JP2015514564A - Method and apparatus for recovering product using adsorptive separation and fractionation - Google Patents

Abstract

Methods and apparatus according to various approaches for separating components from a feed stream using adsorptive separation are provided. The method further includes sending one of the extract stream and the raffinate stream to a high pressure distillation column. Further, the method includes pumping one of the extract stream and the raffinate stream to increase the pressure of the stream and flowing one of the extract stream and the raffinate stream into the inlet of the distillation column. [Selection] Figure 1

Description

  [0001] This application is based on US provisional applications 61 / 609,250 and 61 / 609,254, both filed March 9, 2012; and US application 13, filed both February 25, 2013. Claims / 775,450 and 13 / 775,460.

  [0002] The present invention relates to a method for recovering a product using adsorptive separation and fractionation of components from a feed stream. More specifically, the invention relates to an apparatus and method for separating preferentially adsorbed components that uses one or more pumps to pump the stream from the adsorption separation unit into a fractionation column.

[0003] Para-xylene and meta-xylene are important raw materials in the chemical and textile industries. Terephthalic acid derived from para-xylene is used to produce polyester fabrics and other articles that are widely used today. Meta-xylene is a raw material for producing many useful products such as insecticides and isophthalic acid. Ortho-xylene is used to produce phthalic anhydride that is supplied to a large but relatively well-grown market. Ethylbenzene generally is present in xylene mixtures, although sometimes recovered for styrene production, generally are considered to be more undesirable components of C ₈ aromatics. One or a combination of adsorptive separation, crystallization, and fractional distillation is used to obtain these xylene isomers, and adsorptive separation is the market share of newly constructed plants for the major paraxylene isomers. Accounts for a large percentage of the rate.

[0004] Among aromatic hydrocarbons, the overall importance of xylenes is comparable to that of benzene as a feedstock for industrial chemicals. Xylenes and benzene are produced from petroleum by reforming naphtha, but not enough to meet demand, thus converting other hydrocarbons to increase the yield of xylenes and benzene It is necessary to make it. Often, either the production of benzene by dealkylation of toluene, or selected disproportionation give benzene and C ₈ aromatics, is now recovered individual xylene isomers.

  [0005] Aromatic compound complex flow schemes are disclosed by Meyers in the Handbook of Petroleum Refining Processes, 2nd edition, 1997, McGraw-Hill (incorporated herein by reference).

[0006] Aromatic complex facilities typically perform one or more adsorptive separations to separate one or more xylene isomers from a feed stream containing the desired isomer and one or more other isomers. It includes one or more adsorption separation vessels for performing. Adsorption separation methods are widely described in the literature. For example, an overview on the recovery of para-xylene is given on page 70 of the September 1970 edition of Chemical Engineering Progress (vol. 66, No. 9). There is a long history of available adsorbents and desorbents, available mechanical references for simulated moving bed systems including rotary valves to distribute liquid streams, the interior of adsorbent chambers, and control systems. . The principle of continuously separating the components of a fluid mixture by contacting a solid adsorbent using a simulated moving bed is shown in US-2,985,589. US-3,997,620 is applied the principle of simulated moving bed to the recovery of para-xylene from a feed stream containing _{C 8} aromatics, _{C 8} aromatics in US-4,326,092 The recovery of metaxylene from the stream is taught.

[0007] adsorption separation unit for processing C ₈ aromatics generally use a simulated countercurrent movement of the adsorbent and the feed stream. This simulated operation keeps the adsorbent in place in one or more cylindrical adsorbent chambers and slowly introduces the flow involved in the process into and out of the chamber along the length of the bed. And using established commercial technology to shift. A typical adsorptive separation unit is shown in FIG. 6, which includes at least four streams (feed stream, desorbent, extract, and raffinate) used in this procedure, introducing the feed stream and desorbent stream into the chamber, The positions where the extract stream and raffinate stream are discharged from the chamber are simultaneously shifted in the same direction at set intervals. By shifting the position of the transfer point respectively, the liquid is moved to or removed from different floors in the chamber. In general, to mimic the counter-flow movement of the adsorbent relative to the fluid flow in the chamber, the flow is shifted in the chamber in the overall direction, i.e., downstream, and moved in the opposite, i.e., upstream direction. Simulates a solid adsorbent.

  [0008] It is recognized in the art that the presence of residual compounds in the transfer line can have deleterious effects on the simulated moving bed process. In US-3,201,491; US-5,750,820; US-5,884,777; US-6,004,518; and US-6,149,874, the extract or adsorption recovered. As a means to increase the purity of the mass components, it is taught to flush the lines used to supply the adsorbent chamber with the feed stream. In addition to the four main lines discussed above, additional flushing streams can be present in the adsorption separation process or unit.

  [0009] Aromatic complex facilities that produce xylenes consume significant energy, particularly in distillation / fractionation operations that produce the feed and separate the product from the conversion process. In particular, separating xylenes from heavy aromatic compounds represents a considerable potential for energy saving.

  [0010] Recently, energy efficiency of aromatic compound facilities has been achieved by modifying traditional aromatic compound flow schemes. Saving energy in such a process not only reduces processing costs, but also addresses current concerns regarding carbon emissions. US patent applications 12 / 868,286; 12 / 868,309; 12 / 868,179; and 12 / 868,123, each of which is hereby incorporated by reference in its entirety, are xylenes by adsorption separation. Methods and apparatus for energy savings in heavy hydrocarbon distillation, such as isomer separation, are provided.

  [0011] The system described in the above-mentioned application derives energy efficiency from heat integration at least partially between fractionation columns. For this purpose, one or more distillation columns in an aromatic compound complex are compared to each other, such as extract and / or raffinate distillation columns, compared to previous complex design and in some approaches. Drive at different pressures. It should be noted that distillation and fractionation are used interchangeably herein. There may also be additional heat exchangers at various locations within the complex such as the extract column supply line. More specifically, by operating a plurality of distillation columns at different pressures, the heat from the columns can then be used to provide heat to reboil one or more other columns. In some approaches, direct heat exchange can be used. For example, a pressurized extract distillation column can provide heat to reboil one or more of the benzene fractionation column and the finishing column. The pressurized raffinate distillation column can provide heat to reboil one or more of the reformer separator, toluene distillation column, and deheptanizer. Indirect heat exchange can also be provided by generating medium pressure steam in the same or different approaches. For example, the high pressure xylene column 133 can provide heat to reboil the low pressure xylene column 130 and the extract column 152, and then the benzene column 123 and finishing column 155 can be reboiled.

  [0012] In this regard, in addition to including additional heat exchangers in the extract and / or raffinate column supply line, the energy of the extract can be increased by operating the extract distillation column and / or raffinate distillation column at elevated pressure. Although this can provide savings, this increased pressure often lines or conduits fluid from the adsorption separation unit operating under traditional conditions and pressure, due to the pressure difference between the adsorption separation unit and the fractionation column. Too high to provide a drive mechanism for moving through the fractionation column. The operating pressure of the adsorption section traditionally ensures that the process fluid in the chamber is in the liquid phase and forces the discharged stream, such as extract and raffinate, into the downstream distillation column without the need for a pump. Set to be able to. These flows must always be carefully controlled in order for the adsorptive separation unit to operate properly. The pressure difference between the adsorptive separation unit and the extract and raffinate distillation columns provides a drive mechanism to move the extract stream and raffinate stream to it, so that increasing the pressure in these columns increases the extract and raffinate stream. May affect the appropriate flow of In this regard, the fluid between the point of discharge from the adsorption separation unit and the point of flow through the line or conduit connecting the adsorption separation unit and fractionation column and any other devices encountered along the line. Considering the pressure loss experienced by the flow, the pressure in the adsorptive separation unit must be sufficiently higher than the traditional operating pressure to provide a pressure difference for driving the fluid flow.

