Process for the removal of carbon monoxide from alphaolefins and saturated hydrocarbons

Abstract: The carbon monoxide contained in α-olefins and saturated hydrocarbons, in particular α-olefins and C₂₋₄ saturated hydrocarbons, is removed, by contacting such α-olefins and saturated hydrocarbons, at a temperature ranging from 0 o to 150 o C, with a catalyst system comprising a mixture and/or the reaction product of: A) one or more oxides of metals selected from the group consisting of Cu, Fe, Ni, Co, Pt, Pd; and B) one or more oxides of metals selected from the group consisting of metals of groups V B, VI B, or VII B of the Periodic Table; thus reducing the content of carbon monoxide to values lower than 0.03 ppm.

Description: The present invention concerns a process for the removal of carbon monoxide from propylene in the liquid state, in order to make said propylene suitable for use in Ziegler-Natta polymerization processes. In particular, the process of the present invention can be used advantageously for the purification of propylene obtained by way of thermal cracking processes, which constitute the primary production source of said propylene. BACKGROUND OF THE INVENTION It is known how α-olefins obtained by thermal cracking of mineral oils , even after complex separation and refining treatments, contain small quantities of impurities, many of which, carbon monoxide included, have a detrimental effect on the Ziegler-Natta catalysts, particularly the high-yield catalysts, which generally contain a halogenated titanium halide compound supported on magnesium chloride, and an aluminum alkyl compound as the co-catalyst. The carbon monoxide is generally present in the above mentioned α-olefins in a quantity ranging from 0.5 to 10 ppm (hereinafter understood to be ppm in moles), and at such levels it reduces considerably the efficiency of the Ziegler-Natta catalysts. On the other hand, it is not easy to further reduce the above mentioned concentrations of carbon monoxide in C₂₋₄ α-olefins by simple distillation, given the low boiling point of said α-olefins. In particular, when the concentration of carbon monoxide is lower than or equal to 2 ppm, distillation becomes remarkably burdersome even from an economic standpoint. The economic damage which derives from the presence of carbon monoxide in a polymerization process can be even worse when, as it often happens, the concentration of carbon monoxide fluctuates within the above mentioned range, thus causing a similar fluctuation of the polymer yield at the point where the latter exits the polymerization reactors, and this forces one to undertake continuous and costly operations to adjust the catalyst feeding systems, and not always with positive results. This proves how important it is to reduce the concentration of carbon monoxide in the α-olefins to levels below 0.03 ppm, where the influence on the behavior of the Ziegler-Natta catalysts is negligible. The methods used up to date to reduce said carbon monoxide content in the α-olefins obtained by refining mineral oils (including thermal cracking), consist of using the capacity of some transition metal compounds, in particular copper compounds, in an aqueous solution form, or dispersed on inert solid supports (such as alumina or silica), to form complexes with the carbon monoxide. For example, according to U.S. patent 3014973, the α-olefins to be purified, in particular ethylene and propylene, are absorbed in aqueous cuproammonium solutions, and subsequently selectively desorbed in such a way as to separate them from the carbon monoxide which remains complexed with the copper compound. In order to further lower the carbon monoxide content, an additional treatment of the α-olefins by way of contacting them with the hydroxide of an alkali metal at temperatures higher than 170°C is expected. From the data shown in U.S. patent 3014973, it is not obvious if by using the above mentioned process it is possible to reduce the concentration of carbon monoxide to less than 0.03 ppm. However, the above process is complex and costly, and requires an additional liquefying stage of the purified olefin, whenever, as it often happens in the case of propylene and 1-butene, one wants to carry out the polymerization in liquid monomer. Published Japanese patent application JP-A-55154921 discloses a method for removing carbon monoxide from olefins, by contacting olefins with a catalyst containing cupric oxide and chromic oxide. Only a contact in the gas phase is