Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – By alkyl transfer – e.g. – disproportionation – etc.
Reexamination Certificate
2000-07-06
2003-03-25
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Unsaturated compound synthesis
By alkyl transfer, e.g., disproportionation, etc.
C585S324000, C585S643000, C585S646000
Reexamination Certificate
active
06538168
ABSTRACT:
The present invention relates to a process for converting olefinic C
4
-hydrocarbons, for example from steam crackers or FCC plants, into pentenes and hexenes by means of a metathesis reaction. Propene is obtained as desired process coproduct.
Olefinic metathesis (disproportionation) describes, in its simplest form, the reversible, metal-catalyzed transalkylidenation of olefins by rupture and reformation of C═C double bonds in accordance with the following equation:
In the special case of the metathesis of acyclic olefins, a distinction is made between self-metathesis in which one olefin is transformed into a mixture of two olefins of differing molar mass (for example: propene→ethene+2-butene) and cross-metathesis or co-metathesis which describes the reaction of two different olefins (propene+1-butene→ethene+2-pentene). If one of the reactants is ethene, this is generally referred to as an ethenolysis.
Suitable metathesis catalysts are, in principle, homogeneous and heterogeneous transition metal compounds, in particular from transition groups VI to VIII of the Periodic Table of the Elements, and also homogeneous and heterogeneous catalyst systems in which these compounds are present.
Various metathesis processes starting from C
4
streams have been described.
U.S. Pat. No. 5,057,638 relates to a process for preparing 1-hexene, comprising the process steps:
a) metathesis of 1-butene to give a mixture of 3-hexene and ethene,
b) separation of the 3-hexene from the product mixture obtained in step a),
c) reaction of the 3-hexene with an electrophile containing reactive hydrogen, preferably derived from water or carboxylic acid, under acid conditions which allow the addition of the electrophilic components onto the C═C bond (e.g. hydration), and
d) cracking of the product from step c), e.g. by dehydration, to prepare a mixture of n-hexenes in which 1-hexene is present in economically acceptable amounts.
U.S. Pat. Nos. 3,646,143 and 3,595,120 (May 5, 1969), Gulf Res. & Dev.Co. describes the conversion of short-chain C
4
-C
12
-olefins (preferably &agr;-olefins) into higher olefins by metathesis. The process comprises bringing the starting olefin into contact with a catalyst comprising aluminum, molybdenum or rhenium and silver or copper at from 100 to 240° C., with relatively low-boiling by-products, e.g. ethene, being able to be removed from the equilibrium in situ.
The present invention further relates to a combined process for preparing C
5
/C
6
-olefins together with propene as secondary product from C
4
fractions from steam crackers or FCC plants.
Steam crackers represent the main source of basic petrochemicals, for example ethene, propene, C
4
-olefins and higher hydrocarbons. In the cracking process, it is necessary to introduce large amounts of energy at high temperatures within a time which is sufficient for cracking to occur but does not allow further reaction of the cracking products. In the cracking of hydrocarbons, the yield of ethene and propene is therefore determined essentially by
the type of hydrocarbons used (naphtha, ethane, LPG, gas oil, or the like),
the cracking temperature,
the residence time
and the partial pressures of the respective hydrocarbons.
The highest yield of ethene and propene is achieved at cracking temperatures of from 800 to 850° C. and residence times of from 0.2 to 0.5 s. In this range the main product is always ethene, and the C
3
/C
2
product ratio can be increased from about 0.5 to 0.7 by slight variation in the cracking conditions. The world-wide demand for propene is increasing more rapidly than that for ethene. This has the consequence, inter alia, that processes for downstream utilization of the higher hydrocarbons formed in the cracking process, e.g. C
4
-hyrocarbons, are gaining increasing importance in respect of the optimization of the propene yield.
It is an object of the present invention, in the context of work on improving the value added derived from steam cracker by-products, to develop a flexibly controllable catalytic process for obtaining pure C
5
-/C
6
-olefin streams from inexpensive olefin-containing C
4
-hydrocarbon mixtures without introduction of ethene.
