JPH0226616B2 - - Google Patents

Description

[Detailed description of the invention]

FIELD OF THE INVENTION The field of the invention relates to a method for producing an alpha-abeta ethylenically unsaturated carboxylic acid compound, which method comprises: (1) feeding a saturated aliphatic monocarboxylic acid compound and formaldehyde into a reactor; 2)
The above saturated monocarboxylic acid compound and formaldehyde are condensed under gas phase conditions to produce an alpha arbor ethylenically unsaturated monocarboxylic acid compound having one more carbon atom than the saturated carboxylic acid compound in the presence of a solid catalyst. , (3) After coke is deposited on the solid catalyst in the reactor, the supply of the aliphatic monocarboxylic acid compound and formaldehyde compound to the reactor is stopped, and diluted oxygen is removed.
Pass the above catalyst over the above catalyst at a temperature not exceeding 650〓 (343℃), preferably at a temperature not exceeding 550〓 (288℃), while suppressing the exotherm to about 10 to 30〓 (5.6 to 16.7℃). Increase the oxygen content incrementally with a mixture of 80% oxygen and 80% inert gas, e.g. air, while suppressing the exotherm from about 10 to 30°C (5.6 to 16.7°C) until the exotherm disappears, then from 25 to 16.7°C.
Incrementally increase the temperature in increments of 75〓 (13.9 to 41.7 °C) with an exotherm of about 10 to 30〓 (from 5.6
16.7℃). More particularly, the field of the invention relates to a process for producing methacrylic acid from propionic acid and formaldehyde in a gas phase aldol-type condensation reaction in the presence of a solid catalyst in one or more reactors. , in which case after the coke is deposited on the solid catalyst in the first reactor,
The propionic acid-formaldehyde feed is diverted to the second reactor or stopped completely and diluted oxygen is passed over the coke-deposited solid catalyst at a temperature below 550°C (288°C) to decoke the catalyst. The solid catalyst preferably consists of at least one cation of a Group or Group metal and a silica support, which support preferably has a surface area of from 20 to 275 m ² /g;
Pore volume from 0.1 to 0.8 cc/g and from 75 Å
It has an average pore size of 200Å. BACKGROUND OF THE INVENTION Unsaturated acids such as methacrylic acid and acrylic acid, acrylonitrile, and esters of such acids such as methyl methacrylate are widely used in the preparation of corresponding polymers, resins, and the like. Various methods and catalysts have been proposed for converting alkanoic acids, such as acetic acid or propionic acid, and formaldehyde to the corresponding monocarboxylic acids, such as methacrylic acid, by Hairdol-type reactions.
Generally, the reaction between acid and formaldehyde takes place in the vapor or gas phase in the presence of a basic or acidic catalyst. There is a wealth of literature disclosing the reaction of aliphatic carboxylic acid compounds with formaldehyde to form alpha-abator ethylenically unsaturated aliphatic monocarboxylic acid compounds having one more carbon than the saturated carboxylic acid compound. Kirk Osmer's Volume 5, 3rd Edition (1981)
On pages 364 and 374 it is mentioned that the propionate-formaldehyde route is being considered in the production of methacrylic acid or methyl methacrylate. Kirk Osmer states that a suitable catalyst should provide high selectivity and conversion and have a lifetime of at least 6 months. Effective catalysts include alkali metal or alkaline earth metal aluminosilicates, silica treated with potassium or cesium hydroxide, alumina, and lanthanum oxide. Kirk-Othmer has shown that their results span a range of conversions and selectivities and that generally the best results are >80% selectivity at about 50% conversion. , these conversions and selectivities would be too high unless Kirk-Osmer mentions a method that uses a substantial molar excess of propionic acid over formaldehyde, and those conversions and selectivities are based on formaldehyde. . Both selectivity and percent conversion are low when propionic acid is used in molar equivalents with formaldehyde and conversion and selectivity are based on propionic acid. Even with a careful overview of the prior art, the reaction may last for more than 1 day or even 2 days.