  [0013] To maintain the traditional design of the adsorption section in the new scheme, the operating pressure of the adsorption separation chamber must be increased. Current pumps at the bottom of the extract and raffinate column as shown in FIG. 6, as well as other pumps throughout the current design, can be modified to produce this increasing pressure, which is at least It turned out to be undesirable for a reason. First, this increases the pressure across the aromatic compound complex, including the adsorption separation unit and chamber. Because the adsorptive separation unit must be carefully adjusted to provide maximum separation of the preferred xylene isomers, this change in operating pressure can adversely affect the operation of the adsorptive separation chamber. Second, increasing the pressure in the adsorption separation chamber and the entire system can have its own energy penalty, which offsets the energy benefits obtained by the new scheme discussed above. there's a possibility that. Third, the ability to withstand increasing pressures, and forming the necessary foundation to support reinforced equipment, increases the materials and difficulties that exist in manufacturing, and thus aromatic compound composites. Increase the capital cost of the facility.

  [0014] Finally, some quasi-adsorption separation units are described, for example, in US-3,040,777 and US-3,422,848, which are hereby incorporated by reference. A rotary valve for delivering fluid into different ports of the adsorption separation chamber. These rotary valves include a rotary valve seal sheet. It has been found that the life of the seal sheet decreases at higher operating pressures in the adsorption separation chamber.

U.S. Pat. No. 2,985,589 U.S. Pat. No. 3,997,620 U.S. Pat. No. 4,326,092 U.S. Pat. No. 3,201,491 U.S. Pat. No. 5,750,820 US Pat. No. 5,884,777 US Pat. No. 6,004,518 US Pat. No. 6,149,874 US patent application Ser. No. 12 / 868,286 US patent application Ser. No. 12 / 868,309 US patent application Ser. No. 12 / 868,179 US patent application Ser. No. 12 / 868,123 U.S. Pat. No. 3,040,777 U.S. Pat. No. 3,422,848

Meyers, Handbook of Petroleum Refining Processes, 2nd edition, 1997, McGraw-Hill Chemical Engineering Progress, September 1970 edition (vol.66, No.9), page 70

[0015] FIG. 1 is a simplified diagram of an aromatic compound complex and method with energy savings. [0016] Figure 2 shows the application of energy saving in the distillation of C ₈ aromatics from heavy aromatics. [0017] FIG. 3 shows an example of a specific unit in an aromatic compound complex that can achieve energy savings by direct heat exchange. [0018] FIG. 4 illustrates an aromatic compound complex that applies some of the energy saving concepts described herein as additional or alternative to other energy savings. [0019] FIG. 5 illustrates the generation of steam from a particular unit within an aromatic compound complex. [0020] FIG. 6 is a simplified diagram of a traditional aromatic compound complex including an adsorption separation unit and a raffinate and extract fractionation column. [0021] FIG. 7 is an enlarged view of the rotary valve with the valve head removed. [0022] FIG. 8 is a simplified diagram of an aromatic compound complex that includes at least one pump between the adsorption separation unit and the fractionation column; [0023] FIG. 9 is a simplified diagram of the aromatic compound complex of FIG. 8 showing a multiple pump system.

  [0024] Those skilled in the art will recognize that components in the drawings are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and / or relative positions of some components in the figures may be exaggerated relative to other components to help improve understanding of various aspects of the invention. Also, the usual but well-understood components useful or necessary in commercially feasible aspects are intended to facilitate a more unobstructed view of these various aspects of the invention. Often not shown. Further, although some actions and / or steps may be described in a particular order of appearance, those skilled in the art will appreciate that such specificity for order is not actually necessary. Will be further recognized. In addition, the terms and expressions used in this specification are ordinary technical terms given to those terms and expressions by those skilled in the technical fields shown above, except where different specific meanings are indicated in this specification. It will also be understood that it has meaning.

[0025] The feed stream to the method and apparatus is generally of the general formula: C ₆ H _(6-n) R _n , where n is an integer from 0 to 5, each R is in any combination And may be CH ₃ , C ₂ H ₅ , C ₃ H ₇ , or C ₄ H ₉ ). The aromatics-rich feed to the process of the present invention includes, without limitation, catalytic reform, light olefins and heavier aromatics-rich by-products (often referred to as “pigas” in the gasoline range). Derived from various sources such as steam pyrolysis of naphtha, distillate, or hydrocarbons, and catalytic cracking or pyrolysis of distillates and heavy oils that give products in the gasoline range. Can do. Products from pyrolysis or other cracking operations generally adversely affect product quality and / or damage the catalyst used in processing such feedstock prior to filling the complex. Hydrotreating according to processes well known in the industry to remove potential sulfur, olefins, and other compounds. Light cycle oils from catalytic cracking can also be beneficially hydrotreated and / or hydrocracked to give gasoline range products according to known techniques. The hydrotreatment here also includes catalytic reforming to give a feed stream that is preferably rich in aromatics. When the feed stream is a catalytic reforming oil, the reformer is preferably operated at high severity to achieve high aromatic yield with low concentrations of nanoaromatic compounds in the product.

  [0026] The method and apparatus according to the present invention includes an adsorptive separation unit 150 for separating the components of a hydrocarbon stream. Adsorption separation is applied to the recovery of various hydrocarbons and other chemical products. Chemical separations using this disclosed approach include separation of mixtures of aromatic compounds into specific aromatic isomers, separation of linear compounds from non-linear aliphatic and olefinic hydrocarbons, aromatics Separation of either paraffin or aromatic compounds from feed mixtures containing both compounds and paraffins, separation of chiral compounds for use in medicine and fine chemicals, separation of oxygenates such as alcohols and ethers, and sugars Carbohydrate separation is mentioned. Examples of the separation of the aromatic compound include a mixture of a dialkyl-substituted monocyclic aromatic compound and dimethylnaphthalene.

[0027] The main commercial applications that form the focus of the conventional references and the following description of the invention without limitation are usually C ₈ aromatics because of the high purity needs of these products. Recovery of para-xylene and / or meta-xylene from a mixture of compounds. Such C ₈ aromatics usually in aromatics complex facility performs catalytic reforming of naphtha rich in then either by the extraction and fractionation, or aromatic compounds such composite facility flow Is transalkylated or isomerized. Here, C ₈ aromatics generally comprise a mixture of xylene isomers and ethylbenzene. Processing of C ₈ aromatics using a simulated moving bed adsorption are generally directed to the recovery of high purity paraxylene or high purity meta-xylene. Here, high purity is usually defined as the desired product of at least 99.5% by weight, preferably at least 99.7% by weight. Although the following detailed description focuses on the recovery of high purity para-xylene from a mixed stream of xylene and ethylbenzene, the present invention is not so limited and other components may be removed from a stream containing two or more components. It should be understood that it can also be applied to separation. As used herein, the term “preferential adsorption component” refers to one or more components of a feed stream that are preferentially adsorbed over one or more non-preferential adsorption components of the feed stream.

