WO2023132895A1

WO2023132895A1 - Catalyst and method for thiophene production

Info

Publication number: WO2023132895A1
Application number: PCT/US2022/050226
Authority: WO
Inventors: Guang Cao; Kun Wang; Partha Nandi; August W. Bosse; Vera GRANKINA
Original assignee: ExxonMobil Technology and Engineering Company
Priority date: 2022-01-05
Filing date: 2022-11-17
Publication date: 2023-07-13

Abstract

A catalyst is provided that can provide improved results when producing thiophene by conversion of n-butane (and/or other alkanes) and a gas phase sulfur-containing compound, such as CS₂, H₂S, S₂, or another form of sulfur. The catalyst can correspond to chromium sulfide(s) supported on a zeotype support, such as a substantially alkali-metal form zeotype support or alkaline earth-metal form zeotype support. Methods for producing the catalyst and a corresponding catalyst precursor are also provided. Additionally, methods for producing thiophene and/or alkylated thiophene are also provided.

Description

CATALYST AND METHOD FOR THIOPHENE PRODUCTION

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the priority of U.S. Provisional Patent Application No. 63/296,643, filed January 1, 2022, which is incorporated by reference in its entirety.

FIELD OF THE INVENTION

[0002] This invention relates to a catalyst composition for production of thiophene, along with systems and methods for thiophene production.

BACKGROUND OF THE INVENTION

[0003] Thiophene and alkyl-substituted thiophenes are currently produced commercially by vapor phase reaction of alcohols with a sulfur source (such as carbon disulfide) in the presence of an oxide catalyst. An example of an oxide catalyst is CnOs supported on a substrate including AI2O3 and K2CO3. While this can allow for thiophene production, the alcohols needed as reagents correspond to specialty chemicals. This substantially increases the cost for production of thiophene, which limits the potential applications for products made from such thiophene.

[0004] It would be desirable to have alternative methods to allow for production of thiophene at reduced cost. This could potentially increase the number and/or type of applications available for use of thiophene. For example, polythiophene corresponds to a conjugated polymer. Conjugated polymers (such as Kevlar®) can often have favorable tensile strengths and/or other properties that are beneficial for use as structural materials. Thus, if thiophene (and therefore polythiophene) could be produced at lower cost, applications for use of polythiophene as a structural material could become attractive. Additionally, oxidized and/or doped polythiophenes can potentially be used as conductive polymers.

[0005] One example of an alternative process for thiophene production is to use n-butane (or another alkane) in place of the alcohol. U.S. Patent 3,939,179 describes an example of a catalytic process for conversion of n-butane and H2S to form thiophene. A variety of metal oxides supported on refractory oxides are described as catalyst precursors, including a combination of potassium oxide and chromium oxide supported on alumina.

[0006] Another option can be to operate with increased temperature without the use of a catalyst. U.S. Patent 2,450,658 describes an example of this type of process. While this type of process can result in thiophene production, the per-pass conversion rate for n-butane is limited, meaning that substantial recycle is needed in order to achieve high net conversion. Additionally, the thiophene synthesis conditions result in substantial formation of a tar-like product. It is further noted that the results reported for the example for thiophene synthesis from n-butene, based on mass balance, appear to be missing a substantial amount of the carbon from the input flows. Based on the relatively thorough characterization of the other products, this potentially indicates that a substantial amount of coke was made, which would be consistent with the higher temperature operation required for achieving substantial conversion of n-butane without a catalyst.

SUMMARY OF THE INVENTION

[0007] In various aspects, a sulfided catalyst is provided. The sulfided catalyst includes a support corresponding to a) a substantially alkali-metal form zeotype framework structure, b) a substantially alkaline earth-metal form zeotype framework structure, or c) a substantially alkali- metal and alkaline earth-metal form zeotype framework structure. The zeotype framework structure can have a 10-member ring pore channel or a 12-member ring pore channel as the largest pore channel. Additionally, the sulfided catalyst includes 1.0 wt% to 10 wt% of chromium sulfide relative to a weight of the sulfided catalyst. The chromium sulfide can have an average stoichiometry of CrSx, where x is greater than 1.0.

[0008] In various additional aspects, a catalyst precursor is provided. The catalyst precursor can include a support corresponding to a) a substantially alkali-metal form zeotype framework structure, b) a substantially alkaline earth-metal form zeotype framework structure, or c) a substantially alkali-metal and alkaline earth-metal form zeotype framework structure. The zeotype framework structure can have a 10-member ring pore channel or a 12-member ring pore channel as the largest pore channel. Additionally, the catalyst precursor can include 1.0 wt% to 10 wt% of CnOs relative to a weight of the catalyst precursor. Optionally, the support can be in substantially alkali-metal form, substantially alkaline earth-metal form, or substantially alkali- metal and alkaline earth-metal form prior to adding chromium to the support.

[0009] A method of making thiophene, an alkylated thiophene, or a combination thereof using a sulfided catalyst as described herein is also provided. The method includes exposing a first feedstock comprising one or more C4 to Ci6 alkanes and a second feedstock comprising a gas phase sulfur source to a sulfided catalyst as described herein under thiophene synthesis conditions, to form an effluent comprising thiophene, an alkylated thiophene, or a combination thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 shows an example of a reaction system for synthesis of thiophene. [0011] FIG. 2 shows a transmission electron micrograph of a sulfided catalyst a layered chromium sulfide phase.

[0012] FIG. 3 shows examples of compounds produced during a thiophene synthesis process.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0013] All numerical values within the detailed description and the claims herein are modified by “about” or “approximately” the indicated value, and take into account experimental error and variations that would be expected by a person having ordinary skill in the art.

Overview

[0014] In various aspects, a catalyst is provided that can provide improved results when producing thiophene by conversion of n-butane (and/or other alkanes) and a gas phase sulfur- containing compound, such as CS2, H2S, S2, or another form of sulfur. The catalyst can correspond to chromium sulfide(s) supported on a zeotype support, such as a substantially alkali-metal form zeotype support or alkaline earth-metal form zeotype support. Methods for producing the catalyst and a corresponding catalyst precursor are also provided. Additionally, methods for producing thiophene and/or alkylated thiophenes are also provided.

[0015] Conventionally, processes for thiophene production have used catalysts with catalytic metals (such as Cr) supported on an oxide support. Such conventional processes have typically focused on using starting reagents other than alkanes due to relatively low conversion rates and/or relatively high yields of coke from the process.

[0016] It has been discovered that a catalyst corresponding to chromium sulfide(s) supported on a zeotype support, optionally enhanced by the presence of alkali metals and/or alkaline earth metals in order to neutralize acidic sites, can provide improved combinations of increased alkane conversion, increased thiophene yield, and/or decreased coke yield. The catalyst can be formed by impregnating a zeotype support with chromium, oxidizing the impregnated support to form a catalyst precursor including chromium oxide(s), and then sulfiding the catalyst precursor to form chromium sulfide(s) on the zeotype support.

[0017] In some aspects, still further improvements in catalyst performance related to increased thiophene yield and/or decreased coke yield can be achieved by incorporating / associating sufficient alkali metal and/or alkaline earth metal into the zeotype framework structure prior to addition of the Cr. In some aspects, the alkali metals / alkaline earth metals can be associated with the zeotype framework structure based on being present in the synthesis mixture. For example, a base used for adjustment of pH in the synthesis mixture can correspond to a base that uses an alkali metal or alkaline earth metal as the counter-ion. In other aspects, alkali metal and/or alkaline earth metal can be added by ion exchange to form a substantially alkali- / alkaline earth-metal form zeotype.

[0018] In some aspects, it is believed that the presence of alkali metals and/or alkaline earth metals associated with the zeotype framework structure can allow for improved production of thiophene (including alkylated thiophenes) and/or can allow for reductions in coke formation. This is believed to be due to increased formation of CrSx phases with a stoichiometric ratio of Cr to S that is greater than 1. Chromium is capable of forming a variety of CrSx phases, including (but not limited to) CrS, CnSs, and CrsS4. In these CrSx phases, the oxidation state of the sulfur is generally understood to be -2. Thus, in CrS, the oxidation state of Cr is generally understood to be +2. In CnSs, the oxidation state of Cr is generally understood to be +3, while in CnS4, the oxidation state is generally understood to be a mixture of +2 and +3.

