Chemistry of hydrocarbon compounds – Purification – separation – or recovery – By addition of extraneous agent – e.g. – solvent – etc.
Reexamination Certificate
2000-10-27
2002-01-08
Knode, Marian C. (Department: 1764)
Chemistry of hydrocarbon compounds
Purification, separation, or recovery
By addition of extraneous agent, e.g., solvent, etc.
C585S860000, C585S833000, C208S317000, C208S313000, C208S320000, C208S326000, C208S330000, C208S333000
Reexamination Certificate
active
06337429
ABSTRACT:
The present invention relates to a process for separating a C
4
-hydrocarbon mixture essentially containing 1,3-butadiene, butenes, butanes and other C
4
-hydrocarbons into at least 4 fractions,
a) the fraction (a) essentially comprising 1,3-butadiene,
b) the fraction (b) essentially comprising butenes,
c) the fraction (c) essentially comprising butanes and
d) one or more fractions (d) essentially comprising [lacuna] the other C
4
-hydrocarbons,
by extractive distillation by means of N-methyl-2-pyrrolidinone or an aqueous solution of N-methyl-2-pyrrolidinone (NMP),
wherein
1. the gaseous C
4
-hydrocarbon mixture is first brought into contact with NMP in an extraction zone (I), the 1,3-butadiene and the other C4-hydrocarbons being essentially completely absorbed by the NMP but the butenes and butanes remaining essentially in the gas phase;
2. the unabsorbed butenes and butanes (gas stream bc) and the extraction solution formed in step 1 (extraction solution ad) are removed from the extraction zone (I);
3. the extraction solution (ad) is transferred to a desorption zone (I) at a lower pressure and/or higher temperature than the extraction zone (I) and 1,3-butadiene is desorbed from the extraction solution (ad), the main part of the other C
4
-hydrocarbons remaining in the liquid phase;
4. the extraction solution formed in stage 3 (extraction solution d) and the desorbed 1,3-butadiene (fraction a) are removed separately from the desorption zone (I) and, if required, a part of the fraction (a) is returned to the extraction zone I;
5. the extraction solution (d) is transferred to a second desorption zone (II) at a lower pressure and/or higher temperature than the desorption zone (I) and having a pressure and/or temperature gradient, and the other C
4
-hydrocarbons and the 1,3-butadiene still remaining therein are fractionally desorbed from the extraction solution (d) as at least two separate fractions (d), with the content of the other C
4
-hydrocarbons being at least 10 times higher in at least one of the fractions (fractions d) than in the extraction solution (d), based on the content of all C
4
-hydrocarbons, and the content of the other C
4
-hydrocarbons being correspondingly lower in at least one of the fractions (fractions dR) than in the fractions (d), based on the content of all C
4
-hydrocarbons,
6. the NMP, formed in the desorption zone (II) and essentially free of C
4
-hydrocarbons, and the fractions (d) and (dR) are removed separately from the desorption zone II, and one or more fractions (dR) are returned to the desorption zone (I),
7. the gas stream (bc) is first brought into contact with the NMP formed in step 6 in an extraction zone (II), the butenes being essentially completely absorbed by the NMP but the butanes remaining essentially in the gas phase;
8. the unabsorbed butanes (fraction c) and the extraction solution formed in step 1 (extraction solution b) are removed from the extraction zone (II);
9. the extraction solution (b) is transferred to a desorption zone (III) at a lower pressure and/or higher temperature than the extraction zone (II) and the butenes are desorbed from the extraction solution (b);
10. the NMP, formed in step 9 and essentially free of C
4
-hydrocarbons, and the desorbed butenes (fraction b) are removed from the desorption zone (III);
11. the NMP formed in step 9 is recycled to one of the extraction zones.
This process is shown schematically in FIG.
1
.
