Process for obtaining high-purity 1-butene from C4 hydrocarbon mixtures

Abstract

A process is described for obtaining high-purity 1-butene starting from C.sub.4 hydrocarbon mixtures containing isobutene, n-butane, isobutane, 1,3-butadiene, 1-butene, 2-butenes and also optionally C.sub.3 and C.sub.5 hydrocarbons, comprising the following stages: conversion of isobutene effected in a double stage, wherein each stage consists of one or more reactors followed by a distillation column for the recovery of the reaction product; recovery of the excess alcohol; recovery of 1-butene using at least two distillation columns; characterised in that it also uses a further conversion stage, consisting of one or more reactors in series, for completing the isobutene removal.

Claims

1. A process, comprising: an initial conversion stage of converting isobutene from a FCC or stream cracking C4 hydrocarbon mixture comprising isobutene, n-butane, iso-butane, 1,3-butadiene, 1-butene, and a 2-butene by performing at least one of: etherifying the isobutene with an alcohol; dimerizing the isobutene in the presence of an alcohol; dimerizing the isobutene in the presence of water; and dimerizing the isobutene in the presence of an ether, wherein the initial conversion stage is conducted in two reaction steps, each reaction step occurring by (i) performing the converting in at least one reactor, optionally with intermediate cooling, and then immediately (ii) performing a single distillation in a distillation column that is separate from the at least one reactor and is suitable for recovery of an initial reaction product; then, immediately following the initial conversion stage a further conversion stage of completely removing isobutene from the initial reaction product in a reactor or reactors in series, thereby producing a further reaction product comprising at least one oxygenated compound comprising dimethyl ether; recovering excess alcohol if present in the initial reaction product or in the further reaction product; removing the dimethyl ether and any other oxygenated compounds from the further reaction product produced in the further conversion stage, by distillation in a distillation column downstream therefrom; and an additional stage of selectively hydrogenating a diene from the further reaction product in at least one reactor situated immediately upstream of a recovery stage that is performed by recovering 1-butene with at least a first distillation column having an outflow that is an inflow to a second distillation column, thereby obtaining a high-purity 1-butene.

2. The process according to claim 1, wherein the initial conversion stage of converting isobutene comprises etherifying the isobutene with a linear alcohol.

3. The process according to claim 1, wherein the initial conversion stage of converting isobutene comprises selectively dimerizing the isobutene in the presence of a linear alcohol, a branched alcohol, an alkyl ether, or any combination thereof.

4. The process according to claim 3, wherein the isobutene is selectively dimerized in the presence of a branched alcohol having a number of carbon atoms of from 3 to 6.

5. The process according to claim 3, wherein the isobutene is selectively dimerized in the presence of an alkyl ether having a number of carbon atoms of from 5 to 10.

6. The process according to claim 1, wherein the further conversion stage comprises reacting the isobutene with a linear alcohol.

7. The process according to claim 2 or 6, wherein the linear alcohol has a number of carbon atoms of between 1 and 5.

8. The process according to claim 1, wherein the further conversion stage comprises reacting the isobutene with water.

9. The process according to claim 1, wherein the recovering of the excess alcohol comprises recovering the excess alcohol in two columns, of which a first column is a washing column with water.

10. The process according to claim 1, wherein the recovering of the excess alcohol comprises recovering the excess alcohol in an absorption system with molecular sieves.

11. The process according to claim 1, wherein the further conversion stage occurs before the recovery stage.

12. The process according to claim 1, wherein the further conversion stage occurs before the recovering of the excess alcohol.

13. The process according to claim 1, wherein the dimethyl ether and any other oxygenated compounds produced in the further conversion stage are removed with at least one distillation column situated downstream of the further conversion stage.

14. The process according to claim 1, wherein the removing of the dimethyl ether and any other oxygenated compounds produced in the further conversion stage comprises feeding the distillation column with a C4 hydrocarbon stream comprising 2-butene and n-butane.