[0019] Without being bound by any particular theory, it is believed that the combination of having chromium sulfides that includes chromium in an elevated oxidation state; the presence of a zeotype framework structure to provide a “cage-like” environment; and the presence of alkali metals and/or alkaline earth metals associated with the zeotype framework structure, can contribute in a synergistic manner to provide improved activity and/or selectivity for thiophene production in combination with reduced or minimized selectivity for coke production.

[0020] With regard to chromium sulfides, it is believed that the presence of chromium in a higher oxidation state can facilitate allowing a chromium sulfide phase to donate a sulfur atom for formation of thiophene and/or an alkylated thiophene in combination with an alkane precursor. It is believed that removing the sulfur from the chromium sulfide results in a change in oxidation state for a Cr atom in a CrSx compound. When only CrS is available, removing a sulfur atom requires a Cr atom to undergo a change from a +2 oxidation state to metallic Cr. By contrast, when a phase such as CnSs or CrsS is available, a sulfur atom can be removed from the chromium sulfide while having only changes in oxidation state for Cr atoms from +3 to +2. [0021] It is further believed that the cage-like structure of the pore network of a zeotype framework may limit the speed of formation of substances with larger numbers of carbon-carbon bonds. By limiting the formation of larger complexes of carbons, this can increase the opportunities for formation of a carbon-sulfur bond as part of a complex containing eight atoms or less, or seven atoms or less, or six atoms or less, or five atoms or less. These small complexes can then have an increased opportunity to form a thiophene ring, as opposed to adding further carbon-carbon bonds and forming coke or a coke precursor.

[0022] Additionally or alternately, it is believed that a catalyst including a zeotype support can facilitate formation of layered domains of carbon sulfides. These layered domains can be viewed in a transmission electron microscope image of the sulfided catalyst. It is believed that these layered domains can contribute to the increased activity of chromium sulfides when supported on a zeotype support. Such layered domains are believed to correspond to a CnSs phase.

[0023] It is still further believed that the presence of the alkali metals and/or alkaline earth metals associated with the zeotype framework structure can assist with formation of thiophene and/or alkylated thiophenes in several ways. First, the presence of the alkali metals and/or alkaline earth metals associated with the zeotype framework structure may allow for formation of sulfide phases corresponding to mixtures of chromium and an alkali metal or alkaline earth metal. These mixed sulfide phases may further facilitate the ability for a sulfide phase to participate in a reaction to form a thiophene or alkylated thiophene. Additionally or alternately, the alkali metals and/or alkaline earth metals can be associated with acid sites in the zeotype framework structure. The presence of such metals can neutralize the acid sites (as opposed to having a hydrogen atom). It is believed that this neutralization of acid sites can reduce or minimize formation of coke during thiophene synthesis.

Definitions

[0024] In this discussion, a zeotype is defined to refer to a crystalline material having a porous framework structure built from tetrahedra atoms connected by bridging oxygen atoms. Examples of known zeotype frameworks are given in the “Atlas of Zeolite Frameworks” published on behalf of the Structure Commission of the International Zeolite Association”, 6^th revised edition, Ch. Baerlocher, L.B. McCusker, D.H. Olson, eds., Elsevier, New York (2007) and the corresponding web site, www.iza-structure.org/databases. In this discussion, a zeolite generally refers to crystalline structures having zeotype frameworks that contain only oxides of silicon and aluminum. In this discussion, a zeotype generally refers to crystalline structures having zeotype frameworks that are either zeolites or that may also containing oxides of heteroatoms different from silicon and aluminum. Such heteroatoms can include any heteroatom generally known to be suitable for inclusion in a zeotype framework, such as gallium, boron, germanium, phosphorus, zinc, and/or other transition metals that can substitute for silicon and/or aluminum in a zeotype framework. It is noted that under this definition, a zeotype can include materials such as silicoaluminophosphate (SAPO) materials, silicophosphate (SiPO) materials, or aluminophosphate (A1PO) materials.

[0025] A support material that includes a zeotype framework structure (i.e., a crystalline structure corresponding to a zeotype framework) can be referred to as a zeotype support. Optionally, a zeotype support (such as a zeolitic support) can include one or more oxides as a binder material in the support.

[0026] In this discussion, alkali metals include metals from Group 1 of the IUPAC Periodic Table, including lithium, sodium, potassium, rubidium, and cesium. In this discussion, alkaline earth metals include metals from Group 2 of the IUPAC Periodic Table, including magnesium, calcium, strontium, and barium.

[0027] In this discussion, an alkylated thiophene is defined as a thiophene that includes one or more alkyl chains attached to the thiophene ring.

[0028] In this discussion, Alpha value is a measure of the cracking activity of a catalyst and is described in U.S. Pat. No. 3,354,078 and in the Journal of Catalysis, Vol. 4, p. 527 (1965); Vol. 6, p. 278 (1966); and Vol. 61, p. 395 (1980), each incorporated herein by reference as to that description. The experimental conditions of the test used herein include a constant temperature of 538° C. and a variable flow rate as described in detail in the Journal of Catalysis, Vol. 61, page 395.

Alkali-Metal Form and Alkaline Earth-Metal Form Zeotypes

[0029] In various aspects, a catalyst for thiophene synthesis can include a zeotype support where the zeotype is substantially in alkali-metal form, substantially in alkaline earth-metal form, or substantially in alkali-metal and alkaline earth-metal form. This is in contrast to an “H- form” zeotype, where a substantial portion of of the acid sites of the zeotype framework structure are terminated by a hydrogen. Such H-form zeotypes can have higher Alpha values based on this increased acidity. Due to the nature of the thiophene synthesis reaction conditions, it is believed that such higher acidity zeotypes contribute to coke formation. This is also in contrast to zeotypes where the counterion for the acid sites is an amine or ammonium style counterion, or some other type of counterion that does not correspond to an alkali metal or an alkaline earth metal.

[0030] In this discussion, a “substantially alkali-metal form zeotype” or a “substantially alkali-metal form zeotype framework structure” is defined as a zeotype where a substantial portion of the acid sites in the zeotype framework structure are associated with / exchanged / occupied by an alkali metal ion. In this discussion, a “substantially alkaline earth-metal form zeotype” or a “substantially alkaline earth-metal form zeotype framework structure” is defined as a zeotype where a substantial portion of the acid sites in the zeotype framework structure are associated with / exchanged / occupied by an alkaline earth metal ion. In this discussion, a “substantially alkali-metal and alkaline earth-metal exchanged zeotype” or a “substantially alkali-metal and alkaline earth metal-exchanged zeotype framework structure” is defined as a zeotype where a substantial portion of the acid sites in the zeotype framework structure are associated with / exchanged / occupied by an alkali metal ion and/or an alkaline earth metal ion. It is noted that under these definitions, a “substantially alkali-metal and alkaline earth-metal form zeotype” is broad enough to cover zeotypes that include only alkali metals or only alkaline earth metals.

[0031] Based on current experimental methods, it is not usually feasible to directly quantify the number of potential acid sites in a zeotype that are associated with an alkali metal / alkaline earth metal, as opposed to being associated with a different counter-ion. However, it is well-understood how to form zeotypes that are substantially in alkali-metal form, in alkaline earth-metal form, or alkali-metal and alkaline earth-metal form. There are various ways for forming such zeotype framework structures.

[0032] One option for forming a substantially alkali-metal / alkaline earth-metal form zeotype is based on the initial synthesis of the zeotype. For many zeotypes, the typical synthesis solution for forming the zeotype framework structure includes addition of a base to achieve a desired pH in the synthesis mixture. One option for forming a substantially alkali-metal / alkaline earth-metal form zeotype is to include the alkali metal and/or alkaline earth metal as the counter-ion for at least a portion of the base included in the synthesis mixture. This can correspond to, for example, including sodium hydroxide (alkali metal counter-ion) or calcium hydroxide (alkaline earth metal counter-ion) as the base. In this discussion, if a synthesis mixture includes a hydroxide base (such as sodium hydroxide or calcium hydroxide), and if 50 wt% or more of the hydroxide base corresponds to an alkali metal hydroxide, the zeotype resulting from the synthesis mixture is defined as a substantially alkali-metal form zeotype. In this discussion, if a synthesis mixture includes a hydroxide base, and if 50 wt% or more of the hydroxide base corresponds to an alkaline earth metal hydroxide, the zeotype resulting from the synthesis mixture is defined as a substantially alkaline earth-metal form zeotype. In this discussion, if a synthesis mixture includes a hydroxide base, and if 50 wt% or more of the hydroxide base corresponds to at least one of an alkali metal hydroxide and an alkaline earth metal hydroxide, the zeotype resulting from the synthesis mixture is defined as a substantially alkali-metal and alkaline earth-metal form zeotype. It is noted that a “substantially alkali-metal or alkaline earth-metal form zeotype” can be formed directly from the initial synthesis mixture for forming the zeotype if the synthesis mixture includes a suitable source of alkali metal and/or alkaline earth metal.