  [0028] FIG. 1 is an example of an energy efficient aromatic compound complex facility according to various aspects of the present invention. The feed stream passes through line or conduit 110 and is sent to reformer separator 114 through heat exchangers 112 and 113 that raise the temperature of the feed stream. Heat exchange is supplied through conduits 212 and 213, respectively, from the net paraxylene product discussed later in this paragraph and from the desorbent recovered from the adsorptive separation process.

[0029] In one example, aromatic compounds C ₈ and heavier is discharged as bottom stream in conduit 116, whereas, toluene and more light hydrocarbons are recovered at the top of the column through conduit 118, extractive distillation Sent to process unit 120 to separate most of the aliphatic raffinate in conduit 121 from the benzene-toluene aromatics stream in conduit 122. The aromatics stream in conduit 122 is fed into conduit 124 in fractionator 123 along with the stripped transalkylation product in conduit 145 and the overhead from the paraxylene finishing column in conduit 157. And a toluene and heavier aromatics stream in conduit 125 (which is sent to toluene column 126). Toluene is recovered overhead from this column into conduit 127, which can be partially or wholly sent to the transalkylation unit 140 shown and discussed below.

[0030] The bottom stream from the toluene column 126 passes through conduit 128 through the bottom of the bottom stream from the reformer separator in conduit 116 after being treated by the clay processor 117, and heavy aromatics in conduit 138. Along with the purge stream, it is sent to the low pressure first xylene column 130. The feed to this column is generally characterized as a higher boiling feed because it contains more than 5 wt% _{C9 +} aromatics, often more than 10 wt% _{C9 +} aromatics. Other C ₈ aromatics stream which has a large content of aromatics of C ₉ and heavier including flow obtained from a source outside the complex may also be added the more high boiling feed stream . A portion of the deheptanizer bottoms stream in stream 165 can also be included depending on the overall energy balance. The low pressure xylene column is fed from a stream of high boiling first C ₉ and heavier compounds containing C ₉ , C ₁₀ , and heavier aromatics as a bottoms stream in conduit 132 into conduit 131. separating the first C ₈ aromatics stream which is enriched as the overhead stream.

[0031] At the same time, the isomerized C ₈ aromatics stream is sent through conduit 165 to a high pressure second xylene column 133. This is characterized as a lower boiling feed stream containing a lower concentration of degradable heavy material than the feed stream to the column 130, thus increasing the pressure in the second column to achieve energy savings. be able to. Other C ₈ aromatics containing stream having a similarly low content of C ₉ and heavier aromatic compounds such as flow obtained from a source outside the complex is also included in the feed stream to the column Can be made. The second xylene column separates the second C ₈ aromatics stream from the second C ₉ and heavier compound stream in conduit 132 as a top stream in conduit 134. Preferably, at least a portion of the overhead vapor from the high pressure xylene column in conduit 134 is used to reboil the low pressure xylene column 130 in reboiler 135, and condensate and column to xylene separation process 150 in conduit 136. Drain as reflux to 133 (not shown). Further, the overhead in conduit 134 may be used to provide energy to the reboiler of extract column 152, or other such equipment as described below or will be apparent to those skilled in the art. it can.

[0032] The C ₉₊ bottom stream sent to the reboiler 137 is a heavy aromatic compound via one or both of the pre-reboiler stream in conduit 270 and the heated stream from the reboiler in conduit 259, respectively. Energy can be provided to reboil one or both of column 170 and raffinate column 159; the bottoms stream after heat exchange is sent to heavy aromatics column 170. Other similar heat exchange operations will be apparent to those skilled in the art. The net bottoms stream in conduit 138 can typically be passed through column 130 or mixed directly with the stream in conduit 132 in conduit 139 and sent to heavy compound column 170. Heavy compounds column gives the flow in a conduit 171 that includes at least a portion of the C ₉ and C ₁₀ aromatics at the top, higher boiling compounds, mainly C ₁₁ and higher alkyl aromatic compounds, It discharges as a bottom stream through a conduit 172. This column can be reboiled by the bottom stream of the xylene column in conduit 270 as discussed above. Also, the overhead vapor from columns 130 and 170 can generate vapor through conduits 230 and 271, respectively, as shown, and the condensate is either refluxed to the respective column or stream 131 or respectively. 171 can function as a net overhead stream.

[0033] C ₉₊ aromatics from the heavy compound column in conduit 171 are contained in conduit 127 as a feed stream to transalkylation reactor 140 that produces transalkylation products including xylenes. Mix with the toluene-containing top. Transalkylation product in conduit 141 is stripped in the stripper 142, the gas in the conduit 143, and C ₇ and higher extraction liquid lighter, the latter through the conduit 144, stable in the isomerate stripper 166 And then returned to extractive distillation 120 for recovery of light aromatics. The bottom stream from the stripper is sent to benzene column 123 in conduit 145 to recover the benzene product and unconverted toluene.

[0034] given by the xylene column 130 and 133, paraxylene, meta-xylene, ortho-xylene, and the first and second _{C 8} aromatics stream comprising ethylbenzene, xylene isomers separation process 150 through conduit 131 and 136 Send to. The description herein can be applied to the recovery of one or more xylene isomers other than paraxylene, but this description is described with respect to paraxylene for ease of understanding. The separation process takes place in an adsorptive separation unit 150, which operates by a moving bed adsorption process and feeds a first mixture of paraxylene and desorbent to extract column 152 through conduit 151, where conduit 154 Paraxylene is separated from the returned desorbent through conduit 153. In one approach, the adsorption separation unit is a pseudo countercurrent adsorption separation unit 150 as described further below.

  [0035] According to one approach, the extract column 152 is preferably operated at a pressure increase of at least 300 kPa, more preferably 500 kPa or more, so that the overhead stream from the column passes through the conduit 256 into the finishing column 155, Alternatively, pressure and temperature sufficient to re-boil deheptanizer 164 through conduit 265. The heat supplied for the reboiling work through conduits 256 and 265 causes the extract to condense in these streams and either or both return to column 152 (not shown). Alternatively, it is sent to finishing column 155 as a net flow in conduit 153. Para-xylene is purified in finishing column 155 to produce para-xylene product through conduit 156 and light material returned to benzene column 123 through conduit 157.

[0036] The second mixture of raffinate as non-equilibrium blend of C ₈ aromatics and desorbent from separation process 150 may send through a conduit 158 to the raffinate column 159, the desorbent is returned within the conduit 161, The raffinate to isomerization in conduit 160 is separated. The raffinate column can be operated at higher pressures to produce steam through conduit 260 or to exchange heat in other areas of the complex. The condensate from such heat exchange serves as reflux to the raffinate column or as a net overhead stream in conduit 160. In one approach, the raffinate column is operated at a pressure increase of at least 300 kPa, more preferably 500 kPa or more. The recovered desorbent in conduits 154 and 161 and the net finishing column bottoms stream can heat the input feed stream in conduit 110 through conduits 213 and 212, respectively.

