JPH0510976B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Field of Application) The present invention relates to a catalyst used in a process for oxidizing olefins to produce α,β-unsaturated carboxylic acids. More specifically, this method is a method for producing a novel olefin-activated palladium catalyst, and its use provides an improved method for oxidizing propylene in one step under mild reaction conditions to produce acrylic acid in high yield and high selectivity. is provided. In a similar manner, isobutylene and butene-1 can be oxidized to methacrylic acid and crotonic acid, respectively. The invention further relates to the novel activated palladium catalyst itself and the method for producing the same. (Related applications) This application is related to the following simultaneously filed applications. ``Increased selectivity in the oxidation of olefins to α,β-unsaturated carboxylic acids'' by James, E. and Lyon, ``Increased selectivity in the oxidation of olefins to α,β-unsaturated carboxylic acids'' by Lyon et al. Also related are the following applications filed on the same date using the catalyst system described herein in other oxidation processes. Lion et al., “Catalytic Oxidation of Propylene to Allyl Acetate,” Lion et al., “Method for the Oxidation of Butenes to Linear Acetates.” BACKGROUND OF THE INVENTION The oxidation of propylene to acrylic acid in one step using a palladium metal catalyst supported on carbon black is described in US Pat. No. 3,624,147. However, this process is characterized by yields of 60% or less based on the amount of propylene converted, the operating temperature is generally above 90° C., and it is carried out at high pressure. Moreover, substantial amounts of CO ₂ are reported as unwanted by-products and low reaction rates are reported. A similar method was reported by Seeman et al. in J. Catal. 173 (1972), where palladium black and palladium activated charcoal were used to convert propylene to acrylic acid. However, only stoichiometric, non-catalytic conversions based on palladium metal are taught, thus providing an even less efficient process than the above US patent. Furthermore, several patents describe conventional methods for the preparation of supported palladium metal catalysts, for example by reduction of palladium salts, using reducing agents such as hydrogen, lower alcohols, hydrazine, or various olefins. For example US Patent 3275680
(Holzrichter) or 4435598 (Hinnenkamp). These teach the reduction of palladium salts with hydrogen or hydrazine. US Patent 4016200
(Onoda) also teaches that palladium compounds can be reduced to palladium metal using formalin, hydrazine, hydrogen, methanol, or olefins such as ethylene, propylene, butenes as reducing agents. Similarly, US Pat. No. 3,970,713 (Soharfe) also teaches the reduction of palladium and other metal salts to metal catalysts using hydrogen, alcohols, olefins, etc. as reducing agents. However, none of these references teach the preparation of highly activated palladium metal species with olefins under unique time and temperature conditions, nor do these catalysts teach the preparation of highly activated palladium metal species than was previously possible. It does not teach a surprisingly effective method for oxidizing olefins to alpha, beta unsaturated acids under mild operating conditions. Finally, FR Hartley “The Chemistry of Platinum and Palladium” Willie and Sons 380−
390 and 412-417 (1973) discloses the formation of complexes of ethylene with palladium chloride to give palladium ⁺² metal catalysts. However, as described below, the use of ethylene or chloride and the formation of a palladium ⁺² metal catalyst deactivates the catalyst of the present invention for the purpose of forming the desired product claimed herein. I understand. [Means for Solving the Problems] The object of the present invention is to convert olefins such as propylene to α, acrylic acid, etc. with higher yield and selectivity than the reported prior art methods.
