WO2004067487A2

WO2004067487A2 - Method for the production of non-aromatic hydrocarbons

Info

Publication number: WO2004067487A2
Application number: PCT/EP2003/014308
Authority: WO
Inventors: Rüdiger FORSTER; Peter Wasserscheid; Christiane Werth
Original assignee: Ruhrgas Aktiengesellschaft
Priority date: 2003-01-28
Filing date: 2003-12-16
Publication date: 2004-08-12
Also published as: DE10303304A1; AU2003293899A8; WO2004067487A3; EP1587776A2; AU2003293899A1

Abstract

The invention relates to a method for the production of long-chain, branched-chain and/or cyclic hydrocarbons. A low molecular weight alkyl halide and a fused salt are firstly prepared. The fused salt contains an electrophilic compound and a reducing agent and is free from oxygen and oxygen compounds. The alkyl halide is then brought into contact with the fused salt such that long-chain, branched-chain and/or cyclic hydrocarbons are formed in the fused salt. The hydrocarbons formed in the fused salt are drawn off and can subsequently be separated from unreacted starting materials. By means of the above method, hydrogen can be produced during the reaction of the low molecular weight alkyl halide. The risk of oxidation of the alkane produced to give carbon monoxide or carbon dioxide is avoided by means of the reducing conditions in the fused salt. The product distribution can be controlled by means of suitable selection of the composition of the fused salt. Highly-branched hydrocarbons are produced with the preferred application of a sodium chloroaluminate fused salt.

Description

Process for the production of non-aromatic hydrocarbons

The invention relates to a process for the homologation of lower alkanes or haloalkanes, that is to say a process for producing longer-chain and / or branched-chain and / or cyclic hydrocarbons from a lower alkane or haloalkane or a mixture of these substances.

In the context of this description, the term “homologization” is intended to describe the production of any longer-chain and / or branched and / or cyclic hydrocarbons. A lower alkane or haloalkane should preferably be a linear alkane or haloalkane with one carbon atom or only a few linked carbon atoms, the invention preferably being aimed at the homologation of methane as the main constituent of natural gas.

As can be seen, inter alia, from the article by Robert H. Crabtree, "Aspects of Methane Chemistry", Chem. Reviews, 1995, Vol. 95, pages 987-1007, the homologation of methane has an enormous economic significance. Almost 60% of the world's known natural gas reserves are outside the consumer markets. The transportation of natural gas by pipeline is only economical up to a distance of around 4000 to 6000 km. It is therefore not economically viable to use these reserves without converting natural gas into a transportable form. For this reason, there has long been an effort to convert natural gas into a liquid that can be transported inexpensively to the consumer markets with conventional tankers.

There are a number of so-called gas-to-liquid (GTL) processes in which natural gas, in particular its main component methane, is converted into a liquid. At a older processes, the Fischer-Tropsch synthesis, a natural gas, a mixture of CO and H ₂ , is produced from the natural gas in a reforming step. The synthesis gas is then converted into hydrocarbons using catalysts. Alternatively, methanol can be produced from the synthesis gas, which is then converted into olefins or fuels after the tanker transport near the consumer markets. An economic disadvantage of the older processes mentioned is based on their two-stage process and the associated increased investment costs. In addition, synthesis gas generation is an endothermic process with a low energy efficiency.

More recently, alternative, one-step processes have been developed, with the help of which a direct conversion of natural gas or methane into longer-chain or branched hydrocarbons is possible (cf. the overview article mentioned at the beginning). The homologation of methane to ethane or longer-chain and branched hydrocarbons with the release of hydrogen is a highly endothermic process. The previous teaching assumes that homologation is achieved by introducing the lower alkane, for example at temperatures of 50-60 ° C., into a super acidic solution to which a mild oxidizing agent has been added, alternatively also an oxidizing one

Super acid can be used (cf. in the above-mentioned review article section F). When using oxygen-containing oxidizing agents, which makes sense for economic reasons, the hydrogen released during the reaction is oxidized to water. The formation of water in connection with the super acidic systems leads to problems in maintaining the required reaction conditions and / or in the regeneration of the catalyst. The object of the invention is to provide an alternative

Possibility of direct production of long-chain and / or to create branched-chain and / or cyclic hydrocarbons from at least one lower alkane or at least one lower haloalkane.

