DESC:METHOD OF PRODUCTION OF ETHANOL FROM SUGAR
Field of the invention
The present invention generally relates to a method of production of ethanol and more particularly it relates to a method of production of ethanol from sugar supplementing with nutrients from spent wash.
Background of the invention
Due to excess production of sugarcane, the sugar inventory has been piling up in India. In addition, due to depressed international prices of sugar, paying fair and remunerative price (FRP) to the farmers has also become a challenge. In view of above sugar crises, the Government of India (GoI) took a policy decision to continue ethanol blending program (EBP) and to go for 10% blending throughout the country and cut oil imports by 10% by 2022 and 20% by 2030. GoI has also taken decision in allowing fuel ethanol production from heavy molasses, sugarcane juice and sugar.
Enhancing ethanol production using sugarcane juice, sugar and B-heavy molasses can help to reduce the sugar stock and increase the availability of fuel ethanol for blending with petrol. The proactive decisions taken by GoI will provide new opportunities to the sugar and distillery industry in the country. The sugar industry therefore is passing through a very significant transformation in view of many steps already taken by GoI to maximize the production of ethanol.
Sugar mills in India run seasonally (November-March) whereas the distilleries run throughout the year depending on availability of feedstock. With differential prices offered for fuel ethanol, it is possible to operate distilleries with multiple feedstock. As sugarcane juice is perishable item, it is used for fuel ethanol production only during sugarcane crushing season. Molasses (C-molasses or B-heavy molasses) is stored and used in distillery for ethanol production in season as well as in off-season. In case of smaller crushing season (drought or flood situation), it becomes very difficult to operate distillery with maximum capacity due to shortage of molasses. To overcome these challenges and exploit benefit of higher rate for ethanol, sugar can be used to produce ethanol for maximal utilization of distillery capacity and flexibility in choosing feedstock.
The most commonly used yeast for ethanol production is S. cerevisiae (Bai et al. 2008; Pereira et al. 2011) because of its better productivity, high ethanol tolerance and the capacity to grow under the anaerobic conditions (Mussatto et al. 2010). Plantation white sugar, raw sugar, refined sugar, damaged sugar or khandsari also can be used for alcoholic fermentation. However, it has to be supplemented with various nutrients for optimum fermentation performance. During ethanol production, medium composition strongly influences the physiological state and the fermentation performance of S. cerevisiae. Ethanol production is mainly dependent on glucose concentration (the theoretical alcohol yield is 0.51 g of ethanol per g of glucose) but also on specific nutrients, such as trace elements (Azenha et al. 2000), vitamins (Alfenore et al. 2002) and nitrogen (Martínez-Moreno et al. 2012).
On a laboratory scale, media are often supplemented with peptone and yeast extract or yeast nitrogen base, but such additions are too expensive at industrial scale, so it is necessary to explore inexpensive nitrogen, vitamins and salts sources to supply all nutritional requirements to yeast growth and fermentation (Azenha et al. 2000; Alfenore et al. 2002; Izmirlioglu & Demirci 2012). Sugarcane molasses is generally used as feedstock for alcohol production in the distilleries. Molasses contains about 50% total sugar of which 30 to 33% is sucrose and the rest are reducing sugars. Apart from these fermentable sugars, molasses has dissolved inorganic solid matters containing Ca, Mg, Na, K salts. Before the fermentation, the brix of the molasses is generally adjusted to 22-25 o brix (average sugar content 16.0-17.0%) by diluting with water. After 24 to 30 h of fermentation, 9.0 to 10.0 % (v/v) ethanol is obtained in fermented wash with fermentation efficiency of about 89.0-90.0 %.
In the distillation section of distillery, the ethanol in fermentation wash (9.0-10.0 %) is distilled to achieve higher ethanol level. In analyzer column, 35-50 % (v/v) ethanol is taken out from the top of column and water along with other impurities (spent wash) is removed from bottom of the column. Due to unutilized nutrient in molasses after fermentation, the spent wash obtained from the analyzer column of the distillery contains various organic and inorganic nutrients. The spent wash generation may vary from 7-15 L per litre of alcohol produced depending upon the technology and quality of molasses used for fermentation. Due to high chemical oxygen demand (1,10,000- 1,60,000 ppm) and biological oxygen demand (40,000- 60,000 ppm), the spent wash generated in distillery needs to be disposed using proper effluent treatment method (composting or incineration). This adds a lot of operational as well capital cost to distillery.
Accordingly, there exists a need for ethanol production throughout the year and minimization of operational cost for disposal of spent wash by effectively utilizing the nutritional content of spent wash.
Object of the invention
An object of the present invention is to provide a method of production of ethanol from all types of sugar by minimizing cost of nutrient addition without compromising on ethanol concentration and fermentation efficiency.
