45 to 0.55 kg of single-cell protein per kg of methanol; in the case of yeast, this value is 0.4 to 0.45, so about 10% lower.

From Table I it can be seen that by recycling carbon dioxide into the steam reforming stage, the supply of hydrocarbons, in the example of natural gas, is reduced by approx. 8%. At the same time, the heat balance improves, so that Excess steam is generated, which can be used in yeast drying. This will add another 4% Natural gas saved for heating purposes. So in this way becomes the difference in the utilization of the carbon source roughly balanced between bacteria and yeast.

Table I.

Production of 100,000 t / y dry yeast Methanol requirement: approx. 30 t / h

^onne with CC ^ -Rück "CO ₂ management leadership

Natural gas demand (process and heating) 996.9 kmol / h 1088.2 kmol / h

CO ₂ recirculation 218.4 kmol / h

Surplus steam 16.3 t / h of natural gas required for production

the difference in steam volume - 44.5 kmol / h

Total natural gas requirement 996.9 kmol / h 1132.7 kmol / h

Difference 135.8 kmol / h

Percentage (based on 1132.7 kmol / h) 12.0%

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AO

In principle, the method according to the invention can also be used for the cultivation of bacteria or fungi can be used.

Basically it is possible to get carbon dioxide from the in the cultivation of microorganisms in a fumigated with air To use culture medium formed exhaust gas. To do this, however, the carbon dioxide would first have to be separated from the exhaust gas. If air is used for the fumigation, the exhaust gas consists mainly of nitrogen with small amounts of carbon dioxide, Oxygen etc .. For the separation of the highly diluted carbon dioxide from the remaining exhaust gas components (cf. gas balance according to Table II), however, a complex process is required, which essentially follows Steps include: compression of the exhaust gas, carbon dioxide separation (carbon dioxide scrubbing, regeneration of the carbon dioxide-containing Detergent and the production of a carbon dioxide-rich fraction under low pressure, or PSA) again Compression of the carbon dioxide for recycling in the synthesis gas and / or methanol production. These steps are so expensive that the carbon dioxide obtained is too expensive to be recycled economically could be. According to a preferred embodiment of the invention, the exhaust gas used in the cultivation of Microorganisms are used in an exhaust gas formed in a culture medium gassed with oxygen-enriched air. In In this case, the carbon dioxide content in the exhaust gas is higher than in an exhaust gas resulting from air gassing, so that the carbon dioxide separation is correspondingly easier and more economical.

According to another variant of the method according to the invention it is therefore of particular advantage to aerate the culture medium with oxygen. The resulting exhaust gas exists therefore largely from carbon dioxide with admixtures of oxygen, water, nitrogen and traces of methanol.

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1 In this case, the cleaning of the exhaust gas is special simple. If cleaning of the carbon dioxide is provided, the residual gas fraction consists essentially of Oxygen with small amounts of nitrogen. This gas

According to a preferred embodiment, 5 is advantageously used directly for gassing the fermenter.

Table II Typical fermenter waste gas

with O ₂ gassing with air gassing times * kmol / h * mol% kmol / h *

59.9 2.59 3.5 2.59 30.6 1.32 13.0 9.62 0.8 0.03 75.8 56.09 200ppm 0.000 9 200ppm 0.015 8.7 0.38 7.7 5.70

* based on the production of 100 kg / h SCP, dry temperature: 40 ⁰ C

25 Since the use of pure oxygen also the yield increased in oxygen, the purity of the carbon dioxide in the exhaust gas is improved even further compared to fumigation with air.

3Q According to a further embodiment of the invention Process can be the exhaust gas produced during the cultivation of microorganisms in a culture medium gassed with oxygen is formed, cleaned. The components contained in the exhaust gas interfere in the synthesis gas generation in general

35 mean not. Traces of pollution in the exhaust

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However, cleaning agents such as chlorine can be removed by chemisorption, for example. If desired, the exhaust gas can be cleaned even further, e.g. according to a further embodiment of the invention in a PSA system. In this way, a practically 100% pure, moist carbon dioxide can relatively easily be recycled for synthesis gas production and / or methanol production are obtained. In a further advantageous embodiment According to the invention, the exhaust gas can be cleaned by gas scrubbing. As already mentioned, the residual gas fraction can be used directly for fermenter aeration.

According to an advantageous variant of the invention the carbon dioxide is preheated and that of the synthesis gas generation stage added hydrocarbons mixed.

In a further embodiment of the invention, the carbon dioxide is in the raw material before the synthesis gas generation stage and / or in the synthesis gas after the synthesis gas generation stage mixed in. This measure enables a particularly flexible adaptation to existing systems for methanol production.

According to another advantageous feature of the invention, steam reforming is preferred as the synthesis gas generation stage used by hydrocarbons. As a hydrocarbon raw material Methane or natural gas can advantageously be used to generate synthesis gas.

In the following, an exemplary embodiment of the invention will be explained with the aid of a schematic sketch.