[0037] A raffinate comprising a non-equilibrium blend of xylene isomers and ethylbenzene is sent to isomerization reactor 162 through conduit 160. In the isomerization reactor 162, giving a product which was close to the equilibrium concentration of C ₈ aromatics isomers isomerized raffinate. This product is sent through conduit 163 to deheptanizer 164 to remove C ₇ and lighter hydrocarbons, preferably reboiled using the overhead stream from extract column 152 in conduit 265. The bottoms from the deheptanizer are sent through conduit 165 to xylene column 133 to separate C ₉ and heavier material from the isomerized C ₈ aromatics. The overhead liquid from the deheptanizer 164 is sent to a stripper 166 where the light material overhead in conduit 167 is connected to an extractive distillation unit 120 for recovery and purification of benzene and toluene valuables in conduit 168. separated from _{C 6} and _{C 7} material is fed through. The pressure in the deheptanizer 164 and stripper 166 is selected to exchange heat or generate steam in a manner similar to the xylene columns discussed elsewhere herein.

[0038] FIG. 2 illustrates the heat exchange of the present invention between parallel xylene distillation columns 130 and 133 in more detail. The feed stream to the low pressure xylene column 130 comprises a bottom stream from the toluene column through conduit 128, a clay treated bottom stream from the reformer separator through conduit 116, and a purge C ₈ aromatics through conduit 138. Including other C ₈ aromatics containing streams that are not suitable for processing in a high pressure xylene column, and a portion of the deheptanized stream 165 can be included as appropriate for energy balance. The mixed feed stream of heavy reformate and toluene column bottoms may contain heavy aromatics that are susceptible to decomposition at high temperatures, and by operating at a pressure below 800 kPa, at the bottom of the column and reboiler Such decomposition can be avoided by maintaining the temperature. The low pressure xylene column allows the concentrated C ₈ aromatics to enter the top of conduit 131 from a high boiling stream containing C ₉ , C ₁₀ , and heavier aromatics as bottoms in conduit 132. Separate as a stream. The overhead stream from column 130 is used at least in part through conduit 230 of FIG. 1 to generate steam or reboil other columns, thereby concentrating to the column, as discussed above. As well as a net overhead stream for xylene separation in conduit 131.

At the same time, the isomerized C ₈ aromatics stream is sent through conduit 165 to high pressure xylene column 133. This stream contains a lower concentration of degradable heavy material than the feed to column 130, and the column pressure can be used to exchange heat at useful levels, as discussed above. Concomitantly, in order to save energy due to the higher temperature, it is raised compared to that of the low-pressure xylene column according to the invention. Thus, the temperature of the overhead vapor from the high pressure xylene column 133 is sufficient to provide useful energy to other equipment in the aromatic compound complex. As shown, the overhead vapor temperature is sufficient to reboil the low pressure xylene column 130 in the reboiler 135 to provide reflux to the column 133 and net flow in the conduit 136. . Bottom stream of a small amount of net in the conduit 138 is preferably sent to the lower pressure column 130 for recovery of C ₈ aromatics remaining.

  [0040] Alternatively or additionally, the temperature of the overhead vapor from the high pressure xylene column 133 is sufficient to produce steam useful for heating equipment or to reboil the column in other processing units. It is. Such steam is usually generated at a pressure above 300 kPa, preferably at least 500 kPa, most preferably 1000 kPa or more. The overhead stream can be indirectly heat exchanged with the water circuit fed to the steam drum. Most commonly, boiler feed water is heated in a heat exchanger separated from the steam drum. Multiple water circuits with different exchanges are arranged in parallel with each other and fed to a single steam drum to give a steam product of the desired pressure. For this, only one set of instruments is required. Such steam systems are well known and details can be added by the teachings found in US-7,730,854 (incorporated herein by reference).

  [0041] Energy recovery according to the present invention, often involving a proximity temperature approach between process fluids, is enhanced by using an exchanger with an accelerated nucleate boiling surface. Such accelerated boiling surfaces are, for example, US-3,384,154; US-3,821,018; US-4,064,914; US-4,060,125; US-3,906,604; US-4 , 216,826; US-3,454,081; US-4,769,511; and US-5,091,075, all of which are incorporated herein by reference. This can be achieved in various ways. Such high flux piping is particularly suitable for heat exchange between the top of the second high pressure xylene column and the reboiler of the first low pressure xylene column or for generating steam from the top of the xylene column. is there.

  [0042] Typically, these promoted nucleate boiling surfaces are included on the tube of a shell and tube type heat exchanger. These promotion tubes are formed in a variety of different ways well known to those skilled in the art. For example, such a tube can include an annular or helical cavity that extends along the tube surface created by the mechanical action of the tube. Alternatively, fins can be provided on the surface. In addition, the tube can be scratched to provide ribs, grooves, porous layers, and the like.

  [0043] Generally, more efficient facilitating tubes are those that have a porous layer on the boiling surface of the tube. The porous layer can be provided in a number of different ways well known to those skilled in the art. The most efficient of these porous surfaces have what are called concave cavities that trap vapor in the layer cavities through the confined cavity openings. In one such method, a porous boiling layer is bonded to one side of a thermally conductive wall, as described in US-4,064,914. An important feature of the porous surface layer is the capillary-sized interconnected pores, some of which communicate with the outer surface. The liquid to be boiled is introduced into the subsurface cavity through the outer pores and the interconnected pores below the surface and is heated by the metal that forms the walls of the cavity. At least a portion of the liquid is vaporized within the cavity and the resulting bubbles grow in contact with the cavity wall. At least a portion of it is finally evacuated from the cavity through the outer pores, and then rises through the liquid film on the porous layer and dissociates into the gas layer above the liquid film. Additional liquid flows into the cavity from interconnected pores and this mechanism is repeated continuously. An accelerator tube containing such a porous boiling layer is commercially available under the trade name High Flux Tubing manufactured by UOP LLC, Des Plaines, Illinois.

  [0044] FIG. 3 illustrates an aromatic compound complex in which energy savings can be achieved by directly exchanging the overhead stream from one or more higher temperature columns to one or more lower temperature column reboilers. An example of a specific unit is shown using a numerical representation of the process from FIG. The overhead stream from the high pressure xylene column 133 in conduit 134 has a temperature sufficient to provide the energy to reboil the extract column 152 by the reboiler 235, and the xylene overhead stream is as a reflux or net overhead stream. Condensate in conduit 236 to return to 133. The extract column is pressurized so that the top in conduit 256 has a temperature sufficient to reboil the finishing column 155 by reboiler 257 and condense the extract column overhead stream into conduit 258. To do. As described above, the product para-xylene is recovered in conduit 156.

  [0045] FIG. 4 summarizes the multiple or non-exclusive possibilities of direct heat exchange associated with FIG. The high pressure xylene column 133 can provide heat to reboil one or more of the low pressure xylene column 130, the extract column 152, and the raffinate column 159. The low pressure xylene column 130 can provide heat to reboil the extract distillation column 120. The pressurized extract column 152 can provide heat to reboil one or more of the benzene column 123 and the finishing column 155. Pressurized raffinate column 159 can provide heat to reboil one or more of reformate separator 114, toluene column 126, and deheptanizer 164.

