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    • 专利摘要:
    The conventional process for the recovery of ethylene oxide produced by the silver catalyzed, vapor phase, partial oxidation of ethylene with molecular oxygen involves a sequence of steps including absorption in water of the ethylene oxide contained in the reaction effluent. The ethylene oxide-containing absorbate is then stripped and the vapor thus generated is subjected to reabsorption, also in water. This invention provides an improved stripper-reabsorption system and includes the steps of partial condensation of the stripper overhead and introduction of an additional absorbent stream into the readsorption step.
    公开号:SU831076A3
    申请号:SU762337307
    申请日:1976-03-18
    公开日:1981-05-15
    发明作者:Дж.Озеро Брайан
    申请人:Халкон Интернэшнл Инк (Фирма)；
    IPC主号:
    专利说明:

    The invention relates to methods for extracting ethylene oxide from a gas stream resulting from the vapor-phase oxidation of ethylene with molecular oxygen in the presence of silver as a catalyst, specifically to the improvement of the desorption-absorption system used for this purpose. When ethylene oxide is produced by the vapor-phase oxidation of ethylene with molecular oxygen in the presence of silver, a gaseous reaction stream is formed as a catalyst. A known method for extracting ethylene oxide from a gas stream. Taking into account the fact that this gas stream is highly diluted relative to the ethylene oxide to be obtained and usually contains 0.3–5 mol% of ethylene oxide, and the attraction of ethylene oxide from this gas stream involves countercurrent contact of the gas stream with a water wash. to obtain an absorbent containing ethylene oxide, which is stripped in a stripping zone containing several contact vapor-liquid, to produce ethylene oxide-containing effluent from the top of the stripping column and reabsorbing ethylene oxide internally re-absorption zones containing several vapor-liquid contact elements by countercurrent contact of steam from the top of the stripping zone with water. With this sequence, the main function of the absorption stage is the selective absorption of ethylene oxide from the gas reaction stream with other materials that are not reacted. compounds, diluents of the reaction medium and secondary products of the reaction, which are also contained in the reaction stream. However, since the absorber operates at relatively high pressure, somewhat lower than the pressure in the reactor, significant amounts of such compounds present in the reaction stream as carbon dioxide, minor admixtures of aldehydes and acid-type secondary products / resulting from the oxidation reaction are also absorbed along with ethylene oxide. In the stripping zone, the absorbed ethylene oxide evaporates as a result of the action of the vapor, and significant amounts of carbon dioxide and the addition of the δdehydes, evaporating along with the oxide, are evaporated. The main purpose of the reabsorber is the separation of ethylene oxide and carbon dioxide evaporating in the stripping zone. Thus, in the Rea Sorber, a countercurrent contact of the stream leaving the stripping zone with water is made, as a result of which liquid reabsorbate is formed as a bottom liquid, consisting mainly of ethylene and eodes, but also containing residual amounts of carbon dioxide. , allegide and acid impurities. The ab sorber operates at relatively high pressure, whereas both the spinning zone and the reabsorber operate at shading pressures close to atmospheric pressure. Such a pressure differential facilitates the processing of products in the desorption – adsorption system, mainly, the separation of ethylene oxide and carbon dioxide. The disadvantages of the method are due to the need to obtain products of higher purity at the lowest cost. The temperatures in the stripping chambers are high enough that, as a result of thermal hydration, some of the ethylene oxide is converted to ethylene glycol, contaminated with different impurities, which is difficult to clean and use in areas where extremely high purity products are required, for example, fiber production, and in areas where product purity requirements are lower, for example, upon receipt of antifreeze. Attempts to reduce the pressure in the stripping zone and thus reduce the temperature are impractical, since as a result, the pressure in the reabsorber also decreases if there are no means for vapor compression between the stripping area and the reabsorber. Such devices are rather expensive and difficult to operate. Without additional compression, the lower the pressure in the stripping zone, the lower the pressure in the reabsorber and the greater amount of water is required to absorb ethylene oxide in the reabsorber. This means that the cube liquid (reabsorbate — a solution of ethylene oxide in water) in the reabsorber will be more diluted with respect to ethylene oxide, respectively; subsequent processing to extract ethylene oxide from it becomes more expensive and time consuming. Even if reabsorbate is not recyclable in order to extract ethylene oxide from it, but undergoes thermal hydrogenation to obtain ethylene oxide dissolved in it, mono-ethylene glycol directly, an insignificant amount of impurities dissolved in reabsorbate affects the quality glycol, in addition, the production of glycol from reabsorbate is more advantageous when using solutions with a relatively high concentration of dissolved ethylene oxide, since solutions from the reabsorber contain less than Å by weight,% oxide and ethylene, but it is not appropriate to use. Due to the need to use large quantities of carbon dioxide, which is the diluent of the reaction in the oxidation stage, respectively, more carbon dioxide is absorbed in the absorber, evaporates in the stripping zone and, thus, is in the gas stream feeding the reabsorber, which in turn necessitates the use of significant amounts of water in the reabsorber, and leads to the formation of reabsorbate, more diluted relative to ethylene oxide. The presence of these drawbacks significantly complicates the technology for extracting ethylene oxide from. gas