WO2016110867A1

WO2016110867A1 - Preparation of ethanol by continuous fermentation process

Info

Publication number: WO2016110867A1
Application number: PCT/IN2015/000457
Authority: WO
Inventors: Baburao Deshpande Ghansham; Avinash Kulkarni Mahesh; Ram Shinde Pandurang; Shankar Kumbhar Pramod; Bhalewadikar Abhishek; Pandurang Patil Deepak; Devidas Budgujar Mahesh
Original assignee: Praj Industries Limited
Priority date: 2015-01-05
Filing date: 2015-12-22
Publication date: 2016-07-14

Abstract

The invention relates to a process for the preparation of ethanol by continuous fermentation of starch containing feedstock by using a set of fermentors so arranged that the product of fermentation is continuously produced at the end of process with continuous addition of feedstock without need to stop the production process for any process preparation activities.

Description

PREPARATION OF ETHANOL BY CONTINUOUS FERMENTATION PROCESS

FIELD OF THE INVENTION

BACKGROUND

The conversion of starch to ethanol is rapidly expanding industry. Ethanol has widespread applications as an industrial chemical, a gasoline additive or a liquid fuel by itself, besides in potable ethanol and liquor industry.

A typical process of ethanol production from starch containing feed stocks comprises two steps: 1] starch liquefaction and 2] fermentation where feed stocks like grains, tubers or pure starchy biomass are cleaned, milled and a slurry is prepared as required to attain the expected final ethanol concentration in fermentation process. However, starch polymers are not effectively utilised by yeast for fermentation and a liquefaction step is used to convert starch into dextrin units using hydrolysing enzymes. Liquefaction is well known process in the art of producing syrups and fermentation products from starch containing feed stocks. Before initiation of liquefaction starch containing feedstock is reduced in size and mixed with water to prepare aqueous slurry. The aqueous slurry is heated above the initial gelatinization temperature. This results in increased viscosity. Then a portion of liquefying enzyme is added at this point to initiate thinning of slurry. Next, this partial slurry is subjected to jet cooking at a high temperature and finally subjected to a secondary liquefaction with or without jet cooking using another portion of liquefying enzyme.

Here liquefaction is carried out in two or three steps at temperature between 60 to 90 °C. The liquefying enzymes are added in different steps in different portions. In the step of jet-cooking said slurry is subjected to a temperature between 95 to 140 °C for up to 15 minutes. In this process, multiple doses of enzymes are added before and after the thermal treatment of starch to achieve effective depolymerisation of starch to dextrins.

One well-known method of liquefaction adopted by practitioners is preparing slurry in a slurry tank having 30 - 40% dry solids. The pH is adjusted to about 4.0 to 6.5 with sodium hydroxide. Then liquefying enzymes are added to it. The slurry is pumped continuously through a jet cooker where the temperature is raised to 110 - 140 °C by direct injection of steam. The slurry is maintained at this high temperature in the pressurized holding vessel for about 5 min, after which it is flashed into a reaction tank, where enzyme action is allowed to continue for about 2 hours at 90 °C.

After the liquefaction of starch or in case of molasses, which contains sucrose, the ethanol fermentation is carried out principally in batch mode in large fermentors in anaerobic conditions using the yeast. However, the batch fermentation process is time consuming and requires more resources like periodic cleaning and preparation time. To reduce the fermentation time and increase the productivity of the ethanol. production process, various methods are suggested in the art like use of high-density yeast culture or high initial sugar concentration. However, these processes have inherent limitations like contamination of process or inhibition of yeast high sugar and product concentrations. The present invention provides a novel method for the continuous fermentative production of ethanol from starch containing feed stocks like grains, tubers or pure starchy biomass, including liquid glucose obtained from starch and any fermentable sugar containing feed stock. Further, the present invention provides reduction in operating cost for operation of the fermentors and related processes due to continuous operation of the process without any time delays caused by non- product steps like preparations for the process, etc. BRIEF DESCRIPTION OF THE DRAWINGS

Particular examples of a method in accordance with this invention will now be described with reference to accompanying drawing, in which: FIGURE 1 is an exemplary plan of the invention showing the process of continuous fermentative production of ethanol from a sugary or starchy feedstock. The feedstock [3] along with process water [4] enzymes and nutrients [2] and active yeast cell mass [1] are fed to a set of two fermentors [A & B] that operate in [biostatic mode] a staggered manner such that the operation of second fermentor starts when, the first has completed its operational cycle and sends it content to next larger fermentor [C] and then when said second fermentor completes its operational cycle, said first fermentor again starts its operation leading to continuous supply of partially fermented beer [5] to said larger fermentor [C] by said set of two fermentors operating in biostatic state. The larger fermentor [C] operates in continuous cycle in chemostatic state in which the level of fermented beer is maintained at a predetermined level to achieve complete conversion of sugars present in the media to ethanol. On complete consumption of sugars in the larger fermentor [C], fermented beer or wash [6] is send a yeast separation unit to remove yeast from the beer before sending it [7] to distillation unit to recovery of ethanol. This scheme has several elements that significantly contribute to the process of the invention. DETAILED DESCRIPTION OF THE INVENTION

In one embodiment of present invention, as illustrated in FIGURE 1 a continuous fermentative production of ethanol from a starchy or sugary feedstock. The feedstock [3] along with process water [4] enzymes, nutrients [2] and active yeast cell mass [1] are fed to a set of two fermentors [A & B] that operate in [biostatic mode] a staggered manner such that the operation of second fermentor starts when the first has completed its operational cycle and sends it content to next larger fermentor [C] and then when said second fermentor completes its operational cycle, said first fermentor again starts its operation leading to continuous supply of partially fermented beer [5] to said larger fermentor [C] by said set of two fermentors operating in biostatic state. The larger fermentor [C] operates in continuous cycle in chemostatic state in which the level of fermented beer is maintained at a predetermined level to achieve complete conversion of sugars present in the media to ethanol. On complete consumption of sugars in the larger fermentor [C], fermented beer or wash [6] is send a yeast separation unit to remove yeast from the beer before sending it [7] to distillation unit to recovery of ethanol.

