Process for ring opening of cyclic compounds

Abstract: Catalyst for ring opening of cyclic organic compounds comprising on a carrier of alumina, silica, zirconia and mixtures thereof; from 0.1 to 10 per cent by weight based on the total weight of the catalyst of a catalytic active metal selected from platinum, palladium, rhodium, rhenium, iridium, ruthenium, nickel, cobalt and mixtures or combinations thereof and from 0.01 to 20 per cent by weight based on the total weight of the catalyst of a metal modifier selected from tungsten, molybdenum lanthanum and rare earth metals and mixtures and combinations thereof.

Description: INTRODUCTION The present invention relates in general to a process for ring opening of cyclic compounds with at least 6 carbon atoms in the ring structure. More particularly, the invention concerns a process for ring opening of cyclic compounds including derivatives of cyclohexane, decaline, idane (indene), benzene, and naphthalene being present in diesel fuel in presence of hydrogen to linear or branched paraffinic molecules. BACKGROUND OF THE INVENTION One of the approaches to the improvement of the cetane number of diesel fuel is to increase the content of paraffinic compounds with linear chains in the diesel fuel. The content of non-cyclic paraffins in the hydrocarbon mixture can be increased by carrying out ring opening of cycloparaffins formed upon hydrogenation of aromatic compounds present in the fuel. Commercially available catalytic systems based on 1% Pt/H-Beta zeolite are disclosed in US Patent No. 5,382,730. The described catalysts exhibit rather high activity in ring opening of C 6 cyclic compounds and are used in combination with isomerization catalysts to improve quality of a C 5 -C 6 downstream feed. In this case, however, a 1:3 mixture of normal and isoparaffins was formed at conversion rates of ∼80% at 230-270°C under high-pressure conditions. Another catalyst is proposed in US Patent No. 5,382,731 for ring opening of C 6 cyclic compounds comprising a 1% Pt/WO 3 /ZrO 2 system. The performance of this catalyst is similar to that of Pt/H-Beta zeolite, at slightly different reaction conditions. WO Patent No. 97/09290 discloses a process for selective opening of compounds having at least one C 5 ring, using catalysts based on one or more metals selected from the group consisting of iridium, ruthenium and rhodium on a catalyst support material. Different feedstocks such as n-pentylcyclopentane, bicyclic and tricyclic with fused 5-membered rings have been tested for ring opening, using the above mentioned catalysts in composition with platinium supported catalysts. In contrast to the prior art mentioned in this disclosure, the process of the invention is directed to ring opening of at least 6-membered cyclic organic compounds. It is also generally acknowledged in the art that C 5 rings are much easier to cleave than C 6 rings, and include a different reaction mechanism. Only a very limited number of prior art publications are available, which are related to decalin conversion on zeolite and oxide catalysts. In most of these publications decalin cracking is studied, which leads to more than 100 products in the C1-C10 range. Decalin conversion has also been studied from the point of view of its cis trans isomerization. There is no available reported data on decalin conversion on oxide catalysts. The general object of this invention is to provide a process for ring opening of cyclic compounds having at least 6 carbon atoms in the ring structure in the presence of hydrogen by use of efficient heterogeneous metal-supported catalysts based on various oxide carriers. Various types of oxides, hydroxides or mixed oxides and hydroxides can be used as supports for active metal components in ring opening of cyclic organic compounds. The carriers for the ring opening catalysts are the commercial forms of alumina, silica, zirconia and mixtures thereof. The oxides are modified with lanthanum and rare earth metals. Metals supported on the appropriate carriers are noble and transition metals, such as platinum, rhodium, rhenium, iridium