flow. Thus, there arises the need to develop a desorption-reabsorption system used in the process of extracting ethylene oxide, which could be easily controlled, in which a minimal amount of glycol would be formed and in which minimal impurity transfer would occur. In addition, such a system must be adapted to process materials with a higher carbon dioxide content, without the formation of aqueous reabsorbates diluted with ethylene oxide. The purpose of the invention is to simplify the process technology. The goal is achieved by extracting ethylene oxide from a gas stream produced by silver-catalyzed vapor-phase incomplete oxidation of ethylene with molecular oxygen, providing a countercurrent contact of the gas stream with an aqueous washing solution to obtain an absorbent containing ethylene oxide which is stripped in a stripping zone containing several vapor-liquid contact stages, to produce an ethylene oxide containing effluent of a steam stripping column and reabsorption of ethylene oxide inside the zone the lateral absorption containing several contact vapor – liquid stages, by countercurrent contact of the vapor from the top of the stripping zone with water, the vapor emerging from the top of the stripping zone is partially condensed in such a way that 50-99% of water and i-20% ethylene oxide containing steam, is condensed and the resulting condensate is fed as flagella into the upper part of the stripping zone, the uncondensed part of the steam from the top of the stripping zone is introduced into the reabsorption zone, the part of the reabsorbate is cooled and the cooled reabsorbate is recycled and they are introduced into the re-absorption zone by stopping the entry points of the uncondensed part of the steam discharged from the top of the stripping zone and water with the weight ratio of the cooled reabsorbate to the non-cooled reabsorbate equal to 0.2–20: 1. The process is carried out at the cooled reabsorbate temperature less than the temperature of the non-condensed portion of the vapor exiting the stripping zone. The process is carried out at a difference between the temperature of the injected steam and the temperature of the cooled reabsorbate equal to 2-50 s, preferably. In addition, between the point at which the uncondensed part of the vapor exiting from the top of the stripping zone is introduced into the re-absorption zone and the point at which the cooled reabsorbate is introduced into the stripping zone, there are 2-10 theoretical vapor-liquid contact points. In accordance with the proposed method, it is intended to use a conventional desorption-reabsorption system with two main MO detections. The first of these concludes with the fact that the steam leaving the stripping zone must be partially condensed so that about 50% of the water, but not more than 204 of ethylene oxide contained in it, condenses. This condensate in the form of reflux returns to the stripping zone. The non-condensed steam is discharged and supplied to the lower part of the reabsorber, while the water flows countercurrently from the upper part. Thus, in the reabsorber, the exit and the exit of steam and water from the upper part of the stripping zone are carried out, displaced by countercurrent flow, resulting in the preferred absorption of ethylene oxide and the formation of the required reabsorbate. The second modification provides for the separation of reabsorbate into two parts, the first of which is cooled and re-supplied to the reabsorber at a point located between the feeding points of the steam and water leaving the upper part of the stripping zone. The second part of the reabsorbate is removed and subjected to the slightest processing to extract the ethylene oxide dissolved in it, to convert the ethylene oxide dissolved in it into ethylene glycols, split into two parts, one of which is intended to extract ethylene oxide from it and . FIG. 1 shows a diagram of a known desorption-reabsorption system; in fig. 2 - the scheme suggests my desorption-reabsorption i system; in fig. 3 - scheme - the same, option. According to a known method (Fig. 1), an aqueous solution (absorber) resulting from the absorption of a gas reaction stream by water obtained by vapor-phase partial oxidation of ethylene with molecular oxygen in the presence of a silver catalyst, in line 1 is introduced into the upper part of the stripping zone 2 . Line 3 supplies steam to the bottom of the stripping zone 2. As a result of countercurrent movement of the absorber and vapor in the stripping zone 2, the ethylene oxide dissolved in it evaporates from the absorbate, and ethylene oxide mixed with steam, also containing significant amounts of carbon dioxide and trace impurities, is removed from the upper part of the stripping zone 2 via line 4. The desorbed absorber, which does not contain a significant amount of dissolved ethylene oxide, is withdrawn from line 5 from the bottom of the stripping zone 2 and, after cooling along line b, is returned to the absorber for secondary use in the extraction process Lena. To prevent uncontrolled accumulation of glycols formed in the stripping zone and traces of impurities, part of the desorbed absorbate can be removed from the system via line 7 and sent for further processing or discarded. In a known process, the feed rate of the stripping zone is soyergite of 0.5-5% by weight of ethylene oxide, and the operation of the stripping zone is controlled so that the degree of extraction of ethylene oxide from the feed of the stripping zone of the stream (i.e., absorbate} exceeds 90% ( 99%). To facilitate the desorption process that takes place in the stripping zone 2, it is usually supplied with nozzles, which make it more efficient to contact vapor and liquid (plates, rings, nozzle, etc.) equivalent to at least about 3 th theoretical theoretical vapor contact liquid 5 such stages, but not more than 50 and theoretical contact levels, pargid, usually 5–40 (6–30, 7–20). The efficiency of the desorption process depends on the amount of de-orb. along line 3, relative to the amount of absorber flowing through line 1 into the stripping zone 2, as well as the number of polysaccele desorption stages.
