CS239820B1 - A method for separating pyrolysis gas - Google Patents

Abstract

The invention relates to a method for separating pyrolysis gas from high-temperature pyrolysis in an absorption-desorption system using acetone as an absorbent. This method separates from the pyrolysis gas the most soluble components in acetone, such as acetylene and carbon dioxide, and at the same time the less soluble ethylene. Simultaneous complete absorption of ethylene is achieved by dividing the pyrolysis gas stream into the absorption unit and recycling part of the ethylene obtained by desorption from acetone saturated with acetylene and carbon dioxide in the absorption-desorption unit operating at a pressure of 0.45 to 0.9 MPa. Absorption is carried out at a pressure in the range of 1.25 to 2.5 MPa in acetone, supplied at a temperature of -33°C to -40°C. This method produces ethylene of a purity suitable for the chlorination of ethylene to 1,2-dichloroethane in the production of vinyl chloride.

Description

The present invention relates to a method for separating pyrolysis gas from high temperature pyrolysis with a method of separating components which provides improved efficiency. In the case of high temperature pyrolysis, multi-component gaseous compounds are formed, containing in addition to ethylene and ethylene. intermediates, especially for the production of vinyl chloride, as well as other gaseous substances such as methane, carbon dioxide, hydrogen and carbon monoxide.

These substances are contained in the pyrolysis gas in relatively large amounts. The content of acetylene, carbon dioxide, ethylene, methane, and carbon monoxide is usually about the same concentration level and the conditions of pyrolysis range from 9 moles. % to 20 mol. %. The content of the conductive material is higher, usually at 30 mole% to 40 mole, in conventional conditions of pyrolysis. %. The pyrolysis gas contains a wide spectrum of other substances in the smaller concentrations, except in trace amounts only. These include ethane and other hydrocarbons, oxygen, nitrogen, alkynes, nitrogen oxides, collectively referred to as NOX, sulfur compounds, and the like. This multi-component gaseous mixture of pyrolysis gases is purified in a washer-absorber system. After cleaning or reducing the content of hazardous and harmful substances, alcohols are, for example, compounds and oxides of nitrogen, for example an acceptable or safe concentration, with acetylene and ethylene as the products of the other components of the gaseous mixture in the adsorption-desorption systems with acetone dimethylformamide as selective solvents and a low temperature rectification for increased pressure. In this process, the mixture of acetylene and carbon dioxide is separated from the other gaseous components by absorption in acetone in an absorption-desorption system in a so-called acetone wash. recycled to approximately equimolar mixtures of ethylene and carbon dioxide, and then carbonated acetylene from the acetylene gas-carbon dioxide gas mixture by selective absorption in dimethylformamide. The acetylene obtained has a purity satisfactory for the production of vinyl chloride.

The gaseous mixture leaving the absorption part of the acetone wash at this stage comprises, in particular, ethylene, methane, uphosphate oxide and hydrogen. Ethylene is separated from this gas mixture by a low temperature rectification from a mixture of methane, carbon monoxide and hydrogen, which is used both as a fuel in pyrolysis at the start of the production process and / or a raw material for further processing, or as a heating gas for production. steam. The ethylene fraction produced by the low temperature rectification is suitable for the production of vinyl chloride used in the downstream polymerization technology. The main purities are methane and ethane. The content of ethane is dependent on the pyrolysis conditions and practically all of the incoming ethane to the low temperature rectification leaves it together with the ethylene. The methane content of ethylene from the low temperature rectification varies from 0.5 to 2.5% ob, depending on the operation of the rectification device.

The separation of ethylene from pyrolysis gases in low temperature equipment is costly. The disadvantage is that the production equipment is technically very demanding and therefore expensive. In addition, safe operation requires that the NOX content of the inlet gas be less than 0.5ppm, which increases the need for prior purification of the pyrolysis gas and analytical control. If the NOX content is higher, the equipment must often be shut down and cleaned, thereby increasing ethylene loss and energy consumption. As a result of these disadvantages, new, more efficient ways of separating the ethylene from pyrolysis gases which would eliminate or at least alleviate these disadvantages are sought.

