MXPA98001343A - Process of production of tertiary olefins by the decomposition of eter alquilico tercia - Google Patents

Abstract

The present invention relates to a process for the production of a tertiary olefin by the decomposition of the tertiary alkyl ether which comprises a) the decomposition of at least one ether in a product containing an alcohol and a tertiary olefin, b) the fractionation of at least one part of the product from a) to a fractionation zone (C1) which makes it possible to obtain on the one hand the tertiary olefin and on the other hand the alcohol, c) the purification of at least a part of the tertiary olefin obtained in stage b) wherein said part is sent to an extraction zone (L1) by washing with the water from which a fraction (D) containing the tertiary olefin is recovered, and d) and a step in which at least one part of the fraction (D) leaving C) is sent to a separation zone (Co) from which an aqueous liquid fraction (Le) and a liquid hydrocarbon fraction (LC) containing most of the olefin to tertiary

Description

PROCESS OF PRODUCTION OF TERTIARY OLEFINS BY THE DECOMPOSITION OF TERQUEARY ALKYL ETHER Field of the Invention The present invention relates to a process for the decomposition of high purity tertiary olefin (s). It refers in particular to a process of production of isobutene of very high purity, and methanol, from the methyl ether of tert-butyl alcohol (MTBE) by the English initials of Methyl Tertio-Butyl-Ether). The process according to the present invention is applied to the synthesis of any tertiary olefin from the tertiary alkyl ether [for example ETBE (ethyl ether of tert-butyl alcohol by the English initials of Ethyl-Tertium-Butyl-Ether), ETAE (methyl ether tertioamyl alcohol by the English initials of Tertio-Ayl-Methyl-Ether), TAME, isopropyl-tertium-butyl-ether ether]. The description that follows, and very particularly the operating conditions, are given as an indication for the synthesis of isobutene from MTBE.

