GB1581643A

GB1581643A - Fermentation process for the production of hydrocarbon utilising yeast

Info

Publication number: GB1581643A
Application number: GB3950176A
Authority: GB
Original assignee: BP PLC
Current assignee: BP PLC
Priority date: 1976-09-23
Filing date: 1976-09-23
Publication date: 1980-12-17
Also published as: IT1086374B; FR2365631A1; FR2365631B1

Description

(54) FERMENTATION PROCESS FOR THE PRODUCTION OF HYDROCARBON UTILISING YEAST (71) We, THE BRITISH PETROLEUM COMPANY LIMITED, of Britannic House, Moor Lane, London EC2Y 9BU, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a fermentation process for the production of hydrocarbon utilising yeast.

Fermentation processes for the production of hydrocarbon utilising yeast are known and have been used for the production of the yeast for use as a feedstuff. In processes of this type a hydrocarbon utilising yeast is cultivated in a broth comprising an aqueous nutrient medium in the presence of a gas containing free oxygen and a hydrocarbon which can be utilised by the yeast.

The hydrocarbon can be of petroleum origin and consist of or contain straight chain hydrocarbons. The yeast is usually a straight chain hydrocarbon utilising strain. Such yeast can be selected from the genus Candida and in particular from the species Candida lipolytica or tropicalis. Operation is usually continuous with fresh aqueous nutrient medium, hydrocarbon and gas containing free oxygen supplied to the broth continuously in quantities which are sufficient to meet the nutritional requirements of the yeast.

Two important features in the economics of the process are the yield factor and nitrogen content of the yeast. The yield factor is the relationship between the quantity of yeast produced (dry weight) and the quantity of hydrocarbon utilised by the yeast. It is a measure of the efficiency of the yeast to convert hydrocarbon into cell material. The nitrogen content of the yeast is the quantity of nitrogen present in a unit quantity of yeast. This is an indication of the protein content of the yeast.

It is desirable that the process should be operated at a temperature which gives an optimum or near optimum yield factor and nitrogen content. This temperature is known as the optimum temperature. It is well known that a variation in temperature of more than 2 or 3"C from the optimum can have a detrimental affect on the yield factor and/or the nitrogen content. It is also known that the optimum temperature is specific to the strain of yeast which is used.

The process is exothermic. Various techniques have been proposed for preventing the fermentation temperature from exceeding the optimum for optimum yield factor and nitrogen content. These techniques include the use of cooling means such as external heat exchangers through which broth can be passed.

We have now devised a method of operation whereby the optimum fermentation temperature can be increased without having a detrimental effect on the yield factor and nitrogen content.

Accordingly the present invention is a process for the production of hydrocarbon utilising yeast which comprises continuously cultivating a straight chain hydrocarbon utilising yeast in a broth comprising an aqueous nutrient medium in the presence of a gas containing free oxygen and a straight chain hydrocarbon and maintaining a dissolved oxygen content in the broth at a value in the range 20 to 90 percent of the saturated dissolved oxygen content of the broth with respect to air and maintaining a dilution rate at a value in the range 0.20 h- ' to 0.40 Most suitably the dissolved oxygen content can have a value in the range 30 to 50 percent of the saturated dissolved oxygen content of the broth with respect to air. The oxygen content can be measured by a polargraphic probe. Techniques are known for maintaining the dissolved oxygen content of fermentation broth at a desired value and any of these techniques can be used in the present process to maintain the value of the dissolved oxygen content within the required range. Some examples of such techniques are adjusting the over pressure, sophisticated aeration devices such as sintered steel cylinders, chemical and biological additives, limiting the feed of the hydrocarbon substrate and controlling the air flow rate or the oxygen content of the gas applied to the broth. In a preferred technique the value of the dissolved oxygen content can be maintained within the desired range by controlling the quantity of air applied to the broth in response to a measurement of the value of the dissolved oxygen content in the broth. For example where the process culture is a straight chain hydrocarbon utilising strain of Candida e.g. C. tropicalis and in particular strain C.B.S. 6373 air flow rates most suitably can be in the range 50 to 300 volumes/volume hour and preferably in the range 100 to 180 volumes/volume hour.