[0033] For a zeotype that is in substantially alkali-metal form and/or substantially alkaline earth-metal form based on the nature of the synthesis mixture, it is understood that if a subsequent ion exchange procedure is performed on the zeotype, the exchanged zeotype may be converted to another form, such as H-form or ammonia-form. Thus, in order to achieve the unexpected benefits described herein of using a substantially alkali-metal form / alkaline earthmetal form zeotype, after forming a zeotype from a suitable synthesis mixture, such ion exchange should be avoided.

[0034] Another option for forming a substantially alkali-metal form / alkaline earth-metal form zeotype is to associate alkali metals / alkaline earth metals with the zeotype after synthesis but prior to impregnation / other addition of chromium to the zeotype support. This can be accomplished, for example, by ion exchange, incipient wetness impregnation, and/or any other convenient method for exposing the zeotype to a solution containing alkali metal ions and/or alkaline earth metal ions. For this type of ion exchange, an excess of the alkali metal ions / alkaline earth metal ions should be available. Many options are available for determining whether an excess is present. If the number of acid sites available per gram of zeotype is known, then a stoichiometric calculation can be performed. If the number of acid sites is not known, then one of various types of proxies can be used for providing an excess of alkali metal ions / alkaline earth metal ions. One proxy can be if the zeotype is exposed to a soluble form (such as a water soluble form) of metal salt, where a) 50 mol% or more of the metals in the solution correspond to alkali metals and/or alkaline earth metals, and b) the weight of the alkali metal salt and/or alkaline earth metal salt in the solution is equal to or greater than the weight of the zeotype that is contacted by the solution.

[0035] If the above condition is not met, another proxy can be based on the Alpha value of the resulting zeotype. After performing ion exchange on a zeotype, the Alpha value can be measured. If the Alpha value is 30 or less, a sample of the zeotype can then be exposed to ion exchange conditions using a second solution where the only metal ions in the second solution are the alkali metal ions / alkaline earth metal ions from the initial ion exchange, and where such ions are present in substantial excess. If the Alpha value prior to exposure to the second solution differs from the Alpha value after exposure to the second solution by 10% or less of the initial Alpha value, the initial zeotype can be considered to be substantially in alkali-metal form and/or alkaline earth-metal form. It is noted that such Alpha value characterization is typically not performed on a sulfided catalyst, and instead would be performed on the zeotype support prior to sulfidation, or possibly even prior to addition of chromium to the zeotype support.

[0036] Still another option for converting a zeotype framework structure to substantially alkali-metal form / alkaline earth-metal form is to perform ion exchange during and/or after addition of chromium to the zeotype support. The proxies described above can be used to determine whether such a zeotype is converted to substantially alkali-metal form / alkaline earthmetal form by this type of later addition of alkali metal / alkaline earth metal to the zeotype support.

Thiophene Catalyst and Synthesis Method

[0037] In various aspects, thiophene synthesis can be performed using a catalyst prepared by impregnating a zeotype support with chromium, calcining the impregnated support to form a catalyst precursor that includes chromium oxide(s), and then sulfiding the catalyst precursor to form a catalyst corresponding to chromium sulfide(s) supported on the zeotype support. In some aspects, additional benefits can be achieved if a zeotype support is a substantially alkali-metal and alkaline earth-metal form zeotype prior to addition of Cr. Such alkali metals and/or alkaline earth metals can be associated with a zeotype framework structure based on the presence of such metals in the synthesis solution for forming the zeotype framework structure. After synthesis, performing ion exchange with an alkali metal is an example of this type of neutralization of acid sites that can provide enhanced catalyst performance. Additionally or alternately, addition of alkali metals to neutralize acidic sites can also be performed during Cr impregnation and/or after Cr impregnation.

[0038] Without being bound by any particular theory, it is believed that the improved activity of the thiophene synthesis catalyst is related to the formation of chromium-sulfur compounds and/or complexes within the zeotype framework structure. Having alkali metals and/or alkaline earth metals associated with substantially all of the acidic sites (90% or more) of the zeotype framework structure appears to allow for formation of CnSs and/or CrsSr phases that do not appear to form when chromium is simply deposited on an oxide substrate. The CnSs and CnSr phase can be observed via XRD. Additionally, after using a catalyst for thiophene synthesis, layered chromium-sulfide phases can be observed via transmission electron microscopy (TEM). These layered phases are believed to correspond to CnSs. Additionally or alternately, neutralizing the acid sites with alkali metal may provide stabilization for chromium sulfides that have a higher oxidation state for the chromium. CnSs and CrsSr are examples of chromium sulfides with chromium in a higher oxidation state.

[0039] In various aspects, the unexpectedly improved activity for synthesis of thiophene (including alkylated thiophenes) and/or reduced coke production during thiophene synthesis can be due in part to having a catalyst where the average stoichiometric ratio of sulfur to chromium in the catalyst is greater than 1.0 to 1. In other words, expressed as a stoichiometric formula, the chromium sulfides in the catalyst can be described as having the formula CrSx, where “x” is greater than 1.0. In this definition, the value of “x” is not limited to integers. In this discussion, the average stoichiometry of chromium sulfides on a catalyst sample can be determined by using X-ray diffraction (XRD) on a sulfided catalyst. This can correspond to a catalyst prior to use, or a catalyst after use in thiophene synthesis. Although XRD cannot be used to quantitatively determine the relative amounts of various chromium sulfide phases, it is known that the lowest ratio of sulfur to chromium present in a chromium sulfide is a 1.0 to 1 ratio (CrS). All other phases of chromium sulfides have a ratio of sulfur to chromium greater than 1.0 to 1. Therefore, if any additional phases of chromium sulfide are detected by XRD, such as CnSs or CrsSi. the average stoichiometry for the sample will correspond to a sulfur to chromium ratio of greater than 1.0 (i.e., CrSx with x greater than 1.0). Thus, even though XRD cannot make quantitative comparisons between phases, XRD can be used to determine whether only CrS is present (x = 1.0) or whether chromium sulfide phases other than CrS are present (x > 1.0).

[0040] A wide variety of zeotype frameworks can be used as the support for a thiophene synthesis catalyst. Suitable zeotype frameworks can include “large pore” zeotypes and “medium pore” zeotypes. Large pore zeotypes have a largest pore channel with an average pore diameter of -0.65 nm or more, or -0.70 nm or more, such as possibly up to -1.0 nm. In some aspects, such large pore zeotypes can have a largest pore channel that corresponds to a 12-member ring in the zeotype framework. Medium pore zeotypes can have a largest pore channel with an average pore diameter of less than -0.70 nm, such as -0.50 nm to -0.70 nm. In some aspects, such medium pore zeotypes can have a largest pore channel that corresponds to a 10-member ring in the zeotype framework.

[0041] Some examples of large pore molecular zeotype frameworks can include FAU, which includes zeotypes such as USY and faujasite, and MWW, which includes zeotypes such as MCM-22 and MCM-49. Additional large pore zeotypes that can be employed in accordance with the present invention include both natural and synthetic large pore zeotypes. Non-limiting examples of natural large-pore zeotype frameworks include gmelinite, chabazite, dachiardite, clinoptilolite, faujasite, heulandite, analcite, levynite, erionite, sodalite, cancrinite, nepheline, lazurite, scolecite, natrolite, offretite, mesolite, mordenite, brewsterite, and ferrierite. Nonlimiting examples of synthetic large pore zeotype frameworks are zeolites X, Y, A, L. ZK-4, ZK-5, B, E, F, H, J, M, Q, T, W, Z, alpha, beta, omega, REY, and USY, as well as MSE framework materials (such as MCM-68). In some aspects, a large pore zeotype support can correspond to a zeolitic support (i.e., only oxides of silicon and aluminum in the zeotype framework structure).

