HK1171230A - Decarbonylation process - Google Patents

Description

Decarbonylation process

Cross Reference to Related Applications

This patent application claims priority to U.S. provisional application 61/238,270 filed on 8/31/2009, which is incorporated herein in its entirety for all purposes.

FIELD OF THE DISCLOSURE

The present disclosure relates to the manufacture of furans and related compounds, and to their industrial use for the synthesis of other useful materials.

Background

Furans and related compounds are useful starting materials for industrial chemicals used as pharmaceuticals, herbicides, stabilizers, and polymers. For example, furan is used to prepare tetrahydrofuran, polytetramethylene glycol, polyetherester elastomers, and polyurethane elastomers.

Known transition metal catalyzed vapor phase processes for the production of furan by decarbonylation of furfural are limited by the selectivity or the lifetime of the supported catalyst. This is complicated by the fact that the conversion of furfural to furan tends to form polymeric or carbonized by-products that foul the catalyst surface and hinder reaction rate and catalyst life. In the decarbonylation of furfural to furan, Pd has been shown to be an excellent catalyst in both liquid phase and vapor phase reactions. A difficulty with this chemistry is that fouling reactions, which are believed to proceed primarily through acid-catalyzed oligomerization reactions, deactivate the catalyst. Alkaline buffers have been added to catalysts, either as surface treatments (vapor phase) or as solid materials in liquid phase slurry reactors. It is important to find a catalyst support that enhances decarbonylation activity while minimizing deactivation reactions, such as carbon deposition, for the success of Pd-based processes. Treatment of the support with an alkaline buffer and an alkaline treatment agent has been shown to be effective in previous work, but the solid support, which is active, stable and resistant to high temperatures, in this process would have an expensive price.

Supported palladium catalysts are known for catalyzing furfural decarbonylation reactions, which have high selectivity but are limited by short lifetimes. For example, U.S. Pat. No. 3,007,941 proposes a process for producing furan from furfural, which comprises heating a liquid phase consisting essentially of furfural in the presence of an alkaline salt of palladium metal and an alkali metal; the basic salt is not part of the catalyst itself but is added continuously to the liquid phase during the reaction. Us patent 3,257,417 also proposes a process for the production of furan, which comprises contacting liquid furfural with a palladium catalyst in the presence of calcium acetate. Both of these processes suffer from rapid catalyst deactivation and difficult catalyst regeneration processes. Us patent 3,223,714 proposes a continuous low pressure vapor phase decarbonylation process for the production of furan, which comprises contacting a supported palladium catalyst with furfural vapor. The preferred catalyst has about 0.3 wt.% Pd supported on alumina. The catalyst can be regenerated in situ, but the catalyst cycle life is short and the yield of furan per cycle is low. It is preferred to use a catalyst comprising platinum and/or rhodium to which cesium has been added.

Co-pending U.S. provisional patent application 61/138,754, which is hereby incorporated by reference in its entirety, provides a process for the vapor phase decarbonylation of furfural to furan using heating a Pd/alumina catalyst that has been promoted with an alkali metal carbonate.

There remains a need for vapor and liquid phase decarbonylation catalysts for furfural to furan that have improved life and high yields.

Description of the invention

The invention disclosed herein includes methods of making furans and related compounds, as well as methods of making products into which those compounds can be converted.

Features of certain methods of the invention are described herein in the context of one or more specific embodiments that combine various such features. The scope of the invention, however, is not limited to the description of only a few of the features in any particular embodiment, and the invention also includes (1) sub-combinations of less than all of the features of any of the described embodiments, which sub-combinations may be characterized by the absence of features omitted to form the sub-combinations; (2) each feature is independently included in any combination of the embodiments; and (3) combinations of other features formed by categorizing only selected features from two or more of the described embodiments, optionally together with other features disclosed elsewhere herein. Some specific embodiments of the methods herein are as follows:

in one embodiment herein, the present invention provides a method of synthesizing a compound represented by the structure of the following formula (I), by the steps of:

providing a compound represented by the structure of the following formula (II) in a gaseous form,

heating the Pd/metal aluminate catalyst and contacting the compound of formula (II) with the catalyst to produce a product of formula (I); wherein R is¹、R²And R³Each independently selected from H and C₁-C₄A hydrocarbyl group.

