Chemistry of hydrocarbon compounds – Plural serial diverse syntheses – To produce aromatic
Reexamination Certificate
2001-02-26
2002-07-09
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Plural serial diverse syntheses
To produce aromatic
C585S449000, C585S450000, C585S455000, C585S446000
Reexamination Certificate
active
06417420
ABSTRACT:
FIELD OF THE INVENTION
This invention is an improvement in a process for the production of alkylated aromatic compounds.
BACKGROUND OF THE INVENTION
Nearly forty years ago, it became apparent that household laundry detergents made of branched alkylbenzene sulfonates were gradually polluting rivers and lakes. Solution of the problem led to the manufacture of detergents made of linear alkylbenzene sulfonates (LABS), which were found to biodegrade more rapidly than the branched variety. Today, detergents made of LABS are manufactured worldwide.
LABS are manufactured from linear alkyl benzenes (LAB). The petrochemical industry produces LAB by dehydrogenating linear paraffins to linear olefins and then alkylating benzene with the linear olefins in the presence of HF or a solid alkylation catalyst. The linear paraffins are straight chain (unbranched) or normal paraffins. Normally, the linear paraffins are a mixture of linear paraffins having different carbon numbers. The linear paraffins have generally from about 6 to about 22, preferably from 10 to 15, and more preferably from 10 to 12 or from 11 to 13, carbon atoms per molecule.
LAB processes are described in the book edited by R. A. Meyers entitled “Handbook of Petroleum Refining Processes” (McGraw Hill, N.Y. 1986) and “Ullmann's Encyclopedia of Industrial Chemistry,” Volumes A8 and A13, Fifth Edition (VCH, Weinheim, Germany). Flow schemes are illustrated in U.S. Pat. No. 3,484,498 issued to R. C. Berg, U.S. Pat. No. 3,494,971 issued to E. R. Fenske, U.S. Pat. No. 4,523,048 issued to Vora which teaches use of a selective diolefin hydrogenation zone, and U.S. Pat. No. 5,012,021 issued to B. Vora which teaches use of a selective monoolefin hydrogenation zone. Solid alkylation catalysts are illustrated in U.S. Pat. No. 3,201,487 issued to S. Kovach et al.; U.S. Pat. No. 4,358,628 issued to L. Slaugh; U.S. Pat. No. 4,489,213 issued to S. Kovach; and U.S. Pat. No. 4,673,679 issued to D. Farcasiu. Zeolitic solid alkylation catalysts are disclosed in U.S. Pat. Nos. 3,751,506; 4,387,259; and 4,409,412.
It is well known that aromatic byproducts are formed during the catalytic dehydrogenation of paraffins. For instance, the article starting at page 86 of the Jan. 26, 1970 issue of “Chemical Engineering” states that the product of the dehydrogenation of linear paraffins includes aromatic compounds. The nature of the particular aromatic byproducts that are formed in dehydrogenation is not essential to this invention. Without limiting this invention in any way, these aromatic byproducts are believed to include, for example, alkylated benzenes, dialkylated benzenes, naphthalenes, other polynuclear aromatics, diphenyl compounds, alkylated polynuclear hydrocarbons in the C.
10
-C.
