Patent Application
20110035993
1. Field of the Invention
Embodiments disclosed herein relate generally to the production of biodiesel. In one aspect, embodiments disclosed herein relate to processes for the production of fatty acid alkyl ester-based biodiesel and the production of tri-isoalkyl glycerols. In other aspects, embodiments disclosed herein relate to processes for the production of fatty acid methyl ester (FAME) based biodiesel and the production of tri-isobutyl glycerols.
2. Background
Diesel fuel is a fractional distillate of petroleum that is used as fuel in diesel engines. Diesel engines power most of the world's trains, ships, and large trucks. The raw material for diesel, petroleum, is a fossil fuel and therefore a non-renewable resource of finite supply. Further, diesel engines produce fifteen percent more greenhouse gas emissions per liter as compared to gasoline. Acute shortages and resultant dramatic price increases in petroleum and petroleum-derived refined products have fueled interest in alternative fuels. Accordingly, extensive research efforts are now being directed towards replacing some or all petroleum-based diesel fuels with cleaner-burning alternative fuels such as biodiesel.
Biodiesel is produced from biomaterials high in fats and oils, for example vegetable oils. The basic chemistry involved in producing biodiesel is the catalytic exchange of natural esters, mainly glycerides, with a primary alcohol. Biodiesel is therefore a mixture of methyl or ethyl esters of various saturated and unsaturated fatty acids with a co-product of glycerol.
Biodiesel is a diesel-equivalent processed fuel which can be used in any diesel engine, without the need for mechanical alterations, and is compatible with existing petroleum distribution infrastructure. A blend of 20% biodiesel with 80% petroleum (B20) can be used in all diesel-burning equipment, including compression-ignition engines and oil heat boilers, without modification. Higher blends, including pure biodiesel, can be used in many engines made after 1994, but slight modifications may be necessary.
Biodiesel is biodegradable and non-toxic, and typically produces about sixty percent less net greenhouse gas emissions than petroleum-based diesel. Even in blends as low as 20% biodiesel, biodiesel can substantially reduce the emission levels and toxicity of diesel exhaust. Biodiesel is recognized worldwide as a substitute and supplement for petroleum diesel. For example, biodiesel has been designated as an alternative fuel by the United States Department of Energy and the United States Department of Transportation, and is registered with the United States Environmental Protection Agency as a fuel and fuel additive.
Since the introduction of biodiesel in South Africa prior to World War II, significant effort has been expended to increase its viability as a fuel substitute. In more recent years, environmental and economic pressures, for example, events such as oil embargoes and laws such as the Clean Air Act of 1990, have provided impetus for the continued development of this technology.
Biodiesel may typically be produced by the acid or base catalyzed transesterification of triglycerides found in biological material. The transesterification process is a low temperature (about 65° C. (about 150° F.)), low pressure (about 1.4 bar to 2.4 bar (about 20 psia to 35 psia)) reaction having a high conversion (for example, 98%) with few side reactions and short reaction times. A side product of the transesterification reaction of triglycerides is glycerol.
In transesterification, a fat or oil is reacted with an alcohol (such as methanol or ethanol) in the presence of a catalyst to effectuate the exchange of natural esters such as glyceride with the primary alcohol to produce glycerol and fatty acid methyl esters (FAME), the latter of which forms the biodiesel. The alcohol is usually charged in a stoichiometric excess to drive the reaction and may be recovered for reuse. The catalyst may be methoxide, or sodium or potassium hydroxide, which is mixed with the alcohol prior to the transesterification reaction. The resultant FAME (biodiesel) and glycerol may then be separated.
Biodiesel was produced in 1937 by G. Chavanne of the University of Brussels (Belgium) by the transesterification of vegetable oils using ethanol or methanol. Variations, improvements, and modifications of this general process are described in, for example, U.S. Patent Application Publication No. 20040034244 and U.S. Pat. Nos. 6,953,873, 4,300,009, and 4,433,184.
