The invention relates to a field of petrochemistry, particularly to setective purification of alkyl-tcrt-alkyl ethers by ionic liquid and application of them in the industry as the high-octane, oxygenate components to fuels.

It is known that upon ethcrification of olefins and olefin-containing fractions (particularly, C ₃ -C ₇ fractions) with various C ₁ -C ₅ monoatomic alcohols in the presence of catalysts the main products of the reaction are alkyl-lert-alkyl ethers which are the components of high-octane, oxygenate fuels, as well as υnreacted hydrocarbons and mixture of alcohols. Since these products form tile azeotropic mixtures, the separation of them in a pure form by simple distillation is not possible. The assigned task is the development of available methods for effective separation of azeotropic mixture consisting of alkyl-tert-alkyl ethers, alcohol and hydrocarbons, as well as the development of extragents possessing high selectivity. in the known patent [I], for selective separation of azeotropic mixtures consisting of alkyl- tert-butyl ether (ETBE), ethanol and hydrocarbons an adsorbent was used. The proposed adsorbent consists of silica, 13X zeolite, 4A zeolite, 5 A zeolite, silica gel and a mixture of Y zeolite Na (in the amount of 10-40 %) with alumina or each individually. A stainless steel container is filled with adsorbent having sizes of 177 or 250 microns. On the surface of an adsorbent the ETBE, obtained by reaction of olefins with monoatomic alcohols, iuireacted alcohol and hydrocarbon mixtures are fed under pressure. This mixture contains about 10 % of ethanol. The adsorbent provides selective separation, and about 0,1 % of ethanol remains in the mixture. After passing the stream through the separation container the adsorbent undergoes desorption by n-hexane vapors or heated to 230 ⁰ C helium. After desorplion the adsorbent is cooled. Disadvantages of the invention are the multistage separation process in spite of high selectivity of adsorbent and the need of use of additional recoverable gases and solvents on each stage; the production of adsorbents are very expensive since the complex composition zeolites are used as adsorbents, that is evidenced of unprofitability of the process from economic consideration.

In another known inventions [2, 4], the processes of purification of alkyl-tert-alkyl others obtained as a result of ethcrification reaction of olefins, contained in the C ₄ -C ₅ fractions, with monoatomic alcohols, are described. As is seen from the source, upon preparation of alkyl-terl- alky! ethers some changes have been done in process flowsheet, particularly the reaction column is joined to a distillation column. Such obtained ether (4-5 % of unreacted alcohol in its composition) is withdrawn from the lower portion of the column. Unreacted hydrocarbons and residue of alcohol are withdrawn from an upper portion of the column. For full separation of alkyl-tert-alkyl ethers from unreacted alcohol and returning an alcohol again to reaction zone the zeolite adsorbents are required on next stage of the process. An adsorbent consists of mixtures of silica, 13X zeolite, 4A zeolite, 5A zeolite, silica gel, Y zeolite Na, alumina or each individually. After adsorption of an alcohol the zeolite adsorbent undergoes desorption by rapid stream of hydrocarbon recurrent gases of the reaction. Separated alcohol is relumed back to the process. Disadvantages of the proposed invention are the followjngs: in spite of improvement of process flowsheet and selectivity of an adsorbent, after each adsorption process some changes are observed in the composition of zeolite containing adsorbents. For retaining the selectivity of an adsorbent it is required its milling to micron sizes and also special membrane sieves for prevention of losses during washing that leads to the increase of cost of zeolite containing adsorbenLs. On the other hand, in order to maintain the vapor pressure and temperature constantly, in the used containers the additional heat exchangers and thermostats are required that leads to technologically multicapacitive process. In addition, each stage requires the preparation of additional solvents, recovering compositions, etc., that leads to a process of low profit from economic considerations.

In ihϋ known source [5], for separation of αzeotropic cther-alcohol-hydrocarbon mixtures, formed upon preparation of alkyl-tert-alkyl ethers by etherification of olefins, contained in C ₄ -C ₅ fractions, and monoatomic alcohols, the ion-exchange resins having exchange capacity (EC) of 1,7 mg eqv. H ⁺ /g arc suggested. Such ion-exchange resins have low EC and are nonreactive, deactivated and aggregative catalysts. Using them without special milling at 10-30 ⁰ C it is possible the separation of ether-alcohol-hydrocarbon azeotropic mixtures.

