JPH0339492B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Field of Application) The present invention relates to the separation of hydrocarbons. More particularly, the present invention provides a method for separating 1,3-butadiene from a feedstock mixture consisting of 1,3-butadiene and at least one other _C4 hydrocarbon using specific adsorbent and desorbent materials. Regarding how to. BACKGROUND OF THE INVENTION It is well known in the separation art that certain crystalline aluminosilicates can be used to separate one type of hydrocarbon from another.
For example, separation of normal paraffins from side chain paraffins can be achieved by using type A zeolites with pore openings of about 3-5 Å. Such separation methods are described in US Pat. No. 2,985,589 and
Disclosed in No. 3201491. These adsorbents are
Separation is achieved based on physical size differences in the molecules by passing smaller or positive hydrocarbons through cavities within a zeolite adsorbent while removing larger or side chain molecules. In addition to being used in processes for separating hydrocarbons, adsorbents made of X- or Y-type zeolites have also been used in processes for separating individual hydrocarbon isomers. For example, US Patent No. 3626020, US Patent No. 3663638,
No. 3665046, No. 3668266, No. 3686343, No. 3700744,
Nos. 3734974, 3894109, 3997620 and British patents
In the process described in No. 426274, a specific zeolite adsorbent separates para-isomers of bi-alkyl-substituted monocyclic aromatics from other isomers, and in particular para-xylenes from other xylene isomers. used in There are also separation techniques that specifically deal with the separation of 1,3-butadiene from other _C4 hydrocarbons, especially monoolefins. US Pat. Nos. 3,311,671 and 3,992,471 teach the use of alkali metal-aluminosilicates on zeolites to perform this separation. US patent
No. 3596436 discloses the use of activated carbon to separate diolefins from monoolefins, but requires that the entire process be carried out in the vapor phase, and requires that the solid adsorbent (removal of diolefins) be separated by superheated steam. Showing regeneration. PROBLEM SOLVED BY THE INVENTION In contrast to the above references, the present invention uses activated carbon or molecular sieve carbon and uses a hydrocarbon desorbent to _Four
It achieves separation from hydrocarbons. SUMMARY OF THE INVENTION In summary, the present invention provides, in one embodiment, the production of 1,3-butadiene from a feedstock mixture consisting of 1,3-butadiene and at least one other _C4 hydrocarbon.
- A method for separating butadiene. The process consists of contacting the feedstock mixture under adsorption conditions in the liquid phase with an adsorbent consisting of activated carbon or molecular sieve carbon that selectively adsorbs 1,3-butadiene. The unadsorbed portion of the feedstock is then removed from the adsorbent and the 1,3-butadiene is recovered by desorption with a liquid desorbent material comprising a hydrocarbon under desorption conditions.
The feedstock mixture and desorbent material have boiling points that differ by at least 5°C. Other embodiments of the invention include details regarding feedstock mixtures, flow regimes, and operating conditions, all of which are disclosed below. First, in order to clarify the operation, objects, and advantages of the present invention, we will first define terms used herein. A "feedstock mixture" is a mixture that includes one or more extractive components and one or more ruffinate components that are fed to the adsorbent of the process. "Feedstock Flow" refers to the flow of the feedstock mixture through the adsorbent used in the process. "Extract components" are the compounds that are more selectively adsorbed by the adsorbent, and "ruffinate components" are the compounds that are less selectively adsorbed. In this process, 1,3-butadiene is the extract component and one or more other _C4 hydrocarbons are the raffinate component. The term "ruffinate stream" or "ruffinate output stream" refers to a stream through which the roughinate components are removed from the adsorbent. Roughinate flow composition is virtually 100%