Ether derivatives of glycerol, such as tri-isobutyl glycerol (TIG), are also suitable components for use in biofuels. TIG may be produced, for example, by etherification of an olefin, such as etherification of isobutylene with glycerol using an acid catalyst. The isobutylene is typically charged in a stoichiometric excess to drive the reaction and may be recovered for reuse. The etherification of glycerol includes complex reversible equilibrium reactions. Reaction variables, such as temperature and amount of catalyst, may be used to control the concentrations of mono-, di-, and tri-ethers produced.
For example, U.S. Pat. No. 5,476,971 discloses the reaction of pure glycerol with isobutylene in the presence of an acid catalyst in a two-phase reaction to produce tertiary butyl ethers. The etherification process is likewise a low temperature (about 93° C. (about 200° F.), low pressure (about 10 bar (about 150 psia)) reaction having a high conversion (for example, 98%).
Etherification of glycerol and isobutylene to produce TIG typically requires the importation of glycerol and relatively pure isobutylene. High purity feeds are generally required to avoid the separation and return of mixed butenes and butanes.
Accordingly, there exists a need for improved processes for the production of biodiesel fuels, including FAME and TIG.
In one aspect, embodiments disclosed herein relate to a process for the production of a biodiesel fuel, the process including: feeding a tertiary alkyl ether to a decomposition reaction zone containing at least one decomposition catalyst; contacting the tertiary alkyl ether with the at least one decomposition catalyst at a temperature and a pressure to decompose the tertiary alkyl ether into an alcohol and an isoolefin; separating the alcohol and isoolefin to recover a fraction comprising the alcohol and a fraction comprising the isoolefin; feeding at least a portion of the fraction comprising the alcohol and at least one of a vegetable oil and an animal fat to a transesterification reaction zone; contacting the alcohol and the at least one of a vegetable oil and an animal fat in the presence of at least one transesterification catalyst under conditions of temperature and pressure sufficient to transesterify the vegetable oil or animal fat to form a transesterification product comprising fatty acid alkyl esters and glycerol; separating the transesterification product to recover a fraction comprising the fatty acid alkyl esters and a fraction comprising the glycerol; feeding at least a portion of the fraction comprising the glycerol and at least a portion of the fraction comprising the isoolefin to an etherification reaction zone; contacting the isoolefin and the glycerol in the presence of at least one etherification catalyst under conditions of temperature and pressure to form an etherification product comprising at least one of mono-tertiary alkyl glycerol, di-tertiary alkyl glycerol, and tri-tertiary alkyl glycerol; separating the etherification product to recover a fraction comprising di-tertiary alkyl glycerol and tri-tertiary alkyl glycerol.
In another aspect, embodiments disclosed herein relate to a process for the production of a biodiesel fuel, the process including: feeding methyl tertiary butyl ether to a decomposition reaction zone containing at least one decomposition catalyst; contacting the methyl tertiary butyl ether with the at least one decomposition catalyst at a temperature and a pressure to decompose the methyl tertiary butyl ether into methanol and isobutylene; separating the methanol and isobutylene to recover a fraction comprising the methanol and a fraction comprising the isobutylene; feeding at least a portion of the fraction comprising the methanol and at least one of a vegetable oil and an animal fat to a transesterification reaction zone; contacting the methanol and the at least one of a vegetable oil and an animal fat in the presence of at least one transesterification catalyst under conditions of temperature and pressure sufficient to transesterify the vegetable oil or animal fat to form a transesterification product comprising fatty acid methyl esters and glycerol; separating the transesterification product to recover a fraction comprising the fatty acid methyl esters and a fraction comprising the glycerol; feeding at least a portion of the fraction comprising the glycerol and at least a portion of the fraction comprising the isobutylene to an etherification reaction zone; contacting the isobutylene and the glycerol in the presence of at least one etherification catalyst under conditions of temperature and pressure to form an etherification product comprising at least one of mono-tertiary butyl glycerol, di-tertiary butyl glycerol, and tri-tertiary butyl glycerol; separating the etherification product to recover a fraction comprising di-tertiary butyl glycerol, and tri-tertiary butyl glycerol.
