WO2007027832A2

WO2007027832A2 - A method for the production of propylene glycol

Info

Publication number: WO2007027832A2
Application number: PCT/US2006/033946
Authority: WO
Inventors: Ian C. Purtle; Aharon Eyal; Luca Zullo
Original assignee: Cargill, Incorporated
Priority date: 2005-08-30
Filing date: 2006-08-30
Publication date: 2007-03-08
Also published as: WO2007027832A3

Abstract

The present invention is a method for the production of propylene glycol that includes fractionating a carbohydrate material into at least a first fraction and a second fraction. The method further includes the steps of processing the first fraction to generate a hydrogen product and processing the second fraction to generate a carbohydrate product. The hydrogen product and the carbohydrate product can then be reacted to form a reaction mixture including propylene glycol. The method of the present invention also includes separating propylene glycol from the reaction mixture.

Description

A METHOD FOR THE PRODUCTION OF PROPYLENE GLYCOL

FIELD OF THE INVENTION

The present invention generally relates to a method for the production of a propylene glycol system. The present invention more particularly relates to a method for the production of propylene glycol, and optionally also ethylene glycol and other products in an economic and environmentally friendly way.

BACKGROUND OF THE INVENTION

There are known methods for the production of propylene glycol. One such known method includes hydrogenolysis of carbohydrates or sugar alcohols. However, such known methods have several disadvantages including high production costs and being less favorable to the environment.

Accordingly, there is a need for a method for the production of propylene glycol and optionally also ethylene glycol and other products at lower production cost. There is also a need for a method for the production of such products in an environmentally friendly method. It would be advantageous to provide a method for the production of propylene glycol filling any one or more of these needs or having other advantageous features.

SUMMARY OF THE INVENTION

In one embodiment of the present invention is a method for the production of propylene glycol that includes the steps of fractionating a carbohydrate material into at least a first fraction and a second fraction, processing the first fraction to generate a hydrogen product and processing the second fraction to generate a carbohydrate product. The method further includes the step of reacting the hydrogen product and the carbohydrate product to form a reaction mixture that contains propylene glycol and then separating propylene glycol from the reaction mixture. In an alternative embodiment of the present invention is a method for the production of propylene glycol that includes the steps of fractionating a starch material to form at least one fiber-enriched fraction, at least one starch- enriched fraction and purified starch, fermenting at least one of the starch- enriched fraction and the purified starch to form an ethanol-containing fermentation liquor and separating ethanol from said fermentation liquor. The method further includes the steps of dehydrogenating the separated ethanol to generate a hydrogen product and at least one of acetaldehyde, ethyl acetate and acetic acid, hydrolyzing the purified starch to generate a glucose product as well as reacting the hydrogen product and the glucose product to form a reaction mixture having propylene glycol and ethylene glycol. The method of the present invention can also include the step of separating the propylene glycol from the ethylene glycol.

BRIEF DESCRIPTION OF THE DRAWING

Figure 1 is a flow diagram of a process for the production of propylene glycol according to an embodiment of the present invention.

DETAILED DESCRIPTION

According to the present invention, propylene glycol, and optionally also other polyols such as ethylene glycol, and additional products are produced from a carbohydrate material. Any carbohydrate material is suitable, including materials comprising monosaccharides, such as glucose, fructose and xylose; disaccharides, such as sucrose, trisaccharides, oligosaccharides and polysaccharides, such as starch, cellulose and hemicellulose. According to one embodiment, the carbohydrate material comprises starch. Suitable starch- containing carbohydrate materials include corn, wheat, rice and potato. According to another embodiment, the carbohydrate material comprises at least one of corn kernels and fractions of corn kernels. The carbohydrate material is fractionated into at least a first fraction and a second fraction. According to one embodiment of the invention, fractionating comprises at least one step selected from steps of corn dry milling, corn wet milling and a combination thereof. Such steps include debranning, oil extraction, steeping, starch separation from gluten, hydrolysis and saccharification. Those and other methods referred to in the following are described in well-known publications, such as Corn: Chemistry and Technology, edited by Watson and Ramstad (American Association of Cereal Chemists Inc., St. Paul, Minnesota, USA). According to another embodiment, the carbohydrate concentration in the second fraction is greater than that in the first fraction, when determined on the same basis, e.g. on dry basis.