Ref.026813 Background of the Invention There are several production routes of high purity isobutene exploited industrially. The oldest is the process for the extraction of sulfuric acid, but it is expensive and obsolete; It is famous polluter because it produces rejections of the acid used. In addition, the yield of isobutene does not exceed 90%. The firm ARCO uses the route by dehydration of tertiary-butyl alcohol (ABT), the latter is a by-product obtained with its production process of propylene oxide. The process for the dehydrogenation of isobutane has been developed over the last few years due to a significant and growing demand for MTBE. However, this process is not used profitably more than for very high production capacities. The production of high purity isobutene by fractionation of MTBE has also been well adapted for both small capacities and large capacities. In addition, this route benefits any infrastructure in relation to the growing importance of ethers in the reformulated essences. Numerous refineries, all over the world, have facilities for the production of MTBE, for example. On the other hand, there is also an MTBE exchange market worldwide. This means that the production of high purity isobutene, from MTBE, can be obtained or put into operation worldwide, even externally to refineries. The idea of producing isobutene by decomposition of the ether, and more particularly of MTBE, has been known for some time, but the procurement processes proposed by the prior art present certain drawbacks. Thus, in the process developed by SUMITOMO, described for example in patent application EP-A-68 785, the decomposition reaction of MTBE is carried out in liquid phase, in the presence of an acid solid catalyst of the exchange resin type. ions. Two streams of the product are obtained: isobutene and methanol. As described in the scheme, isobutene is obtained directly at the top of a distillation column without another purification step. The isobutene thus obtained contains a certain number of impurities, starting with a small fraction of methanol that is distilled by azeotropy, the dimethyl ether (DME) volatile compound formed by the condensation of methanol in the presence of an acid catalyst. It is likely that the purity of isobutene is then insufficient for use such as in the manufacture of polyisobutene or other copolymers. In addition, no means apparently allows the accumulation of heavy impurities such as the dimers of isobutene or the methyl ether of secondary butyl alcohol (MSBE) to be prevented, which in the end fatally results in a low purity of the products. In the process developed by ERDOLCHEMIE, described for example in the patent US-A-4 409 421, the purification of isobutene, which consists of eliminating the residual alcohol entrained with the tertiary olefin, is carried out by adsorption. This method has the disadvantage of having to regenerate the adsorbent regularly. In addition the recovery of most of the alcohol left from the decomposition is not solved. More recently, the same company discloses, in US-A-5 095 164, the start-up of the decomposition reaction in a distillation apparatus. The catalyst is then placed at the bottom of the column at the level of the reboiler. This particular operation is limiting on the plane of the reaction temperature, imposed directly by the nature of the ether and the operating pressure. In addition, it probably favors the formation of reaction by-products such as the formation of isobutene dimers and / or the formation of dimethyl ether. For this purpose, the quality and / or development of the products is not clearly explained. On the other hand, the company BASF describes, in the patent US-A-4 287 379, a scheme that integrates at the same time the stage of synthesis of the ether, its separation then the decomposition step of the ether to produce the isobutene. However, to avoid certain stages of the purification, the etherification is made with an alcohol with 3 or 4 carbon atoms, which is a major drawback to the international MTBE market. Finally, we can mention the two SNAMPROGETTI process schemes presented in Chemical Economy &; Engineering Review, vol. 14 No. 6 June 1982, which include both the stage of synthesis of MTBE and the stage of decomposition of MTBE for the production of isobutene. It seems in these schemes that a certain loss of water by entrainment and / or saturation of the flow of isobutene, at the level of the washing of isobutene to remove alcohol, is not taken into account. This can be translated in the end either in a reduction of the flow rate of the washing water, or in a loss of the efficiency of this washing section. This can then impair the quality of the isobutene produced. On the other hand, according to these schemes, the hydrocarbon fraction leaving the water extraction column containing a relatively large amount of free water, is sent in its entirety to the fractionation column that allows to recover the purified isobutene, which implies that this column it must treat a quantity of the important product and thus have the important sizing characteristics which makes the process particularly burdensome and delicate for its operation. The process according to the invention makes it possible to remedy the aforementioned drawbacks. It refers to a production process of the tertiary olefin (s) characterized by a very high purity, starting from a tertiary alkyl ether. The invention relates to a process of decomposition of the tertiary alkyl ether (s), in particular such as that defined above, preferably MTBE or ETBE. , for the production of tertiary olefin (s), of isobutene in particular, of high purity. In the case of the decomposition of other ethers, a mixture containing a plurality of tertiary olefins can be obtained. Thus, in the case of decomposition of TAME, a mixture is obtained which contains 2-methyl-l-butene and 2-methyl-2-butene. In addition to the reaction zone itself, the process according to the invention comprises purification or recovery zones or the recycling of the various products in such a way that the evaluation of the products obtained is optimized and losses are minimized. The present invention relates to a process for the production of tertiary olefins by the decomposition of tertiary alkyl ether comprising: a) a stage of decomposition of at least one tertiary alkyl ether in a reaction zone comprising at least one reactor (Rl) containing a decomposition catalyst of said ether, the step is carried out under conditions that allow decomposition at least of said tertiary alkyl ether in a product containing at least one alcohol and at least one tertiary olefin, b) a stage of fractionation of at least part of the product from step a), and preferably of the whole of this product, in a fractionation zone (Cl) that allows obtaining on the one hand a fraction (A) that contains most of the tertiary olefin and optionally a minor fraction of the alcohol and optional light compounds generally contained initially in the product from step a), and on the other hand a fraction (B) containing most of the alcohol formed in step a) and possibly the ether not decomposed in step a), c) a purification step of at least a portion of the fraction (A) in which said part is sent to an extraction zone (Ll) by washing with water, from which an aqueous fraction is obtained (C ) containing most of the alcohol initially present in said part and a fraction (D) containing most of the tertiary olefin initially present in said part, fraction (D) contains the tertiary olefin, water, optionally light compounds and they are substantially free of alcohol, the process is characterized in that it carries a step d) in which at least a part of the fraction (D) leaving the stage c) is sent to a separation zone (Co) from which an aqueous liquid fraction is recovered (Le) and a liquid fraction (Lc) containing most of the tertiary olefin initially present in the fraction (D), the fraction (Lc) contains the tertiary olefin, a reduced amount