  [0046] FIG. 5 summarizes a non-exhaustive example of the possibility of indirect heat exchange by generating medium pressure steam. The overhead steam 230 from the low pressure xylene column 130 (FIG. 1) and the overhead steam 260 from the pressurized raffinate column 159 (FIG. 1) are 0.6-2 MPa, preferably 0.7, in the header 100. ~ 1.5 MPa of medium pressure steam can be generated, which can be used to reboil one or more of the reformer separator 114, extract distillation column 120, and toluene column 126, A further possibility of transferring steam to the unit is given. Such steam generation and use can be considered as an additional or alternative to other energy savings such as those described in FIG. For example, the high pressure xylene column 133 can provide heat to reboil the low pressure xylene column 130 and the extract column 152 (which then reboils the benzene column 123 and the finishing column 155).

  [0047] As noted above, the system and apparatus according to the present invention includes at least one adsorptive separation unit 150 for separating para-xylene. FIG. 6 shows a simplified traditional adsorptive separation unit within the flow scheme of the aromatics recovery process of FIG. 1, shown with an extract and raffinate fractionation column.

  [0048] In one approach, the adsorption separation unit 150 mimics the countercurrent flow of the adsorbent and the liquid surrounding it, which is also disclosed in US-4,402,832 and US-4,478,721. It can also be carried out in a countercurrent continuous process such as that described. The functions and properties of adsorbents and desorbents in the chromatographic separation of liquid components are well known, and US-4,642,397 (incorporated herein by reference) for further explanation of these adsorption principles. You can refer to it. Counterflow moving bed or simulated moving bed counterflow systems are much larger than fixed bed systems because continuous feed streams are used for continuous production of extract and raffinate with continuous adsorption and desorption operations. Having separation efficiency for such separation. A complete description of the simulated moving bed process is given in the Advertising Separation paragraph (p. 563) of Kirk-Othmer Encyclopedia of Chemical Technology.

  [0049] The adsorption separation process of unit 150 separates extract stream 15 and raffinate stream 20 by sequentially contacting feed stream 5 with adsorbent and desorbent stream 10 contained within the vessel. In a simulated moving bed counterflow system, the adsorbent contained within the chambers is directed upward by progressively shifting the multiple liquid feed and product access points or ports 25 below the adsorbent chambers 30 and 35. Simulates the movement of The adsorbent in the simulated moving bed adsorption process is contained in multiple beds in one or more containers or chambers. Although two chambers 30 and 35 in series are shown in FIG. 6, a single chamber or other number of chambers in series can be used. Each container 30 and 35 includes a plurality of beds of adsorbent in the processing space. Each vessel has a number of ports 25 associated with the number of adsorbent beds, and the feed stream 5, desorbent stream 10, extract stream 15, and raffinate stream positions are shifted along the port 25. Simulate an adsorbent bed. Circulating liquid containing desorbent, extract, and raffinate is circulated through the chamber by pumps 40 and 45, respectively. Although a system for controlling the flow of circulating liquid is described in US-5,595,665, the details of such a system are not critical to the present invention. For example, a rotating disk type valve 300 characterized in US-3,040,777 and US-3,422,848 shifts the flow along the adsorbent chamber to simulate counterflow. Although a rotating disk valve 300 is described herein, for example to control the flow to and from the adsorbent chambers 30 and / or 35 described in US-6,149,874. Other systems and devices for shifting flow along the adsorbent chamber are also contemplated by the present invention, such as systems using multiple valves at the same time.

  [0050] Referring to FIG. 7, a simplified enlarged view of an exemplary rotary valve 300 for use in an adsorption separation system and process is shown. Base plate 474 includes a plurality of ports 476. The number of ports 476 is equal to the total number of transfer lines on one or more chambers. Base plate 474 also includes a plurality of channels 478. The number of channels 478 is equal to the number of net inlets, outlets, and flush lines (not shown in FIG. 7) for the adsorption separation unit. The net inlet, outlet, and flush line are each in fluid communication with a dedicated channel 478. Crossover line 470 places a given flow path 478 in fluid communication with a given port 476. In one example, the net inlet includes a feed inlet and a desorbent inlet, the net outlet includes an extract outlet and a raffinate outlet, and the flash line includes between one and four flash lines. When the rotor 480 is rotated as shown, each flow path 478 is placed in fluid communication with the next port 476 by a crossover line 470. The rotary valve is also rotated stepwise to move the transfer line 470 to a different port 476 so that a seal sheet 472 is also provided to seal the flow within the rotary valve 300 during operation. The rotary valve also includes a head 305 (shown in FIG. 6) that houses the rotary valve. The head 305 applies pressure to hold the seal sheet 472 in contact with the base plate 474. As described above, operating the adsorption / separation unit at a higher pressure requires that the pressure in the head 305 is also operated at a higher pressure, which may cause premature deterioration of the seal sheet 472. I understood.

  [0051] The adsorption conditions generally include a temperature range of 20 ° C to 250 ° C, and preferably 60 ° C to 200 ° C for the separation of paraxylene. Adsorption conditions also include sufficient pressure to maintain the liquid phase, which can be from atmospheric pressure to 2 Mpa. Desorption conditions generally include a range of temperatures and pressures equivalent to those used for adsorption conditions. Different conditions may be preferred for other extract compounds.

  [0052] The various flows involved in the simulated moving bed adsorption shown in the figures and discussed further below in connection with various aspects of the invention described herein can be characterized as follows. A “feed stream” is a mixture comprising one or more extract or preferential adsorbed components and one or more raffinate or non-preferential adsorbed components that are separated by the process. An “extract stream” includes extract components, usually the desired product, that are more selectively or preferentially adsorbed by the adsorbent. A “raffinate stream” includes one or more raffinate components that are less selectively adsorbed or non-preferentially adsorbed. “Desorbent” refers to a substance that is generally inert to the components of the feed stream and is capable of desorbing the extract components that can be easily separated from both the extract and raffinate, for example, by distillation.

[0053] The extract stream 15 and the raffinate stream 20 in the scheme shown include desorbent at a concentration between 0% and 100% for each product from the process. The desorbent is generally separated from the raffinate and extract components by conventional fractionation in the raffinate column 159 and the extract column 152 shown in FIG. 6, respectively, and the raffinate column bottom pump 60 and the extract column bottom pump 65. Is recycled to stream 10 'and returned to the process. Although FIG. 6 shows the desorbent as the bottom from each column, in some applications, the desorbent can be separated at different locations along the fractionation columns 152 and 159. The raffinate product 70 and extract product 75 from the process are recovered from the raffinate stream and the extract stream in columns 159 and 152, respectively. The extract product 75 from the separation of the C ₈ aromatics usually contains mainly one or both of para-xylene and meta-xylene, and the raffinate product 70 is mainly unadsorbed C ₈ aromatics.