An improved method for converting to β-unsaturated carboxylic acids in one step is provided. It is a further object of the present invention to oxidize isobutylene to methacrylic acid and butene-1 to crotonic acid in a similar manner. A further object of the present invention is to provide a novel palladium catalyst useful for achieving the above objects, and a method for producing the catalyst. Other objects of the invention will become apparent from the description and examples given below. When an activated palladium catalyst supported on carbon or alumina is used in accordance with the present invention, an olefin such as propylene is
It has been found that α,β-unsaturated carboxylic acids such as acrylic acid can be produced in high yield and with high selectivity by oxidation in the liquid phase under mild reaction conditions. Here, the supported palladium metal catalyst is first activated with an olefin, preferably an olefin corresponding to that to be oxidized, under conditions detailed below, before the oxidation. Originally
This uniquely advantageous catalyst, which should be inactive at temperatures below 60°C, is not only active at much lower temperatures, but they give a molar selectivity to acrylic acid of at least close to 90%, thus demonstrating the fact that Eliminate the production of unwanted CO ₂ . The same catalyst system is also effective in oxidizing isobutylene to methacrylic acid and butene-1 to crotonic acid. Thus, olefins having from 3 to about 4 carbon atoms can be oxidized by the catalysts prepared by the process of this invention. General methods for oxidizing propylene to acrylic acid are well described in the prior art and need not be described in detail here. Using a catalyst produced by a novel method discussed in detail below,
The oxidation reaction of propylene to acrylic acid is about 25~
Suffice it to say that it can be carried out uniquely at temperatures in the range of 120 DEG C. and pressures of 1 to 100 atmospheres. Preferably temperatures of 25 to 80°C and pressures of 1 to 10 atmospheres can be used, in contrast to the harsh conditions used in US Pat. No. 3,624,147. Moreover, as a result of this new catalyst, the reaction rate, selectivity, and thus yield are significantly increased over the use of catalyst alone, as shown in the examples below. In one preferred embodiment of the process, the liquid reaction medium is passed downwardly through a fixed catalyst bed to increase the reaction rate and simultaneously reduce the reactor volume, and the acrylic acid product is recovered from the bottom. It has been found to be advantageous to carry out the reaction in a trickle-bed reactor. Alternatively, the oxidation reaction can be carried out using an elaborating bed catalyst with circulating gas and solvent. The starting material from which the catalyst of the invention is prepared is any finely divided palladium in the metallic state on a support such as carbon or, less preferably, alumina;
Commercially available 5%, available from standard catalyst suppliers such as Engelhard Industries or Johnson Massey, Inc.
10% and 20% palladium on carbon. The term "palladium metal catalyst" or "palladium in the metallic state" is used commercially or in the US patent of Schiffre et al.
3,970,713 or by any known reduction means such as that shown in Holzlichter et al. U.S. Pat. means a palladium catalyst. While not specifically intending to be bound by theory, Applicants believe that in the normal course of handling and using prior art reduced catalysts following reduction of palladium, due to exposure to the atmosphere, some of the palladium surface species oxidation. It is this air-exposed palladium catalyst that is used as a starting material in the preparation of Applicants' new olefin-activated catalysts. ("Surface species" means any palladium species found on the surface of the catalyst itself, as recognized by those skilled in the catalysis art.) Without intending to be bound by this, when this partially oxidized palladium surface described above is contacted with propylene in accordance with Applicant's invention, it is It is with these positions that the propylene is converted and then forms the novel surface active species that are the activated catalysts of the present invention. Starting with, for example, a commercially reduced palladium metal catalyst, in the novel activated catalyst of the present invention, as evidence that commercially available reduced palladium is reoxidized under normal handling and exposure to air, for example, Two parts of propylene are used to activate the catalyst under oxygen-free conditions as described below.
1 part acetone and 1 part active catalyst species. In preparing the activated oxidation catalyst for use in the present invention using a carbon or alumina supported palladium metal catalyst as defined above with propylene or similar olefins, the activation treatment is carried out at a temperature of at least about 60°C. Temperatures up to 150℃, preferably approx.