of water and optionally light compounds. In a particular embodiment of the process according to the invention, which makes it possible in general to obtain a tertiary olefin of high purity, at least a part of the liquid fraction (Lc) recovered in step d) is sent to a step e) towards a fractionation zone (C2) in which the part of the fraction (Lc) is fractionated on the one hand into a fraction (E) containing the tertiary olefin and on the other hand a fraction (F) that contains most of the compounds occasional light and occasionally a small amount of residual water. The fraction (F) can be excised in a gaseous fraction that is evacuated for example to the torch and in a liquid fraction that is sent back at least partly to the fractionation zone (C2) of stage e) [line (20b ) output of line (20) and / or line (22)]. According to this particular form, it is usually preferable that the fractionation zone of step e) has at least one medium that allows a light fraction that is substantially anhydrous to be recovered from fraction (F). More frequently this means will allow to excise or separate at least a part of the fraction (F) in a lightly anhydrous fraction and in an aqueous fraction. This means will be for example a separating ball flask provided with at least one medium, for example a boot, which allows the decanting and the transfer of an aqueous fraction. In this case at least part of the aqueous fraction obtained in step e) is preferably recycled to step c) in the extraction zone (Ll) by washing with the water. Then, the substantially anhydrous light fraction is usually cleaved or separated into a gas fraction which is evacuated for example to the torch and in a generally substantially anhydrous liquid fraction that is sent back at least partly to the fractionation zone (C2) from stage e). According to another mode of operation, the fraction (F) [or the light fraction obtained from said fraction (F)] that has left step e) is sent back at least partially to a catalytic fractionation zone. According to another variant, the fraction (F) [or the light fraction obtained from the fraction (F)], which has left the stage e), is sent back at least partially to an area of synthesis of the ether by the reaction between at least one tertiary olefin and at least one alcohol. According to still another variant, the fraction (F) [or the light fraction obtained from the fraction (F)], which has left the stage e), is at least partially sent towards the torch. More frequently the process of the present invention comprises a step f) in which at least a part of the aqueous fraction (C) exiting from step c) is sent to a fractionation zone (C3) from which it is recovered a fraction (G) containing most of the alcohol initially present in said part and an aqueous fraction (H) removed from most of the alcohol initially present in said part. According to this mode of operation, at least a part of the fraction (G) obtained in step f) containing the alcohol can be sent to an area of synthesis of the ether by the reaction between at least one tertiary olefin and at least one alcohol . It is also possible to send all of this alcohol to the ether synthesis zone. In the same way, this alcohol can be partially or completely recovered for other uses. According to this mode of operation, at least a part of the aqueous fraction (H) obtained in stage f) can also be recycled at least partly towards stage c) in the zone (Ll) extraction by washing with water. According to this mode of operation, at least a part of the aqueous fraction (H) obtained in step f) can also be sent at least partially to a water treatment section. In a preferred form of operation of the process of the present invention, at least a part of the fraction (B) obtained in step b), which contains most of the alcohol formed in step a) and possibly of the ether not decomposed in step a) can be sent to an area of synthesis of the ether by the reaction between at least one tertiary olefin and at least one alcohol. It is also possible to send the entire fraction to the synthesis zone of the ether. In the same way, this fraction can be recovered in part or in its entirety for other uses. In a preferred form of operation of the process of the present invention, at least a part of the aqueous fraction (Le) obtained in step d) is recycled to step c) in the extraction zone (Ll) by washing with water . These various water recycles are independent of each other and can be carried out jointly or separately. Water that is not recycled is usually purged then sent routinely to a treatment area for the water used. This purge is present more frequently at least on the aqueous fraction (H) obtained in step f). This purging makes it possible in particular to avoid an eventual accumulation of the so-called heavy compounds, for example heavy alcohols. The operating conditions of step a) of the present invention are the classical conditions of decomposition of the tertiary alkyl ether well known to the person skilled in the art. In a preferred embodiment this step a) will be put into operation without the addition of additional water to the product introduced in the decomposition zone. However, it will be possible to add a certain amount of water, for example up to the limit of the solubility of the water in the ether to be decomposed. Usually the starting conditions of this step a) are chosen so that most of the tertiary alkyl ether decomposes to obtain an alcohol and a tertiary olefin. In this decomposition zone the absolute pressure is usually between approximately 1 and approximately 12 bars (1 bar is equal to 0.1 Mpa), the temperature is usually between 50 ° C and 300 ° C, and preferably between 100 ° C and 250 ° C, WH (space velocity per hour) is usually between 0.1 and 200 h_1 and more frequently between 0.5 and 100 h "1. In this zone all acid catalysts well known to the expert in the art can be used. It is usually preferred to employ acidic solid catalysts, and the catalyst can also be selected from the group consisting of organic acid resins and mineral acid resins, which are generally solid under the conditions of the decomposition reaction of said ether. more often those chosen from the group consisting of grafted mineral solids carrying at least one organic group of the alkyl sulphonic type, aryl sulphonic or alkylaryl sulfonic. One of the preferred embodiments of this step a) uses a catalyst chosen from the group consisting of polysiloxanes grafted by at least one alkylsulfonic group. The general operating conditions of step b) of fractionation of the product from stage a) of decomposition of the ether, is a stage whose conditions are chosen in particular according to the characteristics of the alcohol and the tertiary olefin formed. The person skilled in the art also has to choose these conditions in order to obtain the desired separation between a fraction containing most of the alcohol and a fraction containing most of the olefin. A) Yes, as for example, in the case of the decomposition of MTBE and the formation of methanol and isobutene, the absolute pressure in the distillation column is from about 1 to about 15 bar, preferably from about 1 to about 10 bar, identical or different from the one in the decomposition zone. The temperature of the bottom of the column depends both on the pressure prevailing in said column and on the composition of the bottom product, in particular the molar ratio between the methanol and the MTBE optionally present after a partial decomposition of this ether in stage a). In the case of a unit treating 1 kg / h of MTBE, the distillation column usually takes 3. and 80 theoretical dishes and more frequently between 10 and 50 theoretical dishes. In step c) of purification of at least a part of fraction (A), the part of the fraction is sent to an extraction zone (Ll) by washing with water; the amount of water used for this washing is usually such that the volumetric ratio between the volume of said amount of water introduced in the extraction