FI97546B - Process for making olefins - Google Patents

Description

97546

The present invention relates to a process for the production of light olefins according to claim 5, which comprises contacting a feed of dehydrating hydrocarbons with a catalyst at an elevated temperature for the production of light olefins.

10 There are several ways to make light olefins. These methods include thermal cracking, catalytic fluidized bed cracking and dehydration. These methods can be briefly characterized as follows: - in thermal cracking, the main product of the cracking process is ethylene. Propylene and heavier olefins are the main by-products and their yields cannot be significantly increased by changing the operating conditions. Other by-products are fuel gas, aromatic tar and coke, which are harmful to the process and have little or no economic value.

- in catalytic fluidized bed cracking (FCC), the yield of light olefins is low.

- catalytic dehydration takes place at relatively high temperatures. The dehydration reaction is very endothermic, requiring 25 large, carefully controlled heat inputs to the reaction zone. This is the most important challenge in process design.

The latter group of methods is of particular interest.

It can be divided into two types according to how the required energy is used in the reaction zone: 1. Adiabatic methods: In adiabatic reactors, both the catalyst bed temperature and the feed temperature are higher than the optimum process temperature at the beginning of the process cycle.

2. Isothermal methods: From the point of view of process technology, the reaction temperature should be as low as possible. Too high a temperature increases coke formation and reduces selectivity to olefins, and too low a temperature reduces conversion. Cracking cannot be prevented in isothermal processes because the temperature exceeds the safe temperature limit near the inner surfaces of the reactor tubes.

Commercial dehydrogenation catalysts are currently either chromium oxy-5 dia or platinum on the support surface. These catalysts have several disadvantages: chromium has numerous oxidation states from which Cr (VI) is known to cause cancer and allergies. The price of platinum is very high. For these reasons, the use of these catalysts is difficult in processes from which they can escape (e.g., in fluidized bed processes where some of the catalyst disappears with the products). Other possible dehydrogenation catalysts are based on vanadium oxide, molybdenum oxide and metal carbides. These catalysts are currently under development.

15

As can be seen from the above, there is clearly a need for new dehydrogenation processes using more efficient catalysts.

It is an object of the present invention to obviate the problems associated with the prior art and to provide a new process for the preparation of olefins.

This invention is based on the idea of replacing the conventional catalysts used in conventional dehydrogenation processes with newly developed new materials. In particular, the novel catalysts for dehydrogenation processes contain molybdenum oxycarbide, optionally supported on a silicon carbide support.

The present invention is characterized in more detail by what is set forth in the characterizing part of claim 1.

As mentioned above, the present invention provides a process 35 for the dehydration of hydrocarbons at elevated temperatures with a catalyst containing or consisting essentially of porous molybdenum oxycarbides in bulk form or preferably 3,97546 supported on a silicon carbide support, neat or doped. The process is carried out in the presence of water vapor or small amounts of oxygen or oxygen-containing compounds to stabilize the oxycarbide phases.

Recently, high surface area silicon carbides or oxycarbides or carbides or oxycarbides of other elements such as Mo, W, V, etc. have been developed. They are used in petrochemical catalytic reactions or in the purification of exhaust gases from internal combustion engines (European patents EP 0 313 480, EP 0 396 475, EP 0 474 570, EP 0 534 867 and EP 0 624 560). Said catalysts can be used as such and / or activated and / or supported on a support and / or mixed with elements such as rare earth metals. In particular, molybdenum carbide and oxycarbide are preferred in cracking, reforming and dehydrogenation reactions (European patent EP 0 396 475).

The active phase of the catalysts used in this process, molybdenum oxycarbide, has a high specific surface area (1 to 200 m 2 / g). Its general formula is MoOxCyf where x is 0.01 to 5 and y is 0.01 to 10.

The molybdenum oxycarbides used in the present invention can be prepared by any suitable method, and preferably by the methods disclosed in the above-mentioned patents.

By way of example, molybdenum oxycarbide 30 may be prepared by reduction and carbonization of the corresponding oxide (e.g. MoO 3). The production process includes the steps of initially oxidizing the parent metal in an oxygen-containing air stream at a temperature of 300 to 450 ° C for 3 to 15 hours. This is preferably done by treatment in a hydrogen stream at 35 to 600 ° C for 1-2 hours. The oxide formed, for example MoO 3, is then taken up in a gaseous mixture of hydrogen and an alkane, such as n-hexane, whereby the conversion reaction 4,97546 is an isomerization of n-hexane. The carbonate of the oxide catalyst is made in situ to form the carbide / oxycarbide product.