    The amount of wax required for treating the invoice amount of absorbate is usually 0.03 (0.4, O, -5). Higher parabsorbate ratios can be used, although the advantages can be achieved if you use ratios. 0.2 mol of vapor per mole of absorbate, insignificant (0.03-0.20, 0.04-0.10, O., 04-0.08 are used). These vapor-absorber ratios imply the use of certain pressures in the stripping zone, as a rule, 1.04-3.9 kg / cm - abs., 1D3, 0 and preferably 1.2-2.5 kg / cm abs is acceptable. To some extent, these vapor-absorber ratios also depend on the number of theoretical vapor-liquid contact stages in the stripping zone, i.e. The use of a larger number of such stages reduces the steam consumption, although the reduction of the cr cr ratio is only for desorbers containing 3--20 (or) theoretical stages:; vapor-liquid contact. The use of a larger number of such stages for the purposes of the consumption of steam by an ecocom cescap is inexpedient, since it is the result of a differential drop of dazzle ;; At the stripping zone and, respectively, at the lower temperatures of 3 cubes by stripping the zone, the thermal hydrolysis of ethylene oxide and the formation of ethylene glycols increase.
    In the case of a stripping zone of known construction, the steam coming out from its upper part along line 4 usually contains 10-40 (15-30, 1825) mole,% of ethylene oxide. The primary diluent for this vapor stream is water, although up to 15 (10, 7-8) mol% of this stream consists of non-condensable gases, mainly CO2, as well as nitrogen, argon, oxygen, ethane, ethylene, and the like.
    Outdoor steam is depicted in FIG. 1 3 when it is injected into the column, although this is not necessary, since the bottom fraction of the stripping zone discharged through line 5 contains mainly water, and steam can be regenerated if there are corresponding heating devices, heat exchangers, etc.
    The vapors leaving the stripping zone 2 through line 4 are then cooled in a heat exchanger 8 to optimal temperatures from an economical point of view, typically up to 25-30 ° C, preferably 30 to 30 ° C, as a result of which they are partially creeped. The mixture of liquid and vapor thus obtained is then fed to the lower part of the reabsorber 9 through line 10, and water through line 11 to the upper part of the reabsorber 9. In the reabsorber 9, the vapor and water moving from the upper part of the stripping zone are in contact, resulting in which absorbs the maximum possible amount of ethylene oxide entering the reabsorber through line 10. Thus, it is common to absorb 90 and above 95-99 mol,% of ethylene oxide. The resulting aqueous solution of ethylene oxide is withdrawn from the cube of the reabsorber through line 12, while non-absorbing vapors containing mainly CO and entering the system through line 1 along with other uncondensed gases (for example, ethylene, oxygen, nitrogen, argon, etc.). ) withdrawing the top of the reabsorber through line 13, and they can be thrown away or further processed, for example, to remove traces of ethylene or purified CO. Thus, the reabsorbate solution withdrawn from reabsorber 9 through line 12 contains mainly ethylene oxide and water, and only traces of dissolved CO2 and impurities and along line 14 can be introduced into the cleaning zone 15. Conversely, all or part of the reabsorbate Directly directed to thermal hydrolysis via line 16 to reactor 17, in this case ethylene oxide dissolved in the reabsorbate. Convert to ethylene glycol at elevated temperature and pressure ..
