JP2009220099A - Method for producing catalyst for production of lower aliphatic carboxylic acid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst for producing lower aliphatic carboxylic acid with improved activity and selectivity, such as acetic acid, from lower olefins and oxygen. <P>SOLUTION: The catalyst is obtained by contacting an alkaline substance with metal oxide carriers such as silica, alumina, and silica alumina unlike conventional methods and then loading a compound comprising at least one element selected from among elements of groups 8, 9 and 10 of the periodic table (hereinafter, referred to as (a) group compound), a compound comprising at least one element selected from a gallium, indium, thallium, germanium, tin, lead, phosphorus, arsenic, antimony, bismuth, sulfur, selenium, tellurium and polonium (hereinafter, referred to as (b) group compound) and at least one type of chloride of an element selected from among elements of Group 11 of the Periodic Table and zinc (hereinafter, referred to as (c) group compound), on the carriers. A heteropoly acid may also be loaded if necessary. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a catalyst for producing a lower aliphatic carboxylic acid used when synthesizing a lower aliphatic carboxylic acid from raw materials of lower olefin and oxygen, and a method for producing a lower aliphatic carboxylic acid using the catalyst.

  Various proposals have been made on a method for producing acetic acid from ethylene by a one-step reaction because of many industrial and economical advantages. For example, a liquid phase one-step oxidation method using a redox catalyst of a metal ion pair such as palladium-cobalt or palladium-iron (French Patent No. 1448361), a catalyst comprising palladium-phosphoric acid or a sulfur-containing modifier is used. Gas phase one-step oxidation method using a method (Japanese Patent Publication No. Sho 46-006763) using a method (Japanese Patent Publication Nos. 47-013221 and 51-029425) and a three-group oxygen compound is disclosed. ing. Further, as a method for producing acetic acid using a catalyst containing a palladium compound and a heteropolyacid, a gas phase one-step oxidation method using a catalyst comprising a phosphovanadomolybdic acid palladium salt has been proposed (Japanese Patent Laid-Open No. 54-57488). ).

Recently, as a catalyst for obtaining acetic acid from ethylene and oxygen, a catalyst in which metal palladium and a group 14, 15, or 16 element of the periodic table are supported on a carrier has been proposed (Patent Document 1: Japanese Patent Application Laid-Open No. 11-347412). Issue gazette). These supported catalysts are prepared in the following order of steps.
First step: A step of supporting a compound containing palladium on a carrier Second step: A step of performing an alkali treatment Third step: A step of reducing a compound containing palladium into metallic palladium Fourth step: Periodic table No. 14, A step of supporting a group 15 or 16 element

  In the supported catalyst, an egg shell type palladium catalyst is advantageous. The egg shell type refers to a type in which the palladium loading position in the carrier is in the vicinity of the surface of the carrier. Since the reaction substrate is difficult to diffuse into the internal region of the catalyst support, the metal component supported inside the support has a low probability of coming into contact with the reaction substrate and has a small contribution to the reaction. In the egg shell type, since many metal components having a catalytic action are present on the surface of the support, the efficiency is higher for the reaction than in the normal type even with the same amount of metal components. In order to obtain an egg shell type palladium catalyst, a production method including an alkali treatment step such as sodium metasilicate is known (Patent Document 2: JP-A-7-89896). Japanese Unexamined Patent Publication No. 2000-308830 (Patent Document 3) discloses a method for producing an egg shell type palladium-supported catalyst including a step of treating with an alkaline earth metal salt such as barium hydroxide.

  The process for producing a catalyst for producing acetic acid disclosed in Patent Document 1 includes an alkali treatment step for making a metal component such as palladium unevenly distributed on the surface of the carrier (eg, making it an egg shell), followed by a third component loading step. have. Although the catalyst obtained by this process has high catalytic activity, there is a problem that the catalyst preparation process is long and the catalyst is deteriorated during the reaction. Therefore, the present inventor decided to proceed with the development of a simple method for preparing a catalyst capable of suppressing deterioration while maintaining high activity.

  Further, in the production method in which acetic acid is obtained by reacting ethylene and oxygen, carbon dioxide is generated as a by-product. For example, according to the description in Patent Document 2, the carbon dioxide selectivity is about 5%. The generation of carbon dioxide means that the yield of acetic acid is lowered. Further, in recent years, suppression of carbon dioxide production has become a major issue from the viewpoint of preventing global warming and reducing environmental burden. In the industrial aspect, in order to process the by-product carbon dioxide, a large amount of capital investment and operation and maintenance costs of the equipment are required. Therefore, the present inventor decided to study further reduction of by-product carbon dioxide in the production of acetic acid.

JP-A-7-89896 JP-A-9-67298 JP 2000-308830 A

The main object of the present invention is to solve the problems of the background art as described above. That is, the present invention improves the yield of lower aliphatic carboxylic acid, and lowers the production of carbon dioxide (CO ₂ ), which is a by-product, from the conventional method, such as lower olefin such as ethylene and oxygen. It is an object of the present invention to provide a supported catalyst for producing a lower aliphatic carboxylic acid such as acetic acid and a method for producing the same.

  As a result of intensive studies on the above problems, the present inventors, as opposed to the conventional method, contacted an alkaline substance with a metal oxide support such as silica, alumina, silica alumina or the like first, and then the periodic table was added thereto. A compound containing at least one element selected from Group 8, 9 and 10 elements (hereinafter referred to as (a) group compound), gallium, indium, thallium, germanium, tin, lead, phosphorus, arsenic, antimony, bismuth , A compound containing at least one element selected from sulfur, selenium, tellurium and polonium (hereinafter referred to as (b) group compound) and a chloride of an element selected from group 11 elements and zinc in the periodic table (hereinafter referred to as ( c) a method for producing a supported catalyst, wherein at least one of the group compounds) is supported on a carrier (hereinafter sometimes referred to as a catalyst preparation method) Heading, it has led to the completion of the present invention.

That is, the present invention relates to the following items [1] to [12].
In the present invention, “periodic table” refers to the periodic table of the revised IUPAC inorganic chemical nomenclature (1989).