Preferably the dilution rate can be in the range 0.25 h-' to 0.30 h-'.

The present process is applicable to any known continuous process for the production of yeast in which a hydrocarbon is used as a carbon source. For example a basic process has been described in the British Petroleum Company Limited British Patent number 1,017,584 and further processes have been described in the British Petroleum Company Limited Patents 1,401,277 and 1,421,155.

Most suitably the hydrocarbon can be a straight chain hydrocarbon having a chain length in the range C10 to C3. The hydrocarbon can be a petroleum fraction such as for example a gas oil. Typical gas oils contain about 10 to 25 percent by weight of straight chain saturated hydrocarbons in admixture with about 35 to 50 percent by weight of branched chain and cyclic saturated hydrocarbons and about 40 percent of aromatic hydrocarbons. Preferred straight chain hydrocarbons are present in petroleum fractions having kerosine or gas oil boiling ranges. Particularly preferred gas oil boiling range straight chain hydrocarbons have 11 to 23 and mainly 14 to 21 carbon atoms per molecule and particularly preferred kerosine boiling range normal paraffins have 10 to 13 carbon atoms per molecule.

Any known straight chain hydrocarbon utilising yeast can be used in the present process.

The yeast can be a member of the Cryptococcaceae and in particular the sub-family Cryptococcoideae or Saccharomycetoideae. Some examples of genera of Cryptococcoideae to which the micro-organism can belong are Torulopsis (also known as Torula), Candida and Mycoderma. Some species of yeasts are as follows. The preferred strains are indicated by a reference number. The reference CBS indicates stock held by the Central Bureau voor Schimmelculture, Baarn, Holland; CMI indicates stock held by the Commonwealth Mycological Institute. Kew, England; and NCYC indicates stock held by the National Collection of Yeast Cultures, Nutfield, England.

Species Preferred strain Candida brumptii " catenulata " clausenii humicola " intermedia " krusei " lipolytica CBS No. 2078: No. 599 and No. 6331 CMI No. 93743; No. 6331 NCYC No. 376; No. 153 melibiosi mellblosl " parapsilosis CMI No. 83350. NCYC No. 458 pulcherrima " rugosa " stellatoidea Candida tropicalis NCYC No. 4 CBS No. 6373 " utilis CMI No. 2331 Debaryomyces kloeckeri Hansenula anomala Pichia guilliermondii CBS No. 2084; No. 2031 Rhodotorula glutinis Torulopsis famata " magnoliae Of the above Candida lipolytica and C. tropicalis are particularly preferred. The alternative generic name of Saccharomycopsis has been proposed for mating strains of Candida.

Aqueous nutrient media for use in the cultivation of hydrocarbon utilising yeasts are known. Any known medium can be used in the present princess.

The pH of the broth can be in the range 3 to 6 and preferably in the range 3.5 to 5.5. Most suitably the process can be carried out in a stirred aerated vessel, and preferably in an air lift fermenter. When a strain of the yeasts Candida tropicalis or lipolytica is used as the process culture it is preferred to operate the process in accordance with the techniques described in The British Petroleum Company Limited British Patents 1,421,155 and 1,401,277 respectively.

The present process permits the use of operational temperatures which are higher than those which have been used hitherto for the particular strain of process yeast with little or no deleterious effect on the nitrogen content and yield factor. The operational temperature can have a value in the range 5"C to 10 C higher than the normal optimum growth temperature for the yeast. Where the yeast is a strain of Candida tropicalis and the carbon source is a straight chain hydrocarbon the process can be operated at temperatures of up to 380C with similar yield factors and nitrogen contents as can be obtained using the normal optimum temperature of 30 to 310C.

The present invention is illustrated by but not limited to the following Example.