The first fraction is processed to generate a hydrogen product. Suitable hydrogen products comprise hydrogen. According to one embodiment of the inventoin, the hydrogen product is a gaseous stream. According to another embodiment, hydrogen concentration in the hydrogen product, as such or after some treatment, is greater than 80%, preferably greater than 90%, most preferably greater than 95%. According to yet another embodiment, the processing of said first fraction comprises at least one of dehydrogenation, fermentation and reforming. According to still another embodiment, in addition to said first fraction, other organic compounds are processed to generate hydrogen. Such other organic compounds could include other products or co-products of the process according to the method of the invention. As used herein, hydrogen produced from the first fraction or from any other organic compound is referred to as biohydrogen.

The processing of the first fraction comprises fermentation to generate ethanol. According to an embodiment of the present invention, the fermentation is of a simple carbohydrate, such as glucose, fructose, xylose and sucrose. Alternatively, polysaccharides, such as starch, cellulose and hemicellulose, are fermented. Such polysaccharides could be hydrolyzed to simple carbohydrates prior to fermentation or hydrolyzed and fermented in the same operation, which is sometimes referred to as simultaneous saccharification and (co-)fermentation (SSF or SSCF). Fermentation can use known organisms and conditions and forms ethanol-containing fermentation liquor. Ethanol is separated and dried and then dehydrogenated to generate a hydrogen product and optionally at least one additional product. According to another embodiment, the additional product is selected from a group consisting of acetaldehyde, ethyl acetate and acetic acid.

According to the method of the present invention, processing the second fraction generates a carbohydrate product. In one aspect of the inventon, the carbohydrate product is a solution of a simple carbohydrate, e.g. one selected from a group including glucose, fructose, xylose, mannose, sucrose ribose, arabinose and mixtures of those. According to another embodiment, total carbohydrate concentration in the carbohydrate product, as such or after some additional treatment, is greater than 80% on dry basis, alternatively greater than 90%, or greater than 95%. According to yet another embodiment, the main carbohydrate in the carbohydrate solution is glucose. In one instance, processing of the second fraction includes at least one step selected from a group consisting of hydrolysis, purification and concentration.

According to the method of the present invention, hydrogen from the hydrogen product is reacted with the carbohydrate in the carbohydrate product. The reaction includes a step of cleaving at least one of (i) RC-CR' bonds and (ii) R"C-OR'" bonds in the carbohydrate molecule to form (i) RCH + HCR' and (ii) R"CH and HOR'" fractions, respectively. Such reaction is referred to here as hydrogenolysis. In one instance, hydrogenolysis is conducted on the carbohydrate. Alternatively, the carbohydrate is first reacted to form another hydrogenolysis precursor.

According to an embodiment of the present invention, the carbohydrate is hydrogenated to form a sugar alcohol, such as sorbitol, xylitol and mannitol, and the sugar alcohol is then hydrogenolyzed. According to one embodiment, most of the hydrogen consumed in the reaction with the carbohydrate is biohydrogen. According to a particular embodiment, practically all the consumed hydrogen is biohydrogen. The hydrogenolysis reaction generates a reaction mixture comprising propylene glycol and optionally also other products of commercial value, such as ethylene glycol, glycerol, butanediol, pentanediol and erythritol. The reaction mixture is treated to separate propylene glycol as well as other components of commercial value.

The invention will now be described in connection with certain embodiments and with reference to the following illustrative figure so that it may be more fully understood.

With specific reference now to the figure in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

Figure 1 is a flow diagram of an embodiment of the present invention. Corn kernels (12) are debranned in (20) to form a fiber-enriched fraction (22 and/or 23) and a starch-enriched fraction (28). The fiber-enriched and the starch-enriched fractions have higher fiber and higher starch, respectively, compared to their concentration in the corn kernels, when measure on the same basis, e.g. on dry basis.

According to one embodiment, the corn kernels are tempered and then mechanically debranned in (20), e.g. as in corn dry milling. Mechanical debranning forms a fiber-enriched fraction, which also contains corn oil (22). According to a preferred embodiment, that oil is extracted using known methods and known extractants such as hexane. Alternatively, azeotropic ethanol or dried ethanol, e.g. as formed in the process of the invention method (streams (66) and (72), respectively), is used as an extractant. The miscella of oil in extractant that forms in the extraction is further treated for solvent removal and oil refining to generate refined com oil (32). The extracted meal is desolventized and used as an ingredient in animal feed (36), as a nutrient or as a hydrogen source. Alternatively, part or all of the extracted meal (34) is gasified or combusted (operation 40). According to another embodiment, part or all of the fiber-enriched fraction (23) is gasified or combusted in (40) with no prior oil extraction. Optionally, other organic products are also gasified or combusted in (40). Such organic compounds include, according to one embodiment, additional plant materials, such as corn stalk and co-products formed in other parts of the process. The treatment in (40) generates thermal energy and ashes (42).