zone and that of the fraction part (A) introduced in the extraction zone (Vagua / VA ) is from about 0.005 to about 20. Most often this amount of water is such that the Vagua / VA ratio is from about 0.005 to about 10, preferably from about 0.01 to about 5, still more preferably from about 0.02 to about 1. The flow of water in this wash zone (Ll) is regulated more frequently depending on the maintenance of the bottom level in the fractionation zone (C3) of the water and alcohol in the case of the presence of such zone (C3) . This level of the fund can be defined as the minimum level necessary for the proper functioning of the area (C3). This parameter is a classic parameter well known to the person skilled in the art. This regulation is often done in a manual mode for operators, but it is possible that this regulation is carried out by an automatic regulation circuit called LCR by the Anglo-Saxon initials Level Control Regulation (Regulation by Level Control). Whichever mode of regulation is chosen, the amount of water can be adjusted in general with the aid of a means of introducing the complement water in the zone (Ll). This water supplement makes it possible in particular to compensate for water losses due to water drag and / or saturation of the treated hydrocarbon flow and replacement of the water purged, if necessary. This extraction zone (Ll) is usually a plate column operating at a temperature of about 1 to about 100 ° C, preferably about 10 to about 60 ° C. The absolute pressure in this zone will be from about 1 to about 20 bar, more frequent in the approximate form of 1 to about 15 bar, identical or different to that prevailing in the fractionation zone of step b). Step d) comprising a separation zone of at least a part of the fraction (D) of an aqueous liquid fraction (Le) and a liquid hydrocarbon fraction (Lc) in a zone (Co), is a well-known classical stage by the person skilled in the art. This stage is usually put into operation in an apparatus called a coalescer, in which water is collected in the lower part of the apparatus for coalescence. The prevailing temperature and pressure conditions in this zone are in the same ranges as those prevailing in stage c) of water extraction. The pressure (respectively the temperature) can be identical or different from that prevailing in the area (Ll) of stage c). In this zone, the free water contained in the product from stage c) is thus separated. In addition, this zone also has, more frequently, a zone or discharge ball function for the purification zone (C2) of isobutene, in the case of the presence of one of said zones (C2). Any other means known to the person skilled in the art can be employed within the framework of the present invention. By way of example, the use of an absorbent having a preferred selectivity for one of the aqueous or organic fractions can be mentioned. The step e) eventual fractionation of the fraction (Lc) in a zone (C2) of a fraction (E) containing the tertiary olefin and a fraction (F) containing most of the light compounds eventually present in said fraction (Lc) and the residual water contained in the liquid fraction (Lc), is usually effected in a distillation column operating under an absolute pressure of about 1 to about 15 bar, more frequently in an approximate form of 3 to about 10 bar, identical or different from that prevailing in the separation zone of step d). For a unit that produces 0.6 kg / h of isobutene, this column usually has in approximate form 3 to approximately 80 theoretical plates and more frequently in approximate form 5 to approximately 50 theoretical plates. The temperature of the bottom of the column depends in particular on the pressure in the column. The eventual stage f) of fractionation, in a zone (C3), of the aqueous fraction (C), which contains most of the alcohol initially present in the fraction (A), of a fraction (G) that contains the greater part of the alcohol initially present in fraction (C) and of an aqueous fraction (H) released from most of the alcohol initially present in fraction (C), is usually made or obtained in a distillation column (C3) under a pressure absolute from about 1 to about 12 bar, preferably from about 1 to about 8 bar, identical or different from that prevailing in the water extraction zone of step c). The temperature of the bottom of the column depends in particular on the pressure in the column; it is usually in the form of about 50 to about 300 ° C and more frequently about 65 to about 200 ° C. The column usually ranges from about 2 to about 80 plates and more frequently from about 3 to about 60 theoretical plates. Figure 1 is a schematic of the principle illustrating one of the preferred variants of putting into operation the present invention. The strokes with dashed lines show the various possible options. The charge containing the tertiary alkyl ether is introduced by line 1 to the reactor (Rl) for decomposition of said ether. This reactor contains an acid catalyst. The decomposition product leaves the reactor (Rl) and is sent to a fractionation column (Cl) on line 2 from which a product containing a tertiary effine is recovered on line 4 and a product on line 3 which contains an alcohol and if necessary ether not decomposed. The product that leaves the column (Cl) by line 3 can be sent partially for example by line 18 to a synthesis zone of tertiary alkyl ether. The product containing the tertiary olefin is introduced through line 4 to an area of water extraction (Ll) in which water is introduced through line llb and from which a fraction (D) poor in alcohol is recovered through line 5, which is sent to the separation zone Co, from which line 23 an aqueous liquid fraction (Le) is recovered and line 24 a liquid hydrocarbon fraction (Lc) containing most of the the tertiary olefin initially present in fraction (D), said fraction (Lc) contains the tertiary olefin, a reduced amount of water and optionally light compounds that are sent by line 24 to a fractionation zone (C2). Line 6 recovers an aqueous product containing the alcohol that is introduced into the fractionation zone (C3). From the fractionation zone (C2), the tertiary olefin, very frequently ultrapure, is recovered through line 8 and line 7, the light products that are partially sent, for example, to the torch, but which can also be sent to an area of catalytic fractionation or towards an ether synthesis zone, and partly recycled, by way of reflux through lines 19, 20 and 20b towards the fractionation zone (C2). It is also possible, in a preferred embodiment, to send at least a portion of these light products through lines 19 and 21 to a separation zone (DI) from which line 5 is recovered a fraction constituted in its most of water, by line 22 a liquid fraction of the light products that are sent back to reflux column (C2) by line 20b; 12, at least part of the gaseous light products that are sent, for example, in part to the torch are recovered through line 12, but can also be sent to a catalytic fractionation zone or to an ether synthesis zone. It is still possible to combine the two embodiments described above. The aqueous fraction can be recovered by line 13 or it can be sent again, for example partly through lines 14, 15, 11 and llb to the water extraction area Ll, in addition to an optional external supply of water along line 15b . From the fractionation zone (C3), alcohol is recovered via line 10, which can be sent again, for example partially through line 16, to a synthesis zone of tertiary alkyl ether. From this zone (C3), an aqueous fraction is also recovered by line 9 which can be sent at least partially to a water treatment area on line 17b or recycled by lines 17, 11 and 11b at least partly towards the area of water extraction (Ll). The aqueous liquid fraction (Le) recovered by line 23 from the separation zone (Co) can be sent at least partly to a water treatment zone on line 26 or recycled by lines 25, 15, 11 and 11b at least partly towards the water extraction area (Ll).