[1] A method for producing a supported catalyst for producing a lower aliphatic carboxylic acid using a lower olefin and oxygen, comprising the following first, second and third steps in that order.
Step 1 Contacting the support with an alkaline substance to obtain an impregnated support (A) Step 2 In the impregnated support (A), at least one element selected from Group 8, 9 and 10 elements of the periodic table is added. And at least one selected from gallium, indium, thallium, germanium, tin, lead, phosphorus, arsenic, antimony, bismuth, sulfur, selenium, tellurium, and polonium. A compound containing a seed element (hereinafter referred to as (b) group compound) and at least one chloride of an element selected from group 11 element and zinc in the periodic table (hereinafter referred to as (c) group compound) The step of obtaining the impregnated carrier (B) by contacting with it The third step The step of obtaining the supported catalyst (C) by bringing the impregnated carrier (B) into contact with the reducing substance

[2] The method for producing a supported catalyst according to [1], further comprising a fourth step of supporting at least one compound selected from a heteropolyacid and a salt thereof (hereinafter referred to as (d) group compound) on a carrier. .

[3] The method for producing a supported catalyst according to [1] or [2], wherein the (c) group compound contains at least two substances of gold chloride and zinc chloride.

[4] The method for producing a supported catalyst according to any one of “1” to “3”, wherein the (a) group compound is a compound containing at least one element selected from palladium, nickel, and platinum.

[5] The carrier according to any one of “1” to “4”, wherein the (b) group compound is a compound containing at least one element selected from gallium, germanium, tin, lead, bismuth, selenium and tellurium. Type catalyst production method.

[6] The method for producing a supported catalyst according to any one of “2” to “5”, wherein the polyatom of the heteropolyacid of the group compound (d) and / or a salt thereof is tungsten and / or molybdenum.

[7] The support according to any one of “2” to “6”, wherein the heteroatom of the heteropolyacid of the compound (d) and / or a salt thereof is at least one element selected from phosphorus, silicon, and boron. Type catalyst production method.

[8] (2) “2”, wherein the heteropolyacid of the group compound and / or a salt thereof is at least one compound selected from silicotungstic acid, phosphotungstic acid, silicomolybdic acid, phosphomolybdic acid and salts thereof. -The manufacturing method of the supported catalyst in any one of "7".

[9] A lower fat by reaction of a lower olefin and oxygen, characterized in that a supported catalyst for producing a lower aliphatic carboxylic acid produced by the method according to any one of [1] to [8] is used. For producing aromatic carboxylic acid.

[10] The process for producing a lower aliphatic carboxylic acid according to “9”, wherein the lower olefin is ethylene.

  By using the supported catalyst obtained by the method for producing a supported catalyst of the present invention, in the production of a lower aliphatic carboxylic acid by the reaction of a lower olefin and oxygen, the productivity of the lower aliphatic carboxylic acid is improved and carbon dioxide gas is produced. It became possible to suppress the by-product. Thereby, the manufacturing cost of lower aliphatic carboxylic acids such as acetic acid can be reduced.

  Hereinafter, preferred embodiments of the present invention will be described. However, the present invention is not limited to these embodiments, and it is understood that various modifications can be made within the spirit and scope of the present invention. I want to be.

  The supported catalyst obtained by the production method of the present invention comprises a lower olefin, that is, an olefin compound having 1 to 6 carbon atoms (preferably ethylene) and oxygen (preferably in the gas phase) to react with the corresponding lower fat. It can be suitably used as a catalyst for the production of an aromatic carboxylic acid (acetic acid when the lower olefin is ethylene).

Hereinafter, a preferred method for producing a supported catalyst of the present invention will be described in detail.
First, the following first to third steps are performed in that order. In order to improve the performance of the catalyst, it is preferable to further perform the following fourth step.
Step 1 Contacting a carrier with a solution of an alkaline substance (hereinafter referred to as “alkaline solution”) to obtain an impregnated carrier (A) Second step (a) Group compound (for example, Pd Compound), (b) group compound (for example, compound containing Te), and (c) group compound (for example, Au chloride and Zn chloride) are impregnated, and impregnated support (B) is obtained. Step of obtaining Step 3 of contacting the impregnated support (B) with a reducing substance (for example, hydrazine) to reduce the compounds of groups (a) and (c) to obtain a supported catalyst (C). Step of supporting the supported catalyst (D) by supporting the (d) group compound (for example, silicotungstic acid and / or a salt thereof) on the supported catalyst (C).

  In the present invention, it is important to continue the second step after the first step without performing a treatment such as drying. Then, the impregnated support (A) is impregnated with the solution A in which the (a) group compound, (b) group compound, and (c) group compound are dissolved. The total amount of the alkaline solution and the solution A is preferably 1.1 to 10.0 times the amount of water absorption of the carrier.

  In the second step, the solution of the group compound (a), the solution of the group compound (b), and the solution of the group compound (c) may be separately brought into contact with the support and impregnated. It is preferable from the viewpoint of simplifying the process that they are simultaneously contacted and impregnated. In addition, when contacting each solution separately, it is preferable to make the solution of (a) group compound first. In addition, other additional steps may be included for the purpose of improving the performance of the catalyst of the present invention.

  Since the reduction treatment in the third step is for converting the metal element in the (a) group compound and (c) group compound into a metal, it must be performed after the second step.

  It is more preferable that the supported catalyst for producing a lower aliphatic carboxylic acid obtained by the method of the present invention further supports a group (d) group compound (heteropolyacid and / or salt thereof). Therefore, within the range not impairing the effects of the present invention, a step of supporting the (d) group compound may be included in each of the first to third steps or before and after each step, as described above. It is preferable to provide a step (fourth step) for supporting the group compound (d) after the third step. Hereinafter, each process will be described in detail.

1st process The process of impregnating a support | carrier with an alkaline solution In this process, the support | carrier is made to impregnate the support | carrier with the amount of alkali solutions exceeding 0.9 mass times and 1.3 mass times or less of the water absorption amount (a definition is mentioned later). The operation can be performed at room temperature. The alkaline solution is uniformly impregnated on the support. When the impregnation operation is completed, the operation proceeds to the next step without performing an operation such as drying.

<Carrier>
The carrier used for the production of the supported catalyst of the present invention is not particularly limited, but it is preferable to use a porous material generally used as a catalyst carrier. Specific examples include silica, silica-alumina, diatomaceous earth, montmorillonite, and titania. More preferred is silica.
Moreover, there is no restriction | limiting in particular in the shape of a support | carrier. Specifically, a powder form, a spherical form, a pellet form, etc. are mentioned. An optimum shape may be selected according to the type of reaction and reactor used.

