Charged Polymers for Ethanol Dehydration

Abstract

The systems and methods described herein provide for modified lignins and other compositions that may be useful as entrainers. In embodiments, they may be useful for dehydrating ethanol so that it can be used as an energy source.

Description

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 60/843,815, filed on Sep. 12, 2006. The entire teachings of the above application are incorporated herein by reference.

FIELD OF APPLICATION

This application relates generally to surfactant compositions useful for production of fuel-grade ethanol.

BACKGROUND

As world-wide energy needs continue to grow, there is concern that demand for energy may outstrip its supply. Alternative fuel technologies are desirable to reduce economic dependency on petroleum-based fuels. As an example, anhydrous ethanol (99.5 vol. % ethanol) may be combined with gasoline for use in internal combustion engines, thereby decreasing the amount of petroleum-based fuel that automobiles consume.

Currently, automobile engines can run efficiently with gasoline mixtures containing up to 20% anhydrous ethanol, and many states have mandated that automobile fuel contain a certain percentage of anhydrous ethanol, typically 5-10%. With engine modifications, anhydrous ethanol may be used alone to fuel vehicles. Although production and blending of ethanol with gasoline have been used throughout the world for several decades, use of these technologies has been limited by the high costs of producing anhydrous alcohol.

Ethanol is typically produced by fermentation of biomass material and distillation to form a single liquid phase containing approximately equal volumes of ethanol and water. The EtOH/water mixture may then be separated using chemicals like cyclohexane to yield an anhydrous alcohol phase, which may contain minor amounts of other alcohols, such as propanol or butanol. Adsorption and solvent extraction are alternative or supplemental methods of separating alcohol and water.

Ethanol distillation techniques and their modifications produce 95% by weight ethanol solutions efficiently. However, concentrating an ethanol solution beyond 96.4% by weight has been difficult. At approximately this concentration, equilibrium is reached between the liquid and the vapor phases, where both phases have the same concentration of ethanol and water. This solution in equilibrium is called an azeotrope, or a constant-boiling mixture. For ethanol, a binary, minimum-boiling azeotrope is formed.

To dehydrate an ethanol solution beyond the 96.5% concentration, one of two main procedures may be employed. One procedure involves azeotropic distillation. This method has been used for decades as a means for purification of chemicals from azeotropic mixtures. The distillation procedure involves adding a third chemical called an entrainer to the system. This third component interacts with both of the water and ethanol to create a ternary azeotrope which is stronger than the original binary azeotrope. A typical ternary phase separation is achieved through the use of benzene as an entrainer. This system yields three distinct regions on the column that represent different compositions. The uppermost region yields anhydrous ethanol.

As an alternative procedure for dehydrating ethanol beyond the 96.5% concentration, molecular sieves may be used for the dehydration step. Molecular sieves include zeolites, which are highly ordered aluminosilicates having very precise pore sizes. They are produced as small beads or pellets. The pore structure is capable of performing size exclusion on the molecular level. Ethanol is on the order of4.4 Angstroms and water is approximately 2.8 Angstroms. Molecular sieves selected with a pore size of3.0 Angstroms can therefore be used to separate the water from the ethanol via size differences. To use this dehydration method, the azeotropic stream of vaporized alcohol and water is passed through a vessel containing the molecular sieves. The water is then adsorbed into the pores and the larger ethanol passes by and is condensed into tanks. Since the water adsorption occurs via a surface phenomenon, the particles can be regenerated for reuse by drying with heat or by vacuum. While this system is efficient and does not impart chemical contamination, it does require the use of expensive zeolites.

While a variety of techniques exist for dehydrating the water-ethanol azeotrope, none are cheap or efficient, and all have significant drawbacks. There remains a need in the art for efficient and cost-effective systems and methods to facilitate ethanol dehydration, so that anhydrous ethanol may become more readily available for energy production.

SUMMARY

The invention relates to novel materials and methods useful in dehydrating ethanol. In embodiments, the invention relates to methods for dehydrating an ethanol solution comprising distilling the ethanol solution in the presence of a molecular sieve characterized by a porous core and a water-permeable polymeric coating impermeable to ethanol. In particular, the molecular sieve can be characterized by a high charge density. This can be achieved by using a porous core comprises a polyanionic polymer. In embodiments, the coating comprises a polycationic polymer or nonionic polymer, either of which can be optionally crosslinked. Alternatively, the porous core comprises a polycationic polymer. In embodiments, the coating comprises a polyanionic polymer or nonionic polymer, either rof which can be optionally crosslinked.