At least about 10 minutes to about 120 minutes at a temperature of 65-95℃,
It is essential that the reaction be carried out under oxygen-free conditions as described below, preferably for at least about 30-60 minutes. This is generally at least about 1 atm, about 100
It is carried out at propylene pressures up to about 2-20 atmospheres, preferably about 2-20 degrees. When these catalysts are palladium on carbon activated in this way, it is used for the purpose of oxidizing propylene below about 60°C, which would otherwise be relatively unreactive, but here at about 25°C. It is surprisingly active. As mentioned previously, the speed and selectivity towards acrylic acid are considerably improved by this treatment. The term "activated palladium metal catalyst" is therefore used for the purposes of the present invention to refer to catalysts made according to the above process which are supported at higher speeds and at lower temperatures than known supported palladium catalysts. , meaning a catalyst that can oxidize propylene to acrylic acid. During the preparation of the catalysts described above, activation is carried out in the substantial absence of oxygen and preferably under essentially oxygen-free conditions in order to derive maximum activity from the catalyst. It is necessary to do so. Although the presence of small amounts of oxygen, to the extent readily determined by one skilled in the art, can result in a catalyst that performs under somewhat milder conditions than the commercially available catalysts described above, The fullest and most complete benefits are derived by activating the catalyst under conditions as free of oxygen as possible, at least within commercially possible levels. These oxygen-free conditions are achieved by known methods, such as by using degassed water, or a solvent and pure olefin gas during activation of the catalyst. Degassing is easily accomplished by holding the liquid under vacuum until it boils or by bubbling the desired olefin through the liquid until oxygen can no longer be replaced. Pure olefins are commercially available in various grades, such as chemically pure, research pure, or polymeric grades;
The latter two are preferred due to their high purity of over about 99.7% (the latter two are e.g.
Matheson, Division of Searle Medical
Products, and Sun Co., respectively). Once Applicant's catalyst is formed, at least a slight excess of olefin is added to prevent any deactivation, and preferably during the oxidation step a stoichiometric amount of reactor oxygen to oxidize the olefin to acrylic acid. Preferably, it is retained in an amount no greater than. It is understood that the presence of those metals or metal salts that may poison or alter the catalyst should be avoided in preparing the catalyst of the present invention. Examples include iron, manganese, copper, and oxidized forms of rhodium salts, chlorides, benzoquinones, heteropolyacids, and all other reagents that will oxidize palladium to palladium ⁺² . Other such harmful substances can be determined in a routine manner by those skilled in the art. For example, in addition to this, amines,
Materials such as hydrazine and ethylene have been found to be harmful and should be avoided when preparing and using the catalysts of the present invention. Moreover, it has been found that attempts to use hydrogen to prepare this catalyst should be avoided as it can cause an explosion when the catalyst is then exposed to the O ₂ propylene mixture. Although the catalyst of the invention can be prepared separately and kept in an active state provided it is kept in an oxygen-free atmosphere, more conveniently the catalyst of the invention is the same as that used for propylene oxidation. Preparation may be carried out in a reactor. This can be done, for example, by adding commercially available finely ground palladium on activated carbon to an aqueous medium in a sealed reactor, flushing the system with propylene gas, and then transferring the mixture under propylene pressure to the desired temperature for catalyst preparation. This can be conveniently accomplished by heating the mixture at that temperature for at least 30 minutes, again in the absence of oxygen and preferably in the presence of a slight excess of olefin. After preparation of the catalyst, the propylene is replaced by a mixture of propylene and oxygen, preferably the oxygen is present in near stoichiometric proportions to avoid deactivation of the catalyst, and the oxidation reaction is carried out at a pressure of about 1 to 10 atmospheres. Implemented. The pressure is maintained by adding additional gas mixture from time to time until the desired propylene conversion is achieved. Air can be used instead of oxygen, but in this case the amount of propylene must be adjusted accordingly. The activator of the catalyst is preferably propylene, but if desired it can be replaced by allylic hydrogen and other light olefins containing from 3 to 6 carbon atoms, preferably corresponding to the olefin to be oxidized. It can be used for. Most preferred are butene-1, butene-2, or isobutylene in addition to propylene. Olefin-activated