WO1987007260A1 - Process for the synthesis of methyl-tert-alkyl ethers with suppression of corrosion - Google Patents

Process for the synthesis of methyl-tert-alkyl ethers with suppression of corrosion Download PDF

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Publication number
WO1987007260A1
WO1987007260A1 PCT/EP1987/000257 EP8700257W WO8707260A1 WO 1987007260 A1 WO1987007260 A1 WO 1987007260A1 EP 8700257 W EP8700257 W EP 8700257W WO 8707260 A1 WO8707260 A1 WO 8707260A1
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WO
WIPO (PCT)
Prior art keywords
methanol
oxygen
tert
olefins
synthesis
Prior art date
Application number
PCT/EP1987/000257
Other languages
French (fr)
Inventor
Roberto Trotta
Francesco Ancillotti
Ermanno Pescarollo
Original Assignee
Snamprogetti S.P.A.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Snamprogetti S.P.A. filed Critical Snamprogetti S.P.A.
Priority to RO13588187A priority Critical patent/RO101207B1/en
Priority to BR8707693A priority patent/BR8707693A/en
Priority to HU873325A priority patent/HUT47892A/en
Publication of WO1987007260A1 publication Critical patent/WO1987007260A1/en
Priority to NO880344A priority patent/NO167198C/en

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Classifications

    • CCHEMISTRY; METALLURGY
    • C07ORGANIC CHEMISTRY
    • C07CACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C41/00Preparation of ethers; Preparation of compounds having groups, groups or groups
    • C07C41/01Preparation of ethers
    • C07C41/05Preparation of ethers by addition of compounds to unsaturated compounds
    • C07C41/06Preparation of ethers by addition of compounds to unsaturated compounds by addition of organic compounds only

Definitions

  • the present invention relates to a process for the preparation of methyl-tert-alkyl ethers by starting from methanol and branched C 4 -C 8 olefins, with the double bond being on a tertiary C atom.
  • the branched olefins are isobutene and isoamylenes (2-methyl-butene-2 and 2-methyl-butene-1) and produced ethers are MTBE and TAME.
  • methanol used in the synthesis of MTBE stored under an air atmosphere at the temperature of 20o C and under the pressure of 760 mm Hg' dissolves about 80 ppm weight/weight (w/w) of oxygen and 180 ppm w/w of nitrogen; the presence of this latter, however, does not create any problems.
  • a certain amount of dissolved oxygen can be occasionally present also in the C 4 fraction containing liquified isobutene and isobutadiene, in particular when such a fraction has been stored at low temperatures, at which the vapour pressure of the mixture becomes lower than atmospheric.
  • a last source of oxygen is the wash water, but, in as much as the process is normally run by feeding it with the water removed from the bottom of methanol recovery column, such an entry way is nullified. Occasional and short openings of water cycle do not normally cause negative effects.
