HK1164301B - Vapor phase decarbonylation process - Google Patents

Description

Vapor phase decarbonylation process

Cross Reference to Related Applications

This patent application claims priority to U.S. provisional application 61/138,754 filed on month 12 and 18 of 2008, which is incorporated in its entirety as part of this document for various purposes.

FIELD OF THE DISCLOSURE

The present disclosure relates to the manufacture of furans and related compounds, and 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 make tetrahydrofuran, polytetramethylene glycol, polyetherester elastomers, and polyurethane elastomers.

Known transition metal catalyzed, vapor phase processes for the production of furan by the decarbonylation of furfural are limited by the selectivity or the life of the supported catalyst. The conversion of furfural to furan is complicated by the tendency to form polymeric or carbonized byproducts that foul the catalyst surface and hinder reaction rate and catalyst life. For example, U.S. patent 3,223,714 teaches a continuous low pressure vapor phase decarbonylation process for the production of furan, which involves contacting furfural vapor with a supported palladium catalyst. A preferred catalyst has about 0.3 wt% palladium supported on alumina. The catalyst can be regenerated in situ, but the catalyst has a short life cycle and produces less furan per cycle.

There remains a need for a process for the vapor phase decarbonylation of furfural to furan with improved rates.

Detailed Description

The invention disclosed herein includes processes for the preparation of furan and for the preparation of products into which furan 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) subcombinations of less than all of the features of any of the described embodiments, where such subcombinations are characterized by the absence of features omitted from forming such subcombinations; (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 formula (I) below by:

(a) providing a vapor phase mixture of water and a compound represented by the structure of formula (II):

wherein water is present at about 1 to about 30 weight percent based on the weight of water plus the compound of formula (II);

(b) optionally, co-feeding a compound of formula (II) with hydrogen, (c) heating the supported palladium catalyst, and (d) contacting the vapor phase mixture 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 the preparation of a product of formula (I) as described above, further comprising the step of subjecting furan to a reaction (including a multi-step reaction) to thereby prepare a compound (such as one useful as a monomer), oligomer or polymer.

Advantageous features of the process herein include higher decarbonylation rates, higher conversion of the compound of formula (II), and higher selectivity to the product of formula (I), while operating at lower temperatures than similar processes operating with substantially dry compounds of formula (II).

In one embodiment of the methods described herein, R¹、R²And R³Are all equal to H; thus, 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 compound of formula (II) used in the process described herein is preferably obtained from a 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 freshly distilled before use because it oxidizes and changes color, forming undesirable high boiling oxidation products.

In the processes described herein, the decarbonylation reaction is catalyzed by a supported palladium catalyst. In one embodiment, the palladium is supported on alumina. The amount of palladium is not critical; in one embodiment, it is present at 0.1 to 2 wt% (based on the total weight of palladium + alumina or catalyst).

The reaction is carried out by injecting a vapor phase mixture of water and the compound of formula (II) into a reactor loaded with the desired catalyst. As used herein, the term "vapor phase mixture" means that the components of the mixture are gases. Water may be added to the compound of formula (II), as a liquid to the liquid compound of formula (II) prior to vaporization, or as a gas to the gaseous compound of formula (II).

Wherein liquid water is added to the liquid compound of formula (II) to form a mixture, heating the mixture to a temperature sufficiently high to vaporize the mixture; when the compound of formula (II) is furfural and water is present at about 3 wt%, this is about 180 ℃. A non-reactive internal standard (e.g., dodecane) may be present in the compound of formula (II) at about 0.5 wt% for analytical purposes, i.e., to confirm the mass balance.

In one embodiment, hydrogen is co-fed to help vaporize the compound of formula (II); hydrogen is also known to extend catalyst life. The molar ratio of hydrogen to formula (II) is generally between 0.1 and 5.0.

The reaction may take place in the vapour phase (i.e. the gas phase), suitably at a temperature in the range of from about 200 ℃ to about 400 ℃, typically from about 270 ℃ to about 330 ℃. 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, once furfural contacts the catalyst, the selected temperature is present in the catalyst zone of the reactor.

The reaction is generally carried out at ambient pressure or 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 minutes or less, or from about 5 to about 10 seconds, or from about 1 to about 2 seconds, or less than one second. 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 palladium in the reactor. Lifetimes of greater than 10,000 grams per gram of palladium are desirable, even more so than 100,000 grams per gram of palladium. 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).

Supported palladium catalysts are known to decrease in activity over time through a variety of mechanisms: 1) contamination, i.e. coverage of the active sites by carbon ("carbonization"), 2) poisoning, i.e. deactivation of the active sites due to reaction with process impurities, and 3) sintering, i.e. migration of palladium on the catalyst surface to produce a larger average palladium crystallite size and thus a reduction of the available palladium area for the reaction. Passivation via route 1 carbonization can be reversed by burning off carbon from the catalyst surface using an oxygen-containing gas stream. However, palladium catalysts are known to be susceptible to passivation by sintering via route 3 at temperatures normally associated with oxidative regeneration. Alternatively, the catalyst may be regenerated under a dilute oxygen stream with an excess of the gas stream rapidly blowing off heat generated by the exothermic oxidation from the catalyst surface. Dilution with nitrogen is also possible, however this is less preferred due to its lack of heat capacity for cooling the catalyst bed. Regeneration may be accomplished by passing air, or a mixture of air and steam or nitrogen, to the catalyst bed for between about 10 seconds and about 100 hours at a temperature in the range between about 300 ℃ and about 500 ℃. The concentration of air in the air mixture containing water vapor or nitrogen is at least 0.1 vol%, at least 1 vol%, at least 5 vol%, at least 10 vol%, at least 20 vol%, at least 30 vol%, at least 40 vol%, at least 50 vol%, at least 60 vol%, at least 70 vol%, at least 80 vol%, at least 90 vol%, at least 95 vol%, or at least 99 vol%.