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.
Embodiments disclosed herein relate generally to the production of biodiesel. In one aspect, embodiments disclosed herein relate to processes for the production of fatty acid alkyl ester-based biodiesel and the production of tri-isoalkyl glycerols. In other aspects, embodiments disclosed herein relate to processes for the production of fatty acid methyl ester (FAME) based biodiesel and the production of tri-isobutyl glycerols.
Referring now to
The decomposition products may then be separated into an alcohol fraction and an isoolefin fraction, recovered via flow lines 20 and 22, respectively. The alcohol may then be fed via flow line 20 to transesterification reaction zone 14. In transesterification reaction zone 14, at least a portion of the fats, oils, or waxes present in the biomaterial are reacted with superheated water and/or alcohol under conditions of pressure, temperature and time sufficient to perform the transesterification of the reactants to produce fatty acid carboxylic acids, fatty acid alkyl esters, and co-product glycerols. The fatty acid alkyl products (esters and carboxylic acids), glycerol, and unreacted alcohol may then be separated and recovered via flow lines 24, 26, and 28, respectively.
The unreacted alcohol recovered via flow line 28 may be recycled to transesterification reaction zone 14 for reuse. If necessary to maintain the desired stoichiometric ratio of alcohol to triglyceride in transesterification reaction zone 14, additional alcohol and/or water may be fed to transesterification reaction zone 14 via flow line 30.
The co-product glycerol recovered via flow line 26 and the isoolefin recovered via flow line 22 may then be fed to an etherification reaction zone 32. In etherification reaction zone 32, the glycerol and the isoolefin may be reacted in the presence of an etherification catalyst to produce tri-isoalkyl glycerol, which may be recovered via flow line 34. If necessary, unreacted isoolefin may be separated from the reaction product and recycled to etherification reaction zone 32 for reuse.
The tri-isoalkyl glycerol recovered via flow line 34 and the fatty acid alkyl ester recovered via flow line 24 may then be independently used as biodiesel fuels or fuel additives. As illustrated, the tri-isoalkyl glycerol and the fatty acid alkyl ester may be combined to form a biodiesel fuel or biodiesel fuel additive stream 36.
In some embodiments, the tertiary alkyl ether fed to decomposition reaction zone 18 may include methyl tertiary butyl ether (MTBE). MTBE production units currently exist in many refineries. Additionally, it is desired to remove MTBE from the motor gasoline pool. Processes according to embodiments disclosed herein may thus provide for one or more of a) an outlet for MTBE, where necessary or desired, b) a convenient and economical mode for transportation of the raw materials (alcohol and isoolefin, in the form of a tertiary alkyl ether) in the required stoichiometric ratio to the transesterification and etherification reaction zones 14, 32, and c) conversion of the glycerols produced during the transesterification reaction to biofuels or biofuel additives, among other benefits.
With regard to the decomposition of tertiary alkyl ethers, one or more tertiary alkyl ethers may be fed to the decomposition reaction zone, and may be selected, in some embodiments, based upon the resulting alcohol and/or isoolefin for use in the transesterification and etherification reaction zones. Tertiary alkyl ethers that may be used in embodiments disclosed herein may include methyl tertiary butyl ether (MTBE), ethyl tertiary butyl ether (ETBE), tertiary amyl methyl ether (TAME) and tertiary amyl ethyl ether (TAEE), among others. Preferably, the resulting alcohol and olefin are readily separable. The decomposition reaction (also referred to as a cracking or dehydration reaction) may be performed in one or more fixed bed reactors in the presence of a catalyst. Addition of water or a tertiary alcohol (such as TBA, used as a water equivalent, decomposing to an isoolefin and water) to a tertiary alkyl ether feed stream, for example, may be beneficial to suppress unwanted side reactions. Other water equivalents may additionally be used.