Mechanical debranning also forms debranned kernels, which are starch- enriched. According to one embodiment, part of the debranned kernels are made into corn grits for food applications (24). According to an embodiment of the present invention, at least part of the starch-enriched fraction (26) is treated in (100) for starch purification. In one instance, starch purification includes the steps of steeping, e.g. in SO2 solution, and starch separation from gluten. According to one embodiment, steeping time is smaller than that in corn wet milling, since the kernel is already debranned. A gluten stream is formed (102) and could be used as an ingredient in animal feed or as a nutrient. Also formed is a purified starch stream (104).

According to an alternative embodiment, the corn kernels (12) are steeped in SO2 solution and then debranned in (20), e.g. as in corn wet milling. Optionally, both bran and germ are separated. The bran is the fiber-enriched fraction and is used as an animal feed ingredient (36) or gasified or combusted in (40). The separated corn germ is extracted to generate corn oil (32) and a meal, which could be used as a feed ingredient, as a nutrient, gasified or combusted. Steeping and debranning also forms a starch-enriched fraction (26), which consists mainly of kernel endosperm containing gluten and starch. The starch- enriched fraction is further treated in (100) for starch purification in an operation comprising a step of starch separation from gluten. A gluten stream is formed (102) and could be used as an ingredient in animal feed. Also formed is a purified starch stream (104).

The starch-enriched fraction, e.g. mechanically debranned corn or kernel endosperm (28) or the purified starch (104) is fermented to ethanol in (50), using known organisms, methods and conditions. The fermentation generates a fermentation liquor (52), which is an ethanol solution, containing also other components, such as proteins and sugars. The fermentation liquor is treated in (60) for ethanol separation. Such separation uses known methods such as distillation that generates three products: water (62), solids, which are dried to form dry distillation grain (DDG) (64) and azeotropic ethanol (66). The water is preferably reused as process water. DDG is used as an ingredient in animal feed, as a nutrient and/or gasified or combusted. According to a preferred embodiment, the azeotropic ethanol (66) is dried (dehydrated) in (70), e.g. on molecular sieve or in contact with dry process products or streams, such as grits. Also dried, simultaneously or separately is ethanol recycled from the separation in (90) and optionally from other ethanol-generating steps, such as the hydrolysis of ethyl acetate described in the following. According to one embodiment of the present invention, part of the dried ethanol (72) is used as biofuel. The rest of the ethanol, or practically all of it (74), is used to generate biohydrogen in step (80).

Step (80) involves reacting organic matter to generate biohydrogen from sources such as dried ethanol (74), coproducts of other steps of the process (e.g. dehydrogenation and hydrogenolysis) and other organic matter, such as fiber- enriched fractions, plant material and products of their processing. Various methods of hydrogen production are known, such as fermentation with hydrogen- forming organisms, reforming and dehydrogenation. Biohydrogen production forms, according to certain embodiments, coproducts selected from a group consisting of ethyl acetate, acetic acid, acetone, formaldehyde, propionic acid, butyric acid, lactic acid, ethanol and propanol.

According to one embodiment, step (80) involves dehydrogenation of dried ethanol. A method of catalytic dehydrogenation of ethanol is disclosed in US Patent 6,809,217 and in its background description, the teaching of which is incorporated here by reference. Two ethanol molecules are converted into two molecules of hydrogen and a molecule of ethyl acetate. Due to side reactions, co- products are also formed. Such coproducts include water, acetaldehyde, methane, di-ethyl ether and butanols. US Patent 6,809,217, which is incorporated by reference in its entirety, reports a copper containing catalyst used in the dehydrogenation process, which is conducted at a temperature of between 100C and 260C and pressure of between 6bar and 30bar. The biohydrogen formed in (80) is used partially or practically completely in the hydrogenolysis step (130).

