Chemistry of hydrocarbon compounds – Purification – separation – or recovery – By plural serial diverse separations
Reexamination Certificate
1998-10-27
2001-04-10
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Purification, separation, or recovery
By plural serial diverse separations
C585S810000, C585S820000, C585S829000, C210S660000, C210S690000, C208S31000R
Reexamination Certificate
active
06215037
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process, and specifically selected adsorbents, for selective adsorption to separate a diene from a mixture, particularly one containing mono-olefin.
BACKGROUND OF THE INVENTION
In the preparation of commercial hydrocarbon product, it is often necessary to separate the desired product from other hydrocarbons having similar boiling points. For example, butene is synthesized commercially by processes which yield butadiene mixed with 1-butene. Conversely, butadiene product may also be contaminated with butene. Depending on the process used, the mixture may include other C
3
and C
4
hydrocarbon components including but not limited to 2-butene, other n-butenes, n-butane, isobutane, and isobutylene.
Purifying the mono-olefin, 1-butene, is particularly troublesome due to the closeness of its boiling point to that of 1,3-butadiene. In order to increase the purity of 1-butene, it is necessary to separate it from other hydrocarbons. Ordinarily, fractionation alone is incapable of completely separating 1,3-butadiene to achieve the desired purity of 1-butene in these mixtures. Presently, butadiene is separated from olefins and paraffins primarily by distillation with selective solvents and by absorption using solutions of absorbents. Extractive distillation is relatively energy-intensive, complex and not economical. Selective absorption with metal salt solution involves a significant number of stages with recycling of streams between stages. This method has the disadvantage of being energy-intensive and requiring handling and recirculating of solvent streams which themselves contain contaminants or are subject to degradation. Current processes for olefin/paraffin separation have not been sufficiently selective to economically achieve the desired result for purifying mixtures of unsaturated hydrocarbons. Therefore, there remains the need for an improved method and improved adsorbents for use in methods to effectively and economically purify unsaturated hydrocarbons.
SUMMARY OF THE INVENTION
The invention provides new methods for separating unsaturated hydrocarbons from a mixture comprising the unsaturated hydrocarbons. The invention provides adsorbents specifically selected for accomplishing the separation. The adsorbents and separation methods are particularly useful for selective adsorption of a diene from mixtures containing the diene; and are very effective for separating dienes from mono-olef ins. In one aspect the invention provides methods and adsorbents to separate butadiene, hexadiene and/or octadiene from hydrocarbon mixtures; particularly where the hydrocarbon mixture contains a mono-olefin such as butene, hexene and/or octene.
Diene and mono-olefin compounds are often found together as a result of industrial processing. The separation of dienes from mono-olefin is difficult to achieve due to the closeness of their respective boiling points. This difficulty is illustrated by considering 1,3-butadiene, which has a boiling point of −4.4° C. and 1-butene which has a boiling point of −6.3° C.
The invention in one aspect, is particularly suited to cause such separation. Other important diene\mono-olefin separations include separation of hexadiene from hexene and separation of octadiene from octene. In the process of the invention, the diene is separated from a mixture comprising the diene by contacting the mixture with an adsorbent which preferentially adsorbs the diene. This produces a non-adsorbed component and a diene-rich adsorbed component.
In one aspect, the adsorbent comprises an ion-exchanged zeolite X, zeolite Y, and/or zeolite LSX. The selected zeolite has exchangeable cationic sites, with silver cation or copper cation present at some or all of the exchangeable cationic sites. Substantial cation exchange is preferred so that at least half of the cationic sites of the ion exchange zeolite contain a copper or silver cation. It is preferred that the ion exchange be substantially or essentially complete so that the silver or copper ion exchange level of the exchangeable ion content is substantial enough to change the adsorption characteristic. In the case of the silver ion-exchanged zeolite, desirably a silver ion exchange level of the exchangeable ion content is at least 70%, more desirably at least 80%, most desirably at least 85%, preferably at least 90% and more preferably at least 95%. Most preferably, substantially all (i.e., 99%) of the exchangeable ion sites are occupied by silver cations. Alternatively, the X-zeolite, Y-zeolite or zeolite LSX is a copper ion-exchanged zeolite. It is preferred that the ion exchange be as complete as described immediately above with respect to the silver cation. That is, at least half of the cationic sites of the copper ion exchanged zeolite are occupied by copper. In the case of copper ion-exchanged zeolite, the same level of high exchange content applies, according to the progressive levels stated above for silver. It is preferred that essentially complete ion exchange occur whereby substantially all (i.e., 99%) of the exchangeable cationic sites are occupied by copper cations.
The copper and silver ion exchanged zeolites provide a unique advantage in that diene\/mono-olefin separation is facilitated by formation of &pgr;-complexation bonds. Therefore, the silver ion exchanged zeolite, when used as adsorbents, have the unique ability to form &pgr;-complexation bonds for releasibly retaining the targeted unsaturated hydrocarbon desired to be selectively removed. By formation of &pgr;-complexation bond, the silver or copper ion exchange zeolite is able to retain the targeted unsaturated hydrocarbon at a selected temperature and pressure. Thereafter, the silver or copper ion-exchanged zeolite releases the adsorbed targeted hydrocarbon when either or both of temperature and pressure are changed to cause desorption (release).
In another aspect, separation of a targeted unsaturated hydrocarbon compound is achieved by contacting a mixture containing the targeted compound with an adsorbent which comprises a type A zeolite. The type-A zeolite is usable in its calcium form. The type A zeolite may also be used for selective adsorption where metal cations selected from the group of alkaline metal cation and alkaline earth metal cation are present. Therefore, the Type-A zeolite may be represented by the nominal general formula M
+1
x
Z
+2
y
A
+3
b
[(AlO
2
)
12
(SiO
2
)
12
] wherein M
+1
is an alkali cation, Z
+2
is an alkaline earth cation, and A
+3
is a tri-valent cation, the value of x is 0 to 12, the value of y is 0 to 6, and the value of b is at minimum zero and at maximum less than the sum of x plus y, provided that: x+2y+3b is 12. For charge balance, the maximum value of b is 4. It is preferred that b is less than 4. The alkaline metal cation is selected from lithium, sodium, potassium, rubidium and cesium and mixtures thereof and the alkaline earth metal cation is selected from the group consisting of beryllium, magnesium, calcium, strontium, barium and mixtures thereof. The trivalent cation is preferably a metal compound capable of a trivalent valence condition. Examples include aluminum and boron.
In another aspect, the adsorbents of the invention are used in a method for separating an unsaturated hydrocarbon from a mixture by accomplishing adsorption at a first selected pressure and temperature and then accomplishing release or desorption by changing at least one of the pressure and temperature. Preferential adsorption is achieved at a pressure greater than the desorption (release) pressure. Preferential adsorption pressure may be as high as about 35 atmospheres or more; and the desorption pressure may be as low as sub-atmospheric, significant vacuum, 0.01 atmosphere or less. Desirably, the pressure of preferential adsorption is in a range of about 1 atmosphere to about 35 atmospheres; and most desirably about 1 to 2 atmospheres. Desirably, the pressure of release is in a range of about 0.1 atmospheres to
Munson Curtis L.
Padin Joel
Yang Ralph T.
Griffin Walter D.
Nguyen Tam M.
The Regents of the University of Michigan
Young & Basile P.C.
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