The following example illustrates the invention without limiting the foregoing.

Example 1 A pilot type equipment is used comprising a tubular reactor (Rl), of 10 milliliters in volume, operating under a relative pressure of 7 bar, at an average temperature of 160 ° C containing 3 grams of polysiloxane type catalyst grafted by alkyl sulfonic groups. A commercial catalyst based on polysiloxanes grafted by at least one alkyl sulphonic group is used. The reactor (Rl) is fed by a load containing 100% by weight of MTBE, under a WH of 15 h "1. Table 1 shows the composition of the charge introduced into the RL decomposition reactor of the MTBE and the composition of the product collected at the reactor outlet (Rl).

Table 1 With the help of the software sold by the American company SIMSCI (SIMulation SCIence INC.) Under the tradename Pro II, the various purification sections are calculated. A distillation column (Cl), which operates under a relative pressure of 7 bar and carries 10 theoretical plates, is used in step b) of the process of the invention to obtain a bottom product (B) and a product of the upper part (A). A column for extraction by washing with water Ll, which is a column of dishes and operating at a temperature of 30 ° C under a relative pressure of 12 bar, is used in step c) of the process of the invention to obtain a fraction aqueous (C) and an organic fraction (D). A system for extracting the free water drawn to stage c) in the fraction (D), of the coalescer (Co) type, allows to obtain an aqueous fraction (Le) and an organic fraction (Lc). It works under a relative pressure of 12 bars at a temperature of 30 ° C.