According to the invention, this object is achieved by a method having the features of patent claim 1.

In the method according to the invention, at least one lower haloalkane and a molten salt which contains an electrophilic compound and a reducing agent are initially provided, the molten salt being free of oxygen and / or oxygen compounds. The term "molten salt" is intended here to mean both the classic molten salt (melting point> 100 ° C) and the so-called ionic liquids (lower melting point) (cf. article by Peter Wasserscheid and Wilhelm Keim, "Ionic liquids - new" solutions "for Transition metal catalysis ", Angewandte Chemie, 2000, 112, pages 3926-3945). The electrophilic compound is said to be electrophilic in the Pearson concept. The reducing agent should be able to release electrons in such a way that hydrogen can be formed in protic media.

In the process according to the invention, the at least one lower haloalkane is brought into contact with the molten salt in such a way that the longer-chain and / or branched-chain and / or cyclic hydrocarbons are formed in the molten salt (possibly via several intermediate stages). The longer-chain and / or branched-chain and / or cyclic hydrocarbons formed are removed from the molten salt. The method according to the invention is based on the im

State of the art prescribed way of homologization under oxidizing conditions and carries out the homologation under reducing conditions. This can generate hydrogen. Due to the reducing conditions, the risk of oxidation of the alkane or haloalkane to carbon monoxide or carbon dioxide is avoided. The required reaction energy is supplied in part by the oxidation of the reducing agent. This is combined with providing the reducing agent in a molten salt with an electrophilic compound. A halomethane is preferably provided as the haloalkane and the longer-chain and / or branched-chain and / or cyclic compounds have at least 2 carbon atoms, preferably 5 to 10 carbon atoms. In a preferred embodiment, as

Halomethane methyl chloride provided. Methyl chloride is an important basic chemical in the chemical industry, is easily accessible and can be produced on an industrial scale, for example by thermal chlorination of methane. In a further development of the invention, the at least one lower haloalkane can also be provided by bringing at least one lower alkane, preferably methane, into contact with the molten salt and reacting with a halogen and / or halide contained in the molten salt. By providing the at least one haloalkane in this way, one process step, namely the production of the haloalkane, can be omitted, which allows the process to be carried out more cheaply. After the at least one haloalkane has been provided and before the formation of the longer-chain and / or branched-chain and / or cyclic hydrocarbons, preparation of the product mixture can be interposed.

In a preferred embodiment, the at least one lower alkane contains a maximum of 3 carbon atoms, and the longer-chain and / or branched-chain and / or cyclic hydrocarbons have at least twice the number of carbon atoms compared to the at least one lower alkane. The at least one lower alkane is preferably methane and the longer-chain and / or branched and / or cyclic hydrocarbons have at least 2 carbon atoms, preferably 5-10 carbon atoms.

In one embodiment, the at least one lower alkane can be brought into contact with the molten salt as part of a gas mixture. For example, natural gas can be used as the gas mixture. The secured world reserves of conventional natural gas have increased steadily in recent years and were around 145 x 10 ¹² m ³ at the end of 1997. By using the natural gas available in large quantities, the method according to the invention can be carried out particularly inexpensively.

The electrophilic compound is preferably part of an acidic salt melt which contains the reducing agent. The molten salt preferably contains complex anions, each with at least one central atom. At least one alkyl ligand can preferably be attached to the at least one central atom. The complex anions preferably contain at least one central atom from a group comprising aluminum, tin, iron, zinc, copper, titanium, scandium, gallium, vanadium and zirconium, the complex anions

Halogen ligands can contain.