mentioned and the examples relate only to ethylene. In the best example a carbon monoxide concentration of less than 0.1 ppm is reached. US-A-3676516 discloses a process for purifying propylene or ethylene from carbon monoxide by contacting the olefin in the gas phase with a catalyst comprising copper oxide and barium and chromium compounds as promoters. The examples relate only to ethylene. SUMMARY OF THE INVENTION The process for removing carbon monoxide from propylene according to the present invention comprises contacting the propylene in the liquid state containing the carbon monoxide, at temperatures ranging from 20° to 95°C, with a catalyst system comprising a mixture and/or a reaction product of: A) one or more oxides of metals selected from Cu, Fe, Ni, Co, Pt and Pd; and B) one or more oxides of metals selected from V, Nb, Cr, Mo and W. DETAILED DESCRIPTION The process of the present invention provides for the removal of carbon monoxide from propylene, which allows operation in a particularly simple and effective manner, at low temperatures, and maintaining the propylene in the liquid state. As previously stated, the process of the present invention allows one to reduce the content of carbon monoxide in propylene until the concentration falls below 0.03 ppm, particularly until the concentration goes below 0.02 ppm. Although it is not meant for the operation mechanism to limit the present invention, it has been found that the above catalyst systems, including the mixture and/or the reaction product of (A)+(B), are oxidizing catalyst systems, and therefore, they are capable of transforming the carbon monoxide present in the α-olefin or saturated hydrocarbon into carbon dioxide. Since the levels above which carbon dioxide can influence the activity of the Ziegler-Natta catalysts are considerably higher that those of carbon monoxide, and usually higher than 5 ppm, the presence in quantities up to 5 ppm of carbon dioxide which replaces the carbon monoxide in the propylene purified with the process of the present invention, does not generally lead to polymerization problems. The initial concentration levels of carbon monoxide within which the process of the present invention can be used most advantageously, therefore, are those that are lower than or equal to about 5 ppm, particularly from 0.5 to 5 ppm. If necessary, the content of carbon dioxide in the propylene can easily be reduced to contents lower than or equal to 5 ppm, by contacting, according to technical reports, with alkali metal hydroxides, particularly Na or K, optionally supported on inert supports, such as calcium carbonate or activated carbon. It is possible, for example, to make the propylene flow on fixed beds containing the above mentioned hydroxides in the solid state and homogeneously distributed; in this manner, the carbon dioxide is fixed as carbonate. Among the catalyst systems used in the process of this invention, particularly preferred are the ones where component (A) comprises or is made up of copper oxide (CuO); for component (B) the preferred catalyst systems are the ones where said component comprises or is made up of chromium oxide (Cr₂O₃). Depending on the preparation method, the catalyst systems can also comprise reaction products of oxides (A) and (B). For example, a catalyst system obtained from CuO and Cr₂O₃ can comprise or be made up of CuCr₂O₄. Components (A) and (B), as a mixture or as products of a reaction between them, are generally present, in the catalyst system used according to this invention, in molar ratios (A):(B) ranging from 1:10 to 10:1, preferably from 1:2 to 5:1. Particularly preferred are the catalyst systems comprising CuO and Cr₂O₃, as such and/or as CuCr₂O₄, in the above mentioned proportions. The catalyst systems used in the process of this invention can also be supported on inert supports such as silica, alumina, diatomaceous earth, and activated carbon. The methods for preparation of the above mentioned catalyst systems vary mainly depending on the desired chemical composition and morphology. By way of example, it is possible to operate by mixing the (A) and (B) oxides, by co-milling for example, or by thermal decomposition of mixtures of various compounds of the respective metals, which can be converted into oxides by way such thermal decomposition. The compounds that can be converted into oxides by way of thermal decomposition are generally selected from the organic and inorganic acid salts, such as for example alcoholates, nitrates