FIELD OF THE INVENTION

The present invention relates to production of ethanol and more particularly producing ethanol by oversaturated substrate fermentation.

BACKGROUND OF THE INVENTION

Across the world, there are attempts of development of renewable energy for sustainable development. Among the various renewable energies, fuel ethanol production is considered the most realistic and eco-friendly approach. Ethanol is produced using sugarcane, sugar beet, grains, starch or hydrolysates of lignocellulosic materials, corn kernels, wheat kernels, etc. Sugarcane, sweet sorghum and other sugar-bearing stalks are non-food crops grown annually in large parts of world that are now considered for fuel ethanol production.

In the conventional ethanol process, whole sugarcane is first cut and fiberized in small pieces and formed into a mat. These fiberized pieces are crushed in multiple roller mills by adding large quantity of imbibition water to extract most of the sugar. The dilute juice is clarified, concentrated by heating to make syrup. This syrup is stored, diluted again when necessary and fermented into dilute ethanol by yeast or like organism. From this dilute ethanol solution, 95% ethanol is distilled out by traditional columns using steam.

The conventional process of submerged fermentation has many drawbacks. It requires heavy machinery to ‘crush’ the tough mat. It is a capital- and energy-intensive equipment. Also, large quantity of water is required to maximize sugar extraction resulting in juice dilution. Clarification and evaporation of the dilute juice needs large heat energy. The fermented wash obtained after the ethanol is distilled out, has high COD and BOD. Expensive equipment and high energy expenditure is required to treat this effluent. The only saleable product is ethanol and the surplus bagasse is used mainly as low value fuel.

To overcome the drawbacks of conventional process, many techniques especially solid state fermentation (SSF) is being implemented in the prior art. The prior art shows that in SSF, mixing solid biomass and inoculum is an energy intensive process and often fails to make a uniform mix. A research paper titled “Solid state fermentation of sugars in sweet sorghum” to W. L. Bryan published in Enzyme and Microbial Technology, Volume 12, Issue 6, June 1990 teaches the use of mechanical means to mix the yeast and substrate in Solid State Fermentation (SSF).

A research article titled “A demonstration study of ethanol production from sweet sorghum stems with advanced solid state fermentation technology” to Shizong Li and others published in Applied Energy, Volume 102, February 2013 discloses converting sweet sorghum into ethanol by Advanced Solid State Fermentation without squeezing out juice but employing mechanical means to rotate a drum fermenter to facilitate blending of yeast and substrate. The rotary fermenter achieves both mixing and removal of heat generated during fermentation, but requires large mechanical energy to move the solid biomass.

US Patent 4490469 to Kirby K.D. and others teaches a process for production of ethanol from sugar containing material using SSF. The process requires mixing of suspension of yeast with the substrate, requiring large mechanical energy so as to assure intimate continuous contact between yeast and substrate particles. Also, the patent describes a step of ‘squeezing’ the fermented pulp requiring mechanical energy. This patented process results in liquid effluent.

US Patent US4560659 to Asturias C. reveals SSF to produce ethanol from pulverized sugarcane, making a slurry with added yeast suspension, fermenting the same, separating liquid by a sieve and further mechanical pressing to remove entrapped liquid for yeast recycling. This process requires mechanical pressing for extracting ethanol and also produces liquid effluent, requiring equipment for treating the same. There is a need for a Zero Liquid Discharge (ZLD) and eco-friendly process for producing ethanol. Further, there is a need for an equipment for carrying out the said process.

SUMMARY OF THE INVENTION

The present invention discloses an oversaturated Substrate Fermentation process for producing ethanol by solid state substrate fermentation, the process is commercially known as OSFAY™ process. Accordingly, the process includes several stages for producing ethanol by solid state fermentation. The first stage is of preparation of rind/pith biomass 105, followed by a second stage of oversaturation of the biomass 110, and third stage of steam disinfection 115. The fourth stage is of cooling of the biomass 120, followed by fifth stage of inoculum addition 125. The next stage that is the sixth stage of fermentation 130, followed by a seventh stage of distillation 135 and finally, an eighth stage of dried biomass preparation 140.

