WO2015019362A1

WO2015019362A1 - Preparation of ethanol from lignocellulosic materials

Info

Publication number: WO2015019362A1
Application number: PCT/IN2014/000433
Authority: WO
Inventors: Waman Joshi Satyendra; Ganpat Kashid MOHAN; Subhash Rathi SHRIKANT; Baburao Deshpande GHANSHYAM
Original assignee: Praj Industries Limited
Priority date: 2013-08-06
Filing date: 2014-06-27
Publication date: 2015-02-12
Also published as: IN2013MU02596A; WO2015019362A8; BR112016002565A2

Abstract

The invention relates to a process and system for the preparation of ethanol from lignoceilulosic materials and more particularly from lignoceilulosic materials like corncob, corn stover, sugarcane/ beet bagasse or any other lignoceilulosic materials.

Description

TITLE: PREPARATION OF ETHANOL FROM LIGNOCELLULOSIC MATERIALS

FIELD OF INVENTION

The invention relates to a process and system for the preparation of ethanol from lignocellulosic materials and more particularly from lignocellulosic materials like com cob, corn stover, sugarcane/ beet bagasse or any other lignocellulosic materials.

BACKGROUND Due to the future limitations on the availability of fossil fuels particularly crude oil, many national governments are promoting the use of alternate fuels such as ethanol in motor vehicles. Ethanol is a major motor vehicle fuel in Brazil and is used at a large scale in other countries like the US and Europe; while in India it has been promoted significantly since past few years. However, preparation of fuel ethanol is mostly done from food crops like maize, sugarcane or beet, causing major social and economic issues of use of these food materials for non-food applications. Therefore, the governments are promoting use of non-food feedstocks like lignocellulosic materials for the preparation of fuel ethanol at large scales to fulfil the growing demands for the renewable energy sources.

Lignocellulosic materials [LCM] from the agriculture industry are waste by-products. It is mostly used inefficiently as an energy source or fed to animals; however a large part is wasted as such without any use. LCM is a complex structure of cellulose, hemicellulose and lignin forming a composite which depending on its source is differentially resistant to hydrolysis compared with other carbohydrate based materials like starch. LCM form structural^' components of plants and has varying composition based on its location in host or type of the host. In the art there are present several methods of chemical and thermal hydrolysis of LCM using high temperature water, acid, alkali and other chemicals. These treatments are performed to achieve effective degradation of LCM to fermentable sugars like xylose and glucose. These sugars on fermentation by yeasts lead to ethanol that is used in various applications including as a fuel additive.

LCM biomass refers to plant biomass that is composed of cellulose, hemicellulose, and lignin. This biomass comes in many different types such as wood, wood residues, municipal waste,, agricultural residues and energy crops like fast growing tall and woody grasses. In all these categories the carbohydrate polymers (cellulose and hemicelluloses) are tightly bound to the lignin by hydrogen and covalent bonds forming the strong structures of LCM. One barrier to the production of ethanol from LCM is that a large fraction of the sugars necessary for fermentation present in the form of lignocelluloses. LCM has evolved to resist degradation and to confer hydrolytic stability and structural robustness to the cell walls of the plants. This "recalcitrance" is attributable to the cross linking between the polysaccharides (cellulose and hemicellulose) and the lignin via ester and ether linkages thus creating a material that is physically hard to access. This means that for an efficient use of these components, said LCM should be disintegrated, separated and/or decrystallized.

Although there are several methods of hydrolysis of LCM known; however, there exists a need to find more effective and economic methods of treating LCM in more benign and economic conditions as the ethanol is a commodity product and the prices are very competitive. Besides, during LCM treatment using chemical and thermal treatment several inhibitors of the fermentative process are produce that lead to marked reduction of efficiencies of fermenting organisms as these inhibitors are toxic to these microbes. These inhibitors are mainly phenolics, certain organic acids and other organics produced from the components of LCM during the treatment of hydrolysis.