catalysts remain active for extended periods of time as long as at least a small amount of acceptable olefin is present. It has therefore proved advantageous to carry out the reaction by constantly sparging the propylene/oxygen or air reaction mixture through the aqueous solution. By this method propylene is kept in excess and the catalyst remains highly active thereby preserving high selectivity and other advantages mentioned above. When the oxidation is carried out in batches, the ratio of catalyst to reaction medium desirably ranges from about 0.05 to about 5.0, preferably from about 0.1 to 1.0, gram atoms of palladium per liter of reactant. In a continuous process using, for example, a fixed bed reactor, the reaction is varied in a manner known in the art to achieve the high yields and selectivities described herein. It can be implemented effectively by The following examples are intended to illustrate the invention. Examples 1-6 and Comparative Examples 1-3 In the following Examples 1-9, several reactions were carried out according to the following general procedure. on carbon (Ingelhard Industries)
One gram of 10% palladium metal was added to an 85 ml Fisher Porter Aerosol tube. Next, 30 ml of degassed distilled water was added and the filter tube was attached to the pressure manifold. The mixture was flushed three times with pure propylene gas (research purity grade) at 50 psi. The mixture was then heated with stirring under 50 psi of pure propylene until the desired activation temperature was reached, whereupon the mixture was stirred for 30 minutes. The stirred mixture was then brought to the desired reaction temperature and the propylene was replaced with a gas mixture developing a composition of 60% 0 ₂ /40% pure C ₃ H ₆ to a total pressure of 100 psig. In most cases the reaction proceeded immediately and the pressure dropped. The total pressure
Bring the O ₂ /C ₃ H ₆ gas mixture to total pressure when 80 psig is reached.
I put it in to make it 100 psig. This was repeated as often as necessary during the course of the experiment. After the measured reaction time, the mixture was cooled, the gas was captured and analyzed, and the mixture was filtered. The catalyst was washed with both organic and aqueous solutions to remove small amounts of acrylic acid retained on the surface. The filtrate was analyzed by standard gas chromatography to determine the product composition. The conditions for making the catalyst and for oxidizing propylene as shown in Table 1 below were varied experimentally to better illustrate the scope of the invention. Small amounts of by-products such as acetone, acrolein, acetic acid, and _CO2 were also reported. The results in Table 1 show that using temperatures between 65 and 80°C results in catalysts that are active at 40 or 50°C. A similar treatment at 40-50°C gives an inactive catalyst at these temperatures. Catalysts produced at 80°C are also more selective for oxidation at lower temperatures than those produced at 65°C. Reactions carried out at 65°C were faster and more selective than those carried out at 50°C at equivalent activation temperatures. The catalyst treated at 80°C was active for oxidation at 30°C, but the rate and selectivity to acrylic acid was lower than at 65°C. In contrast, Comparative Examples 1-3 demonstrate that yield and selectivity are negligible when commercially available catalysts are not subjected to the activation process described above.

【table】

[Table] was tested.
The following Examples 7-9 illustrate the oxidation of isobutylene and butene-1 using the procedures of the previous examples. Example 7 The reaction was carried out according to the procedure of Example 2 except that propylene was replaced by isobutylene and methacrylic acid was obtained as the main product in a high yield of approximately 65%. Example 8 The reaction was carried out according to the procedure of Example 4, except that propylene was replaced by isobutylene, giving methacrylic acid as the main product in a high yield of approximately 65%. Example 9 The reaction was carried out according to the procedure of Example 2 except that propylene was replaced by butene-1 and crotonic acid was obtained as the major product in a high yield of approximately 55%. Example 10 When 10% palladium on carbon was activated with propylene under the conditions of Example 6 and the propylene was oxidized in a similar manner, but at a reaction temperature of 30°C, acrylic acid was formed as the main product. .

Claims (1)

Claims: 1. A supported palladium metal catalyst in an aqueous liquid medium with a _C3 - _C6 olefin at a temperature of at least 60°C.
A method for preparing an activated palladium metal catalyst for the oxidation of _C3 - _C4 olefins to α,β-unsaturated carboxylic acids, comprising contacting in the absence of oxygen for at least 10 minutes at a temperature of . 2. The method of claim 1, wherein the catalyst is contacted with the olefin at a temperature of 60°C to 150°C for at least 10 to 120 minutes. 3. The method of claim 1, wherein the catalyst is contacted with the olefin under a pressure of 1 to 100 atmospheres.