Ethanol is only partially reacted in the process of US Patent 6,809,217, which is also incorporated by reference in its entirety, so that the reaction mixture contains, after separation of the hydrogen, ethanol, ethyl acetate and the coproducts. That reaction mixture (82) is separated in operation (90). A method for separation of the reaction mixture components is disclosed in US Patent 6,809,217, also incorporated by reference, which involves catalytic partial re- hydrogenation followed by distillation at multiple pressures. Another separation method is described , that includes contacting with a solution resulting from hydrogenolysis. The separated ethanol (96) is optionally recycled to the dehydrogenation step (80), , after drying in operation (70). According to various embodiments, the co-products (92) are used as such, burned for energy, processed to generate hydrogen or a combination of those. The separated ethyl acetate (94) is used as such.

In an alternative embodiment, the main reaction product besides hydrogen is acetic acid, rather than ethyl acetate. According to this embodiment, the hydrogen produced per ethanol molecule is about doubled, which increases the overall yield of converting carbohydrates into propylene glycol and to other products of hydrogenolysis. Furthermore, the related amount of CO2 produced (as coproduct of ethanol formation) is decreased. According to one embodiment, at least part of the separated ethyl acetate is hydrolyzed (not shown in Figure 1) to acetic acid and ethanol, which are then separated. Acetic acid is used as such or further converted, e.g. to generate additional biohydrogen, to produce a deicer, etc. Separated ethanol is preferably recycled to dehydrogenation in (80), optionally via the drying step in (70). According to an alternative embodiment, ethyl acetate contained in the reaction mixture (82) is hydrolyzed to acetic acid and ethanol prior to separation in (90). The formed acetic acid is easier to separate than ethyl acetate, using known methods, such as solvent extraction (e.g. amine-based), resins, electrodialysis and distillation. The ethanol formed in the hydrolysis is recycled to the dehydrogenation along with the non-reacted ethanol (96). Ethanol separation from reaction coproducts is also simplified. According to a preferred embodiment, re-hydrogenation is obviated, omitting a hydrogen-involving process step, further increasing the yield of biohydrogen production, and decreasing catalyst cost. Hydrolysis of ethyl acetate to ethanol and acetic acid is straightforward and is accelerated, according to a preferred embodiment, by treatment with a chemical catalyst (e.g. an acid) a biological catalyst, e.g. a lipase enzyme, or a combination of those.

As presented in Figure 1, purified starch (104) is hydrolyzed in (110).

According to a first embodiment, the starch-enriched fraction formed in a mechanical debranning step (e.g. dry-milling type operation), is fractionated into at least two fractions. One of those (28) forms the raw material for fermentation and the other (26) is processed to generate the purified starch (104). Fractionating may use various methods, such as cracking and sifting, preferably methods that generate a fraction that is further enriched in starch and a fraction that is somewhat depleted in starch. In one instance, those fractions are directed to starch purification and to fermentation, respectively. According to a second embodiment, corn kernels are steeped, e.g. as in corn wet milling, and the fiber and germ fractions are separated. At least part of the endosperm is further treated for starch purification to form the purified starch (104). According to this second embodiment, purified starch and/or endosperm is fermented, and purified starch is hydrolyzed. According to a third embodiment, corn kernels are fractionated into two fractions. One of those is treated in a mechanical debranning operation (e.g. in a dry-milling type operation) to form the fermentation feedstock, while the other fraction is processed in a wet-milling type operation to generate the purified starch.

Starch hydrolysis could be conducted by known methods, such as the ones used in com wet milling, e.g. including chemical catalysis (e.g. using an acid as a catalyst), enzymatic catalysis (using enzymes such as amylases) or combinations of those. Optionally, the formed hydrolyzate is further purified, using means such as ion-exchange and adsorbents. Optionally, part of the formed glucose is used for products such as high-fructose corn syrup (HFCS). Alternatively, practically all of it is used in the reaction with hydrogen. The composition of the formed glucose product is optionally adjusted to generate a glucose stream (112) suitable for reaction with biohydrogen from the dehydrogenation process (86). Adjustment involves, according to a preferred embodiment, generating a glucose solution in a suitable solvent selected from a group consisting of water, organic solvents and combinations of those. According to a preferred embodiment, a product of the process is used as an organic solvent.