  • the object of the present invention is a process for the synthesis of methyl-tert-alkyl ethers by starting from methanol and branched C 4 -C 8 olefins, preferably isobutene, in hydrocarbon charges containing, besides said branched olefins, straight olefins and saturated hydrocarbons, which comprises reacting the branched olefins with an excess of methanol, relatively to the stoichiometric amount thereof, in a reaction section provided with an acidic catalyst in the form of an ionexchange resin of Amberlyst 15, Dowex 50 or Lewatit SPC type, at a temperature of from 50 to 80o C and furthermore comprising the separation of formed methyl-tert-aIkyI ether from the mixture of unreacted hydrocarbon components and from the excess of methanol, by distillation, and furthermore comprising the washing, with water, of the mixture of unreacted hydrocarbon components and excess methanol to the purpose of separating said
  • the procedures for oxygen removal are those known in the art for the removal of inert gases dissolved in liquid products, such as, e.g., the use of a suitable stripper consisting of a distillation column, from the bottom of which the oxygen-free product is obtained, whilst oxygen is discharged as the overhead vent from the reflux accumulator.
  • the oxygen removal can be obtained by a stripping with a stream of a suitable inert gas, such as nitrogen, methane, hydrogen, fuel gas, ethane or mixtures thereof.
  • a suitable inert gas such as nitrogen, methane, hydrogen, fuel gas, ethane or mixtures thereof.
  • the olefinic cut (1) has a content of dissolved oxygen lower than 1 ppm, whilst methanol, which is stored inside a tank under an air atmosphere, has an oxygen content ranging from 30 to 60 mg/l.
  • the reaction product (4) containing an average amount of 27.8% of MTBE, which justifies an isobutene conversion of 92%, is fed to a fractionation tray column (11), in such an intermediate point, that the rectification section represents 40% of column. From the top of said fractionation column, the unconverted hydrocarbons are removed together with azeotropic methanol (6), from the bottom of the column a stream (5) being removed, which is constituted by practically pure MTBE.
  • the column is operated under a pressure of 4.9 bars, the overhead, feed and bottom temperatures are respectively 4o C, 60o C and 125o C.
  • Oxygen dissolved in stream (4) fed to column (11) is only partly eliminated as an overhead vent from reflux accumulator (12); most of oxygen remains dissolved in stream (6), which is fed to a perforated-trays column
  • MTBE synthesis and fractionation are carried out under analogous operating conditions as of Example 1, with the variant that methanol is treated as reported in Figure 2.
  • Stream (2) which contains an amount of oxygen ranging from 30 to 60 mg/l, is delivered to the upper section of a stripping column (18), to the bottom of which a stream of nitrogen (16), containing an oxygen level lower than 150 ppm, is sent in countercurrent flow.
  • the oxygen-depleted methanol, stream (3) is recovered from the bottom of the column, with oxygen levels constantly lower than 1 mg/l, and is sent to the reaction, after to it recycled methanol (9) being added.
  • the oxygen-enriched stripping gas (17) is sent to blowdown.
  • column (13) has been, operating for 8000 hours with no drawbacks, and an inspection thereof showed the complete absence of polymerization phenomena.