There is no example in the art that has been continued for more than 1 day. This is not surprising, since our experience has shown that catalyst lifetimes are generally short and coke deposits on the catalyst, resulting in a rapid drop in catalyst activity. In our study on coke-deposited catalyst surfaces,
It has been shown that coke deposition reduces the activity capacity of certain areas of the catalyst surface, and that continued catalytic activity capacity depends not only on the amount of coke deposited on the catalyst surface, but also on the catalyst composition. Although 2g or 3g of coked silica catalyst bed can be regenerated with air at 100 °C (538°C), larger coked silica catalyst beds will sinter under these regeneration conditions. Our studies showed that when using approximately equimolar concentrations of propionic acid and formaldehyde, silica-supported catalysts provide relatively high conversions and selectivities relative to propionic acid. Generally, the higher the reaction temperature, the greater the percent conversion of propionic acid and the lower the selectivity of the catalyst.
Our studies also showed that silica supports tend to degrade over time in the sense that the catalyst surface area decreases while the average pore size increases. The surface area drops to about 10 to 20 m ² /g.
Catalytic activity drops rapidly as the number of pores with diameters below 1200 Å decreases. This deterioration is also a function of the water content of the reaction medium. The more water present, the faster the silica gel carrier deteriorates. Although substantially anhydrous reactants can be used, there is one molecule of product water per molecule of product. Moreover, there is a tendency for the alkali metal or alkaline earth metal cations to volatilize from the catalyst support, so that the catalyst activity (% conversion and/or % selectivity) falls off rapidly. As Kirk Othmer points out, there is a need for catalyst systems that can operate for longer periods of time. Although Kirk Osmer states that the catalyst life should be at least 6 months, we are unaware of any prior art process that discloses condensation reactions lasting longer than 24 to 48 hours. Accordingly, there is a need for suitable catalysts and/or processes for converting propionic acid compounds to methacrylic acid compounds that can be used over extended periods of time without substantial catalyst deterioration. A general object of the present invention is to provide a new catalyst regeneration process suitable for use in the catalytic condensation of saturated aliphatic monocarboxylic acid compounds and formaldehyde compounds to alpha arbor ethylenically unsaturated monocarboxylic acid compounds. That's true. Other purposes will become clear later. The object of the present invention can be achieved by a method for producing an alpha-abator ethylenically unsaturated carboxylic acid compound, which method comprises: (1) supplying a saturated aliphatic monocarboxylic acid compound and formaldehyde to a reactor; , (2) Condensing the above saturated monocarboxylic acid compound with formaldehyde under gas phase conditions to produce an alpha-abator ethylenically unsaturated monocarboxylic acid compound having one more carbon atom than the saturated carboxylic acid compound in the presence of a solid catalyst. (3) After coke is deposited on the solid catalyst in the reactor, the supply of the aliphatic monocarboxylic acid compound and the formaldehyde compound to the reactor is stopped, and the coke is diluted onto the catalyst. Oxygen at a temperature not exceeding 650°C (343°C), preferably not exceeding 550°C (288°C), with an exotherm of about 10 to 30°C (5.6 to
16.7℃), about 20% oxygen and 80%
Increase the oxygen content incrementally with reduced exotherm from about 10 to 30〓 (5.5 to 16.7 °C) until the exotherm disappears with a mixture of an inert gas, e.g. air, and then 25 to 75〓 (13.9 to 41.7 °C). ) and increase the exotherm from about 10 to
30°C (5.5 to 16.7°C) and possibly decoking. By suppressing the exotherm during regeneration, it is possible to prevent catalyst loss and/or sintering of the catalyst bed and reduce changes in the pore structure and surface area of the silica catalyst. Therefore, the catalyst can be used repeatedly even after multiple regenerations. On a commercial basis, the process diverts the flow of alpha-abeta ethylenically unsaturated monocarboxylic acid compound and formaldehyde from a first reactor to a second reactor, while the first reactor undergoes regeneration. Therefore, it can be carried out advantageously. If regeneration is carried out for half the time that the aldol-type condensation is being carried out, three reactors and two downstream processing sections are employed, one reactor receiving regeneration and carrying out two reactions. The device is capable of producing alpha arbor ethylenically unsaturated monocarboxylic acid compounds. In summary, the silica support of the present invention gels an aqueous silica colloid, dries the composition to remove substantially all water other than water of hydration, and
It can be made by baking. The alkali metal and/or alkaline earth metal cations of the catalyst are on a silica support on a dry solids basis.
