Process for the conversion of propane und butane

Abstract: A modified natural clinoptilolite, produced by treating a natural clinoptilolite with a suitable mineral acid or with a suitable alkali and then with a suitable mineral acid, is used as a catalyst in a process for the conversion of propane or butane to give a product containing at least 40% of ethene, propene or C₄ hydrocarbons or a mixture thereof.

Description: Background of the Invention This invention relates to a process for the conversion of propane using a modified natural clinoptilolite as a catalyst. Synthetic zeolite catalysts have been used for many years in the chemical and petrochemical industry; for example, Zeolite Y is used in hydrocarbon cracking processes. More recently it has been found that the synthetic Zeolite ZSM-5, suitably modified, e.g., by the addition of zinc or gallium compounds, can convert propane and butane into hydrocarbons rich in benzene, toluene and xylenes. This process, known as the CYCLAR process (which is referred to in a paper presented at the N.P.R.A Annual Meeting, San Antonio, T.X., March 1987, J.A. Johnston, J.A. Weiszmann, G.K. Hiler and A.H. Hall) is useful in the preparation of high octane gasoline from propane and butane. This conversion process does not yield high selectivities to ethene and propene. The chemical industry would prefer a process, and thus a catalyst for the process, which results in the formation of ethene and propene as well as C₄ hydrocarbons, as these products are more flexible for further use. Further, the ZSM-5 zeolite catalyst is expensive and produces a very broad product range of aromatic compounds which are of poor suitability for use as chemical feedstocks. Summary of the Invention According to the present invention, there is provided a process for the conversion of propane to give a product containing at least 40% by weight of C₄ hydrocarbons in a reactor in the presence of a modified natural clinoptilolite produced either (1) by treating a natural clinoptilolite with a suitable mineral acid at a concentration of greater than 1M for a treatment time of longer than 24 hours and at a suitable treatment temperature, or (2) by treating a natural clinoptilolite with a suitable alkali at a concentration greater than 0,5M for a treatment time of longer than 1 hour and at a suitable treatment temperature, washing the resulting product, and treating the resulting product with a suitable mineral acid at a concentration of greater than 0,1M for a treatment time of longer than 1 hour and at a suitable treatment temperature, which includes the steps of: (a) feeding the propane to the reactor containing the catalyst; (b) converting the propane to said product in the reactor in the presence of the catalyst at a temperature of from 400°C to 800°C inclusive and a pressure of from 1 to 20 atmospheres inclusive; and (c) recovering said product. Description of Embodiments There are various processes by which the natural clinoptilolite may be modified to render it suitable for use as a catalyst, and these processes are set out below. The first method is that disclosed in an article in Applied Catalysis, 16 (1985) 249-253, by Sakoh, Nitta and Aomura. This article discloses two methods for the modification of a natural clinoptilolite from Futatsui, Japan. The first method involves treating the natural clinoptilolite with 1M HCl at 80°C for 24 hours after which the sample is filtered off, washed with distilled water and dried in air. The second method involves impregnating the clinoptilolite with 0,05M and 0,5M H₂SO₄, whereafter the samples are filtered off, dried in air and then calcined at 400°C for 3 hours in air. These catalysts were utilised in the conversion of methanol to light olefins in a fixed bed continuous flow reactor under atmospheric pressure. The second method is disclosed in South African Patent No. 88/6733 and EP-A-0370239. These documents disclose a method for the modification of a natural clinoptilolite to produce a modified clinoptilolite for use in a reaction for the preparation of or transformation of hydrocarbons which method includes the step of treating the natural clinoptilolite with a suitable mineral acid such as hydrochloric acid at a concentration of greater than 1M, preferably from greater than 1M up to and including 2,5M, more preferably 2M, for a treatment time of longer than 24 hours, and at a suitable treatment temperature, preferably of from 40°C to 80°C, to produce the modified clinoptilolite. Further, after the acid treatment step, the clinoptilolite is preferably calcined at a suitable calcining temperature, e.g, from 450°C to 550°C, more preferably 500°C, for a suitable calcining time, e.g, 3 or 4 hours. The modified catalyst so produced may be used in a process for the conversion of methanol and/or dimethyl ether to hydrocarbon reaction products, and in a process for the cracking of hydrocarbon products. The third method is disclosed in South African Patent No. 89/3131. This patent discloses a method for the modification of a natural clinoptilolite to produce a modified clinoptilolite for use in a reaction for the preparation of hydrocarbons, which method includes the step of treating the natural clinoptilolite with a phosphorus containing acid such as phosphoric acid, pyrophosphoric acid, metaphosphoric acid, hypophosphorous acid, phosphorous acid and pyrophosphorous acid, at a concentration of 0,5M or greater, preferably from 0,5M up to and including 2M, for a treatment time of equal to or longer than 24 hours, preferably up to and including 96 hours, and at a suitable treatment temperature, preferably of from 40°C to 80°C inclusive, to produce the modified clinoptilolite. After the acid treatment step, the modified clinoptilolite may be calcined at a suitable calcining temperature of from 400°C to 550°C for a suitable calcining time from 3 hours, more preferably 4 hours. The modified clinoptilolite so produced may be used in a process for the conversion of methanol and/or dimethyl ether to hydrocarbon reaction products. The fourth method is disclosed in South African Patent No. 89/3132. This patent discloses a method for the modification of a natural zeolite to produce a modified zeolite for use in a reaction for the transformation of hydrocarbons which method includes the steps of treating the natural zeolite with a suitable alkali such as sodium hydroxide at a concentration greater than 0,5M preferably a concentration from 0,5M up to and including 5M, more preferably 2M, for a treatment time of longer than 1 hour preferably up to and including 48 hours, and at a suitable treatment temperature preferably from 30°C to 80°C inclusive, washing the resulting product, and treating the resulting product with a suitable mineral acid such as hydrochloric acid at a concentration of greater than 0,1M preferably a concentration from longer than 0,1M up to and including 2M, for a treatment time of longer than 1 hour, preferably up to and including 48 hours, and at a suitable treatment temperature preferably from 40°C to 80°C inclusive, to produce the modified zeolite. Thereafter, the modified zeolite is preferably calcined at a suitable calcining temperature of from 400°C to 500°C for a suitable calcining time of 3 hours. In terms of the present invention, the natural clinoptilolite may be modified by any of the methods described above. The modified clinoptilolite may be produced starting from a natural clinoptilolite mined in Zululand, South Africa, or Fututsui, Japan or from any other suitable natural clinoptilolite. The conversion of propane to hydrocarbon products is well known and may be carried out according to the method of the present invention using the known reaction conditions. The reaction will generally be carried out in a fixed bed or a fluidized bed reactor at the temperatures and pressures mentioned above. An example which illustrates the invention will now be given. Example A sample (50g) of unmodified natural clinoptilolite was suspended with stirring in a solution (500 ml) of 2M sodium hydroxide at 50°C for eight hours. Following this treatment the sample was collected by filtration and washed with de-ionised water. The sample was then suspended with stirring in 0,5M aqueous hydrochloric acid (500 ml) at 60°C for 15 hours. The sample was collected by filtration and washed with de-ionised water, and dried at 120°C for 4 hours, then calcined at 400°C for 4 hours. The modified clinoptilolite was then used as a catalyst for propane conversion. Using a fixed bed downflow glass microreactor, propane was reacted over the modified clinoptilolite at 550°C and at a weight hourly space velocity (WHSV) of 0,9h⁻¹. Products were collected and analysed by standard gas chromatographic techniques. The results, shown in the Table below, demonstrate that the modified clinoptilolite is effective for the conversion of propane to give a product containing a high proportion of C₄ hydrocarbons. Similar experiments in the absence of the modified clinoptilolite catalyst demonstrated that some conversion of the propane was possible, but higher conversions were obtained using the modified clinoptilolite catalyst.