or carbonates. Said salts can also be used in solution in appropriate solvents, preferably in water, for the purpose of impregnating the above mentioned inert supports, thus obtaining, by evaporation of the solvent and subsequent thermal decomposition, supported catalyst systems. The thermal decomposition is appropriately carried out by way of heating at a temperature generally ranging from 150° to 800°C in the presence of air or oxygen. Some of the above mentioned catalyst systems are normally used in the reduced state, i.e., after having been treated with hydrogen, as hydrogenation-dehydrogenation or hydration catalysts in various organic syntheses, and therefore, they are available commercially. Contrary to the above mentioned application methods after hydrogen treatment, in the process of the present invention the catalyst systems described above are used as such, or after treatment in air or oxygen flow generally at temperatures ranging from 80°C and 500°C and time spans ranging from 1 to 100 hours. Examples of catalyst systems commercially available which can be used advantageously in the process of the present invention, are the Cu-0203T and Cu-1230E types, produced by ENGELHARD. The catalyst Cu 0203 T contains CuO and Cr₂O₃ in quantities by weight equal to 79% and 17% respectively. The catalyst Cu 1230 E contains CuO and Cr₂O₃ in quantities by weight equal to 30% and 31% respectively, and is supported on alumina. It is believed that a part of the oxides in these is in the form of CuCr₂O₄. The operating pressure generally used is that necessary to maintain the α-olefin or saturated hydrocarbon in the liquid state, corresponding to the process temperature used. For example, the operation usually takes place at a pressure ranging from 1 x 10⁵ to 200 x 10⁵ Pa (from 1 to 200 atm), preferably from 2 x 10⁵ to 50 x 10⁵ Pa (from 2 to 50 atm). According to the process of the present invention, the catalyst systems described above are generally used in the form of dispersed particles placed on fixed or stirred beds. The average diameter of the particles ranges preferably from 500 to 10,000 µm. The propylene to be purified is caused to flow on the above mentioned catalyst beds at a space velocity generally ranging from 2 to 20 h⁻¹. The operation is generally continuous, and lasts anywhere from 10 to 500 hrs, preferably from 40 to 250 hrs. Said time periods correspond to the life of the catalyst system, i.e., the period of time during which the catalyst system maintains a satisfactory level of efficiency in the removal of the carbon monoxide, depending mainly on the chemical composition and the physical and morphological structure of the catalyst system used; the conditions of use; and the content of carbon monoxide and other impurities present in the propylene to be purified. By operating under the above mentioned conditions, one can remove quantities of carbon monoxide equal to approximately 1 Kg of CO per 100 Kg of catalyst system, thus purifying the liquid propylene containing 1-3 ppm of carbon monoxide. An additional advantage of the process of the present invention is that the previously mentioned catalyst system can be regenerated and reutilized. The regeneration is generally carried out by heating the catalyst system in air or oxygen, to 80°-500°C, preferably to 150°-200°C for 1-100 hrs, preferably for 4-30 hrs. The following examples are given in order to illustrate, but not limit, the present invention. In all the examples the concentration of CO and CO₂ are determined by way of gas-chromatographic analysis. Control Example 1 In order to verify the efficiency of the catalyst system in the removal of carbon monoxide from liquid propylene, a test was carried out at a high concentration of carbon monoxide using the following methods. In a 1.8 l stainless steel autoclave equipped with agitator and a silicone oil heating device, in nitrogen atmosphere, are introduced 50 g of ENGELHARD Cu 1230 E 1/16-3F catalyst, previously activated by way of air flow treatment at 170°C for 4 hours. 