It can be used at cation concentrations of 0.001 to 0.2 equivalents (gram atoms) per 100 g. It is generally preferred to have about 0.004 to 0.1 equivalents of cation per 100 g of silica support on a dry solids basis, as the higher the cation concentration, the more The temperature is low, and the selectivity and life of the catalyst are large. The lower the cation concentration, the higher the condensation temperature required to obtain the desired conversion to the alpha-abeta ethylenically unsaturated monocarboxylic acid compound, and the lower the catalyst selectivity and the shorter the lifetime. Suitable sources of alkali metals and alkaline earth metals are sodium hydroxide, potassium hydroxide, cesium hydroxide, lithium hydroxide, rubidium hydroxide,
Strontium hydroxide, magnesium hydroxide, lithium phosphate, trisodium phosphate, cesium phosphate,
Contains sodium borate, barium hydroxide, sodium carbonate, cesium fluoride, cesium nitrate, etc.
Among these, alkali metal cations are preferred. Any commercially available colloidal silica can be used, especially those with an average particle size of 40 to 1000 Å, a surface area of 20 to 275 m ² /g, and a pore volume of 0.1
Commercially available colloidal silica having a particle size of about 50 to 250 Å is preferably used to produce a silica-supported catalyst with an average pore size of about 75 to 200 Å, as described in US Pat. Showa 61-15737
No. 6,007,100, which is incorporated herein as a document. As pointed out in the above publication, the periodic table of elements (Handbook of Chemistry and Physics, 46th edition,
Chemical Rubber Co., Cleveland, Ohio, back cover) and a silica support, the support having a surface area of 20 to 275 m ² /g;
Pore volume from 0.1 to 0.8cc/g, and 75 to 200
Although it has an average pore diameter of 1.5 Å, it has a relatively high activity capacity (conversion rate and selectivity) and a relatively long lifetime. Pore volume, surface area and average pore diameter are interdependent variables. Holding one variable constant, as surface area increases, pore volume increases, as surface area increases, average pore size decreases, and as pore volume increases, average pore size increases.
In the above publication, it is important that the catalyst satisfy each of the pore volume, surface area, and average pore diameter. For example, if the catalyst has a porosity greater than 0.8 cc/g, the catalyst will lack the abrasion strength necessary for long-term use. Porosity is 0.1
If it is less than cc/g, the surface area is too small and/or the average pore size is too large. However, as explained above, the catalyst loses activity as pores with diameters smaller than 1200 Å disappear. Therefore, it is desirable to use a catalyst with a substantially smaller average pore size so that the catalyst has an adequate lifetime. A substantial reduction in catalyst life occurs if the average pore size of the starting catalyst is substantially greater than 200 Å. A pore size of at least 75 Å is necessary to allow gas diffusion of the reaction products of the reactants. The silica can be treated with cations either before drying or before calcination. Catalysts made by adding cations to colloidal silica before or during gelation can be viewed as co-formed catalysts;
No. 502,524, which application is incorporated herein as a document. As pointed out in the above publications, co-formed catalysts are substantially more water resistant and easier to decoke than those made by treating calcined silica with a cationic aqueous solution. They are advantageous in this sense because, other things being equal, they do not generate as much heat as catalysts made by impregnation. This is apparently due to a more uniform distribution of the cations in the carrier. The silica support of the present invention has a dry basis of about 20 to 60%
