CS240510B1 - A process for the purification of ethylene and the apparatus for its performance - Google Patents

Abstract

The invention provides a method and apparatus for purifying ethylene obtained by desorption from acetone in the process of extracting ethylene from pyrolysis gases by absorption in acetone, containing acetone as the main undesirable substance, by scrubbing.

Description

240510

SUMMARY OF THE INVENTION The present invention provides a method for purifying ethylene obtained by desorption from acetone in a process for separating ethylene from pyrolysis gases by scrubbing in acetone containing acetone as the main undesirable substance.

Ethylene, produced by the high-temperature pyrolysis of gasoline having a boiling point of 30 to 130 ° C and / or petroleum fractions having a boiling point of 130 to 450 ° C and / or gasoline having a boiling point of 30 to 130 ° C with the addition of propane-butane mixtures and / or or> with the addition of a mixture of C4 fractions, is obtained from the multi-component gas mixture either by partial low temperature condensation and rectification after separation of the acetylene and carbon dioxide by absorption in acetone or is obtained in a subsequent absorption-desorption system using additional acetone as absorbent. In both cases, but especially in obtaining ethylene in the downstream absorption-desorption system, ethylene contains, besides methane and ethane, undesirable substances and acetone, the content of which needs to be reduced to a minimum and, on the other hand, the purity of ethylene in its further processing. and, on the other hand, in terms of economy to minimize the loss of acetone used for absorption.

In the production of ethylene by low temperature partial condensation and rectification of the acetone, it passes through a set of condensers and heat exchangers together with ethylene in the form of a non-condensing mist, so that the ethylene thus obtained contains a significant amount of acetone despite the avoidance of deep cooling. The average content of acetone in ethylene is 300 ppm and increases the yield of the production equipment to a value close to 0.1 mol%, which is an unacceptable value for producing high quality vinyl chloride. Acetone content in ethylene obtained by absorption in another acetone in the manner described in MS. Copyright Certificate No. 211 020or in MS. No. 232,632 depends mainly on the temperature and pressure of ethylene under-absorption from acetone. Typically, this temperature ranges from 256 to 240 K at a pressure of about 0.8 MPa. '

The acetone content, as in the previous low-temperature separation of e-ethylene, also exceeds the theoretical amount calculated from the condition conditions and the corresponding vapor pressure of acetone and is usually greater than 0.5% mol.

Ethylene produced by the above processes is used mainly for the production of vinyl chloride via 1,2-dichloroethane. Strict requirements for the lowest acetone content in ethylene also arise from the hillfort, since the synthesis of 1,2-dichloroethane by chlorination of ethylene containing acetone and water, respectively, produces substances, and undesirable presynthesis of 1,2-dichloroethane. harmful and dangerous.

In addition, chlorinated acetone compounds are formed, which then pass to the vinyl chloride monomer. Their content already increases the suspension polymerization of vinyl chloride, especially the production of the annual microporous types of suspension polyvinyl chloride. These are briefly mentioned mainly for the reasons for which there is a strict requirement to reduce the acetone content produced by ethylene.

In the current processes for removing acetone from ethylene, either the cooling and the compression of the ethylene is used, followed by adsorption on the various adsorbents or absorption in the solvent.

By compressing and subsequently cooling, the predominant part of the acetone can be removed, but with the desire to remove the acetone deeply from the ethylene, this relatively common and technically readily available process is effective and at the same time very costly, in particular due to the refraction energy consumption and cooling.

The washing of the acetone residues from the various gas streams, including, but not limited to, stream ethylene, water or aqueous solutions of cetone is described in U.S. Pat. This method is effective and economical, but cannot be used for the purification of ethylene intended for the production of 1,2-dichloroacetic acid, since the ethylene removed to the chlorination must be dry to prevent production equipment. Ethylene for this purpose must not contain more than 10 ppmvod.