Examples of fixed bed reactors useful in embodiments disclosed herein may include tubular reactors, boiling point reactors, bubble column reactors, traditional fixed bed reactors, catalytic distillation column reactor systems, pulsed flow reactors, and combinations thereof. One or more of such reactors may be used in parallel flow or series flow, and each reactor may include one or more reaction zones containing one or more suitable decomposition catalysts.
Within the scope of this application, the expression “catalytic distillation reactor system” denotes an apparatus in which the catalytic reaction and the separation of the products take place at least partially simultaneously. The apparatus may comprise a conventional catalytic distillation column reactor, where the reaction and distillation are concurrently taking place at boiling point conditions, or a distillation column combined with at least one side reactor, where the side reactor may be operated as a liquid phase reactor or a boiling point reactor. While both catalytic distillation reactor systems described may be preferred over conventional liquid phase reaction followed by separations, a catalytic distillation column reactor may have the advantages of decreased piece count, reduced capital cost, increased catalyst productivity per pound of catalyst, efficient heat removal (heat of reaction may be absorbed into the heat of vaporization of the mixture), and a potential for shifting equilibrium. Divided wall distillation columns, where at least one section of the divided wall column contains a catalytic distillation structure, may also be used, and are considered “catalytic distillation reactor systems” herein.
Catalysts suitable for use in the decomposition reaction zone of processes disclosed herein may include any decomposition catalyst. In some embodiments, the decomposition catalyst may include an HF treated amorphous synthetic alumina-silica catalyst or a selectively poisoned HF treated amorphous synthetic alumina-silica catalyst, such as disclosed in U.S. patent application Ser. No. 12/260,729, assigned to the assignee of the present disclosure and which is incorporated herein by reference.
The reactions may be carried out in the vapor phase, liquid phase, or dual phase of liquid and vapor. Because of the equilibrium nature of the reactions, carrying out the reactions in the vapor phase or dual phase of vapor and liquid may result in a higher conversion per pass or higher olefin productivity than a liquid phase reaction, which may also require higher pressure.
Decomposition reaction conditions may vary based on the feed mixture used and the desired olefins produced. Decomposition temperatures may range from 100° C. to 500° C. in some embodiments; from 130 to 350° C. in other embodiments and from 150° C. to 300° C. in yet other embodiments. The decomposition reaction may be carried out under pressures in the range from 1 to 22 bar (0 to 300 psig) in some embodiments; from 1 to 11 bar (0 to 150 psig) in other embodiments. In some embodiments, the pressure is maintained such that the product olefin is in the liquid phase or partially in the liquid phase at the reaction temperature used. The liquid hourly space velocity (LHSV) (the volume of liquid per volume of catalyst per hour) at which the reaction is carried out may be within the range from 0.5 to 200 h−1 in some embodiments; from 1 to 50 h−1 in other embodiments; and from 1 to 10 h−1 in yet other embodiments.
Separation of the resulting decomposition products may be performed using one or more separators in series or parallel. When a distillation column reactor system is used, separation of the products may be performed concurrently with the reaction. Separators useful in embodiments disclosed herein may include distillation, liquid-liquid separation, extraction, or other separation processes known to those of skill in the art.
For example, in some embodiments, a decomposition reactor effluent may be fed to a first distillation column to separate and recover the isoolefins. For example, isobutylene may be separated from unreacted MTBE, methanol, and any heavies, recovering an isobutylene-rich overhead fraction. The isoolefin-rich overheads, in some embodiments, may be a high purity isoolefin stream, having a concentration of at least 99.5 weight percent isoolefin. Unreacted MTBE, methanol, and heavies may be recovered as a bottoms fraction from the first distillation column and fed to a second distillation column, where the unreacted MTBE may be separated from the heavies and the methanol. The unreacted MTBE may be recovered as an MTBE-rich overheads fraction, a portion of which may be recycled to decomposition reaction zone 18 in some embodiments. The heavies and methanol may be recovered as a bottoms fraction from the second distillation column. The methanol may then be separated from the heavies, such as by feeding the heavies and methanol to a third distillation column. A methanol-rich overheads fraction and a heavies-rich bottoms fraction may be recovered, where the methanol-rich overheads may be fed to transesterification reaction zone 14.