Reactors suitable for use in the processes 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); and a fluidized bed reactor. The reactants may flow into and through the reactor (e.g., on a continuous basis) to provide a corresponding continuous product stream at the outlet end of the reactor. These reactors, as well as other suitable reactors, are described in more detail in, for example, Fogler, Elements of Chemical reaction engineering, 2nd Edition, Prentice-Hall Inc. (1992). In one embodiment, the incoming lines are heat traced to maintain the reactants at the appropriate temperature, and the temperature of the catalyst zone is controlled by a separate heating element in that zone. The product of formula (I), as obtained from the reactor in gaseous form, can be concentrated by cooling to a liquid for easy 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 distilled product can then be separated and recovered.

However, the distilled product may also be subjected to a further step, with or without recovery, from the reaction mixture to convert it to another product, for example another compound (as of a useful type, for example 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 methods such as those described above, and then converted to tetrahydrofuran by dehydrogenation. 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 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 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 elements and components of the invention. This is done merely for convenience and to give a general sense of the invention. Such description should be understood 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 utilities of the process of the present invention can be appreciated from a series of examples (examples 1-2) as 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.

Raw materials。

The following materials were used in the examples.

Furfural was obtained from HHI, China with a pre-distillation purity of 98.5%. It was used with minimal air contact prior to running after a fresh distillation (1 inch (2.54cm)20 tray Oldershaw column, batch).

A palladium on alpha-alumina catalyst (0.1% palladium) was obtained from Johnson Matthey PLC, London, England.

Deionized water was used.

The abbreviations have the following meanings: "cm" means centimeter, "conv" means conversion, "g" means gram, "GC/MS" means gas chromatography/mass spectrometry, "h" means hour, "mL" means milliliter, "min" means minute, "sel" means selectivity, "temp" means temperature, and "wt%" means weight percent.

Example 1

Run 1A. A distilled furfural mixture containing 3 wt% added water was prepared. The liquid was fed at a liquid feed rate of 1 mL/hour into an 1/2' (1.27cm) tubular downflow reactor at 290 deg.C to a 2 gram catalyst bed made from 0.1% palladium on an alpha-alumina support. Hydrogen at 8.5cm³The/minute rate is co-fed to help prevent deactivation of the palladium catalyst.

Run 1B. Run 1A was repeated without addition of water and at 330 ℃ instead of 290 ℃.

The reaction products were analyzed using GC/MS.

The following table shows the results from the reactor after 1 hour of operation for both of the above. Although the dry furfural feed reactor (B) was at a significantly higher temperature and used twice the amount of catalyst, the furfural conversion was significantly lower (90% versus almost 100%). These results demonstrate the effect of water in the reaction feed.

TABLE 1

Example 2

Example 1 was repeated except that the reactor temperature was 270 ℃ instead of 290 ℃ and 4 grams of catalyst was contained instead of 2 grams. Over several hours, data showing furfural conversion, selectivity to furan, and selectivity to Tetrahydrofuran (THF) are listed in table 2. Samples were plotted at the indicated times and analyzed using GC/MS. The use of wetted furfural (3 wt% water addition) achieved significantly higher decarbonylation activity and better selectivity to furan.

TABLE 2

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 (9)

1. A process for the synthesis of a compound represented by the structure of formula (I) below by:

(a) providing a vapor phase mixture of water and a compound represented by the structure of formula (II):

wherein water is present at 1 to 3 weight percent based on the weight of water plus the compound of formula (II);

(b) optionally, hydrogen is co-fed with the compound of formula (II),

(c) heating the supported palladium catalyst, and

(d) contacting the vapor phase mixture and the catalyst 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 process according to claim 1, wherein the compound of formula (II) is mixed with hydrogen in a ratio of 0.1 to 5.0 moles of hydrogen per mole of the compound of formula (II).

4. A process according to claim 3, wherein the compound of formula (II) is mixed with hydrogen in a ratio of from 0.5 to 2.5 moles of hydrogen per mole of compound of formula (II).

5. The process according to claim 1, wherein contacting the compound of formula (II) with the catalyst to produce the product of formula (I) occurs in the gas phase at a temperature in the range of from 200 ℃ to 400 ℃.

6. The method according to claim 5, wherein the temperature is in the range of 270 ℃ to 330 ℃.

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

8. The method of claim 1 wherein the palladium is supported on alumina.

9. The process according to claim 1, further comprising regenerating the catalyst by feeding a mixture of air and steam to the catalyst bed at a temperature between 300 ℃ and 500 ℃ for a time between 10 seconds and 100 hours, the mixture having a composition of between 2% and 40% by volume of air.