The desorbent material can range from substantially 100% roughinate components. The term "extract stream" or "extract output stream" means the stream through which the extract material desorbed by the desorbent material is removed from the adsorbent. The composition of the extract stream can similarly range from substantially 100% desorbent material to substantially 100% extract components. Although it is possible to produce highly purified extract or raffinate products with high recoveries by the method of the present invention, the extract components are never completely adsorbed by the adsorbent and It is recognized that the roughinate component is not completely non-adsorbed by the adsorbent. Therefore, small amounts of raffinate components can be found in the extract stream, and likewise small amounts of extract components can be found in the raffinate stream. Furthermore, the extract and raffinate streams are distinguished from each other and from the feedstock mixture by the ratio of the concentrations of extract components and specific raffinate components. For example, the ratio of the concentration of more selectively adsorbed 1,3-butadiene to the less selectively adsorbed concentration of other _C4 hydrocarbons is:
It is highest in the extract stream, next highest in the feedstock mixture, and lowest in the raffinate stream. Similarly, the ratio of the concentration of less selectively adsorbed other _C4 hydrocarbons to the more selectively adsorbed 1,3-butadiene is highest in the raffinate stream and in the feedstock mixture. the next highest and lowest in the extract stream. The term "desorbent material" generally refers to a material capable of desorbing extract components. The term "desorbent stream" or "desorbent input stream" refers to the flow through which the desorbent material passes to the adsorbent. When the extract stream and the raffinate stream contain desorbent material, at least a portion of the extract stream and preferably at least a portion of the raffinate stream from the adsorbent are passed through a separation means, typically a rectification column; At least a portion of the desorbent material is then separated under separation conditions to produce an extract product and a raffinate product. The terms "extract product" and "raffinate product" refer to products produced by a process that contain extract and raffinate components, respectively, at concentrations higher than those found in the respective extract and raffinate streams. means. The term "selective pore volume" of an adsorbent is defined as the volume of the adsorbent that selectively adsorbs extract components from the feed oil mixture. The term "non-selective void volume" is the volume of the adsorbent that does not selectively retain extract components from the feedstock mixture. This volume includes the cavity of the adsorbent without the adsorptive portion and the interstitial spaces between the adsorbent particles.
Selective pore volume and non-selective pore volume are generally expressed in terms of volume and define the appropriate flow rate of fluid required to pass through the process for efficient operation performed on a given amount of adsorbent. is important. 1,3, which is the most industrially important diolefin.
-Butadiene is used, for example, to produce polymeric components used in synthetic rubber and as a chemical intermediate for many types of compounds. Butadiene can be produced in four main ways: (1) by catalytic dehydrogenation of concentrated n-butylene, (2) by catalytic dehydrogenation of n-butene, and (3) by the formation of unsaturates. (4) is commercially synthesized from ethyl alcohol by a combination of catalytic dehydrogenation and dehydration as a by-product in low yields from the severe high temperature decomposition of liquid hydrocarbons. The first two methods are the most frequently used methods. All of these conversion processes produce products in which 1,3-butadiene is mixed with other hydrocarbons of similar boiling points. For example, when concentrated 2-butene and 1-butene are catalytically dehydrogenated to produce 1,3-butadiene, the stabilized effluent of this operation contains, in addition to 1,3-butadiene, unreacted n-
Contains components heavier than butenes, some isobutane, isobutylene, appreciable concentrations of _C3 components, and small concentrations of _C4 hydrocarbons. Table 1 lists the hydrocarbons often found in crude butadiene fractions and indicates the composition of feedstock mixtures that are expected to be used in the process of the present invention. The relative amounts of these hydrocarbons present in the crude butadiene vary significantly depending on the type of hydrocarbon conversion process used. Other C ₄ unsaturations, primarily monoolefins, are always present in large amounts. Unconjugated diolefins and acetylene are minor components, but generally increase with increasing temperature during hydrocarbon conversion. However, these are primarily very bad contaminants in purified butadiene and therefore their concentration in purified butadiene must be carefully controlled.