After adsorption of an alcohot the described adsorbent of ion-exchange type undergoes desorption by rapid stream of unreacted return hydrocarbon gases. Separated alcohol returns back to the process. Disadvantages of the proposed invention arc the followings: in spite of relative cheapness of an adsorbent used for selective separation of ether-alcoliol-hydrocarbon mixtures, after each adsorption and desorption stages EC indices of ion-exchange resins arc reduced, and this leads to the decrease in selectivity of subsequent adsorption process and requires the filling of an adsorption column by a new portion of an adsorbent each time.

In another known patent [6], for separation of an alcohol from azeotropic mixtures consisting of ethcr-aicohol-hydrocarbons formed upon etherification of olefins, contained in C ₃ - C ₄ fractions, with monoatormic alcohols producing alkyl-tcrt-alkyl ethers, the washing of a mixture by water several times in scrubber is proposed. Disadvantage of the proposed invention is; the recycling of an alcohol after washing with water is fully complicated since upon containing of residue water in. composition of alcohol the recovering of the latter becomes practically impossible. As in this case the catalytic activity of an ion-exchange resin used as a catalyst drops sharply before the expiry of service life, on the other hand, a large amount of waste water is accumulated that evidenced of unprofitability of the process from both economic and ecological standpoints,

In the patent which is more close to the proposed invention [7], a separation process of ether, returned from reaction alcohol and hydrocarbon mixtures obtained in the etheriiication of C ₃ -C ₇ olefins with monoatomic alcohols C ₁ -C ₅ , by extractive distillation is described. In this invention, the processes of separation of ethers and aliphatic hydrocarbons from alcohols by extractive distillation and returning of separated and completely recovered alcohols and hydrocarbons to reaction zone are described, Tn the patent, for separation of ethers containing 3-7 carbon atoms from alcohols containing 1-5 carbon atoms and a hydroxyl group the various solution mixtures are supposed. These solutions are called as extracting and azeotropoforming. Tt is supposed to use them not individually, but as the following mixtures such as sulfolane comprising 4-8 carbon atoms, diaikylsυlfolane, N-aIkyl-2-pyrrohdone comprising 1-3 carbon atoms and glycol component having a general formula:

After adding corresponding solutions to a column for conducting extractive distillation the ethcr-alcohol-hydrocarbon mixture is fed. Distillation column may be charged with extractant from 50% up to 99%. However, more efficient filling such as 80% and 99%, as well as the use of corresponding solutions and ethcr-alcohol-hydrocarbon mixture at weight ratio of 1 : 1-40, preferably at J : 3-20, is offered. The conducting an extractive distillation at 37,7°C - 203,5 ⁰ C and pressure of 0,05 - 1 ,64 MPa, preferably at 65,5°C - 160 ⁰ C and pressure of 3,28 - 1 ,09 MPa, is recommended. Disadvantages of proposed invention arc the followings: in spite of selective separation of ether-alcohol-hydrocarbon azcotropic mixtures by extractive distillation method in mild conditions the composition of an exlractant is complicated, a component synthesis is multistage, insignificant change in the extractable composition requires the preparation of a new individual extracting solution. In case of containing more than 10% alcohol in the ethcr-alcohol- hydrocarboii mixture the proposed process is considered to be unprofitable.