and ruthenium. The metal loading in the catalyst may range from 0.1 to 10 wt%. In accordance with the above finding, this invention provides a process for the ring opening of cyclic organic compounds with at least 6 carbon atoms in the ring structure by contacting the compounds in presence of hydrogen with a catalyst comprising a carrier of alumina, silica, zirconia and mixtures thereof from 0.1 to 10 per cent by weight of a catalytic active metal selected from platinum, rhodium, rhenium, iridium and ruthenium characterised in that the catalyst further comprises mixtures or combinations thereof from 0.01 to 20 per cent by weight of a metal modifier selected from lanthanum and rare earth metals. When operating the process of the invention, hydrogen or a mixture of hydrogen with an inert gas is used as a reducing agent. Hydrocarbons or mixtures thereof are introduced in a flow-type high-pressure reactor as a mixture with hydrogen or with a mixture of hydrogen and an inert gas. Convenient process conditions are a hydrogen-to-hydrocarbon ratio ranging from 1:1 to 1:50, more preferably, from 1:5 to 1:20; a liquid hourly space velocity ranging from 0.1 to 10, more preferably, from 0.5 to 2; and a total pressure from 1 to 100 atm, more preferably from 20 to 50 atm. The reaction is preferably carried out at a temperature from 450 to 670°K. The products evolving from the process comprise typically a mixture of gas products and liquid products, including paraffinic linear or branched hydrocarbons, cyclic compounds (both naphtenes and aromatics). In order to further illustrate the present invention and the advantages thereof, the following specific examples are given below. In the Examples, the following parameters (in per cent) are used: C=percentage of conversion, S=selectivity, Y=yield based on the product passed=C x S. Example 1 A γ-alumina carrier with a specific surface area of 170 m 2 /g is impregnated to incipient wetness with a solution of [Rh(NH 3 ) 5 Cl]Cl 2 so that the metal loading will be n0.5, 1.0, or 2.0 wt%. The samples obtained were dried and then reduced in a hydrogen flow at 450°C for 1 h. The thus prepared catalysts were tested in cyclohexane transformations in a flow reactor at the following conditions: Reaction temperature = 260-320°C, VHSV = 2 h -1 , Total pressure = 1-5 Mpa, Hydrogen-to-cyclohexane ratio (molar) = 10:1. 3 ml of a catalyst in powder form (particle size of 0,2-0,5 mm) were placed into a tubular reactor made of quartz or stainless steel (with an internal diameter of 14 mm). The results are summarized in Table 1. The C, S and Y parameters were measured in 30 min. after the beginning of the reaction. Example 2 Bimetallic catalysts containing Rh+Pt in different molar ratios, Rh+Re, and Rh+Ru were prepared on the basis of the same alumina carrier, which was impregnated with a solution containing the complexes, salts or other compounds of the above metals, such as [Rh(NH 3 ) 5 Cl] Cl 2 , RhCl 3 , H 2 PtCl 6 , (NH 4 ) 2 ReO 4 , with an appropriate concentrations of the components so that the overall metal loading was 1.0 or 1.5 wt%. The catalysts thus obtained were tested in cyclohexane conversion under conditions of Example 1. The results are summarized in Table 1. Example 3 The same γ-alumina carrier was impregnated with platinum so that the metal loading was 1 wt%. The catalyst testing was carried out under the same conditions as described in Example 1. The results of testing in ring opening of cyclohexane are presented in Table 2. Example 4 Similarly the catalyst 1%Ru/γ-alumina was prepared on the basis of the same support. The results of this catalyst testing in cyclohexane transformations under conditions of Example 1 are given in Table 2. Example 5 A SiO 2 carrier with a specific surface area of 450 m 2 /g was impregnated to incipient wetness with [Rh(NH 3 ) 5 Cl]Cl 2 , so that the metal loading was 1 wt%. The data on cyclohexane conversion and ring opening selectivity for this catalyst are collected in Table 1. Example 6 ZrO 2 (surface area ∼150 m 2 /g) was modified with 3 wt% La 2 O 3 supported by impregnation with lanthanum