[Table] In order to separate 1,3-butadiene from a feedstock oil mixture according to the present invention, the mixture is contacted with an adsorbent, and more 1,3-butadiene is selectively adsorbed and retained by the adsorbent. The other components of the feedstock mixture are relatively unadsorbed and are removed from the pore space between the adsorbent particles and the adsorbent surface. Adsorbents containing more selectively adsorbed 1,3-butadiene are referred to as "rich" adsorbents. next,
1,3-butadiene is recovered from the rich adsorbent by contacting the rich adsorbent with a desorbent material. As used herein, the term “desorbent material” refers to
Refers to a particulate material that can selectively remove adsorbed feedstock components from an adsorbent. in general,
In rocking bed systems where selectively adsorbed feedstock components are removed from the adsorbent by a purge stream, the choice of desorbent material is not critical;
Desorbent materials consisting of gaseous hydrocarbons such as methane, ethane, etc., or other types of gases such as nitrogen, hydrogen, etc., are used at high or low temperatures to effectively purge the adsorbed feedstock components from the adsorbent. used in both. However, in adsorption separation processes that are generally operated continuously at substantially constant pressure and temperature to maintain a liquid phase, the desorbent material must be judiciously selected to satisfy several criteria. No. First, the desorbent material can be extracted at a moderate flow rate without itself being adsorbed too strongly so that the extract components do not unduly displace the desorbent material in the next adsorption cycle. Components must be displaced from the adsorbent. In terms of selectivity, it is preferred that the adsorbent be more selective for the extract components with respect to the raffinate components than for the desorbent material with respect to the raffinate components. Second, the desorbent material must be compatible with the particular adsorbent and the particular feedstock mixture. More particularly, the desorbent material reduces the selectivity of the adsorbent for extract components with respect to raffinate components;
It must not be destructive or destructive. The desorbent material used in the process of the present invention should also be a material that can be easily separated from the feedstock mixture entering the process. After desorbing the extractive components of the feedstock, both the desorbent material and the extractive components are typically mixed and removed from the adsorbent. Similarly, the ruffinate component(s) are typically removed from the adsorbent in admixture with the desorbent material and cannot be extracted without a method of separating at least a portion of the desorbent material, such as distillation. The purity of the product and the purity of the ruffinate product are not very high. Therefore, the desorbent material used in this process has an average boiling point that is substantially different from the feedstock mixture and is separated from the feedstock components in the extract and raffinate streams by simple rectification. , thereby allowing reuse of the desorbent material in the process. As used herein, the term "substantially different" means that the difference in average boiling point between the desorbent material and the feedstock mixture is at least about 5°C. The boiling range of the desorbent material may be higher or lower than that of the feedstock mixture. In the preferred isothermal, isobaric, liquid phase operation of the process of the invention, the effective desorbent materials are hydrocarbons,
In particular, it has been found to consist of _C3 or _C5 to _C10 n-olefins. The ability to operate in the liquid phase, in contrast to the aforementioned US Pat. No. 3,596,436, is a significant advantage from the standpoint of energy savings and ease of operation. It has been recognized in the prior art that certain properties of adsorbents are highly desirable, although not absolutely necessary, for the successful operation of selective adsorption processes. Such properties include the adsorption capacity for a given volume of extract components per volume of adsorbent; the selective adsorption of extract components with respect to raffinate components and desorbent materials; and the adsorption and adsorption of extract components onto the adsorbent. There is a sufficiently fast rate of desorption from the adsorbent. The capacity of the adsorbent to adsorb a specific volume of one or more extract components is, of course, essential.
Without such capacity, the adsorbent is useless for adsorptive separations. Furthermore, the higher the capacity of the adsorbent for extract components, the better the adsorbent. Increasing the capacity of a particular adsorbent makes it possible to reduce the amount of adsorbent required to separate extractive components contained in a feedstock mixture for a particular charging rate. Reducing the amount of adsorbent required for a particular adsorptive separation reduces the cost of the separation process. It is important that a good initial capacity of the adsorbent be maintained during its practical use in separation processes over an economically desirable lifetime. A second necessary property of the adsorbent is its ability to separate the components of the feedstock. In other words, it has adsorption selectivity (B) for one component compared to other components. The expression relative selectivity is used not only for one feedstock component relative to other components, but also between feedstock mixture components and desorbent materials. Selectivity (B), as used herein, is defined as the ratio of the same two components in the adsorbed phase to the ratio of the two components in the unadsorbed phase at equilibrium. The relative selectivity is shown as Equation 1. Formula 1 Selection rate (B) = [Vol.%C/Vol.%D] _A / [Vol.%
C/Vol.%D] _Uwhere , C and D are 2 of the raw oil expressed in volume%.