We have found that this object is achieved by a process for preparing C
5
-/C
6
-olefins from an olefinic starting stream comprising C
4
-hydrocarbons, which comprises
a) carrying out a metathesis reaction in the presence of a metathesis catalyst comprising at least one compound of a metal of transition group VIb, VIIb or VIII of the Periodic Table of the Elements so as to convert the 1-butene, 2-butene and isobutene present in the starting stream into a mixture of C
2
-C
6
-olefins and butanes,
b) firstly fractionating the resulting product stream by distillation to give a low boiler fraction A comprising C
2
-C
4
-olefins and butanes, which is discharged, and a high boiler fraction comprising C
4
-C
6
-olefins and butanes,
c) subsequently fractionating the high boiler fraction from b) by distillation to give a low boiler fraction B comprising butenes and butanes, an intermediate boiler fraction C comprising pentene and methylbutene and a high boiler fraction D comprising hexene and methylpentene,
d) where all or part of the fractions B and/or C are recirculated to the process step a) and the fraction D is discharged as product.
The expression “comprising” allows for the presence of relatively small amounts of other hydrocarbons.
In this process, carried out in a single stage, a fraction comprising C
4
-olefins, preferably n-butenes, isobutene and butanes is converted over a homogeneous or preferably heterogeneous metathesis catalyst into a product mixture of (inert) butanes, unreacted 1-butene, 2-butene and possibly isobutene and also the metathesis products ethene, propene, 2-pentene, possibly 2-methyl-2-butene, 3-hexene and possibly 2-methyl-2-pentene in a metathesis reaction according to the following equation:
The amount of branched C
5
- and C
6
-hydrocarbons in the metathesis product depends on the isobutene content of the C
4
feed and is preferably kept as small as possible (<3%).
To explain the process of the present invention in its different variations in more detail, the above equilibrium reaction (without taking isobutene into account) will be divided into three important individual reactions:
1. Cross-metatathiesis of 1-butene with 2-butene
2. Self-metalhesis of 1-butene
3. Ethenolysis of 2-butene
Depending on the prevailing demand for the target products propene, 2-pentene and 3-hexene (the term 2-pentene includes any isomers formed, e.g. cis/trans or 2-methyl-2-butene, and the same applies analogously to 3-hexene), the external mass balance of the process can be influenced in a targeted manner by shifting the equilibrium by recirculation of particular substreams. Thus, for example, the 3-hexene yield is increased when the cross-metathesis of 1-butene with 2-butene is suppressed by recirculation of 2-pentene into the metathesis step, so that very little, if any, 1-butene is consumed by the cross-metathesis. The self-metathesis of 1-butene to 3-hexene which then proceeds preferentially forms additional ethene which reacts in a subsequent reaction with 2-butene to form the desired product propene.
Olefin mixtures comprising 1-butene, 2-butene and isobutene are obtained, inter alia, in various cracking processes such as steam cracking or FCC as C
4
fraction. Alternatively, it is possible to use butene mixtures as are obtained in the dehydrogenation of butenes or by dimerization of ethene. Butanes present in the C
4
fraction behave as inerts. Dienes, alkynes or enynes are removed before the metathesis step of the present invention by means of customary methods such as extraction or selective hydrogenation.
The butene content of the C
4
fraction used in the process is from 1 to 100% by weight, preferably from 60 to 90% by weight. The butene content refers to 1-butene, 2-butene and isobutene.
Preference is given to using a C
4
fraction as is obtained in steam cracking or FCC or in the dehydrogenation of bu
Huber Sylvia
Schulz Michael
Schulz Ralf
Schwab Peter
BASF - Aktiengesellschaft
Dang Thuan D.
Keil & Weinkauf
LandOfFree
Preparation of C5-/C6-olefins does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Preparation of C5-/C6-olefins, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Preparation of C5-/C6-olefins will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3001949