Method for separation of di- and TRI-carboxylic acids from an oil shale oxidation reaction mixture

Abstract

The present invention provides a selective method for separating di- and tri-carboxylic acids from the reaction mixture of oil shale oxidation and for separating even-numbered di-carboxylic acids from odd-numbered di-carboxylic acids and tri-carboxylic acids. This goal is achieved by a method that uses different steps of extraction and crystal separation, the key process being extraction of the neutralized oxidized reaction mixture with dimethyl tert-butyl ether and crystallization of the extract. The noncrystallized part of the concentrated extract is esterified and distilled. The distilled esterified mixture is hydrolyzed with alkali and crystallized, which separates non-crystallized even-numbered dicarboxylic acids and oddnumbered dicarboxylic acids and tricarboxylic acids.

Description

[0001] METHOD FOR. SEPARATION OF DI- AND TRI-CARBOXYLIC ACIDS FROM AN OIL SHALE OXIDATION REACTION MIXTURE

[0002] TECHNICAL FIELD OF INVENTION

[0003] The invention belongs to the field of chemical industry and more specifically, the invention provides a method for separating di- and tricarboxylic acids from an oil shale oxidation reaction mixture.

[0004] PRIOR ART

[0005] Oil shale, is a valuable mineral resource that must be valorised to the maximum possible extent to produce valuable products. Oil shale is sedimentary rock, which consists of the organic component - mainly kerogen and mineral part (depending on the origin, for example carbonate, silicate part, clay, pyrite, and / or feldspar). Oil shale kerogen is the organic part that is not soluble in ordinary organic solvents. In order to obtain valuable products from oil shale kerogen, it is necessary to decompose it, for example by oxidising kerogen with nitric acid. The resulting dicarboxylic acids can be used to produce plastics and polymers, in the pharmaceutical industry, as well as in the manufacture of body care products. Various tricarboxylic acids are also used, which can be used in the food and pharmaceutical industries, as well as in cosmetics and cleaning products.

[0006] However, such methods, which could effectively separate di- and tricarboxylic acids from the reaction mixture of the oxidation of oil shale, are often complicated and require extensive use of several different complex methods. One possibility is to first separate nitric acid from the oxidised mixture and evaporate water and then distill the mixture under vacuum and at high temperature. In this way, a mixture of dicarboxylic acids can be obtained from which succinic acid can be separated by crystallisation. However, a disadvantage of such a method is that the distillation of dicarboxylic acids takes place at high temperature and in order to carry out the distillation in a way that excludes the decomposition of dicarboxylic acids, it is necessary to apply a deep vacuum. Despite the high temperature used (230 ° C) and a vacuum of 8 torr, dicarboxylic acids with a carbon number above 8 are not distilled from the reaction mixture, and neither are tricarboxylic acids.

[0007] After the succinic acid is separated from the oxidation product of oil shale, the remaining mixture of dicarboxylic acids is separated into individual dicarboxylic acids by rectification and non-selective crystallisation, which is very time-consuming and requires expensive and specialised equipment.

[0008] The oxidation product of oil shale, that has been evaporated dry can be extracted with methanol. The disadvantage of this method is that during evaporation, dicarboxylic acids partially decompose in the presence of nitrates and other impurities in the mixture. In the presence of an acidic environment, the formation of explosive nitroesters of methanol is possible. Also, dissolving the solid residue that has been evaporated dry with a suitable solvent is time-consuming and incomplete, since dicarboxylic acids have formed stable complexes with mineral salts and are not extracted. Among other things, it is difficult to separate di- and tricarboxylic acids from each other, because they are similar to each other and, in addition, the reaction mixture of oil shale oxidation contains many other starting materials, by-products and other reaction products, which increase the complexity of the separation process.