Example A straight chain hydrocarbon utilising strain of the yeast Candida tropicalis CBS number 6373 was grown in a continuously operated fermenter having a working volume of 5.13 metres3 in the presence of an aqueous nutrient medium having the following composition: H3P04 1.84 grams KC1 1.16 Mg(OH)2 0.078 MnSO4.H2O 0.024 FeSO4.2H2O 0.080 CuS04.5H20 0.0004 ZnSO4.7H2O 0.158 Yeast extract 0.015 H2S04 1.8 Tap water 1,000 ml The carbon source was a mixture of gas oil n-paraffins having a specific gravity of 0.776, a boiling range of 200"C to 3000C and a carbon chain length in the range 13 to 18.

The fermenter was operated at a dilution rate of 0.25 h- and a temperature of 35"C. The pH was controlled at 4.2 by addition of gaseous ammonia which also served as a nitrogen source. The n-paraffins were added continuously to give a concentration of 9.8 grams per litre of added aqueous nutrient medium. The n-paraffin feed rate was 12.5 kilograms per hour.

The aeration rate was 1000 metres 3/ hour at N.T.P. The dissolved oxygen content in the broth had a value of about 35 percent of that of saturation with respect to air. The yield factor, nitrogen content and productivity of the fermentation are given in the Table.

The fermentation conditions described above were altered in the following manner. The aeration rate was increased to 1250 metres3/hour at N.T.P., the n-paraffin feed rate was increased to 14.5 kilograms per hour to give an n-paraffin concentration of 11.5 grams per litre of added aqueous nutrient medium. The dissolved oxygen content in the broth was about 30 percent of saturation with respect to air. The yield factor, nitrogen content and productivity of the fermentation are given in the Table.

Comparative Experiment By way of comparison the fermentation conditions were altered in the following manner.

The aeration rate was reduced to 1000 metres 3/ hour at N.T.P. The n-paraffin feed rate was left at 14.5 kilograms per hour. Under these conditions the content of dissolved oxygen in the broth was about 5 percent of saturation. The yield factor, nitrogen content and productivity were reduced. The data is given in the Table. By way of a further comparison the temperature of the fermentation was decreased to the normal optimum for the strain of yeast i.e. 30"C without altering the remaining fermentation parameters. The yield factor, nitrogen content and productivity are given in the Table.

The data given in the Table demonstrates continuous operation at a temperature which is 5"C above the normal optimum for the culture without a reduction in the yield factor or nitrogen content by maintaining the dissolved oxygen content in the broth at 30 or 35 percent of the saturated dissolved oxygen content with respect to air.

TABLE

Data Dissolved oxygen content Example Comparative Experiment %ofsaturation 35 30 5 5-10 Temperature "C 35 35 35 30 Dilution rate 0.25 0.25 0.25 0.25 hours-' n-paraffin feed rate 12.5 14.5 14.5 14.5 kilograms hours~ Aeration rate metres3 per hour 1000 1250 1000 1000 N.T.P Yield factor on 1.02 - 1.04 1.02 - 1.05 0.93 - 0.97 1.05 n-paraffins Nitrogen content 9.1 - 9.3 9.2 - 9.4 8.6 - 8.9 9.2 - 9.5 % nitrogen Productivity kilograms per 2.5 2.5 2.2 2.5 Ixetres3 l0ours1 WHAT WE CLAIM IS: 1. A process for the production of hydrocarbon utilising yeast which comprises continuously cultivating a straight chain hydrocarbon utilising yeast in a broth comprising an aqueous nutrient medium in the presence of a gas containing free oxygen and a straight chain hydrocarbon and maintaining a dissolved oxygen content in the broth at a value in the range 20 to 90 percent of the saturated dissolved oxygen content of the broth with respect to air and maintaining a dilution rate at a value in the range 0.20 h- t to 0.40 h-'.