Adsorption processes for the purification of ethylene, e.g., aluminum, silica gel, or active charcoal and similar sorbents, are effective in removing acetone, water, and other undesirable substances to the desired degree. However, the operation is quite complicated and expensive. The greatest drawback of the adsorption processes for the purification of ethylene is the possibility of accumulating sulfur and nitrogen compounds on the sorbents used up to the critical mass in terms of the risk of explosion. The advantage is that the ethylene adsorptive purifiers make it possible to reduce the non-contaminant content, satisfying even the most demanding purity requirements of ethylene. Typically, however, it is desirable for the impurity content of the ethylene feed to be low in adsorption in order to achieve an adequate lifetime of the relatively expensive adsorbents.

According to the present invention, the process for purifying ethylene by desorption from acetone in the process of separating ethylene from pyrolysis gases by absorption in acetone, containing acetone as the main undesirable substance, is carried out by bringing desorbed ethylene into acetone from the acetone. a transition portion of the integrated absorption-desorption system, wherein a 1,2-dichloroethane at a pressure of 0.2 to 0.9 MPa and at a temperature of 245 to 300 K and in the absorptive portion of the system operating at 240510 litho 270 up to 323 K is desorbed with ethylene, and the 1,2-dichloroethane used together with the washed impurities, mainly acetone, is passed through a docking system in which the recovered acetone is recovered by means of a two-stage condensation and boiled off the acetone and the washings. 1,2-dichloroethane is recycled. . The ethylene purification apparatus of the invention consists of an absorption-desorption and distillation apparatus and ancillary devices, the cross-flow of the ethylene conduit connected to the absorption column connected via an absorption-desorption stage with a desorption heat exchanger which is connected by the feed line with a rectification column provided with a single-condensate condenser and a total condenser, and a cooker, a conduit of boiled dichloroethane with a desiccant heat exchanger connected to the conduit, provided with a fresh dichloroethane inlet conduit and a suction conduit connected to the pump. an aqueous pipeline of dichloroethane with an absorption column provided in the upper part with a tube of pure ethylene.

In the process of the present invention, ethylene is practically completely depleted of acetone with reduced methane content and methane, depending on the temperature and pressure conditions in the absorption-desorption co-solvent. It has been found that the unusual solution of the heat exchanger and its constructional connection with the absorption column creates favorable conditions for optimum process control according to a predetermined optimality criterion, taking into account both the requirement to minimize ethylene losses and the reduction requirement. methane and ethane content in pure ethylene. Further advantages of the novel process are attributable to the combination of said effective adsorption-desorption system with the regeneration column and also to the unusual resolution of recovery of the recovered acetone by two-stage condensation in a quench water cooled condenser and a total condenser cooled by evaporating the liquid propylene. In this way, the operation efficiency is not only greatly improved, but also the recovery yield of the acetone contained in the ethylene for cleaning is high. The economical operation of the absorption-desorption system is, however, believed that the effect is achieved by utilizing the fermentation of the boiled 1,2-dichloroethane, which can then practically be carried out without further treatment, after addition of fresh 1,2-dichloroethane. as an effective absorption agent.

Another important element of the ethylene purification process that has been developed is that it does not practically cause the loss of 1,2-dichloroethane absorbent - when conventional handling losses are not considered - the product is the product of the subsequent chlorination of ethylene. It is true that the disadvantage of this process is that the ethylene purification process is exclusively developed for the specific purification of ethylene to be synthesized. 1,2-dichloroethane. In the process of the present invention, acetone is removed from ethylene with high efficiency even though it is relatively low inlet concentration. The positive element of the novel process is the very low loading of the absorbent pad with liquid 1,2-dichloroethane, which enables a substantial reduction in the cost of the apparatus and the regenerative part of the apparatus. Purification of ethylene by absorption in dichloroethane and effective acetone control are achieved by the apparatus shown in the accompanying drawing.