[0042] Medium-pore size zeotype materials can include, but are not limited to, crystalline materials having a zeotype framework of MFI, MFS, MEL, MTW, EUO, MTT, HEU, FER, and TON. Non-limiting examples of such medium-pore size zeotypes include ZSM-5, ZSM-12, ZSM-22, ZSM-23, ZSM-34, ZSM-35, ZSM-38, ZSM-48, ZSM-50, silicalite, and silicalite 2. An example of a suitable medium pore zeotype can be ZSM-5, described (for example) in U.S. Pat. Nos. 3,702,886 and 3,770,614. Other suitable zeotypes can include ZSM-11, ZSM-12, ZSM-21, ZSM-38, ZSM-23, and ZSM-35. As mentioned above SAPOs, such as SAPO-11, SAPO-34, SAPO-41, and S APO-42 can also be used herein. Non-limiting examples of other medium pore zeotype frameworks that can be used herein include chromosilicates; gallium silicates; iron silicates; aluminum phosphates (A1PO), such as A1PO-11; titanium aluminosilicates (TASO), such as TASO-45; boron silicates; titanium aluminophosphates (TAPO), such as TAPO-11, and iron aluminosilicates.

[0043] The large-pore size zeotype framework structures and/or medium-pore size zeotype framework structures used herein can include "crystalline admixtures" which are thought to be the result of faults occurring within the crystal or crystalline area during the synthesis of the zeotypes. Examples of crystalline admixtures of ZSM-5 and ZSM-11 can be found in U.S. Pat. No. 4,229,424, incorporated herein by reference. The crystalline admixtures are themselves zeotypes, in contrast to physical admixtures of zeotypes in which distinct crystals of crystallites of different zeotypes are physically present in the same catalyst composite or hydrothermal reaction mixtures.

[0044] Optionally, prior to addition of Cr to a zeotype framework structure material, the zeotype framework structure can be combined with a binder. Any convenient weight ratio of zeotype framework structure to binder can be used. The amount of binder in the combined zeotype and binder composition can correspond to 10 wt% to 90 wt% of the composition, based on the weight of zeotype and binder only.

[0045] In some aspects, prior to addition of Cr to a zeotype support, the zeotype support can be in a form where the acidic sites in the zeotype framework structure are substantially neutralized. This can be achieved in any convenient manner. In some aspects, the initial synthesis of a zeotype material can allow for formation of a zeotype material with neutralized acid sites. For example, some zeotype synthesis methods use an alkali hydroxide (such as NaOH) and/or an alkaline earth hydroxide (such as CaOH) as part of the synthesis mixture for forming the zeotype. This results in a zeotype where substantially all of the acidic sites (90% or more) in the zeotype framework structure are neturalized with ions of an alkali metal (such as Na or K) and/or an alkaline earth metal (such as Mg or Ca). In other aspects, ion exchange can be performed on a zeotype to exchange acidic sites (typically terminated by hydrogen) with an alkali metal. In yet other aspects, alkali metal ion exchange can be performed during and/or after impregnation of a zeotype support with Cr. While this can be at least partially effective, it is believed that unexpectedly improved activity / selectivity for thiophene production can be achieved when neutralization with an alkali metal / alkaline earth metal is performed prior to impregnation with Cr. It is believed that still further unexpectedly improved activity / selectivity for thiophene production can be achieved when sufficient alkali metal and/or alkaline earth metal is present in the synthesis solution to form a substantially alkali metal- and alkaline earthmetal form zeotype.

[0046] In addition to having a substantially alkali metal- and alkaline earth-metal zeotype, the zeotype support can also be impregnated with Cr. This can be performed in any convenient manner, such as by incipient wetness. For example, a solution of a Cr salt can be formed, such as a solution of chromium (III) nitrate nonahydrate in water. A material containing a zeotype framework structure (such as USY, MCM-49, or ZSM-5) can be exposed to the solution containing the Cr salt. The resulting material can then optionally be dried to remove water while leaving behind the Cr. Examples of drying steps can include exposing the resulting material to a temperature of 80°C to 200°C. Drying can be performed for a convenient period of time, such as 0.5 hours to 24 hours. Due to the relatively low temperature during a drying procedure, either an inert atmosphere or an oxygen-containing atmosphere (such as air) can be used during the drying procedure.

[0047] In various aspects, the amount of Cr supported on a zeotype support can be from 1.0 wt% to 20 wt%, or 1.0 wt% to 12 wt%, or 1.0 wt% to 8.0 wt%, or 3.0 wt% to 20 wt%, or 3.0 wt% to 12 wt%, or 3.0 wt% to 8.0 wt%, or 5.0 wt% to 20 wt%, or 5.0 wt% to 12 wt%, or 5.0 wt% to 8.0 wt%. In aspects where the zeotype support includes both a zeotype framework structure and a binder, the amount of Cr on the zeotype support corresponds to the amount of Cr on the combined weight of zeotype plus binder.

[0048] Optionally, an additional ion exchange / incipient wetness procedure using an alkali metal salt and/or an alkaline earth metal salt can be performed after impregnating the zeotype support with the Cr. This optional addition of alkali metal and/or alkaline earth metal after impregnation with Cr can assist with further neutralization of acidic sites after impregnation with Cr.

[0049] After impregnating the zeotype support with Cr (and after any other metal impregnation / ion exchange, such as addition of alkali metals and/or alkaline earth metals to neutralize acid sites), the resulting Cr-impregnated zeotype support can be exposed to a calcining step in an oxygen-containing environment in order to form a catalyst precursor that includes chromium oxide. Calcination can be performed at a temperature of 300°C to 650°C. Air, such as flowing air, is an example of a suitable oxy gen-containing atmosphere. Calcination can be performed for a convenient period of time, such as 0.5 hours to 24 hours.

[0050] After forming a catalyst precursor, the catalyst precursor can be sulfided to form a thiophene synthesis catalyst. For example, a catalyst precursor can be exposed to a gas-phase sulfiding agent, such as H2S, at a sulfidation temperature for a period of time. During sulfidation, the H2S can be mixed with one or more diluent gases, such as N2, to allow for control over the rate of sulfidation. Sulfidation of the catalyst precursor can be performed at a temperature ranging from 400°C to 600°C, or 500°C to 600°C. The catalyst precursor can be sulfided for a period of time ranging from 1.0 hours to 8.0 hours. Examples of sulfiding agents can include, but are not limited to, H2S, CS2, S2, dimethyl disulfide, and t-butyl polysulfide.

[0051] Sulfidation of the catalyst precursor results in formation of a catalyst that includes chromium sulfide(s) supported on the zeotype support. The sulfide(s) on the zeotype support, as detectable by X-Ray Diffraction (XRD), can include but are not limited to CnSs. CrS, CrsSi. and combinations thereof.

Alternative Catalysts for Thiophene Synthesis

[0052] In addition to chromium sulfide(s) supported on a zeotype support, various other types of catalysts can potentially be used for thiophene formation based on a gas phase reaction of alkanes with a gas-phase sulfur compound.

[0053] One example of an alternative catalyst can be formed from a catalyst precursor including Sr Os. The SrrnOs can be supported on a refractory oxide (such as silica or alumina) and/or on a zeotype support. Optionally, an alkali metal can also be impregnated on such a catalyst precursor. The catalyst precursor can be converted to a catalyst by gas phase sulfidation. [0054] Another example of an alternative catalyst corresponds to a catalyst including chromium sulfide and an alkali metal oxide supported on alumina (or another refractory oxide). This is the type of catalyst currently used for thiophene production when using alcohols (instead of alkanes) as the starting reagent.

[0055] Still other examples of alternative catalysts can be catalysts that include Ni, Co, Mo, W, V, or a combination thereof, supported on a support. The support can correspond to a refractory oxide and/or a zeotype support. Optionally, an alkali metal can also be impregnated on the catalyst precursor for forming such a catalyst prior to sulfidation.