  [0054] Extract and raffinate streams from the adsorption separation unit are important in the operation of the adsorption separation process. Specifically, adsorptive separation relies on achieving a composition profile between different components in the chamber, such as at least a preferential adsorbing component, one or more non-preferential adsorbing components, and a desorbent in the adsorptive separation chamber. Yes. The composition profile shifts along one or more chambers as the feed and recovered streams are shifted during operation of the adsorption separation unit 150. The extract and raffinate streams are exhausted from the chamber at different ports 25 depending on the composition profile at a particular port to achieve a high purity stream. For example, the extract stream is removed from the adsorption separation chambers 30 and 35 from a position along the chamber where the fluid composition contains a large amount of preferentially adsorbed components and a small amount of non-preferential adsorbed components. The system produces an extract stream and raffinate stream flow away from the adsorptive separation unit 150 to generate and control the flow to generate and control (this was at risk of failure or failure) To avoid problems in achieving product purity, traditionally relies on passive means, i.e. pressure differences between the adsorption separation unit 150 and downstream fractionation columns 159 and 152. This is considered important for successful separation in the separation unit 150, as the stagnation of the extract stream and / or raffinate flow may change the flow pattern and thereby the composition profile in the adsorption separation unit 150. It has been. This can affect the throughput and product purity achieved by the system. This can have a negative impact on business as many adsorptive separation systems require high purity.

  [0055] According to one approach, a pump 550 is provided for pumping one of the extract stream and the raffinate stream from the adsorption separation unit 150 to the respective fractionation column. Turning to the schematic diagram of FIG. 8, a portion of the apparatus and process of one aspect of the present invention is shown, showing an adsorption separation unit 150 and a fractionation column 510. For simplicity, the apparatus and process are generally described with respect to transferring fluid between the adsorption separation unit 150 and the fractionation column 510, but the present invention is directed to the extract stream through line 15 '. Should be understood with respect to one or both of entering the extract fractionation column 152 and flowing the raffinate stream into the raffinate fractionation column 159 through line 20 '. A conduit or line 505 is provided between the adsorption separation unit 150 and the fractionation column 510 to carry the stream. In one approach where the adsorptive separation unit 150 includes a rotary valve 300, line 505 connects between rotary valve 300 and fractionation column inlet 515, and the extract stream passes through line 505 and the extract stream line and column of rotary valve 300. It is transferred between the inlet 515. It should be understood that line 505 can include one or more lines or conduits in fluid communication between adsorption separation unit 150 and fractionation column 510. It should also be understood that the fractionation column 510 can include one or more fractionation columns arranged in series or in parallel. Further, additional equipment or devices can be placed along line 505 while remaining within the scope of the present invention. For example, one or more heat exchangers or reboilers 555 may be placed in line 505 to increase the temperature of the stream introduced into fractionation column 510, as shown in FIG. 8, or to transfer heat to or from the system. Can be arranged along.

  [0056] In one approach, as described above, fractionation column 510 operates at an elevated pressure compared to traditional systems to provide energy savings. In one approach, the increased internal pressure of the fractionation column 510 increases the pressure at the fractionation column inlet 515 so that the flow from the adsorption section does not flow into the fractionation column or at a sufficient flow rate. Become. The operating pressure in the adsorption section must be higher than the sum of the pressure at the fractionation column inlet 515 and the pressure drop along line 505. The pressure drop along line 505 is typically along the fluid flow and lines or conduits 505, such as heat exchangers or reboilers 555 located along walls, pipes, piping, valves, and lines 505, for example. Caused by friction between other devices. It should be understood that the flow always flows in the direction from higher pressure to lower pressure. A lower pressure in the adsorption section relative to the pressure at the column inlet 515 means that the liquid flow in line 505 is in the opposite direction. If the pressure is lower, the flow from the adsorption separation unit 150 into the fractionation column 510 cannot be propelled. This includes operating fractionation column 510 at a pressure higher than one or more locations along transfer line 505, such as inlet 515, as a result of a pressure drop while the flow travels through line 505. . This may also occur when the fractionation column 510 is operated at a higher pressure than the adsorption separation unit 150, such as one or more chambers 30 and 35.

  [0057] Moving to more details, the fractionation column 510 may have an operating pressure between atmospheric pressure and 2 MPa. In one example, fractionation column 510 has an operating pressure greater than 300 kPa. In other examples, fractionation column 510 has an operating pressure greater than 500 kPa. In yet another example, the fractionation column 510 has an operating pressure between 550 kPa and 2 MPa. In yet another example, fractionation column 510 has an operating pressure between 550 kPa and 600 kPa.

  [0058] The adsorption conditions within the adsorption separation unit 150 include a pressure sufficient to maintain a liquid phase (which may be between atmospheric and 2 MPa). In another example, the adsorption separation unit has an operating pressure between 800 kPa and 1100 kPa. In yet another example, the adsorption separation unit has an operating pressure between 850 kPa and 900 kPa. In one approach, the pressure drop between the adsorption separation chambers 30 and 35 and the fractionation column 510 is between 600 and 800 kPa. In other approaches, the pressure drop is between 700 and 750 kPa. Thus, since the sum of the pressure drop in line 505 and the inlet pressure 515 exceeds the pressure in the adsorption separation unit 150, the pressure from the adsorption separation unit 150 is insufficient to provide flow into the fractionation column 510. It was confirmed that.

  [0059] In one approach, the extract stream line 505 is used to overcome the increased pressure in the fractionation column 510 so that the flow flows through the line 505 between the adsorption separation chamber 150 and the fractionation column 510. Along with a pump 550. The pump 550 is disposed between the adsorption separation chamber 150 and the separation column 510 along the line 505. Pump 550 substantially divides fractionation column 510 from adsorption separation chamber 150 to overcome the difficulties due to column 510 being operated at higher pressures. Pump 550 provides sufficient head pressure to overcome the pressure differential between the adsorption separation chamber along line 505 and fractionation column 510 to pump the flow into fractionation column 510. In other words, the pump 550 must supply enough energy to the flow in line 505 to raise its pressure above the downstream column pressure. This is usually called the head. Lifting the device affects the hydrostatic head between the fractionation column 510 and the adsorption unit 150, which is also included in the head. In one approach, the pump 550 is installed so that suction is applied directly from the adsorption separation chambers 30 and 35. In this regard, in one approach, if the adsorptive separation unit 150 includes a rotary valve 300 as shown in FIG. 6, the pump 550 may be suitable depending on how the invention is implemented. A suction force is applied through a rotary valve 300 from a simple extract line or raffinate line.

  [0060] In one approach, the pressure of the stream is increased by 50 kPa to 2.5 MPa by pump 550 (which can include more than one pump) to pump the stream into the fractionation column. In another approach, pump 550 increases the flow pressure by 150-500 kPa. In another approach, pump 550 increases the flow pressure by 200-400 kPa. In yet another approach, pump 550 increases the flow pressure by 250-350 kPa.

  [0061] As discussed above, it is important that the stream flow continuously through line 505 to fractionation column 510. In this regard, the pump must remain operational at all times and therefore further process control may be required. In one approach, one in pump 550 to limit flow backflow or other interruption of flow in the downstream direction if one of the pumps fails or is otherwise not operated. Include more pumps. Backflow of the flow towards the adsorptive separation unit 150 or interruption in the direction of the flow can reduce the purity and / or throughput of the product as described above. According to this approach, the pumps are arranged in parallel. In addition, more than one pump can be configured in various operating arrangements that provide a generally uninterrupted flow during a pump failure or outage, as further described below.