In another embodiment herein is provided a process for preparing a product of formula (I) as described above, further comprising promoting the Pd/metal aluminate catalyst with an alkali metal carbonate.

In another embodiment herein, there is provided a process for preparing a product of formula (I), the process comprising providing a compound represented by formula (II) in liquid form, and heating the compound of formula (II) in contact with a Pd/metal aluminate catalyst in a reactor. In another embodiment, the process further comprises promoting the Pd/metal aluminate catalyst with an alkali metal carbonate.

In another embodiment herein is provided a process for the preparation of a product of formula (I) as described in any of the processes above, further comprising the step of subjecting furan to a reaction (including a multi-step reaction) to prepare therefrom a compound (such as one useful as a monomer), oligomer or polymer.

The advantageous features of the process herein are the lifetime and high yield of the Pd/metal aluminate catalyst and the alkali metal carbonate promoted Pd/metal aluminate catalyst relative to other catalysts previously used in the vapor phase.

In one embodiment of the methods described herein, R¹、R²And R³Are all equal to H; therefore, the temperature of the molten metal is controlled,the product of formula (I) is furan and the compound of formula (II) is furfural. Thus, the decarbonylation of furfural to produce furan can be represented by the following reaction scheme:

the compounds of formula (II) used in the process described herein are preferably obtained from biological material, which is an excellent source of hemicellulose. Examples include, without limitation: straw, corncobs, corn stover (hay), sugar cane bagasse, hardwood, cotton stalks, kenaf, oat hulls, and hemp. The compound of formula (II), especially when it is furfural, should be distilled fresh before use as it oxidizes and changes color, forming undesirable high boiling oxidation products.

In the process embodiments described herein, the decarbonylation reaction is catalyzed by a Pd/metal aluminate catalyst. As used herein, the term "metal aluminate" stands for alumina (Al)₂O₃) And a metal oxide. This can be clearly shown by the chemical formula. For example, the chemical formula LiAlO of lithium aluminate₂Can be written as Li₂O·Al₂O₃. Such catalyst supports are themselves less acidic than alumina. Using a catalyst which is inherently less acidic than Al₂O₃The Pd carrier can reduce the surface carbonization of the catalyst and reduce the deactivation rate of the catalyst, thereby prolonging the service life. Examples of suitable metal aluminates include, without limitation, the following aluminates: alkali metals such as lithium, sodium and potassium; alkaline earth metals such as calcium, barium and strontium; lanthanum; gallium; and yttrium. As described in U.S. patent 3,663,295, alkali metal aluminates can be prepared by reacting an alkali metal salt, such as an alkali metal carbonate, with a reactive transition alumina, such as gamma alumina, at elevated temperatures of up to about 600 c to 700 c for up to 24 hours. Other metal aluminates can be similarly prepared. In one embodiment, the catalyst support is lithium aluminate LiAlO₂(CAS registry number 12003-67-7), which is commercially available (e.g., from Johnson Matthey, Royston Herts, England).

In another embodiment of the process described herein, the decarbonylation reaction is carried out using an alkali metal carbonate such as sodium carbonate (Na)₂CO₃) Potassium carbonate (K)₂CO₃) Or cesium carbonate (Cs)₂CO₃) Promoted Pd/metal aluminate catalysts. The catalyst has an alkali metal content of between about 1mg/g and about 100mg/g of catalyst. In some embodiments, the alkali metal content is between and optionally includes any two of the following values: 1.5, 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100mg/g catalyst. In one embodiment, the alkali metal carbonate is cesium carbonate.