In the transesterification reaction zone, a fat or oil is reacted with an alcohol (such as methanol or ethanol) in the presence of a catalyst to effectuate the exchange of natural esters such as glyceride with the primary alcohol to produce glycerol and fatty acid alkyl esters, such as FAME, the latter of which forms the biodiesel. In the processes described herein, the alcohol (e.g., methanol) feed to the transesterification process is received as a product of the tertiary alkyl ether (e.g., MTBE) decomposition.
Feedstocks for the production of fatty acid alkyl ester-based bio-diesel fuels and fuel additives, such as FAME, may include vegetable oils and animal fats, which are esters of higher fatty acids. The term fat (vegetable or animal oil, if liquid) is usually confined to esters (glycerides) of fatty acids with glycerol, and the term wax to esters of other alcohols. As natural vegetable oils may contain various minor amounts of free fatty acids, the free fatty acids may be removed by pretreatment prior to performing the transesterification reactions with an alcohol.
The basic chemistry involved in producing bio-diesel is the catalytic exchange reaction of natural esters (mainly glycerides) with a primary alcohol (typically methanol or ethanol). An alcoholic solution of a base (usually NaOH, KOH, potassium methoxide, or sodium methoxide) may be used as a catalyst. Therefore, bio-diesel is a mixture of methyl or ethyl esters of various saturated and unsaturated fatty acids. Co-product is glycerol, which amounts from 16 to 25 wt %. Biodiesel may also contain some fatty acids (hydrolysis products of esters) in minor amounts depending on the amount of water in the feed or the catalyst used.
The alkyl groups R1, R2 and R3 of the natural product glyceride are, in general, different in the chain length and degree of unsaturation. The alkyl groups are usually straight chain and have even number of carbon atoms from 4 to 26. The exception is branched isovaleric acid (CH3)2CHCH2COOH, which occurs in relatively large amounts in dolphins. Some unsaturated fatty acids have two or three double bonds in the alkyl chains. Unsaturated fatty acids have lower melting points than their saturated counter parts. The chain length of unsaturated fatty acids is generally in the range of C10-C24. Canola oil has a higher degree of unsaturation in C16-C20 chain length than corn oil.
In general, base catalysts are more effective for transesterification of carboxylic esters with an alcohol than acid catalysts. Catalysts suitable for use in the transesterification reaction zone of processes disclosed herein may include any heterogeneous transesterification catalyst, used as a fixed bed, moving bed, or slurry, or may be a homogeneous catalyst, co-fed with the reactants. In some embodiments, the transesterification catalyst may include a heterogeneous transesterification catalyst where a homogeneous transesterification catalyst is co-fed with the reactants at low concentrations (about 0.1 to 150 ppm), such as disclosed in U.S. patent application Ser. No. 12/029,283, assigned to the assignee of the present disclosure and which is incorporated herein by reference.
Heterogeneous catalysts useful for the transesterification of vegetable oils and animal fats may include catalysts may include metal oxides, such as magnesium oxide, calcium oxide, zinc oxide, sodium oxide, potassium oxide, lanthanum oxide, etc., supported on a support, such as silica, alumina carbon and/or carbonaceous material. Carbon and carbonaceous supports will preferably have surface functional groups such as hydroxyl or carbonyl or both to immobilize organometallic compounds on the surface of the support. The total amount of active metal or metal components on a solid metal alkoxide, metal hydroxide or metal oxide catalyst is from about 0.05 wt % to about 20 wt % in some embodiments, and from about 0.07 wt % to about 12 wt % in other embodiments.
