Method of extraction of ethylene oxide

 

The invention relates to a method for selection of the ethylene oxide absorption from the gas mixture obtained in the oxidation of ethylene with molecular oxygen in the presence of silver-containing catalyst, and can be used in the production of ethylene oxide. The ethylene oxide is recovered from the gas mixture produced during ethylene oxidation of oxygen-containing gas by absorption in an aqueous solution of ethylene glycol. Received rich absorbent is heated in the heat exchanger-recuperator and carry out its desorption at elevated temperature. Allocated ethylene oxide is subjected to subsequent multi-stage flash distillation. The absorbent after stage desorption process antifoam and an alkaline reagent, submit it to the heat exchanger-a heat exchanger and recycled to the stage of absorption. In the heat exchanger-recuperator flow rate of saturated absorbent is maintained within the range of 0.5 to 5.0 m/s and cooling of the adsorbent in the heat exchanger-recuperator lead to a temperature of 70-90oC. the Technical result - the reduction of losses of ethylene oxide selecting it, ensuring stable operation of the site heat recovery at the stage of absorption-desorption. 2 Il., table 1.

The image is placed ethylene with molecular oxygen in the presence of silver-containing catalyst, and can be used in the production of ethylene oxide.

Currently, the industrial production of ethylene oxide in the world is carried out by oxidation of ethylene at a temperature of 230-280oC, pressure of 2.0-2.5 MPa in the presence of silver-containing catalyst using as the oxidizing agent is air or oxygen [Lake B. O., ProCell D. C. improving the processes for the production of ethylene oxide. - Journal of Oil, gas and petrochemicals abroad", 3, 1984, S. 88-93]. A feature of the process of oxidation of ethylene with air is carrying out of the process as a series of two reactors with an intermediate stage of selection of the ethylene oxide from the gas mixture by absorption after the first stage of oxidation. Using this technology at the first stage of oxidation in the gas mixture, support almost the same concentration of ethylene and oxygen, after the separation of ethylene oxide from the reaction gas of the first stage of the circulation gas is fed to the second stage of oxidation, where more stringent temperature conditions hold additional oxidation of ethylene. After separation of the resulting stream of ethylene oxide gas mixture through the catalyst afterburners organic products discharged into the atmosphere. This process is suitable for all kinds of the constituent of the catalyst, the average selectivity reaches 70-73%. The most perfect method of producing ethylene oxide is the process of oxidation of ethylene by oxygen: this technology through the process of oxidation of ethylene in an excess of ethylene relative to oxygen, the oxidation process is carried out by only one stage and the selectivity of the process can reach 78-82%.

Despite possible differences in the technology of conducting oxidation of ethylene, known methods of allocation of ethylene oxide from the contact strip of the oxidation of ethylene with air or pure oxygen in the presence of silver-containing catalyst are common [Lebedev N. N. Chemistry and technology of basic organic and petrochemical synthesis. - M.: Chemistry, 1988, pp. 420-424; RF patent 1790179, C 07 D 303/04, 301/32, 1990] and usually include the stage of absorption of ethylene oxide with water or aqueous solutions of etilenglikola, desorption of ethylene oxide with subsequent recycling of the sorbent to the stage of absorption, circulation gas after the absorption of the ethylene oxide is directed to stage further oxidation (depending on the oxidation method or recycling or second stage of oxidation). To ensure full recovery of ethylene oxide and stable operation of the absorption Colo is at the stage of oxidation of ethylene, and avoid foaming of the sorbent in the heated regenerated sorbent is injected aqueous emulsion of antifoam, and water with a dilute solution of alkali metal hydroxide to maintain the pH of the sorbent, close to neutral. Usually as antifoam sorbent used water emulsion of silicone fluid on the basis of Polymetal and polyethylsiloxane with molecular weight of 500-10000. In addition, to avoid accumulation in the sorbent of heavy etilenglikola and reduce the loss of the ethylene oxide portion of the sorbent is continuously output to the node selection etilenglikola, thus the sorbent provide the content of monoethylene glycol in the range of 5.0-20.0 wt.%. At the specified way to reduce energy costs at the stage of allocation of ethylene oxide regenerated sorbent after stage desorption and processing a defoamer, an alkaline reagent, enters the heat exchanger-recuperator, where the preliminary heating of the saturated sorbent to the stage of desorption of the ethylene oxide. Cooled to a temperature of 40-60oWith the regenerated sorbent is then pumped to the next heat exchanger water cooling and then 20-30 temperatureoServed with in recycling at the stage of absorption of the oxide is x problems associated with the formation of hydrophobic deposits of antifoam (hydrophobic siloxane fluids in the annular space of the heat exchanger-the heat exchanger in the cooling of the regenerated sorbent and the loss of salt precipitation in the pipeline feeding the saturated sorbent in the process of heating it in the presence of ethylene oxide, as well as loss of ethylene oxide by passing an unmanaged catalytic reaction of hydration of ethylene oxide.