The assigned in the invention task is preparing less expensive, less ecologically harmful, selective, versatile extractant having simple composition for separation of alkyl-tert-alkyl ethers from uπreactcd alcohols and hydrocarbons of ether-alcohoi-hydrocarbon azeotropic mixtures, obtained as a result of reetherification of C ₃ -C ₇ olefins with C ₁ -C ₅ mono atomic alcohols, avoiding losses, and conducting a selective extraction with its participation and recycling an ionic liquid and alcohol as well,

The assigned task is solved by means of selective purification of alkyl-tcrt-alkyl ethers by ionic liquid, consisting of extraction stage of azeotropic mixtures obtained by ctherifi cation reaction, by a selective solvent, separation of ethers from mixtures, and recovery of a selective solvent. An extraction is carried out at weight ratio of an ionic liquid - liquid salts of valeric acid, diethanolamine or triethanolamine, used as selective solvent, to azcotropic mixture of 0,5÷10 : 1 , at temperature of 40-60 ⁰ C and vigorous stirring during 30-40 min. Λt subsequent stage after separation of ether from extract by layering, an ionic liquid being separated from the extract solution by direct rectification method is returned to extraction stage again.

Unlike the prototype, in the proposed invention the used liquids called as ionic liquids arc complex salts and consist of ions. Corresponding chemical structure of them provides more efficient solvation in the extraction processes and hereby creates favourable conditions for separation of aikyl-tcrt-alkyl ethers from ether-alcohol-hydrocarbon azeotropic mixtures. The use of ethanolamine as amine component provides the similarity in the compositions of liquid salts and alcohol hydroxyl groups and leads to selective adsorption of an alcohol by ionic liquid salts during extraction process, Alkyl-lerl-alkyl ethers not being mixed with ionic liquid salts are separated in a pure form. Extracted alcohol is easily separated from ionic liquid by rectification. So ionic liquids not being undergone to any changes as complex salts and not losing an extractive ability, are recycled. The structure of proposed ionic liquids and some of their physical-chemical characteristics are given in Table 1. The preparation of proposed ionic liquids is described in following examples: Example L The reaction components - 204,2 g of valeric acid and 105,1 g of diethanolamine are prepared in weight ratios, A corresponding amount of diethanolamine is filled to a 500 ml three-neck round-bottom flask equipped with drop funnel, backflow condenser, stirrer and thermometer, A corresponding amount of valeric acid is added to diethanolamine by means of drop funnel and a reaction mixture is stirred vigorously, A reaction is accompanied by release of heat and increase of viscosity. So as a result of stirring during 30-40 min at 35-40 ^; 'C, diethanolamine salt of valeric acid — ionic liquid (IL-I) is formed.

On the TR spectrum of IL-I recorded by spectrometer, the absorption bands (2200 cm ^{' 1} , 3300 cm ^"1 , 3600 cm ^"1 ) corresponding Io amine salts and Oil-groups arc observed. They are also called "ammonium" absorption bands, Absorption bands at 1500 cm ^-1 and 800 cm ^"1 , characteristic for deformational oscillations of NEL ₂ ^+' groups, are revealed. There are also absorption bands at 1610 cm ^"1 , 1550 cm ^-1 , and 1400 cm ^-1 , characterizing - COO" groups. On the basis of these corresponding absorption bands it is established that supposed for selective purification of alkyl-tert-alkyl ethers TL-I is actually liquid salt consisting of ions. The ionic liquid nature of IL-I is also confirmed by the results of eJectroconductivϊty method.

Example 2. The reaction components 204,2 g of valeric acid and 105,1 g of triethanol amine are prepared in weight ratios, A corresponding amount of tricthjuiolaniine is filled to a 500 ml thrcc-ncck round-bottom flask equipped with drop funnel, backflow condenser, stirrer and thermometer. A corresponding amount of valeric acid is added on the surface of triethanolaminc by means of drop funnel and a reaction mixture is stirred vigorously. A reaction is accompanied by release of heat, The color of the liquid is changed, and it becomes more viscous. So as a result of reaction at intensive stirring during 30-40 min at 35-40 ⁰ C, triβthanolamine salt of valeric acid - ionic liquid (IL-2) is formed, On IR spectrum of IL-2 the absorption bands (2200 cm ^-1 , 3200 cm ^-1 , 3300cm ^-1 , 3400 cm ^-1 ) corresponding to amine salts arc observed. Absorption bands at 3300 cm ^"1 corresponding to OH- groυps which are in the composition of triethanolamine are more intensive than those in IL-I based on diethanolamiiie, On spectra the absorption bands at 2735 cm" ¹ , 2500 cm ^'1 , 2325 cm" ¹ with deformational oscillations characteristic for NH ⁺ groups, and also the absorption bands at 1610 cm ^-1 , 1550 cm ^-1 , and 1400 cm ^-1 , characterizing -COO ^" groups, are observed. On the basis of corresponding absorption bands it is established that IL-2 is actually liquid salt consisting of ions. The ionic liquid nature of IL-2 is also confirmed by electroconductivity index, determined using eleclrocondυctjvity method.

