JPH06329577A - Production of lower fatty acid from lower aliphatic ketone - Google Patents

Abstract

PURPOSE:To efficiently obtain a lower fatty acid useful as a raw material for industrial products in high selectivity and in high yield by bringing a specific aliphatic ketone into contact with a zeolite catalyst in the presence of water at a given reaction temperature in a vapor phase. CONSTITUTION:A lower aliphatic ketone of the formula (R is lower alkyl; R' is H or lower alkyl) such as methyl ethyl ketone is brought into contact with a zeolite catalyst in the presence of water (the amount of water used is preferably 0.1-50wt.% based on the lower aliphatic ketone) at 300-50O deg.C in a vapor phase to give the objective compound.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a lower fatty acid from a lower aliphatic ketone in one step with good selectivity. 2. Description of the Related Art Since lower aliphatic ketones have a carbonyl group, they are highly reactive, and chemicals of high utility value can be synthesized by reactions such as aldol condensation. Is used as. For example, from acetone, methyl methacrylate, bisphenol A, methyl isobutyl ketone, ketene (a raw material such as acetic anhydride), etc. are produced. However, no literature has been found synthesizing lower fatty acids directly from lower aliphatic ketones or by reacting lower aliphatic ketones with water, and a method for producing lower fatty acids from lower aliphatic ketones is described in the case of synthesizing acetic acid from methyl ethyl ketone. As represented, it is limited to liquid or gas phase air oxidation processes. However, as is well known, since the air oxidation method proceeds as a radical reaction, the selectivity is poor, so that there is a problem that the separation and purification costs are high and the safety measures cost is also high. An object of the present invention is to establish a technique for efficiently producing lower fatty acids from lower aliphatic ketones. The present inventors have completed the present invention as a result of intensive studies to solve the above problems. That is, according to the present invention, a lower aliphatic ketone represented by the following general formula (1) is brought into contact with a zeolite catalyst in the gas phase at a reaction temperature of 300 to 500 ° C. in the presence of water. A method for producing a fatty acid is provided. In the above formula, R represents a lower alkyl group and R'represents hydrogen or a lower alkyl group. Examples of the lower alkyl group include those having 1 to 6 carbon atoms, and preferably those having 1 to 4 carbon atoms. In the present invention, the lower aliphatic ketone (hereinafter,
The lower fatty acid production mechanism from (also referred to as lower ketone) is presumed as the following formula. That is, the lower ketone as a raw material forms an aldol condensate (intermediate 2) from a dimer (intermediate 1), and the intermediate 2 produced here is a carbonium ion (intermediate) on an acid catalyst in the presence of water. It is presumed that an unstable intermediate (intermediate 4) is obtained via 3), and this is converted to a lower fatty acid and a lower olefin for stabilization. [Chemical 1] (In the above formula, R represents a lower alkyl group, and R'represents a hydrogen atom or a lower alkyl group.) As can be seen from the above presumed mechanism, in order to smoothly proceed the lower fatty acid production reaction of the present invention, Requires the presence of acid sites and water, but since water is a by-product during the aldol condensation that produces intermediate 2, fatty acids are produced even in the absence of water, but the reaction proceeds smoothly by the addition of water from the outside. Can be made. In addition, the water present in the reaction system not only directly participates in the reaction, but also greatly contributes to the promotion of desorption of the product adsorbed on the catalyst surface and the removal of the carbonaceous material deposited on the catalyst by the side reaction. It also plays the role of sustaining the reaction with good selectivity for a continuous time. As is well known, various acid points having different acid strengths are present on a solid acid catalyst, and it is required to have a specific acid point in order to selectively proceed a specific reaction. That is, an acid point that is too strong or too weak for a particular reaction has almost no catalytic action on the main reaction and promotes only a side reaction. It is well known that the zeolite catalyst used in the present invention has various types of acid sites. Therefore, the lower ketone conversion rate in the initial stage of the reaction is high, but a wide variety of side reactions occur to lower the lower fatty acid selectivity. . The side reaction in this case is mainly an aromatic formation reaction and a carbonaceous material formation reaction, and it is presumed that it is due to an excessively strong acid point, but its activity duration is not so long and it is selected after the disappearance of the strong acid point. Converts to a catalyst that efficiently produces lower fatty acids. That is, it was confirmed that the zeolite catalyst used in the present invention becomes a selective lower fatty acid production catalyst in the stationary activity period when the reaction is continued under the reaction conditions of the present invention. In the present invention, the ZSM-5 type zeolite catalyst is preferably used, and the pore structure of the zeolite catalyst can be said to be one of the important factors that determine the selectivity. As is clear from the MTG method (method for producing gasoline from methanol), the shape effect of the zeolite catalyst is large, and in the present invention, the intermediate 2 does not react with the lower ketone and proceeds to the intermediate 4 via the intermediate 3. Is presumably due to the contribution of