The task of the invention is the elimination of technological problems driving heat exchangers, and thus ensuring stable operation of the site heat recovery sorbent, reduction of losses of ethylene oxide.

The problem is solved in that in the process of separation of ethylene oxide from the gaseous mixture produced during ethylene oxidation of oxygen-containing gas in the presence of silver-containing catalyst, the absorbance of the aqueous solution of ethylene glycol, pre-heating the obtained saturated sorbent in the heat exchanger-recuperator and desorption him at elevated temperature, followed by a multi-stage rectification of ethylene, processing of the sorbent after the stage of desorption of the antifoam and seacreatures the flow rate of the saturated sorbent maintained within the range of 0.5 to 5.0 m/s and the cooling of the sorbent heat exchanger-recuperator lead to a temperature of 70-90oC.

Evaluation of the effectiveness of the proposed method of allocation of ethylene oxide was carried out in a continuously operating laboratory setup (Fig. 1), which includes the absorption column 2 and the desorption column 9, the capacity for accumulation of intermediate and final products 5, 8, 12, and 13, dosing pumps 6, 7, 15, refrigerators, 4, 11, heat exchanger-recuperator 14. Working conditions of installation are given in the examples. As criteria for assessing the effectiveness of this method of allocation of ethylene oxide and the stability of the site heat recovery heated sorbent selected change indicator "foaming" of the sorbent and the nature of changes in the concentration of sodium salts in the sorbent during testing of the sorbent at the outlet of the heat exchanger 14. The rate of accumulation of monoethylene glycol in the sorbent, as well as visual assessment of the presence of deposits on the surface of the tubes of the heat exchanger-recuperator 14 after the end of the test. The concentration of mono - and diethylenglycol in the sorbent determine chromatography using a flame ionization detector: sorbent 5% polyethylene glycol (PEG)-20000 on chromatone fraction of 0.16-0.25 mm, the temperature of thermostat columns 170oC evaporator 200oC. the definition of the parameter "spin the model was determined spectrophotometrically on a monochromatic flame photometer brand PFM.

The invention is illustrated by the following examples.

Example 1 (the prototype). The process of separation of ethylene oxide from the gas mixture formed during oxidation of ethylene with air in the layer of a silver catalyst at a temperature of 250-270oWith the pressure of 2.3 MPa (23 kg/cm2), is carried out in continuous mode in a laboratory setup.

The source gas mixture containing 0,9-1,1 vol.% of ethylene oxide; 3,4-3,6% vol. ethylene; of 3.5-3.7% oxygen; 8,0 an 8.4% vol. carbon dioxide, the rest is nitrogen and other inert gases, under a pressure of 2.0 to 2.3 MPa from the original network in the lower part of the absorption column 2. The pressure at the column inlet support of 1.9-2.0 MPa. The absorption column 2 nozzle type filled with a nozzle made of glass helices size 2.0 x 2.0 mm, the absorption process is carried out at a temperature of 24-28oWith the pressure drop in the column 0,02-0,03 MPa. As absorbent use the regenerated sorbent from the system absorption of the production of ethylene oxide to monoethylene glycol content of 5.2 wt.%, containing in its composition as antifoam polymethylsiloxanes liquid PMS-1000 and the indicator "foaming" of the sorbent is: the height of the foam 10 cm, the time of defoaming 10, concubine 8 through the condenser 4, where is cooled to 22-25oC. the feed Rate of the absorbent 0.8 l/h, the flow rate of the gas mixture in the absorber 7.0 l/min, the amount of sorbent in the system of absorption and desorption of 2.0 L. of Saturated sorbent containing 1.1-1.3 wt.% of ethylene oxide and other dissolved impurities, flows into the collector 5; in this collection to avoid evaporation of ethylene oxide by nitrogen supply support pressure of 0.3-0.4 MPa. Next, the saturated sorbent pump 6 with a linear velocity of 0.3 m/s is fed through a pipe of the heat exchanger-recuperator type "pipe" in desorber 9 representing the Packed column filled with a nozzle made of spirals size of 2.0 x 2.0 mm In the heat exchanger-recuperator 14 saturated sorbent is heated to a temperature of 85-90oWith regenerated sorbent entering the jacket of the heat exchanger-the heat exchanger 14 from the bottom of column 9. Warded off in column 9 ethylene oxide accumulates in the receiver 12, and after the sampling time is discharged into the collector 13. Modes desorption of ethylene oxide in the column 9: the pressure of the top of the column of 0.3-0.32 MPa, the temperature of the cube 145-147oWith, reflux 20. The regenerated sorbent from the cube column 9 passes through the jacket of the heat exchanger-the heat exchanger 14 and is discharged into the collector 8. T is 48-50oC and the pH of the sorbent regulate in the range of 6.5-7.5. During the test by decreasing the pH of the sorbent collected at the exit of the heat exchanger 14, below 6.0 constantly served with a 0.5% aqueous solution of sodium hydroxide. Testing of this mode is carried out in the course of 150 hours during the test in addition to the evaluation of spanelement sorbent is continuously determine the concentration of sodium salts and the concentration of monoethylene glycol. The degree of recovery of the ethylene oxide in the absorption column 2 is controlled by the content of ethylene oxide in the exhaust gas (the top of column 2), while the residual content of ethylene oxide in the circulation gas is within 0,0003-0,0006% vol., moreover, the concentration of ethylene oxide in the source gas mixture, exhaust gas, saturated chromatographic sorbent is carried out using a flame ionization detector: sorbent - 20% of apiezon on the Polisorb fraction of 0.16-0.25 mm; length of columns 3 m, the temperature of thermostat columns 90oWith the temperature of the evaporator 150oC.