A distillation column (C2), the last stage of purification of isobutene, which operates under a relative pressure of 7 bar, and which carries 10 theoretical plates, is used in step e) to obtain a bottom product (E) which is purified isobutene and a product of the upper part (F) containing light compounds. The column (Cl) is fed by the effluent of (Rl). The product (A) collected in the upper part of (Cl) is sent to the extraction column (Ll) where it is washed with an amount of water whose volumetric flow is equal to one tenth of the flow of (A) . An aqueous fraction (C) containing most of the methanol contained in (A) is recovered, and a hydrocarbon fraction (D) containing a small amount of free water entrained. This fraction of free water is finally removed after decanting in the decantation system (Co) in the form of a fraction (Le) and a hydrocarbon organic fraction (Lc) is recovered. Finally, the hydrocarbon fraction (Lc) is treated in column (C2) to produce at the bottom of the column a fraction (E) which is of high purity isobutene and in the upper part a light fraction (F) containing in particular dimethyl ether (DME).

The material balances obtained are given in table 2 and table 3 below. Table 2 Table 3 Thus, the process according to the invention makes it possible to obtain a very high purity of the isobutene.

Example 2 Assume a pilot type equipment comprising a tubular reactor Rl, operating under a relative pressure of 7 bar, at an average temperature of 140 ° C. The Rl reactor containing the Deloxan ASP (catalyst of the polysiloxane type grafted by alkyl sulfonic groups). Rl is fed by a load containing 100% by weight of TAME, under a WH of 6 h-1. The product collected at the output of Rl has the composition given in table 4: Table 4: Decomposition reaction section of MTBE With the help of the Pro II software, the various purification sections are calculated as in the previous example.

The summary material balance is given in table 5 by way of illustration.

Table 5 Isoamylenes are thus produced with a minimum yield of 84% (performance that can be improved by the deviation or recycling channel of the non-converted ether) and with a purity greater than 99%.

It is noted that in relation to this date the best method known by the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, property is claimed as contained in the following

Claims (18)

