METHOD FOR SEPARATING NON-LINEAR OLEFINS FROM AN OLEFIN FEED BY REACTIVE DISTILLATION

Abstract

The present invention relates to a process for treating, by reactive distillation, an olefinic feedstock comprising linear olefins containing n carbon atoms, and branched olefins, the branched olefins comprising tertiary branched olefins, for example a mixture of n-butenes and of tertiary branched olefins comprising isobutene, so as to produce an olefinic effluent with a mass content of tertiary branched olefin of less than or equal to 3% by weight and a heavy hydrocarbon effluent, said process comprising the feeding of a reactive distillation section with said olefinic feedstock and with an alcohol feedstock comprising a primary alcohol, said reactive distillation section comprising a column composed at least of an upper reflux zone into which is introduced said alcohol feedstock, comprising, for example, ethanol, an intermediate reaction zone comprising at least 6 reactive doublets, and a lower fractionation zone at the level of which said section is fed with said olefinic feedstock, said reactive distillation section being operated at a relative pressure of between 0.3 and 0.5 MPa, a column head temperature of between 40° C. and 60° C., with a reflux ratio of between 1.8 and 2.2.

Claims

1. A process for treating, by reactive distillation, an olefinic feedstock comprising linear olefins containing n carbon atoms, n being an integer between 4 and 10, and branched olefins, the branched olefins comprising tertiary branched olefins, so as to produce an olefinic effluent with a mass content of tertiary branched olefins of less than or equal to 3% by weight and a heavy hydrocarbon effluent, said heavy hydrocarbon effluent being an effluent comprising at least 50% by weight of hydrocarbons comprising more than n carbon atoms, said process comprising the feeding of a reactive distillation section with said olefinic feedstock and the feeding of said reactive distillation section with an alcohol feedstock, said alcohol feedstock comprising at least one primary alcohol, characterized in that: said reactive distillation section comprises a column comprising a column head reflux zone, an intermediate reaction zone comprising at least 6 reactive doublets, each reactive doublet comprising a catalytic bed followed by a separating theoretical plate, and a lower fractionation zone comprising between 5 and 25 theoretical plates, said reactive distillation section is operated at a relative column head pressure in the reflux zone of between 0.3 and 0.5 MPa, a column head temperature in the reflux zone of between 40° C. and 60° C. and a molar reflux ratio of between 1.8 and 2.2, said reactive distillation section is fed with said olefinic feedstock in the fractionation zone of the column and with alcohol feedstock in the reflux zone, such that the mole ratio of the primary alcohol introduced relative to the tertiary branched olefins, having a number of carbon atoms of less than or equal to (n+1), of the olefinic feedstock is between 0.8 and 1.1.

2. The process as claimed in claim 1, in which the olefinic feedstock comprises a mixture of n-butenes and of branched olefins comprising isobutene and tertiary branched olefins containing 5 carbon atoms.

3. The process as claimed in claim 1, in which the column head reflux zone is composed of two or three theoretical plates.

4. The process as claimed in claim 1, in which the intermediate reaction zone comprises between 6 and 12 reactive doublets.

5. The process as claimed in claim 1, in which the catalytic bed comprises a cation-exchange resin.

6. The process as claimed in claim 1, in which the lower fractionation zone comprises between 7 and 23 theoretical plates.

7. The process as claimed in claim 1, in which the feeding with said olefinic feedstock is located in the upper third of the fractionation zone.

8. The process as claimed in claim 1, in which the olefinic feedstock is in gaseous form and the alcohol feedstock is in liquid form.

9. The process as claimed in claim 1, in which the primary alcohol of the alcohol feedstock introduced into the column reflux zone is ethanol.

10. The process as claimed in claim 1, in which the mole ratio of primary alcohol introduced relative to the tertiary branched olefins with a number of carbon atoms of less than or equal to (n+1) of the olefinic feedstock is between 0.9 and 1.0.