the shape effect of the zeolite catalyst. It is considered that the presence of the intermediate 4 on the catalyst and the fact that the intermediate 4 is decomposed into the lower fatty acid and the lower olefin and stabilized are due to the surface state and the shape of the catalyst. Such a specific shape is present on the zeolite surface from the beginning, and may be secondarily formed on the catalyst by carbonaceous substances by-produced in the early stage of the reaction or coexisting water. Although sufficient measurement is difficult, it is considered that the lower fatty acid can be produced from the lower ketone due to the influence of the shape effect and the electronic state of the catalyst surface represented by the acid point. The aliphatic ketone as the raw material of the present invention must be compatible with the zeolite catalyst pores, and those having too large a molecular size do not react smoothly. Since the lower aliphatic ketone molecule used in the present invention can easily enter the catalyst pores suitable for fatty acid production, it is efficiently converted into lower fatty acid here. The reaction temperature in the present invention is 300 to 500.
C., preferably 350 to 450.degree. If the reaction temperature is too low, the reaction does not proceed sufficiently, and thus many intermediate products are produced. For example, when acetone is used as the starting ketone, diacetone alcohol and mesityl oxide are the main products. If the reaction temperature is too high, the reaction becomes excessive and the production of aromatic compounds and carbonaceous substances increases, and the selectivity of lower fatty acids decreases significantly. The amount of water added is 0.1 to 50% by weight, preferably 1 to 40% by weight of the raw material ketone. If the amount of water added is too small, the reaction of forming intermediate 4 is suppressed. And the desorption effect of the adsorbate by water and the removal effect of the carbonaceous material are also reduced, so that the deposition rate of the carbonaceous material on the catalyst is increased and the catalyst life is reduced. When the amount of water added is too large, the negative effect on the catalyst and the reaction is smaller than when the amount added is too small, but when a large amount of water is present, the reaction rate decreases and the reaction rate decreases, resulting in poor productivity. Further, the presence of a large amount of water lowers the energy efficiency and the product separation efficiency, and the presence of excess water is not preferable from an industrial viewpoint. The method of the present invention is carried out by passing a lower ketone through the zeolite catalyst layer. In this case, the liquid hourly space velocity (hereinafter abbreviated as LHSV) is 0.1 to 10 hr ⁻¹ , preferably 0.2 to 5 hr ⁻¹ , and if it is too large, the reactivity decreases, and if it is too small, it moves onto the catalyst. Since the residence time becomes longer, side reactions such as carbonaceous material production increase. The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples. Examples 1 to 12 and Comparative Examples 1 to 4 An ordinary vapor phase flow reactor using a quartz reaction tube having an inner diameter of 30 mm was used, and 20 ml of hydrogen type ZSM-5 zeolite catalyst was filled in the central portion. To obtain a catalyst layer. This reaction tube was installed in a tubular electric furnace so that the temperature of the catalyst layer could be controlled by a thermocouple pushed into the center of the catalyst layer. Acetone and water as raw materials are supplied to the catalyst layer in a gas state from the inlet of the reaction tube through the vaporizer, and the reaction product is collected in the receiver through the water-cooled cooler provided at the outlet of the reaction tube, and then the dry ice-
The low boiling point components were collected by a cold trap using methanol as a cooling agent. For the cold trap, make the pipe diameter of the inlet part thicker and pay attention to the clogging of the cold trap due to ice sticking to the pipe wall due to the condensation of water, and make the cold trap outlet part a serpentine type to escape the low boiling point component in the form of gas Was prevented. By doing so, almost all of the reaction product can be collected. After reacting acetone alone or acetone and water for 14 hours in the reaction system shown above, the reaction products were collected and analyzed by gas chromatography to obtain the results shown in Table 1. Example 13 In the same manner as in Examples 1 to 12, methyl ethyl ketone was used in place of the starting material acetone, the reaction temperature was 375 ° C., and L was L.
The reaction was carried out for 14 hours with HSV being 2 hr ⁻¹ and H ₂ O being 5% by weight of the amount of methyl ethyl ketone used. The reaction rate was 8.9%, the carboxylic acid selectivity was 52.3 wt% and the olefins selectivity was 40.8 wt. %, The main component of carboxylic acid was propionic acid, and the main component of olefins was pentenes. [Table 1] According to the present invention, a lower fatty acid can be obtained from a lower aliphatic ketone by a simple one-step reaction with good selectivity. The reaction of the present invention has never been reported so far, and the present invention provides a novel method for producing a lower fatty acid from a lower ketone, and its industrial significance is great.

Claims (1)

[Claims] (Wherein R represents a lower alkyl group, R'represents a hydrogen atom or a lower alkyl group),
A method for producing a lower fatty acid, which comprises contacting with a zeolite catalyst in a gas phase at a reaction temperature of 300 to 500 ° C in the presence of water. 2. The method for producing a lower fatty acid according to claim 1, wherein the amount of water present is 0.1 to 50% by weight of the amount of the lower aliphatic ketone used as a raw material.