nitrate, followed by calcination at 500 C. Then 1 wt% of rhodium was supported by incipient wetness impregnation. After reduction, the catalyst was tested in cyclohexane ring opening, the results are presented in Table 1. Example 7 ZrO 2 modified with 3 wt% La 2 O 3 by impregnation with lanthanum nitrate was further impregnated with platinum using [Pt(NH 3 ) 6 ] (HCO 3 ) 2 . The metal loading was 1 wt%. The data on this catalyst performance in cyclohexane ring opening under conditions of Example 1 are shown in Table 2. Example 8 The γ-alumina carrier was modified with 1 wt% of iridium. The catalytic data on cyclohexane conversion obtained after reduction in hydrogen are given in Table 2. Example 9 The 1%Rh/γ-alumina catalyst prepared as described in Example 1 was reduced in different ways: at different temperatures in a hydrogen flow with or without the preliminary oxidative treatment in an oxygen flow. The comparative data on cyclohexane ring opening on the thus prepared and reduced catalysts are presented in Table 3. Example 10 The catalysts prepared according to Examples 1 and 2 were tested in the reaction of trans-1,2-dimethylcyclo-hexane conversion under conditions of Example 1. The results are given in Table 4. Example 11 The catalysts prepared according to Examples 1 and 2 were tested in the reaction of trans-1,4-dimethylcyclo-hexane conversion under conditions of Example 1. The catalytic data are collected in Table 5. Example 12 The catalysts prepared according to Examples 1 and 2 were tested in the reaction of ethylcyclohexane transformations under conditions of Example 1. The results are presented in Table 6. For Pt-containing Al 2 O 3 -based catalysts, the formation of aromatic hydrocarbons substantially decreases at high pressures, but still high reaction temperatures are required to provide a reasonable conversion (350-400°C). The highest n-C 6 H 14 yield (17.5%) was achieved at 400°C, 3 MPa. The ring-opening selectivity is 50% and n-paraffin is the main product at a selectivity of 42%. Bracking is not as decisive as at atmospheric pressure and the cumulative yield of C 1 -C 4 hydrocarbons does not exceed 0.3 wt%. Nevertheless, dehydrogenation (the benzene yield is 15.7%) still contributes substantially to the reaction network. On the contrary, isomerization processes are suppressed and the overall yield of iso-C 6 and MCP is close to 7%. Rhodium-containing catalyst systems were shown to be most active and selective in ring opening of cyclic hydrocarbons. The reaction proceeds at substantially lower temperatures compared to Pt-catalysts and dehydrogenation is suppressed to a considerable extent. Thus, at 260°C and 3 MPa, the 2%Rh/Al 2 O 3 catalyst provides a yield of n-hexane from cyclohexane of 33.4% at a selectivity of 94%. No isomerization (iso-C 6 H 14 , MCP) or dehydrogenation (C 6 H 6 ) products were identified under these conditions. The highest n-C 6 yield (70.5%) was achieved on this catalyst at 280°C at the ring-opening selectivity of 85%. The Rh/Al 2 O 3 catalyst containing 0.5 wt% Rh shows about the same performance as the 1% Rh/Al 2 O 3 sample, which is somewhat lower as compared to the sample containing 2 wt% Rh; therefore, in principle, the metal loading can be decreased. Thus, the highest yield of n-hexane for the 0.5% Rh/Al 2 O 3 catalyst reaches 26.4% at the selectivity close to 60% at 320°C, 1 MPa. The egg-shell 1%Rh/Al 2 O 3 catalyst shows similar catalytic properties, and the n-hexane yield is about 30% at 320°C at the selectivity of 54%. The 1% Rh/Al 2 O 3 catalyst tested at the pressure of 3 Mpa provides the yield of n-hexane close to 60% at 300°C at the ring-opening selectivity of 69%. The 1% Rh/SiO 2 catalyst is less active in cyclohexane conversion, as compared with Al 2 O 3 -based systems and the selectivities are lower. At high pressures (5 MPa), the n-hexane yield reaches ∼52% at 320 C. The selectivity is 56%. Ru-containing catalysts show advantageous catalytic properties in ring opening of cyclohexane. The cyclohexane conversion on the 1 Ru/Al 2 O 3 catalysts is high (up to 30%) even at low temperatures of 200-210°C, i.e., at