Examples of soluble (homogeneous) catalytic compounds include zinc 2-methoxyethoxide, calcium 2-methoxyethoxide, zinc 2-methoxypropoxide, zinc ethoxide, zinc alkoxy alkyl carbonate, calcium 2-methoxyproxide, calcium ethoxide, calcium methoxide, calcium alkoxy alkyl carbonate, magnesium 2-methoxyethoxide, magnesium 2-methoxyproxide, magnesium ethoxide, magnesium methoxide, magnesium butoxide, magnesium alkoxy alkyl carbonate, lanthanum alkoxide, lanthanum alkoxy alkyl carbonate, zinc salts of carboxylic acids, magnesium salts of carboxylic acids, calcium salts of carboxylic acids, and Mg, Ca, and Zn glycerides, among others. A mixture of these may also be used. Soluble compounds of Ca, Mg, Zn and La may be obtained by reacting oxide or hydroxide of these metal with an organic carbonate or a mixture of organic carbonate and an alcohol, or carboxylic acids or a mixture of organic carboxylic acid and an alcohol such as methanol, 2-methoxyethanol, etc. at temperature from 93° C. to 260° C. (200° F. to 500° F.), preferably from 121° C. to 232° C. (250° F. to 450° F.) in liquid phase or presence of liquid and vapor. Such prepared solutions are useful for catalyzing the transesterification reaction (when used at a sufficient concentration). Such prepared solutions are also useful for adding trace amount of these metals into the feed stream of a reactor to obtain a long catalyst cycle time. The heterogeneous catalysts disclosed herein are typically also base catalysts.
Initially in the transesterification process, feedstock, water, and any additional reactants, solvents, catalysts, or other optional components, may be introduced into a transesterification reaction zone. This introduction into the transesterification reaction zone may be through any means known to one of skill in the art for transporting solids, liquids, or mixed phase compositions. In some embodiments, for example, the feedstock may be introduced via a hopper. In other embodiments, the feedstock may be introduced into the transesterification reaction zone via a feed line or conduit. Contact of the components within the transesterification reaction zone may be effectuated by countercurrent flow, continuous or intermittent stirring, static mixing, or by other means known in the art.
The transesterification reaction may be performed in one or more reactors in the presence of one or more homogeneous and/or heterogeneous catalysts, as described above. When homogeneous catalysts are used, the homogeneous catalyst may be subsequently separated from the reactor effluent and recycled, if desired or necessary for product specifications. Examples of transesterification reactors useful in embodiments disclosed herein may include tubular reactors, boiling point reactors, bubble column reactors, traditional fixed bed reactors, catalytic distillation column reactors, divided wall distillation column reactors, pulsed flow reactors, and combinations thereof. One or more of such reactors may be used in parallel flow or series flow, and each reactor may include one or more reaction zones for contact of the reactants with one or more suitable transesterification catalysts.
Once introduced into the transesterification reaction zone, the reactants are contacted under conditions of temperature and pressure sufficient to convert at least some of the triglycerides in the feedstock to carboxylic acids and glycerol. The feedstock is allowed to remain in the reaction zone for a time sufficient to convert at least some triglycerides in the feedstock to carboxylic acids and glycerol, and such reaction times may be achieved via batch, semi-batch, or continuous processes. In addition to alcohol reactants, water may be fed as a transesterification reactant, reacting with the fats, oils, and waxes to produce carboxylic acids and glycerol. For example, water may be fed to the transesterification reaction zone, and/or water, fed as a reaction modifier or resulting from the decomposition of a water-equivalent and recovered from the decomposition of tertiary alkyl ethers, may be introduced as a reactant to the transesterification reaction zone. When water is used, the transesterification reaction shown above is illustrative, where R4=hydrogen.
The temperatures used in the transesterification reactor may range from about 150° C. to about 500° C. In other embodiments, the operational temperatures may range from about 200° C. to about 450° C. The pressure in the transesterification reactor should be sufficiently high so as to maintain water in its liquid phase or at liquid-like viscosities at the elevated operational temperatures (e.g., when operating at temperatures greater than the supercritical temperature of water, 374° C.).