The active phase may be applied to a silicon carbide support having a high specific surface area. Suitable silicon carbide materials are, for example, described in more detail in the following prior art publications: EP 2 621 904, EP 0 313 480 B1, EP 0 440 569 A2, EP 0 511 919 A1, EP 0 543 752 A1, EP 0 543 751 A1, US 5,217,930, US 4,914,070.

10

To mention only one exemplary production method, finely divided SiC (particles less than 200 micrometers in size and having an area of at least 200 m 2 / g) can be prepared as follows: SiO gas is generated in the first reaction zone, SiO 2 + Si is heated to 1100 to 1400 ° C: n, at a pressure of 0.1 to 1.5 mmPa, and in the second reaction zone, the SiO gas is reacted with finely divided carbon having a carbon surface area of at least 200 n 2 g at 1,100 to 1400 ° C. it is particularly preferred to form SiO 2 at a temperature of 1200 to 1300 ° C or 1100 to 1200 ° C.

The reaction temperature of SiO and C is 1100 to 1200 ° C. The SiO can be blended as described below, and then the product can be post-calcined in air at 600 to 800 ° C for about 0.5 to 2 hours. The reaction is preferably carried out in an inert atmosphere (argon or helium).

The silicon carbide support may be pure or doped with rare earth metals, lanthanides or actinides or mixtures thereof. Examples of preferred doping elements are Ce, U, Ti, Zr and Hf. The mixing can be done by impregnating with a solution which is an aqueous solution of a soluble compound (such as acetylacetonate or nitrate) or another solution which is decomposed by heat treatment before preparing the heavy metal carbide. The specific surface area of carbon 35 decreases slightly during alloying, but generally remains higher than 200 m 2 / g. A doping element such as Ce. the amount is 0.5 to 20% by weight, usually about 1 to 10% by weight.

tl 5 97546

The doping can be used to modify the catalytic properties of the catalysts. This feature is evident by comparing the results obtained in Examples 3 and 5 below; Doping the SiC-supported molybdenum oxycarb-5 bidicatalyst support with Ce greatly increases the C4 selectivity of the catalyst.

The hydrocarbon feed to be treated by the process of this invention, hereinafter referred to as "dehydrating hydrocarbons", may contain at least alkanes having from 2 to 12 carbon atoms per molecule. Non-limiting examples of suitable alkanes include: ethane, propane, n-butane, isobutane, 2-methylbutane, n-pentane, 2-methylpentane, and n-hexane, and the like. Preferred alkanes are those containing from 2 to 5 carbon atoms per molecule.

The hydrocarbon feed may also contain at least one cycloalkane having 5 to 10 carbon atoms per molecule. Non-limiting examples of suitable cycloalkanes include: cyclo-pentane, cyclohexane, methylcyclohexane, 1,3-dimethylcyclohexane and ethylcyclohexane, and the like.

The hydrocarbon feed may also be a petroleum fraction or a catalytic cracker removal, or a shale oil fraction, or a product obtained by extracting or liquefying coal, or a similar hydrocarbon feedstock. Preferably, a petroleum fraction having a boiling point at atmospheric pressure of about 0 to 220 ° C, such as gasoline or naphtha, is used as feed. These fractions generally contain as alkanes alkanes having from 4 to 12 carbon atoms per molecule.

The presence of water vapor in the reaction is preferable. Water vapor prevents the formation of a carbide phase that catalyzes hydrogenolysis and increases the methane content of the cracked product. The solution content of steam moo-35 is generally 0.01 to 25%, preferably about 0.1 to 5%.

Water can be replaced by an oxygen-containing compound, such as alcohols or ethers, in concentrations of about 6,97546 0.01 to 25 mol%, or a small amount, less than 1% by weight, of free oxygen in the gas phase.

Any device in which close contact of the hydrocarbon feed stream and the catalyst of this invention at elevated temperature is possible can be used. The method is in no way limited to any particular hardware. The process can be carried out in a batch process, e.g. in an autoclave, which can be heated and pressurized, and which preferably includes 10 internal mixing or recycling devices. The catalyst may be dispersed in the feed or may be used as a solid bed. The process can also be carried out continuously, e.g. in a tubular reactor containing the catalyst as a solid bed, or in a fluidized bed reactor in which the flowing catalyst is separated after the reaction and preferably regenerated in another reactor. The term "hydrocarbon feed stream" is used herein in connection with both the batch process and the continuous process.