Therefore, the control of LCM hydrolysis treatment [also called pretreatment] is a major step in the processing of LCM for the preparation of ethanol. In the art current methods of the pretreatment use acids, alkalis or other chemicals like ammonia at high temperatures to hydrolyze the hemicellulose part of LCM liberating xylose sugar in the first step. Next, the cellulose rich remaining part is subjected to enzymatic or chemical hydrolysis to liberate glucose sugar and remaining lignin rich part is burned to generate energy. These two sugars are then fermented to make ethanol or used to prepare other bio-based chemicals. However, two major problems occur with such a treatment: 1] the heating may only be short, because otherwise too many unwanted by-products are formed from the carbohydrates; and 2) it is difficult to produce a biomass slurry with more than 30% solids by weight, which is necessary for an economic use in further processing.

The invention disclosed herein in addresses several problems of previous methods like: 1] high concentration of inhibitors in hydrolysates, 2] low efficiency of the hydrolysis of LCM at benign conditions and 3] low efficiency of conversion of LCM derived sugars to ethanol in the fermentative process. To this end a novel method is disclosed having advantages like: 1] low level of inhibitors that do not limit the growth of microbes, 2] more benign and economic processing conditions of LCM and 3] higher efficiency of conversion of sugars to ethanol in a novel two step fermentation process. DESCRIPTION OF DRAWINGS

90 These and other features; aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings, wherein:

FIGURE 1 depicts a block diagram of mass flow during the production of ethanol from a LCM. Different elements of the process are identified and directional movement of different additives and streams formed during the process are shown to describe the features of one embodiment of the present invention.

FIGURE 2 is an exemplary plan of the invention showing several 100 features that control the process of production of ethanol from a lignocellulosic feedstock. The whole system may be divided into five units, namely: 1] hydrolysis unit (TV), 2] enzymatic hydrolysis and C6 [hexose sugar] fermentation unit ('Β'), 3] distillation and ethanol recovery unit ('C'), 4] C5 [pentose sugar] fermentation unit (Ό'), and 5] evaporation unit (Έ'). η one embodiment of the present invention, said distillation and ethanol recovery unit used to recover, ethanol from C6 fermented wash as well as C5 fermented wash leading to recovery of ethanol made from both glucose and xylose sugars. A person skilled in the art may appreciate variations of the system to achieve the 110 conversion of sugars to ethanol as disclosed herein.

DETAILED DESCRIPTION OF THE INVENTION

In one embodiment of the disclosed invention as illustrated in FIGURE 1 to produce ethanol from , LCM biomass, said biomass like corn cob, bagasse, stover or other similar agricultural material is size reduced to a particulate matter. This particulate matter of about 40 mm size is then soaked and washed in water to remove any soil or other contaminating agents. Next, said soaked biomass is pretreated in the presence of one or more acids [inorganic or organic] at certain high pressure and

120 temperature provided by high pressure steam as energy and water source. On performing said pretreatment process for desired time period at desired conditions, a hydrolyzed stream of LCM is obtained, which is subsequently subjected to a neutralization and enzymatic hydrolysis process. The pretreatment on said LCM releases xylose from the hemicellulosic part, while crystalline cellulose fibres are loosen so that it may be further treated with cellulolytic enzymes. The said hydrolyzed stream is first neutralized with an alkali like NaOH or CaOH to increase the pH to about 6 and then one or more celllulases are added, and reaction is allowed for several hours at desired conditions.

130 This step releases glucose from the cellulose fibres leading to substantial increase of glucose in formed first stream. The said first stream is then subjected to a hexose fermenting yeast like a Saccharomyces sp. leading to conversion of said hexose to ethanol forming a first fermented stream. This stream contains ethanol produced from said glucose present in said first stream. Then said first fermented stream is subjected to a first distillation to separate aqueous ethanokleading to formation of a spent stream. The aqueous ethanol so afforded is further processed to obtain anhydrous ethanol or other ethanol products. Next, said spent stream is collected and under

140 desired conditions subjected to a second fermentation by a pentose • fermenting yeast like Pichia sp, leading to the conversion of xylose present in it to ethanol forming a final fermented stream. This final fermented stream is subjected to a second distillation to separate aqueous ethanol, which is further processed to obtain anhydrous ethanol or other ethanol products. A spent wash stream obtained at the end of this process is then subjected to solid/ liquid separation using a device like a filter press to remove the solids [which is mostly lignin] from waste water. These solids are burnt in a boiler to generate energy that is further used to run said system described herein. The wastewater is subjected to evaporation and further treatment to obtain process water for recycle/ reuse in said system. Again solids obtained in said evaporation step are burnt in said boiler.