11. The process as claimed in claim 1, in which the relative column head pressure in the reflux zone is between 0.35 and 0.40 MPa.

12. The process as claimed in claim 1, in which the column head temperature in the reflux zone is between 45° C. and 55° C.

13. The process as claimed in claim 1, in which the molar reflux ratio is between 1.9 and 2.1.

14. A process for the isomerizing dehydration of a feedstock comprising from 40% to 100% by weight of an alcohol substituted in position 2 with an alkyl group and the hydroxyl group —OH of which is borne by a primary carbon atom, said dehydration process comprising at least one step of converting said substituted alcohol into olefins and a step involving the process as claimed in claim 1 for treating the olefinic raffinate produced in the conversion step.

Description

FIGURE(S)

[0066] FIG. 1: Scheme of the reactive distillation section of the process according to the invention, said reactive distillation section comprising a reflux zone at the top of the column into which is introduced the reflux (4), an intermediate reaction zone (5) comprising at least 6 reactive doublets and a lower fractionation zone (6) comprising between 5 and 25 theoretical plates, said reactive distillation section being fed with the olefinic feedstock (1) in the fractionation zone (6) of the column and with the alcohol feedstock in the reflux zone of the column, the olefinic effluent (3) being extracted at the top of the column and the heavy hydrocarbon effluent (7) at the bottom of the column.

EXAMPLES

[0067] The examples that follow are based on process simulations integrating thermodynamic data matching experimental points (binary liquid-vapor equilibrium data, liquid-liquid partition coefficient and degree of conversion of the etherification reaction as a function of the operating conditions).

Example 1 (in Accordance)

[0068] An olefinic feedstock, obtained from the dehydration of isobutanol, comprising 21.8% by weight of isobutene and 2.15% of tertiary branched C5 olefins, feeds, in gaseous form, a reactive distillation column including 42 theoretical plates in total and equipped with a reflux system with a condenser. A stream of ethanol (EtOH) in liquid form is injected into the column in the reflux zone, on theoretical plate 3. The catalyst used is a sulfonic acid resin, Amberlyst® 15, sold by Dow.

[0069] Several tests are performed, varying a few parameters, in particular the localization of the feed on the column and the number of reactive doublets. The column characteristics and the operating conditions are summarized in Table 1.

[0070] Table 1 also relates, for each test performed, the results obtained in terms of content of tertiary branched C4 olefins (i.e. olefins containing 4 carbon atoms, i.e. isobutene) and C5 olefins of the effluent recovered at the top and the total losses of ethanol. The ethanol losses (weight %) are calculated in the following manner:

[00001]$100\times \frac{\begin{array}{c}\left(\mathrm{amount}\mathrm{of}\mathrm{ethanol}\mathrm{in}\mathrm{the}\mathrm{top}\mathrm{effluent}\right)+\\ (\mathrm{amount}\mathrm{of}\mathrm{ethanol}\mathrm{in}\mathrm{the}\\ \mathrm{bottom}\mathrm{heavy}\mathrm{hydrocarbon}\mathrm{effluent})\end{array}}{\left(\mathrm{amount}\mathrm{of}\mathrm{ethanol}\mathrm{introduced}\right)}$

[0071] It is seen from Table 1 that the objective as regards the content of isobutene tertiary branched olefins and tertiary branched C5 olefins (less than or equal to 3% by weight) in the effluent extracted at the top is achieved, irrespective of the parameters used, and for limited ethanol losses (<10% by weight).