In yet another embodiment of present invention, continuous fermentation process is designed to achieve about 8 to 15 % ethanol by volume in the final product stream. Herein the hydrolyzed starch slurry or liquid molasses is used as sugary feed for fermentation in the set of two fermentors working [in fed-batch/ biostatic mode] for about 8 to 16 h in staggered manner and continuously fed with hydrolyzed starch slurry or liquid molasses to achieve fast growth of yeast biomass as well as production of ethanol from sugars between 50 to 80 % of the total conversion. The rest of sugar is then converted while transfer to the fermentor operating in continuous mode or that fermentor itself before ^'distillation of ethanol from totally fermented beer or wash. Herein said transfer of said semi-fermented stream is done over a period of up to 12 h. Further said large fermentor is operated in continuous mode with a retention time of between about 8 to 60 h. Optionally, the yeast [Saccharomyces sp.] present in the beer may be recovered and reused in the process with increase in efficiencies of the system. The final continuously operating fermentor provides several advantages over the convention process of batch fermentation such as:

1. Since the overall process of the ethanol production is continuous the relative productivity of in the process is at least two times compared with the batch process.

2. Operational parameter like cleaning, priming and operation of the fermentors are also substantially reduced increase the efficiency of the process as well as economics of production of ethanol.

3. Higher ethanol titer in the final stream for distillation is achieved for efficient and economic distillation of ethanol. 4. Due to increase in the throughput the operational and capital expenses are substantially reduced relative to conventional methods.

5. Yeast biomass produced in the process is separated at the end of conversion for reuse in the fermentors operating as biostat [batch-fed /synchronous fermentors].

6. Said process has efficiency of conversion of sugar to ethanol of at least 97% of theoretical value.

In another embodiment of the disclosed invention, a starch containing feedstock was milled prior to liquefaction. Said feedstock containing about 20% to 50% of solids by weight [about 10% to 30% starch by weight] is subjected to a mixer. In said mixer said feedstock is mixed with recycled water stream and hydrolysing enzymes forming said slurry of starchy or sugary feedstock. In said mixer, temperature is maintained about 55 °C to 60 °C. Then said slurry was collected in a slurry tank, pH adjusted to 4.0 to 6.5 if required with ammonia or caustic soda. Then said slurry was injected with steam to raise the temperature to about 75 °C to 140 °C. Next, said slurry was maintained at this elevated temperature for about 10 to 120 minutes and on the completion of liquefaction of starch, formed liquid stream was cooled to about 30 to 34 °C for further processing. Said liquid stream contains dextrins as hydrolysis product of starch polymers. The pressure in said stream tank was maintained at about 1 to 2 bar[a] and said slurry is continuously agitated for effective liquefaction, which then used in the fermentation medium of the invention disclosed herein.

In one of the embodiments of the present invention, the hydrolysed starch or sugary feed stocks are obtained from the starch-based materials that include tubers, roots, whole grains, grits or flour, or combinations thereof. Further, it includes, but is not limited to, cassava, corn, millet, rice, oat, wheat, barley, buckwheat, rye, triticale, sorghum, potato, or combinations thereof. Said material was cleaned to remove foreign particles and subjected to milling or size reduction operation to form feed stocks of desired particle size. Then slurry was formed by mixing said feed stocks recycled water streams from downstream processes.

Embodiments provided above give wider utility of the invention without any limitations as to the variations that may be appreciated by a person skilled in the art. A non-limiting summary of various embodiments is given above, which demonstrate the advantageous and novel aspects of the process disclosed herein.

Claims

CLAIMS We claim:

1. A process for fermentation of ethanol comprising:

(a) providing a fermentable medium and a yeast in a set of two fermentors;

(b) operating said set of two fermentors as biostats in a staggered manner such that one fermentor is ready with a semi-fermented stream at defined interval of time period followed by second fermentor;

(c) transferring said semi-fermented stream to a larger fermentor over defined time period;

(d) fermenting said semi-fermented stream in said larger fermentor operating as a chemostat causing rapid fermentation of ethanol for a desired time period forming a fermented stream; and

(e) subjecting said fermented stream to distillation to obtain ethanol. -

2. The process of claim 1 , wherein said fermentable medium

comprises molasses, sugary juice, or any starch containing feedstock obtained from grains of barley, corn, millet, rice, rye, sorghum, triticale, wheat or tubers of cassava or potato.

3. The process of claim 1 , wherein said set of fermentors is used to increase biomass of said yeast.

4. The process of claim 1 , wherein said larger fermentor is used for complete conversion of sugar remaining in said semi- fermented stream to ethanol by said yeast.

5. The process of claim 1 , wherein said fermentor is operated in fed-batch mode with a retention time of between about 8 hours to about 12 hours.

6. The process of claim , wherein said large fermentor is

operated in continuous mode with a retention time of between about 8 hours to about 60 hours.

7. The process of claim 1 , wherein said transfer of said semi- fermented stream is done over a period of up to 12 hours.

8. The process of claim 1 , wherein said yeast is a Saccharomyces sp.

9. The process of claim 1 , wherein said yeast is recovered and reused in the process.

10. An apparatus for running a continuous fermentation process for producing ethanol according to FIGURE 1.