There are no particular restrictions on the size of the carrier particles. When the production of the lower aliphatic carboxylic acid is carried out in a tubular reactor having a fixed bed for gas phase reaction, when the support is spherical, the particle diameter is preferably 1 to 10 mm, more preferably 2 to 8 mm. is there. When the reaction is carried out by filling the tubular reactor with a supported catalyst, if the particle diameter is smaller than 1 mm, a large pressure loss occurs when the gas is circulated, and there is a possibility that the gas cannot be circulated effectively. On the other hand, if the particle diameter is larger than 10 mm, the reaction gas cannot be diffused to the inside of the catalyst, and the catalytic reaction may not proceed effectively. The pore structure of the carrier preferably has a pore diameter of 1 to 1000 nm, more preferably 3 to 200 nm. Carrier, specific surface area measured by the BET method is preferably from ^{30~700m 2 / g, 50~300m 2 /} g is more preferable. The bulk density of the carrier is preferably 50 to 1000 g / l, more preferably 300 to 500 g / l.

Here, the water absorption amount and water absorption rate of the carrier are values measured by the following measuring methods.
1. About 5 g of the carrier is weighed with a balance (W ₁ g) and placed in a 100 cc beaker.
2. About 15 ml of pure water (ion exchange water) is added to the beaker so as to completely cover the carrier.
3. Leave for 30 minutes.
4). Empty the carrier and pure water on the wire mesh and drain the pure water.
5. The water adhering to the surface of the carrier is removed by gently pressing with a paper towel or the like until the surface is no longer glossy.
6). The weight of the carrier + pure water is measured (W ₂ g).
7). The water absorption rate of the carrier is calculated from the following formula.

Water absorption (g / g- _{carrier) = (W 2 -W 1)} / W 1
The water absorption amount (g) of the carrier is calculated by the water absorption rate of the carrier (g / g-carrier) × the weight (g) of the carrier used.

<Alkaline solution>
The alkaline solution used in the present invention may be any alkaline solution. For example, alkali metals such as alkali metal or alkaline earth metal hydroxides, alkali metal or alkaline earth metal bicarbonates, alkali metal or alkaline earth metal carbonates, alkali metal or alkaline earth metal silicates A solution of the compound may be mentioned. As the alkali metal, lithium, sodium and potassium are used. Barium or strontium is used as the alkaline earth metal. Preferably, sodium metasilicate, potassium metasilicate, sodium hydroxide, potassium hydroxide, barium hydroxide, or strontium hydroxide is used.

An alkaline compound is used excessively with respect to the sum total of the below-mentioned (a) group compound, (b) group compound, and (c) group compound. The amount is 1 to 10 times, more preferably 1.2 to 5 times the total molar concentration of each compound.
Examples of the solvent for the alkaline solution include water, methanol, ethanol and the like. Preferably it is water.

  The method for impregnating the carrier into the alkaline solution is not particularly limited.For example, (I) after immersing the carrier in a large amount of alkaline solution for a while and then removing the carrier impregnated with the alkaline solution for the amount of water absorption, (II) A method of immersing the carrier in a solution obtained by dissolving an alkaline compound in a solvent and increasing the amount of water absorbed by the carrier. From the viewpoint of reducing the amount of waste liquid treated, the method (II) is desirable.

  The alkaline solution is preferably contained in the carrier in an amount corresponding to more than 0.9 mass times and 1.3 mass times or less of the water absorption amount of the carrier. If the amount of the alkali solution is 0.9 mass times or less of the water absorption amount of the carrier, the content may be uneven. If it exceeds 1.3 times the mass, the carrier cannot absorb all of the alkaline solution. The water absorption amount of the carrier is a value measured with pure water, and although strictly different from the value for an alkaline solution (alkaline aqueous solution), it is used as it is for convenience.

Step 2 Step of impregnating impregnated carrier (A) in solution A to obtain impregnated carrier (B) In this step, impregnated carrier (A) obtained by impregnating into an alkaline solution is added to (a) group compound, ( b) Impregnation of the solution A in which the group compound and (c) the group compound are dissolved is impregnated by contact.

<(A) Group Compound>
The (a) group compound is a compound containing at least one element selected from Group 8, 9 and 10 elements of the periodic table. The Group 8, 9 and 10 elements of the periodic table are iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium and platinum, preferably palladium, platinum and nickel, particularly preferably palladium.
(A) Group compounds may be in any state. Compounds containing Group 8, 9, and 10 elements, such as chlorides, nitrates, acetates, phosphates, sulfates, oxides and oxides containing the elements (metal state) may be used as they are. Absent. That is, the element may be ionic in the compound or a zero-valent so-called metallic state.

  (A) Group compounds include metal palladium, metal platinum, metal nickel, halides such as palladium chloride, chloroplatinic acid and nickel chloride, organic acid salts such as palladium acetate and platinum acetate, palladium nitrate, platinum nitrate and nickel nitrate. And nitrates such as palladium oxide, nickel oxide, sodium tetrachloropalladate, potassium tetrachloropalladate and the like, and may be complexes having an organic compound such as acetylacetonate, nitrile, and ammonium as a ligand. . Particularly preferred are sodium tetrachloropalladate, hexachloroplatinic acid, potassium tetrachloropalladate, palladium nitrate and the like. Moreover, these (a) group compounds may be used independently, respectively, and multiple types can also be used together.

  (A) The group compound can be supported on the carrier by preparing a homogeneous solution containing at least one kind of the (a) group compound and impregnating an appropriate amount of the carrier with the solution. More specifically, the (a) group compound is dissolved in a suitable solvent such as water or acetone, or an inorganic acid or organic acid such as hydrochloric acid, nitric acid, or acetic acid to obtain a homogeneous solution.

<(B) Group Compound>
The (b) group compound is a compound containing at least one element selected from gallium, indium, thallium, germanium, tin, lead, phosphorus, arsenic, antimony, bismuth, sulfur, selenium, tellurium and polonium. Examples of the “compound containing at least one element” include the element itself (metal) or a chloride, nitrate, acetate, phosphate, sulfate, oxide and the like containing the element, Examples include complexes having an organic substance such as acetylacetonate and nitrile as a ligand.

