Production of ethers

The present invention relates to the production of ethers, especially tertiary alkyl ethers.

It is known to produce ethers by reacting olefins and alcohols in the presence of suitable catalysts. For example, tertiary alkyl ethers may be prepared by reacting a tertiary olefin and an alcohol, e.g. isobutene and methanol to give methyl t-butyl ether, in the presence of catalysts such as mineral acids, e.g. sulphuric acid, and a range of solid catalysts such as heteropolytungstic or molybdic acids doped with phosphorus or boron, acidified alumina, and various acidified ion-exchange resins.

The use of mineral acid catalysts can give rise to corrosion problems which make it difficult to apply such catalysts on a commercial scale. Commercial processes are known using acidified ion-exchange catalysts, especially for the production of methyl t-butyl ether, which is particularly useful as a gasoline additive with high octane properties, but such catalysts often have poor thermal stability and this limits the reaction temperature which can be used, e.g. in many cases reaction temperatures not in excess of 80°C. The use of lower reaction temperatures can in turn result in long reaction times and low throughput per unit volume of reaction vessel.

Another problem which can arise with known processes is the formation of dialkyl ether byproducts deriving from the alcohol used.

Polish Patent No. 103379 describes a method of making methyl t-butyl ether by reacting methanol and isobutene in the presence of a catalyst comprising zeolite X or Y or a partially dealuminated, modified or ion-exchanged form thereof, the process being carried out in a vapour or liquid phase. Using zeolite Y in a vapour phase process at 120°C, a liquid product is obtained consisting of 8.1 % methyl t-butyl ether and 91.8% methanol. The same zeolite is used in a liquid phase process at 160°C and a pressure of 31 atmospheres and a partially dealuminated zeolite Y is used at 125°C and a pressure of 23 atmospheres.

According to US Patent No. 2882244, zeolite X has a silica/alumina ratio in the range 2-3 and according to US Patent No. 3130007, zeolite Y has a silica/alumina ratio in the range 3-6.

East German Patent No. 133661 describes the reaction of alcohols and olefins to form ethers using a zeolite catalyst, the zeolite being either mordenite or faujasite. The activity and selectivity of these zeolites is generally rather low and appreciable amounts of side-products are also formed. In example 5, for instance, the amount of ether in the product is less than 40% while the amount of di-isobutene is nearly 60%.

We have now found that tertiary alkyl ethers may be prepared from tertiary olefins and alcohols in the presence of certain zeolite catalysts having higher activity and better selectivity than those used in the East Germany patent and under milder conditions than are described in the Polish patent. These catalysts and conditions allow the prouction of the tertiary alkyl ethers at high selectivity and in good yield, with low yields of undesirable by-product dialkyl ethers and oligomers of the olefin.

According to the present invention we provide a process for the production of an ether which comprises contacting an olefin and an alcohol with a catalyst comprising a zeolite having an XO₂/Y₂O₃ ratio equal to or greater than 10, wherein X is silicon and/or germanium, and Y is one or more of aluminium, iron, chromium, vandadium, molybdenum, arsenic, manganese, gallium or boron, the zeolite being predominantly in the hydrogen form.

The said zeolites have acid sites within zeolite pore systems active in the catalysis of tertiary alkyl ether formation. The entry port size in the preferred zeolites is such that reactants and products can move into and out of the pore systems, i.e. with a Lennard Jones diameter α (A) of from about 5.0 to 8.0 A (the Lennard Jones diameter a (A) is defined by D W Breck in "Zeolite Molecular Sieves", Wiley Interscience, 1947, page 636).

The preferred zeolites for use as catalyst are based on X0₂ as silica (Si0₂) and Y_z0₃ as alumina (AI_z0₃). Suitable zeolites which may be employed as catalysts in the process of the invention include: <tables id="tabl0001" num="0001"><img file="EP0055045B1_D0001.tif" /></tables><tables id="tabl0002" num="0002"><img file="EP0055045B1_D0002.tif" /></tables>

The zeolites may be converted to their hydrogen form by methods which have been fully described in the prior art, for example by calcination of the as-made zeolite and subsequent acid exchange. If desired, the zeolites may be ion-exchanged or impregnated so as to comprise cations or oxides selected from the following, Cu, Ag, Ca, Sr, Zn, Cd, B, Al, Sn, Pb, V, P, Sb, Cr, Mo, W, Mn, Re, Fe, Co, Ni, noble metals and lanthanides. The formation of olefin oligomers may be further inhibited by treating the zeolite with a bulky-organic base, for example phenanthridine. It is believed that the base neutralises the surface acidic sites whilst being unable, because of its bulk, to enter the pore system of the zeolite.