temperatures when both Pt and Rh catalysts are inactive. However, at temperatures above 230°C, the Ru-containing catalysts catalyze solely cracking, i.e., the temperature intervals favourable for ring opening on Ru-catalysts are very narrow (200-220°C). Modification of ZrO 2 with La 2 O 3 (3 wt%) completely suppresses the isomerization side reactions in the case of the 1% Rh/3%La 2 O 3 /ZrO 2 catalyst. However, light products (C 1 -C 4 ) are still formed in a considerable amount, probably, not by a cracking mechanism but via hydrogenolysis of cyclohexane and products of ring opening. Nevertheless, the yield of n-hexane is rather high (up to 34% at 280°C, 3 MPa) at a ring-opening selectivity of 71%. In the case of the 1% Pt/3%La 2 O 3 /ZrO 2 catalyst, the pattern with the formation of ring opening products is very similar to that found for 1% Rh/3%La 2 O 3 /ZrO 2 and the maximum yield of n-hexane (43.4%) was achieved at 400°C, 3MPa; the selectivity to n-hexane was 52%. Unlike the Rh-containing catalyst, for the Pt-sample, isomerization products (isohexanes) were also formed, which can be explained by the peculiarities of the procedure used for supporting platinum: H 2 PtCl 6 was used as a source of Pt and this acid introduced some acidity in the support. Also, dehydrogenation processes occur in the case of the Pt catalyst, which can be substantially suppressed by increasing the reaction pressure to 3 MPa. Reasonably high selectivity of 96% was achieved on this catalyst at 370°C and 2 MPa, the n-hexane yield was equal to 18%. It is interesting to note that for the 1% Pt/3%La 2 O 3 /ZrO 2 sample, the effect of switching from the complex pattern to pure cracking is observed when the reaction temperature increases from 400 to 420°C at 3 MPa. Interesting results were obtained with 1% Ir/Al 2 O 3 (Table 2): the maximum yield of n-hexane was 24.9% at 341°C, 1.0 MPa and dilution of 10:1; the ring-opening selectivity was 74.1%. Only small amounts of cracking products were found at the reactor outlet. To summarize, the given Examples show that the catalysts according to the invention for the process of ring opening of cyclic compounds with at least 6 carbon atoms in the presence of hydrogen exhibit the following advantages over the known catalysts disclosed in US Patent Nos. 5,382,730 and 5,382,731 (1995): (i) The yield of ring opening products on the inventive catalysts may be increased to 50-70% at the selectivity of 70-95%; (ii) Mainly normal paraffins are formed in cyclohexane ring opening, whereas the reactions of skeletal isomerization and cracking, as well as dehydrogenation are substantially suppressed; (iii) Bimetallic Rh-Pt and Rh-Ru catalysts show a good performance at a lower overall metal loading as compared to monometallic catalysts and the range of the reaction temperatures and pressures that are optimal for the ring opening process is wider. While the invention has been described in terms of various preferred embodiments, the skilled artisan will appreciate that various modifications, substitutions, omissions and other changes may be made without departing from the spirit thereof. Accordingly, it is intended that the scope of the present invention be limited solely by the following claims, including equivalents thereof.

Claims: Process for ring opening of cyclic organic compounds with at least 6 carbon atoms in the ring structure by contacting the compounds in presence of hydrogen with a catalyst comprising a carrier of alumina, silica, zirconia and mixtures thereof from 0.1 to 10 per cent by weight of a catalytic active metal selected from platinum, rhodium, rhenium, iridium, ruthenium and mixtures or combinations thereof characterized in that the catalyst further comprises from 0.01 to 20 per cent by weight of a metal modifier selected from lanthanum and rare earth metals. Process according to claim 1 characterized in that the cyclic organic compounds are contained in diesel fuel.

Inventors: ZEUTHEN PER, ZEUTHEN, PER
Applicants: TOPSOE HALDOR AS, HALDOR TOPSOE A/S
Application year: 1998
Main classification: B01J23
IPC codes: C10G45, B01J23