15. The process according to claim 1, wherein the first distillation column of the recovery stage stabilizes the additional stage of selectively hydrogenating the diene.

16. The process according to claim 1, further comprising: a bond isomerization stage of bond isomerizing a stream comprising 2-butenes and n-butane, following the recovery stage.

17. The process according to claim 1, further comprising: a skeletal isomerization stage of skeletal isomerizing a stream comprising 2-butenes and n-butane, following the recovery stage.

18. The process according to claim 1, wherein the first and second distillation columns of the recovery stage are thermally integrated.

19. The process according to claim 1, further comprising: providing a reboiler heat to one distillation column of the recovery stage from a total or partial condensation of a stream from the top of another distillation column of the recovery stage.

20. The process according to claim 1, further comprising: providing a reboiler heat to one distillation column of the recovery stage and to a distillation column for removal of heavy products in the further conversion stage from a total or partial condensation of a stream from the top of another distillation column of the recovery stage.

21. The process according to claim 9 or 18, wherein the first and second distillation columns of the recovery stage are thermally integrated with an alcohol recovery column.

22. The process according to claim 21, further comprising: providing a partial or total condensation of a vapor from a top of the alcohol recovery column as a reboiler to the first and second distillation columns of the recovery stage.

23. The process according to claim 22, further comprising: providing a reboiler heat to the first and second distillation columns of the recovery stage by a total or partial condensation of the vapor from the top of the alcohol recovery column and from the first or the second distillation column of the recovery stage.

24. A process, comprising: an initial conversion stage of converting isobutene from a FCC or stream cracking C4 hydrocarbon mixture comprising isobutene, n-butane, iso-butane, 1,3-butadiene, 1-butene, and a 2-butene by performing at least one of: etherifying the isobutene with an alcohol; dimerizing the isobutene in the presence of an alcohol; dimerizing the isobutene in the presence of water; and dimerizing the isobutene in the presence of an ether, wherein the initial conversion stage is conducted in two reaction steps, each reaction step occurring by (i) performing the converting in at least one reactor, optionally with intermediate cooling, and then immediately (ii) performing a single distillation in a distillation column that is separate from the at least one reactor and is suitable for recovery of an initial reaction product; then, immediately following the initial conversion stage, a further conversion stage of completely removing isobutene from the initial reaction product in a reactor or reactors in series, thereby producing a further reaction product comprising at least one oxygenated compound comprising dimethyl ether; recovering excess alcohol if present in the initial reaction product or in the further reaction product; removing the dimethyl ether and any other oxygenated compounds from the further reaction product produced in the further conversion stage, by distillation in a distillation column downstream therefrom; and a recovery stage that is performed by recovering 1-butene with at least a first distillation column having an outflow that is an inflow to a second distillation column, thereby obtaining a high-purity 1-butene.

25. The process according to claim 1, wherein the recovery stage is performed such that the outflow of the first distillation column is a bottom product comprising the 1-butene and a mixture of heavy compounds, and the high-purity 1-butene is obtained as a distillate of the second distillation column.

26. The process according to claim 3, wherein the initial conversion stage comprises dimerizing the isobutene in the presence of a linear alcohol having a number of carbon atoms of between 1 and 5.

27. The process of claim 1, wherein each reaction step of the initial conversion stage occurs by (i) performing the converting in the at least one reactor, then immediately (ii) performing the intermediate cooling of reactor contents, and then immediately (iii) performing the single distillation of the reactor contents in the distillation column that is separate from the at least one reactor and is suitable for recovery of the initial reaction product.

28. The process of claim 24, wherein each reaction step of the initial conversion stage occurs by (i) performing the converting in the at least one reactor, then immediately (ii) performing the intermediate cooling of reactor contents, and then immediately (iii) performing the single distillation of the reactor contents in the distillation column that is separate from the at least one reactor and is suitable for recovery of the initial reaction product.

Description

EXAMPLE 1

(1) This example shows the limits of a 1-butene recovery plant, having a configuration similar to that shown in FIG. 1, if ethanol is used instead of methanol in the isobutene conversion section (etherification reaction).