The first stage of rind/pith biomass preparation 105 includes separating the outer rind of sugarcane and comminuting the inner soft portion, and feeding the mixture of rind and pith into a multipurpose Oversaturated Substrate Fermentation reactor i.e., OSFAY™ reactor 205. The second stage of oversaturation of biomass 110 includes adding water to the reactor 205 enough to oversaturate the substrate 225 i.e., the rind / pith biomass mixture, obtaining a percolate of quantity between 15% to 25% of the substrate weight; and collecting this percolate in a jacketed percolate vessel 230.

The third stage of steam disinfection 115 includes heating the substrate 225 in the reactor 205 by steam from a boiler by direct injection of steam in the substrate at about 125°C or by passing steam in jackets 210, 215 and 220. The percolate is recirculated by a pump 235 to the top of the reactor 205 by spray nozzles 250 and heated by the jackets 210, 215 and 220. In the third stage, uniform heating of the substrate 225 is carried out till temperature of about 90°C is obtained.

The fourth stage of cooling of the biomass 120 includes circulating the cold water in all the jackets 210, 215 and 220 and recirculating the percolate on the substrate 225. The fifth stage of inoculum addition 125 includes adding yeast inoculum to the percolate in the percolate vessel 230 and recirculating the percolate on the substrate 225 many times so that each of the substrate particle comes in contact with the inoculum for homogenous distribution of inoculum for initiation of the fermentation process.

The sixth stage of fermentation 130 includes fermenting the substrate 225 for about 24 hours by recirculating the percolate to the reactor 205 continuously assuring intimate contact of all substrate particles with the yeast inoculum. The percolate coming out of reactor 205 is continuously cooled by circulating cold water in the jacket of the percolate vessel 230 to enable control over the fermentation temperature. Any nutrients or other ingredients are added to the substrate through the percolate ensuring uniform distribution of the ingredients.

All the percolate is added back to the reactor 205 after the fermentation process is over. The valve regulating the flow of percolate between the reactor 205 and the percolate vessel 230 is closed. The seventh stage of distillation 135 includes passing steam through a lower jacket 215 of the reactor 205 and producing a first distillate containing about 25 to 50% ethanol. The first distillate is sent to conventional fractionation column to obtain rectified spirit of about 94% ethanol or the ethanol vapors are directly sent to the fractionating column thereby obtaining 94% ethanol.

The eighth stage of dried biomass preparation 140 includes removing the residual biomass containing the absorbed liquid and fresh yeast cell mass from the reactor via an outlet 270. The residual biomass is then sent to the drying equipment 275. The dried mixture of rind pieces and pith is conveyed to a sieving equipment 280. The rind and the pith are separated and stored in rind bin 285 and pith bin 290.

The equipment 200 for producing ethanol by oversaturated substrate fermentation process 100 includes an oversaturated substrate fermentation reactor i.e., OSFAY™ reactor 205 for carrying out the three phases of steam disinfection 115, fermentation 130 and distillation 135. The equipment further includes reactor 205 for circulating steam and cooling water and has an upper jacket 210 for heating/cooling the upper portion of the reactor 205 and a lower jacket 215 for heating/cooling the lower portion of the reactor 205. A percolate vessel 230 collects the percolate from oversaturated substrate. A percolate vessel jacket 220 heats/cools the percolate vessel 230.

The equipment further has a pump 235 that pumps the percolate to the reactor 205 through spray nozzles 250. A strainer 245 prevents the biomass particles from entering the percolate vessel 230. A valve 240 isolates the reactor 205 and the percolate vessel 230. An outlet for distillation vapor 255 leads the distillation vapor to a condenser 260 and the condensate is collected in a condensate vessel 265. An outlet 270 removes the residual biomass mixture containing pith and rind pieces from the reactor 205 after distillation. A drying equipment 275 dries the residual biomass. A sieving equipment 280 sieves the dried biomass. A rind bin 285 and a pith bin 290 is provided for separately collecting the separated matter.