15
range, indanes, and tetralins, that is, they are aromatics of the same carbon number as the paraffin being dehydrogenated and may be viewed as aromatized normal paraffins. Some aromatic byproducts may be more detrimental than others in deactivating solid alkylation catalysts. It is believed that aromatic byproducts with few or small alkyl groups are more detrimental to solid alkylation catalysts than aromatic byproducts with multiple or long alkyl groups. It is also believed that aromatic byproducts having multiple aromatic rings are more detrimental to solid alkylation catalysts than aromatic byproducts having single aromatic rings. The particular side reactions that lead to the formation of the aromatic byproducts are also not essential to this invention. Again, without limiting this invention in any way, an illustration of some of the parallel thermal cracking reactions that can lead to the formation of aromatic byproducts is found in the diagram at the top of page 4-37 of the book mentioned above entitled “Handbook of Petroleum Refining Processes”. Typically, from about 0.2 to about 0.7 weight percent, and generally to the extent of no more than 1 weight percent, of the feed paraffinic compounds to a dehydrogenation zone form aromatic byproducts. Although some commercially available dehydrogenation catalysts are more selective than others at minimizing the formation of aromatic byproducts, it is believed that these byproducts are formed at least to a small extent at suitable dehydrogenation conditions in the presence of most if not all commercially available dehydrogenation catalysts. Since it is an economic advantage to operate the dehydrogenation zone at conditions that produce a high conversion of the feed paraffinic compounds and a high yield of the desired olefins, these aromatic byproducts are produced at least to a small extent in most if not all commercial dehydrogenation zones. But, since these aromatic byproducts have the same number of carbon atoms as both the unconverted feed paraffins and the product olefins, they have boiling points close to that of these paraffins and olefins. Thus, using conventional distillation, the aromatic byproducts are difficult to separate from a mixture such as the dehydrogenation effluent which also contains these paraffins and olefins.
The aromatic byproducts from the dehydrogenation section enter the alkylation section. In the selective alkylation zone containing a solid alkylation catalyst, several possibilities can then occur. First, some of the aromatic byproducts deposit on the surface of the catalyst and as mentioned above deactivate the catalyst. Second, as mentioned above some of the aromatic byproducts are alkylated by monoolefins to form heavy alkylate. Each mole of heavy alkylate formed by this route represents the loss of two moles of feed paraffinic compound toward the production of a less-valuable product and reduces both dehydrogenation selectivity and alkylation selectivity. Third, some of the aromatic byproducts pass through the selective alkylation zone unreacted, are recovered with the overhead liquid stream of the paraffin column which is recycled to the dehydrogenation zone, and ultimately accumulate to unacceptable concentrations. In the prior art processes employing a solid alkylation catalyst, the concentration of aromatic byproducts in the stripping effluent stream can typically accumulate to 4-10 weight percent, which leads to rapid deactivation of solid alkylation catalyst. Where the alkylation catalyst is HF in the prior art processes, the concentration of aromatic byproducts in the stripping effluent stream can typically accumulate to 3-6 weight percent.
Processes for removing the aromatic byproducts that are formed during the catalytic dehydrogenation of paraffins are also known. Suitable aromatics removal zones may be selected from any processing methods which exhibit the primary requirement of selectivity for the aromatic byproducts. Suitable aromatics removal zones include, for example, sorptive separation zones and liquid-liquid extraction zones. See U.S. Pat. No. 5,276,231 and U.S. Pat. No. 5,334,793, the contents of each are incorporated herein by reference. Where the aromatics removal zone is a sorptive separation zone, a fixed bed or a moving bed sorbent system may be used, but the fixed bed system is more common. The sorbent usually comprises a particulate material. In a fixed bed system, the sorbent is typically installed in one or more vessels in a parallel flow arrangement, so that when the sorbent bed in one vessel is spent by the accumulation of the aromatic byproducts thereon, the spent vessel is bypassed while continuing uninterrupted operation through another vessel. A purge stream comprising a purge component, such as C
5
or C
6
paraffin (e.g., normal pentane), is passed through the spent sorbent bed in the bypassed vessel in order to purge or displace unsorbed components of the stream containing the aromatic byproducts from the void volume between particles of sorbent. After purging, a regenerant or desorbent stream comprising a desorbent component such as C
6
or C
7
aromatic (e.g., benzene), is passed through the sorbent bed in the bypassed vessel in order to desorb aromatic byproducts from the sorbent. Following regeneration, the sorbent bed in the bypassed v
O'Brien Dennis E.
Stewart Douglas G.
Dang Thuan D.
Moore Michael A.
Spears, Jr. John F.
Tolomei John G.
UOP LLC
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