Abstract

Methyl-tert-alkyl ethers coming from a synthesis section are separated from unreacted hydrocarbons by means of a rectification operation, in which the unreacted hydrocarbons are drawn as overhead fraction, in the form of an azeotropic mixture with methanol. To the purpose of removing methanol, and of therefore allowing a suitable use of said unreacted hydrocarbons, the azeotropic mixture is washed with water inside a washing column, which gets very rapidly corroded. The invention solves the corrosion problem by resorting to the removal of oxygen from the hydrocarbon charge and/or of methanol, before these are sent to the synthesis.

Description

"PROCESS FOR THE SYNTHESIS OF METHYL-TERT-ALKYL ETHERS
WITH SUPPRESSION OF CORROSION"
The present invention relates to a process for the preparation of methyl-tert-alkyl ethers by starting from methanol and branched C4-C8 olefins, with the double bond being on a tertiary C atom. In a preferred form of the present invention, the branched olefins are isobutene and isoamylenes (2-methyl-butene-2 and 2-methyl-butene-1) and produced ethers are MTBE and TAME.
It is known that for the synthesis of said ethers it not necessary to use the reactive olefins at a high purity level, but it is enough to use hydrocarbon cuts which contain them even at a low concentration. The reaction between alcohols and tertiary olefins is catalyzed by acidic catalysts and in the presence of the most suitable catalysts, for example the ion-exchange resins in the acidic form, such as Amberlyst 15, Dowex 50, Lewatit SPC, the thermodynamic equilibrium is reached also at relatively low temperatures of 50-8º C.
It is known that the excess of either of reactants allows an increase in conversion of the other reactant, so that a wide range exists of operating schemes and conditions directed to the optimization of either of unconverted reactants. The separation of produced ether from unconverted reactants is carried out by distillation in a fractionation column, from the bottom of which the ether, and from the top of which the hydrocarbons are separated.
It is known that unconverted methanol is either totally or partly recovered from the column head as an azeotropic mixture with the hydrocarbons. This behaviour allows methanol-free ethers to be obtained even when from the reactor a reaction product containing an unconverted methanol portion exits. This fact is exploited to the purpose of operating with a certain alcohol excess, so to force, by so doing, the conversion rate, as referred to the olefin. However, the presence of methanol in the hydrocarbons often jeopardizes the further exploitation thereof, such as, e.g., their use as a charge for processes of the oligomerization or alkylation type, so that, often, it has to be removed.
For methanol removal, several techniques have been described, which range from an absorption on beds of solid absorbents, to countercurrent-flow liquid-liquid extraction. As the extraction solvents, water or organic glycoltype solvents are described, but water is undoubtedly the choice solvent. However, the use of water in the liquidliquid extraction column causes severe corrosion problems, so that for the construction of 'such a column, such valuable materials as stainless steel must be used, or burdensome procedures of lining by inert materials, or of coating by special paints must be adopted.
It was surprisingly found, and is the basis of our invention, that it is possible to overcome all of corrosion problems affecting the washing column, even when carbon steel is used as the construction material, on condition that oxygen present as dissolved gas inside the charges fed to the extraction column is preliminarily removed. Such oxygen is basically arising from the presence of dissolved air inside the fed aliphatic alcohol (either methanol or ethanol), as a consequence of the modalities of product transportation and storage. For example, methanol used in the synthesis of MTBE, stored under an air atmosphere at the temperature of 20º C and under the pressure of 760 mmHg' dissolves about 80 ppm weight/weight (w/w) of oxygen and 180 ppm w/w of nitrogen; the presence of this latter, however, does not create any problems.
A certain amount of dissolved oxygen can be occasionally present also in the C4 fraction containing liquified isobutene and isobutadiene, in particular when such a fraction has been stored at low temperatures, at which the vapour pressure of the mixture becomes lower than atmospheric. A last source of oxygen is the wash water, but, in as much as the process is normally run by feeding it with the water removed from the bottom of methanol recovery column, such an entry way is nullified. Occasional and short openings of water cycle do not normally cause negative effects.
To the purpose of controlling the corrosive effects, it is generally enough to eliminate the main oxygen entry point, i.e., that occurring through methanol.