TABLE-US-00001 TABLE 1 Column characteristics, operating conditions used and performance obtained (content of tertiary branched C4 and C5 olefins of the olefinic effluent and ethanol losses) Test 1 (in Test 2 (in Test 3 (in accordance) accordance) accordance) Isobutene content of the feedstock 21.8% 21.8% 21.8% (weight %) Tertiary branched C5 olefins content of the 2.15 2.15 2.15 feedstock (weight %) Total number of theoretical plates 42 42 42 Number of reactive doublets 6 8 10 Catalyst Amberlyst ® 15 Amberlyst ® 15 Amberlyst ® 15 First/last theoretical plate of the reaction 5/16 5/20 5/24 section Number of theoretical plates in the 25 21 17 fractionation zone EtOH injection theoretical plate* 3 3 3 Feedstock injection theoretical plate* 18 22 26 EtOH/isobutene mole ratio 1.025 1.025 1.025 EtOH/tertiary branched C4 and C5 olefins 0.95 0.95 0.95 mole ratio Relative head pressure (MPa) 0.37 0.37 0.37 Head temperature (° C.) 50 50 50 Molar reflux ratio 2.06 1.97 1.97 Tertiary branched C4 and C5 i olefins  <3%  <3%  <3% content of the effluent (weight %) EtOH losses (weight %) <10% <10% <10% *the theoretical plates being numbered in the direction of flow of the liquid in the column, i.e. from the top to the bottom of the column, the condenser being counted as plate 1, the reflux being injected at plate 2

[0072] Table 2 collates the mass compositions of the feedstock and of the olefinic effluent extracted at the top in the case of test 2.

[0073] Table 2 shows that the content of tertiary branched olefins (2.76% by weight), i.e. of isobutene and tertiary branched C5 olefins, in the head olefinic effluent less than 3% by weight relative to the total weight of the olefinic effluent.

[0074] From Table 2, it is also seen that the column allows good separation of the butenes from the heavy hydrocarbon compounds (impurities) contained in the feedstock. Specifically, the hydrocarbon impurities, which represent 10.57% by weight of the olefinic feedstock, represent no more than 0.3% in the olefinic effluent recovered at the top (the ethanol introduced as alcohol feedstock is not counted).

TABLE-US-00002 TABLE 2 Mass compositions of the olefinic feedstock and of the olefinic effluent extracted at the top Compositions (weight %) FEEDSTOCK EFFLUENT Cis-2-BUTENE 21.34 30.02 Trans-2-BUTENE 30.56 43.19 1-BUTENE 15.56 22.04 ISOBUTENE 21.80 2.76 H2O 0.16 0.23 ETHANOL 0.00 1.47 ACETIC ACID 0.35 0.00 TERTIARY BRANCHED C5 2.15 0.00 OLEFINS ISOBUTANAL 0.07 0.00 BUTANOL 0.01 0.00 s-BUTANOL 0.04 0.00 t-BUTANOL 0.03 0.00 i-BUTANOL 2.36 0.00 2,3,3-TRIMETHYL-1-BUTENE 0.54 0.00 2,4,4-TRIMETHYL-1-PENTENE 4.26 0.00 ETBE 0.00 0.00 OTHER HYDROCARBONS 0.76 0.29

Example 2 (not in Accordance)

[0075] Introduction of Ethanol into the Feedstock Upstream of the Column

[0076] An olefinic feedstock, obtained from the dehydration of isobutanol, comprising 21.8% by weight of isobutene and 2.15% by weight of tertiary branched C5 olefins, is treated by means of a process involving a reactive distillation column. A stream of ethanol is introduced into the feedstock upstream of the reactive distillation column. The catalyst used is a sulfonic acid resin, Amberlyst® 15, sold by Dow.

[0077] Table 3 collates the parameters used (column characteristics and operating conditions) and the performance of the reactive distillation section in terms of isobutene content of the olefinic effluent extracted at the top and ethanol losses.

[0078] The content of tertiary branched C4 and C5 olefins in the head effluent is equal to 23.4% by weight. It is thus much higher than the targeted objective (less than or equal to 3% by weight). The ethanol losses are also very high (90.0% by weight). The tertiary branched olefins of the feedstock were virtually not converted into ethers and were thus not able to be separated from the linear butenes when the ethanol is introduced into the column with the feedstock.