According to one embodiment, glucose in (112) is hydrogenated in (120) in a reaction with biohydrogen to form sorbitol, using known methods, catalysts and conditions. The formed sorbitol solution (122) is reacted in (130) with biohydrogen in a hydrogenolysis process. Alternatively, hydrogenolysis is conducted directly on glucose in the glucose solution (112). Hydrogenolysis is conducted using known methods, catalysts and conditions, e.g. as those of US Patent 6,841 ,085 and in its background section. The main products of hydrogenolysis are propylene glycol (PG) and ethylene glycol (EG). Other coproducts are also formed. The reaction mixture is separated in (140) to generate purified PG (142), purified EG (144) and other coproducts, which are present in a mixture (146), or further separated. Presently, PG is the most valuable compound and is preferably used as such. EG is preferably also used as such. Separated coproducts could be further processed to generate commercial products, burned for energy, converted to biofuel or processed to generate biohydrogen. be further processed to generate commercial products, burned for energy, converted to biofuel or processed to generate biohydrogen.

Separation of hydrogenolysis products in (140) can use known methods, such as distillation and separation on zeolites. According to one embodiment of the present invention, at least part of the hydrogenolysis products are chemically derivatized prior to separation or simultaneously with it, e.g. into acetales, in order to facilitate separation. According to an embodiment of the present invention, separation uses a solvent extraction process, wherein the extracting solvent comprises ethyl acetate, preferably from the dehydrogenation process (80). In another embodiment, the reaction mixture from (80), after separation of hydrogen is used as the extractant. The reaction mixture is used as such, or after some pretreatment, such as partial removal of ethanol. Other system adjustments may include adjusting the water content, adding another organic solvent and possibly removal or recycle or other organic compounds present in the dehydrogenation reaction mixture, in the hydrogenolysis reaction mixture or both.

According to one aspect of the present invention, stream (82), optionally modified, and stream (132), optionally modified, are counter-currently contacted to form a hydrophilic stream and a less hydrophilic stream. The hydrophilic stream contains mainly EG, ethanol and water. Ethanol is distilled out of that stream and recycled to hydrogen production. EG is then separated from the solution, e.g. by distillation. The less hydrophilic stream contains ethyl acetate, PG and possibly EG and other impurities. Optionally, that stream is extracted with a small amount of water to separate EG, which could then be recycled to the extraction operation. Then the less hydrophilic stream is distilled to remove ethyl acetate and to form a solution out of which PG is separated.

Several steps of the process are energy consuming, including solutions concentration and various products separation by distillation (e.g. separation of ethanol from the fermentation liquor in (60), separation of components in the dehydrogenation reaction mixture in (90), separation of components in the hydrogenolysis reaction mixture in (140) and separation of products in the hydrophilic and less hydrophilic streams of the solvent extraction method).

According to one embodiment, the energy for those and other process steps is derived from a renewable source. According to a particular embodiment, a combustion step (40) is operated where energy is produced by burning organic compounds selected from plant material (e.g. corn stalk), processing coproducts and reaction coproducts. Suitable processing coproducts include fiber-enriched fractions (23), desolventized meal (34), DDG (64), gluten (102), etc. Suitable reaction coproducts include separated coproducts form the dehydrogenation process (92) and separated coproducts from the hydrogenolysis step (146). According to another embodiment, the thermal energy produced in such combustion is more than required for the process and extra energy is sold as such or after conversion to electricity. Alternatively, those processing and reaction coproducts, their fraction or modification products are converted into biofuel to be combusted or for use as transportation fuel. Such conversion uses gasification (40) according to a preferred embodiment. It should also be kept in mind that many of those components have an alternative value, e.g. as ingredients in animal feed and/or as biohydrogen precursors (increasing thereby the yield on starch consumed). The optimal use of those compounds is therefore a matter of economic optimization based on local value of components, local needs and transportation costs.

Combustion generates ashes, containing minerals originally present in the processed carbohydrate source, e.g. corn. Those minerals can be used as nutrients in agriculture, i.e. as fertilizers or as precursors for fertilizers. Fertilizer costs are reduced and so is the overall energy input, where fertilizer production is an important contributor. Also suitable for use as nutrients are gluten, desolventized meal and DDG.

The present invention further provides, process products or coproducts that can be reacted with other process products or coproducts or with other reagents to generate new products of commercial value. Thus, for example, the process generates ethanol and potentially also other alcohols, such as methanol, propanol, butanol glycerol, butanediol, pentanediol and erythritol. It may produce carboxylic acids, such as acetic, propionic, butyric and glycolic. According to a preferred embodiment, it also produces the ethyl acetate ester. Esterification and trans-esterification reactions between those generate a large variety of products with commercial value. Such reactions also save on separation costs. Instead of separating the process products and coproducts prior to the reaction, those are first reacted and the reaction products are separated, which in many cases is easier and less energy consuming.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative examples and that the present invention may be embodied in other specific forms without departing from the essential attributes thereof, and it is therefore desired that the present embodiments and examples be considered in all respects as illustrative and not restrictive, reference being made to the appended claims, rather than to the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Unless otherwise stated, patents and publication materials called out within this document are incorporated herein by reference.