1. A process for the production of a tertiary olefin by the decomposition of the tertiary alkyl ether, comprising: a) a stage of decomposition of at least one tertiary alkyl ether in a reaction zone comprising at least one reactor containing a decomposition catalyst of said ether, the step is carried out under conditions that allow the at least partial decomposition of the alkyl ether tertiary in a product containing at least one alcohol and at least one tertiary olefin, b) a step of fractionating at least a part of the product from stage a) in a fractionation zone that allows obtaining on the one hand a fraction (A) containing most of the tertiary olefin and optionally a smaller fraction of alcohol and any lightweight compounds, and on the other hand a fraction (B) containing most of the alcohol formed in step a) and possibly of the non-decomposed ether in step a), c) a purification step of less a part of the fraction (A) in which said part is sent to an extraction zone by washing with the water from which an aqueous fraction (C) is obtained which contains most of the alcohol initially present in said part and a fraction (D) containing most of the tertiary olefin initially present in said part, fraction (D) contains the tertiary olefin, water, optionally light compounds and is substantially free of alcohol. hol, the process is characterized in that it carries a step d) in which at least a part of the fraction (D) leaving the stage c) is sent to a separation zone (Co) from which an aqueous liquid fraction is recovered (Le) and a liquid fraction (Lc) containing most of the tertiary olefin initially present in fraction (D), the fraction (Lc) contains the tertiary olefin, a reduced amount of water and optionally light compounds.

2. A method according to claim 1, characterized in that at least a part of the liquid fraction (Lc) recovered in step d) is sent to a step e) in a fractionation zone (C2) in which said part of the fraction (Lc) is fractioned, on the one hand, into a fraction (E) containing the tertiary definition and, on the other hand, into a fraction (F) containing most of the possible light compounds and occasionally a reduced amount of wastewater.

3. The process according to claim 2, characterized in that the fractionation zone of step e) carries at least one medium that allows recovering a substantially light-anhydrous fraction from the fraction (F).

4. The method according to claim 3, characterized in that the medium comprises a separating ball or flask, provided with at least one means that allows the decanting and transfer of an aqueous fraction.

5. The process according to claim 4, characterized in that the aqueous fraction obtained in step e) is recycled at least partly to stage c) in the extraction zone (Ll) by washing with water.

6. The process according to one of claims 2 to 5, characterized in that at least a part of the fraction (F) or of the substantially anhydrous light fraction obtained in step e) from fraction (F) is at least sent partially towards a catalytic fractionation zone.

7. The process according to one of claims 2 to 5, characterized in that at least a part of the fraction (F) or of the substantially anhydrous light fraction obtained in step e) from said fraction (F), is at least in part sent to an area of synthesis of the ether by the reaction between at least one tertiary olefin and at least one alcohol.

8. The method according to one of claims 1 to 7, characterized in that it comprises a step f) in which at least a part of the fraction (C) output from stage c) is sent to a fractionation zone (C3) to from which a fraction (G) containing most of the alcohol initially present in said part is recovered and "an aqueous fraction (H) released from most of the alcohol initially present in said part.

9. A process according to claim 8, characterized in that at least a part of the fraction (G) is sent to an area of synthesis of the ether by the reaction between at least one tertiary olefin and at least one alcohol.

10. A method according to one of claims 8 or 9, characterized in that at least part of the aqueous fraction (H) is sent at least partly to a water treatment section.

11. A process according to claims 8 to 10, characterized in that at least part of the aqueous fraction (H) is recycled at least in part to step c) in the extraction zone by washing with water.

12. A process according to one of claims 1 to 11, characterized in that at least a part of the fraction (B) is sent to an area of synthesis of the ether by the reaction between at least one tertiary olefin and at least one alcohol.

13. A process according to one of claims 1 to 12, characterized in that at least part of the aqueous fraction (Le) obtained in step d) is recycled at least in part to step c) in the extraction zone by the washed with water.

14. A process according to one of claims 1 to 13, characterized in that, in step c) of purification of at least part of the fraction (A), an amount of water is introduced into the extraction zone by washing with the water. water such that the volumetric ratio between the volume of said water quantity introduced in the extraction zone and that of the fraction part (A) (Vagua / VA) is from 0.005 to 20.

15. A method according to one of claims 1 to 14, characterized in that the extraction zone by washing with the water of stage c) carries at least one means for introducing the complement water.

16. A process according to one of claims 1 to 15, characterized in that the catalyst of stage a) is selected from the group consisting of organic acid resins and mineral acid resins.

17. A process according to one of claims 1 to 16, characterized in that the catalyst of step a) is selected from the group consisting of grafted mineral solids carrying at least one organic group of the alkyl sulphonic, aryl sulphonic or alkylaryl type. -sulfonic.

18. A process according to one of claims 1 to 17, characterized in that the catalyst of stage a) is selected from the group consisting of polysiloxanes grafted by at least one alkyl sulphonic group.