  [0062] According to one approach, one or more pumps along line 505 are primary pumps and one or more other pumps along line 505 are backup pumps in standby mode during normal operation. For example, referring to FIG. 9 where two pumps are used, the first pump 605 is the main pump and the second pump 610 is the backup pump. The first main pump 605 is normally operated to pump a fluid stream along line 505 into the fractionation column 510 during normal operation, while the second backup pump 610 is the first pump. Can be configured to operate when not operated or with reduced capacity. In this regard, the second pump 610 is configured to automatically operate when the first pump stops operation or to be manually operated before the operator stops the first pump 605. can do. Alternatively, even if the first pump has not failed, the first and second pumps 605 and 610 are alternated as the main pump and the second pump, for example to maintain the lifetime of both pumps. be able to.

  [0063] In another approach, two or more pumps can each provide a percentage of the total workload. Referring again to FIG. 9, both the first and second pumps 605 and 610 can act as main pumps, each pump being less than 100% of the desired operating capacity to handle a portion of the flow. Drive at a rate. For example, the first and second pumps can each provide 50% of the total operating flow capacity. An optional third pump 615 can function as the backup pump described above with respect to the above approach. The optional third pump 615 can begin operation when either the first pump 605 or the second pump 610 stops operating and is no longer operating by the third pump. You can give the percentage of capacity previously given by the pump. In this way, the pumping operation of the main pump does not stop completely at the time between when one of the main pumps 605 and 610 fails and when the second pump 615 begins operation. As will be appreciated, this approach can provide additional main and backup pumps, each providing a percentage of the total capacity.

  [0064] According to various approaches where pump 550 includes more than one pump, each pump, eg, 605 and 610 shown in FIG. 9, may be provided with its own power supply (620 and 625, respectively). it can. In this way, if one of the power supply devices 620 and 625 fails during operation and one of the pumps 605 and 610 cannot be operated, the other power supply device 620 or 625 will send it to the other pump 605 or 610. Can continue to be pumped to the fractionation column 510.

  [0065] According to one aspect, one of the power supplies 625 can include a different power supply type than the power supply type of the first power supply 620. For example, the second power supply 625 may be a steam turbine drive. In this way, if the first power supply 620 stops functioning due to a power failure or other accident, power can continue to be supplied to the second pump 610 by the second steam turbine drive. The steam-driven pump approach is where surface condenser systems for other process equipment exist and can be sized to accommodate intermittent increasing loads from the booster pump drive. It is the most economical in the driving location. Other types of alternative power supplies are also contemplated, which can include, for example, uninterruptible power from gas turbine drives, batteries or similar local energy storage devices, or facility distribution networks.

  [0066] According to various approaches, a pump 550 that includes one or more pumps can include a variable speed pump with a variable speed drive when including more than one pump. In this way, the pump 550 can be configured to handle the dynamic flow of the flow discharged from the adsorption separation unit 150 without the need for a control valve. In this regard, the traditional control valve provided along line 505 to control the amount of fluid flowing through line 505 can be eliminated, and the speed of the variable speed pump can be adjusted instead. The flow velocity of the flow can be controlled. Alternatively, a control valve can be included to control the flow of material between the adsorption separation unit 150 and the fractionation column 550. This can provide further economic advantages by reducing the equipment and manufacturing costs and maintenance required for the control valve.

  [0067] A surge vessel 630 may also be provided to be in fluid communication with the line 505. Surge vessel 630 can be used to hold fluid from line 505 when pump 550 has been disabled for a period of time and no flow can flow into fractionation column 510. Active or passive control can be provided to divert at least a portion of the flow into the surge vessel 630. For example, the valve can be closed during normal operation, but can be opened if the pump stops functioning, allowing flow to flow into the surge vessel 630 through line 635. Alternatively, an increased amount of pressure in line 505, for example due to fluid accumulation, can provide a driving force to divert flow through line 635 into the surge vessel. When pump operation is restored, fluid retained in the surge vessel can be pumped back or otherwise back into line 505 and into line 510 through line 505.

  [0068] According to various approaches, a control system 640 can be provided for controlling a pump 550 that includes one or more pumps as described above. When more than one pump is used as shown in FIG. 9, the control system 640 controls the operation of each of the pumps 605 and 610. In one example, when the first pump is a main pump and the second pump is a backup pump, the control system 640 detects that the first pump has stopped functioning and starts operating the second pump. The flow can then continue to be pumped through line 505 into fractionation column 510. In this regard, the control system can include an automated start function. Appropriate equipment and hardware, such as a solenoid operated shut-off valve, can be included to immediately bring the second backup pump 610 online in the event of a main pump outage.

  [0069] According to the various approaches described above, the flow is removed from the adsorption separation unit 150 even when the fractionation column is operating at elevated pressure, for example to provide energy savings or for other reasons. A pump 550 can be provided to flow to the fractionation column 510. Reduce the risk of disruption of the continuous flow from the adsorption separation unit 150 by including a suitable pump outage protection scheme such as a spare pump, surge vessel, alternative power supply, and / or control system Thus, the operation of the adsorption separation unit 150 can be prevented from being interrupted.

  [0070] According to one approach, the fractionation column 510 shown in FIG. 9 is the extract fractionation column 152 shown in FIGS. 1 and 6, and the line or conduit 505 connects the extract stream from the adsorption separation unit 150 to the extract fractionation column 152. Carry to. According to another approach, the fractionation column 510 shown in FIG. 9 is the raffinate fractionation column 159 shown in FIGS. 1 and 6, and the line or conduit 505 carries the raffinate stream from the adsorption separation unit 150 to the extract fractionation column 159. Furthermore, the invention described herein can be applied to both extract streams and raffinate streams in hydrocarbon conversion processes such as those shown in FIGS.

  [0071] According to one approach, a method is provided for separating one or more preferentially adsorbed components from a feed stream comprising preferentially adsorbed components and one or more non-preferential adsorbed components. The method includes separating preferentially adsorbed components in an adsorption separation process.

  [0072] The method can include separating the preferentially adsorbed component using pseudo countercurrent adsorbent separation in an adsorbent separation unit. In one approach, the method includes transferring one of the extract stream and the raffinate stream from the adsorption separation unit to a fractionation column to separate one or more components in the stream.

  [0073] The method also includes operating the fractionation column at elevated pressure. According to one approach, the fractionation column is operated at a pressure such that the sum of the column inlet pressure and the pressure drop in the transfer line and apparatus between the adsorption section and the column is higher than the pressure of the adsorption unit. The method includes pumping a stream from an adsorptive separation unit along a transfer line into a fractionation column to overcome one or more locations along the stream and the pressure differential of the fractionation column. This method can include using high pressure steam from a fractionation column to heat the other streams, reboilers, columns, or heat exchangers described above.

  [0074] In one approach, the method includes transferring an extract stream from an adsorptive separation unit to an extract fractionation column to separate extract products. In this approach, the method involves pumping the extract stream into an extract fractionation column. In other approaches, the method includes transferring the raffinate stream from the adsorptive separation unit to the raffinate fractionation column to separate the raffinate product. In this approach, the method involves pumping the raffinate stream into a raffinate fractionation column.

  [0075] Turning to more details, the only limitation in the selection of adsorbent for the simulated moving bed process is the effectiveness of the particular adsorbent / desorbent combination in the desired separation. An important feature of the adsorbent is the exchange rate of the desorbent with respect to the extract component of the feed mixture material, or in other words the relative desorption rate of the extract component. This feature is directly related to the amount of desorbent material that must be used in the process of recovering the extract components from the adsorbent. Faster exchange rates can reduce the amount of desorbent material required to remove the extract components and thus reduce the operating costs of the process. Faster exchange rates result in less desorbent material that must be pumped through the process and separated from the extract stream for reuse in the process.