TABLE-US-00003 TABLE 3 Column characteristics, operating conditions used and performance obtained (content of tertiary branched C4 and C5 olefins of the olefinic effluent and ethanol losses) Test not in accordance Isobutene content of the feedstock 21.8% (weight %) Tertiary branched C5 olefins content of the 2.15 feedstock (weight %) Total number of theoretical plates 42 Number of reactive doublets 8 Catalyst Amberlyst ® 15 First/last theoretical plate of the reaction 5/20 section Number of theoretical plates in the 21 fractionation zone Injection of EtOH into the feedstock Feedstock injection theoretical plate* 22 EtOH/isobutene mole ratio 1.025 EtOH/tertiary branched C4 and C5 olefins 0.95 mole ratio Relative head pressure (MPa) 0.37 Head temperature (° C.) 47 Molar reflux ratio 1.97 Tertiary branched C4 and C5 olefins 23.4% content of the effluent (weight %) EtOH losses (weight %) 90.0% *the theoretical plates being numbered in the direction of flow of the liquid in the column, i.e. from the top to the bottom of the column, the condenser being counted as plate 1, the reflux being injected at plate 2

Example 3 (not in Accordance)

[0079] Several Relative Column Head Pressures not in Accordance with the Present Invention are Tested.

[0080] An olefinic feedstock, comprising 21.8% by weight of isobutene and 2.15% of tertiary branched C5 olefins, is injected into the reactive distillation column in gaseous form. A stream of ethanol, in liquid form, is introduced into the column at the level of the reflux zone. The catalyst used is a sulfonic acid resin, Amberlyst® 15, sold by Dow.

[0081] Table 4 collates the column characteristics, the operating conditions used and the performance of the reactive distillation section (content of tertiary branched C4 and C5 olefins of the head effluent and ethanol losses).

TABLE-US-00004 TABLE 4 Column characteristics, operating conditions and performance obtained (content of tertiary branched C4 and C5 olefins of the olefinic effluent and ethanol losses) Test a Test b (not in accordance) (not in accordance) Isobutene content of the feedstock 21.8% 21.8% (weight %) Tertiary branched C5 olefins content of 2.15 2.15 the feedstock (weight %) Total number of theoretical plates 42 42 Number of reactive doublets 8 8 Catalyst Amberlyst ® 15 Amberlyst ® 15 First/last theoretical plate of the reaction  5/20  5/20 section Number of theoretical plates in the 21 21 fractionation zone EtOH injection theoretical plate* 3 3 Feedstock injection theoretical plate* 22 22 EtOH/isobutene mole ratio 1.025 1.025 EtOH/tertiary branched C4 and C5 olefins 0.95 0.95 mole ratio Relative head pressure (MPa) 0.29 0.7 Column head temperature (° C.) 43 71 Molar reflux ratio 1.97 2.02 Min/max temperatures in the 43/74 75/85 catalytic section Tertiary branched C4 and C5 olefins 3.07% >3.0% content of the effluent (weight %) EtOH loss (weight %) <10% 12% *the theoretical plates being numbered in the direction of flow of the liquid in the column, i.e. from the top to the bottom of the column, the condenser being counted as plate 1, the reflux being injected at plate 2

[0082] From Table 4, when the relative column head pressure is low (0.29 MPa), the content of tertiary branched C4 and C5 olefins in the effluent extracted at the top is greater than 3% (3.07%). When the relative column head pressure is low, the conversion of the tertiary branched olefins into ethers is insufficient to allow efficient separation and consequently to achieve a content of tertiary branched olefins of less than or equal to 3% by weight in the head olefinic effluent.

[0083] When the relative column head pressure is high (0.7 MPa), greater than 0.5 MPa, the temperature in the reaction section varies and becomes higher than 80° C. Beyond this temperature, the etherification reaction is no longer optimal and the unconverted tertiary branched olefins become readily oligomerized on contact with the acid catalyst. Thus, the ethanol is less consumed, leading to increased ethanol losses. The content of tertiary branched olefins in the olefinic effluent also increases.