The object of the present invention is a process for the synthesis of methyl-tert-alkyl ethers by starting from methanol and branched C4-C8 olefins, preferably isobutene, in hydrocarbon charges containing, besides said branched olefins, straight olefins and saturated hydrocarbons, which comprises reacting the branched olefins with an excess of methanol, relatively to the stoichiometric amount thereof, in a reaction section provided with an acidic catalyst in the form of an ionexchange resin of Amberlyst 15, Dowex 50 or Lewatit SPC type, at a temperature of from 50 to 80º C and furthermore comprising the separation of formed methyl-tert-aIkyI ether from the mixture of unreacted hydrocarbon components and from the excess of methanol, by distillation, and furthermore comprising the washing, with water, of the mixture of unreacted hydrocarbon components and excess methanol to the purpose of separating said methanol from said unreacted hydrocarbon components, characterized in that methanol and/or the hydrocarbon charges are deprived of the therein contained oxygen gas before they are fed to the reaction section.
The procedures for oxygen removal are those known in the art for the removal of inert gases dissolved in liquid products, such as, e.g., the use of a suitable stripper consisting of a distillation column, from the bottom of which the oxygen-free product is obtained, whilst oxygen is discharged as the overhead vent from the reflux accumulator.
In some cases, the oxygen removal can be obtained by a stripping with a stream of a suitable inert gas, such as nitrogen, methane, hydrogen, fuel gas, ethane or mixtures thereof. In the following examples, some oxygen removal procedures are described, which are however supplied to purely exemplifying purposes, and in no way are limitative of the present invention.
Example 1 Reference is made to Figure 1.
100 parts by weight of a C4 olefinic charge (1), containing 22,0% by weight of isobutene, is mixed with 14.33 parts of methanol (2) and the resulting charge (3) is fed to a reactor (20) containing an ion-exchange resin in the acidic form, of Dowex 50 type.
The olefinic cut (1) has a content of dissolved oxygen lower than 1 ppm, whilst methanol, which is stored inside a tank under an air atmosphere, has an oxygen content ranging from 30 to 60 mg/l.
The reaction product (4) containing an average amount of 27.8% of MTBE, which justifies an isobutene conversion of 92%, is fed to a fractionation tray column (11), in such an intermediate point, that the rectification section represents 40% of column. From the top of said fractionation column, the unconverted hydrocarbons are removed together with azeotropic methanol (6), from the bottom of the column a stream (5) being removed, which is constituted by practically pure MTBE. The column is operated under a pressure of 4.9 bars, the overhead, feed and bottom temperatures are respectively 4º C, 60º C and 125º C.
Oxygen dissolved in stream (4) fed to column (11) is only partly eliminated as an overhead vent from reflux accumulator (12); most of oxygen remains dissolved in stream (6), which is fed to a perforated-trays column
(13) for liquid-liquid extraction, totally made from carbon steel. Inside said column, the azeotropic methanol-containing hydrocarbon stream is treated in countercurrent-flow with water (10) drawn from the bottom of methanol recovery column (14). Methanol inside C4 fraction is extracted by water, exits the bottom of column (13) as a water-alcohol solution (8), and is sent to a recovery column (14) (distillation column equipped with reflux accumulator (15), the overhead product of which is methanol (9), which is sent to the synthesis).
Overhead column (13), C4 hydrocarbons are recovered (7), with a methanol content lower than 5 ppm. By operating under the above-said conditions, after about
1000 operating hours an increase is observed in pressure drop, with the apperance of C4 products together with stream (8). The malfunctioning is so serious as to jeopardize the operativity of the facility.
Inspection of column evidences an extensive formation of a mixture of iron oxides identified as Fe3O4
(magnetite), Fe2O3.H2O (goethite) and Fe23 .H2O (lepidocrocite).
The deposit of such oxides is such as to considerably reduce the free passage opening through the tray holes, and from here the difficulties arise for C4 products to move upwards along the column. Example 2
MTBE synthesis and fractionation are carried out under analogous operating conditions as of Example 1, with the variant that methanol is treated as reported in Figure 2. Stream (2), which contains an amount of oxygen ranging from 30 to 60 mg/l, is delivered to the upper section of a stripping column (18), to the bottom of which a stream of nitrogen (16), containing an oxygen level lower than 150 ppm, is sent in countercurrent flow. The oxygen-depleted methanol, stream (3), is recovered from the bottom of the column, with oxygen levels constantly lower than 1 mg/l, and is sent to the reaction, after to it recycled methanol (9) being added.
The oxygen-enriched stripping gas (17) is sent to blowdown. By resorting to such a measure, column (13) has been, operating for 8000 hours with no drawbacks, and an inspection thereof showed the complete absence of polymerization phenomena.
In Figure 2, the other find numbers have the same meaning as in Figure 1.