Preferably, it is made by forming an aqueous composition comprising % by weight of colloidal silica and alkali metal and/or alkaline earth metal cations. Colloidal silica is gelled with alkali metal or alkaline earth metal cations by adjusting the pH to a range of about 3 to 10, preferably about 6.0 to about 9.0. Salts such as NH ₄ NO ₃ can be used to promote gelation. Silica hydrogels can be aged for two weeks or more, but aging appears to have no effect on the properties of the catalyst, so aging is not necessary. The composition is then dried by any suitable means, such as in a microwave bath, to constant weight and to an apparent dryness, eg, about 4 to 5% moisture on a dry solids basis. After drying to a constant weight, only the hydration water is clearly retained by the silica gel. The silica gel is then calcined at about 300°C to 800°C, preferably about 300°C to 600°C. As pointed out in JP-A-61-15737, at calcination temperatures exceeding about 800°C, the surface area tends to decrease, the pore volume decreases, and the pore diameter increases, and as a result, the catalyst Unexamined Japanese Patent Publication 1986
- Exceeds the scope required by Publication No. 15737. However, such catalysts can be used in the present invention. The process of the present invention can be used for the aldol-type condensation of a saturated aliphatic monocarboxylic acid compound to an alpha-abator ethylenically unsaturated monocarboxylic acid compound having one more carbon atom than the starting saturated aliphatic carboxylic acid compound. Suitable aliphatic monocarboxylic acid compounds that can be converted in aldol-type condensation reactions include acetic acid, propionic acid, methyl acetate, methyl propionate, ethyl propionate, acetonitrile, propionitrile, and the like. Preferred saturated monocarboxylic acid compounds are propionic acid compounds, especially propionic acid, since the catalyst of the present invention is primarily designed for large-scale production of methacrylic acid. Although any suitable source of formaldehyde compounds can be used, such as formalin, paraformaldehyde, methanolic formaldehyde, trioxane, etc., substantially anhydrous formaldehyde, particularly decomposed monomeric gaseous substantially anhydrous formaldehyde, is used. is preferable. In summary, alpha arvator ethylenically unsaturated monocarboxylic acid compounds combine saturated aliphatic monocarboxylic acid compounds and formaldehyde compounds under gas phase conditions at a concentration of about 0.001 to 0.2 equivalents per 100 g of silica support on a dry solids basis. a silica catalyst with at least one cation of a Group or Group metal, preferably a support with a surface area of 20 to 275 m ² /g, a pore volume of 0.1 to 0.8 cc/g, and an average pore size of 75 to 200 Å. It can be prepared by condensation in the presence of a catalyst consisting of: This reaction can be carried out in the presence of water-immiscible hydrocarbons or halohydrocarbons containing from 6 to 12 carbon atoms with an azeotropic point of about 95°C or less, and are described in US Pat. It is disclosed in Publication No. 15859/1983, which is incorporated herein as a document. Since the product stream contains significant amounts of unreacted propionic acid and unreacted formaldehyde as well as water, selection of a suitable solvent in the preferred method of operation for distilling the reactor effluent to separate the components is
It is determined by the boiling point of the azeotrope of propionic acid and methacrylic acid. Both propionic acid and methacrylic acid form a water azeotrope with a boiling point of approximately 99°C. Distillative separation of _C6 - _C12 hydrocarbons in the presence of water requires that the water:hydrocarbon azeotrope formed have a boiling point below the boiling point of the water azeotrope with propionic acid and methacrylic acid. do. Preferably, the boiling point of the water:hydrocarbon azeotrope is 95°C or less. Typical hydrocarbons: water azeotrope boiling points and percentages of water are as follows: Hydrocarbon Water % Boiling Point °C n-hexane 5 - n-heptane 13 79 n-octane 23 90 n-nonane 40 95 95 Water with a boiling point below °C: branched _C6 - _C12 saturated aliphatic hydrocarbons, aromatic hydrocarbons with 6 to 12 carbon atoms, forming hydrocarbon azeotropes; 6 to 12 cycloalkanes and mixtures thereof can also be used. As pointed out in JP-A-61-15859, diluents are advantageous in that they increase the production yield by about 3 (mol)% without reducing the selectivity of the catalyst. Moreover, as explained below, the