[0009] The closest to the present invention is the previously described method for the oxidation of a kerogen concentrate suspension with nitric acid in a cascade of four reactors with continuous addition of air to obtain dicarboxylic acids (DE2259502A1, Inst chimii Akademii Nauk Estonskoi; Slansechimitscheskii kombinat Kiwiyli). According to this method, the oxidation of >80% of a kerogen concentrate suspension with 30% nitric acid takes place in a cascade of reactors, which does not ensure sufficiently intensive mixing of the gas / liquid / solid phases. The fact that a concentrate with a high kerogen content is used requires a complex and multi-stage enrichment of the used oil shale raw material, which makes the raw material significantly expensive. The long reaction time (2.3 - 3.5 hours) makes the productivity of the cascade low. Nitric acid is used in the process in an excess of >60%, and unreacted nitric acid must be regenerated, which is difficult in the case of aqueous solutions and in the presence of organic material. Nitric acid is separated from the reaction mixture by distillation, which causes prolonged contact of the main reaction products - dicarboxylic acids - with high concentrations of nitric acid and partial decomposition of the compounds, which in turn leads to a decrease in yield and and problems with explosiveness arise. The result of the process is a partially solid residue, from which dissolving the dicarboxylic acids with methanol is a time-consuming process. The nitric acid residue must be completely separated from the mixture so that explosive compounds are not formed when methanol is added. According to the presented method, the oxidation process takes place in four interconnected reactors with air flowing through the reaction mass while stirring with paddle stirrers. This method of carrying out the process is cumbersome and material-intensive. In addition, mechanical stirring in the presented manner does not ensure sufficiently intensive mixing of the reagents and air.

[0010] Due to the above circumstances, a new, effective and selective method was needed for the separation of di- and tricarboxylic acids from the reaction mixture of oil shale oxidation.

[0011] LIST OF DRAWINGS

[0012] FIG. 1. shows an electropherogram of crystals containing dicarboxylic acids.

[0013] FIG. 2. shows an electropherogram of the non-crystallised portion. FIG. 3. shows an electropherogram of glutaric acid separated from the hydrolysed mixture of the distilled esterified mixture.

[0014] FIG. 4. shows an electropherogram of pimelic acid separated from the hydrolysed mixture of the distilled esterified mixture.

[0015] DESCRIPTION OF THE INVENTION

[0016] The aim of the solution is to efficiently and selectively separate di- and tri-carboxylic acids from a reaction mixture of the oxidation of oil shale. The aim is achieved by a technical solution that uses different extraction and crystal separation stages.

[0017] The present solution describes a method for separating di- and tricarboxylic acids from a reaction mixture of oil shale oxidation, characterised in that the method includes the following stages:

[0018] - the oxidation reaction mixture is neutralised to pH 2.1-3.5;

[0019] - the neutralised oxidised reaction mixture is extracted with methyl tertbutyl ether to obtain an extract;

[0020] - the extract is concentrated by distillation to obtain a concentrated extract;

[0021] - a mixture containing crystallised di-carboxylic acids with an even number of carbons is separated from the concentrated extract;

[0022] - a non-crystallised part of the concentrated extract is esterified with methanol to obtain a mixture of di-carboxylic acid esters;

[0023] - the mixture of esters is distilled;

[0024] - the distilled ester mixture is hydrolysed with a strong base to obtain di- and tri-carboxylic acids.

[0025] The present invention consists in neutralising the reaction mixture containing di- and tri-carboxylic acids obtained by the nitric acid oxidation of oil shale in the presence of air, regardless of the reactor used and the oxidation method, to a pH of 2.1-3.5 and extracting the neutralised oxidised reaction mixture with methyl tert-butyl ether (MTBE) at room temperature. In the present description, the term "oxidation reaction mixture" means the reaction mixture containing di- and tri-carboxylic acids obtained by the oxidation of oil shale in the presence of air. The advantage of using MTBE is that it chemically more stable than ethyl acetate for example. The advantage of lowering the pH of the reaction mixture is that at low pH, the di-carboxylic acids are in a neutral or nonionic form and are more soluble in MTBE. Consequently, the extraction of di-carboxylic acids from the oxidised reaction mixture is in a higher yield. In a neutralised oxidised reaction mixture, fewer basic compounds dissolve in MTBE because the low pH reduces the presence of other ions that would interfere with the extraction process. Also, by controlling the pH, residual nitric acid is neutralised.

[0026] Before separating the crystals containing dicarboxylic acids, the extract is concentrated by distillation to obtain a concentrated extract. This allows the MTBE to be regenerated and reused. Also, the separation of crystals from the concentrated extract has a higher yield and produces crystals containing dicarboxylic acids of higher purity.