Claims

C l a i m s
1. Process for the synthesis of methyl-tert-aIkyI ethers by starting from methanol and branched C4-C8 olefins, preferably isobutene, in hydrocarbon charges containing, besides said branched olefins, straight olefins and saturated hydrocarbons, which comprises reacting the branched olefins with an excess of methanol relatively to the stoichiometric amount thereof, in a reaction section provided with an acidic catalyst in the form of an ion-exchange resin of Amberlyst 15, Dowex 50 or Lewatit SPC type, at a temperature of from 50 to 80º C and furthermore comprising the separation of formedmethyl-tert-aIkyI ether from the mixture of unreacted hydrocarbon components and from the excess of methanol, by distillation, and furthermore comprising the washing, with water, of the mixture of unreacted hydrocarbon components and excess methanol to the purpose of separating said methanol from said unreacted hydrocarbon components, characterized in that methanol and/or the hydrocarbon charges are deprived of the therein contained oxygen gas before they are fed to the reaction section.
2. Process according to claim 1, characterized in that oxygen is removed in a stripper consisting of a distillation column, said oxygen being discharged as a overhead vent from the reflux accumulator.
3. Process according to claim 1, characterized in that oxygen is removed by means of stripping by a stream of an inert gas.
4. Process according to claim 3, characterized in that the inert gas is selected from nitrogen, methane, hydrogen, fuel gas, ethane, or mixtures thereof.
PCT/EP1987/000257 1986-05-27 1987-05-07 Process for the synthesis of methyl-tert-alkyl ethers with suppression of corrosion WO1987007260A1 (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
RO13588187A RO101207B1 (en) 1987-05-07 1987-05-07 Methyl-tertalkyl ethers synthesis method
BR8707693A BR8707693A (en) 1986-05-27 1987-05-07 PROCESS FOR THE SYNTHESIS OF METHYLTERALKYL ETHERS WITH CORROSION SUPPRESSION
HU873325A HUT47892A (en) 1986-05-27 1987-05-07 Process for producing methyl-terc.alkyl-ethers without corrosion
NO880344A NO167198C (en) 1986-05-27 1988-01-27 PROCEDURE FOR THE SYNTHESIS OF METHYL-TERT-ALKYLETERS.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
IT20573A/86 1986-05-27
IT20573/86A IT1190017B (en) 1986-05-27 1986-05-27 PROCESS FOR THE SYNTHESIS OF ETERIMETILTERALCHILICI WITH CORROSION SUPPRESSION

Publications (1)

Publication Number Publication Date
WO1987007260A1 true WO1987007260A1 (en) 1987-12-03

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PCT/EP1987/000257 WO1987007260A1 (en) 1986-05-27 1987-05-07 Process for the synthesis of methyl-tert-alkyl ethers with suppression of corrosion

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EP (1) EP0311614A1 (en)
JP (1) JPH01502748A (en)
BR (1) BR8707693A (en)
CS (1) CS273639B2 (en)
DD (1) DD260924A5 (en)
ES (1) ES2006491A6 (en)
GR (1) GR870748B (en)
HU (1) HUT47892A (en)
IT (1) IT1190017B (en)
PL (1) PL150602B1 (en)
WO (1) WO1987007260A1 (en)
YU (1) YU95287A (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0537636A1 (en) * 1991-10-10 1993-04-21 Phillips Petroleum Company Etherification process
RU2544553C1 (en) * 2013-12-25 2015-03-20 Открытое акционерное общество "Газпромнефть-Московский НПЗ" (ОАО "Газпромнефть-МНПЗ") Method of obtaining high-octane additive to automobile petrol

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0103870A2 (en) * 1982-09-20 1984-03-28 Phillips Petroleum Company Combined ether and alkylate production

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0103870A2 (en) * 1982-09-20 1984-03-28 Phillips Petroleum Company Combined ether and alkylate production

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0537636A1 (en) * 1991-10-10 1993-04-21 Phillips Petroleum Company Etherification process
RU2544553C1 (en) * 2013-12-25 2015-03-20 Открытое акционерное общество "Газпромнефть-Московский НПЗ" (ОАО "Газпромнефть-МНПЗ") Method of obtaining high-octane additive to automobile petrol

Also Published As

Publication number Publication date
HUT47892A (en) 1989-04-28
IT8620573A0 (en) 1986-05-27
GR870748B (en) 1987-09-23
JPH01502748A (en) 1989-09-21
CS273639B2 (en) 1991-03-12
EP0311614A1 (en) 1989-04-19
IT1190017B (en) 1988-02-10
DD260924A5 (en) 1988-10-12
CS354287A2 (en) 1990-08-14
BR8707693A (en) 1989-08-15
PL150602B1 (en) 1990-06-30
PL265892A1 (en) 1988-07-21
YU95287A (en) 1988-06-30
ES2006491A6 (en) 1989-05-01

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