A halogenoaluminate salt melt, in particular an alkali and / or alkaline earth metal haloaluminate salt melt, is preferably used as the salt melt. A sodium chloroaluminate or a sodium bromoaluminate salt melt is particularly preferably used, this preferably consisting of aluminum halide (as Lewis acid) and sodium halide in the molar ratio 90:10 to 10:90, preferably about 70:30 to 30:70, is formed. Depending on the selected molar ratio, the

Sodium chloroaluminate salt melt contains, in addition to the complex anion A1C1 ₄ ^", the complex anions of the general formula Al _n Cl _{3n + 1} and A1 ₂ C1 _6. The properties of chloroaluminate melts have been extensively investigated; in addition, these melts are relatively inexpensive to produce Use of a sodium chloroaluminate salt melt Advantageously, highly branched hydrocarbons, which cannot be obtained by rectification of petroleum, the octane number of which is in some cases considerably higher than that of the isooctane. These are suitable, for example, as additives for fuels to increase their knock resistance or directly as fuel. By contrast, when using a sodium bromoaluminate salt melt, cyclic hydrocarbons are preferably formed, which serve as starting products for a number of important chemical reactions. For example, cyclohexane can be converted into caprolactam, the starting compound of polyamide-6, in several subsequent steps.

In the method according to the invention, a reducing agent is preferably provided which is less noble than hydrogen in the electrochemical voltage series.

In a preferred embodiment, when the molten salt is provided, the reducing agent is formed by an electrochemical reduction in the molten salt. In one embodiment, the reducing agent could simultaneously be one of the ions of the salts forming the salt melt, which simplifies the provision. For example, a complex anion of the melt itself could serve as a reducing agent if it can pass into a higher oxidation state. This is possible, for example, in the case of a melt containing dimethyltin dichloride.

In a preferred embodiment of the process according to the invention, a metal, preferably the metal corresponding to the complex anion contained in the molten salt, or a metal-alkyl compound is provided as the reducing agent. In the case of a chloroaluminate salt melt, this is preferably aluminum. Alternatively, gallium or a mixture of aluminum and gallium could also be used as a reducing agent in a chloroaluminate salt melt. In a preferred embodiment, the at least one lower haloalkane is converted into a molten salt at a temperature between 50 ° C and 650 ° C, preferably at a temperature between 130 ° C and 250 ° C, and at a pressure between 1 and 200 bar, preferably between 1 and 50 bar. In a preferred development of the invention, the haloalkane and / or reducing agent consumed in the formation of longer-chain and / or branched-chain and / or cyclic hydrocarbons in step c) is constantly replaced by supplying at least one lower haloalkane and / or reducing agent, which is the used reducing agents replacing the reducing agents supplied to the salt melt or formed therein by electrochemical reduction. It is advantageously possible to separate unreacted starting materials derived from the products in step d) and to make them available again to the process. In this embodiment, it is possible to operate the process according to the invention for the production of longer-chain and / or branched and / or cyclic hydrocarbons continuously by providing the starting materials to the extent that they are consumed by the reaction and are subsequently removed. This is particularly advantageous if the process for producing longer-chain and / or branched and / or cyclic hydrocarbons is carried out at a pressure of 1 to 200 bar, preferably 1 to 50 bar. Since the reducing agent consumed in the reaction can be provided by electrochemical reduction, there is no need to open a reactor filled with the molten salt for feeding in used reducing agent.

Advantageous and / or preferred developments of the invention are characterized in the subclaims.

The invention is explained in more detail below on the basis of preferred embodiments.

Embodiment I In an autoclave equipped with a gas inlet device, a stirring device and a gas outlet device, 21.34 g of A1C1 ₃ (0.161 mol), 14.00 g of dry NaCl (0.240 mol) and approximately 0.05 g of Al-flitter (0.002 mol) are placed under protective gas. weighed. An AlCl ₃ / NaCl molar ratio of 40:60 results from the weighed quantities of substance. The mixture is heated to 180 ° C. and then stirred at the same temperature for 2 hours, methyl chloride being passed through the molten salt via a gas inlet device. The outgoing gas flow is analyzed. In addition to the starting material methyl chloride, the following components can be detected: methane, isobutane, neopentane, isopentane, 2-methylbutane, 2, 2-dimethylbutane, 2, 3-dimethylbutane, 2-methylpentane, 3-methylpentane, 2, 4-dimethylpentane, 2, 2,3-trimethylbutane, 3, 3-dimethylpentane, 2-methylhexane, 2-methylhexane, and 2, 2, 3, 3-tetramethylbutane.