[0027] By selective separation of even-numbered dicarboxylic acids by crystallisation from MTBE, even-numbered dicarboxylic acids are selectively separated from the mixture, which greatly simplifies the separation of the mixture of dicarboxylic acids from the reaction mixture of oil shale oxidation into individual acids, because their concentration is higher than the concentration of odd-numbered dicarboxylic acids. A pure mixture of even-numbered dicarboxylic acids can find use as a separate product in the polymer industry. Also, after separating the even- numbered dicarboxylic acids, the non-crystallised part is more concentrated in relation to the acids with odd numbers of carbon numbers, which also makes their separation easier. The non-crystallised portion of the concentrated extract is esterified to obtain a mixture of dicarboxylic acid esters. During esterification, tricarboxylic acid esters are formed from tricarboxylic acids, which are more stable to handle and allow for more selective separation. The ester mixture is distilled to obtain a purer and more concentrated mixture. The distilled ester mixture is hydrolysed with a strong base to obtain di- and tricarboxylic acids. Hydrolysis is necessary to restore the original di- and tricarboxylic acids. Methanol is often the best choice for esterification due to its high reactivity, good solubility, low boiling point, catalytic efficiency, low cost, wide availability, environmental friendliness, and improved product properties.

[0028] The present method can be used to selectively separate di- and tricarboxylic acids from the reaction mixture of oil shale oxidation in a simple and effective manner, which is applicable on a large scale.

[0029] In alternative embodiments, the method comprises additional steps: the extract is further concentrated by distillation; a mixture containing crystallised even-carbon di-carboxylic acids is separated from the distilled concentrate extract. Additional distillation of the extract allows for the recovery of even more di-carboxylic acids from the oil shale oxidation reaction mixture. That is, additional distillation allows for an increase in yield.

[0030] In alternative embodiments, the method uses at least one hydroxide from the following selection for neutralisation: sodium hydroxide, potassium hydroxide. These hydroxides are strong bases and their use is widespread. They react quickly and completely with acids, which is necessary when nitric acid has been used in the oxidation of oil shale and must be neutralised. Sodium hydroxide and potassium hydroxide provide effective and rapid neutralisation.

[0031] In alternative embodiments, the method uses an organic solvent to dissolve the dicarboxylic acid crystals, which is at least one of the following: ethyl acetate, diethyl ether, dichloromethane. Ethyl acetate, diethyl ether and dichloromethane are solvents that are sufficiently polar in nature to dissolve the dicarboxylic acids, but not too polar in nature to cause them to crystallise in the solvent. Dicarboxylic acids are polar in nature due to their polar functional groups and therefore dissolve well in solvents that can appropriately balance their polarity. These solvents offer good solubility, which allows the dicarboxylic acids to be dissolved effectively, but at the same time the dicarboxylic acids are not too soluble, which allows the crystals to precipitate under suitable conditions. This balance is critical for crystallisation processes, where the solubility of the solvent must be carefully controlled. Ethyl acetate, diethyl ether, and dichloromethane do not form strong hydrogen bonds, which helps prevent dicarboxylic acid molecules from bonding together in solution. This property helps dissolve dicarboxylic acids and keep them in a dissolved state until the solvent concentration decreases and crystals begin to form. Ethyl acetate, diethyl ether, and dichloromethane are solvents with relatively low boiling points. This is important because these solvents can be easily removed by vacuum distillation or evaporation, which is the process required to obtain crystals. The low boiling point also helps prevent dicarboxylic acids from decomposing when heated.

[0032] In alternative embodiments, the extraction is carried out at a temperature of 10-30°C. The advantage of low temperatures is that di- and tri-carboxylic acids can be sensitive to heat and may decompose or react undesirably with other compounds at higher temperatures. Lower temperatures help to maintain the chemical stability of the acids, preventing decomposition and the formation of by-products. Among other things, at lower temperatures, the evaporation of solvents is slower, which helps to keep the concentration of solvents stable and reduces evaporation losses. This is important for the control and efficiency of the extraction process. Lower temperatures help to improve the selectivity of the extraction process, allowing the separation and extraction of di- and tri-carboxylic acids more efficiently, without the extract containing too many impurities or contaminants. Carrying out the extraction at moderate temperatures helps to reduce the energy costs associated with heating and cooling the samples. This makes the process more economical, environmentally friendly and also safer.