Thiophene Synthesis Conditions

[0056] In various aspects, thiophene synthesis can be performed by exposing a plurality of gas phase feedstocks to a thiophene synthesis catalyst. At least one feedstock can correspond to a feedstock containing C4+ alkanes, such as n-butane, a mixture of butanes, n-pentane, a mixture of n-butane and n-pentane, a mixture of butane(s) and pentane(s), n-hexane and/or any other convenient combination of alkanes that contain 4 or more carbons. The C4+ alkanes in the plurality of gas phase feedstocks can correspond to any convenient combination of n-alkanes and branched alkanes (i.e., alkanes that contain at least one branch but that do not include a ring structure). In some aspects, branched alkanes can correspond to 25 wt% or less of the total weight of alkanes in the gas phase feesdstocks, or 10 wt% or less, or 5.0 wt% or less, or 1.0 wt% or less, such as down to having substantially no content of branched alkanes. In some aspects, the plurality of gas phase feedstocks can include 10 wt% or less of C5+ hydrocarbons relative to the total weight of hydrocarbons in the gas phase feedstocks, or 5.0 wt% or less, or 1.0 wt% or less, such as down to having substantially no C5+ hydrocarbons. In some aspects, the C4+ alkanes can correspond to C4 to Ci6 alkanes, C4 to C12 alkanes, or C4 to Cs alkanes.

[0057] In some aspects the plurality of gas phase feedstocks can include 50 wt% or more of alkanes relative to the total weight of hydrocarbons in the gas phase feedstocks, or 75 wt% or more, or 90 wt% or more, or 95 wt% or more, or 99 wt% or more, such as up to having alkanes as substantially the only hydrocarbons in the gas phase feedstocks. Additionally or alternately, in some aspects the plurality of gas phase feedstocks can include 50 wt% or more of n-alkanes relative to the total weight of hydrocarbons in the gas phase feedstocks, or 75 wt% or more, or 90 wt% or more, or 95 wt% or more, or 99 wt% or more, such as up to having n-alkanes as substantially the only hydrocarbons in the gas phase feedstocks. Further additionally or alternately, in some aspects the plurality of gas phase feedstocks can include 50 wt% or more of n-butane relative to the total weight of hydrocarbons in the gas phase feedstocks, or 75 wt% or more, or 90 wt% or more, or 95 wt% or more, or 99 wt% or more, such as up to having n-butane as substantially the only hydrocarbon in the gas phase feedstocks.

[0058] Optionally, the plurality of feedstocks can also include C4+ alkenes. In some aspects, relative to the total hydrocarbons in the input flow(s), the C4+ alkenes can correspond to 25 wt% or less of the input flow(s), or 10 wt% or less, or 5.0 wt% or less, or 1.0 wt% or less, such as down to have substantially no alkenes in the gas phase feedstocks. The C4+ alkenes can correspond to n-butene (corresponding to 1 -butene, cis-2-butene, trans-2 -butene, or a combination thereof), isobutene, n-pentene, isopentane, n-hexene and/or any other convenient combination of n-alkenes and branched alkenes. Optionally, the C4+ alkenes can include dienes. [0059] Additionally, at least one feedstock can correspond to a gas phase source of sulfur. Gas phase sources of sulfur can include, but are not limited to, H2S, CS2, S2, and/or other forms of sulfur that can be present in a gas phase flow at temperatures near the reaction temperature for thiophene synthesis. [0060] The plurality of gas phase feedstocks can be introduced into a reactor as a single stream, or the gas phase feedstocks can be introduced as a plurality of streams. The reactor volume (or a portion thereol) can serve as the reaction environment for the thiophene synthesis reaction. Optionally, when a plurality of streams are introduced into the reaction environment, different input streams can have different compositions. For example, one option can be to have a first feed stream containing one or more alkanes and a second feed stream containing one or more gas phase sulfur sources. Any convenient type of vessel can be used as a reactor, so long as the vessel is suitable for maintaining the reactants in the reaction environment at the synthesis conditions for an average synthesis residence time.

[0061] In various aspects, a molar ratio of sulfur atoms in the reaction environment to hydrocarbons in the reaction environment can range from 0.9 to 30 (i.e., range from 0.9 moles of sulfur atoms per mole of hydrocarbons to 30 moles of sulfur atoms per mole of hydrocarbons). In some aspects, the molar ratio of sulfur atoms to hydrocarbons in the reaction environment can be from 0.9 to 30, or 0.9 to 15, or 0.9 to 10, or 1.0 to 30, or 1.0 to 15, or 1.0 to 10, or 1.5 to 30, or 1.5 to 15, or 1.5 to 10, or 2.5 to 30, or 2.5 to 15, or 2.5 to 10. Additionally or alternately, the molar ratio of H2S to hydrocarbons in the reaction environment can be from 0.9 to 15, or 0.9 to 10, or 1.0 to 15, or 1.0 to 12, or 1.0 to 10, or 1.5 to 15, or 1.5 to 10, or 2.5 to 15, or 2.5 to 10.

[0062] In the reaction environment, the average residence time can be 0.01 seconds to 100 seconds, or 0.1 seconds to 100 seconds, or 1.0 second to 100 seconds, or 0.01 seconds to 50 seconds, or 0.1 seconds to 50 seconds, or 1.0 seconds to 50 seconds, or 0.01 seconds to 10 seconds, or 0.1 seconds to 10 seconds, or 1.0 seconds to 10 seconds. The temperature in the reaction environment can be 450°C to 750°C, or 450°C to 650°C, or 450°C to 600°C, or 450°C to 550°C, or 500°C to 750°C, or 500°C to 650°C, or 500°C to 600°C, or 550°C to 750°C, or 550°C to 650°C. The pressure in the reaction environment can range from 0 kPa-g to 1750 kPa- g, or 0 kPa-g to 1050 kPa-g, or 0 kPa-g to 350 kPa-g, or 15 kPa-g to 1750 kPa-g, or 15 kPa-g to 1050 kPa-g, or 15 kPa-g to 350 kPa-g, or 150 kPa-g to 1750 kPa-g, or 150 kPa-g to 1050 kPa-g, or 150 kPag- to 350 kPa-g.

[0063] Exposing a feedstock corresponding to a gas phase sulfur source and a feedstock including alkanes (such as n-butane) to a thiophene synthesis catalyst can result in production of thiophene along with side products and/or unreacted reagents. The products from the reaction can include, but are not limited to, thiophene and/or alkylated thiophene; coke; a purge stream corresponding to C4- or C3- hydrocarbons; C4 to C10 hydrocarbons (including unreacted C4+ hydrocarbons); one or more sulfur compounds (such as H2S, CS2, S2, and/or other forms of gas phase sulfur; and C10+ hydrocarbons. The C10+ hydrocarbons can, for example, be sent to a hydroprocessing unit for production of fuels. The C4 to C10 hydrocarbons can, for example, be used as a light alkane product; can be recycled back to the reactor; or a separation can be performed to at least partially separate olefins from the C4 to C10 hydrocarbons prior to recycle to the reactor. It is noted that other choices could be made for which hydrocarbons are recycled versus sent to hydroprocessing for forming fuels. For example, the intermediate hydrocarbon stream (optionally used for recycle) can correspond to a C4 to Ce stream, or a C4 to Cs stream, or a C4 to C10 stream, or a C4 to C12 stream, or a C4 to Ci6 stream. Depending on the hydrocarbons chosen for inclusion in the lighter hydrocarbon stream, the hydrocarbons used for fuel production can correspond to Ce+ hydrocarbons, or Cs+ hydrocarbons, or C10+ hydrocarbons, or C12+ hydrocarbons, or Ci6+ hydrocarbons. Still another option could be to separate the hydrocarbons into a larger plurality of fractions. In some aspects, depending on the efficiency of the separation, the “heavy” stream sent to hydroprocessing for fuel production may not have any overlap in composition with the recycle stream. For example, if the recycle stream corresponds to a C4 to Cs stream, the “heavy” stream may optionally correspond to a stream containing C9+ compounds, with a Cs- content of 5.0 wt% or less, or 1.0 wt% or less, such as down to having substantially no content of Cs- hydrocarbons.