(B) As an element contained in a group compound, gallium, germanium, tin, lead, bismuth, selenium and tellurium are preferable, and tellurium or selenium is particularly preferable.
Specific examples of the (b) group compounds include telluric acid (H ₆ TeO ₆ ), telluric acid (H ₂ TeO ₃ ), selenic acid (H ₆ SeO ₆ ), and selenious acid (H ₂ SeO ₃ ). It is done.

<(C) Group Compound>
The (c) group compound is a chloride of an element selected from Group 11 elements (namely, gold, silver, copper) and zinc of the periodic table. The group 11 element is preferably gold. The (c) group compound is not particularly limited as long as it is a chloride (including a salt) of an element selected from Group 11 elements and zinc. More specifically, a _{ZnCl 2, CuCl 2, AgCl,} AuCl 3, HAuCl 4 and chloroauric acid salt.

Examples of the chloroaurate include LiAuCl ₄ , NaAuCl ₄ , KAuCl ₄ , RbAuCl ₄ , CsAuCl ₄ , Mg (AuCl ₄ ) ₂ , Ca (AuCl ₄ ) ₂ , Sr (AuCl ₄ ) ₂ , and Ba (AuCl ₄ ) _2. Illustrated. Among these, LiAuCl ₄ , NaAuCl ₄ , and KAuCl ₄ are preferable, and NaAuCl ₄ is particularly preferable.
(C) It is preferable in terms of catalyst performance to use both gold chloride (including chloroaurate) and zinc chloride as the group compound.

  The total amount of the alkali solution and the solution A is 1.1 mass times or more and 10.0 mass times or less of the water absorption amount of the carrier (a). More preferably, it is 1.5-8.0 mass times, Most preferably, it is 2.0-6.0 mass times. If the total amount is less than 1.1 times by mass, the catalyst component may be unevenly supported on the carrier, which is not preferable. If it exceeds 10.0 mass times, the catalyst performance will not be affected, but it is not preferred because problems in catalyst production such as an increase in the amount of wastewater may occur.

In the second step, each compound may be brought into contact with the impregnated carrier (A) individually. That is, (a) group compound solution A ¹ , (b) group compound solution A ² , (c) group compound solution A ³ were prepared, and each solution was brought into contact with the impregnated carrier (A) individually. May be. In this case, the total amount of the alkaline solution and the solution A is the total amount of the alkaline solution, the solution A ¹ , the solution A ² and the solution A ³ . Further, the impregnation operation may be performed with the solution A ¹ , the solution A ² , and the solution A ³ as one solution (referred to as a solution A ^{1 + 2 + 3} ). In this case, the sum of the solution A ^{1 + 2 + 3} and the alkali solution corresponds to the total amount of the alkali solution and the solution A. Similarly, the total amount of the alkaline solution and the solution A is calculated for other combinations of solutions.

  The amount of the solution A is preferably 1.0 to 10.0 times the amount of water absorption of the impregnated carrier (A), more preferably 2.0 to 8.0 times, and most preferably 2.0 to 6. It is 0 mass times.

  In the second step, the impregnated support (A) and the solution A are contacted to convert the raw metal salt into a water-insoluble substance, and a catalyst precursor in which a metal component such as Pd or Au is supported on the support in an egg shell form. Can be formed. The conditions are not limited, but the contact time is preferably 0.5 to 100 hours, preferably 3 to 50 hours. If it is less than 0.5 hour, a desired amount of the catalyst component is hardly supported, and the catalyst performance may not be sufficient. Further, the contact with the impregnated carrier (A) for longer than 100 hours may be eroded, which is not preferable.

  The contact temperature is not particularly limited, but is desirably 10 to 80 ° C, preferably 20 to 60 ° C. If it is lower than 10 ° C, the conversion reaction may be insufficient. If it exceeds 80 ° C., aggregation of catalyst components such as palladium and gold may proceed.

3rd process The process which makes a reducing substance contact an impregnation support | carrier (B), and performs a reduction process to (a) group compound and (c) group compound.
In this step, for example, sodium chloropalladate as the group (a) compound is reduced to metallic palladium. (C) Group compounds are also reduced to the metal state of each element. The coexisting group (b) compounds are also subjected to reduction treatment. These compounds are reduced to a trivalent or lower valence state.
The reduction treatment is preferably performed on the compound in which the (a) group compound and (b) group compound are supported on a carrier. By this operation, when the (a) group compound is in an ionic state, the interaction with the (b) group compound can be achieved.
Further, the reduction treatment may be performed after supporting the heteropolyacid and / or its salt as the (d) group compound on the impregnated carrier (B). That is, the fourth step and the third step may be interchanged. An example is shown below.

  First, the first step: the step of bringing the carrier into contact with an alkaline substance to obtain the impregnated carrier (A) is performed, and then the second step: the (a) group compound, (b) group compound, (c ) Impregnating a solution containing a group compound to obtain an impregnated carrier (B), and fourth step: impregnating the impregnated carrier (B) with a solution containing the (d) group compound to obtain a supported catalyst (D). Step and third step: A step of performing a reduction treatment on the supported catalyst (D) is sequentially performed.

  Examples of the reducing substance include hydrazine, hydrogen, ethylene, carbon monoxide and the like. By bringing these substances into contact with the impregnated carrier (B) or the supported catalyst (C) in the liquid phase or gas phase, the (a) group compound or the like can be reduced.

The liquid phase reduction may be performed either in a non-aqueous system or an aqueous system using alcohol or hydrocarbons. As the reducing agent, carboxylic acid and its salt, aldehyde, hydrogen peroxide, saccharide, polyhydric phenol, diborane, amine, hydrazine and the like are used. Examples of the carboxylic acid and its salt include oxalic acid, potassium oxalate, formic acid, potassium formate, and ammonium citrate, and examples of the saccharide include glucose. Preferred reducing agents include hydrazine, formaldehyde, acetaldehyde, hydroquinone, sodium borohydride, potassium citrate and the like, and the most preferred reducing agent is hydrazine.
When the reduction treatment is performed by the liquid phase method, the temperature is not particularly limited, but the temperature of the impregnated support (B) or the supported catalyst (C) is preferably about 0 to 200 ° C., more preferably 10 ~ 100 ° C.

  The reducing agent used for the gas phase reduction is selected from olefins such as hydrogen, carbon monoxide, alcohol, aldehyde, ethylene, propene and isobutene. Preferably it is hydrogen. In gas phase reduction, an inert gas may be added as a diluent. Examples of the inert gas include helium, argon, and nitrogen.