Any suitable temperature can be used in the dehydrogenation process of this invention. In general, due to thermodynamics, the reaction temperature ranges from about 400 to 700 ° C, preferably from 500 to 600 ° C.

Any suitable reaction pressure can be used in the dehydrogenation process of this invention. In general, the reaction pressure can vary from almost vacuum (0.1 bar absolute pressure) up to 30 bar (abs).

Any reaction time, i.e., the contact time of the hydrocarbon feed stream with the catalyst, can be used in the process of this invention. The actual reaction time may depend greatly on factors such as the effective reaction temperature, the type of feed used, the type of catalyst used, and its particle size. Usually, the reaction time ranges from about 0.5 to 100 seconds, preferably from about 1 to 50 seconds. In a continuous process, the reaction time is usually reported as mass states! 7,97546 as a flow rate per catalyst volume (WHSV weight Hourly space velocity), which may range from about 0.1 to 12 t feed / t catalyst / hour, preferably 0.2 to 4 t feed / t catalyst / hour.

The products formed by the process of this invention are preferably separated from the reaction mixture by any separation method, e.g. fractional distillation. The unreacted hydrocarbons in the feed are preferably recycled back to the reaction zone and the hydrogen gas generated during the manufacturing process can be used as a fuel or reagent in chemical syntheses (hydrogenation).

If the catalyst of the present invention loses its catalytic activity due to coke formation, the nearly deactivated catalyst can be regenerated in the same reactor by interrupting the hydrocarbon feed stream and contacting the catalyst with a free oxygen-containing gas, preferably air, under such regeneration conditions. This regeneration process can also be carried out in a separate reactor. "Nearly deactivated catalyst" as used herein means a catalyst that has lost a sufficiently large portion of its original activity and no longer converts the hydrocarbon feed to the desired products in commercially acceptable yields. A typical regeneration temperature is 400 to 800 ° C when using air or diluted air as the regeneration agent.

Before and after regeneration, the catalyst is purged with lead-30 miles of nitrogen or other inert gas through the catalyst to prevent overheating of the catalyst for safety reasons.

Depending on the hydrocarbon feed, catalyst and production conditions, this production process produces olefins, in particular ethylene, propylene, butenes and / or amylenes, of which butenes are generally the main components of the reaction product mixture.

8 97546

The following examples are presented to further illustrate the invention without limiting the scope of this invention.

Example 1 This example illustrates the dehydration of n-butane with a Mo-oxycarbide catalyst without support. The catalyst can be prepared as described in European patent publication EP 0 396 475.

10 Test conditions. The feed of reactants was a mixture of n-butane (WHSV 2 h1) and hydrogen. The molar ratio of gases was H2 / n-C4 = 9 and 500 mg of catalyst was used. The temperature was raised at a rate of 50 ° C / min from 350 ° C to 550 ° C, which was the reaction temperature. The reaction pressure was atmospheric pressure. No water vapor or oxygen was used during reaction 15.

Cycle of regeneration. Oxidative regeneration was performed in a stream of air (20 cm 3 / min) at the same reaction temperature for 10 min, after rinsing the apparatus with helium (50 20 cm 3 / min).

The results of these experiments are shown in Table 1.

Example 2 This example illustrates the dehydration of n-butane with a catalyst containing a physical mixture of molybdenum oxycarbide (500 mg) and silicon carbide (400 mg). (SiC can be prepared as described in one of the references in the general part of the specification).

30 Test conditions. The reaction conditions were the same as in Example 1.

Cycle of regeneration. The catalyst was regenerated for 2 hours at 350 ° C in a stream of air (20 cm 3 / min).

The results of these experiments are shown in Table 2.

35 ti 9 97546

Example 3 This example illustrates the dehydration of n-butane with molybdenum oxide on a support. The catalyst is molybdenum oxide carbide on a SiC support (10 to 20% by weight). The manufacturing process uses 5 torr of water vapor in the gas stream.

Test conditions. The reaction conditions were the same as in Example 1 except that the total weight of the catalyst sample was 1500 mg (WHSV = 0.67 h'1).

10

Cycle of regeneration. The regeneration conditions were the same as in Example 1, the only difference being the presence of water vapor during this operation.