The invention also relates to molecular sieves characterized by a porous core and a water-permeable polymeric coating impermeable to ethanol, the molecular sieves being those described above.

In embodiments, the invention relates to a method for dehydrating an ethanol solution comprising distilling the ethanol solution in the presence of an entrainer comprising a lignin or lignin derivative. The lignin or lignin derivative can be solid in ethanol. The entrainer can be a carboxylated lignin, such as can be produced by reacting a lignin with an anhydride, including a succinic anhydride or alkylated succinic anhydride. The lignin can also be a kraft lignin characterized by hydroxyl groups. In embodiments, between about 50 and 100% of the hydroxyl groups of the lignin are functionalized. In addition, or alternatively, the entrainer is further characterized by a hydrophilic polymer substituent, such as a polyethylene oxide and a polypropylene oxide.

DESCRIPTION

In other embodiments useful for ethanol dehydration, particles may be formed from highly charged (hence hydrophilic) polyelectrolyte cores and an alcohol-insoluble skin to create an organic analog of a molecular sieve. While it is known in the art that high charge density coatings are capable of dehydrating ethanol via permvaporation methodologies (see Toutianoush, and Tieke Materials Science and Engineering C 22 (2002) 459-463), a similar method might be efficiently utilized without the use of energy intensive distillative process. For example, a selectively adsorbent particle may be used in a typical filtration manner to remove residual water and produce dehydrated ethanol in accordance with the systems and methods disclosed herein.

In embodiments, water may be absorbed onto such a particle, and ethanol may be excluded. In one embodiment, the particle may comprise a polyanion core material, and the exterior may be covered with a polycation that creates a complex at the interface and an insoluble skin with a high crosslink density (either electrostatic or physical crosslinks) that excludes ethanol from the particle interior. In other embodiments, the coating around a polyanion core could consist of a nonionic material that is insoluble in ethanol. Polyanions are not the only particles that can be used as the high charge density material. In embodiments, a polycationic material could be used as the core material treated with either a polyanion or nonionic polymer coating. In another embodiment, a nonionic, water soluble core material can be coated with another material, either nonionic, cationic, or anionic.

Not to be bound by theory, the systems and methods disclosed herein may have in common a water soluble core with some type of passivating coating on the surface, whereby the coating maintains water within the core.

In embodiments, the exterior coating may be oppositely charged from that of the core. The coating polyelectrolyte may condense upon the core creating three “zones”, one anionic, one cationic, and a middle phase. The resulting middle phase, consisting of tight ion pairs due to the electrostatic charge attraction, is a passivated, area between the two oppositely charged regions (the core and the surface). Using this middle zone as a semipermeable membrane, water may be preferably kept within the core, with minimal flux back into the ethanol environment.

As an exemplary embodiment, a particle may be formed using a substance such as encapsulated Carbopol, which is a crosslinked polyacrylic acid. A protective skin may be formable on such a particle using a polycation such as chitosan to complex the cationic charges on the surface. In embodiments, the desired particle may be formed with layering to control its porosity. In another embodiment, a micron sized particles such as Carbopol may be surrounded by polycationic polymers such as branched or linear polyethyleneimine with molecular weights between 2000 and 100,000 gmol⁻¹. Oligomeric entities may also be usable to create the layered core-shell morphology. Mixing the particles into an anhydrous solution of polycation may form a coating on the surface of the particle upon introduction. The coating may be less than 100 nm in thickness for increased transport properties across the coating. In embodiments, naturally occurring polysaccharide multi-carboxylates could also be used to form the exterior complex, for example materials such as pectin and carboxymethylcellulose. In these illustrative embodiments, the charge on the core particle may be varied to alter the thickness of the coating.

In other embodiments, particles may be formed comprising an inorganic-organic hybrid. For example, the core may be formed with an inexpensive porous silicate or other naturally occurring or synthetic desiccant. In embodiments, the porous substrate may first be loaded with salts that would be effective in absorbing water, for example potassium carbonate, before encapsulating the assembly with a skin formed in situ. In embodiments, the skin may be a charge-charge complex (a tight molecular network) to exclude alcohol from penetrating into the core. For example, chitosan can be deposited spontaneously on silica, then complexed with a polyanion. A composite such as this would allow water absorption and ethanol exclusion to be separately performed by the core and skin of such engineered particles. In embodiments, to concentrate ethanol using such particles, they may be added to hydrated alcohol in an appropriate amount so that water may be absorbed onto the particles and dehydrated effluent alcohol may be collected for use as a fuel additive. The water-containing particles may be dried out and reused, thus enhancing the efficiency of the process.

