Maleic anhydride purification method

FIELD: chemistry.

SUBSTANCE: method of purifying maleic anhydride involves heating molten initial crude product to 60-65C and then cooling to 53-54C and filtering at temperature of 51.5-53C. Filtration is carried out on a filter with hole size of 0.01-0.05 mm and the molten mass is thermally processed in an atmosphere of dry inert gas or in sealed conditions in an atmosphere of dry inert gas.

EFFECT: high technological effectiveness of the process owing to its short duration and use of lower temperature parametres and higher degree of purification of maleic anhydride.

1 cl, 1 ex

 

The present invention relates to methods of purifying maleic anhydride used as starting product in obtaining various chemical materials, such as synthetic resins, plasticizers, synthetic fibers, adhesives.

Maleic anhydride, as you know, usually produced by the catalytic oxidation of benzene or hydrocarbon fraction and subsequent distillation for separation of reaction products. However, this product contains a significant number of impurities, which are byproducts of the oxidation reaction of the feedstock. These impurities adversely affect thermal stability of the obtained maleic anhydride, which, in turn, leads to undesirable staining of the product when heated. In addition, the crude maleic anhydride is unstable and during prolonged storage. It has a negative impact on consumer properties of products derived from maleic anhydride.

Distillation purification of the synthesized maleic anhydride does not clear it from the by-products of synthesis, in particular maleic and sabatinovka acids.

To improve the stability of maleic anhydride and removal of coloring impurities are various ways of cleaning it. For example, the widely used method of chemical clicks the processing of maleic anhydride with various chemical compounds. Known for a wide range of different chemical compounds, which are the stabilizers of maleic anhydride from undesired coloring by heat treatment or during prolonged storage. Such stabilizers include the halides and oxides of metals (copper chloride, zinc chloride, aluminium chloride, zinc oxide, copper oxide, aluminium oxide) /US 2296218/, malodorants acid /US 3903117/, phenols and hydrochinone, monochloramine aliphatic alcohols (chloropropanols, chlorbutanol, chlorbutanol, chlorocresol and others) /EP 0428746, C07D 307/60, 1994; EP 1144354, SS 51/54, 2001/, polyesters organophosphorus acids, esters of Gallic acid /EP 0381362 C07C 57/145, 1994/. However, as practice has shown, some chemical stabilizers, in particular phenols and catechins, esters of organic acids during prolonged storage or when exposed to light and oxygen become unstable when using them in large quantities may cause undesirable staining of maleic anhydride.

Another known method of purification of maleic anhydride is recrystallization using organic solvents such as acetone, toluene, benzene. This method get purified maleic anhydride in the form of fine particles. However, this method, as stated in the description of known patent (EP 214645, C07D 307/60, 1992), is relatively the izkuyu output. In addition, the use of large quantities of organic solvents makes this method of fire-hazardous and polluting the environment. The disadvantage of this method is the fact that traces of water present in the organic solvent leads to the formation of the maleic anhydride impurities maleic acid.

Another known method used for the purification of maleic anhydride, a method of crystallization from the melt /Chemical Abstracts, vol.75, abstract no.26211t/. This method is used for the purification of maleic anhydride in a known method of obtaining fine maleic anhydride /EP 0214645, C07D 307/60, 1992/. In the last cited how finely crystalline maleic anhydride is produced by melting the source of the crude maleic anhydride at a temperature of 55-100C, the rotation of the molten mass in a sealed container with a speed 1-30 rpm and slow cooling of the melt in a rotating container for at least 3 hours. Obtained in this way is cleared fine maleic anhydride is collected from the walls of the rotating container. Crystalline particles of a certain size are collected on the filter. The known method are fine maleic anhydride having a melting point 52,7C, containing about 99.9 wt.% basically what about the product 0.09 wt.% maleic acid with the following distribution of particle sizes: 28-42 mesh. - 60 wt.%, 42-60 mesh. - 20 wt.% and the others in size from 10 to 100 mesh. - 20%.

The considered method of obtaining fine maleic anhydride provides a clean source of maleic anhydride from impurities maleic acid, but does not include the cleaning of impurities sabatinovka acid, which limits the application of this known method. In addition, this method achieves the maximum degree of cleaning on the content of the basic substance to 99.9 wt.%, that does not always meet the cleanliness requirements in the applicable field.