diluent has an additional function in the overall process of producing methacrylic acid from propionic acid. Suitable diluents include n-hexane, n-heptane, n-octane, 2-ethylhexane, n-decane, n-dodecane, o, p, or m-xylene, benzene, toluene, cycloalkanes and mixtures thereof. include. The concentration of diluent can range from about 10 to 50% by weight of the reactants in the main reactor. The molar ratio of monocarboxylic acid compound to formaldehyde can range from 25:1 to 1:25. However, best results with this catalyst in methacrylic acid production can be obtained using a molar ratio of propionic acid compound to formaldehyde of about 0.5-2.0 to 1. Generally, the lower the molar ratio, the
High conversion rate based on the amount of converted propionic acid. The aldol-type condensation can be carried out at about 280 to 500°C, but it is preferably operated at about 280 to 350°C, since the lower the reaction temperature, the higher the selectivity. As pointed out in JP-A-61-15857, (1) the amount of the undesired unsaturated cyclic ketone by-product that is a catalyst for the polymerization of the alpha-abator ethylenically unsaturated monocarboxylic acid is greater than the starting propionic acid compound; from 4 mol% at 390°C on a basis to approximately 2.5 mol% or less at 350°C (approximately 1% at 325°C), or (2) 24 hours of condensation followed by 24 hours of desorption. Over 80 days of repeated coking, the loss of cations is 75% at 390°C, with a concomitant drop in catalyst activity, and 10% at 350°C, with a constant activity capacity. In some detail, this integrated method of producing methacrylic acid involves (1) feeding propionic acid and formaldehyde compounds into a reactor containing a silica catalyst, and (2) condensing the formaldehyde and propionic acid under gas phase conditions to produce water. , formaldehyde, propionic acid, and methacrylic acid; (3) distilling the reaction product to remove water, unreacted formaldehyde, and at least some propionic acid from the reaction product; Approximately 95% distillate
contact in a distillation column with a co-distilling agent consisting of a water-immiscible diluent having an unboiling point of 0.degree. C. or less to remove at least some of the water and formaldehyde overheads. In a more preferred form of this method, a side wall extraction pipe is disposed at least in the middle of the distillation column to take out the composition comprising propionic acid and formaldehyde. The use of a side wall outlet pipe is as pointed out in Patent Application Publication No. 61-502535, which is incorporated herein by reference. facilitates removal of a portion of the distillation column, thereby eliminating formaldehyde polymerization at the top of the distillation column, thereby eliminating or reducing the possibility of blockage at the top of the distillation column. Regardless of whether or not a side wall extraction pipe is used, formaldehyde is extracted from an aqueous formaldehyde solution collected at the top of the tower, which is reacted with an alcohol having 6 to 12 carbon atoms to form hemiacetal, and water is extracted from this hemiacetal. The hope is to distill the substantially anhydrous hemiacetal and then decompose the substantially anhydrous hemiacetal to recover formaldehyde. This formaldehyde is
Advantageously removed from the alcohol by the overhead addition of a water-immiscible diluent with an azeotropic point of about 95°C or less to facilitate the removal of formaldehyde from the alcohol used to form the hemiacetal. separated into The process of the invention can be carried out at a weight hourly space velocity (WHSV) of about 0.1 to 10, preferably 0.5 to 6.5. Generally, the lower the weight hourly space velocity, the lower the required reaction temperature. The higher the weight hourly space velocity, the higher the required reaction temperature. The catalyst decokes after about 12 to 72 hours of operation. To prevent sintering of the silica gel, dilute the oxygen to about 450-650〓 (232-343℃), preferably 450℃.
to 550〓 (232 to 288 °C) with a reduced exotherm of about 10 to 30〓 (5.5 to 16.7 °C), increasing the oxygen content incrementally and reducing the exotherm from about 10 to 30 °C.