After 16 hours of testing observed increase spanelement sorbent at the outlet of the heat exchanger 14 (foam height of 25-30 cm, the time of defoaming 20-25 seconds), therefore, to ensure the height of the foam sorbent in the range of 10-15 cm, time Gachet is hidcote PMS-1000 with a flow rate of 4.0-6.0 g/hour.

Example 2. The experience is conducted under the conditions of example 1. The flow rate of the gas mixture in an absorption column of 7.0 l/min, absorbent 0.8 l/h For the process of absorption of the ethylene oxide used sorbent containing glycols of 5.2 wt. per cent, sodium salt, in terms of ions of sodium 150 mg/l, pH value 6.8 and figures spanelement: lifting height of the foam 10 cm, the time of defoaming 10 sec. In this experience, the linear speed of passage of the saturated sorbent through the pipe of the heat exchanger-the heat exchanger 14 is 0.6-0.7 m/s the change in the rate of passage of the sorbent through the heat exchanger 14 is provided by the use of a modified heat exchanger design (changing the cross-section of the pipe and the annulus of the heat exchanger without changing its volume). Modes desorption of ethylene oxide in the column 9: the pressure of the top of the column of 0.30-0.32 MPa, the temperature of the cube 145-147oWith, reflux 20. The temperature of the sorbent at the outlet of the heat exchanger-the heat exchanger 14 is supported within 72-74oC. during the test, the residual content of ethylene oxide in the exhaust gas of the top of the column 2 is 0,0003-0,003%, the residual content of ethylene oxide at the outlet of desorber 9 changes in the range of 0.0004-0.002 wt.%. To maintain the value is 150 hours of testing indicator of the height of the foam sorbent is in the range of 10-16 cm, time damping foam in the range of 6.0-10.0 sec without the filing of an emulsion of antifoam in the sorbent. The results of the experiment are shown in the table and in Fig.2.

Examples 3-6. The test conditions are similar to examples 1 and 2. The feature of these experiments is to replace the design of the laboratory setup (Fig. 1) heat exchanger-the heat exchanger 14, which is achieved by changing the conditions of the experiment in terms of "linear flow rate of the saturated sorbent and the temperature of the sorbent at the outlet of the heat exchanger-recuperator". The test conditions and the results obtained are presented in the table and in Fig.2.

A comparative analysis of the results shows that the process of selection of the ethylene oxide absorption with an aqueous solution of monoethylene glycol while ensuring the flow rate of the saturated sorbent in the heat exchanger-the heat exchanger in the range of 0.5-5.0 m/s and the temperature of the cooling of the sorbent at the outlet of the heat exchanger-recuperator in the range of 70-90oAllows you to resolve technological problems driving pipe and the annulus of the heat exchanger-recuperator, reduce the dosage of antifoam in the sorbent to provide low spanevello and desorption of ethylene oxide.

Claims

The method of separation of ethylene oxide from the gaseous mixture produced during ethylene oxidation of oxygen-containing gas in the presence of silver-containing catalyst, the absorbance of the aqueous solution of ethylene glycol, pre-heating the obtained saturated sorbent in the heat exchanger-recuperator and desorption him at elevated temperature, followed by a multi-stage rectification of ethylene oxide, the treatment of the sorbent after the stage of desorption of the antifoam and an alkaline reagent, feeding it to the heat exchanger-recuperator and recycling at the stage of absorption, characterized in that in the heat exchanger-recuperator flow rate of the saturated sorbent maintained within the range of 0.5 to 5.0 m/s and the cooling of the sorbent heat exchanger-recuperator lead to a temperature of 70-90C.

 

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