The catalyst is promoted by immersing the Pd/metal aluminate catalyst in powder, pellet, rodlet, sphere or any extruded or pressed form in an aqueous solution of alkali metal carbonate with stirring. The concentration of the alkali metal carbonate solution is not critical and is generally in the range of about 0.1% to about 20% by weight. The optimum immersion time will depend on the surface area of the Pd/metal aluminate catalyst, the temperature and the alkali carbonate concentration and can be readily determined by one of ordinary skill in the art. In one embodiment, the palladium/metal aluminate catalyst is immersed in a 5 wt% to 10 wt% alkali metal carbonate solution at room temperature for about 4 to 6 hours. The wetted catalyst is then removed from the solution and dried, for example, in a hot air oven at about 110-; the catalyst may also be initially dried at ambient conditions before oven drying. The dried catalyst is calcined at about 200 and 500 ℃ for about 2 to about 8 hours.

The decarbonylation reaction can be carried out as a vapor (gas) phase process or a liquid phase process. The terms "gas" and "steam" are used interchangeably herein. In the vapor phase process, the reaction is carried out by injecting the compound of formula (II) in gaseous form into a reactor loaded with the desired catalyst. In one embodiment, the compound of formula (II) is provided in gaseous form by heating the liquid compound of formula (II) to a sufficiently high temperature to cause vaporization thereof; for furfural, this temperature is about 180 ℃. A non-reactive internal standard, such as dodecane, may be present in the compound of formula (II) at about 0.5% by weight for analytical purposes, i.e. to confirm the mass balance. Hydrogen may be co-fed to assist in vaporizing the compound of formula (II); hydrogen is also known to extend catalyst life. Typical hydrogen feed rates are from about 0.25 to about 5.0 moles of hydrogen per mole of furfural. Water may also be added to the compound of formula (II) before the liquid compound is vaporized, or separately to the liquid or gaseous compound of formula (II), as described in co-pending U.S. provisional patent application 61/138,754.

The reaction may take place in the gas phase at a temperature, suitably in the range of from about 200 ℃ to about 400 ℃, typically in the range of from about 270 ℃ to about 330 ℃. In some embodiments, the reaction temperature is between and optionally includes any two of the following values: 200 ℃, 220 ℃, 240 ℃, 260 ℃,270 ℃, 280 ℃, 290 ℃, 300 ℃, 310 ℃, 320 ℃, 330 ℃, 340 ℃, 360 ℃, 380 ℃ and 400 ℃. Reference herein to reaction temperature is to the temperature of the catalyst in the catalytic zone provided to the reactor. Temperatures in these ranges may be provided by heating various parts of the reactor by means of another external source, in particular a heating element designed to surround the catalytic zone of the heated reactor, thereby heating the catalyst itself. Thus, the selected temperature is present in the catalyst zone of the reactor when the furfural contacts the catalyst.

The vapor phase decarbonylation reaction is typically carried out at ambient pressure or at a slightly elevated pressure. The pressure is not critical as long as the compounds of formula (I) and formula (II) remain in the gas phase in the reactor. The reaction residence time may be one minute or less; in some embodiments, the reaction time may be less than one second. In some embodiments, the reaction residence time is between and optionally including any two of the following values (seconds): 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55 and 60. The reaction is carried out with a continuous feed of the compound of formula (I) and preferably hydrogen is maintained for a period of time suitable to determine the lifetime of the catalyst. For example, the lifetime is calculated as grams of furan produced per gram of Pd in the reactor. Lifetimes greater than 10,000 grams per gram pdd are desirable, particularly greater than 100,000 grams per gram pdd. In all cases, however, the reaction is carried out at a temperature and pressure and for a time sufficient to obtain a gas-phase product of the compound of formula (I). The amount of Pd is not critical; in one embodiment of the vapor phase process, it is present in an amount of from 0.1 to 2.0 wt.% (based on the total weight of the Pd + metal aluminate). In some embodiments, the amount of Pd is between and optionally including any two of the following values (wt%): 0.1, 0.3, 0.5, 0.7, 0.9, 1.1, 1.3, 1.5, 1.7, 1.9 and 2.0.