When the reduction treatment is performed by a gas phase method, the temperature is not particularly limited, but the impregnated carrier (B) or the supported catalyst (C) is preferably heated to about 30 to 350 ° C., more preferably 100 to 300 ° C. In the case where the heteropolyacid is first supported, the reaction at 350 ° C. or higher is not preferable because the heteropolyacid may be decomposed.
It is practically advantageous that the processing pressure of the vapor phase reduction treatment is 0.0 to 3.0 MPaG (gauge pressure) from the viewpoint of equipment, but it is not particularly limited thereto. More preferably, it is the range of 0.1-1.5 MPaG (gauge pressure).

When circulating the gaseous reducing substance, it may be carried out at any reducing substance concentration, and nitrogen, carbon dioxide, or a rare gas can be used as a diluent as required. Further, the reduction may be carried out in the presence of vaporized water in the presence of ethylene, hydrogen or the like.
After the catalyst before the reduction treatment is charged into the reaction system reactor and reduced with ethylene, oxygen may be further introduced to produce acetic acid from ethylene and oxygen.
The mixed gas containing the gaseous reducing substance is preferably brought into contact with the catalyst at a space velocity (hereinafter referred to as SV) of 10 to 15000 h ⁻¹ , particularly 100 to 9000 h ⁻¹ in a standard state.
The treatment format is not particularly limited, but it is practically advantageous to employ a fixed bed in which a reaction tube having corrosion resistance is filled with the above-described catalyst.

  The reduced carrier is washed with pure water or the like as necessary. Washing may be performed continuously or batchwise. The washing temperature is preferably in the range of 5 to 200 ° C, more preferably in the range of 15 to 80 ° C. There is no particular limitation on the cleaning time. A sufficient condition may be selected for the purpose of removing the remaining undesirable impurities. Undesirable impurities include sodium and chlorine. After washing, the solvent is dried and removed.

Step 4 (d) Step of supporting group compound on carrier <(d) Group compound: heteropolyacid and / or salt thereof>
The (d) group compound is at least one compound selected from heteropolyacids and salts thereof. The heteropolyacid used in the present invention is preferably a heteropolyacid containing tungsten or molybdenum as a poly atom. Heteroatoms include, but are not limited to, phosphorus, silicon, boron, aluminum, germanium, titanium, zirconium, cerium, cobalt, chromium, and the like. Preferred are phosphorus, silicon and boron.

  Specific examples of heteropolyacids include silicotungstic acid, phosphotungstic acid, silicomolybdic acid, phosphomolybdic acid and borotungstic acid. Preferred are silicotungstic acid, phosphotungstic acid, silicomolybdic acid, and phosphomolybdic acid represented by the following formula. The structure of the polyacid is not particularly limited, but a heteropolyacid having a Keggin structure is preferable.

Silicotungstic acid: H ₄ SiW ₁₂ O ₄₀ · nH ₂ O
Phosphotungstic acid: H ₃ PW ₁₂ O ₄₀ · nH ₂ O
Silicomolybdic acid: H ₄ SiMo ₁₂ O ₄₀ · nH ₂ O
Phosphormolybdic acid: H ₃ PMo ₁₂ O ₄₀ · nH ₂ O
(In the formula, n represents 0 or an integer of 1 to 40)

  The salt of the heteropolyacid used in the present invention is a metal salt or onium salt in which part or all of the hydrogen atoms of the acid formed by condensation of two or more inorganic oxygen acids are substituted. The metal in which the hydrogen atom of the heteropoly acid is substituted is preferably at least one element selected from the group consisting of Group 1, 2, 11 and 13 elements in the periodic table, and the onium salt of the heteropoly acid is ammonium. Examples thereof include salts. Of these heteropolyacid salts, metal salts of lithium, sodium, potassium, cesium, rubidium, calcium, magnesium, barium, copper, gold, silver and gallium are particularly preferable.

  Preferred heteropolyacid salts for catalytic performance include phosphotungstic acid lithium salt, phosphotungstic acid sodium salt, phosphotungstic acid copper salt, silicotungstic acid lithium salt, silicotungstic acid sodium salt and silicotungstic acid salt. A copper salt can be mentioned.

  (D) The group compound may be one kind or a combination of plural kinds. Examples of the method for supporting the heteropolyacid and / or salt thereof on the carrier include means such as impregnation and spraying. As the solvent used in the impregnation, (c) a heteropoly acid and a salt thereof are preferably dissolved, and water, an organic solvent or a mixture thereof can be used. More preferably, water, alcohol or ether is used.

  The support after completion of the third step or the fourth step is freed from the solvent by an operation such as drying, and becomes a supported catalyst for producing a lower aliphatic carboxylic acid of the present invention.

  (D) The step of supporting the group compound on the carrier (fourth step) is preferably after the third step (reduction treatment), but may be before the third step as described above. Alternatively, it can be included in the second step. That is, in the second step, the (a) group compound, (b) group compound, (c) group compound and (d) group compound may be supported simultaneously. Furthermore, you may carry | support separately from these compounds before or immediately after a 2nd process.

  In the second step, the method of simultaneously supporting (a) group compound, (b) group compound, (c) group compound and (d) group compound is a method in which all compounds are simultaneously supported on a carrier as a homogeneous solution. Is mentioned. More specifically, an appropriate solvent such as water or acetone, or an inorganic acid or organic acid such as hydrochloric acid, nitric acid, or acetic acid, (a) group compound, (b) group compound, (c) group compound, and (d) There is a method in which the group compound is dissolved to obtain a homogeneous solution, which is then impregnated into a carrier, and then dried. Further, after obtaining a heteropolyacid metal salt prepared from the (a) group compound, (b) group compound, (c) group compound and (d) group compound, it may be dissolved in an appropriate solvent and supported. . Preferred heteropolyacids used in the heteropolyacid metal salt include phosphotungstic acid, silicotungstic acid, phosphomolybdic acid and silicomolybdic acid, and preferred metals include palladium.