The present invention advantageously overcomes the problem of removal of fermentation heat from poor heat conducting biomass as that in case of conventional Solid State Fermentation reactors. The present invention eliminates the steps of cane milling, juice clarification, syrup making and liquid effluent treatment as in the conventional process, therefore leading to a considerable reduction in the capital cost as well as running and maintenance costs of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a plurality of stages in the Oversaturated Substrate Fermentation process 100 for producing ethanol by oversaturated substrate fermentation in accordance with the present invention;

FIG. 2 shows the schematic representation of the equipment 200 for producing ethanol by oversaturated substrate fermentation in accordance with the present invention; and

FIG. 3 shows a schematic comparison of equipment 200 in accordance with the present invention with an equipment 300 used for conventional ethanol production processes known in the prior art.

DETAILED DESCRIPTION OF THE INVENTION

The invention described herein is explained using specific exemplary details for better understanding. However, the invention disclosed can be worked on by a person skilled in the art without the use of these specific details.

References in the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.

References in the specification to “preferred embodiment” means that a particular feature, structure, characteristic, or function is described in detail thereby omitting known constructions and functions for a clear description of the present invention.

The foregoing description of specific embodiments of the present invention has been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed and many modifications and variations are possible in light of the above teaching.

In one aspect, the present invention teaches a process for producing ethanol by oversaturated solid state substrate fermentation.

In another aspect, the present invention describes the equipment for carrying out the process for producing ethanol by oversaturated solid state substrate fermentation in accordance with the present invention.

The present invention describes a process for production of ethanol by subjecting a comminuted substrate material directly to disinfection, fermentation and distillation in a single Oversaturated Substrate Fermentation reactor i.e., OSFAY™ reactor. In accordance with the present invention, the process enables Zero Liquid Discharge (ZLD) and does not require any liquid effluent treatment. Further the steps of milling, juice clarification, evaporation, storage and dilution in conventional ethanol production are eliminated.

In accordance with a preferred embodiment, the present invention discloses an Oversaturated Substrate Fermentation process 100 for producing ethanol by oversaturated substrate fermentation, hereinafter referred to as “the OSFAY process 100” advantageously includes a plurality of stages for producing ethanol.

Now, referring to Figure 1, the OSFAY process 100 includes a first stage of rind/pith biomass preparation 105, a second stage of oversaturation of the biomass 110, a third stage of steam disinfection 115, a fourth stage of cooling of the biomass 120, a fifth stage of inoculum addition 125, a sixth stage of fermentation 130, a seventh stage of distillation 135, and an eighth stage of dried biomass preparation 140. The stages are performed in an equipment 200 for producing ethanol by oversaturated substrate fermentation in accordance with the present invention. The first stage of rind / pith biomass preparation 105 of the OSFAY process 100 includes separating the outer rind of sugarcane and comminuting the inner soft portion.

In this preferred embodiment, the first stage 105 is performed by a proprietary technology and equipment developed by an Indian company 4E Cane Multi Products (P) Ltd. for preparing rind/pith biomass from sugarcane including a sugarcane separation system 202 that removes the outer skin (Rind) of the sugarcane and converts the inner white pithy portion to a comminuted biomass of small (l-2mm) particles.

The rind pieces have intact bamboo-like fibers that have higher lignin content as compared to soft, highly absorbent pith. As a result, all the juice remains absorbed in the comminuted pith. This absorbent property of the pith enables direct fermentation of the rind / pith biomass without conventional milling and imbibition process. Thus, a mixture of rind and pith is prepared in the stage 105 by the sugarcane separation system 202, and is fed into a multipurpose Oversaturated Substrate Fermentation reactor i.e., OSFAY™ reactor 205.

The second stage of overs aturation of biomass 110 of the OSFAY process 100 includes adding water to the reactor enough to oversaturate the substrate i.e., the rind / pith biomass mixture. Further a percolate of quantity between 15% to 25% of the substrate weight is obtained. This percolate is collected in a jacketed percolate vessel.