Embodiment II 62.32 g of AlBr ₃ and 10.31 g of NaBr are weighed in under an inert gas, mixed and heated to 110.degree. The solution is electrolyzed with 0.08 A for two hours (two W electrodes), with 20 ml / min of methane being passed through the melt at the same time. The melt is then heated to 200 ° C. and flushed with argon for 30 minutes. The

The product gas mixture is collected and contains 12% isobutane and 2-methylbutane, 88% cyclic alkanes, especially methylcyclohexane (24%), 1,3-dimethylcyclohexane (ice and trans) (38%), 1,2-dimethylcyclohexane (4%) , 1,3,5-trimethylcyclohexane (7%), 1, 1, 3-trimethylcyclohexane (5%),

1, 2, 4-trimethylcyclohexane (7%) (percentages refer to the total amount of hydrocarbon).

Embodiment III 8.31 g of AlBr ₃ (0.0312 mol) with 1.37 g of NaBr (0.0168 mol) and 1.00 g of aluminum flake (0.0370 mol) weighed. An AlBr ₃ / NaBr substance ratio of 70:30 results from the weighed substance quantities. 4.8 g of methyl chloride (0.0954 mol) are condensed in and the solution is stirred for 2 hours at 110 ° C. in an oil bath. The analysis of the hot gases released into a gas mouse showed the following composition: 4.4% methane, 93.6% ethane, 0.3% propane and butanes, 0.7% pentanes, 0.4% hexanes and 0.02% higher Hydrocarbons (C7 and higher). In addition, the gas mixture contained considerable amounts of methyl bromide; the conversion of methyl chloride was above 90%.

Embodiment IV

Gallium as a reducing agent

8.67 g of A1C1 ₃ (0.0650 mol) and 2.63 g of NaCl (0.0450 mol) and 2.58 g of Ga (0.0370) are introduced into an autoclave using a stirring fish. The quantities of substance weighed in result in an AlCl ₃ / NaCl substance ratio of 60:40. 4.8 g of methyl chloride (0.0954 mol) are condensed in. The autoclave is placed in an oil bath for 2 hours at 130 ° C. with stirring. Then the hot gases are released into a gas mouse. The analysis of the gas mixture showed the following hydrocarbon quantities: 6.5% methane, 0.1% ethane, 1.8% propane, 6.9% butane, 79.3% pentane, 1.3% hexane, and octane (the latter 30 % 2, 2, 3, 3 -tetramethylbutane in the C8 fraction), 1% heptanes (thereof 22.8% triptan) and nonanes and 0.6% decanes.

Embodiment V Aluminum as reducing agent 8.67 g A1C1 ₃ (0.0650 mol) and 2.63 g NaCl (0.0450 mol) as well as 1.00 g aluminum flake (0.0370) are filled into an autoclave with a stirring fish. The quantities of substance weighed in result in an AlCl ₃ / NaCl substance ratio of 60:40. 4.8 g of methyl chloride (0.0954 mol) are condensed in. The autoclave is placed in an oil bath for 2 hours at 150 ° C. with stirring. Then the still hot gases relaxed in a gas mouse. Analysis of the gas mixture showed the following hydrocarbon amounts: 9.8% Cl, 54.3% C2, 0.9% C3, 1.4% C4, at least 6.9% C5, 16.3% C6 and 5.5% C7 (thereof 18% triptan), 4.03% C8 (thereof 68% 2, 2, 3, 3-tetramethylbutane) and 0.5% C9. The conversion of methyl chloride is approximately 80%.

Claims

claims

1. A method for producing longer chain and / or branched chain and / or cyclic hydrocarbons, wherein: a) at least one lower haloalkane is provided; b) a molten salt is provided which contains an electrophilic compound and a reducing agent, the molten salt being free from oxygen and / or oxygen compounds; c) the at least one lower haloalkane is brought into contact with the molten salt in such a way that longer-chain and / or branched-chain and / or cyclic hydrocarbons are formed in the molten salt from the at least one lower haloalkane; and d) the longer-chain and / or branched-chain and / or cyclic hydrocarbons formed in step c) are removed from the molten salt.

2. The method according to claim 1, characterized in that halomethane is provided as the haloalkane, the longer-chain and / or branched-chain and / or cyclic hydrocarbons having at least 2 carbon atoms, preferably 5 to 10 carbon atoms.