subscripts A and U represent the adsorbed phase and unadsorbed phase, respectively. Equilibrium conditions are determined when the feedstock passing through a bed of adsorbent does not change in composition after contacting the bed of adsorbent. In other words, there is no movement of substances between the adsorbed phase and the unadsorbed phase. If the selectivity of the two components approaches 1.0,
There is no preferential adsorption of one component by the adsorbent with respect to other components. Both are adsorbed to the same extent with respect to each other. As (B) becomes smaller or larger than 1.0, there is preferential adsorption by the adsorbent for one component with respect to other components. When comparing the selectivity of one component C by the adsorbent with respect to component D, (B) greater than 1.0 indicates preferential adsorption of component C in the adsorbent. (B) smaller than 1.0 indicates that component D is preferentially adsorbed, leaving an unadsorbed phase containing a large amount of component C and an adsorbed phase containing a large amount of component D. Separation of the extract component from the roughinate component is theoretically possible if the selectivity of the adsorbent for the extract component with respect to the roughinate component just exceeds a value of 1.0, but such selectivity is only 2. Preferably, the values are close to each other or greater than 2. As with relative volatility, the higher the selectivity, the easier the separation will be. The higher the selectivity, the lower the amount of adsorbent used in the process. Ideally, the desorbent material should be approximately equal to 1 for all extractant components, or It should have a selectivity less than 1. A third important characteristic is the relative rate of exchange, or in other words, desorption, of extractive components of the feed oil mixture material. This property is directly related to the amount of desorbent material that must be used in the process to recover extract components from the adsorbent. The faster the exchange rate, the lower the amount of desorbent material required to remove the extract components, thus reducing the operating costs of the process. The faster the exchange rate, the less desorbent material must be pumped into the process and separated from the extract stream for reuse in the process. A fourth important property of the adsorbent is the extent to which it chemically reacts with, or causes chemical changes in, the feed oil and desorbent components. For example, the aforementioned US Pat. Nos. 3,311,671 and 3,992,471 show the use of zeolitic materials as adsorbents. Such materials, however, are known to react with hydrocarbons, especially olefins. In contrast to such chemically active adsorbents, the carbon adsorbents of the present invention are chemically inert to the components of the process stream. A dynamic test device is used to test various adsorbent and desorbent materials with specific feed oil mixtures to determine the adsorbent properties of adsorption capacity and selectivity and exchange rate. The apparatus consists of an adsorbent chamber of approximately 70 c.c. volume with an inlet and an outlet section at each end. This chamber is contained within a temperature control means and a pressure control device is used to operate at a predetermined constant pressure. A chromatographic analyzer can be attached to the outlet of the chamber and used to analyze the effluent stream leaving the adsorbent chamber "on-stream." Pulse tests performed using this equipment and the following general method are used to measure selectivity and other data for various adsorbent systems. The adsorbent is loaded into equilibrium with the desorbent by passing the desorbent material into the adsorbent chamber. At appropriate times, pulses of feedstock containing a specific feedstock mixture of _C4 hydrocarbons diluted in a known concentration of unadsorbed paraffinic tracer (e.g. n-nonane) and desorbent are entered for a duration of several minutes. do. The desorbent flow is resumed and the tracer and components of the feedstock mixture are eluted as in a liquid-solid chromatographic operation. The effluent can be analyzed by an on-stream chromatographic device to develop envelope traces of the corresponding component peaks. Alternatively, samples of the effluent can be collected periodically and later analyzed separately by gas chromatography. From the information obtained from the chromatographic traces, the performance of the adsorbent depends on its capacity index for the extract components, its selectivity for one _C4 hydrocarbon with respect to other hydrocarbons, and the rate of desorption of the extract components by the desorbent. It can be evaluated accordingly. Capacity index is characterized by the distance between the center of the peak envelope of the selectively adsorbed component and the peak envelope of the tracer component or some other known reference point. It is expressed as the volume in cubic centimeters of desorbent pumped during this time interval. The selectivity (B) for the extract component with respect to the roughinate component is determined by the distance between the center of the peak envelope of the extract component and the peak envelope of the tracer (or other reference point) and the distance between the center of the peak envelope of the roughinate component and the tracer. is characterized by the ratio of the corresponding distance between the peak envelope of The rate of exchange of extract components with the desorbent is generally characterized by the width of the peak envelope at half strength. The narrower the width of this peak, the faster the desorption rate. The desorption rate is also characterized by the distance between the center of the peak envelope of the tracer and the vanishing point of the extract component just desorbed. This distance is the volume of desorbent pumped during this time interval. The adsorbent used in the process of the invention consists of activated carbon, otherwise known as molecular sieve carbon. Activated carbon is
Commonly commercially available materials such as Calgon Corporation's "Type PCB" granular carbon or Union Carbde Corporation's products bearing the trademark "PURASIV" It is. calgon 1987
The PCB type described in Cat. No. 23-108a dated August 2013 is a type of PCB with a diameter of 15-20 Å penetrated by a system of macropores larger than 1000 Å in diameter.