    Like the stripping zone 2, the reabsorber 9 is equipped with nozzles to increase the contact area of the liquid and increase the contact efficiency of countercurrent of moving water introduced into reabsorber 9 through line 11 and the steam introduced from the upper part of the stripping zone through line 10. The number of nozzle assemblies in reabsorber 9 is equivalent to 5 (7, 10 theoretical vapor-liquid contact stages, and this is not the maximum number of stages limited by economic considerations. Proceeding from such economic considerations In addition, the number of such theoretical vapor – liquid contact stages in the reabsorber is less than 50 (10, 30). The amount of water needed to achieve the desired degree of absorption in the reabsorber depends on the pressure in the reabsorber and the number of moles of vapor passing through the reabsorber. the number of moles of steam (denoted by Y) as the arithmetic average of moles of steam entering the reabsorber through line 10, and the number of moles of steam leaving the reabsorber through line 13, then the number of moles of water supplied through line 11 (indicated by L) should be like ovo, so that the L / Y ratio is 5-50 V8-40, and preferably Yu-ZO).
    The values of the L / Y ratios suggest such a mode of operation of the reabsorber, when the pressure in the upper part is 1.0-3.8 (1.05-3, o), and preferably 1 / 1-2, .O kg / cm abs. , while the pressure in the upper part of the re-heater is slightly lower than the pressure in the steam zone. Thus, the reabsorbates obtained in accordance with known systems contain 5-25 wt.% Of ethylene oxide, and the rest is water and small amounts, less than 1 wt.%, Of impurities, mainly dissolved carbon dioxide and ethylene glycol. In general, reabsorbate contains 7-20, and preferably 8-15% by weight ethylene oxide. The known method makes it possible to obtain reabsorbates of comparable compositions that can be obtained by the proposed method from flowing out of the absorber, whose composition varies considerably more widely than that obtained by the known method of absorbates. When considering the desorption-absorption system by a known method (Fig. L), it is clear that some of the characteristic parameters of the process are very important. Thus, the steam that escapes from the stripping zone 2 must be at a sufficiently high pressure so that under the action of the pressure gradient to pass not only through the heat exchanger 8, but also through the whole reabsorber 9, and also to maintain a pressure sufficient to pass it via line 13. Thus, the lowest pressure in the system (Fig. 1) should be on line 13, and be different from atmospheric if the system does not provide for the use of additional compression. To create such a pressure gradient, the pressure of the vapor zone 9 must be significantly higher than the atmospheric pressure, even if it is economically more efficient for a desorption process (but with minimal hydrolysis of ethylene oxide), the pressure in the stripping zone should be as low as possible, since the higher the pressure in the stripping zone, the higher the temperature in it. Therefore, ultimately, the pressure difference in the stripping zone and the reabsorber is not more than 0.5 kg / cm, as a rule, not more than 0.3-0.2 kg / cm. However, in order for the size of the connecting piping to be minimal, and in order to be able to install the necessary instruments and control devices, there must be a difference between the pressure in the upper part of the stripping zone and the pressure in the cube of the reabsorber, usually 0.01 kg / cm. As a result of the increase in water flow through line 11 (i.e., with increasing L / Y in reabsorber 9), the pressure drop in reabsorber 9 increases, the temperature in the stripping zone rises, and as a result more dilute reabsorbates are formed, passing along line 12. For example , the amount of non-condensing; P5ihs gases in the upper part of the stripping zone 2, and accordingly, the pressure in the system, or the amount of water flowing through line 11, or both of these parameters increase significantly, since the number of such non-condensable dihs gases like carbon dioxide Increases sharply. This is also seen in the formation of a reaction stream with a lower content of COj. To obtain reabsorbate with a comparable content of ethylene oxide from the enriched, gaseous reaction stream, the amount of feed reabsorber of water is increased by 5%, and the pressure in the upper part of the reabsorber is increased by 23%, respectively, the glycol content (corresponding decrease, yield) is increased by 8- 10%, and also the steam consumption in the zone is increased. The design and performance of the stripping zone in FIG. 2 are the same as in FIG. 1. However, steam coming from the top of the stripping zone, passing through line 4, is treated differently. This steam is partially condensed in the heat exchanger 18, from which the vapor-liquid flow through line 19 is diverted to the tank 20. In the tank 20, the vapor and liquid phases are separated. The liquid phase is withdrawn from reservoir 20 via line -21, and then through the injection pump 22 via line 23 is fed into the upper part from the stripper and zone 2 as reflux, preferably to that part of the stripping zone 2 where the absorber is introduced. However, in FIG. 2, the absolute amount of steam supplied to the stripping zone along line 3 (or regenerated) is somewhat larger than in the diagram in FIG. 1. And if the ratios of the number of moles of steam supplied to the stripping zone to the molar-absorbed absorbate remain unchanged, then in the embodiment of FIG. 2, these ratios relate to the sum of moles of incoming