The third stage of steam disinfection 115 of the OSFAY process 100 includes heating the substrate in the reactor by steam from a boiler. The disinfection is carried out by direct injection of steam in the substrate at about 125°C or by passing steam in jackets. The percolate that is heated by the jacket is recirculated by a pump to the top of the reactor by spray nozzles. This leads to uniform heating of the substrate till temperature of about 90°C is obtained. Further, a strainer arrests entry of the pith into the percolate vessel. A valve is provided to isolate the reactor and percolate vessel and regulate the flow between them. The stage of steam disinfection 115 disinfects the substrate.

The fourth stage of cooling of the biomass 120 of the OSFAY process 100 includes circulating the cold water in all the jackets along with the percolate being recirculated on the substrate. This stage of cooling of the biomass 120 cools the substrate to a temperature suitable for fermentation.

The fifth stage of inoculum addition 125 of the OSFAY process 100 includes adding yeast inoculum to the percolate in the percolate vessel. This percolate is then recirculated on the substrate many times so that each of the substrate particle comes in contact with the inoculum and the inoculum is distributed homogenously for initiation of the fermentation process.

The sixth stage of fermentation 130 of the OSFAY process 100 includes fermenting the substrate for about 24 hours. During this stage, the percolate is recirculated to the reactor intermittently or preferably continuously. This recirculation assures intimate continuous contact of all substrate particles with the yeast inoculum. Secondly, the temperature of percolate coming out of reactor increases because of heat of fermentation. This percolate is continuously cooled by circulating cold water in the jacket of the percolate vessel. If required, the percolate can be heated, by circulating hot water in the jacket. Thus, the recirculation of percolate enables controlling the fermentation temperature.

During the sixth stage of fermentation 130 of the OSFAY process 100, any nutrients or other ingredients can be added to the substrate, as per requirements, through the percolate ensuring uniform distribution of the ingredients. Further, after the fermentation is over, all the percolate is added back to the reactor and the valve regulating the flow of percolate between the reactor and the percolate vessel is closed.

The seventh stage of distillation 135 of the OSFAY Process 100 includes passing steam through the lower jacket of the reactor. This process is similar to pot still distillation and produces first distillate containing about 25 to 50% ethanol. This first distillate is sent to conventional fractionation column to obtain rectified spirit of about 94% ethanol. Alternatively, the ethanol vapors are directly sent to the fractionating column thereby obtaining 94% ethanol.

The eighth stage of dried biomass preparation 140 of the OSFAY process 100 includes post-fermentation processing of the biomass. The residual biomass containing the absorbed liquid and fresh yeast cell mass is removed from the reactor via an outlet. The residual biomass is further sent to drying equipment. The dried mixture of rind pieces and pith is conveyed to a sieving equipment. The rind and the pith are separated and are stored in separate bins for further use.

In an embodiment, the OSFAY process 100 of the present invention is carried out by employing renewable crops like sweet sorghum and other sugar- bearing stalks.

In an alternate embodiment, the OSFAY process 100 of the present invention employs biomass substrates like conventionally prepared cane, sorghum, or saccharified biomass.

In another embodiment, vacuum distillation is employed in the seventh stage of distillation 135 of the OSFAY process 100 to reduce heat energy required.

In yet another embodiment, vacuum is employed from the beginning of the sixth stage of fermentation 130 of the OSFAY process 100 to minimize ethanol inhibition thereby minimizing the fermentation time.

In an embodiment, the eighth stage of dried biomass preparation 140 in the OSFAY process 100 of the present invention is performed in a solar dryer alone or assisted by flue gases from a boiler.

In an embodiment, thermic fluid is used in place of steam. Now referring to Figure 2, a schematic representation of the equipment 200 for producing ethanol by oversaturated substrate fermentation in accordance with the process 100 is described. Figure 2 shows the OSFAY reactor 205 wherein the three phases of steam disinfection 115, fermentation 130 and distillation 135 in accordance with the OSFAY process 100 are carried out. The OSFAY reactor 205 has jackets for circulating steam and cooling water. An upper jacket 210 heats/cools the upper portion of the reactor 205, while a lower jacket 215 heats/cools the lower portion of the OSFAY reactor 205. The OSFAY reactor 205 contains a substrate 225 that is a mixture of rind pieces and comminuted pith as prepared in the rind / pith biomass preparation phase 105.