According to the Czechoslovak authorial specification No. 211020, absorption by vacetone is used to separate the ethylene from pyrolysis gases, which is used after the desorption of ethylene to absorb acetylene and carbon dioxide, and then, after desorption of the gaseous mixture of ethylene and carbon dioxide, acetone is reused. as an absorption agent for ethylene absorption. The process and apparatus described in the aforementioned author's certificate, more preferably than in the low temperature ethylene earning, therefore provide a substantial increase in operational safety and reliability of operation. As a result, the lower consumption standards of raw materials and energies and low-temperature separation of ethylene.

The ethylene separation process described in the Czechoslovak Patent No. 2110.20 has been amended and improved in the manner described in OA No. 232 632. According to an improved process, ethylene is washed with fresh acetone in a common absorption step from which some of the ethylene-saturated ethylene is removed to the absorption range. acetylene and carbon dioxide, and a portion corresponding to the total amount of ethylene entering the pyrolysis gas is discharged into the ethylene purification step. In this way, the beneficial effect of the internal recycle of ethylene between the two absorption stages is used to increase the solubility of the ethylene, resulting in a reduction in the circulating acetone in the ethylene purification system, resulting in a reduction in the circulating equipment and in the savings. energy by reducing heat losses and reducing the amount of circulating acetone.

It is an object of the present invention to further enhance the absorption-desorption process by separating ethylene on the one hand and gaseous acetylene-carbon dioxide on the other by absorption in acetone.

According to the present invention, the process is divided

The pyrolysis gas of high temperature pyrolysis, consisting of hydrogen, carbon monoxide, methane, ethylene, carbon dioxide, acetylene as the main constituents by absorption and desorption using acetone as an adsorbent, performs talk, that the pyrogenic gas separated into at least two streams is fed to the absorbent node, while at least one stream of ε-ethylene is recycled in the amount of 1/10 to 2/5 of the desorbed ethylene from the absorption-desorbing node; the two said nodes are continuously fed with acetone at -33 to 40 ° C and absorbed in the absorption compartment by ethylene, carbon dioxide and acetylene at a pressure of 1.25 to 2.5MPa and the resulting acetone solution at -5 to 5 ° C. -30 ° C is fed to an absorption-desorption node operating at a pressure of 0.45 to 0.9 MPa and from this node the liquid phase is fed to a desorption node for separating acetylene and carbon dioxide.

The main advantage of such a new process for the uptake of ethylene by the absorption in acetone is that, in addition to the complete absorption of acetylene and carbon dioxide, ethylene is virtually completely absorbed from the supplied pyrolysis gases to obtain a relatively high fraction of ethylene in the acetone leaving the absorption. This is achieved in an original way to increase the steam pressure of the ethylene in the absorbent node, which, together with the finding of suitable conditions in the desorption-desorption node for desorbent ethylene, makes it possible to obtain ethylene in a quality suitable for the chlorination of ethylene to 1,2-dichloroethane in the production of vinyl chloride. . In this way, the ethylene desorption plant due to the reduced amount of gaseous re-cycle is simplified in the prior art. This results in a reduction in the cost of the production plant and, on the other hand, in a reduction in the need for propylene cold in the amount corresponding to the heat of absorption of the pre-recycled carbon dioxide and part of the ethylene. In contrast to the low-temperature separation of ethylene, this is retained! all the advantages in safety and reliability of operation, in fact, the absorption of ethylene.

BACKGROUND OF THE INVENTION The present invention relates to a process for the absorption of pyrolysis gases containing acetylene, carbon dioxide, ethylene, methane, oxide. U-nickel and hydrogen as the main constituents, in particular the separation of ethylene, or its concentrated mixture with carbon dioxide and methane, suitable as an intermediate in the production of vinyl chloride, by absorption in acetone in the non-desorption system with simultaneous separation of the mixture hydrogen, carbon monoxide, and methane as the combust gas and a mixture of acetylene and carbon dioxide removed for further separation by selective absorption of acetylene in dimethylformamide. More particularly, the invention relates to a method for separating pyrolysis gases from a high temperature pyrolysis of gasoline having a boiling point of 30 ° C to 130 ° C and / or petroleum fractions having a boiling point of 130 ° C to 450 ° C and / or a gasoline with a boiling point of 30 ° C to 130 ° C. ° C with addition of methane and / or with addition of a mixture of Cd fr, action.