[0033] In alternative embodiments, the method uses countercurrent extraction. In countercurrent extraction, two immiscible liquids (solvent and solute rich phase) flow through the extraction column in opposite directions. This has the advantage of allowing for continuous and efficient mass transfer between the two liquids. Since fresh solvent is constantly in contact with the most concentrated solute, maximum mass transfer and more efficient separation are achieved. This allows for very high purity and yield. Since the solvent flows in the opposite direction to the solute, the solvent is used with optimum efficiency. This allows for a reduction in the amount of solvent required to perform the process and reduces costs.

[0034] In alternative embodiments, in the method, the esterification with methanol is carried out under acid catalysis. The acid catalysis helps to speed up the esterification reaction and increase its efficiency. The catalyst helps to reduce the activation energy, allowing the reaction to proceed more quickly and at lower temperatures. The use of an acid catalyst helps to achieve completeness of the reaction, as it helps to prevent the reverse reaction. This means that a greater proportion of the carboxylic acid is converted to the desired ester, which increases the yield. Acid catalysis reduces the occurrence of side reactions and the formation of by-products. This means that the resulting di- and tricarboxylic acids are purer and require less further purification.

[0035] In alternative embodiments, the oil shale is kukersite. Kukersite is an Estonian oil shale. Kukersite is rich in organic matter, containing large amounts of kerogen, being a good feedstock for the extraction of di- and tricarboxylic acids. Modifications of the embodiments of the invention described above are possible without departing from the scope of the invention as defined by the claims. Expressions such as "comprises", "includes", "includes", "has", "is", used in describing and claiming the invention, should be interpreted in a non-exclusive manner, i.e., allowing the use of units, components or elements that are not specifically described. References to the singular should be interpreted as referring to the plural.

[0036] EXAMPLES OF THE INVENTION

[0037] Example 1. Separation of di- and tricarboxylic acids from the reaction mixture of the oxidation of oil shale.

[0038] The oxidation reaction mixture was neutralised to pH 2.1 by adding sodium hydroxide. The neutralised oxidation reaction mixture was extracted in a countercurrent extraction column, where the oxidation reaction mixture solution was pumped at a rate of 2 / h and methyl-tert- butyl ether (MTBE) at 8 L / h. The MTBE phase leaving the column was sent to a vessel where the MTBE was evaporated. The evaporated MTBE was condensed and sent back into circulation. The extract contains di- and tricarboxylic acids. The extraction efficiency for glutaric acid and acids longer than this is greater than 85% (Table 1).

[0039] Table 1. Extraction of the oxidation reaction mixture. 2 kg of concentrated extract contained succinic acid 200 g; glutaric acid 226 g; adipic acid 182 g; pimelic acid 120 g; capric acid 32 g; azelaic acid 16 g; sebacic acid 2 g.

[0040] 35 % of this was crystallised as succinic, 40 % as adipic acid. The resulting crystals consisted of 85 % of succinic acid (C4) and adipic acid (C6), with succinic and adipic acids in a ratio of 1.2: 1.

[0041] To increase the purity and remove non-dicarboxylic acid impurities, crystallisation was performed from organic solvents (ethyl acetate, diethyl ether, dichloromethane), and a mixture consisting of 95.7 % dicarboxylic acids (succinic acid (C4) 51.3 %, adipic acid (C6) 44.4 %, suberic acid (C8) 3.1 % (FIG. 1). The composition of the non-crystallised part is as follows: succinic acid (C4) 3.2%; glutaric acid (C5) 13.1 %; adipic acid (C6) 4.6 %; pimelic acid (C7) 8.7 %; suberic acid (C8) 3.7 %; azelaic acid (C9) 2.0 %; sebacic acid (CIO) 0.4 % (FIG. 2).