3. The method according to claim 2, characterized in that methyl chloride is provided as halomethane.

4. The method according to claim 1, characterized in that the at least one lower haloalkane is provided by at least one lower alkane with the

Brine is brought into contact and reacts with a halogen and / or a halide contained in the molten salt.

5. The method according to claim 4, characterized in that the at least one lower alkane contains a maximum of 3 carbon atoms and the longer-chain and / or branched-chain and / or cyclic hydrocarbons have at least twice the number of carbon atoms compared to the at least one lower alkane.

6. The method according to claim 4, characterized in that the at least one lower alkane is methane and the longer-chain and / or branched-chain and / or cyclic hydrocarbons have at least 2 carbon atoms, preferably 5 to 10 carbon atoms.

7. The method according to any one of claims 4-6, characterized in that the at least one lower alkane is brought into contact with the molten salt as part of a gas mixture, for example in the form of natural gas.

8. The method according to claim 1, characterized in that a molten salt is provided which contains complex anions each having at least one central atom.

9. The method according to claim 8, characterized in that a molten salt is provided, in which at least one alkyl ligand can be attached to the at least one central atom.

10. The method according to claim 9, characterized in that a salt melt is provided, the complex

Anions with at least one central atom from a group comprising aluminum, tin, iron, zinc, copper, titanium, scandium, gallium, vanadium and zirconium, and with halogen ligands.

11. The method according to claim 10, characterized in that a halogenoaluminate salt melt is used.

12. The method according to claim 11, characterized in that an alkali and / or alkaline earth metal haloaluminate salt melt of i) aluminum halide and ii) alkali metal and / or alkaline earth metal halide is used.

13. The method according to claim 12, characterized in that a sodium chloroaluminate salt melt

Aluminum chloride and sodium chloride in the molar ratio 90:10 to 10:90, preferably about 70:30 to 30:70, is used.

14. The method according to claim 12, characterized in that a sodium chloroaluminate salt melt of aluminum chloride and sodium chloride in the molar ratio 90:10 to 10:90, preferably about 70:30 to 30:70, is used.

15. The method according to any one of claims 1-14, characterized in that the reducing agent in the electrochemical series is less noble than hydrogen.

16. The method according to any one of claims 1-15, characterized in that when the molten salt is provided, the reducing agent is formed by an electrochemical reduction in the molten salt.

17. The method according to claim 15, characterized in that at least one of the ions of the salts forming the salt melt simultaneously serves as a reducing agent.

18. The method according to claim 15, characterized in that a metal or a metal-alkyl compound was provided as the reducing agent.

19. The method according to claim 18, characterized in that the metal or the metal of the metal-alkyl compound is a metal which forms central atoms of complex anions of a salt forming the salt melt or at least one of a plurality of salts forming the salt melt

20. The method according to claim 19, characterized in that an alkali and / or alkaline earth haloaluminate salt melt is provided which contains aluminum and / or gallium as a reducing agent.

21. The method according to claim 20, characterized in that a sodium bromoaluminate salt melt of aluminum bromide and sodium bromide in the molar ratio 90:10 to 10:90, preferably about 70:30 to 30:70, is provided.

22. The method according to claim 20, characterized in that a sodium chloroaluminate salt melt of aluminum chloride and sodium chloride in the molar ratio 90:10 to 10:90, preferably about 70:30 to 30:70, is provided.

23. The method according to any one of claims 1-22, characterized in that the at least one lower haloalkane is brought into contact with the molten salt by introducing the at least one lower haloalkane into the molten salt.

24. The method according to any one of claims 1-23, characterized in that the at least one lower haloalkane with the molten salt at a temperature between 50 ° C and 650 ° C, preferably at a temperature between 130 ° C and 250 ° C in contact.

25. The method according to claim 24, characterized in that the at least one lower haloalkane is brought into contact with the molten salt at a pressure between 1 and 200 bar, preferably between 1 and 50 bar.

26. The method according to any one of claims 1-25, characterized in that the halogen alkane and reducing agent consumed in the formation of longer-chain and / or branched-chain and / or cyclic hydrocarbons in step c) are constantly replaced by the supply of haloalkane and reducing agent.

27. The method according to claim 26, characterized in that the reducing agent replacing the used reducing agent is supplied to the molten salt or is formed therein by electrochemical reduction.