Moreover, the process conditions of the invention are evident from the exemplary embodiments, and it is to be understood that only part of the recycled acetone is withdrawn either continuously or at certain time intervals for regeneration and replaced with fresh acetone in to increase the concentration of impurities above the technologically undesirable level. Přikladl

The process used in this example for absorbent separation of ethylene and carbon dioxide gas mixture from other pyrolysis gas components is schematically shown in Figure 1. 1. The stage of the body of the process is divided into a system consisting of an absorbent node 8, an absorption-desorption node 14a of the desorption node 19 of a mixture of acetylene with carbon dioxide: gaseous recycle containing predominantly ethylene is conducted to sleep into the absorption node 8 by means of a recycle gas compressor 17.

According to our new method of separating pyrolysis gases, absorption of acetylene, carbon dioxide and ethylene takes place in the absorbent node. Depending on the technological conditions, methane is also temporarily dissolved. After all, gases such as hydrogen and carbon monoxide, optionally nitrogen and oxygen, do not dissolve virtually in the gaseous state by removing gases from the absorption node 9 for further miscellaneous use, whether in the pyrolysis section of the process, or into the power block of the plant.

The separation of the gaseous ethylene from the liquid mixture of acetone with dissolved acetylene and carbon dioxide is carried out in the absorption-desorption node 14. Dissolved methane occurs in this process with ethylene gas, and a slight amount of very sparingly soluble gases can also occur. tones are alcohols hydrogen and carbon monoxide, which are considered to be 1,2-dichloroethane for further processing of ethylene by chlorination to 1,2-dichloroethane. inert gases. The separation of the gaseous mixture consisting of acetylene and carbon dioxide takes place in the desorption node 19, the acetone fed through the connecting pipe 18 from the absorbent-desorption node 14. The acetylene mixture and the carbon dioxide exit the gaseous mixture 20 and acetone, packed with all dissolved gases, is recycled to the system through recycle of acetone 13.

The most important element of the new pyrolysis gas production is originally

2 3 9 8 .3 O 8 absorption solution in absorption node F «of the system. The iPyrolysis gas is fed to the inlet gas system 1. Its composition is in this case as follows: 48.8% by volume of hydrogen together with carbon monoxide, 13.45% by volume of methane, 13.45% by volume of ethylene. 13.84% by volume carbon dioxide and 10.46% by volume acetylene. Nitrogen, oxygen, and possibly the so-called inert gases are included in the hydrogen content together with the carbon monoxide, which is hereinafter referred to as · Inert against solubility in acetone. The amount of leaving gas in this example is 691.4 millimeters. h ’1. The pyrolysis gas in this amount is fed to the absorption compartment divided into three streams at a ratio of 0.178: 0.438: 0.384, using a computer 8 from the bottom of the absorber. 0.178 parts of the supplied pyrolysis gas is fed through the lower inlet 4 through the inlet gas inlet 1, 0.438 parts are fed through the inlet 3 and 0.384 parts of the supplied pyrolysis gas are fed through the upper inlet 2. In addition, recycle gas is recycled to bottom 4 through a recycle line 7. The amount of ethylene in the recycle gas is 30 kmol. h k Recycling gas in this case contains 73.8% vol. % ethylene, 4.6 vol% methane and 16.6 vol% carbon dioxide. After addition of the recycle gas, the composition of the gas entering the absorption node 8 is the lower inlet 4 following: 37.27% by volume of the so-called inert, 14.48% by volume. carbon dioxide, 11.37% by volume of methane, 7.98% by volume of acetylene and 28.89% by volume of ethylene. In this example, no recycle gas is fed to the intermediate supply 3, so that the composition of the gases entering the absorption node 8 through the intermediate inlet 3 and the upstream inlet 2 is the same as depositing the incoming pyrolysis gas in the feed gas inlet 1.