In a further embodiment of the disclosed invention as illustrated in FIGURE 2 the steps of said process are: 1] the feedstock [30] comprising size reduced and washed corn cob or bagasse particulate material is pretreated in a hydrolysis unit ['A']. Before this a soak tank is used for wetting and removing of foreign matters from said particulate biomass. The LCM biomass is size reduced using a mechanical mechanism comprises a device for cutting, chopping or shredding. Then a plug screw type hydrolyser [1] is fed with said feedstock stream [30]; in the said hydrolyser said feedstock is treated with high pressure steam [21] at about 140 to 210 °C in the present of one or more acids supplied from a tank [2]. In said hydrolyser due to actions of high temperature and pressure as well as acids, the hemicellulose present in LCM is hydrolyzed leading to release of xylose in a hydrolyzed stream [26]. This hydrolyzed stream [26] is directed to a flash tank [3] to remove excess water from it, which is condensed by a condenser [13] and reused in the process. The hydrolyzed stream [31] obtained from said flash tank [3] comprising most of solids in the form of cellulose and lignin and soluble xylose is directed to a reactor or digestion tank [5] which has provisions for supply of an alkali and cellulolytic enzymes in unit ['Β'] In said reactor [5] said hydrolyzed stream [31] is neutralized with addition of suitable alkali solution to increase the pH to make it more suitable for actions of hydrolyzing enzymes. After neutralization said stream rich in cellulose is hydrolyzed by action of cellulases for desired time period leading to the formation of a first stream [32]. This first stream [32] is then subjected to a first fermentation in a fermentor or bioreactor [6] by a hexose sugar fermenting yeast like S. cerevisiae leading to the production of ethanol from glucose present in said stream and formation of a first fermented stream [33]. This stream [33] is subjected to distillation and ethanol recovery unit [7; '], wherein ethanol is recovered and a spent stream [34] rich in xylose sugar is subjected to a second fermentation by a pentose fermenting yeast like P. stipitis in a second fermentor or bioreactor [8; Ό'] leading to the production of ethanol from xylose present in said stream and formation of a final fermented stream [35]. This stream [35] is subjected to distillation and ethanol recovery unit [7; 'C'], wherein ethanol is recovered and a waste stream [36] is formed. Alcohol vapours [41] from said unit ['C'] are condensed [42] in an

190 evaporator [10] and directed back to the said unit for rectification to obtain anhydrous alcohol stream [43]. The said distillation and ethanol recovery unit ['C'] comprises several elements that efficiently distil out ethanol from streams [33] and [35] containing as low as 1 % ethanol by weight and simultaneously rectifies said stream [42] to more concentrated ethanol stream [43]. The said waste stream [36] with solids comprising lignin is subjected to a filter press [9] to remove wastewater [37] from said solids [44]. The solids [44] are burnt in a boiler [14] to generate energy, while wastewater [37] is sent to a flash tank [1 1] to remove vapours [38] that are condensed in a condenser

200 [12] to form a process water stream [39]. The liquid stream from flash tank [1 1] is evaporated in evaporator to recovery water [38], while solids [40] remaining are subjected to incineration on said boiler [14]. A vacuum pump [51] maintains a negative pressure in said system for effective operation of different units of the apparatus.