In a liquid phase embodiment of the decarbonylation process, the reaction is carried out by injecting the compound of formula (II) in liquid form into a reactor loaded with the desired catalyst. The Pd/metal aluminate catalyst in powder form can be used in the liquid phase decarbonylation of compounds of formula (II), such as furfural. In this case, a higher Pd loading is used-in some embodiments, the Pd loading (wt%) is between and optionally includes any two of the following values: 1.2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 and 20. The solids (catalyst) concentration in the slurry reactor can be 0.01-30 wt%; in one embodiment, the concentration is between 0.5 wt.% and 5 wt.% catalyst. In some embodiments, the solids (catalyst) concentration (wt%) is between and optionally includes any two of the following values: 0.01, 0.05, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 29 and 30. The Pd/metal aluminate catalyst powder may also be used in suspension with an alkaline buffer powder such as sodium carbonate, potassium carbonate or calcium acetate as described in U.S.3,007,941 and U.S.3,257,417.

When the compound of formula (II) is furfural, the reaction may occur in the liquid phase at a temperature in the range of about 162 ℃ to about 230 ℃. In some embodiments, the temperature is between and optionally includes any two of the following values: 162 deg.C, 170 deg.C, 175 deg.C, 180 deg.C, 185 deg.C, 190 deg.C, 195 deg.C, 200 deg.C, 205 deg.C, 210 deg.C, 215 deg.C, 220 deg.C, 225 deg.C and 230 deg.C. Reference herein to reaction temperature is to the temperature of the catalyst in the catalytic zone provided to the reactor. Temperatures in these ranges may be provided by heating various parts of the reactor by means of another external source, in particular a heating element designed to surround the catalytic zone of the heated reactor, thereby heating the catalyst itself. Thus, the selected temperature is present in the catalyst zone of the reactor once the compound of formula (II) is contacted with the catalyst. When the atmospheric boiling point of the compound of formula (II) is below the reaction temperature, as is the case when the compound of formula (II) is furfural (boiling point about 162 ℃), the reaction is carried out at above atmospheric pressure, for example about 25-100psi above atmospheric pressure. In addition to providing a reflux temperature in the desired range, this pressure also facilitates the condensation and separation of the compound of formula (I), e.g. furan, from the resulting carbon monoxide gas stream as the reaction proceeds.

Reactors suitable for use in the process herein include fixed bed reactors and tubular, tubular or other plug flow reactors and the like (wherein the catalyst particles are held in place and do not move relative to a stationary resident framework); or a fluidized bed reactor. The compound of formula (II) may flow into and through the reactor (e.g. in a continuous manner) to provide a corresponding continuous product stream at the outlet end of the reactor. These reactors, as well as other suitable reactors, are described more specifically in, for example, Fogler, "Elements of Chemical reaction engineering," second edition, Prentice-Hall Inc. (1992). In one embodiment, the inflow conduit is heat traced to maintain the reactants at a suitable temperature, and the temperature of the catalyst zone is controlled by a separate heating element at that location. The product of formula (I), as obtained in gaseous form from the reactor, may be condensed by cooling to a liquid for further processing. Alternatively, the process may further comprise purifying the product of formula (I), such as by distillation. For example, the product of formula (I) may be fed directly to, for example, a distillation column to remove unreacted compound of formula (II) and other impurities that may be present; the distillation product can then be separated and recovered.