  As a method of supporting (d) group compound separately from (a) group compound, (b) group compound, and (c) group compound immediately before or after the second step, (a) group compound, (b) group A compound, an aqueous solution of the (c) group compound and an aqueous solution of the (d) group compound were prepared, respectively, and an aqueous solution of the (a) group compound, (b) group compound, (c) group compound or (d) group compound was prepared. After impregnating the impregnated carrier (A) to carry the (a) group compound, the (b) group compound, the (c) group compound or the (d) group compound, the (d) an aqueous solution of the group compound or ( A method of impregnating an aqueous solution of a) group compound, (b) group compound, and (c) group compound to carry (d) group compound or (a) group compound, (b) group compound, and (c) group compound. Can be mentioned. The order of carrying the (a) group compound, (b) group compound, (c) group compound or (d) group compound may be any first. More specifically, an appropriate solvent such as water or acetone, an inorganic acid or an organic acid such as hydrochloric acid, nitric acid, acetic acid, (a) group compound, (b) group compound, (c) group compound or (d) After dissolving the group compounds to obtain respective homogeneous solutions, the carrier is impregnated with the homogeneous solution of (a) group compound, (b) group compound, (c) group compound or (d) group compound, Then, after drying, a homogeneous solution of (d) group compound or (a) group compound, (b) group compound, (c) homogeneous solution of group compound is impregnated and dried.

<Supported catalyst for lower aliphatic carboxylic acid production>
In the supported catalyst for producing a lower aliphatic carboxylic acid obtained by the method for producing a supported catalyst of the present invention, the (a) group compound, the (b) group compound, the (d) group compound, and the (c) group compound are used as a support. The composition of (a), (b), (c), (d) in the retained catalyst is not particularly limited. Preferably, as mass% in the whole supported catalyst, (a): (b): (c): (d) = 0.5-10 mass%: 0.03-3.0 mass%: 0.5 -10% by mass: 5 to 60% by mass, particularly preferably (a) :( b) :( c) :( d) = 0.5-3% by mass: 0.05-1.0% by mass: 0.5-5% by mass: 10-50% by mass. In addition, when each group compound consists of a some compound here, let those total amount be a composition ratio of each component. In addition to (a), (b), (c), and (d), there are carriers and other components.

  The catalyst may be dried by any method after supporting at least one compound of (a), (b), (c), and (d) as a solution. For example, a method of performing vacuum treatment at a low temperature, a method of removing the solvent by heat treatment in a hot air dryer, and the like can be mentioned.

  The supported amount and composition ratio of the metal element and heteropolyacid contained in the supported catalyst for the production of the lower aliphatic carboxylic acid produced by the present invention are as follows: high frequency inductively coupled plasma emission spectrometer (hereinafter referred to as ICP), fluorescent X-ray It can be known fairly accurately by chemical analysis such as analysis (hereinafter referred to as XRF) and atomic absorption spectrometry.

  As an example of the measurement method, after a certain amount of catalyst is pulverized in a mortar or the like to make a uniform powder, the catalyst powder is added to an acid such as hydrofluoric acid or aqua regia, heated and stirred, and dissolved to make a uniform powder. Make a solution. Next, the solution is diluted to an appropriate concentration with pure water to obtain a solution for analysis. A method for quantitative analysis of the solution by ICP can be mentioned.

  Next, the production process of the lower aliphatic carboxylic acid using the catalyst obtained in the present invention will be described. Here, for simplicity, the supported catalyst of the present invention is used and ethylene and oxygen in a fixed bed flow reactor are used. The case where acetic acid is obtained by the gas phase reaction of will be described as an example.

  In the method for producing acetic acid of the present invention, there is no particular limitation on the reaction temperature when producing acetic acid by reacting ethylene and oxygen. Preferably it is 100-300 degreeC, More preferably, it is 120-250 degreeC. Moreover, although it is practically advantageous that the reaction pressure is 0.0-3.0 MPaG (gauge pressure) from the point of equipment, there is no restriction | limiting in particular. More preferably, it is the range of 0.1-1.5 MPaG (gauge pressure).

The gas supplied to the reaction system contains ethylene and oxygen, and if necessary, nitrogen, carbon dioxide, or a rare gas can be used as a diluent.
For example, ethylene is in an amount of 5 to 80% by volume, preferably 8 to 50% by volume, and oxygen is 1 to 15% by volume, preferably 3 to 12% by volume with respect to the total amount of the supply gas. Is supplied to the reaction system in an amount of

  Further, in this reaction system, when water is present in the reaction system, it is remarkably effective in improving acetic acid production activity and selectivity and maintaining the activity of the catalyst. The water vapor is preferably contained in the reaction gas in the range of 1 to 50% by volume, more preferably 5 to 40% by volume.

In this reaction system, it is preferable to use high-purity ethylene as the raw material ethylene, but it may be mixed with some lower saturated hydrocarbons such as methane, ethane, and propane. In addition, oxygen can be supplied in a form diluted with an inert gas such as nitrogen or carbon dioxide, for example, in the form of air. However, when the reaction gas is circulated, it is generally high concentration, preferably 99% or more. It is advantageous to use oxygen.
The reaction gas mixture, at standard conditions, SV = 10~15000h ^-1, preferably especially passed through the catalyst at 300~9000h ^-1.

  There is no restriction | limiting in particular as a reaction format, For example, formats, such as a fixed bed and a fluidized bed, can be taken. Preferably, it is practically advantageous to employ a fixed bed in which the above-described catalyst is packed in a reaction tube having corrosion resistance.

The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to the following examples.
<Pretreatment of carrier>
All the carriers used in the examples were dried at 110 ° C. under air for 4 hours as a pretreatment.

<Water>
The water used in the examples is pure water (ion exchange water).
<Carrier>
The carriers used in the examples are all silica carriers [BET specific surface area: 148 m ² / g, bulk density: 405 g / l, size: 5 mmφ, water absorption: 0.82 g / g-carrier, manufactured by Kaigen Co., Ltd.].

<Raw compound>
Hydrochloric acid aqueous solution of sodium chloropalladate [Na ₂ PdCl ₄ ] (manufactured by NP Chemcat Corporation)
Silicotungstic acid 26 hydrate [H ₄ SiW ₁₂ O ₄₀ / 26H ₂ O] (manufactured by Nippon Inorganic Chemical Co., Ltd.)
Phosphomolybdic acid 30 hydrate [H ₃ PMo ₁₂ O ₄₀ / 30H ₂ O] (manufactured by Nippon Inorganic Chemical Industry Co., Ltd.)
Zinc chloride [ZnCl ₂ ] (manufactured by Wako Pure Chemical Industries)
Hydrochloric acid aqueous solution of sodium chloroaurate [NaAuCl ₄ .4H ₂ O] (manufactured by NP Chemcat Corporation)
Sodium nonahydrate metasilicate _{[Na 2 SiO 3 · 9H 2} O] ( Wako Pure Chemical)
Telluric acid [H ₆ TeO ₆ ] (manufactured by Strem Chem. Inc.)
Hydrazine monohydrate [N ₂ H ₄ .H ₂ O] (Wako Pure Chemical Industries, Ltd.)