The equipment 200 further has a percolate vessel 230 that collects the percolate as per the overs aturation of biomass 110 stage. A percolate vessel jacket 220 heats/cools the percolate vessel 230. The percolate vessel 230 can alternatively be positioned below the reactor 205 or as a lower part of the reactor 205. A pump 235 pumps the percolate to the reactor 205 through spray nozzles 250. A strainer 245 prevents the biomass particles from entering the percolate vessel 230. A valve 240 isolates the reactor 205 and the percolate vessel 230. An outlet for distillation vapor 255 leads the distillation vapor generated during the distillation stage 135 of the OSFAY process 100 to a condenser 260 and the condensate is collected in a condensate vessel 265.

After distillation, the residual biomass mixture containing pith and rind pieces from the reactor 205 are removed via outlet 270. As per the dried biomass preparation phase 140 of the process 100, the residual biomass is dried in a drying equipment 275, further sieved in a sieving equipment 280 that separately collects the matter in a rind bin 285 and a pith bin 290.

Referring to Figure 3, a schematic comparison of equipment 200 in accordance with the present invention with an equipment 300 used for conventional ethanol production processes known in the prior art is described. The equipment 200 includes the sugarcane separation system 202, the OSFAY reactor 205, the percolate vessel 230, the condenser 260 and the condensate vessel 265.

The equipment 300 required for conventional ethanol production process includes a cane preparation equipment 305, a cane milling equipment 310, a juice clarification equipment 315, a juice to syrup conversion equipment 320, a fermenter 325, distillation columns 330, rectified spirit vessel 335 and an effluent treatment equipment 340.

The present invention employs a sugarcane separation system 202 that removes the outer skin (Rind) of the sugarcane and converts the inner white pithy portion to a comminuted biomass of small (l-2mm) particles. This eliminates the requirement of conventional cane milling equipment 310 and juice clarification equipment 315. Further the juice to syrup conversion equipment is not required as the juice is not diluted by addition of water to extract the sugar. The three phases of steam disinfection 115, fermentation 130 and distillation are carried out in the OSFAY reactor 205. An effluent treatment equipment is not required as no liquid effluent is generated.

Thus, the OSFAY process 100 of the present invention eliminates the need of equipment used conventionally that includes a cane milling equipment 310, a juice clarification equipment 315, a juice to syrup conversion equipment 320, and an effluent treatment equipment 340. This considerably reduces capital cost as well as the running and maintenance costs.

The foregoing description of specific embodiments of the present invention has been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and many modifications and variations are possible in light of the above teaching. EXAMPLE:

An example is set forth herein below and is illustrative of different types of reactions and reaction conditions that can be utilized in practicing the disclosure. It will be apparent, however, that the disclosure can be practiced with other types of reactions and reaction conditions than those used in the example, in accordance with the disclosure above and as pointed out hereinafter.

EXAMPLE 1: PROCESS OF ETHANOL PRODUCTION BY OVERSATURATED SUBSTRATE FERMENTATION

1) A sugarcane separation system developed by a company 4E Cane Multi Products (P) Ltd. for preparing rind/pith biomass from sugarcane is employed to remove the outer skin (Rind) of the sugarcane and comminute the inner white pithy portion to a biomass of small (l-2mm) particles to prepare the rind/pith biomass. As sugarcane is an agricultural produce, large variations in diameter, rind thickness and sugar content occur. Typically, 1 ton of sugarcane yields 800 kg pith and 200 kg rind. Out of 100 parts of sugar in cane, 90 parts go with pith and 10 parts go with rind.

2) The mixture of rind and pith that is the substrate 225 is fed into the OSFAY reactor 205.

3) Water is added to the OSFAY reactor 205 enough to oversaturate the substrate 225. Between 500 to 600 litres of water per ton of sugarcane is added.

4) A percolate of quantity between 100 to 300 litres is obtained per Ton of sugarcane. This percolate is collected in a jacketed percolate vessel 230.