However, the distillation product may also be subjected to a further step, with or without recovery, from the reaction mixture to convert it to another product, such as another compound (e.g. a useful type, such as a monomer) or an oligomer or polymer. Thus, another embodiment of the process herein provides a process for converting the product of formula (I) into another compound or oligomer or polymer by a reaction, including a multi-step reaction. For example, the product furan of formula (I) may be made from the compound furfural of formula (II) by the method described above, and then converted to tetrahydrofuran by hydrogenation. Tetrahydrofuran in turn can be used to prepare polytetrahydrofuran ethers, which in turn can be reacted with 1, 4-butanediol and terephthalic acid to produce polyetherester elastomers or with diisocyanates to produce polyurethanes.

All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control.

Although methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention, suitable methods and materials are described herein.

All percentages, parts, ratios, etc., are by weight unless otherwise indicated.

When an amount, concentration, or other value or parameter is given as either a range, preferred range, or a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It is not intended that the scope of the invention be limited to the specific values recited when defining a range.

When the term "about" is used to describe a value or an end-point of a range, the disclosure should be understood to include the specific value or end-point referred to.

As used herein, the terms "comprises," "comprising," "includes," "including," "contains," "containing," "characterized by," "has," "having," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Furthermore, unless expressly stated to the contrary, "or" refers to an inclusive "or" and not to an exclusive "or". For example, the condition a or B is satisfied in any of the following cases: a is true (or present) and B is spurious (or absent), a is spurious (or absent) and B is true (or present), and both a and B are true (or present).

"A" or "an" are used to describe an element or component of the invention. This is done merely for convenience and to give a general sense of the invention. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise.

The materials, methods, and examples herein are illustrative only and are not intended to be limiting unless specifically indicated.

Examples

The advantageous features and effects of the process according to the invention can be seen from a series of examples (examples 1 to 3) described below. The embodiments of these methods on which these examples are based are representative only, and the selection of those embodiments to illustrate the invention does not indicate that conditions, arrangements, methods, protocols, steps, techniques, layouts, protocols or reactants not described in these examples are not suitable for practicing these methods, or that subject matter not described in these examples is excluded from the scope of the appended claims and equivalents thereof.

Material

The following materials were used in the examples.

Pd/alumina catalyst (0.5% Pd, gamma alumina support, 3mm pellets) was obtained from Engelhard Corporation, now BASF Catalysts LLC, a division of BASF-The Chemical Company, Ludwigshafen, Germany. Pd/lithium aluminate catalyst (0.5% Pd, lithium aluminate support, 3mm pellets) was obtained from Johnson Matthey (Royston Herts, England).

The furfural was obtained from HHI (China) and had a pre-distillation purity of 98.5%. Before the reaction, it was freshly distilled in portions in a 1 inch (2.54cm) 20-tray Oldershaw column with minimal air contact.

The abbreviations have the following meanings: "cm" means one or several centimeters, "g" means one or several grams, "GC" means gas chromatography, "h" means one or several hours, "kg" means one or several kilograms, "mL" means one or several milliliters, "min" means minutes, "mm" means one or several millimeters, "psig" means pounds per square inch gauge, THF means tetrahydrofuran, and "vol" means volume.

Comparative example A

This comparative example demonstrates vapor phase decarbonylation of furfural in the presence of an un-promoted Pd/alumina catalyst.