Claims: A process for the conversion of propane to give a product containing at least 40% by weight of C₄ hydrocarbons in a reactor in the presence of a modified natural clinoptilolite produced either (1) by treating a natural clinoptilolite with a suitable mineral acid at a concentration of greater than 1M for a treatment time of longer than 24 hours and at a suitable treatment temperature, or (2) by treating a natural clinoptilolite with a suitable alkali at a concentration greater than 0,5M for a treatment time of longer than 1 hour and at a suitable treatment temperature, washing the resulting product, and treating the resulting product with a suitable mineral acid at a concentration of greater than 0,1M for a treatment time of longer than 1 hour and at a suitable treatment temperature, which includes the steps of: (a) feeding the propane to the reactor containing the catalyst; (b) converting the propane to said product in the reactor in the presence of the catalyst at a temperature of from 400°C to 800°C inclusive and a pressure of from 1 to 20 atmospheres inclusive; and (c) recovering said product. A process according to claim 1, wherein the modified clinoptilolite is produced by treating the natural clinoptilolite with hydrochloric acid at a concentration of from greater than 1M up to and including 5M for a treatment time of longer than 24 hours and at a treatment temperature of from 40°C to 80°C inclusive. A process according to claim 1, wherein the modified clinoptilolite is produced by treating a natural clinoptilolite with sodium hydroxide at a concentration of from greater than 0,5M up to and including 5M, for a treatment time of longer than 1 hour up to and including 48 hours and at a treatment temperature of from 30°C to 80°C inclusive, washing the resulting product, and treating the resulting product with hydrochloric acid at a concentration of greater than 0,1M up to and including 2M for a treatment time of longer than 1 hour up to and including 48 hours and at a treatment temperature of from 40°C to 80°C. A process according to any one of claims 1 to 3, wherein the modified clinoptilolite is calcined at a suitable calcining temperature of from 400°C to 500°C inclusive for a suitable calcining time of from 3 hours. A process according to any one of claims 1 to 4, wherein the modified natural clinoptilolite is produced starting from a natural clinoptilolite from Zululand, South Africa.

Inventors: COPPERTHWAITE RICHARD GEORGE, HUTCHINGS GRAHAM JOHN, THEMISTOCLEOUS THERMISTOCLIS, COPPERTHWAITE, RICHARD GEORGE, HUTCHINGS, GRAHAM JOHN, THEMISTOCLEOUS, THERMISTOCLIS
Applicants: ZEOFUELS RES PTY LTD, ZEOFUELS RESEARCH (PROPRIETARY) LIMITED
Application year: 1991
Main classification: B01J29
IPC codes: C07C4, C07C6, B01J37, B01J29