Examples provided below 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 experimental results is given in the examples, which demonstrate the advantageous and novel aspects of the process of using LCM for the preparation of 210 ethanol. EXAMPLE 1

In first step, a batch of about 118 Kg of corncobs having total solids of about 92% by weight, cellulose of about 33% by weight, hemicelluloses of about 27% by weight and lignin of about 13% by weight was used as a feedstock. It was subjected to mechanical shearing for size reduction to less than 40 mm particles affording about 108 Kg of the particulate material. This particulate material was soaked in water for about 30 min. Then about 360 Kg slurry [also called mixture] containing about

220 30% by weight total solids was prepared and continuously introduced into a plug screw type hydrolyser. Here the slurry was mixed with about 240 litres of the admixture of oxalic and sulphuric acids. This admixture of mixed acids contained about 1% by weight oxalic acid and about 2% by weight sulphuric acid on dry biomass weight basis [total 3% acid on dry biomass weight basis]. The resultant reaction mixture was then subjected to hydrolysis in said hydrolyser at a temperature of about 160 °C and pressure of about 6 bar [absolute] for a period of about 24 minutes at pH of about 1.3. At the end of this pretreatment the final slurry of about 700 Kg contained about 13% of total solids; and about

230 0.29% of glucose, about 4% of xylose, about 0.01 % of furfural, about 0.03% of HMF and about 3800 PPM of phenolic components along with undigested cellulose and lignin as detected by the HPLC methods. In this pretreatment, the efficiency of xylan to xylose conversion was about 86%. In second step, this pretreated hydrolysate rich with C5 sugars along with C6 solids [cellulose + lignin] was subjected to enzymatic hydrolysis by cellulases. Before enzymatic hydrolysis, it was neutralized with NaOH to increase pH to about 5. Then a commercially available cellulase cocktail [about 20 mg/g of cellulose] was added to the pretreated material and allowed digest said solids at desired

240 conditions for about 120 h at 52 °C. After said enzymatic hydrolysis, glucose of about 3.95% by weight was afforded in the stream with cellulose hydrolysis efficiency of about 72%. At the end of these treatments, the stream contained xylose of about 4% by weight and glucose of about 3.95% by weight. In third step, said sugar rich stream was subjected to fermentation by yeast S. cerevisiae, which fermented glucose present in said stream to ethanol leading to ethanol • concentration in the stream at about 1 .7% by weight. Here glucose to ethanol conversion efficiency was about 90% of theoretical maximum efficiency after about 36 h of fermentation time. This process also

250 removes inhibitors of fermentation present in said stream as S. cerevisiae is more robust microbe and can sustain wide variations in the growth conditions and toxicants present in the fermentation medium. It also moderates these inhibitors such that subsequently other yeasts may be grown in the same medium. After fermentation, the obtained stream was subjected to distillation to obtain ethanol. In fourth step, this spent stream was again subjected to a second fermentation by yeast P. stipitis, which fermented xylose present in said stream to ethanol leading to ethanol concentration in the stream at about 1 .5% by weight. Here xylose to ethanol conversion efficiency

260 was about 68% of theoretical maximum efficiency after about 72 h of fermentation time. Then this second fermented stream was further subjected to distillation to obtain ethanol. This two part fermentation and distillation afforded ethanol from both xylose and glucose sugars in a more efficient and economic way than previously disclosed. About 27 litres of ethanol was afforded from about 108 Kg of dry corncob biomass.

EXAMPLE 2

In first step, a batch of about 35 Kg of sugarcane bagasse having total 270 solids of about 90% by weight, cellulose of about 35% by weight, hemicelluloses of about 21 % by weight and lignin of about 21 % by weight was used, as a feedstock. It was subjected to mechanical shearing for size reduction to less than 40 mm particles affording about 122 Kg of the particulate material. This particulate material was soaked in water for about 30 min. Then about 489 Kg slurry containing about 25% by weight total solids was prepared and continuously introduced into a plug screw type hydrolyser. Here the slurry was mixed with about 240 litres of the admixture of oxalic and sulphuric acids. This admixture of mixed acids contained about 1 % by weight oxalic acid and about

280 1 .5% by weight sulphuric acid on dry biomass weight basis [total 2.5% acid on dry biomass weight basis]. The resultant reaction mixture was then subjected to hydrolysis in said hydrolyser at a temperature of about 150 °C and pressure of about 5 bar[a] for a period of about 24 minutes at pH of about 1 .2. At the end of this pretreatment the final slurry of about 714 Kg contained about 14.5% of total solids; and about 0.31 % of glucose, about 3.5% of xylose, and about 3800 PPM of phenolic components along with undigested cellulose and lignin as detected by the HPLC methods. In this pretreatment, the efficiency of xylan to xylose conversion was about 85%. In second step, this