15 The results of these experiments are shown in Table 3.

Example 4 This example describes the dehydration of n-butane with molybdenum oxycarbide on SiC strain 20 (10 to 20% by weight) in the presence of 14 torr of water vapor in a gas stream.

Test conditions. The total weight of the catalyst was 5000 mg (WHSV 0.2 h'1). After the second regeneration, the temperature of the dehydration reaction was 570 ° C.

Cycle of regeneration. The regeneration conditions were similar to Example 3.

30 The results of these experiments are shown in Table 4.

Example 5 This example describes the dehydration of n-butane with molybdenum oxycarbide (10 to 20% by weight), which is a cerium alloy-35 on the surface of a SiC support.

10 97546

Test conditions. The reaction conditions were the same as in Example 3.

Cycle of regeneration. Regeneration conditions were similar 5 as in Example 3.

The results of this test are shown in Table 5.

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Ji * 5 o't ® * 2222 o o? 3 u »£ LLI_Il £ 5 <c (J c / 5 £ ® ® ο. O. .Ϋ .2 i- j ί u |> - 16 97546

As can be seen from the results given in Tables 1-5, the dilution of the bulk molybdenum oxycarbide catalyst and the repositioning of the active phase on the SiC support improves the selectivity of the catalyst. The presence of water vapor in feed 5 stabilizes the catalytically active oxycarbide phase and further significantly improves the efficiency of the catalyst. In addition, the isomerization activity of the catalyst increases with the use of water vapor in the feed. The selectivity of the catalyst can be further improved by doping the SiC support.

10 11

Claims (20)

97546 A process for the preparation of light olefins, characterized in that a feed containing at least one dehydratable hydrocarbon is contacted with a molybdenum oxycarbide catalyst at an elevated temperature. A method according to claim 1, characterized in that the feed further comprises at least one oxygen-containing compound. Process according to Claim 1 or 2, characterized in that the specific surface area of the catalyst is from 1 to 1000 m 2 / g. 15 Process according to one of Claims 1 to 3, characterized in that the catalyst is on the surface of the silicon carbide support. Process according to Claim 4, characterized in that the SiC support has a specific surface area of 1 to 1000 m 2 / g. Process according to Claim 4 or 5, characterized in that the support is doped with at least one lanthanide, actinide, rare earth metal or a mixture thereof. Process according to Claim 6, characterized in that the support contains 0.5 to 20% by weight of at least one lanthanide, actinide, rare earth metal or a mixture thereof. Process according to Claim 6 or 7, characterized in that the support contains from 0.5 to 20% by weight of cerium, optionally together with at least one other lanthanide and / or actinoid and / or rare earth metal. 97546 Process according to one of the preceding claims, characterized in that the feed is brought into contact with the catalyst at a temperature of 400 to 700 ° C. Process according to one of the preceding claims, characterized in that the feed is brought into contact with the catalyst for 0.5 to 100 seconds. Process according to one of the preceding claims, characterized in that the feed mass flow brought into contact with the catalyst is from 0.1 to 12 t feed / t catalyst / hour per catalyst mass (WHSV). Process according to one of Claims 2 to 11, characterized in that the feed is brought into contact with the catalyst in the presence of a compound containing 0.01 to 25 mol% of water vapor or oxygen. Process according to Claim 12, characterized in that the oxygen-containing compound contains at least one alcohol or ether. Process according to one of Claims 2 to 11, characterized in that the feed is brought into contact with the catalyst in an amount of 0.01 to 1% by weight of free oxygen. Process according to one of Claims 2 to 14, characterized in that water vapor, at least one oxygen-containing compound or free oxygen are included in the feed. 30 Process according to one of the preceding claims, characterized in that the hydrocarbon feed contains alkanes having 2 to 20 carbon atoms and / or cycloalkanes having 5 to 20 carbon atoms. 35 Process according to one of the preceding claims, i.e. 97546, characterized in that the hydrocarbon feed contains a petroleum fraction, a product fraction from a catalytic cracking unit, or a shale oil fraction, or a product fraction prepared by coal extraction or liquefaction. 5 Process according to Claim 17, characterized in that the hydrocarbon feed contains a petroleum fraction having a boiling point at atmospheric pressure of about 0 to 220 ° C. 10 Process according to Claim 18, characterized in that the feed contains a petrol or naphtha fraction containing alkanes having 4 to 12 carbon atoms per molecule. 15 Process according to one of the preceding claims, characterized in that ethylene, propylene, butenes and / or amylenes are prepared. 97546