About 2 grams of Pd/alumina catalyst (0.5% Pd on gamma alumina support, 3mm pellets) was loaded onto a stainless steel mesh support located in a type 316 stainless steel tube reactor of 18 '. times. 1/2' (45.7 cm. times.1.3 cm) outside diameter (o.d.),the reactor had gas and liquid feed inlets and an internal thermocouple operating at atmospheric pressure. The catalyst was then pretreated in situ by blowing nitrogen into the reactor, initially at room temperature, and then increasing the temperature to 270 ℃ over a 2 hour period, while simultaneously being 15cm³Hydrogen was purged per minute and furfural feed (containing 0.5 wt.% dodecane as an internal standard) was introduced with concurrent generation of reaction data. At the reaction temperature (270 ℃), the hydrogen flow was set at 17 mL/min and the furfural flow at 2.0 mL/hr. The molar ratio of hydrogen to furfural was 2.0. The gas product stream was maintained at 180 ℃ and fed directly to an Agilent equipped with a flame ionization and mass selection detector^TM6890 GC. Furfural conversion (%) was calculated as follows: [ (1 (% area of furfural in product/% area of dodecane in product)/(% area of furfural in feed stream/% area of dodecane in feed stream))]Multiplied by 100. Furan selectivity (%) was calculated as follows: (moles of furan/moles of furfural reacted) multiplied by 100. The selectivities (%) for THF, furfuryl alcohol and methylfuran were calculated similarly. The conversion, furan selectivity and amount of Pd in the reactor during the life study were calculated as kilograms of furan produced per gram of Pd. The initial furfural conversion was 99%, but it was gradually reduced to 93% (3.06kg furan/gPd) over a 23 hour run and to 32% (7.87kg furan/gPd) over 126 hours. Initially the furan selectivity was 83% and for Tetrahydrofuran (THF) 12% selectivity. At 23 hours, the selectivity for furan was 92% and for THF 3%. At 126 hours, furan selectivity had dropped to 89% with 0.3% THF. The by-products are mainly 2-methylfuran and furfuryl alcohol, both resulting from the hydrogenation of furfural.

TABLE 1

Hours number	Kg of furan/g of Pd	Conversion rate of furfural%	THF selectivity%	Selectivity to furan%
					1	0.1	99	12	83
23	3.06	93	3	92
					126	7.87	83	0.3	89

Comparative example B

This example demonstrates Cs₂CO₃Preparation of a promoted Pd/alumina catalyst.

The Pd/alumina catalyst described in comparative example A (0.5% Pd, 20.3125g) was immersed in 20mL of 7.5% Cs₂CO₃(1.50g Cs₂CO₃In 20mL of deionized water) and stirred gently on an orbital shaker at room temperatureFor 5 hours. The mixture was filtered and the rods rinsed with deionized water (3 × 20 mL). The rods were dried in air. The catalyst was further dried in an oven at 120 ℃ for 2 hours in ambient air and cooled to room temperature for 1 hour and weighed. The rods were calcined at 300 ℃ for 4 hours and cooled overnight.

Comparative example C

This example demonstrates vapor phase decarbonylation of furfural in the presence of a Pd/alumina catalyst promoted with cesium carbonate.

A similar process to that described in comparative example a was carried out using a Pd/alumina catalyst treated with cesium carbonate using the process of comparative example B. About 2 grams of Pd/alumina catalyst (0.5% Pd on gamma alumina support, 3mm pellets) was loaded onto a stainless steel mesh support located in a type 316 stainless steel tube reactor of 18 "x 1/2" (45.7cm x 1.3cm) outside diameter (o.d.), with gas and liquid feed inlets and an internal thermocouple operating at atmospheric pressure. The catalyst was then pretreated in situ by blowing nitrogen into the reactor, initially at room temperature, then increasing the temperature to 290 ℃ over a period of 2 hours, while simultaneously operating at 15cm³Hydrogen was purged at a rate of/min and a furfural feed (containing 0.5 wt.% dodecane as an internal standard, and 3 wt.% water) was introduced, with reaction data generated. At the reaction temperature (290 ℃), the hydrogen flow was set at 17 mL/min and the furfural flow at 2.0 mL/hr. The molar ratio of hydrogen to furfural was 2.0. The gas product stream was sampled by condensation for a flow time of 15 minutes in a refrigerated (-10C) glass product vial containing 0.5mL of N-methylpyrrolidone (NMP) for sample dilution. Sample injection into Agilent equipped with flame ionization and mass selective detector^TM6890 GC. Furfural conversion (%) and product selectivity (%) were determined by GC analysis as described in comparative example a. The initial furfural conversion was 99.2%. Furfural conversion stabilized until about 139 hours (21.2kg furan/g Pd), at which point unconverted furfural began to increase in GC analysis, showing a conversion of 87.1%. The reactor temperature was then raised to 310 ℃ to increase furfural conversion. At the time of 144.5 hours,the conversion rate of the furfural is as high as 94.6 percent. At 163.8 hours, the conversion was 90.4% and the temperature was raised to 330C and reacted for a further day (25.8kg furan/g Pd). Furfural feed was stopped at 171 hours. Initially the furan selectivity was 94.1% and for Tetrahydrofuran (THF) 4.8%. At 139 hours, the selectivity for furan was 97.8% and for THF 0.3%. At 171 hours, furan selectivity was 98.6%, with the lowest THF production. During the entire reaction, less than 1% of by-products methylfuran and furancarbinol were observed.