Example 1
Sodium metasilicate nonahydrate: 19.2 ml of an aqueous solution obtained by dissolving 3.34 g was absorbed in a silica carrier (50 cc) to obtain an impregnated carrier (A-1). Next, an aqueous solution of sodium chloropalladate adjusted to a Pd concentration of 20.1% by mass: 1.99 g, an aqueous solution of zinc chloride adjusted to a Zn concentration of 4.8% by mass: 0.89 g, and an Au concentration of 22 with pure water. A sodium chloroaurate aqueous solution adjusted to 1% by mass: 1.81 g and telluric acid: 0.054 g were mixed and diluted with pure water to prepare 40 ml of an aqueous solution (solution A-1). This solution A-1 was brought into contact with the impregnated carrier (A-1) and allowed to stand at room temperature for 20 hours. Thereafter, 6.5 g of hydrazine monohydrate was further added and stirred gently, and then allowed to stand at room temperature for 4 hours. The carrier was collected by filtration, transferred to a glass column with a stopcock, and washed with pure water flowing for 40 hours. Subsequently, it dried at 110 degreeC under air stream for 4 hours, and the impregnation support | carrier (B-1) was obtained.

  Furthermore, silicotungstic acid 26 hydrate: 10.5 g and phosphomolybdic acid 30 hydrate: 65 mg were made into a uniform aqueous solution and made up to 20 ml (B-1 solution). This B-1 solution was impregnated in the impregnated carrier (B-1) prepared previously and absorbed in its entirety. Subsequently, the catalyst 1 for acetic acid manufacture was obtained by drying at 110 degreeC for 4 hours under airflow.

Comparative Example 1
Sodium chloropalladate aqueous solution with Pd concentration adjusted to 20.1 mass%: 1.99 g, zinc chloride aqueous solution with Zn concentration adjusted to 4.8 mass%: 0.89 g, Au concentration 22.2 mass with pure water % Sodium chloroaurate aqueous solution: 1.81 g, telluric acid: 0.054 g mixed, made up with pure water to make a 19.2 ml aqueous solution, absorbed in silica carrier (50 cc), and impregnated Carrier (a-1) was obtained. Thereafter, sodium metasilicate nonahydrate: 3.34 g was dissolved in 40 cc of pure water to prepare an aqueous solution. The solution was impregnated into the impregnated carrier (a-1) and allowed to stand at room temperature for 20 hours. Further, 6.5 g of hydrazine monohydrate was added, stirred gently, and then allowed to stand at room temperature for 4 hours. The carrier was collected by filtration, transferred to a glass column with a stopcock, and washed with pure water flowing for 40 hours. Subsequently, it dried at 110 degreeC under air stream for 4 hours, and the impregnation support | carrier (b-1) was obtained.

  Furthermore, silicotungstic acid 26 hydrate: 10.5 g and phosphomolybdic acid 30 hydrate: 65 mg were made into a uniform aqueous solution and made up to 20 ml (d-1 solution). This d-1 solution was impregnated in the impregnated carrier (b-1) prepared previously and absorbed in its entirety. Subsequently, the catalyst 2 for acetic acid manufacture was obtained by drying at 110 degreeC for 4 hours under airflow.

Example 2
Sodium metasilicate nonahydrate: 19.2 ml of an aqueous solution obtained by dissolving 3.58 g was absorbed in a silica carrier (50 cc) to obtain an impregnated carrier (A-2). Next, a sodium chloropalladate aqueous solution whose Pd concentration was adjusted to 19.7% by mass: 2.03 g, an aqueous zinc chloride solution whose Zn concentration was adjusted to 4.2% by mass: 1.49 g, and the Au concentration was 22 with pure water. A sodium chloroaurate aqueous solution adjusted to 1% by mass: 1.81 g and telluric acid: 0.054 g were mixed and diluted with pure water to prepare 40 ml of an aqueous solution (solution A-2). This solution A-2 was brought into contact with the impregnated carrier (A-2) and allowed to stand at room temperature for 20 hours. Thereafter, 6.5 g of hydrazine monohydrate was further added and stirred gently, and then allowed to stand at room temperature for 4 hours. The carrier was collected by filtration, transferred to a glass column with a stopcock, and washed with pure water flowing for 40 hours. Subsequently, it dried at 110 degreeC under air stream for 4 hours, and the impregnation support | carrier (B-2) was obtained.

  Furthermore, silicotungstic acid 26 hydrate: 10.5 g and phosphomolybdic acid 30 hydrate: 65 mg were made into a uniform aqueous solution and made up to 20 ml (B-2 solution). This B-2 solution was impregnated in the impregnated carrier (B-2) prepared previously and absorbed in its entirety. Next, the catalyst 3 for producing acetic acid was obtained by drying at 110 ° C. for 4 hours under an air stream.

Comparative Example 2
Sodium chloropalladate aqueous solution with Pd concentration adjusted to 19.7% by mass: 2.03 g, aqueous zinc chloride solution with Zn concentration adjusted to 4.2% by mass: 1.49 g, Au concentration 22.2 mass with pure water % Sodium chloroaurate aqueous solution: 1.81 g, telluric acid: 0.054 g mixed, made up with pure water to make a 19.2 ml aqueous solution, absorbed in silica carrier (50 cc), and impregnated A carrier (a-2) was obtained. Thereafter, 3.34 g of sodium metasilicate nonahydrate was dissolved in 40 cc of pure water to prepare an aqueous solution. The solution was impregnated in the impregnated carrier (a-2) and allowed to stand at room temperature for 20 hours. Further, 6.5 g of hydrazine monohydrate was added, stirred gently, and then allowed to stand at room temperature for 4 hours. The carrier was collected by filtration, transferred to a glass column with a stopcock, and washed with pure water flowing for 40 hours. Subsequently, it dried at 110 degreeC under air stream for 4 hours, and the impregnation support | carrier (b-2) was obtained.