A flow diagram is shown schematically in the sketch. Reference number 1 denotes a steam reformer / which is supplied via a line 4 with natural gas and steam

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will. The methanol synthesis gas formed in the steam reformer 1 (Carbon monoxide and hydrogen) is subsequently synthesized to methanol (reference number 2). The methanol will introduced into a fermenter 3 in which there is an aqueous culture medium. The fermenter 3 are not shown Lines are supplied with oxygen for gassing the culture medium and nutrient salts. Yeasts are made in the fermenter cultivated. The exhaust gas formed during the growth of the yeast is drawn off from the fermenter 3. As the culture medium is fumigated with pure oxygen, the exhaust gas flowing out consists largely of carbon dioxide with low levels Additions of oxygen, water, nitrogen and traces of methanol. Therefore it is not necessary to use the carbon dioxide to be separated from the exhaust gas. Rather, the carbon dioxide-rich exhaust gas only has to be by means of a compressor 8, to which it is fed via a line 7, be compressed. The exhaust gas is then fed into the steam reformer 1 - usually together with the mission - initiated.

The processes occurring in the three stages can be represented by the following typical reaction equations will:

Steam reformer :
25th

CH ₄ + H ₂ O + (CO ₂ ) = CO + 3 H ₂ + (CO ₂ ).

The recycled carbon dioxide serves to reduce the formation of carbon dioxide from natural gas and water.

Methanol synthesis:

CO + 2 H ₂ = CH ₃ OH

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SCP production :

χ CH ₃ OH + y O ₂ + ζ NH ₃ + salts = a SCP + b CO ₂ + CH ₃ O

Typical values of a, b, χ, y, ζ are (typical composition by SCP according to E. Klug, Annual Report on Fermentation Processes, Academic Press, New York, Volume 3, pages 141 up to 145):

Table III Yeasts bacteria 7.5 kmol X 6.4 kmol 7.0 kmol y 5.4 kmol 0.6 kmol Z 1.0 kmol 1 kmol a 1 kmol 3.5 kmol b 2.4 kmol

If yeasts are used as microorganisms, the amount of carbon dioxide contained in the exhaust gas is similar to the amount which can be traced back to the steam reformer. Excess carbon dioxide can be drawn off from the system via line 6. However, if necessary carbon dioxide formed in excess can also be fed into the steam reformer. Is used in this variant of the procedure If more methanol is synthesized than can be used in the fermenter, methanol can be extracted from the plant via pipe 9 can be taken.

In summary, it can be stated that by using the exhaust gas one with oxygen or oxygen-enriched Air gassed fermenters the yield of the natural gas used for the methanol production is increased. The method according to the invention enables

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it is particularly important to use the advantages of growing yeasts and at the same time their disadvantage, namely the worse Avoid exploiting the carbon source.

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Claims (1)

(H 1482) H 84/31 Hm / fl 12.3.1984 Claims 1. Process for the production of proteinaceous material by growing microorganisms in a culture medium under aerobic conditions based on methanol, which is produced by synthesis from a synthesis gas containing excess hydrogen, the cultured Biomass is separated and obtained as a single-cell protein, characterized in that carbon dioxide from the exhaust gas formed during the cultivation of the microorganisms into the synthesis gas or into the synthesis gas generation stage is returned. 2. The method according to claim 1, characterized in that yeasts are used as microorganisms. 3. The method according to any one of claims 1 or 2, characterized characterized in that the exhaust gas used in the cultivation of microorganisms in one with oxygen-enriched Air-fumigated culture medium formed exhaust gas is used. 4. The method according to any one of claims 1 to 3, characterized Shape. 5729 7.78 characterized that in the breeding of microorganisms the nisms formed in a culture medium gassed with oxygen Exhaust gas is fed back directly into the synthesis gas generation stage and / or the synthesis gas. 5 5. The method according to claim 4, characterized in that the exhaust gas is cleaned. 6. The method according to claim 5, characterized in that the exhaust gas is cleaned by chemisorption. 7. The method according to any one of claims 5 or 6, characterized characterized in that the exhaust gas is subjected to a psa (pressure swing adsorption) treatment. 8. The method according to any one of claims 5 or 6, characterized in that the exhaust gas through a gas scrubber is cleaned. 9. The method according to any one of claims 7 or 8, characterized characterized in that the residual gas from the carbon dioxide cleaning is used for gassing the culture medium will. 2510. The method according to any one of claims 1 to 9, characterized characterized in that the carbon dioxide is preheated and the hydrocarbons fed to the synthesis gas generation stage is admixed. 3O11. Method according to one of Claims 1 to 10, characterized characterized in that the carbon dioxide is added to the raw material before the synthesis gas generation stage and / or the synthesis gas is admixed after the synthesis gas generation stage. Shape. 5729 7.78 1 12. The method according to any one of claims 1 to 11, characterized in that the synthesis gas generation stage steam reforming of hydrocarbons is used. 13. The method according to any one of claims 1 to 12, characterized characterized in that methane or natural gas is used as a hydrocarbon raw material for the production of synthesis gas will. 10 Shape. 5729 7.78