absorbate plus the number of moles of reflux returned to the stripping zone through line 23. Since the amount of reflux per mole is small TIO compared to the amount of absorbate, this increase in steam consumption from an economic point of view virtually no effect. j Heat exchanger 8 in FIG. 1 and heat exchanger 18 in FIG. 2 work differently. In the embodiment of FIG. 1 degree of flow of condensation is not an important factor: the lower the temperature at the exit of the heat exchanger 8, the less the load on the reabsorber 9, but on the operation of the steam extractor ;. {w this does not affect. Thus, the temperature of the stream flowing through line 10 (the temperature to which the vapors from the heat exchanger 8 leaving the upper part of the stripping zone is cooled) can be equal to the minimum from an economic point of view without using refrigerators, although if necessary it can be used and cooling with the refrigerant in the heat exchanger 8 or with an additional chiller (not shown). With this method, cooling to a temperature less than the minimum required temperature does not harm and leads to a further reduction in steam consumption in the reabsorber 9.- However, in the variant shown in FIG. 2, the temperature of the flow through line 19 is usually higher than the temperature of the flow flowing through line 10 in FIG. 1, i.e. The degree of condensation in the heat exchange 18 is a very important factor, because if it is small, the amount of vapor reabsorber feeding increases and the steam turns out to be very (Dilute relative to ethylene oxide, and if the degree of condensation is large: a, then the amount condensed the reaction cycle to the ethylene oxide stripping zone becomes too large, and, accordingly, the amount of glycol formed in the stripping zone increases. Deficiencies associated with excessive recycling of ethylene oxide in the stripping zone, can be removed without installing additional equipment by introducing additional vapor-liquid contact steps in the stripping zone above the point at which the absorber is fed to the stripping zone via line 1 (these additional steps thus represent the rectification zone). the steps dramatically increase investment and do not completely prevent some decrease in output due to pressure and, consequently, an increase in temperature (in the lower part of the stripping zone). Therefore, it is important that but 50-5 (BO, 80) of water flowing through line 4, and no more than about 20% (Yu, 7) of ethylene oxide flowing through line 4, condensed in heat exchanger 18. Regulation of the degree of condensation in heat exchanger 19 is carried out for example, by adjusting the coolant flow rate in the heat exchanger 18. If we assume that the steam zone operates at a pressure Jc, —pressures lying in the normal range of about 1.04–3.8 kg / cm abs, then the necessary degree of condensation is achieved by cooling of vapors emerging from the upper part of the stripping zone to a temperature, example but 30–80 ° C (35–70 ° C, 40–65 ° C), this will be the temperature of the mixture of liquid and vapor flowing through line 19. Unbound steam, residue; or partially condensed steam leaving the upper part of the stripping zone through line 24 removed from reservoir 20 and fed to the bottom of the reabsorber. Water is fed to reabsorbent 9 through line 11, uncondensed gases are withdrawn from line 13 from the top of the reabsorber, and reabsorbate is withdrawn from the bottom of the reabsorber through line 12. In FIG. 2, the reabsorbate flowing through line 12 passes through the injection pump 25, where its pressure is increased (the corresponding pump in Fig. 1 is not shown), and then flows through line 26 and is divided into two parts. That part which flows through line 27 corresponds to the reabsorbate obtained in a known manner, i.e. through line 14, it enters the purification stage and / or the stage of thermal hydrolysis through line 16. That part of the reabsorbate, which flows through line 28, is cooled. in heat exchanger 29 and in line 30 is returned as a liquid to reabsorber 9. The amount of reabsorbate flowing through line 30 is related to the amount of product flowing through line 27, and must be such that at least 0.2 weight.h . reabsorbate to the weight part of the reabsorbate flowing through line 27, returned to the reaction cycle (line 30). The weight ratio of the recycling reabsorbate to the reabsorbate that enters further transfer is more than 0.2: 1 (0.1: 1, 0.5: l). The system can work at a ratio of 20: 1, but the use of ratios exceeding about 10: 1 is undesirable. and high economic indicators can be achieved with ratios less than 8: 1 (b: 1). The optimal ratio of recycling reabsorbate to absorbate, which is fed to the most advanced processing, is 0.5: 1-2.0: 1. Heat exchanger 29 removes such amount of heat that the heat balance in the reabsorber corresponds to the previously calculated required reabsorbate concentration, and it depends on the quantity and temperature of the irrigated water supplied through line 11 and the temperature of the partially condensed steam leaving the top of the stripping zone. and passing through line 24, as well as the amount of ethylene oxide contained in the partially condensed vapor leaving the upper part of the stripping zone and to be removed in the reabsorber (usually over 99 mol.% ethylene oxide is recovered). Thus, it is impractical to regulate all conditions depending on the temperature of the liquid recirculation reabsorbate. However, in practice, the temperature to which the recirculated reabsorbate is cooled in the heat exchanger 29 is less than the temperature of the partially condensed steam leaving the upper part.