E-ethylene is removed from the desorption vessel in an ethylene pyrolysis gas dispensing apparatus by absorption in acetone (unencapsulated, containing cetone as the main impurity in the further use of ethylene for synthesis 1). Typically, the acetone content is about 0.7 to 0.9% by volume and should not exceed 4.0% by weight. methane, 0.9% by volume of ethane and 0.05% by volume of carbon monoxide.Ethylene is fed via the inlet line 1 to the lower part of the absorption tower 2, equipped with mesh structures, but other types of trays can be used Acetone is washed from ethylene by virtually continuous flowing 1,2-dichloroethane fed to the top of the column via a line 4 of dichloroethane. depending on the temperature and pressure conditions in the absorbent wheel 2 and in the desorption exchanger 8. The purified ethylene is discharged via line 3 of pure ethylene. The lower part of the absorption column is obtained by means of the absorption-desorption stage 5 of the desorption-exchanger column 5, in which 1,2-dichloroethane is sprinkled with acetone, methane and ethane heated with regenerated 1,2-dichloroethane fed from the cooker 24 via a pipe of bent dichloroethane 2.5 and discharged through a conduit 26 to the reservoir 28.

The function of the absorption-desorption step of the 5-column consists in stabilizing the priming and also the concentration processes of the desorption and absorption part of the system according to the given requirements and the purity of the ethylene and the process economy. From a structural point of view, it is a cylindrical device with trays allowing intensive fluid contact and desorbed gases.

The desorption exchanger 6 is connected by means of a feed line 7 to the rectification 24 of the column 8, from which the steam is withdrawn. as the more volatile component together with the desorbed gaseous conduit 0 into the partial condenser 10 provided with the duct of the sewage water, the conduit 14 and the condensate conduit 11 through which the partial condenser is discharged.

The condensation acetone at a condenser temperature of about 303 K. Partial condenser 10 serves both to generate the reflux conduit fed to the column by reflux condenser 12λ to condense the corresponding acetone pair at 309 K, The condenser 18 is connected to a steam conduit 14 with a total condenser 18 provided with a liquid propylene feed conduit 18 and 1 lc. propylene gas, degassing pipe 17 and condensate discharge pipe 20. The total condenser serves for example the complete condensation of the acetone vapor, which results in high wind recovery of the acetone recovery. The regenerated acetone, consisting of a condensate of a condensate condenser and a condensate of the condenser, is recycled for further use via line 21 of regenerated acetone. The lower portion of the rectification column 8 is directly connected to the cooker 24 provided with the steam pipe 22, the steam condensate pipe 23 and the boiled dichloromethane pipe 25 connecting the reboiler 24 to the desiccant heat exchanger 8 and via the connecting pipe 28 to the container 28. Container 28 is provided with a feed line 27 of fresh dichloroethane and is connected via a suction line 29 to a pump 30 connected via an ethylene feed line 1 to the absorption column 2. Thus, a closed acetone wash cycle is formed. regeneration of the effluent acetic acid as well as 1,2-dichloroethane.

The diagram of the device in the attached figure contains the basic devices and their connection needed to create a closed system. It does not show auxiliary devices, measuring and indicating devices, as well as fittings, such as control valves or shut-off valves, or the characteristic device developed and dependent on various technical and economic conditions and from of the present invention allows practically complete removal of the steam from ethylene removed from the de-spinning column in the ethylene separation process from pyrolysis gases by abnwnci At the same time, they allow a simple method of regenerating the dehumidified tone of purity suitable for its reuse in the process of separating ethylene by absorption in acetone. there is no foreign substance introduced into the pure ethylene with respect to the subsequent chlorination of the ethylene to 1,2-dichloroethane on 1,2-dichloroethane as described above; In addition to acetone, other substances, such as methane, ethane, as well as carbon monoxide residues are washed, thereby further increasing the purity of ethylene. Importantly, in this new process, there is no risk of acetone penetration in the mist, as is common with deep-cooling systems, or the danger of accumulating hazardous pyro- metics, which makes this new process of ethylene purification highly compared to the others used so far. The following examples illustrate, but do not define, the mode of use. Přikladl

Ethylene, resulting from the desorption step of the ethylene isolation process from pyrolysis gases by absorption in acetone, is purified as described below in an apparatus schematically shown in the accompanying figure.