Similarly to examples 1 and 2, dicthanolamine salt of caproic acid (IL-3), diβthaiiolamiπe salt of acetic add (IL-4) and monoethanohimine salt υf caproic acid (1L-5) have been synthesized at various weight ratios. A method of selective purification of alkyl-tert-alkyl ethers by prepared ionic liquids, (table

2) consists in following: into a stainless steel container (autoclave) equipped with a stirrer and thermocouple it is charged an ionic liquid to which at weight ratio of 0,5-10 : 1 the alkyl-tert- alkyl ethers obtained in tbe result of interaction of C ₄ or C ₅ olefins with monoatomic alcohols, and also unrcacted alcohol (in the amount of 10-20 % by weight) and unreacted hydrocarbon azeolropic mixture. Charging is earned out at 40-60 ⁰ C, as at higher temperature an evaporation oCalkyl-terl-aDcy! ethers takes place. The mixture is stirred intensively during 30-40 min, as long stirring leads to additional energy loss. Then the stirring is stopped, and after a while as a result of layering the ether is separated from the extract, Then by means of chromatographic analysis on the Auto-System XL-D HΛ (USA, Perkin- Rimer) a selectivity degree of purification of alkyl-terl- alkyl ethers by ionic liquids is determined. The results are given in Table 2.

According to Table 2 the indices of selective purification of alkyl-tert-alkyl ethers by ionic liquids, obtained on the basis of various cαrboxylic acids and ethanolarnines may be compared. As is seen, the selectivity of ether purification is changed depending on tbe ratios of ionic liquids (IL) to azeotropic mixture (AM) consisting of hydrocarbons, alkyl-tert-alkyl ether and unreacted alcohol. So after purification for IL-I and fL-2 taken at ratios of IL:ΛM — 0,5:1 , an amount of olkyl-tert-alkyl ethers constitutes 91,90 % and 91,82 % by weight, correspondingly, As is abovemeπtioned, this index is calculated on the basis of data of chromatographic analysis of purified product, In this case, an amount of residue alcohol constitutes about 1 % by weight (alcohol involved into ionic liquid is recycled). Remainder amount is the share of gases dissolved in ether and formed oligomers. For IL-I and TL-2 at ratio of IL: AM - 1 :1 the efficiency of purification increases, particularly α quantity of alkyl-tert-alkyl ethers constitutes 93,26 % and 94,10 % by weight, correspondingly, The above-mentioned is given in Table 3 (in this case as alkyl-tert-alkyl ethur the ETBE was used, and as alcohol - ethanol). Increase of IL:AM ratio up to 10:1 for IL-I and IL-2 leads to deepening the selectivity of ether purification, However, it must be noted that ratios of TL: ΛM lower or higher than 0,5-10 : 1 are out of limit. So at ratios lower than indicated limits purification does not occur sufficiently, but at ratios higher than limit ones I L itsel f dissolves in AM. TL-3 indicated in Table 2 dissolves in AM _. , i.e. in that case the layering does not occur. IL-4 in comparison with IL-I and IL-2 is extracLanl v/itli a little selectivity, and in its presence the full purification of alkyl-tert.-a.lkyl ethers does not occur,

So it is shown that assigned in the invention task is completely solved, A method of selective purification of alkyl-Lert-alkyl ethers by ionic liquids is developed.

References

1. US 5,475,150. 1995

2. US 5,401,887. 1995

3. US 5,569,787. 1996

4. US 5,621,150. 1997 5. RU 2101273. 1998

6. RU 2209811. 2003

7. US 5,160,414. 1.992