SU827469A1 - Method of isolating aromatic hydrocarbons from their mixtures with nonaromatics - Google Patents

Description

(54) METHOD FOR ISOLATING AROMATIC HYDROCARBONS FROM THEIR MIXTURES WITH NONAROMATIC

one

The invention relates to the field of separation of aromatic hydrocarbons from mixtures with non-aromatic hydrocarbons from petroleum fractions and can be used in the refining and petrochemical industries.

Methods are known for isolating aromatic hydrocarbons from mixtures with non-aromatic by solvent extraction and extractive distillation using MONO-, DI-, tri-, tetraethylene glycol, and diethylene glycol i 1 alkyl ethers as a selective solvent.

Diethylene glycol and carboxylic acid esters are effective extractants, but their use is complicated by the fact that already at room temperature they hydrolyze to form aggressive substances and corrode the apparatus.

Diethylene glycol (DEG) 2 is most widely used as an extractant of aromatic hydrocarbons in the industry. It has a relatively high selectivity to aromatic hydrocarbons, a high boiling point and sufficient stability of DEG, as the extractant has a number of disadvantages:

low dissolving ability of aromatic compounds: 31.4% benzene and 17.2% toluene (in 100 g of solvent);

high freezing point (-8 ° C), which complicates transportation and storage during operation in temperate and cold climates;

35.7 cPZ high viscosity at 20 ° С, which causes diffusion inhibition of mass transfer processes and increases energy consumption for pumping and mixing;

the use of a large weight excess of DEG (8-11) with respect to raw materials and an increase in the extraction temperature to 150 ° C.

To increase the selectivity to DEG x Add water in an amount of 5-7%.

The closest to the invention to the technical essence and the achieved result is the method of separation of aromatic hydrocarbons from their mixtures with non-aromatic by liquid extraction

or extractive distillation with a selective solvent based on a mixture of ethylene glycol and water 3.

In the lime process, the selective solvent is a mixture of diethyleglycol and 0.5-10 wt. % water. However, said solvent has a low recovery rate and a distribution coefficient for aromatic hydrocarbons.

The aim of the invention is to increase the selectivity of the process.

This goal is achieved by the described method of separating aromatic hydrocarbons from their mixtures with non-aromatic by extraction and extractive distillation using as a selective solvent a mixture of diethylene glycol and water, which contains triethylene glycol monomethyl ether.

From the table it can be seen that the freezing temperature of ternary mixtures lies in the range of minus 42 - minus 60 ° C, which allows it to be used practically throughout the country.

The drawing shows state diagrams for the hexane-benzene-extractant system based on TEG ethyl ester. On chart 1 - hexane-benzene-DEG mixture with ethyl TEG ether and water (49.9- 49.9-0.2 wt.%); on diagram II - the same (40-57.5-25 wt.%); in diagram III - the same (40-52.5-7.5 wt.%).

It can be seen from the diagram that insignificant additions of water can regulate the selectivity and dissolving ability of the mixed extractant and obtain aromatic hydrocarbons of the required purity.

In the experimental verification of new extractants, the efficiency of TEG monoalkyl esters was assessed by the results of single-stage extractions; distribution coefficients (Kl), separation factors (p) and

at the following ratio of components, weight. %:

Monomethyl or

triethylene glycol monoethyl ether

(TEG) 35.0-65.0

Water 0.2-7.5

Diethylene glycolErest

The mixture consisting of DEG and monoalkyl ether TEG is comparable with DEG in its thermal stability and hydrolysability, therefore the solvent can be regenerated by the usual method of rectification or stripping with water vapor.

In tab. 1 shows some indicators of binary (azeotropic) DEG mixtures + TEG monoalkyl ether and DEG ternary mixtures, TEG ether and water. Here, for comparison, a mixture of DEG-f water was characterized.

Table 1

extraction degree (/ e). Calculation K.A, P,

/ e carried out by the formulas:

f Al--,

where L and B are the aromatic hydrocarbon content in the extract and raffinate parts, respectively.

about (i-3) y (l-jc)

where X and y - the content of aromatic hydrocarbons in the extract and raffinate. J.

where a and C is the content of aromatic hydrocarbon in the extract part and raw materials supplied to the extraction; А1э and Мс is the weight of the extract part and the raw material supplied for extraction.

Extraction experiments were carried out in toluene-heptane mixtures with 35 wt. % toluene; benzene-hexane with 35 wt. % benzene, flavored gasoline containing

50.4 wt. % of aromatic hydrocarbons. The compositions of the extract and rafiata are analyzed on a chromatograph with a detector with thermal conductivity, on a column 1 m long, 3 mm in diameter, filled with Polysorb-1 solid carrier with a fixed Tween-80 phase deposited on it, the temperature of the thermostat columns was programmed from 100 to 180 ° C, gas The carrier is helium.

Thus, the distribution coefficient is increased by 1.5-3 times, and the degree of recovery to 34-49% instead of 23.8% during extraction (DEG + 7% water), while maintaining the same selective ability of the extractant.

The use of these esters is also convenient in that they form azeotropic mixtures with diethylene glycol, which behave as an individual substance during the regeneration process.