The ethylene to be purified is initially fed to the absorption column 2 by means of an ethylene feed pipe 1, with acetone and other non-gelling agents, such as CPL ·, and C2HG, being bleached in the process. with a small amount of countercurrent 1,2-dichloroethane fed to the absorbent column via a 4-dichloroethane feed line. Purified ethylene leaves the adsorption column through line 3 of pure ethylene attached to the head of the absorption column 2.

Ethylene, intended for purification, has the following average composition: 97.75% by volume CiH4.0.95 0 / v by volume CII4, 0.69% by volume C2H6, 0.61% by volume. acetone and traces of carbon monoxide. The ethylene feed temperature is 253 K. The pressure of the ethylene feed to the absorption column is 0.8 MPa. The total amount of gaseous feed mixture above is 115.5 kmol. h ~ *.

The predominant part of acetone and a portion of methane and otane are washed by countercurrent flowing dichloroethane fed to a 293 K column of absorption column 3.9 in an amount of 3.9 kmol / hr. at 256.4 K. The liquid dichloroethane leaving the bottom of the absorption column 2 passes through the adsorption-desorption stage of the column 5 'to the desorption exchanger fi in which it heats from 259 K to 313 K of 1,2-dichloroethane leaving the cooker 24 of the rectification column 8. This coupling of the desorption heat exchanger 8 and the absorption column 2 by means of the adsorption-desorption stage of the column 5 produces favorable conditions for setting the temperature profile not suitable for either efficient scrubbing of methane residues. aa] tertane from pure ethylene, or in the opposite case, suitable for minimizing ethylene losses dissolved in dichloromethane at the Kanie absorption column. Kva-blaster mixture of 1,2-dichloroethane with rozpustnýmacetónom and n & desorbovanými sapotom gases fed uppermost 7do rectification column through line 3, intended for the regeneration, neráciu 1,2-dichloroethane and acetone. The high-efficiency column 0 is connected via line 9 to a partial condenser 10 provided with a water inlet and outlet line 13, a condensate line 11 and a steam line conduit 14 to remove non-condensing gases containing acetone for total condensation

Condensation in the partial condenser occurs at atmospheric pressure and 303 K. The majority of these condensed acetone conditions are returned to the rectification column by reflux tube 12 and the smaller portion is recycled via line 15 of liquid acetone. The reflection ratio used is 5: 1.

The recovered acetone, condensed in the condenser, contained 99% w / v. acetone and 0.97% mole. ethylene. The amount of recovered acetone is 0.514 km / h. The uncondensed acetone in the partial condenser 10 and the non-condensing gases such as ethylene and optionally methane and ethane leave the steam condenser via the steam conduit 14 to the total condenser 16 provided with the liquid propylene feed line 18 and the 19-propylene gas line. In the total condenser, virtually all of the acetone still containing the gaseous mixture leaving the partial condenser is condensed.

The condensation temperature is 248 K. The propylene used for cooling is evaporated at 236 K. The resulting acetone condensate is removed from the condenser by the condensate discharge conduit 20 and after the regenerator is drawn off from the partial condensation via line 15 of liquid acetone. all of the acetone obtained in this way is removed via line 21 of the recovered acetone for further use in the process of extracting ethylene from pyrolysis gases by absorption in acetone. The total condensate condensate in the total amount of 0.171kmol.h-1 contains 97.0% mol. acetone and 2.92% mol. ethylene. By combining the regenerate stream from the partial condenser with. obtained after conversion to pure acetone, 0.65 kmol.h-1 of pure acetone, representing a 95% yield of re-generation. The loss of acetone from the reagents was a negligible amount of 0.02 kmol .. h-1. .