To create a non-energy-intensive and high-tech process, which allows to increase the degree of purification of maleic anhydride from impurities and maleic sabatinovka acids, developed a new method of purification of maleic anhydride, which is carried out by heating the container to melt the crude source of maleic anhydride to a temperature of 60-65C, cooling the molten mass to 53-54C and subsequent filtering precipitated crystals at a temperature level of 51.5-53C.

The method of heat treatment of the melt is carried out in the atmosphere of dried inert gas or by sealing in the atmosphere of dry air.

The main difference between the new method from its prototype is installed and a specific sequence of three-stage temperature of the melt processing: first at 60-65C, then at 53-54C and at the last stage filtration - when 51,5-53C.

The choice of these temperature parameters selected experimentally, due to the following reasons.

It is known that the melting point of maleic anhydride 52,5C. In the first stage of thermal treatment in the container, the melt of maleic anhydride, having a temperature of about 52,5C, heated to 60-65C, because in this temperature range, an optimum degree of purification of maleic anhydride from impurities and maleic sabatinovka acids. As shown by additional research, the first stage heat treatment of the purified melt of maleic anhydride at a temperature below 60C leads to the solidification of the melt and rapid crystallization occurring with the formation of a very thin, hard filterable crystals. In the case of stage heat treatment at temperatures above 65C significantly reduced the degree of purification of maleic product such impurities as maleic and sabotinova acid due to the translation of the mentioned acids at this temperature in a dissolved state.

The second stage of processing of the melt - cooling up to 53-54C, but not below (as in the prototype) is carried out in order to avoid unwanted crystallization of maleic anhydride together with impurities.

And the last stage of the filter is tion is carried out while maintaining the temperature of the filtered mass at the level of 51.5-53C. It is this temperature interval yields an easily filterable finely dispersed particles of maleic anhydride of high purity. In the case of determining the temperature of the filter below 51,5C is clogging of filters, and in the case of overshooting of the temperature deteriorates the degree of purification of the main product by dissolving unwanted organic impurities.

The cleaning process is carried out in the environment of dried inert gas, or by sealing in an environment of dry air to eliminate the possibility of occurrence of side reactions of hydrolysis of maleic anhydride. As the inert gas may use such widely used gases as argon, nitrogen, and helium. In case of carrying out the process under seal as of the gaseous environment is applied pre-dried air. Below the method is illustrated on one of the examples of its implementation.

The cleaning process is carried out in a stationary container, in which the current nitrogen load melt of maleic anhydride. Then the melt is subjected to heating in a nitrogen atmosphere to 60C and cooled to 54C. After that, the melt is transferred to a filter with a pore size of 0.01-0.05 mm and filtered, keeping the temperature at the level of 51.5-53C.

Get a new way of maleic anhydride contains 99.99 wt.% the main product, 0.01 wt.% maleic acid and 0.01 m is S.% sabatinovka acid.

Similarly, carry out the cleaning process in the environment of any valid inert gas (argon, helium) or in the atmosphere of pre-dried air. The temperature at all stages is carried out in the protected temperature ranges. All of the examples carried out in the scope of the proposed claims, get maleic anhydride containing more than 99.9 wt.% the basic substance and less than 0.05 wt.% maleic acid and less than 0.05 wt.% sabatinovka acid.

The advantage of the new method before the method of the prototype is as follows.

The new method is more economical, because it is held for a shorter time for 0.5-1 hour and at lower temperature settings. Furthermore, the method provides a higher degree of purification of maleic anhydride (content of the basic substance and impurities and maleic sabatinovka acids).

The advantage of the new method before the prototype is and its a great technology, because its implementation does not require the use of energy-intensive and complex equipment.

1. The method of purification of maleic anhydride by heating the melt of the source of the crude product to temperatures above 55C, followed by cooling and isolation of the crystalline product by filtration, characterized in that the melt of the raw product is heated to 60-65C, after which ohlord the Ute up to 53-54C and filtered at a temperature of 51.5-53C.

2. The method according to claim 1, characterized in that the filtering is made on the filter hole size from 0.01 to 0.05 mm

3. The method according to claim 1, characterized in that the process of heat treatment of the melt is carried out in the atmosphere of dried inert gas.

4. The method according to claim 1, characterized in that the process of heat treatment of the melt is carried out in conditions of sealing in the atmosphere of dried inert gas.



 

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