The temperature at the bottom of the absorbent node is -25 ° C and a pressure of 1.50 MPa. In these conditions, almost all of the incoming ethylene, together with the recycled ethylene, is dissolved with a mole fraction of 0.0824 dissolved ethylene in acetone, leaving the absorption node 8 by feeding saturated acetone 10 to the absorption-desorption node 14. the poor gas leaving the absorption node 8 in the exhaust gas 9 contains 0.5 ° / vol. unabsorbed or ethylene; j. 2.14kmol. h_1, which represents a loss of about 2.1% of the ethylene feed. The temperature of the acetone as an absorption agent supplied to the absorbent node by the inlet of acetone 11 is 3030 ° C. Acetone, introduced as reflux into the absorbent-desorption node 14 by the reflux conduit 12, also has an equal temperature. In the absorbent-desorption node 14, a gaseous stream is separated, containing predominantly ethylene, from the liquid acetone mixture. , carbon dioxide and acetylene, and discharged therefrom by concentrating the ethylene 15. The portion corresponding to the amount of ethylene feed after the losses are lost is passed through the intermediate stream for further processing with ethylene pipe 18, a portion of the absorption into the absorbent node as a recycle through the recycle gas pipe 5 recycle gas compressor 17. The temperature at the top of the absorption-desorption bar is -20 ° C, the bottom temperature is + 43 ° C. The pressure is 0.65 MPa. These conditions yield a gas containing 73.83 percent by volume of ethylene. A gaseous mixture of acetylene and carbon dioxide is obtained in a pressurized desorption node 19 at a pressure of 0.3 MPa, consisting of 72 kmol after removal of the acetone residues. acetylene and 78.6 kmol of carbon dioxide. The mixture is then transferred to a dimethylformamide wash to separate the carbon dioxide from the acetylene. C o rt 2

The process is the same as in Example 1, except that an increased pressure is applied to the absorption node 8, compared to Example 1 with a bed pressure of 0.05 MPa. That is, at the bottom of the absorbent. node 8 is a pressure of 1.55 MPa. This has been demonstrated by the reduction of the ethylene content of the gas leaving the gas outlet 9 from the absorption node 3 to an average of 0.25% by volume.

The procedure is the same as in Example 2, except that the temperature at the top of the absorbent-desorption node was reduced by 5 ° C, i.e. at -25 ° C. Under these conditions, the concentration of ethylene in the gas was increased to 85 [deg.]% By volume of the concentrated ethylene conduit 15 at a volume of 4.

The procedure is the same as in Example 3, except that the absorption-desorption pressure is 0.69 MPa and the bottom temperature is 47 ° C. The concentration of ethylene was increased to 91% by volume

The procedure is the same as in Example 1, with the difference that 20 kmol is fed to the lower inlet 4 by re-cycling. ethylene is introduced into the intermediate feed 3 via a line 6 of 10 kmol. Ethylene ethylene. During the absorption, there is no observable change except that on average, the content of the so-called concentrated ethylene of the adsorption-desorption stage has increased by about 0.2% by volume.

Claims (1)

SUBJECT A process for separating pyrolysis gas from high temperature pyrolysis consisting of hydrogen, carbon monoxide, methane, ethylene, carbon dioxide, and acetylene as main constituents by absorption and desorption using acetone as an absorbing agent, characterized in that the pyrolysis gas is divided into at least two the stream is fed to the absorbent node, wherein at least one stream feeds ethylene as a recycle in an amount of 1/10 to 2/5 of the desorbed ethylene from the absorption-desorption node, wherein BACKGROUND OF THE INVENTION To both nodes, acetone at a temperature of -33 ° C to -40 ° C is continuously fed and the absorption node is subjected to absorption of ethylene, carbon dioxide and acetylene at a pressure of 1.25-2.5 MPa and the resulting acetone solution at - 5 to -30 ° C is fed to an absorption-desorption node operating at a pressure of 0.45 to 0.9 MPa and from this node the liquid phase is fed to a desorption node. nodes to divide acetylene and carbon dioxide.