Handling losses are about 0.01 kmo-1 .. ti-1. The total condenser exhaust contains an average of 96.7% moles. ethylene and about 1.5% mol. acetone. The remainder are methane and tartrate. Higher acetone content Compared to the theoretical assumptions given given by the condition (temperature 248 K, atmospheric pressure), it is thought to be due to the presence of the acetone in the form of a mist which cannot be separated in the conventional condenser. The 1,2-dichloroethane, which is virtually completely devoid of acetone, is continuously collected from the rectifier column cooker 24. The cooker 24 is provided with a steam conduit 22, a condensate condensate, and a conduit 23 of boiled dichloroethane to discharge the 1,2-dichloromethane to the desorption exchanger. The heat of the boiled 1,2-dichloroethane is 353 K. The acetone content is boiled. 1,2-dichloroethane is smaller and 0.01% mole. The c-cooled 1,2-dichloroethane heat exchanger is discharged via the conduit 26 to the reservoir 28, into which fresh 1,2-dichloroethane is pumped through the feed line of fresh dichloroethane. the dichloroethane is pumped through the pump 30, connected by suction line 29, to a reservoir 28, and is fed to the absorption column 2 by means of an inlet pipe of dichloroethane. The described apparatus is provided with the necessary apparatuses and regulating means. The pressure, flow, and pressure regimes that are not shown in the diagram are absolutely necessary for stable operation. In this way, in the described apparatus, ethylene is practically completely free of acetone and partly also of methane and ethane residues from the previous manufacturing operations. The average composition of pure ethylene is as follows: 93.65% mole of C2H4, 0.15% mole. dlchlorotane, 0.008% mol. acetone, 0.65% mole. CH4a 0.53% mole. ethane.

The content of methane and ethane depends mainly on their content in the ethylene feed, which is determined for cleaning. However, when using ethylene for the production of vinyl chloride via 1,2-dichloroethane, 1,2-dichloroethane in ethylene is not regarded as an impurity, so that the actual ethylene purity is still greater than 98.65% by volume.

The same procedure as in Example 1 is used for the purification of ethylene. The reason is that the desorption-desorption degree of the column 5 and the desorption exchanger are disabled, so that the temperature of 1,2-dichloroethane leaving the absorption coil 2 is 259. K. Incidentally, the temperature and pressure conditions are the same as in Example 1, and the intersection of the apparatus is the same. As a result, the deposition and regeneration of the acetone have a stable operation, not deviating from the operation of the apparatus described in Example 1. The result of this treatment of the apparatus is a higher amount of ethylene, leaving the degassing conduit. 17 from the condenser 16 of the cooled evaporator

Claims (2)

SUBJECT Ethylene and the 1,2-dichloroethane used together with washed impurities, mainly acetone, are desorbed by 1,2-dichloroethane at a pressure of 0.2 to 0.9 MPa and at a temperature of 245 to 300 K and in the desorption part of the system operating at a temperature of 270 to 323 K it is fed to a rectification system in which regenerated acetone is recovered by means of a two-stage condensation and the 1,2-dichloroethane-free boiling of acetone and other washed impurities is recycled. A process for purifying ethylene obtained by desorption from acetone in a process of separating ethylene from pyrolysis gases by absorption in acetone containing acetone as the main undesirable substance by scrubbing, characterized in that the acetone-desorbed ethylene is fed to the transition portion of an integrated absorption absorber. a desorption system, where it is washed in the absorption part of the system 2. Apparatus according to claim 1, comprising an absorption desorption and rectification apparatus and ancillary equipment, characterized in that the ethylene feed line (1) is connected to an absorption column (2) connected by an absorption desorption stage. (5) with a desorption heat exchanger (6) which is connected via a feed line (7) to a rectification column (8) provided with a partial condenser (10) and a total condenser (16) and a reboiler (24) connected by a line ( (25) boiled dichloroethane with a desorption heat exchanger (6), connected by a connecting line (26) to the reservoir (28), provided with a fresh dichloromethane feed line (27) and a suction line (29) connected to a pump (30) via a dichloroethane feed line (4) connected to an absorption column (2j) provided at the top with a line (3) of pure ethylene.