290 pretreated hydrolysate rich with C5 sugars along with C6 solids [cellulose + lignin] was subjected to enzymatic hydrolysis by cellulases. Before enzymatic hydrolysis, it was neutralized with NaOH to increase pH to about 5. Then a commercially available cellulase cocktail [about 30 mg/g of cellulose] was added to the pretreated material and allowed digest said solids at desired conditions for about 120 h at 52 °C. After said enzymatic hydrolysis, glucose of about 3.3% by weight was ' afforded in the stream with cellulose hydrolysis efficiency of about 52%.

At the end of these treatments, the stream contained xylose of about 3.5% by weight and glucose of about 3.3% by weight. In third step, said

300 sugar rich stream was subjected to fermentation by yeast S. cerevisiae, which fermented glucose present in said stream to ethanol leading to ethanol concentration in the stream at about 1 .3% by weight. Here glucose to ethanol conversion efficiency was about 90% of theoretical maximum efficiency after about 36 h of fermentation time. This process also removes inhibitors of fermentation present in said stream as S. cerevisiae is more robust microbe and can sustain wide variations in the growth conditions and toxicants present in the fermentation medium. It also moderates these inhibitors such that subsequently other yeasts may be grown in the same medium. After fermentation,

310 the obtained stream was subjected to distillation to obtain ethanol. In fourth step, this spent stream was again subjected to a second fermentation by yeast P. stipitis, which fermented xylose present in said stream to ethanol leading to ethanol concentration in the stream at about 1.2% by weight. Here xylose to ethanol conversion efficiency was about 65% of theoretical maximum efficiency after about 80 h of fermentation time. Then this second fermented stream was further subjected to distillation to obtain ethanol. This two-part fermentation and distillation afforded ethanol from both xylose and glucose sugars in a more efficient and economic way than previously disclosed. About 23

320 litres of ethanol was afforded from about 122 Kg of dry sugarcane bagasse biomass.

While the invention has been particularly shown and described with reference to embodiments listed in examples, it will be appreciated that several of the above disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen and unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following 330 claims. Although the invention has been described with, reference to specific preferred embodiments, it is not intended to be limited thereto, rather those having ordinary skill in the art will recognize that variations and modifications may be made therein which are within the spirit of the invention and within the scope of the claims.

Claims

1. A process for the preparation of ethanol from a dry lignocellulosic biomass comprising:

(a) converting said biomass to a particulate matter; 340 (b) preparing a mixture of said matter in water;

(c) contacting said mixture with a blend of acids at a desired temperature for a desired time period to obtain a first stream;

(d) adjusting pH of said first stream with a base to obtain a neutralised stream;

(e) contacting said neutralised stream with one or more of cellulolytic enzymes at desired temperature for a desired time period to obtain a final stream;

(f) subjecting said final stream to a hexose fermenting yeast to obtain a first fermented stream;

350 (g) separating ethanol from said first fermented stream by distillation to obtain a spent stream;

(h) subjecting said spent stream to a pentose fermenting yeast to obtain a final fermented stream; and

(i) separating ethanol from said final fermented stream by distillation.

2. The process of claim 1 , wherein said blend of acids comprises oxalic acid and sulphuric acid.

3. The process of claim 1 , wherein amount of oxalic acid is between 0.1 to 5 percent and amount of sulphuric acid is between 0.1

360 to 5 percent of said biomass by weight.

4. The process of claim 1 , wherein said cellulolytic enzymes comprises one or more of a cellulase, a hemicellulase or a combination thereof.

5. The process of claim 1 , wherein said enzymes are used between 10 mg and 100 mg per gram of cellulose present in said neutralised stream.

6. The process of claim 1 , wherein said desired temperature to obtain said first stream ranges from about 140° C to about 210° C.