[0064] During the thiophene synthesis reaction, some sulfur is consumed for production of thiophene and/or alkylated thiophene. Because the thiophene synthesis conditions often include a stoichiometric excess of sulfur, at least a portion of the reaction products (including unreacted reagents) can typically correspond to some type of sulfur-containing compound. For example, in the reaction product stream identified above, one or more of the purge or light hydrocarbon stream (such as C4-), the intermediate hydrocarbon (such as C4 - C10), and the heavy hydrocarbon stream (such as C10+) can include sulfided organic compounds. Due to the atomic weight of sulfur, this can cause some mixing of the carbon numbers present within a stream. For example, a Cs sulfided compound could potentially correspond to a compound that is separated into a C10+ fraction.

Reaction Products and Further Processing

[0065] After performing thiophene synthesis, various portions of the reaction products can undergo some type of further processing. One type of further processing can be to perform one or more separations to recover the thiophene and/or alkylated thiophenes from the remaining reaction products and/or unreacted reagents. This separation can also produce one or more additional streams, such as a stream of light hydrocarbons (C3-), a stream of intermediate hydrocarbons (such as C4 - C10 hydrocarbons), a stream of heavier hydrocarbons (such as a C10+ stream), and a stream of H2S. Optionally, CS2 can also be a reaction side product. A substantial amount of coke is also formed.

[0066] After separating reaction products, various additional processes can be performed. One type of additional processing can be to hydroprocess the heavier hydrocarbons for use as a fuel. Another type of additional process can be to recycle portions of the reaction effluent back to the reaction environment. For example, at least a portion of the H2S and/or the intermediate hydrocarbons recovered from the reaction environment can be recycled for use as a feedstock. [0067] It is noted that both the intermediate hydrocarbon product (e.g., C4 - C10) and the heavier hydrocarbon product (e.g., C10+ stream) can potentially include compounds that correspond to dimers of thiophene and/or alkylated thiophenes that are different from the target product of the synthesis reaction. These dimers of thiophene and/or alkylated thiophenes can potentially also serve as oligomerization precursors for formation of polythiophene.

[0068] Still another processing option can be to use the H2S recovered from the reaction environment as a source of H2 and gas phase sulfur (such as S2). In this type of aspect, H2S from the reaction environment can be introduced into an electrochemical cell to form H2 and S2 (or another form of sulfur). The S2 can be used as a feedstock for thiophene synthesis. The H2 can be used in any convenient manner.

Configuration Examples

[0069] FIG. 1 shows an example of a reaction system configuration for production of thiophene. In FIG. 1, a feedstock 11 containing alkanes (such as n-butane or n-alkanes) and a gas phase sulfur feedstock 12 corresponding to S2 (and/or other gas phase molecules containing only sulfur) can be introduced into a reactor 20. In the configuration shown in FIG. 1, feedstock 11 and gas phase sulfur feedstock 12 are shown as separate input streams. In other aspects, any convenient number of input flows can be used to introduce feedstock 11 and gas phase sulfur feedstock 12 into reactor 20. In addition to feedstock 11 and gas phase sulfur feedstock 12, one or more recycle streams can optionally be introduced into reactor 20. In the configuration shown in FIG. 1, the recycle streams include an H2S recycle stream 39, an H2S makeup stream 19, and a C4+ hydrocarbon recycle stream 31.

[0070] The reactor 20 can be used to perform a thiophene synthesis reaction. The effluent 25 from the reaction can then be passed into one or more separation stages. In FIG. 1, the one or more separation stages are represented by a fractionator 30. In the example configuration shown in FIG. 1, fractionator 30 can be used to separate effluent 25 into a plurality of streams. This can include hydrocarbon recycle stream 31, H2S recycle stream 39, a light hydrocarbon (C4- or C3-) purge stream 33, a product stream 35 that includes thiophene and/or alkylated thiophenes, and a heavy hydrocarbon stream 37 containing hydrocarbons that are (on average) higher boiling than the hydrocarbons in hydrocarbon recycle stream 31.

Synthesis Catalysts

[0071] Three groups of potential catalyst precursor for thiophene synthesis catalysts were prepared. A first group of catalyst precursors corresponded to transition metal oxides, optionally in combination with an alkali metal oxide, supported on alumina or silica supports. A second group of catalyst precursors corresponded to chromium or molybdenum oxides, optionally in combination with an alkali metal oxide, supported on a zeotype support. A third group of catalyst precursors corresponded to catalyst precursors based on Sr Os.

[0072] After forming the catalyst precursors, the precursors were sulfided in the presence of H₂S at 550°C.

Examples 1 to 5 Catalyst Precursors with Alumina or Silica Supports

[0073] For the first group of catalysts, the general synthesis method was to start with a support corresponding to Versal 300 Alumina. A transition metal reagent was dissolved in water and then impregnated on the alumina. The resulting solid was then dried at 120°C for 3 to 4 hours and calcined at 550°C for 6 hours with continuous air flow at a ramp rate of 3°C per minute with continuous air flow. If an alkali metal oxide was also added, the alkali metal oxide was dissolved in water, impregnated on the support (after impregnation with the transition metal), dried at 120°C for 4 hours and then calcined at 350°C at 6 hours under continuous air flow.

[0074] The catalyst precursors made according to this method were 20 wt% CnOs on alumina (Example 1); 1.5 wt% K2O / 20 wt% CnCh on alumina (Example 2); 20 wt% V2O5 on alumina (Example 3); 1.5 wt% K2O / 20 wt% V2O5 on alumina (Example 4); 20 wt% molybdenum oxide on alumina (Example 5); and C0M0 on silica (roughly 20 wt% C0M0, 4 : 3 molar ratio of Co to Mo). Examples of reagents used for the catalyst synthesis include Versal 300 alumina; chromium (III) nitrate nonahydrate; and ammonium molybdate tetrahydrate. Examples 6 to 10 - Catalyst Precursors with Zeotype Supports

[0075] Example 6: 10 wt% CnCh on ZSM-5. ZSM-5 was synthesized according to a conventional synthesis method using ammonium hydroxide as the base for adjusting the pH of the synthesis mixture. Chromium (III) nitrate nonahydrate, 16.6 g, was dissolved in 24 ml of deionized water. The solution was impregnated onto 30.6 g of ZSM-5. The resulting solid was dried at 120°C for 6 hours, and calcined at 550°C for 6 hours with air flow.

[0076] Example 7: 5.0 wt% MoOs on ZSM-5. Ammonium heptamolybdate tetrahydrate,

1.84 g, was dissolved in 30 ml of deionized water. The solution was impregnated onto 30 g of ZSM-5. The ZSM-5 corresponded to a substantially fully sodium-metal form due to the presence of sodium in the synthesis environment. The resulting solid was dried at 120°C for 4 hrs and calcined at 550°C for 6 hrs under continuous air flow.

[0077] Example 8: 5.0 wt% C'nOs on ZSM-5. Chromium (III) nitrate nonahydrate, 7.9 g, was dissolved in 30 ml of deionized water. The solution was impregnated onto 30 g of ZSM-5. The ZSM-5 corresponded to a substantially sodium-metal form due to the presence of sodium in the initial ZSM-5 synthesis environment. The resulting solid was dried at 120°C for 4 hrs and calcined at 550°C for 6 hrs under continuous air flow.

[0078] Example 9: 5.0 wt% CnCh on USY. 30 g of USY was impregnated with 7.9 g of chromium (III) nitrate nonahydrate dissolved in 30 cc of deionized water. The USY was a low acidity version that was substantially sodium-metal form due to the presence of sodium in the initial USY synthesis environment. The resulting solid was dried at 120°C for 4 hrs. Potassium nitrate, 1.3 g, was dissolved in 30 cc of deionized water and impregnated onto the dried sample. It was dried at 120°C for 6 hrs and calcined at 550°C for 6 hrs under continuous air flow.

[0079] Example 10: 5.0 wt% CnCh on MCM-49. MCM-49, 30 g, was impregnated with 7.9 g of chromium (III) nitrate nonahydrate dissolved in 30 cc deionized water. Due to the nature of the MCM-49 synthesis, the MCM-49 was partially hydrogen-terminated prior to the chromium oxide impregnation, as an alkali metal or alkaline earth metal was not included in the synthesis mixture. The resulting solid was dried at 120°C for 4 hrs and calcined at 550°C for 6 hrs under continuous air flow. After the chromium oxide impregnation, the resulting solid was further impregnated with 1.3 g of KNCh dissolved in 30 cc of deionized water. Same drying and calcination procedure was repeated.