In some embodiments, the water, in addition to acting as a reactant and a solvent, may also serve as a catalyst. Under reaction conditions in the transesterification reactor, liquid water may be considered quite acidic or basic because of the higher ionization constant of water (Kw) than at ambient or at boiling temperature. This may lead to an increase in hydrogen bond acidity, which may in turn result in an increase in acidity at these elevated temperatures. Kw is known to be very temperature dependent, and tends to increase with temperature (that is, from 0.001×10−14 mol2 l−2 at −35° C. (pH 8.5), 0.112×10−14 mol2 l−2 at 0° C. (pH 7.5), to 0.991×10−14 mol2 l−2 at 25° C. (pH 7.0), to 9.311×1014 mol2 l−2 at 60° C. (pH 6.5)), to 10−12 mol2 l−2 at 300° C. (pH 6.0, ˜50 MPa). As such, the liquid water may be at least partially ionized, and the acidic proton (H+/H3O+) of the water may catalyze the reaction by donating a proton to the carbonyl group of the triglyceride, making it more reactive. This activated triglyceride is therefore more susceptible to nucleophilic attack. The ionization of water also generates a basic hydroxyl group (OH−) which may also catalyze the transesterification reaction by nucleophilic attack of the triglyceride.
Water, at the conditions within the transesterification reaction zone, may additionally serve as an effective catalyst for the hydrolysis and degradation of carbohydrates, such as starch, cellulose, or glycerol. Thus, solid materials fed along with the fats, oils, and waxes may be concurrently converted to biofuels in some embodiments.
After conversion of at least a portion of the triglycerides to carboxylic acids, esters, and glycerol, the reaction mixture is removed or recovered from the transesterification reactor, depending upon the type of process used. At this point, the reactor effluent includes one or more of carboxylic acids, esters, glycerols, monoglycerides, diglycerides, triglycerides, and unreacted feedstock and transesterification reactant (water or alcohol).
The transesterification reactor effluent mixture may then be separated, such as by distillation, liquid-liquid separations, extraction, or other separation processes known to those skilled in the art. The transesterification reactor effluent may include one or more of hydrocarbons, FAME, other esters, carboxylic acids, glycerols, monoglycerides, diglycerides, triglycerides, water, alcohols, and low-boiling solvents. The transesterification reactor effluent may be passed through a separation zone, where water is removed from the organic components of the fluid phase and light materials, such as any low-boiling solvents, unreacted alcohols, or various reaction by-products, may be recovered. Additionally, glycerol may be separated from the reactor effluent as a byproduct of the transesterification reaction. The remaining mixture may be comprised mostly of fatty acid alkyl esters, which may be used as a biodiesel or biofuel additive, or may be hydrotreated to upgrade the quality of the fuel or to remove a portion of the oxygen in the product biodiesel.
The byproduct glycerol from the transesterification reaction zone is fed, along with the isoolefin (e.g., isobutylene) from the tertiary alkyl ether (e.g., MTBE) decomposition process, to the etherification reaction zone. In the etherification reaction zone, glycerol is reacted with isobutylene to form mono-tertiary alkyl glycerol, di-tertiary alkyl glycerol, and tri-tertiary alkyl glycerol product (e.g., TIG). Feed of the isoolefin at greater than stoichiometric ratios may favor the production of the desired di-tertiary alkyl glycerol and tri-isoalkyl glycerol products. The acid catalyzed reaction of glycerol and isobutylene takes place in a reactor, which may be, for example, a continuous stirred tank reactor. Acid catalyst may also be fed to the reactor as needed.
The acid catalyst used in the etherification reaction zone may be, for example, a homogenous catalysts (e.g., p-toluene sulfonic acid, methane sulfonic acid, sulfuric acid, and sulfonic acid) and/or a heterogeneous catalysts or large-porous zeolite catalysts. The isobutylene and glycerol are substantially immiscible and with suitable agitation form two phases, a polar glycerol phase and an isoolefin phase. The homogeneous acid catalyst is contained primarily in the glycerol phase. There is some isobutylene dissolved in the glycerol phase and most of the etherification reaction occurs in this phase. Mass transfer from the isobutylene phase to the glycerol phase maintains the supply of isobutylene in the glycerol phase.