Example 1 Extraction of a Toluene Heptane Mixture

 3.8533 g of an extractant consisting of 40 wt.% Is introduced into a sealed thermostatically controlled container with a magnetic stirrer. % diethylene glycol, 57.5 wt. % ethyl ether triethylene glycol, 2.5 weight. % of water and 2.0869 g of raw materials containing 35 wt. % toluene and 65 wt. % heptane. The mixture is thermostatic at 20 ° C and re-dragged for 30 minutes. After settling, the extract phase is separated by shnritsa and raffinate. The raffinate portion weighs 1.7905 g, extract 4.1497.

The composition of the extract phase, wt. %: hexane 2,5; benzene 8.7; solvent 88,8.

The composition of the pink phase, wt. %: hexane 73.4; benzene, 22.3; solvent 4,1.

Hence the composition of the extract, wt. %: hexane 22.86; benzene 77.2.

The composition of the raffinate, wt. %: hexane 77.7; benzene 23.3. Distribution coefficient

From the composition of various solvents of aromatic hydrocarbons according to Table. 2 (experimental conditions for single-stage extraction from toluene-heptane mixture are given in example 1) it can be seen that the extractant based on 3 components exceeds the binary mixture of DEG + water in terms of distribution coefficients and degrees of extraction.

table 2

benzene / CA 0.39. Recovery rate 49.4%.

Example 2 Extraction of benzenehexane mixture 2.73385 g of extractant, consisting of 49.9 wt., Is introduced into the sealed thermostatically controlled container with a magnetic blender. % diethylene glycol, 49.9 wt. % ethyl ether triethylene glycol, 0.2% water and 1.3906 g of raw materials containing

35 wt. % benzene and 65 wt. % hexane. The mixture was incubated at 20 ° C and stirred for 30 minutes. After settling, the extract phase is separated from the raffinate syringe.

The raffinate portion weighs 1.1626 g, extract 2.9665 g. Composition of the extract phase, wt. %: hexane 2.35; benzene 8.7; solvent 88.95%.

The composition of the raffinate phase, wt. %; hexane 76.45; benzene 21.26; 1.6 solvent.

Hence the composition of the extract, wt. %; hexane 21.35; benzene 78.65. The composition of the raffinate, wt. %: hexane 78.38; benzene 21.62. Benzene distributed ratio / Cd 0.409, recovery rate 53%.

Example 3. Extraction of flavored gasoline.

Raw materials - flavored gasoline containing 50.4 wt. % of aromatic hydrocarbons, including 4.11 wt. % benzene, 19,82 weight. % toluene, 26,47 weight. % xylene and above in the amount of 1.1471 g is subjected to a single-stage extraction with a double amount of the mixed extractant-2, 2191 g, cocTOHuiero from 49.9 weight. % DEG, 49.9 wt. % metlenlovogo Efnra TEG, and 0.2% water. After non-stirring by settling according to irimer 1 conditions, the extract phase is separated by a syringe and the composition of both phases is determined.

The weight of the rafia part of 0.8670

The weight of the extract part 2,4992

The composition of the extract phase, wt. %: aromatic hydrocarbons 13.03; non-aromatic hydrocarbons 5.09; extractant 81.88.

The composition of the raffinate phase, wt. %: aromatic hydrocarbons 55,19; non-aromatic hydrocarbons 40.49; extractant 4.32.

The composition of the extract, wt. %: aromatic hydrocarbons 72.93; aromatic hydrocarbons 28.48.

The composition of rafiata, weight. %: aromatic hydrocarbons 42,32; non-aromatic hydrocarbons 57.68.

The distribution coefficients of aromatic hydrocarbons are 0.32. The degree of extraction of aromatic hydrocarbons 56.34%

Example 4: Continuous extraction of benzene-hexane mixture.

Raw materials containing 50 wt. % benzene and 50 wt. % hexane is separated by extraction with a selective solvent consisting of diethylene glycol 47.5 wt. %, simple monoethyl ether TEG 47,5 weight. % and 5 wt. % water. The extraction was carried out on a column with a nozzle with an efficiency of 8 theoretical plates at 20 ° C. The ratio of solvent and raw materials is 8.5: 1.

The composition of the raffinate phase, wt. %: hexane 96.9; benzene 1.7; extractant 1,4.

The composition of the extract phase, wt. %: hexane 1,8; benzene 7.4; extractant 90.8.

The content of aromatic hydrocarbons in the extract and raffinate is 80.8 and 1.74%, respectively.

Example 5. Extractive rectification of a benzene-hexane mixture.

The mixture contains, about 35 weight. % benzene and 65 wt. % hexane is separated by an extractive distillation method using as a selective solvent a mixture consisting of DEG, TEG ethyl ether and oxen (47.5 wt.% + 47.5 wt.% + 5 wt.%). The extraction of aromatic hydrocarbons is carried out on a colonic with an efficiency of 20 theoretical plates with a reflux ratio of 2 and atmospheric pressure. Weight ratio

the solvent and the raw material were 3: 1. In the extractive distillation process, the hexane contained in the raw material was distilled off at a concentration of 99%, the concentration of benzene released was 99%.

Thus, this method allows to increase the yield of aromatic hydrocarbons due to more complete extraction from the raw material, to reduce energy costs in the extraction process while reducing

excess extractant and temperature.

Claims (3)

1. USSR author's certificate number 499255, cl. From 07C 7/10, 1958. 2. US patent number 2770663, cl. 260- 674, published. 1956 3. US patent number 2770664, class. 260-674, publ. 1956 (prototype). ff - hexane Venzene flacmSo / Jume / Jh