Increase the temperature with a mixture of about 20% oxygen and about 80% inert gas, e.g. 41.7℃) and decoking the heat generation by approximately 650 to 800〓(343
to 427℃) until completion at about 10 to 30〓
(5.5 to 16.7℃). Generally, the present invention relates to a method for producing an alpha-abeta ethylenically unsaturated carboxylic acid compound, the method comprising: (1) feeding a saturated aliphatic monocarboxylic acid compound and formaldehyde to a reactor; (2) The above saturated monocarboxylic acid compound and formaldehyde are condensed under gas phase conditions to form an alpha arbor ethylenically unsaturated monocarboxylic acid having one more carbon atom than the above saturated carboxylic acid in the presence of a solid catalyst. (3) After the coke is deposited on the solid catalyst, the supply of the aliphatic monocarboxylic acid compound and formaldehyde compound to the reactor is stopped, and the oxygen-containing gas is About 800〓(427
C) and repeating steps (1) and (2). More specifically, the present invention relates to a method for producing an alpha-abator ethylenically unsaturated monocarboxylic acid compound, which comprises: (1) supplying a saturated aliphatic monocarboxylic acid compound and formaldehyde to a reactor; ) The above saturated monocarboxylic acid compound and formaldehyde are condensed under gas phase conditions to form an alpha arbor ethylenically unsaturated monocarboxylic acid compound having one more carbon atom than the above saturated monocarboxylic acid compound in the presence of a solid catalyst. (3) After coke is deposited on the solid catalyst in the reactor, the supply of the aliphatic monocarboxylic acid compound and formaldehyde compound to the reactor is stopped, and diluted oxygen is added to the catalyst at 650 μl. (5.5 to 16.7 degrees Celsius) at temperatures not exceeding 343 degrees Celsius (343 degrees Celsius); Approximately 20% oxygen and 80% while suppressing until it runs out
enriched with a mixture of an inert gas, e.g. air,
The temperature is then increased incrementally by 25 to 75°C (13.9 to 41.7°C) and the decoking is from about 650 to about 800°C.
(343-427℃)
It consists of controlling the temperature between 10 and 30°C (5.5 to 16.7℃) and decoking. In the following examples, all conversions, yields and selectivities are based on propionic acid (PA) unless otherwise specified. Example This example shows 1.97% by weight based on silica dry weight.
The surface area including cesium is 119m ² /g, and the porosity is
The production of methacrylic acid in a pilot plant using a co-formed cesium phosphate, silica gel catalyst with 0.604 cc/g and an average pore size of 168 Å is described. A slurry of 29 parts by weight of paraformaldehyde, 106 parts by weight of propionic acid (PA:FA molar ratio 3:2) and 47 parts by weight of heptane was continuously evaporated to convert the paraformaldehyde into monomers at 400°C (204°C). It was thermally decomposed to form formaldehyde. This composition was then placed in a thermowell of 1 inch (2.54 cm) outside diameter, 0.834 inch (2.12 cm) inside diameter, and 6 feet (180 cm) long Inconel tubing with an outside diameter of 0.25 inch (0.63 cm). The reactor was transferred to a reaction system consisting of a tube with a 4 foot (120 cm) long catalyst zone containing 200 g of catalyst and 1 inch (2.54 cm) Denstone packing bands on each side. The thermowell was equipped with thermocouples inserted at 6 inch (15.3 cm) intervals and electrical heating means were placed along the reactor. The conversion of propionic acid and formaldehyde to methacrylic acid requires a pilot plant of 660
(350° C.), 10 psig (0.7 Kg/cm ² ), and a weight hourly space velocity of 1.55 for 24 hours. The reaction products were collected and condensed in a heat exchanger. After 24 hours, the feed to the reactor was interrupted and the reactor temperature was lowered to 550°C (288°C). 2% oxygen in nitrogen was slowly added to the reactor to limit the exotherm to about 20°C (11.1°C) during decoking. After the exotherm had ended, the oxygen content was increased to 10%, the exotherm was limited to 20㎓ (11.1°C), and the nitrogen-oxygen mixture was replaced with air. After each exotherm has finished, the reactor temperature is increased by 50〓 (27.8℃).