Disclosed herein are systems and methods useful in energy applications, with particular applicability to the dehydration of azeotropic ethanol solutions. In embodiments, the systems and methods described herein may involve the use of modified lignins and formulations thereof. Lignin is a naturally-occurring cross-linked, polymerized macromolecule comprised of aliphatic and aromatic portions with alcohol functionality interspersed. Lignin polymers incorporate three monolignol monomers, methoxylated to various degrees: p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol. These are incorporated into lignin in the form of the phenylpropanoids, p-hydroxyphenyl, guaiacyl, and syringal respectively. The systems and methods disclosed herein describe how naturally-occurring (i.e., native) and unnatural or modified lignin may be modified through functionalization of the resident alcohol moieties to alter the properties of the polymer. Such a functionalized lignin may be termed a “modified lignin.” The word “lignin”, as used herein is intended to include natural and non-natural lignins which possess a plurality of lignin monomers and is intended to embrace lignin, kraft lignin, lignin isolated from bagasse and pulp, oxidized lignin, alkylated lignin, demethoxylated lignin, lignin oligomers, and the like.

Lignin and oxidized lignin are waste products from the paper industry. Oxidized lignin is characterized by a plurality of hydroxyl groups which can be conveniently reacted. Oxidized lignin is described, for example, in U.S. Pat. No. 4,790,382 and is characterized by a plurality of hydroxyl groups which can be conveniently reacted. Similarly, kraft lignins, such as indulins, including Indulin AT, can be used. For example, the hydroxyl groups can be reacted with succinic anhydride and similar compounds to form a carboxylic acid-substituted lignin, by a ring opening reaction. The systems and methods disclosed herein describe how naturally-occurring (i.e., native) lignin may be modified through functionalization of the resident alcohol moieties to alter the properties of the polymer. Such a functionalized lignin may be termed a modified lignin.

In embodiments, adding a reactive agent such as succinic anhydride or alkylated succinic anhydride to a native lignin may produce a modified lignin of the invention. Alkylated succinic anhydride is commonly used in the paper industry as a sizing agent. The alkyl additions are long chain hydrocarbons typically containing 16-18 carbon atoms. However, alkylated succinic acids having alkyl side chains having more than 1 carbon atom, such as 1 to 30 carbon atoms can be used as well. Such alkyl groups are defined herein to include straight chain, branched cahain or cyclized alkyls as well as saturated and unsaturated alkyls. Examples of alkylated succinic anhydride include EKA ASA 200® (a mixture of C16 and C18 ASA) and EKA ASA 210® (a C18 ASA). Addition of an anhydride, such as a succinic anhydride or alkylated succinic anhydride to the resident alcohol groups result in new ester linkages and the formation of carboxylic acids via a ring opening mechanism. Addition of anhydride to the resident alcohol groups result in new ester linkages and/or the formation of carboxylic acids via a ring opening mechanism. With the newly added carboxylic acid functionality, the lignin becomes more water soluble.

In other embodiments, the hydroxyl group can be reacted with a dicarboxylic acid, such as maleic acid, or activated esters or anhydrides thereof to form a carboxylic acid substituted lignin. For example, the anhydride derived from many acids can be utilized, such as adipic acid, or the functionality can be derived from natural compounds such as a polysaccharide that contains carboxylic acid groups. Non-limiting examples include pectin or alginate, and the like, and synthesized polymers such as polyacrylic or methacrylic acid homo or co-polymers. Further, activated esters can be used in place of the anhydride. Other examples will be apparent to those of ordinary skill in the art. The degree of functionalization (i.e., the percentage of hydroxyl groups that are reacted to present an ionic moiety) can be between 20% and 80%, preferably between 50% and 80%.

In other embodiments, lignin (oxidized or native) may be treated by chemically reacting it with reagents to tune the hydrophilicity to present alcohol groups. Examples of such reagents include hydrophilic molecules, or hydrophilic polymers, such as poly(ethylene glycol) (PEG) or poly(propylene glycol) (PPO) and combinations thereof. In a preferred embodiment, the hydrophilic polymer can have a molecular weight between 700 and 2500 g/mol Addition of PEG or PPO (with or without acidification) can be useful in stabilization of the product in salt solutions, particularly divalent cation salts. In this embodiment, the amount of polymer to lignin is preferably added in an amount between 25% and 75%.