2. A process as claimed in claim 1 in which the dissolved oxygen content in the broth has a value in the range 30 to 50 percent of the saturated dissolved oxygen content of the broth with respect to air.

3. A process as claimed in either of the preceding claims in which the dissolved oxygen content in the broth is maintained at the required value by adjusting the over pressure.

4. A process as claimed in either claim 1 or 2 in which the dissolved oxygen content in the broth is maintained at the required value by controlling the quantity of air applied to the broth in response to a measurement of the value of the dissolved oxygen content in the broth.

5. A process as claimed in any one of the preceding claims in which the gas containing free oxygen is air and the air flow rate is in the range 50 to 300 volumes/volume hour.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. increased to 14.5 kilograms per hour to give an n-paraffin concentration of 11.5 grams per litre of added aqueous nutrient medium. The dissolved oxygen content in the broth was about 30 percent of saturation with respect to air. The yield factor, nitrogen content and productivity of the fermentation are given in the Table. Comparative Experiment By way of comparison the fermentation conditions were altered in the following manner. The aeration rate was reduced to 1000 metres 3/ hour at N.T.P. The n-paraffin feed rate was left at 14.5 kilograms per hour. Under these conditions the content of dissolved oxygen in the broth was about 5 percent of saturation. The yield factor, nitrogen content and productivity were reduced. The data is given in the Table. By way of a further comparison the temperature of the fermentation was decreased to the normal optimum for the strain of yeast i.e. 30"C without altering the remaining fermentation parameters. The yield factor, nitrogen content and productivity are given in the Table. The data given in the Table demonstrates continuous operation at a temperature which is 5"C above the normal optimum for the culture without a reduction in the yield factor or nitrogen content by maintaining the dissolved oxygen content in the broth at 30 or 35 percent of the saturated dissolved oxygen content with respect to air. TABLE Data Dissolved oxygen content Example Comparative Experiment %ofsaturation 35 30 5 5-10 Temperature "C 35 35 35 30 Dilution rate 0.25 0.25 0.25 0.25 hours-' n-paraffin feed rate 12.5 14.5 14.5 14.5 kilograms hours~ Aeration rate metres3 per hour 1000 1250 1000 1000 N.T.P Yield factor on 1.02 - 1.04 1.02 -

1.05 0.93 - 0.97 1.05 n-paraffins Nitrogen content 9.1 - 9.3 9.2 - 9.4 8.6 - 8.9 9.2 - 9.5 % nitrogen Productivity kilograms per 2.5 2.5 2.2 2.5 Ixetres3 l0ours1 WHAT WE CLAIM IS: 1. A process for the production of hydrocarbon utilising yeast which comprises continuously cultivating a straight chain hydrocarbon utilising yeast in a broth comprising an aqueous nutrient medium in the presence of a gas containing free oxygen and a straight chain hydrocarbon and maintaining a dissolved oxygen content in the broth at a value in the range 20 to 90 percent of the saturated dissolved oxygen content of the broth with respect to air and maintaining a dilution rate at a value in the range 0.20 h- t to 0.40 h-'.

6. A process as claimed in claim 5 in which the air flow rate is in the range 100 to 180

volumes/volume hour.

7. A process as claimed in any one of the preceding claims in which the dilution rate is in the range 0.25 h-l to 0.30 h-l.

8. A process as claimed in any one of the preceding claims in which the straight chain hydrocarbon has a chain length in the range C10 to C30.

9. A process as claimed in any one of the preceding claims in which the hydrocarbon utilising yeast is a strain of Candida.

10. A process as claimed in claim 9 in which the Candida is a strain of C. tropicalis or C.

lipolytica.

11. A process as claimed in any one of the preceding claims in which the broth is maintained at a temperature having a value in the range 5"C to 100C higher than that of the normal optimum growth temperature of the yeast.

12. A process as claimed in claim 1 and as hereinbefore described with reference to the Example.

13. Hydrocarbon grown yeast when produced by the process as claimed in any one of the preceding claims.