The temperature was raised to 700㎓ (371℃) by precisely controlling the heat generation. This decoking step typically takes 2 to 4 hours. Air was continuously flowed through the reactor at 700°C (371°C) for a total of 24 hours. Discontinue the air and reduce the reactor temperature to 660〓 (349℃)
The condensation of propionic acid and formaldehyde was disclosed. 80 repetitions of condensation and decoking
40 days were spent on methacrylic acid production.
I was without coke on the 40th. The molar ratio of PA:FA is
The ratio changed from 1.5:1 to 1.34:1. The physical properties of the catalyst before and after 80 days of operation are shown in the table. The yield after the first day and the average for the first 66 days are shown below in the table.

【table】

[Table] The catalyst used in this example was 10302.9 g of Nalcoag, 1034-A colloidal silica (34% solids 200 Å solution) and 111.66 g of 10302.9 g of Nalcoag in 500 c.c. of deionized water.
g of cesium phosphate (having an average of 5 molecules of water per molecule) with vigorous stirring. After 10 minutes of vigorous stirring, a solution of 100 g ammonium nitrate in 150 g deionized water was added to the sol and the mixture was stirred for 2 minutes at which point it began to thicken. This silica gel was allowed to solidify after being left at room temperature overnight. The gel was dried to constant weight in a microwave bath, adjusted to particle size from 20 to 40 meshes, and calcined according to the following heating rate: 165° C. for 2 hours. It was then gradually raised to 540°C over 4 hours and then further heated at 540°C for 8 hours.
It kept time. All steps were performed in flowing air. Examples Commercial colloidal silica, Ludotux(TM)
AS-40 brands [E.
I. du Pont de Nemours and Co. (Inc.),
A 200 ml sample of Industrial Chemicals Dept.] was placed in a beaker. The temperature was 25°C. This material was an aqueous colloidal dispersion of high specific surface area silica particles. The characteristics were as follows:
Specific surface area, 130 m ² /g; average particle size, 21 m〓; silica (as SiO ₂ ), 40% by weight; PH (25° C.), 8.0. While stirring, the pH of the sample was lowered from approximately 10.5 to 3.0 by dropwise addition of concentrated nitric acid (0.16N). The pH was then raised to about 6.0 by dropwise addition of concentrated ammonium hydroxide (0.15N). Mixture at that point for 8 hours
Stir at 25°C, at which point a viscous gel has formed. Gel was dried in a drying bath at a temperature of 120 °C for 2
It was dried for an hour, then ground and sieved into 18/40 mesh grains (US sieves). The resulting catalyst support was then calcined at 525° C. for 16 hours. The analysis value by AA spectroscopy is aluminum: 400ppm,
Sodium: 2100ppm, Zirconium: <
100ppm, titanium: <100ppm, iron by edax spectroscopy: <200ppm. A solution of trisodium phosphate was added to the catalyst support using the incipient wetness method. The resulting catalyst contained 6000 ppm sodium. The reaction system is a 1 inch (2.54 cm) OD x 0.834 ID with a 0.25 inch (0.63 cm) OD thermowell.
Consists of 6-inch (2.12 cm) x 6-foot (180 cm) heated Inconel tubing. The catalyst zone is typically 4 feet (120 cm) long and typically contains 200 grams of catalyst. Thermocouples inserted into the thermowell measure and control temperature at 6 inch (15.3 cm) intervals. The supply system is propionic acid.
Designed to handle slurries of paraformaldehyde. This slurry is transferred to an evaporator in which the paraformaldehyde is pyrolyzed to monomeric formaldehyde at 400°C (204°C). This system allows the use of lower reactor temperatures than feed systems using trioxane and propionic acid. This is because trioxane does not completely decompose into monomeric formaldehyde at temperatures below 750°C (399°C). The reaction conditions were: contact time: 3.2 seconds, reaction temperature: 390
It was ℃ (734〓). The reactor contained 4-8 mesh (US sieve) made to contain 6000 ppm of sodium as described above.