As described above, ethanol is naturally hydrated when it is fermented and must be dehydrated and purified prior to its use as a fuel. In embodiments, a modified lignin base may be formed to create a branched or networked polymer with functional groups that form hydrogen bonds to disrupt the inherent water-ethanol azeotrope during distillation. In embodiments, the dehydration of ethanol may be accomplished by using particles designed to absorb water while excluding ethanol by utilizing a molecularly designed architecture on a porous substrate, for example, or by creating a layered substrate with a water soluble/swellable core with a charge complex exterior shell to exclude ethanol while preferentially absorbing water.

For the dehydration of ethanol, oxidized lignin may be used without further modification, or it may be oxidized further to create a largely branched molecule with a high molecular weight and a large number of alcohol groups of various types (primary, secondary, tertiary and benzylic). Using lignin by itself to act as a solid entrainer added to the distillation apparatus may be possible due to the alcohol functionalities. These functionalities are expected to change the thermodynamic equilibrium enough to create a different azeotropic composition, preferably more than the standard azeotrope at 96.4% by weight. By adding modified or unmodified lignin to an ethanol-water mixture followed by distillation, the resulting distillate may be more pure than the feed.

The solid entrainers of the invention are not removed with the ethanol during distillation and, accordingly, can be readily removed and optionally recycled.

EXAMPLE 1

Indulin AT is used as the lignin source. Indulin AT is a purified form of the lignin obtained from the black liquor in the Kraft pulping process. Here, Indulin AT (5.0 g) is suspended in 150 ml of acetone. Alkyl succinic anhydride in the form of Eka SA 210 (25.0 g) is added to the suspension. The reaction is performed in a bomb and heated to 70° C. over the course of 48 hours.

EXAMPLE 2

Indulin AT (5.0 g) is mixed with 10.0 g Eka SA 210 in a bomb filled with 150 ml of acetone. The mixture is heated to 70° C. over 48 hours, and the product is recovered.

EXAMPLE 3

Indulin AT (5.0 g) is mixed with 5.0 g Eka SA 210 in a bomb filled with acetone. The mixture is heated to 70° C. over 48 hours. The resulting mixture is filtered; the supernatant is recovered and diluted with alkaline water and dried.

EXAMPLE 4

Indulin AT (5.0 g) is mixed with 4.0 g Eka SA 210 in a bomb filled with 150 ml of acetone. The mixture is heated to 70° C. over 48 hours. The resulting mixture is filtered; the supernatant is recovered, diluted with alkaline water and dried.

EXAMPLE 5

Indulin AT (5.0 g) is mixed with3.0 g Eka SA 210 in a bomb filled with 150 ml of acetone. The mixture is heated to 70° C. over 48 hours. The resulting mixture is filtered; the supernatant is recovered, diluted with alkaline water and dried.

EXAMPLE 6

Indulin AT (5.0 g) is mixed with 2.5 g Eka SA 210 in a bomb filled with 150 ml of acetone. The mixture is heated to 70° C. over 48 hours. The resulting mixture is filtered; the supernatant is recovered, diluted with alkaline water and dried.

EXAMPLE 7

Indulin AT (5.0 g) is mixed with 1.0 g Eka SA 210 and3.0 g succinic anhydride in a bomb filled with 150 ml of acetone. The mixture is heated to 70° C. over 48 hours. The resulting mixture is filtered; the supernatant is recovered, diluted with alkaline water and dried.

EXAMPLE 8

Indulin AT (5.0 g) is mixed with 2.0 g Eka SA 210 and 2.0 g succinic anhydride in a bomb filled with 150 ml of acetone. The mixture is heated to 70° C. over 48 hours. The resulting mixture is filtered; the supernatant is recovered, diluted with alkaline water and dried.

EXAMPLE 9

Indulin AT (5.0 g) is mixed with3.0 g Eka SA 210 and 1.0 g succinic anhydride in a bomb filled with 150 ml of acetone. The mixture is heated to 70° C. over 48 hours. The resulting mixture is filtered; the supernatant is recovered, diluted with alkaline water and dried.