5) The substrate 225 is heated in the reactor 205 by steam from a boiler. The disinfection is carried out by passing steam at about 125°C in jackets 210, 215 and 220. The percolate heated by the jacket 220 is recirculated by a pump 235 to the top of the reactor 205 by spray nozzles 250. Uniform heating of the substrate 225 is carried out till a temperature of 90°C is obtained. The strainer 245 arrests entry of the pith into the percolate vessel 230. The valve 240 regulates the flow between the reactor 205 and the percolate vessel 230. 6) Next cold water having temperature between 25 to 30°C is circulated in all the jackets 210, 215 and 220 and the percolate is recirculated on the substrate 225. The substrate 225 is cooled to a temperature 32 to 35°C suitable for fermentation.

7) Yeast inoculum of weight 0.1 per cent of sugarcane weight is added to the percolate in the percolate vessel 230.

8) The percolate is recirculated on the substrate 225 in the OSFAY reactor continuously for 24 hours.

9) The temperature of percolate coming out of OSFAY reactor 205 is measured. 0) The percolate is cooled by circulating cold water in the jacket of the percolate vessel 230 till temperature of 32 to 35°C is obtained. 1) Nutrients or ingredients like urea and antibiotics are added to the substrate 225 via the percolate. 2) After 24 hours, all the percolate is added back to the reactor 205 and the valve 240 between the reactor 205 and the percolate vessel 230 is closed. 3) Steam is passed through the lower jacket 215 of the reactor 205. 4) First distillate containing about 25 to 50%, usually 30% ethanol is obtained.5) This first distillate is distilled in conventional fractionation column to get rectified spirit of about 94% ethanol. 0.1 per cent yeast (by weight of sugarcane) yields between 65 to 75 litres ethanol per ton of sugarcane. 6) The residual biomass containing the absorbed liquid and fresh yeast cell mass, of about one ton per ton of sugarcane is removed from the bottom of the OSFAY reactor 205 via outlet 270. 7) The residual biomass is dried by drying equipment 275. 8) The dried mixture of rind pieces and pith, about 130 to 160 kg per ton of sugarcane, is conveyed to a sieving equipment 280. The rind and the pith are separated and are stored in rind bin 285 and a pith bin 290.

Advantageously, the present invention overcomes the problem of removal of fermentation heat from poor heat conducting biomass as that in case of conventional Solid State Fermentation reactors. Further, heavy machinery conventionally needed to ‘crush’ and/or ‘squeeze’ the tough cane is not required. In conventional processes, large quantity of water is required to be added to maximize sugar extraction resulting in dilution of the juice. Also further conventionally, clarification and evaporation of this dilute juice needs large heat energy. Further, the fermented wash obtained after the ethanol is distilled out has high COD and BOD. Therefore, expensive equipment and high energy expenditure is required to treat this effluent. In the present invention, as the steps of cane milling, juice clarification, syrup making and liquid effluent treatment are eliminated, there is considerable reduction in the capital cost as well as running and maintenance costs of the equipment.

The sieved soft pith containing yeast mass obtained after drying and sieving, is a proteinaceous animal feed supplement that fetches better price than dry bagasse. The intact rind separated during rind / pith biomass preparation 105 is used for making Oriented Strand boards or pulp or activated carbon or biochar. Thus, sale of both the rind and proteinaceous pith are revenue streams in addition to ethanol sale.

The combination of lower capital and running cost, as well as additional revenue streams enables construction of mini distilleries a viable proposition. Alternate cheap fuel can be used for boiler instead of burning value-added rind and pith. Further, the Zero-Liquid-Discharge (ZLD) process of the present invention is environment friendly.

The equipment 200 can also be used for producing other biochemicals like enzymes. If the fermentation is aerobic, the percolate can be first saturated with oxygen and then pumped to the reactor.

While the present invention has been described herein above in connection with preferred embodiments, it will be clearly understood that variations and modifications may occur to those skilled in the art without departing from the spirit and scope of this invention. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others, skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated.

It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the present invention.