Another object of the present invention is to provide a method of production of ethanol using spent wash as nutrient supplementation for S. cerevisiae ethanol fermentation from sugar.
Summary of the invention
The present invention discloses a method of production of ethanol from sugar. In first step, the method comprises preparing a fermentation media by diluting a nutrient medium with water in volume proportion ranging from 1:1 to 1:3 and dissolving from 13% w/v to 16 % w/v of sugar in the fermentation media. The nutrient medium used in the method is a distillery spent wash. pH of the fermentation solution is then adjusted to 4.5 to 5.0 using 3M NaOH and the pH adjusted fermentation media to a fermenter. In next step, the pH adjusted fermentation media is inoculated with 0.01% to 0.1% w/v of dry yeast and fermentation process is continued for a period ranging from 24 hrs to 30 hrs under anaerobic conditions at 30oC to32oC. Ethanol produced during fermentation is recovered by any conventional method. The fermentation efficiency ranging from 75% to 95% is achieved using the fermentation media of distillery spent wash.
Detailed description of the invention
The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art, techniques and approaches are overcome by the present invention as described below in the preferred embodiment.
Accordingly, the present invention provides a method (100) of production of ethanol from sugar using spent wash (hereinafter referred as "the method (100)"). In a distillery, ethanol in fermentation wash (9.0-10.0 %) is distilled to achieve higher ethanol level. In analyzer column, 35-50 % (v/v) ethanol is taken out from the top of column and the effluent water along with other impurities is removed from bottom of the column. This effluent water along with other impurities is a spent wash. Due to unutilized nutrients in molasses after fermentation, the spent wash contains various organic and inorganic nutrients. The present invention provides a novel method (100) for production of ethanol by fermentation of sugar using spent wash. Throughout the description, the term sugar means all types of sugar including plantation white sugar, raw sugar, refined sugar, damaged sugar and khandsari.
In step (10), the method (100) involves preparing fermentation media by diluting the spent wash with water and dissolving 13 to 16 % w/v of sugar in the diluted spent wash. The diluted spent wash solution contains one part of the spent wash and 2 to 3 parts of water.
In step (20), the method (100) involves adjusting pH of the fermentation media prepared in step (10) to 4.5 to 5.0 using 3 M NaOH.
In step (30), the method (100) involves transferring the pH adjusted fermentation media to fermenter.
In step (40), the method (100) involves inoculating the pH adjusted fermentation media in the fermenter with any one fermentation starter selected from 0.01% to 0.1% w/v of dry yeast and 5% to 20% v/v of S. cerevisiae culture developed in propagation vessel and continuing the batch or fed-batch fermentation process for 24 hrs to 30 hrs under anaerobic conditions at 30°C to 32°C. The dry yeast is S. cerevisiae in dry form.
In step (50), the method (100) involves recovering ethanol from the resulting solution in the fermenter, by known methods.
The fermentation efficiency of 75% to 95% is achieved with fermentation media having diluted spent wash.
Examples
The invention is further illustrated hereinafter by means of examples. In the fermentation process, S. cerevisiae in active dry yeast form (Kothari Fermentation & Biochem Company) was used. Batch ethanol fermentation was carried out under anaerobic condition at 31oC. The fermentation was carried out for 30 h. Initial sugar and final sugar was estimated using Fehling solution protocol (Lane 1923). Ethanol was measured using alcohol densitometer (Anton Paar). The details of experiments performed are given in following examples.
Fermentation media without spent wash and with spent wash obtained from different sources were prepared as below:
Media A: Fermentation media A was prepared by dissolving 1188.8 g of sugar in water. Final media volume was adjusted to 8 L using water.
Media B: Fermentation media B was prepared by dissolving 1188.8 g of sugar, 24 g of malt extract, 24 g of yeast extract and 40 g of peptone in water. Final media volume was adjusted to 8 L using water.
Media C: Fermentation media C was prepared by mixing one part of spent wash (Obtained from source I) with three parts of water to give Solution C and dissolving 1188.8 g of sugar in 8 L of Solution C.
Media D: Fermentation media D was prepared by mixing one part of spent wash (Obtained from source I) with two parts of water to give Solution D and dissolving 1188.8 g of sugar in 8 L of Solution D.
The spent wash composition may vary from distillery to distillery depending on quality of molasses and fermentation technology used. To understand effect of spent wash source on ethanol production from sugar, spent wash was used from other distilleries (Source II and source III) for preparing media E and media F.
Media E:Fermentation media E was prepared by mixing one part of spent wash (Obtained from source II) with two parts of water to give Solution E and dissolving 1188.8 g of sugar in 8 L of Solution E.
Media F:Fermentation media F was prepared by mixing one part of spent wash (Obtained from source III) with two parts of water to give Solution F and dissolving 1188.8 g of sugar in 8 L of Solution F.