TABLE 2

Temperature, C	Hours number	Kg of furan/g of Pd	Conversion rate of furfural%	THF selectivity%	Selectivity to furan%
						290	1	0.1	99.2	4.8	94.1
290	139.2	21.2	87.1	0.3	97.8
						310	144.5	21.9	94.6	0.2	98.3
310	163.8	25.2	90.4	0.2	98.3
						330	171	26.3	95.4	0.1	98.6

Example 1

This example demonstrates the vapor phase decarbonylation of furfural in the presence of an un-promoted Pd/lithium aluminate catalyst.

The process described in comparative example C was carried out using a Pd/lithium aluminate catalyst which had not been pretreated in any way. Furfural conversion and product selectivity (%) were determined by GC analysis as described in comparative example a. The initial furfural conversion was 100%. The furfural conversion decreased slowly until about 116 hours (17.5kg furan/g Pd), at which point the conversion was 98.8%, but the selectivity for furfuryl alcohol (furancarbinol) climbed to 2.5%. The reactor temperature was then raised to 310 ℃ to improve furfural conversion and furan selectivity. At 120 hours, furfural conversion was as high as 99.4% and furfuryl alcohol was reduced to 0.5%. At 169 hours, the conversion was 88.5% and the temperature was raised to 330 ℃ for a further day (to 27.1kg furan/g Pd). At 191 hours, furfural feed was stopped as conversion continued to decrease. Initially the furan selectivity was 70.4% and for Tetrahydrofuran (THF) 26%. At 120 hours, the selectivity for furan was 95.2% and for THF 2.5%. At 169 hours, furan selectivity was 93%, with a THF yield of 1.3%. The by-product 2-methylfuran was initially 1.7%, but fell below 0.5% after only 2 hours of reaction and remained low throughout the reaction.

TABLE 3

Example 2

This example demonstrates vapor phase decarbonylation of furfural in the presence of a Pd/lithium-alumina catalyst promoted with cesium carbonate.

A similar process to that described in comparative example a was carried out using a Pd/lithium-alumina catalyst treated with cesium carbonate using the process of comparative example B. About 2 grams of Pd/lithium aluminate catalyst (0.5% Pd on lithium aluminate support, 3mm pellets) was loaded onto a stainless steel mesh support located within a type 316 stainless steel tube reactor of 18 "x 1/2" (45.7cm x 1.3cm) outer diameter (o.d.), with gas and liquid feed inlets and an internal thermocouple operating at atmospheric pressure. The catalyst was then pretreated in situ by blowing nitrogen into the reactor, initially at room temperature, then increasing the temperature to 290 ℃ over a 2 hour periodAt the same time by 15cm³Hydrogen was purged at a rate of/min and a furfural feed (containing 0.5 wt.% dodecane as an internal standard, and 3 wt.% water) was introduced, with reaction data generated. At the reaction temperature (290 ℃), the hydrogen flow was set at 17 mL/min and the furfural flow at 2.0 mL/hr. The molar ratio of hydrogen to furfural was 2.0. The gaseous product stream was sampled by condensation for a flow time of 15 minutes in a refrigerated (-10 ℃) glass product vial containing 0.5mL of N-methylpyrrolidone (NMP) for sample dilution. Furfural conversion and product selectivity (%) were determined by GC analysis as described in comparative example a. The results shown in table 4 demonstrate that the lifetime of alkali metal promoted Pd supported on lithium aluminate is longer than the observed lifetime of alkali metal promoted alumina and un-promoted lithium aluminate. Alkali metal carbonate treatment significantly reduces the hydrogenation activity during decarbonylation.