Examples 11 to 14 - Additional Catalysts

[0080] Example 11: 7.0 wt% SrmOs on SiCh. A samarium precursor was impregnated on a silica support, followed by drying and calcination. 10 g of Sm(NO3)3.6H2O was dissolved in 30 cm³ of water in a glass beaker. This solution was used for the incipient wetness impregnation of 25.75 g of Davisil 646 silica (previously calcined overnight at 500°C under air). After impregnation, the resulting material was calcined overnight at 500°C to yield a material where XRF showed 7% Sm loading.

[0081] Example 12: 7.0 wt% SrmCti on USY. A samarium precursor was impregnated on a highly siliceous USY support, followed by drying and calcination. 11 g of Sm(NO3)3.6H2O was dissolved in 20 cm³ of water in a glass beaker. This solution was used for the incipient wetness impregnation of 21 g of a high silica to alumina ratio USY (previously calcined overnight at 500°C under air). After impregnation, the resulting material was calcined overnight at 500°C.

Testing Apparatus

[0082] The catalysts were loaded into a quartz reactor as a bed and sulfided as described above to form sulfided catalyst. After sulfidation, the resulting catalyst was exposed to a gas flow containing 5.0% N2, 14.0% C4H10, 14.0% S2, and 66.5% H2S. The S2 was added to the feed by using the H2S as a sweep gas over liquid S2 at a temperature of 150°C. The H2S and S2 were then combined with the remaining portions of the feed and the feed was heated to 350°C prior to exposure to the catalyst. The quartz reactor was maintained at 550°C during exposure to the feed. The feed was exposed to the catalyst at roughly atmospheric pressure (roughly 100 kPa-a). The reaction system did not include recycle, so the results generated correspond to “single pass” reactivity.

[0083] Table 1 shows results from exposing the feed to the various catalysts corresponding to Examples 1 to 5. In Table 1, “% conversion” is the amount of conversion of the n-butane in the feed; “% thiophene selectivity” is the weight percent of the conversion product that corresponds to thiophene; “% thiophene yield” corresponds to the weight percent of thiophene relative to the weight of the feed; “% coke yield” is the weight percent of the conversion product that corresponds to coke. It is noted that in Tables 1, 2, and 3, to the degree that the thiophene yield plus coke yield corresponds to less than 100%, the balance of the yield corresponds to either light ends (C3-) or a liquid (optionally sulfided) product. Other than coke formation on the catalyst, a tar-like or solid product was not observed after testing of any of the examples.

Table 1 - Thiophene Synthesis for Examples 1 to 5

[0084] As shown in Table 1, Example 2 provided the best overall combination of thiophene selectivity, thiophene yield, and coke yield. It is noted that the conversion for Example 2 is lower than the conversion for Example 1. However, even if recycle was used, the coke yield for the catalyst in Example 2 would be substantially lower than any of the other catalysts. The addition of the alkali metal in Examples 4 and 5 also appeared to mitigate coke formation, but from a higher baseline level.

[0085] Table 2 shows results from testing of Examples 6 - 10.

Table 2 - Thiophene Synthesis for Examples 6 to 10

[0086] Table 2 illustrates the unexpected nature of the benefits of using chromium sulfides supported on a substantially alkali metal-form (and/or substantially alkaline earth-metal form) zeotype support. As shown in Table 2, using a zeotype support without having alkali metals and/or alkaline earth metals for acid neutralization (Example 6) resulted in low thiophene production combined with high coke selectivity. In Example 7, the same type of zeotype support used in Example 8 was used to support a molybdenum catalyst. This also resulted in substantial coke formation and low thiophene yield. However, by using a substantially alkali-metal form zeotype support in combination with chromium as a catalytic metal (Examples 8 and 9), it was unexpectedly found that high butane conversions were achieved in combination with high thiophene selectivity and low coke yield. It is noted that treatment with alkali metal after impregnation with chromium (Example 10) provided unexpectedly low coke selectivity, but at lower alkane conversion. Thus, it appears that achieving a substantially alkali-metal and/or alkaline earth-metal form for the zeotype support prior to chromium impregnation provided the additional advantage of combining high alkane conversion with low coke yield.

[0087] Table 3 shows the results from thiophene production using the catalysts from Examples 11 - 12.

Table 3 - Thiophene Synthesis for Examples 11 to 12

[0088] As shown in Table 3, the samarium oxide catalysts had relatively low coke selective and reasonable thiophene selectivity, although with only modest alkane conversion. However, the results in Table 3 show that samarium oxide can provide another option for thiophene conversion with favorable amounts of thiophene yield versus coke yield.

[0089] Based on the favorable results for Examples 8 - 9, the catalyst from Example 9 was analyzed further using transmission electron microscopy (TEM). FIG. 2 shows a TEM micrograph of the sulfided catalyst. As shown in FIG. 2, regions 310, 320, and 330 correspond to examples of regions that show a layered structure that is separate from the crystal structure of the USY support. It is believed that the layered structures (such as the structures in regions 310, 320, and 330) are indicators of a layered chromium sulfide phase that can unexpectedly facilitate improved thiophene synthesis results. This phase can be formed when a zeotype support that is substantially in alkali-metal and/or alkaline earth-metal form is used as a support for a chromium sulfide catalyst.

Example 13 - Characterization of Liquid Product

[0090] As noted above a liquid product including at least hydrocarbons and sulfided hydrocarbons was formed under the synthesis conditions. The liquid product generated from the testing of the catalyst in Example 8 was further characterized using gas chromatography - mass spectrometry (GC-MS) to identify compounds within the liquid product.

[0091] FIG. 3 shows examples of compounds that were detected by GC-MS in the liquid product. It is noted that some still larger compounds may have been formed, but the compounds detected were limited based on the compounds that could be readily volatilized in the gas chromatography apparatus. As shown in FIG. 3, a variety of 1 -ring and 2-ring sulfur-containing compounds were formed, including thiophene, various alkylated thiophenes, benzothiophene, various alkylated benzothiophenes, bithiophenes, and bienothiophene (two fused thiophene rings). Additionally, as indicated by the bottom chemical structure in FIG. 3, a variety of alkylated benzenes (as well as unsubtituted benzene) were also detected.

Additional Embodiments

[0092] Embodiment 1. A sulfided catalyst, comprising: a support comprising a) a substantially alkali-metal form zeotype framework structure, b) a substantially alkaline earthmetal form zeotype framework structure, or c) a substantially alkali-metal and alkaline earthmetal form zeotype framework structure, the zeotype framework structure having a 10-member ring pore channel or a 12-member ring pore channel as the largest pore channel; and 1.0 wt% to 10 wt% of chromium sulfide relative to a weight of the sulfided catalyst, the chromium sulfide having an average stoichiometry of CrSx, where x is greater than 1.0.

[0093] Embodiment 2. The sulfided catalyst of Embodiment 1, wherein the sulfided catalyst comprises a layered chromium sulfide phase.

[0094] Embodiment 3. The sulfided catalyst of any of the above embodiments, wherein the zeotype framework structure is in a) substantially alkali-metal form, b) substantially alkaline earth-metal form, or c) substantially alkali-metal and alkaline earth-metal form prior to adding chromium to the support.

[0095] Embodiment 4. A catalyst precursor, comprising: a support comprising a) a substantially alkali-metal form zeotype framework structure, b) a substantially alkaline earthmetal form zeotype framework structure, or c) a substantially alkali-metal and alkaline earthmetal form zeotype framework structure, the zeotype framework structure having a 10-member ring pore channel or a 12-member ring pore channel as the largest pore channel; and 1.0 wt% to 10 wt% of CoOs relative to a weight of the catalyst precursor, wherein the support is in substantially alkali-metal form, substantially alkaline earth-metal form, or substantially alkali- metal and alkaline earth-metal form prior to adding chromium to the support. [0096] Embodiment 5. The catalyst precursor of Embodiment 4, where the catalyst precursor further comprises 0.5 wt% to 2.5 wt% of an alkali oxide, and alkaline earth oxide, or a combination thereof relative to a weight of the catalyst precursor.

[0097] Embodiment 6. The sulfided catalyst or catalyst precursor of any of the above embodiments, wherein the zeotype framework structure comprises a zeotype framework of FAU, MFI, MWW, or a combination thereof.

[0098] Embodiment 7. The sulfided catalyst or catalyst precursor of any of the above embodiments, wherein the support further comprises a binder.