Initial pH of media A and B was adjusted to 4.5 using 3 M H2SO4. and initial pH of media C, media D, media E and media F was adjusted to 4.5 using 3 M NaOH. The fermentation media A to F were transferred to separate New Brunswick fermenters (8 L working volume & 11 L total fermenter volume). Each fermenter was inoculated by adding 8 g of S. cerevisiae in active dry yeast form. Batch ethanol fermentation was carried out under anaerobic condition at 31oC for 30 h. Initial sugar and final sugar was estimated using Fehling solution protocol (Lane 1923). Ethanol was measured using alcohol densitometer (Anton Paar). Table 1 below shows the results of effect of spent wash addition on ethanol production from sugar
Table 1
Time A B C D E F
0 min Total reducing sugar (% w/w) 16.15 16.19 16.03 16.03 16.03 16.86
Ethanol (% v/v) 0.0 0.0 0.0 0.0 0.0 0.0
30 min Residual Sugar (% w/w) 10.87 0.22 0.74 0.84 0.61 0.72
Ethanol (% v/v) 1.31 9.24 9.07 9.15 7.93 8.52
Fermentation Efficiency (%) 13.1 92.40 90.70 91.50 79.30 85.20

In media A (only sugar diluted with water), 1.31 % (v/v) ethanol was obtained with fermentation efficiency of 13.1 %. Almost 10.87 % sugar was not fermented after 30 h of fermentation. This suggests that ethanol fermentation was not completed for media A due to non-availability of nutrients. In media B (enriched media), 9.24 % (v/v) ethanol was achieved with fermentation efficiency of 92.4 % due to supplementation of malt extract, yeast extract and peptone in media. 9.07 % (v/v) and 9.15 % (v/v) ethanol was achieved in media C and D respectively. The fermentation efficiency of 91.5 % was achieved with media D (spent wash to water ratio= 1:2) which was comparable to highly complex and costly media B. The above ethanol fermentation data of sugar supplemented with diluted spent wash (spent wash to water ratio= 1:2 or 1:3) clearly indicates the potential of spent wash to supplement nutrients required for ethanol fermentation.
In media E wherein spent wash was obtained from source II, ethanol was obtained with fermentation efficiency of 79.3 %. In media F wherein spent wash was obtained from source III, 8.52 % (v/v) ethanol was obtained with fermentation efficiency of 85.2 %. Lower ethanol concentrations and fermentation efficiencies were observed for media supplement with spent wash from Source II and Source III as compared to media supplement with spent wash from Source I. The above ethanol fermentation data for spent wash from three different distilleries suggest that spent wash has a potential to supplement nutrients required for ethanol fermentation but final ethanol concentrations and fermentation efficiencies achieved depends on quality of spent wash & its source.
Advantages of the invention
The method (100) enables reduction in cost of nutrient and hence the overall production cost without compromising on ethanol concentration and fermentation efficiency.
The method (100) reduces the consumption of water and total cost for spent wash disposal by utilizing spent wash for dilution of sugar media.
The foregoing objects of the invention are accomplished and the problems and shortcomings associated with prior art techniques and approaches are overcome by the present invention described in the present embodiment. Detailed descriptions of the preferred embodiment are provided herein; however, it is to be understood that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in virtually any appropriately detailed system, structure, or matter. The embodiments of the invention as described above and the methods disclosed herein will suggest further modification and alterations to those skilled in the art. Such further modifications and alterations may be made without departing from the scope of the invention.

,CLAIMS:
We claim:
1. A method (100) of production of ethanol from sugar, the method (100) comprising:
preparing a fermentation media by diluting a nutrient medium with water in volume proportion ranging from 1:1 to 1:3;
dissolving from 13% w/v to 16 % w/v of sugar in the fermentation media;
adjusting pH of the fermentation media to 4.5 to 5.0 and transferring the pH adjusted fermentation media to a fermenter;
inoculating the pH adjusted fermentation media in the fermenter with any one fermentation starter selected from 0.01% to 0.1% w/v of dry yeast and 5% to 20% v/v of S. cerevisiae culture developed in propagation vessel and continuing the fermentation process for 24 hrs to 30 hrs under anaerobic conditions at 30°C to32°C; and
recovering ethanol from the fermented solution by fractional distillation;
characterized in that, the nutrient medium is a distillery spent wash, wherein fermentation efficiency ranging from 75% to 95% is achieved using the fermentation media.
2. The method (100) as claimed in claim 1, wherein the sugar is any one selected from a plantation white sugar, a raw sugar, a refined sugar, a damaged sugar, a khandsari sugar, and mixtures thereof.
3. The method (100) as claimed in claim 1, wherein pH of the fermentation media is adjusted using 3 M NaOH.
Dated this 16th day of June, 2020

Ashwini Kelkar
(Agent for applicant)
IN/PA-2461