(2) Assuming that 100 Kg/hour of C.sub.4 charge is fed (stream 1 of FIG. 1) having the following composition:

(3) TABLE-US-00004 Isobutene 46% wt 1-Butene 30% wt iso + n-Butane 8% wt 2-Butenes 15% wt C.sub.3 and C.sub.5 1% wt
and using a double-stage etherification plant configuration for the removal of isobutene, it is possible to obtain conversions of isobutene of 99.8% in the case of the production of MTBE but only 99% in the case of ETBE, as shown in Table 4.

(4) TABLE-US-00005 TABLE 4 Case: Methanol Case: Ethanol MTBE, Kg/h 72.1 ETBE, Kg/h 83.0 Isobutene conversion, % 99.8 99.0 Isobutene in residual C.sub.4, % 0.17 0.83 Isobutene in 1-Butene, % wt 0.30 1.47

(5) Upon passing therefore from methanol to ethanol, there is a clear increase in the overall production of ether, due to the effect of the higher molecular weight of the ethanol, but the total conversion of isobutene decreases with a consequent increase in the concentration of isobutene in the residual C.sub.4 and production of a 1-butene outside specification.

EXAMPLE 2

(6) This example, instead, shows how the use of the process of the present invention allows the conversion of isobutene to be kept constant in the passage from MTBE to ETBE, consequently continuing to produce a polymer grade 1-butene.

(7) The use of an additional isobutene conversion section, in fact, according to what is shown in FIG. 3, allows, with respect to a traditional MTBE case, a slight increase in both the production of ether and the conversion of isobutene, consequently succeeding in obtaining a 1-butene with a higher degree of purity as shown in table 5.

(8) TABLE-US-00006 TABLE 5 Modified MTBE Synthesis ETBE synthesis FIG. 1 FIG. 3 Isobutene conversion, % 99.80 99.84 Ether, Kg/h 72.1 83.7 Isobutene in residual C.sub.4, % 0.17 0.14 Isobutene in 1-Butene, % wt 0.30 0.25

EXAMPLE 3

(9) This example shows the possible integration of a classical 1-butene recovery scheme (etherification+fractionation) with the additional conversion sections of isobutene and skeletal isomerization of the stream of C.sub.4 heavy, mainly containing 2-butenes and n-butane.

(10) A feeding of 100 Kg/hour of C.sub.4 feedstock is still assumed having the following composition:

(11) TABLE-US-00007 Isobutene 46.0% wt 1-Butene 30.0% wt iso + n-Butane 8.0% wt 2-Butenes 15.0% wt 1,3-Butadiene 0.1% wt C.sub.3 and C.sub.5 1.0% wt
with a reaction scheme similar to that shown in FIG. 13 and a relatively high 1-butene recovery (90%), value close to the limit in industrial practice for this technology.

(12) With this new scheme, it is therefore possible to be able to increase both the productions of ETBE and of 1-butene as shown in table 6, at the same time maintaining the products quality specifications unaltered; it is obviously necessary to draw a limited purge (30%) of the stream sent to the isomerization section to avoid the accumulation of saturated inert hydrocarbons.

(13) TABLE-US-00008 TABLE 6 ETBE 3 stages + ETBE 3 stages Skeletal isom. FIG. 3 FIG. 13 Conv. Isobutene 99.84 99.84 ETBE, Kg/h 83.7 92.2 Isobutene in residual C.sub.4, % 0.14 0.09 Isobutene in 1-Butene, % w 0.25 0.22 1-Butene produced, Kg/h 27.1 30.1

(14) The presence of the selective hydrogenation unit ensures that the specification of 1-butene is respected also for the butadiene content, as shown in Table 7.

(15) TABLE-US-00009 TABLE 7 1,3-Butadiene in stream 1, % wt 0.100 1,3-Butadiene in stream 15, % wt 0.120 1,3-Butadiene in stream 18, % wt 0.001 1,3-Butadiene in 1-Butene, % wt 0.002