[0099] Embodiment 8. The sulfided catalyst or catalyst precursor of any of the above embodiments, wherein the support comprises a substantially alkali-metal form zeotype framework structure, the alkali metal optionally comprising sodium, potassium, or a combination thereof.

[0100] Embodiment 9. The sulfided catalyst or catalyst precursor of any of Embodiments 1 to 4, wherein the support comprises a substantially alkaline earth-metal form zeotype framework structure, the alkaline earth metal optionally comprising magnesium, calcium, or a combination thereof.

[0101] Embodiment 10. The sulfided catalyst or catalyst precursor of any of the above embodiments, wherein the zeotype framework structure comprises a zeolite framework structure.

[0102] Embodiment 11. The sulfided catalyst or catalyst precursor of any of the above embodiments, wherein the zeotype framework structure is synthesized in a) substantially alkali- metal form, b) substantially alkaline earth-metal form, or c) substantially alkali-metal and alkaline earth-metal form.

[0103] Embodiment 12. A method of making thiophene, an alkylated thiophene, or a combination thereof, comprising: exposing a first feedstock comprising one or more C4 to Ci6 alkanes and a second feedstock comprising a gas phase sulfur source to a sulfided catalyst according to any of Embodiments 1 to 3 or 6 to 11 under thiophene synthesis conditions, to form an effluent comprising thiophene, an alkylated thiophene, or a combination thereof.

[0104] Embodiment 13. The method of Embodiment 12, wherein the one or more C4 to Ci6 alkanes comprise n-butane, or wherein the first feedstock further comprises one or more C4 to C10 alkenes, or a combination thereof.

[0105] Embodiment 14. The method of Embodiment 12 or 13, wherein the one or more C4 to Ci6 alkanes comprise one or more C4 to Cs alkanes. [0106] Embodiment 15. The method of any of Embodiments 12 to 14, wherein the effluent further comprises C4+ alkanes, and wherein the first feedstock comprises a recycle portion of the C4+ alkanes.

[0107] Additional Embodiment A. A method of making thiophene, an alkylated thiophene, or a combination thereof, comprising: exposing a first feedstock comprising one or more C4 to Ci6 alkanes and a second feedstock comprising a gas phase sulfur source to a synthesis catalyst under thiophene synthesis conditions, to form an effluent comprising thiophene, an alkylated thiophene, or a combination thereof, the synthesis catalyst comprising i) a support comprising a) a substantially alkali-metal form zeotype framework structure, b) a substantially alkaline earthmetal form zeotype framework structure, or c) a substantially alkali-metal and alkaline earthmetal form zeotype framework structure, the zeotype framework structure having a 10-member ring pore channel or a 12-member ring pore channel as the largest pore channel; and 1.0 wt% to 10 wt% of chromium sulfide relative to a weight of the sulfided catalyst, the chromium sulfide having an average stoichiometry of CrSx, where x is greater than 1.0; or ii) a catalyst formed by sulfidation of a catalyst precursor comprising Sr Os.

[0108] While the present invention has been described and illustrated by reference to particular embodiments, those of ordinary skill in the art will appreciate that the invention lends itself to variations not necessarily illustrated herein. For this reason, then, reference should be made solely to the appended claims for purposes of determining the true scope of the present invention.

Claims

CLAIMS What is claimed is:

1. A sulfided catalyst, comprising: a support comprising a) a substantially alkali-metal form zeotype framework structure, b) a substantially alkaline earth-metal form zeotype framework structure, or c) a substantially alkali-metal and alkaline earth-metal form zeotype framework structure, the zeotype framework structure having a 10-member ring pore channel or a 12-member ring pore channel as the largest pore channel; and

1.0 wt% to 10 wt% of chromium sulfide relative to a weight of the sulfided catalyst, the chromium sulfide having an average stoichiometry of CrSx, where x is greater than 1.0.

2. The sulfided catalyst of claim 1, wherein the zeotype framework structure comprises a zeotype framework of FAU, MFI, MWW, or a combination thereof.

3. The sulfided catalyst of claim 1, wherein the support further comprises a binder.

4. The sulfided catalyst of claim 1, wherein the support comprises a substantially alkali- metal form zeotype framework structure, the alkali metal comprising sodium, potassium, or a combination thereof.

5. The sulfided catalyst of claim 1, wherein the support comprises a substantially alkaline earth-metal form zeotype framework structure, the alkaline earth metal comprising magnesium, calcium, or a combination thereof.

6. The sulfided catalyst of claim 1, wherein the zeotype framework structure comprises a zeolite framework structure.

7. The sulfided catalyst of claim 1, wherein the sulfided catalyst comprises a layered chromium sulfide phase.

8. The sulfided catalyst of claim 1, wherein the zeotype framework structure is synthesized in a) substantially alkali-metal form, b) substantially alkaline earth-metal form, or c) substantially alkali-metal and alkaline earth-metal form.

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9. The sulfided catalyst of claim 1, wherein the zeotype framework structure is in a) substantially alkali-metal form, b) substantially alkaline earth-metal form, or c) substantially alkali-metal and alkaline earth-metal form prior to adding chromium to the support.

10. A catalyst precursor, comprising: a support comprising a) a substantially alkali-metal form zeotype framework structure, b) a substantially alkaline earth-metal form zeotype framework structure, or c) a substantially alkali-metal and alkaline earth-metal form zeotype framework structure, the zeotype framework structure having a 10-member ring pore channel or a 12-member ring pore channel as the largest pore channel; and

1.0 wt% to 10 wt% of CnCh relative to a weight of the catalyst precursor, wherein the support is in substantially alkali-metal form, substantially alkaline earthmetal form, or substantially alkali-metal and alkaline earth-metal form prior to adding chromium to the support.

11. The catalyst precursor of claim 10, wherein the zeotype framework structure comprises a zeotype framework of FAU, MFI, MWW, or a combination thereof.

12. The catalyst precursor of claim 10, where the catalyst precursor further comprises 0.5 wt% to 2.5 wt% of an alkali oxide, and alkaline earth oxide, or a combination thereof relative to a weight of the catalyst precursor.

13. A method of making thiophene, an alkylated thiophene, or a combination thereof, comprising: exposing a first feedstock comprising one or more C4 to Ci6 alkanes and a second feedstock comprising a gas phase sulfur source to a synthesis catalyst under thiophene synthesis conditions, to form an effluent comprising thiophene, an alkylated thiophene, or a combination thereof, the synthesis catalyst comprising i) a support comprising a) a substantially alkali-metal form zeotype framework structure, b) a substantially alkaline earth-metal form zeotype framework structure, or c) a substantially alkali-metal and alkaline earth-metal form zeotype framework structure, the zeotype framework structure having a 10-member ring pore channel or a 12-member ring pore channel as the largest pore channel; and

1.0 wt% to 10 wt% of chromium sulfide relative to a weight of the sulfided catalyst, the chromium sulfide having an average stoichiometry of CrSx, where x is greater than 1.0; or ii) a catalyst formed by sulfidation of a catalyst precursor comprising Sr Os.

14. The method of claim 13, wherein the zeotype framework structure is synthesized in a) substantially alkali-metal form, b) substantially alkaline earth-metal form, or c) substantially alkali-metal and alkaline earth-metal form.

15. The method of claim 13, wherein the zeotype framework structure is in a) substantially alkali-metal form, b) substantially alkaline earth-metal form, or c) substantially alkali-metal and alkaline earth-metal form prior to adding chromium to the support.

16. The method of claim 13, wherein the zeotype framework structure comprises a zeotype framework of FAU, MFI, MWW, or a combination thereof.

17. The method of claim 13, wherein the one or more C4 to Ci6 alkanes comprise n-butane.

18. The method of claim 13, wherein the first feedstock further comprises one or more C4 to C10 alkenes.

19. The method of claim 13, wherein the support comprises a substantially alkali-metal form zeotype framework structure, the alkali metal comprising sodium, potassium, or a combination thereof; or wherein the support comprises a substantially alkaline earth-metal form zeotype framework structure, the alkaline earth metal comprising magnesium, calcium, or a combination thereof.

20. The method of claim 13, wherein the effluent further comprises C4+ alkanes, and wherein the first feedstock comprises a recycle portion of the C4+ alkanes.