[0042] The non-crystallised part of the extract was esterified with methanol using a known method under acid catalysis with H2SO4 and the resulting ester mixture was distilled in a simple distillation apparatus, where of 2149 g of the methylated mixture was distilled and 1253 g of dicarboxylic acid ester fraction and 691 g of non-d istilled residue, which contained 54.9 % methyl esters of tricarboxylic acids were obtained

[0043] Under the conditions used, the non-d istilled residue forms a tri-carboxylic acid fraction with the following content: 1,2,8-octane tricarboxylic acid trimethyl ester according to GC-MS 11.3 %; 1,4,14-tetradecane tricarboxylic acid trimethyl ester according to GC-MS 10.2 %; 1,5,13- tridecane tricarboxylic acid trimethyl ester according to GC-MS 10.2 %; 1,2,4-butane tricarboxylic acid trimethyl ester 2.0 %; total of other tricarboxylic acid trimethyl esters according to GC-MS 21.2 %. (Table 2).

[0044] Table 2. GC-MS analysis results of non-distilled residue

[0045] The dicarboxylic acid ester fraction was rectified and a glutaric acid (C5) diester fraction with 82 % purity and a pimelic acid (C7) diester fraction with 69 % purity were obtained. The obtained fractions were hydrolysed separately according to known methods (by heating in acidic or alkaline aqueous solution) and precipitated from the extraction solvent by gradual crystallisation. From a mixture of 875 grams of simple distilled diesters, after fractionation and hydrolysis, 129 g of 82.5 % glutaric acid (C5) (additives included 10.6 % succinic acid (C4) and 4.2 % adipic acid (C6)) (FIG. 3) and 127 g of 60.6 % purity pimelic acid (C7) (additives included 15.6 % adipic acid and 19.1 % suberic acid (C8)) (FIG. 4) were isolated.

[0046] DETAILED DESCRIPTION OF DRAWINGS

[0047] FIG 1. shows an electropherogram of crystals containing dicarboxylic acids. 102 indicates peak of succinic acid, 104 peak of adipic acid and 106 peak of suberic acid.

[0048] FIG 2. shows an electropherogram of the non-crystallised part, where the following peaks are present: succinic acid (202), glutaric acid (204), adipic acid (206), pimelic acid (208), suberic acid (210), azelaic acid (212), sebacic acid (214).

[0049] FIG 3. shows an electropherogram of glutaric acid separated from the hydrolysed mixture of the distilled esterified mixture. The figure shows the 82.5 % pure glutaric acid peak (302) (added 10.6 % succinic acid (304) and 4.2 % adipic acid (306)). Figure FIG 4. shows an electropherogram of pimelic acid separated from the hydrolysed mixture of the distilled esterified mixture. The figure shows the 60.6 % pure pimelic acid peak (402) (additives 15.6 % adipic acid (404) and 19.1 % suberic acid (406)).

Claims

CLAIMS1. A method for separating di- and tri-carboxylic acids from a reaction mixture of oil shale oxidation, characterised in that the method comprises the following steps:- the oxidation reaction mixture is neutralised to pH 2.1-3.5;- the neutralised oxidised reaction mixture is extracted with methyl tertbutyl ether to obtain an extract;- the extract is concentrated by distillation to obtain a concentrated extract;- a mixture containing crystallised di-carboxylic acids with an even number of carbons is separated from the concentrated extract;- a non-crystallised part of the concentrated extract is esterified with methanol to obtain a mixture of esters of di-carboxylic acids;- the mixture of esters is distilled;- the mixture of distilled esters is hydrolysed with alkali to obtain di- and tri-carboxylic acids.

2. The method according to claim 1, characterised in that the method comprises additional steps:- the extract is further concentrated by distillation;- a mixture containing crystallised dicarboxylic acids with even carbon numbers is separated from the distilled concentrate extract.

3. The method according to any of the preceding claims, characterised in that at least one hydroxide from the following selection is used for neutralisation: sodium hydroxide, potassium hydroxide.

4. The method according to any of the preceding claims, characterised in that an organic solvent is used to dissolve the dicarboxylic acid crystals,which is at least one of the following: ethyl acetate, diethyl ether, dichloromethane.

5. The method according to any of the preceding claims, characterised in that the extraction is carried out at a temperature of 10-30 C.

6. The method according to any of the preceding claims, characterised in that the extraction is carried out by countercurrent extraction.

7. The method according to any of the preceding claims, characterised in that the esterification with methanol is carried out under acid catalysis.

8. The method according to any of the preceding claim, wherein the oil shale is kukersite.

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