    zones of steam entering the reabsorber through line 24, which, neglecting heat losses to the environment, are as large as the temperature of the stream flowing through line 19. There is an optional large temperature difference between the two streams. It is usually enough that between the two streams that flow along lines 30 and 24, the temperature difference is on the order of. However, for relief. process control using a slightly larger temperature difference in the range of 5-15 ° C, it may be more, but not to exceed 40-50s. However, in all cases, the cooled reabsorbate entering recycling must be liquid.
    With the indicated temperature differences, it is assumed that the partially condensed steam coming out of the upper part of the stripping zone and into the heat exchanger 18 has almost the same temperature as the flow entering re-absorber 9 through line 24. For deeper cooling streams flowing through line 24 before they are introduced into the reabsorber, use an additional heat exchanger (not shown in the diagram). In this case, the above temperature difference will no longer exist, and the temperature of the recycle reabsorber can be the same and even higher because the temperature of the partially condensed vapor leaving the upper part of the stripping zone; The basic requirement remains the need to maintain thermal balance.
    The previous reabsorber operates with the same number of theoretical vapor-liquid contact feet and the same L / Y ratios as the known reabsorbers. However, the point of introduction of the liquid recycle to the reabsorber must be above the point at which the partially condensed vapor coming out of the upper part of the stripping zone is fed into the reabsorber so that at least one and preferably two theoretical levels of vapor contact are located between them. - liquid, i.e. The point at which recycling reabsorbate is supplied to the reabsorber is at least one theoretical level of vapor-liquid contact above the point at which partially condensed vapor leaving the upper part of the stripping zone is fed to the reabsorber. If such contact stages exist between the point where partially condensed steam leaving the stripping zone and the recycle reabsorbate are supplied, this will reduce the pressure in the reabsorber, reduce the ratio of re-circulation reabsorbate to raw reabsorbate, exposing further processing, or get reabsorbate with a higher concentration of ethylene oxide. Therefore, it is preferable to use between these two points a greater number of contact stages, for example, up to 20 such stages (preferably 2-10, 3-8) between the points of supply of the partially condensed vapor leaving the Stripping Zone and the recirculation reabsorbate.
    The degree of condensation in the heat exchanger 18 and the amount of recirculation
    5, the reabsorbate is interconnected: the higher the degree of condensation in the heat exchanger 18, the smaller the amount of recycle absorber and vice versa.
    FIG. 3 is presented similar to
    0 depicted in FIG. 2 is a desorption-absorption system, but designed so that the tank 20, the pump 22 and the wire 23 are optional | Due to the location of the heat exchanger
    5 18 in the bottom of the stripping zone 2. Thus, the pipe 4 is connected to the heat exchanger 18, in which partial condensation takes place. Condensate under its own weight drops
    0 directly to the upper part of the stripping zone 2 via line 31. Uncondensed steam is removed from heat exchanger 18 via line 32 and then fed to the lower part of the reabsorber in the same way as
    5 pairs flowing along line 24 in FIG. 2. It should be noted that pipelines 4 and 31 can be omitted in the circuit if heat exchanger 18 is directly connected to the stripping zone 2. In practice, this is easily accomplished by introducing a cooling coil directly into the upper part of the stripping zone 2, at a point above which in the stripping zone line 1 is absorbed.
    five
    Various modifications are possible in these systems. For example, the flow through line 24 in FIG. 2 or along line 32 in FIG. 3, may be subjected to a deeper cooling in the additional heat exchanger, as a result of which the amount of recycle reabsorbate required and / or the amount of heat removed from the recycle sorbate recycle in heat exchanger 29 is reduced.
    The water supplied to the upper part of the reabsorber 9 does not need to be clean, you can use water that is disposed of from different stages of the process.
    0 process containing a significant amount of impurities, for example, up to 1520 wt.% Of ethylene oxide.