Suitable olefins for use in the process of the invention include mono- or di-olefins containing from 4-16 carbon atoms, especially 4 to 9 carbon atoms, e.g. isobutene, 2-methylbut-1-ene, 2-methylbut-2-ene, 2-methylpent-1-ene, 2-methylpent-2-ene, 3-methylpent-2-ene, 2-methylhex-1-ene, 2-methyl- hept-1-ene and 2-methyloct-1-ene, or mixtures thereof.

Suitable alcohols for use in the process of the invention include primary and secondary alkanols containing from 1 to 12 carbon atoms, more preferably containing from 1 to 4 carbon atoms, e.g. methanol, ethanol, n-propanol, iso-propanol, and n-butanol. Also included are ether alcohols, e.g. RO(CH₂CH₂0)_nH where R is H or hydrocarbyl and n is 1-20, e.g. 2-methoxyethanol.

The process of the invention is particularly applicable to the production of tertiary alkyl ethers containing a total of 5 to 10 carbon atoms from the corresponding tertiary olefins and alcohols, and especially to the production of methyl t-butyl ether from isobutene and methanol. The preferred zeolite catalysts for use in the production of MTBE are zeolites Nu-2, Nu-4, Nu-10 and beta.

The etherification reaction may be carried out in the vapour or liquid phase. The liquid phase reaction is typically carried out in a stirred and heated pressure vessel containing the reactants and catalyst. In the gas phase, the reactants may conveniently be passed through a heated tubular reactor containing the catalyst. This process readily lends itself to continuous production of the ether product.

The liquid phase and vapour phase processes may suitably be carried out at a temperature in the range from 50°C to 110°C, for example 70°C to 100°C. The reaction is normally conducted under atmospheric or superatmospheric pressure, e.g. at a pressure in the range 1 to 100 bars.

The molar ratio of the olefin to alcohol may vary widely but is suitably in the range from 0.5 to 5.0 moles of alkanol per mole of olefin.

For the liquid phase process, the proportion of catalyst in the reaction mixture may vary within very broad limits, but is suitably within the range from about 0.1 to about 5% by weight.

Under conditions suitable for the reaction of an alkanol and an olefin to yield tertiary alkyl ethers selectively, the zeolite catalyst is remarkably stable and does not itself suffer damage from degradation reactions which give materials having poor catalytic activity. By virtue of its nature, a zeolite can be rapidly recovered from the reaction mixture in liquid phase processes and can be reused in further batch operations.

Zeolites for use in the process of the invention, and methods for their preparation, have been described in the patent specifications referred to above. Inasmuch as some of these patent specifications are as yet unpublished, further details of zeolites Nu-2, Nu-4, Nu-5, Nu-6, Nu-10, EU-1, EU-2 and FU-9 are provided below.

Zeolite Nu-2 has a molar composition expressed by the formula: <ul id="ul0001" list-style="none"><li>0.5 to 1.8 R₂O : Y₂O₃: at least 10 XO₂ : 0 to 100 H₂O</li></ul> wherein R is a monovalent cation or 1/n of a cation of valency, n, X is silicon and/or germanium, Y is one or more of aluminium, iron, chromium, vanadium, molybdenum, arsenic, manganese, gallium or boron, and H₂0 is water of hydration additional to water notionally present when R is H, and has an X-ray pattern substantially as set out in Tables 1 and 2 (as determined by standard technique using copper Kα radiation). Table 1 shows X-ray data for zeolite Nu―2 as prepared, and Table 2 shows X-ray data for zeolite Nu-2 in the calcined Na-H form. <tables id="tabl0003" num="0003"><img file="EP0055045B1_D0003.tif" /></tables><tables id="tabl0004" num="0004"><img file="EP0055045B1_D0004.tif" /></tables>

Within the above definition of chemical composition, the number of moles of X0₂ is typically in the range 10 to 100 and zeolite Nu-2 appears to be most readily formed in a state of high purity when the number of moles of XO₂ is in the range 25 to 50.

Zeolite Nu-2 may be prepared by reacting an aqueous mixture containing at least one oxide XO₂, at least one oxide Y₂O₃, and at least one alkylated or partially alkylated quaternary ammonium or phosponium or ternary sulphonium compound i.e. (R₁R₂R₃R₄N)⁺ or (R₁R₂R₃R₄P)⁺ or (R₁R₂R₃S)⁺ hereinafter referred to as Q⁺. R₁, R₂, R₃ and R₄ can be from two to four ethyl groups, the remainder can be H, CH₃ or C₃H₇. Alternatively precursors of the quaternary compound can be used e.g. triethylamine plus ethanol, or an ethyl halide or sulphate, in which case the precursor is preferably preheated in a solvent e.g. methyl ethyl ketone, prior to the addition of other reactants.