  Furthermore, silicotungstic acid 26 hydrate: 10.5 g and phosphomolybdic acid 30 hydrate: 65 mg were made into a uniform aqueous solution and made up to 20 ml (d-2 solution). This d-2 solution was impregnated in the impregnated carrier (b-2) prepared previously and absorbed in its entirety. Subsequently, the catalyst 4 for acetic acid manufacture was obtained by drying at 110 degreeC for 4 hours under airflow.

Example 3 and Comparative Example 3
5 ml each of the acetic acid production catalyst 1 obtained in Example 1 and the acetic acid production catalyst 2 obtained in Comparative Example 1 were uniformly diluted with 11 ml of silica support, and then packed into a SUS316L reaction tube (inner diameter 25 mm). A gas mixed at a volume ratio of ethylene: oxygen: water: nitrogen = 10: 6: 25: 59 at a reaction layer peak temperature of 200 ° C. and a reaction pressure of 0.8 MPaG (gauge pressure) at a space velocity of 9000 h. ^The reaction was carried out to obtain acetic acid from ethylene and oxygen. After 4 hours from the start of the reaction, the reaction tube outlet gas was sampled and component analysis was performed.

  As an analysis method, a method was used in which the total amount of the outlet gas that passed through the catalyst packed bed was cooled, and the total amount of the condensed reaction collection liquid was collected and analyzed by gas chromatography. For the uncondensed gas remaining without being condensed, the total amount of the non-condensed gas that flowed out within the sampling time was measured, a part thereof was taken out, and the composition was analyzed by gas chromatography. The produced gas is cooled, and the condensed liquid and gas components after cooling are gas chromatographed (GC-14B, Shimadzu Corporation, FID detector: capillary column TC-WAX (length 30 m, inner diameter 0.25 mm, film thickness 0. 25 μm)).

The activity of the catalyst was calculated as the mass of acetic acid per hour produced per catalyst volume (liter) (space time yield: STY, unit: g / hLcat). The carbon dioxide selectivity was determined by the following calculation formula.
Carbon dioxide selectivity (carbon basis) = carbon dioxide production / product production x 100 (%)

Example 4 and Comparative Example 4
Using each of the catalyst 3 for producing acetic acid obtained in Example 2 and the catalyst 4 for producing acetic acid obtained in Comparative Example 2, a reaction for obtaining acetic acid from ethylene and oxygen was carried out in the same manner as in Example 3 and Comparative Example 3. It was. However, the space velocity was changed to 12000h- ¹ . Further, sampling of the reaction tube outlet gas was performed 4 hours and 432 hours after the start of the reaction, and the amount of decrease in acetic acid STY after 432 hours had elapsed after 4 hours from the start of the reaction was determined by the following equation.
Acetic acid STY decrease amount (kgh ⁻¹ m ⁻³ ) = STY _{432 hours elapsed} −STY _{reaction start 4 hours}

  Table 1 shows acetic acid STY and carbon dioxide selectivity in the early stage of the reaction. Catalysts 1 and 3 obtained in Examples 1 and 2 from Table 1 are catalysts excellent in improvement of acetic acid STY and suppression of carbon dioxide selectivity than catalysts 2 and 4 obtained in Comparative Examples 1 and 2, respectively. You can say that.

  Table 2 shows the amount of decrease in acetic acid STY after 432 hours had elapsed after the start of the reaction. It can be said that the catalyst 3 obtained in Example 2 from Table 2 is a catalyst in which the amount of decrease in acetic acid STY is small even after the reaction for a long time and the deterioration is suppressed as compared with the catalyst 4 obtained in Comparative Example 2. .

  In the production of a lower aliphatic carboxylic acid by the reaction of a lower olefin and oxygen, the present invention uses the obtained supported catalyst to improve the amount of lower aliphatic carboxylic acid produced and suppress carbon dioxide gas by-product. This is industrially useful.

Claims (10)

A method for producing a supported catalyst for producing a lower aliphatic carboxylic acid using a lower olefin and oxygen, comprising the following first, second and third steps in that order.
Step 1 Contacting the support with an alkaline substance to obtain an impregnated support (A) Step 2 In the impregnated support (A), at least one element selected from Group 8, 9 and 10 elements of the periodic table is added. And at least one selected from gallium, indium, thallium, germanium, tin, lead, phosphorus, arsenic, antimony, bismuth, sulfur, selenium, tellurium, and polonium. A compound containing a seed element (hereinafter referred to as (b) group compound) and at least one chloride of an element selected from group 11 element and zinc in the periodic table (hereinafter referred to as (c) group compound) The step of obtaining the impregnated carrier (B) by contacting with it The third step The step of obtaining the supported catalyst (C) by bringing the impregnated carrier (B) into contact with the reducing substance   The method for producing a supported catalyst according to claim 1, further comprising a fourth step of supporting at least one compound selected from a heteropolyacid and a salt thereof (hereinafter referred to as (d) group compound) on a carrier.   The method for producing a supported catalyst according to claim 1 or 2, wherein the (c) group compound contains at least two substances of gold chloride and zinc chloride.   The method for producing a supported catalyst according to any one of claims 1 to 3, wherein the (a) group compound is a compound containing at least one element selected from palladium, nickel and platinum.   The method for producing a supported catalyst according to any one of claims 1 to 4, wherein the (b) group compound is a compound containing at least one element selected from gallium, germanium, tin, lead, bismuth, selenium and tellurium. .   (D) The method for producing a supported catalyst according to any one of claims 2 to 5, wherein the polyatom of the heteropolyacid of the group compound and / or a salt thereof is tungsten and / or molybdenum.   (D) The method for producing a supported catalyst according to any one of claims 2 to 6, wherein the heteroatom of the heteropolyacid of the group compound and / or a salt thereof is at least one element selected from phosphorus, silicon and boron. .   The heteropolyacid of the (d) group compound and / or a salt thereof is at least one compound selected from silicotungstic acid, phosphotungstic acid, silicomolybdic acid, phosphomolybdic acid and salts thereof. The manufacturing method of the supported catalyst in any one.   Production of a lower aliphatic carboxylic acid by reaction of a lower olefin and oxygen, characterized in that the supported catalyst for producing a lower aliphatic carboxylic acid produced by the method according to any one of claims 1 to 8 is used. Method.   The method for producing a lower aliphatic carboxylic acid according to claim 9, wherein the lower olefin is ethylene.