    Example. Continuous vapor phase oxidation of ethylene with molecular oxygen is carried out in the presence of a silver based catalyst. This reaction stream is cooled and washed with water, resulting in an absorber containing ethylene oxide, as well as carbon dioxide, these glycol (formed in small quantities during the absorption process and subsequent desorption stages, a smaller amount of dissolved non-condensable gases (ethylene, oxygen , nitrogen, argon, methane, ethane) and an insignificant amount of organic impurities (aldehydes, acids). Absorbate continuously passes through the desorption-reabsorption system shown in Fig. 1. We use the stripping zone contains 8 theoretical vapor-liquid contact stages, while the reabsorber contains 15 theoretical vapor-liquid contact stages. The recirculation re-sorbate is fed to the reabsorber at a point above the point where the partially condensed vapor leaves the upper part of the stripping zone. and between these two points there are 5 theoretical levels of the vapor-liquid contact.Temperatures, pressures, flow rates and compositions of the reaction streams are presented in Table. li It should be noted that since the absorption proceeds at high pressure and the desorption at low pressure, a small part of the absorbate evaporates when introduced into the stripping zone, so that the actual absorber entering the stripping zone contains about 2% by weight of steam. When considering the above data, it can be seen that over 98% of the ethylene oxide entering the system is absorbed by the absorbate and less than 2% of ethylene oxide is converted to ethylene glycol. The amount of high boiling impurities (aldehydes and acids) in the reabsorbate is approximately 1/20 of their quantity in the absorber. As a result, the steam coming out of the system is under pressure, the value of which is high enough to ensure that it is ejected or fed to subsequent processing without additional compression. Example 2. (Comparative Reaction stream in example 1 is processed to obtain absorbate the absorber of example 1. However, the processing of this absorbate is carried out in a desorption-reabsorption system, similar to the system depicted in Fig. 1. The process parameters are chosen in such a way that Formation of reabsorbate composition similar to the reabsorbate of example 1. To do this, increase the pressure in the stripping zone and in the reabsorber. In this example, as in Example 1, the stripping zone consists of 8 theoretical vapor-liquid contact stages, and the reabsorber of 15 The temperature, pressure, flow rate and composition of the flows are given in Table 2 When comparing the above data with these examples 1 (Table 1), it is clear that 20 times more impurities enter the reabsorber from the Stripping Zone, as evidenced by a much higher soda Neighing impurities in reabsorbate. In addition, to obtain reabsorbate with the same concentration of ethylene oxide, a system operating at a higher pressure and loss of ethylene oxide as a result of thermal hydrolysis and the formation of ethylene glycols in the stripping zone several-Btaue is required. Example 3. The process is carried out according to the known desorption-reabsorption scheme (Fig. 1). As in the preceding examples, a stripping zone with 8 theoretical vapor-liquid contact stages and a reabsorber consisting of 15 such stages are used. However, the pressure in the stripping zone and the reabsorber is maintained at the same level as the pressure in Example 1, in order to minimize the amount of ethylene oxide, which is 1 Cg as a result of hydrolysis. it -. Table 3 shows the temperature, pressure, flow rate and composition of the streams. The content of ethylene oxide in the bottom residue of the reabsorber is lower than the concentration of ethylene oxide in the bottom residue of the reabsorber in example 1 or 2. The cost of extracting ethylene oxide from such reabsorbate is much higher, and the process itself is more complicated than in the case of extracting ethylene oxide from the reabsorbate of Example 1 or 2. Example 4. To obtain a reaction stream containing a conventional amount of CO (less than 15 mol.%), aegilene molecule is continuously oxidized. molecular oxygen in the presence of a silver-based catalyst in a gas phase. This reaction stream is cooled and passed through with water, resulting in an absorber containing ethylene oxide as well as carbon dioxide (in smaller amounts, compared with Examples 1-3), ethylene glycol and more low levels of dissolved non-condensable gazrv (ethylene, oxygen, nitrogen, argon, methane, ethane), as well as a small amount of organic impurities (aldehydes and acidsO. This absorber is continuously fed into the adsorption-reabsorption system, in the same way as shown in Fig. 3, and the stripping zone consists and from 8 theoretical vapor-liquid contact stages, and a reabsorber from 15 theoretical vapor-liquid contact stages ... Recycling reabsorbate falls into the reabsorber at a point located above the feed point of the partially condensed vapor leaving the upper part of the stripping zone and between these two points are the theoretical theoretical levels of the vapor-liquid contact.The values of temperature, flow rate, flow rate and composition of the flows are given in table. four.
    / Examples 5-7. The process is carried out analogously to example 4. The parameters of the process and the results are shown in Table. 5-7.