EXAMPLE 10

Indulin AT (5.0 g) is mixed with 4.0 g Eka SA 210 and 1.0 g polyethylene glycol diglycidyl ether in a bomb filled with 150 ml of acetone. The mixture is heated to 70° C. over 48 hours. The resulting mixture is filtered; the supernatant is recovered, diluted with alkaline water and dried.

EXAMPLE 11

Indulin AT (5.0 g) is mixed with3.0 g Eka SA 210 and 1.0 g polypropylene oxide diglycidyl ether in a bomb filled with 150 ml of acetone. The mixture is heated to 70° C. over 48 hours. The resulting mixture is filtered; the supernatant is recovered, diluted with alkaline water and dried.

EQUIVALENTS

While specific embodiments of the subject invention have been discussed, the above specification is illustrative and not restrictive. Many variations of the invention will become apparent to those skilled in the art upon review of this specification. The full scope of the invention should be determined by reference to the claims, along with their full scope of equivalents, and the specification, along with such variations.

Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention.

Claims

1. A method for dehydrating an ethanol solution comprising distilling the ethanol solution in the presence of a molecular sieve characterized by a porous core and a water-permeable polymeric coating impermeable to ethanol.

2. The method in accordance with claim 1 wherein the surface of the molecular sieve is characterized by a high charge density.

3. The method in accordance with claim 2 wherein the coating has a thickness of less than about 100 nm.

4. The method in accordance with claim 2 wherein the coating comprises pores having a mean diameter less than 4 Angstroms.

5. The method in accordance with claim 1 wherein the porous core comprises silica or a polyanionic polymer.

6. The method in accordance with claim 5 wherein the coating comprises a polycationic polymer.

7. The method in accordance with claim 6 wherein the polycationic polymer is crosslinked.

8. The method in accordance with claim 6 further comprising an additional coating comprising a polyanionic polymer.

9. The method in accordance with claim 3 wherein the coating comprises a nonionic polymer.

10. The method in accordance with claim 1 wherein the porous core comprises a polycationic polymer.

11. The method in accordance with claim 10 wherein the coating comprises a polyanionic polymer.

12. The method in accordance with claim 11 wherein the polyanionic polymer is crosslinked.

13. The method in accordance with claim 11 further comprising an additional coating comprising a polycationic polymer.

14. The method in accordance with claim 10 wherein the coating comprises a nonionic polymer.

15. A molecular sieve characterized by a porous core and a water-permeable polymeric coating impermeable to ethanol.

16. The molecular sieve in accordance with claim 15 comprising the porous core comprises a polyanionic polymer.

17. The molecular sieve in accordance with claim 16 wherein the coating comprises a polycationic polymer.

18. The molecular sieve in accordance with claim 17 wherein the polycationic polymer the coating has a thickness of less than about 100 nm.

19. The molecular sieve in accordance with claim 15 comprising the porous core comprises a polycationic polymer.

20. The molecular sieve in accordance with claim 19 wherein the coating comprises a polyanionic polymer.

21. The molecular sieve in accordance with claim 20 wherein the polyanionic polymer the coating has a thickness of less than about 100 nm.

22. A method for dehydrating an ethanol solution comprising distilling the ethanol solution in the presence of an entrainer comprising a lignin or lignin derivative.

23. The method in accordance with claim 22 wherein the entrainer is a carboxylated lignin.

24. The method in accordance with claim 22 wherein the entrainer is produced by reacting a lignin with an anhydride.

25. The method in accordance with claim 24 wherein the anhydride is a succinic anhydride.

26. The method in accordance with claim 24 wherein the anhydride is an alkylated succinic anhydride.

27. The method in accordance with claim 22 wherein the lignin is a kraft lignin characterized by hydroxyl groups.

28. The method in accordance with claim 27 wherein between about 50 and 100% of the hydroxyl groups are functionalized.

29. The method in accordance with claim 22 wherein the entrainer is a solid.

30. The method in accordance with claim 23 wherein the entrainer is further characterized by a hydrophilic polymer substituent.

31. The method in accordance with claim 30 wherein the hydrophilic polymer substituent is selected from the group consisting of a polyethylene oxide and a polypropylene oxide.

32. The method in accordance with claim 31 wherein the hydrophilic polymer substituent is selected from the group consisting of a polyethylene oxide diglycidyl ether and a polypropylene oxide diglycidyl ether.

33. The method in accordance with claim 32 wherein the hydrophilic polymer substituent has a molecular weight between about 700 and 2500 g/mol.