  [0001] Thus, since different sieve / desorbent combinations are used for different separations, the practice of the present invention does not involve the use of any particular adsorbent or adsorbent / desorbent combination. Or it is not limited to this. The adsorbent may or may not be a zeolite. Examples of adsorbents that can be used in the method of the present invention include carbon-based molecular sieves, silicates, and non-zeolitic molecular sieves such as crystalline aluminosilicate molecular sieves classified as X and Y zeolites. Details regarding the composition and synthesis of many of these microporous molecular sieves are given in US-4,793,984, which is incorporated herein for this teaching. Information on adsorbents can also be obtained from US-4,385,994; US-4,605,492; US-4,310,440; and US-4,440,871;

[0076] In an adsorption separation process that is typically operated continuously at a substantially constant pressure and temperature to ensure a liquid phase, the desorbent material must be selected to meet several criteria. Don't be. First, the desorbent material adsorbs very strongly from the adsorbent at a reasonable mass flow rate without unduly preventing the extract components from replacing the desorbent material in the next adsorption cycle. The extract components must be replaced. Expressed in terms of selectivity, the adsorbent is preferably more selective with respect to all of the extract components with respect to the raffinate component than with respect to the desorbent material with respect to the raffinate component. Second, the desorbent material must be compatible with the specific adsorbent and the specific feed mixture. More specifically, they must not reduce or lose the capacity of the adsorbent or the selectivity of the adsorbent with respect to the extract component relative to the raffinate component. Further, the desorbent material must not chemically react with either the extract component or the raffinate component or must cause these chemical reactions. Both the extract stream and the raffinate stream are typically mixed with the desorbent material and removed from the void volume of the adsorbent, and any chemical reaction involving the desorbent material and the extract component or raffinate component or both of the product. It will complicate or prevent recovery. The desorbent must also be easily separated from the extract and raffinate components, such as by fractionation. Finally, desorbent materials must be readily available and reasonable in terms of cost. Desorbents can include heavy or light desorbents depending on the particular application. The term heavy and light is, C ₈ aromatics, i.e. ortho -, meta -, para - about the boiling point of the desorbent in comparison with xylenes and ethylbenzene. One skilled in the art will recognize that the designation “C ₈ ” refers to a compound containing 8 carbon atoms. In some embodiments, the heavy desorbent is selected from the group consisting of paradiethylbenzene, paradiisopropylbenzene, tetralin, and the like, and combinations thereof. In some embodiments, toluene or the like can be used as a light desorbent. Para-diethylbenzene (p-DEB) has a higher boiling point than C ₈ aromatic isomers, thus p-DEB bottom when separated from C ₈ isomers in the fractional distillation column (i.e., heavy) product It is. Similarly, toluene has a lower boiling point than the C ₈ aromatic isomer, so toluene is the top (ie, light) product when separated from the C ₈ isomer in a fractional distillation column. p-DEB has become a commercial standard for use as a desorbent in the separation of para-xylene.

  [0077] The above description and examples are intended to illustrate the invention without limiting its scope. While particular embodiments of the present invention have been shown and described, numerous changes and modifications will occur to those skilled in the art, and all such changes and modifications within the true spirit and scope of the invention are claimed in the appended claims. It will be appreciated that it is intended to cover

  [0002] The use of the pump 550 to pump the flow into the fractionation column 550 described above with respect to FIGS. 8-9 was evaluated in terms of capital recovery on investment. The base case is the facility described in FIGS. 1 and 6 but did not include the pump 550 described above. Instead, in order to provide a driving force to move the flow into the fractionation column using a positive pressure difference between the adsorption separation unit 150 and the fractionation column 550, the base case system is coupled to the adsorption separation unit 150 and Operate at a constant operating pressure throughout the system, such as in chambers 30 and 35. The preliminary economic analysis of the present invention shows a capital cost savings of container material of about US $ 500,000. Choosing a exchanger in a failed pump circuit is also cheaper due to the lower mechanical design pressure. Net energy savings are estimated at about $ 50,000 per year. The cost of the pump or pumps is expected to be less than $ 100,000.

Claims (10)

A feed stream comprising at least one preferential adsorbing component and at least one non-preferential adsorbing component, and a desorbent stream are introduced into two different ports through two different corresponding transfer lines along the multi-bed adsorbing separation unit; Discharging the extract stream and raffinate stream through two different ports of a multi-bed adsorption separation unit;
One of the extract stream and the raffinate stream is sent through a line running from the outlet port of the adsorption separation unit to the inlet of the high pressure fractionation column so that a pressure drop occurs when one of the extract stream and raffinate stream is sent through the line;
Operating the high pressure fractionation column at a pressure higher than the pressure of the adsorption separation unit minus the pressure drop occurring in one of the extract stream and raffinate stream;
Pumping one of the extract stream and the raffinate stream to increase the pressure in the stream and flowing one of the extract stream and the raffinate stream through the inlet of the fractionation column;
Separating the components in the feed stream by pseudo countercurrent adsorption separation.   The method of claim 1, wherein sending one of the extract stream and the raffinate stream comprises sending the extract stream to an extract fractionation column to separate the preferentially adsorbed component from the desorbent in the extract stream.   The method of claim 1, wherein sending one of the extract stream and the raffinate stream comprises sending the raffinate stream to a raffinate fractionation column to separate non-preferential adsorbent components from the desorbent in the raffinate stream.   Pumping one of the extract stream and the raffinate stream is pumped with the main pump at less than 100% of the total operating capacity and pumped with the second pump at less than 100% of the total operating capacity The method of claim 1, comprising:   Further comprising pumping one of the extract stream and raffinate stream using the main pump during normal operation and pumping one of the extract stream and raffinate stream using the backup pump during interruption of operation of the main pump. The method of claim 1.   The method of claim 1, further comprising pumping one of the extract stream and the raffinate stream at a variable speed. A port for receiving a feed stream and a desorbent stream, and a port for removing an extract stream and a raffinate stream; An adsorption separation unit having an adsorption separation unit operating pressure configured to produce a raffinate stream comprising non-preferred adsorption components;
A fractionation column having a fractionation column operating pressure for separating the desorbent from one of the extract stream and the raffinate stream to produce a product stream;
Separating one of the extract stream and raffinate stream from the adsorption separation unit in fluid communication between the adsorption separation unit and the fractionation column and having a pressure drop that occurs along the line between the adsorption separation unit and the fractionation column The line for sending to the column, where the fractionation column operating pressure is greater than the adsorption separation unit operating pressure minus the pressure drop that occurs along the line; and one of the extract stream and raffinate stream through the line Pump along the line for pumping into the fractionation column;
An apparatus for separating components in a feed stream by pseudo countercurrent adsorption separation.   The apparatus of claim 1, wherein the pump comprises a main pump that is operated during normal operation and a backup pump that is operated during operation interruption of the main pump.   The apparatus of claim 1, wherein the fractionation column comprises an extract fractionation column, and the pump moves the extract stream through the line into the extract fractionation column.   The apparatus of claim 1, wherein the fractionation column comprises a raffinate fractionation column and the raffinate stream is moved through the line by a pump into the raffinate fractionation column.

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