    The data show the advantages of using this method for processing conventional reaction streams with low CO content, as well as reaction streams with high content. If the pressures in the stripping zone and the reabsorber remain almost the same, vat liquids containing more ethylene oxide are formed in the reabsorber compared to the ethylene oxide content in the reabsorbates of Example 1, which affects the economic indicators of the process. In addition, the efficiency of the proposed reabsorber higher.
    table 2
     Numbers in brackets denote lines.
    and
    Expressed in ppm by weight.
    Temperature, ° С
    119,114
    97.4 99.6 Composition, Ethylene oxide Low-boiling impurities and non-condensing gases High-boiling impurities (like acetic acid), ppm by weight
    Numbers in brackets denote lines.
    to “Expressed in ppm by weight.
    Table 3
    48.3 38
    38
    38 1,411,381,38 5 24,019,80,6 4 200-91.9 91.4699.82.2 0.20; 2 -5.9
    yu a
    EH
    权利要求:
    Claims (5)
    [1]
    1. A method of extracting ethylene oxide from a gas stream produced by silver-catalyzed vapor-phase partial oxidation of ethylene with molecular oxygen by countercurrent contact of the gas stream with an aqueous washing solution to obtain an absorbent containing ethylene oxide, which is stripped in a stripping zone containing several contact stages vapor-liquid, to produce ethylene oxide-containing effluent from the stripping zone of steam and reabsorption of ethylene oxide inside the re-absorption zone containing several about vapor-liquid contact stages, by countercurrent contact of steam from the top of the stripping zone with water, which is characterized by the fact that, to simplify the process technology, the steam emerging from the top of the stripping zone is partially condensed in such a way that from 50 to 99% Sides and from 1 to 20% of ethylene oxide contained in the steam are condensed and the resulting condensate, in the form of reflux, is fed to the upper part of the stripping zone, the uncondensed part of the vapor from the top of the stripping zone is introduced into the reabsorption zone, the part of the reabsorbat is cooled and the cooled reabsorb is cooled. podverggiot recirculation and introduced into the absorption zone repeated between points
    entering the non-condensed portion of steam discharged from the top of the stripping zone and water with a weight ratio of cooled reabsorbate to non-cooled reabsorbate equal to 0.2-20: 1.
    [2]
    2. A method according to claim 1, characterized in that the process is carried out at a temperature of the cooled reabsorbate less than the temperature of the uncondensed portion of the vapor exiting from above the stripping zone.
    [3]
    3. Method according to claim 1, characterized in that the process is carried out at a difference between the temperature of the injected steam and the temperature of the cooled reabsorbate equal to 2-50,
    five
    [4]
    4. The method according to p. -3,0 tl and h ay y i. and with the fact that the process is carried out at the difference between the temperature of the injected steam and the temperature of the cooled reabsorbate, equal.
    0
    [5]
    5. A method according to claim 1, characterized in that between the point at which the uncondensed part of the steam exiting from the stripping zone is introduced into the reabsorption zone and the point at which the cooled reabsorbate is introduced into the stripping zone, there is 2- 10 theoretical contact vapor-liquid stages.
    Information sources,
    0 taken into account in the examination 1. US patent 3418338, cl. C 07 O 301/08, 1976 (prototype).
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    同族专利:
    公开号 | 公开日
    ZA761783B|1977-10-26|
    DE2612540C3|1981-02-12|
    IN145102B|1978-08-26|
    PL104357B1|1979-08-31|
    DD124475A5|1977-02-23|
    AR208365A1|1976-12-20|
    JPS51118709A|1976-10-18|
    AU1212676A|1977-09-22|
    IT1058031B|1982-04-10|
    FR2305436A1|1976-10-22|
    AU498179B2|1979-02-15|
    BR7601769A|1976-09-21|
    US3964980A|1976-06-22|
    JPS54882B2|1979-01-18|
    BE839881A|1976-09-22|
    NL7602675A|1976-09-28|
    SE7602214L|1976-09-25|
    NL170001C|1982-09-16|
    GB1539889A|1979-02-07|
    NL170001B|1982-04-16|
    DE2612540B2|1980-05-22|
    ES446306A1|1977-06-16|
    TR18887A|1977-11-10|
    SE425851B|1982-11-15|
    DE2612540A1|1976-10-14|
    BG39112A3|1986-04-15|
    RO72229A|1981-08-30|
    CA1080239A|1980-06-24|
    EG12464A|1981-03-31|
    FR2305436B1|1978-10-13|
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    法律状态:
    优先权:
    申请号 | 申请日 | 专利标题
    US05/561,515|US3964980A|1975-03-24|1975-03-24|Process for the recovery of ethylene oxide|
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