It is an activated carbon with most of the micropore volume in pores in Å. The plasieve described in Union Carbide Catalog F-4866815M is a bead-shaped activated carbon made from molten petroleum pitch formed into spherical particles and subsequently carbonized and activated. “Molecular sieve carbon” used here
The term “activated carbon” is not necessarily intended to distinguish it from the substance referred to as “activated carbon.”
This indicates that materials useful for use in the present invention are not excluded. There is considerable overlap between these two terms, and for the purposes of this invention, they are interchangeable. Particular molecular sieve carbons known to be effective for use in the present invention are those having average pore sizes of about 5 Å or greater. The adsorbent has a desired particle range, preferably from 1.19 to
The particles are in the form of extrudates, aggregates, tablets, macrospheres, or granules having approximately 16 to 60 meshes (US standard mesh) corresponding to an apparent gap of 0.25 mm. From the standpoint of water contamination of the product, it is advantageous for the adsorbent to be low in moisture. The adsorbent is used in the form of a dense fixed bed in alternating contact with the feed oil mixture and the desorbent, the process being semi-continuous. In other embodiments, the feedstock mixture may pass through one or more beds of adsorbent in one set while the desorbent material passes through one or more beds in other beds of one set. As can be seen, a set of two or more fixed bed adsorbents may be used with suitable valve means. A stream of feed oil mixture and desorbent material flows upwardly or downwardly through the adsorbent in such a bed. Any conventional equipment used for fixed bed liquid-solid contacting may be used. However, moving beds, or simulated moving bed flow systems, have significantly greater separation efficiency than fixed bed systems and are therefore preferred. In a moving bed, or simulated moving bed process, the retention and displacement operations occur continuously, allowing continuous production of both extract and raffinate streams and frequent use of feedstock and displacement fluid streams. One preferred embodiment of this process utilizes what is known as a simulated moving bed countercurrent flow system. In such systems, it is the gradual movement of a number of liquid access points down the molecular sieve chamber that simulates the upward movement of the molecular sieve contained in the chamber. This is discussed in U.S. Pat. No. 2,985,589 and U.S. Pat.