Claims

WHAT IS CLAIMED IS:

1. A method for the production of propylene glycol comprising the steps of: a. fractionating a carbohydrate material into at least a first fraction and 5 a second fraction; b. processing said first fraction to generate a hydrogen product; c. processing said second fraction to generate a carbohydrate product; d. reacting the hydrogen product and the carbohydrate productto form a reaction mixture including propylene glycol; and o e. separating propylene glycol from the reaction mixture.

2. The method of Claim 1 , wherein the carbohydrate material is starch.

3. The method of Claim 1 , wherein the carbohydrate material is selected from a group consisting of corn, wheat, rice and potato.

4. The method of Claim 2, wherein the first fraction and the second s fraction contain starch and wherein the second fraction has a starch concentration greater than the starch concentration in the first fraction .

5. The method of Claim 1 , wherein processing the first fraction comprises at least one of dehydrogenation, fermentation and reforming.

6. The method of Claim 1 , wherein processing the first fraction o comprises a step of fermentation to ethanol.

7. The method of Claim 6, further comprising dehydrogenation of ethanol to generate a hydrogen product.

8. The method of Claim 5, further comprising dehydrohgenating organic matter other than ethanol to generate a hydrogen product. 5

9. The method of Claim 7, further comprising dehydrogenation of organic matter further generates a product mixture comprising a product selected from the group consisting of acetaldehyde, ethyl acetate, acetic acid and a combination thereof.

10. The method of Claim 9, wherein the product mixture further comprises ethanol and wherein the method further includes the step of separating the ethanol from the product mixture.

11. The method of Claim 9, wherein the method further comprises the steps of hydrolyzing the ethyl acetate to form ethanol and acetic acid and separating formed ethanol and the acetic acid.

12. The method of Claim 9, wherein said product mixture comprises ethyl acetate, and said method further comprises the steps of hydrolyzing ethyl acetate to form ethanol and acetic acid, and separating said formed acetic acid and ethanol.

13. The method of Claim 2, wherein processing said second fraction comprises starch hydrolysis.

14. The method of Claim 1 , wherein reacting comprises hydrogenolysis.

15. The method of Claim 1 , wherein said reaction mixture of step (d) further comprises ethylene glycol.

16. The method of Claim 1 , wherein said separating of step (e) comprises separating propylene glycol from ethylene glycol.

17. The method of Claim 1 , wherein said carbohydrate material comprises starch and fractionating comprises fractionating into at least one fiber- enriched fraction and at least one starch-enriched fraction.

18. The method of Claim 17, further comprising a step of fractionating a starch-enriched fraction to form a further enriched starch fraction.

19. The method of Claim 18, further comprising a step of processing said starch-enriched fraction, said further enriched fraction or both to generate purified starch.

20. The method of Claim 18, wherein said first fraction comprises said starch enriched fraction, said further enriched fraction, their combination or at least one product thereof.

21. The method of Claim 19, wherein said second fraction comprises said further enriched fraction, purified starch, their combinations or at least one product thereof.

22. A method for the production of propylene glycol comprising the steps of: a. fractionating a starch material to form at least one fiber-enriched fraction, at least one starch-enriched fraction and purified starch; b. fermenting at least one of the starch-enriched fraction or the purified starch to form an ethanol containing fermentation liquor; c. separating ethanol from the ethanol containing fermentation liquor; d. dehydrogenating the separated ethanol to generate a hydrogen product and at least one of acetaldehyde, ethyl acetate and acetic acid; e. hydrolyzing the purified starch to generate a glucose product f. reacting the hydrogen product and the glucose product to form a reaction mixture comprising propylene glycol and ethylene glycol; and g. separating propylene glycol from ethylene glycol.

23. The method of Claim 9, wherein ethyl acetate is formed during dehydrogenation and wherein the reaction mixture of reacting hydrogen and glucose comprises ethylene glycol, wherein separating propylene glycol comprises contacting said reaction mixture with ethyl acetate.

24. The method of Claim 23, wherein separating comprises contacting said product mixture from processing said first fraction with said reaction mixture from reacting hydrogen with said carbohydrate.