676 g of liquid propylene containing 1500 ppm of carbon monoxide and about 2 ppm of CO₂ are then added. The autoclave is maintained under agitation for 6.5 hours at 44°C, and for 15.5 hours at 31°C, after which a sample of liquid propylene is taken. The gas-chromatographic analysis carried out on said sample shows a CO and CO₂ content of 660 ppm and 816 ppm respectively, thus proving that the CO has been quantitatively transformed into CO₂. Control Example 2 Example 1 is repeated, but in this case the propylene used has a CO content equal to 1800 ppm, and about 2 ppm of CO₂, and the autoclave is maintained at a temperature ranging from 42° to 47°C for 21 hours. The final CO content is 640 ppm, showing again that the CO was quantitatively transformed into CO₂. Control Example 3 (comparative) Control Example 1 is repeated, but in this case the propylene used has a content of CO equal to 1300 ppm and about 2 ppm of CO₂, and 50 g of ENGELHARD B 038A-006-06-T 1/8 catalyst are added while maintaining the autoclave at 45°C for 31 hours. The above catalyst is essentially made up of CuO supported on silica. The final CO content is 1200 ppm., thus showing that a catalyst which is solely based on copper oxide is not effective in the removal of carbon monoxide from liquid propylene. Example 4 The same catalyst used in Control Example 1 is used in a series of three tests for the purification of liquid propylene containing a quantity of CO included within the limits commonly found in "polymerization grade" industrially produced propylene. The apparatus used comprises a 20 l stainless steel vessel for feeding the liquid propylene, said vessel being equipped with feed pipes, which are used to introduce the propylene, CO and nitrogen (necessary to maintain a constant feed pressure of the liquid propylene). At the bottom of the vessel is a sampling device for the analysis of the initial CO content, and a tube for the discharge of the propylene to be purified. Said discharge tube is connected to the lower part of the purifier by way of a water/steam preheater. The latter is made up of a stainless steel cylinder with a 50 mm inside diameter and 500 mm high, equipped at both ends with discs and screen filters to prevent the catalyst from leaking. The cylinder is heated to the desired temperature by water/steam circulating in an outside jacket. The propylene which enters from the bottom comes in contact with the catalyst for the desired length of time , and exits purified from the top of the cylinder; before being discharged, a sampling device allows regular removal of samples to be analyzed for the final CO content. 659 g of catalyst were used in all the tests. The principal operating parameters, as well as initial and final concentrations of CO, are shown in Table 1. Example 5 Three liquid propylene purification tests are carried out by using the same apparatus of Example 4, and using, in all the tests, 325 g of ENGELHARD Cu-0203 T 1/8'' catalyst. The principal operating parameters, as well as initial and final concentrations of CO are shown in Table 1. Example 4 Test no. T (°C) P Pa (atm) Time (hrs) C₃ (l/hr) CO¹ (ppm) CO² (ppm) Resid. Time LHSV (hrs⁻¹) 1 44 20 x 10⁵ (20) 15 1.6 1.16 <0.03 26 2.3 2 44 20 x 10⁵ (20) 58 4 3.6 <0.03 10.5 5.7 3 44 20 x 10⁵ (20) 62.5 4 2.3 <0.03 7.5 8 Example 5 Test no. T (°C) P Pa (atm) Time (hrs) C₃ (l/hr) CO¹ (ppm) CO² (ppm) Resid. Time LHSV (hrs⁻¹) 1 45 19 x 10⁵ (19) 18 0.78 3.21 0.006 13.46 4.457 2 45 19 x 10⁵ (19) 24.5 0.79 1.81 0.025 13.29 4.514 3 45 19 x 10⁵ (19) 42 0.84 3.82 0.02 12.5 4.800 Notes for Table 1 P = feeding pressure C₃ = propylene being fed CO¹ = initial concentration of CO CO² = final concentration of CO Resid. Time = Residence time LHSV = Space velocity

Claims: A process for removing carbon monoxide from propylene comprising contacting said propylene in the liquid state containing said carbon monoxide, at temperatures ranging from 20 to 95°C , with a catalyst system comprising a mixture and/or a reaction product of: A) one or more oxides of metals selected from Cu, Fe, Ni, Co, Pt and Pd; and B) one or more oxides of metals selected from V, Nb, Cr, Mo and W. The process of claim 1, wherein said catalyst system has (A):(B) molar ratios of from 1:10 to 10:1. The process of claim 1, wherein component (A) of said catalyst system comprises or is made up of CuO, and component (B) comprises or is made up of Cr₂O₃. The process of claim 3, wherein said catalyst system contains CuCr₂O₄. The process of claim 1, wherein said catalyst system is preheated in air or oxygen flow at 80°-500°C for 1-100 hrs. The process of claim 1, wherein said propylene to be purified contains from 0.05 to 5 ppm in moles of carbon monoxide.

Inventors: FLAMMINI ROBERTO, PATRONCINI GIOVANNI, FLAMMINI, ROBERTO, PATRONCINI, GIOVANNI
Applicants: MONTELL NORTH AMERICA INC, MONTELL NORTH AMERICA INC.
Application year: 1992
Main classification: C07C7
IPC codes: B01J23, C07C11, C07C7, C07C9