7. The process of claim 1 , wherein said desired time period to 370 obtain said first stream ranges from about 5 minutes to about 120 minutes.

8. The process of claim 1 , wherein said desired temperature to obtain said final stream ranges from about 40° C to about 80° C.

9. The process of claim 1 , wherein said desired time period to obtain said final stream ranges from about 36 hours to about 120 hours.

10. The process of claim 1 , wherein pH of said first stream is adjusted to between about 4 and about 6.

1 1 . The process of claim 1 , wherein said first stream comprises 380 pentose sugars derived from thermo-chemical hydrolysis of hemi- cellulose part of said biomass.

12. The process of claim 1 , wherein the efficiency of hydrolysis of hemi-cellulose is at least 60 percent of theoretical efficiency.

13. The process of claim 1 , wherein said final stream comprises hexose sugars derived from enzymatic hydrolysis of cellulose part of said biomass.

14. The process of claim 1 , wherein the efficiency of enzymatic hydrolysis of cellulose is at least 40 percent of theoretical efficiency.

15. The process of claim 1 , wherein the efficiency of conversion of 390 hexose sugars to ethanol is at least 80% of theoretical efficiency.

16. The process of claim 1 , wherein the efficiency of conversion of pentose sugars to ethanol is at least 65% of theoretical efficiency.

1 7. The process of claim 1 , wherein said hexose fermenting yeast is a Saccharomyces sp.

18. The process of claim 1 , wherein said pentose fermenting yeast is a Pichia sp.

19. A system for the preparation of ethanol from a dry lignocellulosic biomass comprising:

400 (a) a mechanical mechanism for converting said biomass to a particulate biomass;

(b) a soak tank for soaking and washing said particulate biomass in water;

(c) a digester for pre-treating said soaked biomass with an acid or a mixture of acids to obtain a first stream with pentose sugars released from hemi-cellulose part of said biomass;

(d) a reactor for adjusting pH of said first stream to obtain a neutralised stream and simultaneously liquefying said neutralised stream with cellulolytic enzymes to obtain a hydrolysed stream;

410 (e) a provision in a second reactor for treating said

hydrolysed stream with additional cellulolytic enzymes to obtain a final stream with hexose sugars released from cellulose part of said biomass;

(f) a first bioreactor for treating said final stream with a microorganism fermenting hexose sugars to obtain a first fermented stream;

(g) a distillation mechanism for recovering aqueous ethanol from said first fermented stream to obtained a spent stream;

(h) a second bioreactor for treating said spent stream with a 420 microorganism fermenting pentose sugars to obtain a final fermented stream;

(i) said distillation mechanism for further recovering aqueous ethanol from said final fermented stream and a waste stream; (j) a rectification mechanism to convert said aqueous ethanol to a concentrated ethanol stream;

(k) a filter press mechanism for separating water from said waste stream to obtained a solid stream as a boiler fuel; and

(I) a purification mechanism for purifying said separated water to reusable water.

430 20. The system of claim 19, wherein said mechanical mechanism comprises a device for cutting, chopping or shredding.

21. The system of claim 19, wherein said soak tank is for wetting and removing of foreign matters from said particulate biomass.

22. The system of claim 19, wherein said digester is a screw type reactor having one or more elements for effective acid hydrolysis of said particulate biomass.

23. The system of claim 19, wherein said reactor is a vessel with provisions for addition of a neutralising agent and an enzyme preparation.

440 24. The system of claim 19, wherein said first bioreactor is a vessel suitable to carry on fermentation using a hexose fermenting

microorganism.

25. The system of claim 19, wherein said second bioreactor is a vessel suitable to carry fermentation using a pentose fermenting microorganism.

26. The system of claim 19, wherein said distillation mechanism is a device with one or more elements for effective distillation of ethanol of a fermented stream.

27. The system of claim 19, wherein said rectification mechanism is a device with one or more elements for effective rectification of ethanol to obtained a concentrated ethanol stream.

28. The system of claim 19, wherein said filter press mechanism is a device for effective removal of water from said solid stream under high pressure.