(1/8 inch) of AS-40 trisodium phosphate. A two day test was conducted with a 1:1 ratio of propionic acid to formaldehyde. The catalyst was regenerated as follows. At a temperature of 550〓 (288℃), a low flow rate of air of 0.05SCFH was fed into the reactor along with 0.5SCFH nitrogen, with an apparent small amplitude of about 20〓 (11.1℃).
caused fever. Gradually reduce the nitrogen flow while increasing the temperature by 20〓(11.1℃) by 650〓(343℃)
Then, the temperature was increased by 50〓 (27.8℃) to 750〓 (399℃). There was no heat generation above 30°C (16.7°C) during this process. Catalyst then for 48 hours
Regenerated at 750°C (399°C). Following regeneration, the reaction conditions used during the two-day test described above were repeated. The results are shown in Table 2. Table 2 shows that mild regeneration has minimal impact on catalyst performance.

[Table] This regeneration method was repeated, but the air was
(538°C). A large fever developed. At an air flow of 250 ml/min and a temperature of 1000° (538°C), during the first 10 minutes the front of the catalyst bed experienced an exotherm of 430° (221°C). The temperature rise rate during this heat generation is also large, approximately 30〓/min (16.7
℃/min). 350〓(177
There was an exotherm of 1350°C (750°C). This occurred after 2 hours on air. Table 3 shows the catalyst performance before and after decoking. The data shows a large yield loss after decoking for both the 6-8 mesh catalyst and the 18-40 mesh catalyst. The catalyst used in these experiments was
Contains 6700ppm Na, incipient
It was a Na ₃ PO ₄ catalyst produced by wetness. The catalyst was then removed from the reactor in three portions and analyzed. These three catalyst cut bodies are
Compared to the initial uniform bed concentration of 6700ppm,
It contained 3500ppm, 6800ppm, and 17600ppm.
A change in the pore structure of the silica gel probably occurred as well. The results are in Table 3.

【table】

【table】

Claims (1)

[Claims] 1. A method for producing an alpha beta ethylenically unsaturated carboxylic acid compound, comprising: (1) supplying a saturated aliphatic monocarboxylic acid compound and formaldehyde to a reactor; (2) gas phase conditions; The above saturated monocarboxylic acid compound and formaldehyde are condensed in the presence of a solid catalyst to produce an alpha beta ethylenically unsaturated monocarboxylic acid compound having one more carbon atom than the saturated carboxylic acid, 3) after the coke has been deposited on the solid catalyst, the supply of the aliphatic monocarboxylic acid compound and the formaldehyde compound is stopped, and (4) the coke is removed by passing an oxygen-containing gas through the catalyst at a temperature below 427°C. A method consisting of decoking the catalyst and repeating steps (1) and (2). 2 Pass the oxygen-containing gas over the catalyst at a temperature not exceeding 288°C while suppressing the heat generation from 5.6°C to 16.7°C; with a mixture of 20% (by volume) oxygen and 80% (by volume) inert gas while increasing; the temperature of the gas was increased from 13.9°C to 41.7°C and the exotherm was increased from 5.6°C to 16.7°C. ℃, and decoking the above temperature of the above gas from 343℃ to 427℃
repeating until completion at a temperature of . 3. The method of claim 2, wherein said 20% (by volume) and 80% (by volume) mixture of oxygen and inert gas is air. 4. The method of claim 1, wherein the alpha beta ethylenically unsaturated monocarboxylic acid compound is methacrylic acid. 5. Converting the raw material supply from the first reactor to a second reactor or a multi-stage reactor, and decoking the catalyst in the first reactor in step (4). The method described in section. 6. The method according to claim 5, wherein the catalyst in the second reactor or the multi-stage reactor is decoked by steps (3) and (4). 7. The method of claim 1, wherein said saturated monocarboxylic acid is selected from the group consisting of acetic acid and propionic acid. 8. The method of claim 1, wherein the solid catalyst comprises at least one Group or Group metal cation and a silica support. 9. The method of claim 8, wherein the catalyst is a co-formed catalyst.