Society of Tokyo, April 2, 1969
DBBroughton Presented to the 34th Annual Meeting of the Society of Chemical Engineers
Mr. “Continuous Adsorptive Processing…A
Reference is made to the paper titled "New Separation Technique", both of which provide a further overview of simulated moving bed countercurrent process flows suitable for use in the process of the present invention. Another example of a simulated moving bed flow system is the co-current high efficiency simulated moving bed process disclosed in U.S. Pat. No. 4,402,832. At least a portion of the extract output stream enters the separation means and is At least a portion of the desorbent material is intended to be separated in separation conditions to produce an extracted product containing a reduced concentration of desorbent material. Although not necessary for operation of this process, it is preferred that the rough At least a portion of the inate output stream also enters a separation means where at least a portion of the desorbent material is separated under separation conditions to produce a desorbent stream that can be reused in the process and a roughinate containing a reduced concentration of desorbent material. Typically, the concentration of the desorbent material in the extraction product and the roughinate product is less than about 5 Vol.%;
Preferably less than about 1 Vol.%. The separation means is typically a rectification column, the design and operation of which is well known in the separation art. Although both liquid-phase and vapor-phase operations can be used in many adsorption separation processes, due to the lower temperatures and lower energy requirements, and the higher extractive production that can be obtained with liquid-phase operation than that obtained with vapor-phase operation. Due to product yield, liquid phase operation is required for this process. The adsorption conditions are
It encompasses a temperature range of about 20-250°C, preferably about 100-200°C and sufficient pressure to maintain a liquid phase. Desorption conditions encompass the same range of temperatures and pressures used for adsorption conditions. The size of units available for the process of this invention can vary arbitrarily from pilot plant scale (see, e.g., US Pat. Can span a range. (Example) Next, the present invention will be specifically explained using examples. However, the invention is not limited to the particular desorbent materials, feedstock mixtures, and operating conditions used in this example. Example 1 In this experiment, three pulse tests were performed to evaluate the ability of the present invention to separate 1,3-butadiene from other _C4 hydrocarbons using three different carbon adsorbents. Ivy. The test equipment was the pulse test equipment described above. For each pulse test, the column was maintained at a temperature of 65°C and sufficient pressure to maintain liquid phase operation. A gas chromatographic analyzer was attached to the tower effluent stream to measure the composition of the effluent material at regular time intervals. The feedstock mixture used for each test consisted of 5 Vol.% each of isobutane, normal butane, isobutylene, trans-butene-2, cis-butene-2, and 1,3-butadiene and 70 Vol.% of the desorbent material. Contained. The desorbent material was hexene-1. The operations performed for each test were as follows. The desorbent material was passed continuously at an apparent liquid hourly space velocity (LHSV) of 1.0. This corresponds to a feed rate of approximately 1.17 cc per minute.
At some appropriate time interval, the desorbent was turned off and the feedstock mixture was passed through at a rate of 1.0 cc per minute for 10 minutes. The desorbent flow is then resumed at 1 LHSV and all feedstock components are eluted from the column, as determined by observing the chromatograph produced by the effluent material exiting the adsorption column. The desorbent stream was continuously passed through the adsorption column until it was exhausted. The operation usually takes about 1
It takes time. The 10 minute pulses of delivery and desorption were repeated sequentially. The chromatographic traces obtained were as shown in Figures 1, 2 and 3. The selectivities derived from these traces are shown in Table 2. The reference curve is isobutane, which is considered completely non-adsorbed.

[Table] Butane
1,3〓Butadiene/A 2.59 2.54 3.74
Sobutylene

[Table] Lance Butene
1,3〓Butadiene/C 2.06 2.18 2/17
Subbutene
The graphical traces for the three tests show clear separation of 1,3-butadiene from other feedstock components. 1,3-Butadiene was the last component to elute from each pulse test and was shown to be the most selectively retained component on all three adsorbents. 1,3- derived from the curve
The high selectivity given in Table 2 for butadiene provides a quantitative measure of the high degree of relative retention of 1,3-butadiene.

[Brief explanation of the drawing]

Figures 1, 2, and 3 show Calgon PCB and Calgon PCB as adsorbents in Example 1, respectively.
2 is a graph showing chromatographic traces of each component in the case of PURASIV and molecular sieve carbon.

Claims (1)

[Claims] 1. A feedstock mixture consisting of 1,3-butadiene and at least one other C ₄ hydrocarbon is
an adsorbent made of activated carbon or molecular sieve carbon that selectively adsorbs 3-butadiene;
in adsorption conditions, contacting in the liquid phase to remove the unadsorbed portion of the feedstock mixture from the adsorbent, and in desorption conditions, desorption with a liquid desorbent material consisting of a _C3 or _C5 - _C10 positive olefin. recovering said 1,3-butadiene by
A method for separating 1,3-butadiene from the raw oil mixture. 2. The method of claim 1, wherein the adsorption and desorption conditions include a temperature in the range of about 20-250°C and a pressure sufficient to maintain a liquid phase. 3. The method of claim 1, wherein the desorbent material comprises hexene-1. 4. The method of claim 1, wherein the method is carried out in a simulated moving bed flow system. 5. The simulated moving bed flow system:
5. The method of claim 4, which is of the countercurrent type. 6. The simulated moving bed flow system:
The method according to claim 4, which is of the codirectional flow high efficiency type.