A process for separating 1,3-butadiene from a C
4
-hydrocarbon mixture is disclosed, for example, in DE-A-2724365. Briefly, a butane/butene mixed fraction, a 1,3-butadiene fraction and a fraction which contains the other C
4
-hydrocarbons are obtained in this process from a C
4
-hydrocarbon mixture which contains butanes, butenes, 1,3-butadiene and other C
4
-hydrocarbons, by extractive distillation with NMP as absorbent over various absorption and desorption stages. In the entire process, the NMP required passes through a closed circulation. NMP which no longer contains any C
4
-hydrocarbons (unladen NMP) is first laden with the C
4
-hydrocarbon mixture at the beginning of a cycle, passes through the various absorption and desorption stages until, at the end of a cycle, unladen NMP is provided by completely desorbing the C
4
-hydrocarbons. The process is distinguished by the fact that the individual stages are particularly advantageously coupled via indirect heat exchange processes.
The separation of 1,3-butadiene and 2-butenes into separate fractions and the separation of 1,3-butadiene and acetylenes into separate fractions from C
4
-hydrocarbon mixtures have been described by V. A. Gorshkov et al. in the publication The Soviet Chemical Industry, No. 11, November 1971.
EP-A-141356 likewise relates to the separation of a 1,3-butadiene fraction from a C
4
-hydrocarbon mixture by means of extractive distillation using NMP. The use of columns in which absorption and desorption zone are integrated in a single column in each case make this process particularly economical.
EP-A-5788 discloses a process for separating a 1,3-butadiene fraction and a butyne fraction from a C
4
-hydrocarbon mixture by means of extractive distillation using NMP.
EP-A-9630 relates to a process for separately removing styrene and 1,3-butadiene from a mixture which otherwise contains C
4
-hydrocarbons, the styrene first being separated from the mixture by distillation and 1,3-butadiene being separated from the remaining mixture by means of extractive distillation.
U.S. Pat. No. 5,242,550 discloses the separation of a butene/butane mixture by means of extractive distillation using NMP as absorbent.
It is an object of the present invention to provide a process which permits the separation of a C
4
-hydrocarbon mixture into a butane fraction, butene fraction, 1,3-butadiene fraction and a fraction which contains the other C
4
-hydrocarbons in a particularly efficient and economical manner. In particular, the required quantities of energy and the capital costs should be particularly low in this process.
We have found that this object is achieved by the process described at the outset.
The process can be applied to C
4
-hydrocarbon mixtures which contain 1,3-butadiene, butenes, butanes and other C
4
-hydrocarbons plus very small amounts of C
3
- and C
5
-hydrocarbon impurities.
Such C
4
-hydrocarbon mixtures are obtained, for example, as C
4
fractions in the production of ethylene and/or propylene by thermal cleavage of a petroleum fraction, for example of liquefied petroleum gas (LPG), naphtha, gas oil or the like as hydrocarbon fraction. Furthermore, such C
4
fractions are obtained in the catalytic dehydrogenation of n-butane and/or n-butene. The C
4
fractions obtain [sic], as a rule, butanes, n-butene, isobutene, 1,2 butadiene, vinylacetylene, ethylacetylene and 1,2-butadiene [sic] and may contain small amounts of C
5
-hydrocarbons, the 1,3-butadiene content being in general from 10 to 80, preferably from 20 to 70, in particular from 30 to 60, percent by weight while the content of vinylacetylenes, ethylacetylene and 1,2-butadiene (referred to below as other hydrocarbons) together in the C
4
fractions generally does not exceed 5 percent by weight.
The novel process can advantageously be employed in particular to those C
4
-hydrocarbon mixtures which contain
from 10 to 80% by weight of 1,3-butadiene;
from 10 to 60% by weight of butenes;
from 5 to 40% by weight of butanes;
from 0.1 to 5% by weight of other C
4
-hydrocarbons and
from 0 to at most 5% by weight of C
3
- and C
5
-hydrocarbons.
The n-methyl-2-pyrrolidinone or its aqueous solution employed as selective solvent (N-methyl-2-pyrrolidinone and its aqueous solution abbreviated to “NMP” for short hereinafter) is generally a conventional industrial product which may contain up to 15% by weight of water.
The extraction zones are preferably in the form of columns through which the gas streams are passed countercurrently to the NMP.
In step 1, the C
4
-hydrocarbon mixture to be separated is first fed in gaseous form with NMP i
Kindler Klaus
Puhl Hubert
BASF - Aktiengesellschaft
Knode Marian C.
Nguyen Tam M.
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