Mono-tertiary butyl glycerol formed in the glycerol phase will mainly remain in this phase. However, di- and tri-tertiary alkyl glycerol products will preferentially transfer to the isobutylene phase.
The etherification reaction effluents may then be separated to recover unreacted reactants and the desired biofuel products. In some embodiments, the etherification reaction mixture may be sent to a distiller to separate into an upper isoalkylene phase comprised of mono-tertiary alkyl glycerol, di-tertiary alkyl glycerol and tri-tertiary alkyl glycerol in addition to the unreacted isoolefin, and a lower glycerol phase comprised of glycerol, mono-tertiary alkyl glycerol, catalyst and small amounts of di- and tri-tertiary alkyl glycerol.
In some embodiments, the glycerol phase may be returned to the reactor with net feed glycerol and make up catalyst. Further, the isobutylene phase may continue to a stripping column where the unreacted isoolefin is stripped as an overheads fraction and returned to the reactor along with net feed isoolefin. The bottoms fraction from the stripping column comprises a small amount of catalyst, glycerol and mono-tertiary alkyl glycerol as well as the di-tertiary alkyl glycerol and tri-tertiary alkyl glycerol products. The bottoms fraction may be contacted with water to extract glycerol, catalyst and mono-tertiary alkyl glycerol for recovery, recycle, or disposal. Product di- and tri-tertiary alkyl glycerol is recovered for use as a biofuel or biofuel additive. In some embodiments, the di- and tri-tertiary alkyl glycerol may be combined with the fatty acid alkyl esters for use as a biofuel or biofuel additive.
It is typically necessary that the net feed to the etherification comprise at least one mole up to four moles of isoolefin per mole of glycerol. A higher concentration of isoolefin will typically result in a higher production of tri-ethers. It is also typical that the reaction mixture in the etherification reaction zone be maintained such that the polar glycerol phase comprises at least 30 wt % of the total reaction mixture, and that the glycerol content of the polar glycerol phase comprise at least 50 wt % and preferably at least 60 wt % of the polar phase. Reaction conditions which are employed for the etherification are temperatures of about 40° C.-150° C., preferably about 50° C.-100° C. Pressures are sufficient to maintain the liquid phase, e.g. about 2 to 20 bar (about 15 to 300 psig). Homogeneous catalysts, when used, are generally used in amounts of about 0.1-5.0 wt % of the reaction mixture, preferably about 0.5-2.5%.
Typical processes for the etherification of glycerol and isobutylene to produce TIG require the importation of glycerol and high-purity isobutylene, increasing process costs. Further, typical processes for the transesterification of triglyceride bio oils and fats require the importation of methanol in addition to other feedstocks.
Embodiments disclosed herein may advantageously integrate decomposition of ethers with production of biodiesel fuels or fuel additives via the transesterification and etherification of feedstocks and reaction byproducts, as described above. Such integration provides isoolefins and alcohols at the necessary stoichiometric ratio, and may eliminate the need to import alcohols, glycerol, and isoolefins.
Further, MTBE is already produced or is capable of being produced in many oil refineries and petrochemical facilities. Processes for producing biodiesel according to embodiments disclosed herein may provide an outlet for MTBE and may additionally be used to employ stranded equipment. As the use of MTBE as a fuel additive is currently being phased out in many countries due to practical and environmental concerns, processes disclosed herein provide a viable alternative use for existing MTBE production units. MTBE is a convenient and economical way to transport the isobutylene and methanol (in the correct ratio) from the oil refinery or other MTBE producing facility to the biodiesel plant for use as feeds to the transesterification and etherification processes.
While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.
This application, pursuant to 35 U.S.C. §119(e), claims priority to U.S. Provisional Application Ser. No. 61/233,695, filed Aug. 13, 2009, which is incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61233695 | Aug 2009 | US |
