Reaction and distillation device and etherification process

Details Reaction and distillation device and etherification process Reaction and distillation device and etherification process

2000-09-07

2002-10-29

Keys, Rosalynd (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

C568S699000, C203S002000, C203S029000, C203S075000, C203S099000, C203SDIG006, C203SDIG001

Reexamination Certificate

active

06472568

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a reaction and distillation device and to a process for preparing a tertiary alkyl ether by reaction of at least one olefin with an aliphatic monoalcohol, generally in excess.
BACKGROUND OF THE INVENTION
It is well-known to prepare tertiary alkyl ethers by reacting an iso-olefin generally contained in a hydrocarbon fraction with an aliphatic alcohol, generally used in excess, in the presence of an acid catalyst, for example sulfuric acid, hydrofluoric acid, aluminium chloride or boron fluoride, or in the presence of carbonaceous matter containing sulfonic groups (−SO3H), for example sulfonated coal, sulfonated phenol-formaldehyde resins, sulfonated coumarone-indene polymers or preferably sulfonated styrene-divinylbenzene copolymer resins or other compounds, notably mineral compounds, comprising sulfonic groups (for example sulfonated polysiloxanes).
It has been known for a long time that the reaction between an aliphatic monoalcohol and a tertiary olefin is balanced and that it is difficult to obtain iso-olefin conversion coefficients with a high purity and yield. Conventional processes such as those described for example in Hydrocarbon Technology International, Autumn 95, p. 21-27, comprise one or more reactor(s) for etherification to tertiary alkyl ethers followed by at least one fractionating zone, generally a distillation zone, whose bottom product is ether containing the lowest possible amount of monoalcohol(s).
This is the reason why the prior art recommended, in order to improve the performances of this synthesis, to add a complementary reaction section to the main reactor, as described for example in patent U.S. Pat. No. 5,364,975 in the name of the applicant. In this patent, the complementary reaction section is included, according to a preferred embodiment, in the reflux device of the fractionating section. It has also been proposed, for example in patent U.S. Pat. No. 4,503,265 or in patent applications WO-A-93/19,031 and WO-A-93/19,032, to draw off a product from an intermediate tray of the fractionating section, to feed this product into a complementary reaction section and to feed the product from this complementary reaction section back into the fractionating section at a level below the draw-off level. The drawback of this embodiment is that it disrupts the smooth running of the distillation process in the fractionating section. A process of the UOP Company known as Ethermax, wherein the effluent from the main etherification section is fed into a distillation-reaction zone, has also been described for example in Hydrocarbon Processing, March 1995, p. 114. As shown hereafter in a comparative example, this process has the drawback of requiring a column of very great height to obtain a very appreciable improvement of the global performances. These conventional processes for preparing tertiary alkyl ethers will be described hereafter in connection with
FIGS. 1
,
2
and
3
.
One of the objects of the invention is to overcome the main drawbacks of the processes described in the prior art and to propose several ether synthesis embodiments allowing to maximize global conversion of the iso-olefins contained in hydrocarbon cuts.
The feed consisting of a mixture of C4, C5, C6 or C7 hydrocarbons comprising iso-olefins and at least one aliphatic monoalcohol generally used in excess is fed into the main reaction section represented by reactor R
1
in
FIGS. 1
to
9
. The mixed reactants are brought into contact with an acid catalyst.
The product from this reaction section R
1
is fed into a distillation zone represented by column F
1
in
FIGS. 1 and 2
and by column F
2
in FIG.
3
. It is distilled in this column in order to produce, at the bottom, through line
9
, a tertiary alkyl ether containing the lowest possible amount of monoalcohol(s), and at the top, through line
2
, a mixture of reactive and non reactive hydrocarbons and of aliphatic monoalcohol(s) carried over by azeotropy. This effluent flowing out through line
2
is condensed in condenser E
1
and collected through line
3
in drum B
1
prior to flowing into pump P
1
through line
4
.
In the instance schematized in
FIG. 1
patent U.S. Pat. No. 5,364,975), part of the effluent leaving pump P
1
is fed through line
10
into a reactor R
2
referred to as finishing reactor, whose effluent is fed through line
12
into column F
1
as reflux and the rest of the effluent flows off as distillate through line
6
.
In the embodiment schematized in
FIG. 2
(patent U.S. Pat. No. 4,503,265), a product is drawn off from an intermediate tray of the distillation column between the effluent introduction point of etherification reactor R
1
and the top of this column, and this product is fed through line
10
into a reactor R
2
referred to as finishing reactor, whose effluent is fed through line
12
into column F
1
at a level below the level of the draw-off point. In the instance schematized in
FIG. 2
, part of the effluent flowing out of pump P
1
is fed through line
5
into column F
1
as reflux and the rest of the effluent flows off as distillate through line
6
.
In the embodiment schematized in
FIG. 3
(Hydrocarbon Processing, March 1995, p.114), the effluent of the reaction section R
1
is fed into a distillation-reaction column beneath the first catalyst bed and part of the effluent flowing out of pump P
1
is fed through line
5
into column F
2
as reflux and the rest of the effluent flows off as distillate through line
6
.
However, such a process requires in the instance schematized in
FIG. 3
a great number of reaction zones in distillation-reaction column F
2
in order to obtain high conversions into iso-olefins and consequently a column of great height. In fact, obtaining high conversions requires a distillation-reaction column containing many reaction zones. Insofar as one of these zones alone occupies about 3 meters in height in the distillation-reaction column, the final height of this column quickly becomes limitative. It would therefore be interesting to have such a high conversion to iso-olefins while keeping a limited number of reaction zones in the column and/or to limit the height of the column. This is one of the objectives of the invention as described hereafter in connection with
FIGS. 4
,
5
,
6
,
7
,
8
and
9
.
DESCRIPTION OF THE INVENTION
The present invention thus relates to a distillation and reaction device comprising:
a) a reaction section,
b) a distillation-reaction section comprising a distillation zone, comprising at least one means intended for circulation of the effluent from the reaction section to said distillation zone, and at least one distillation-reaction zone, comprising at least one catalyst bed, said distillation-reaction zone being distinct from the distillation zone and providing at least partly, preferably for the most part most preferably practically entirely the reflux of the distillation zone.
The device according to the invention preferably comprises at least one means intended for circulation of the effluent between the top of the distillation zone and the bottom of the distillation-reaction zone and at least one means intended for circulation of the effluent between the bottom of the distillation-reaction zone and the top of the distillation zone.
The device according to the invention preferably also comprises at least one means for feeding the reaction section and at least one means for drawing off product at the bottom of the distillation zone.
According to one of the embodiments of the invention, independent or not of the previous embodiments, the device according to the invention is such that the distillation-reaction zone comprises at least one reflux device, which generally comprises at least one draw-off means situated at the top of the distillation-reaction zone, feeding at least one condensation zone, at least one means intended for circulation of part of the effluent from said condensation zone towards the top of the distillation-reaction zone and at least one means for drawing o

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