TABLE 4

Example 3

This example demonstrates the liquid phase decarbonylation of furfural to furan using a Pd/metal aluminate catalyst.

Dry furfural (60.07g) and catalyst (0.3g, 5% Pd on alumina/lithium aluminate) were charged to a 100mL stainless steel Parr reactor equipped with a mechanical stirrer, furfural feed tube, and a vertical stainless steel condenser, included within a pressure regulated vent valve. The vertical condenser was maintained at a temperature to return unreacted furfural to the reactor while passing furan and carbon monoxide vapors through a pressure-regulated vent valve, after which the furan product was condensed and the carbon monoxide production rate was determined using a mass flow meter.

The reaction charge was heated and the temperature was automatically controlled at about 190 ℃. The pressure regulating vent valve was adjusted to maintain a pressure of about 21psig on the reactor contents. The reaction was carried out essentially according to the method described in U.S.3,257,417, example 1, except that the temperature was about 190 ℃ instead of about 215 ℃, and the pressure was about 21psig instead of about 67 psig. Furfural was initially added to the reactor at a rate of about 7.5 mL/h. The measured carbon monoxide production over time showed a reduction of about 75% in the catalyst activity over about 20h of reaction time. The initial yield of about 231g furan/gPd/hour dropped to about 49 after 20 h.

It is to be understood that certain features of the invention, which are, for clarity, described above and below in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any subcombination. Further, reference to values within a range includes each value within the range.

Claims (13)

1. A process for synthesizing a compound represented by the structure of formula (I),

the method is carried out by the following steps: providing a compound represented by the structure of the following formula (II) in a liquid form,

and heating the compound of formula (II) in contact with the Pd/metal aluminate catalyst in a reactor to produce a product of formula (I);

wherein R is¹、R²And R³Each independently selected from H and C₁-C₄A hydrocarbyl group.

2. The method according to claim 1, wherein R¹、R²And R³Each is H.

3. The method according to claim 1, wherein the substituted alumina is an alkali metal aluminate, an alkaline earth metal aluminate, gallium aluminate, lanthanum aluminate, or yttrium aluminate.

4. A process according to claim 3 wherein the alkali metal aluminate is LiAlO₂。

5. The method of claim 1, wherein the temperature is in the range of about 162 ℃ to about 230 ℃

Contacting said compound of formula (II) with said catalyst occurs in said liquid phase at a pressure of about 25-100psi above atmospheric pressure to produce a product of formula (I).

6. The process according to claim 1, wherein the Pd loading of the Pd/substituted alumina catalyst is from about 1% to about 20% by weight.

7. The process according to claim 1, wherein the catalyst concentration in the reactor is from about 0.01 wt% to about 30 wt%.

8. The process according to claim 1, wherein the reaction is carried out in suspension in the presence of an alkaline buffer powder.

9. The method of claim 8, wherein the alkaline buffer is sodium carbonate, potassium carbonate, or calcium acetate.

10. The process according to claim 1, further comprising purifying the formula (I) product.

11. The process according to claim 10, wherein the product of formula (I) is purified by distillation.

12. A process according to claim 1, wherein the Pd/metal aluminate catalyst has been promoted with an alkali metal carbonate.

13. The process according to claim 1, further comprising the step of subjecting the compound of formula (I) to a reaction to prepare therefrom a compound, oligomer or polymer.