The reaction mixtures preferably have the following molar composition <tables id="tabl0005" num="0005"><img file="EP0055045B1_D0005.tif" /></tables>wherein X and Y are as above, Ak⁺ is an alkali metal ion, or mixtures of such ions, which can include ammonium, and refers to free alkali, OH- includes free alkali and free quaternary ammonium hydroxide and Z is OH^- or any acid radical. When Z is an acid radical an equivalent excess of free Ak⁺ must be added as hydroxide in order to maintain the alkalinity of the reaction mixture. Q⁺ is a quaternary ion of N, P or S.

The preferred quaternary compound is tetraethylammonium hydroxide.

Zeolite Nu-4 has a molar composition expressed by the formula: <ul id="ul0002" list-style="none"><li>5 to 15<maths id="math0001" num=""><img file="EP0055045B1_D0006.tif" /></maths> : 0 to 10 Y₂O₃ : 100 XO₂ : 0 to 50 H₂O</li></ul> wherein M¹ is a monovalent cation or ¹/n of a cation of valency n, X is silicon or germanium, Y is aluminium, iron, chromium, vanadium, molybdenum, arsenic, antimony, manganese, gallium or boron, and H₂0 is water of hydration additional to water notionally present when M' is H, and has an X-ray pattern substantially as set out in Table 3 (as determined by standard technique using copper Kα radiation). Table 3 shows X-ray data for zeolite Nu-4 as prepared and in the calcined hydrogen form. <tables id="tabl0006" num="0006"><img file="EP0055045B1_D0007.tif" /></tables><tables id="tabl0007" num="0007"><img file="EP0055045B1_D0008.tif" /></tables>

Within the above definition of chemical composition, the number of moles of Y₂O₃ is typically in the range 0 to 10 and zeolite Nu-4 appears to be most readily formed in a state of high purity when the number of moles of Y₂O₃ is in the range 0 to 4.

Zeolite Nu-4 may be prepared by reacting an aqueous mixture comprising at least one oxide XO₂, at least one oxide Y₂O₃ and at least one polyalkylene polyamine having the formula: <chemistry id="chem0001" num="0001"><img file="EP0055045B1_D0009.tif" /></chemistry>where x is in the range 2 to 6 and y is in the range from 0 to 10, an amine degradation product thereof, or a precursor thereof. In the polyamine, each of R₁ to R₅, independently, represents hydrogen or a C,-C₆ alkyl group. When y is from 2 to 6, the R₃ substituents may be the same or different. When y=0 then x = 2 to 5.

The reaction mixture can have the following molar ratios: <tables id="tabl0008" num="0008"><img file="EP0055045B1_D0010.tif" /></tables>wherein X and Y are as above, M¹ is an alkali metal or ammonium or hydrogen, M² is an alkali metal or ammonium or hydrogen and can be the same as M¹ and Q is the aforesaid polyalkylene polyamine, amine degradation product thereof or a precursor thereof, or a related compound. Z- is a strong acid radical present as a salt of M² and may be added as a free acid to reduce the free M'OH level to a desired value. However, zeolite Nu-10 can be synthesised from a narrow range of molar ratios which falls within this much wider range for zeolite Nu―4 synthesis. Therefore if SiO₂/Al₂O₃ ratios between 70 and 300 are chosen, then to ensure that zeolite Nu-4 is obtained free of zeolite Nu-10 it is necessary to employ either low H₂O/XO₂ ratios or high M¹OH/XO₂ ratios or both.

The preferred ranges for preparing zeolite Nu-4 are as follows: <tables id="tabl0009" num="0009"><img file="EP0055045B1_D0011.tif" /></tables><tables id="tabl0010" num="0010"><img file="EP0055045B1_D0012.tif" /></tables><tables id="tabl0011" num="0011"><img file="EP0055045B1_D0013.tif" /></tables><tables id="tabl0012" num="0012"><img file="EP0055045B1_D0014.tif" /></tables><tables id="tabl0013" num="0013"><img file="EP0055045B1_D0015.tif" /></tables><tables id="tabl0014" num="0014"><img file="EP0055045B1_D0016.tif" /></tables><tables id="tabl0015" num="0015"><img file="EP0055045B1_D0017.tif" /></tables>

The preferred polyalkylene polyamines are triethylene tetramine and tetraethylene pentamine.

Zeolite Nu-5 has a molar composition expressed by the formula: <ul id="ul0003" list-style="none"><li>0.5 to 1.5 R₂O : Y₂O₃ : at least 10 XO₂ : 0 to 2000 H₂O</li></ul> wherein R is a monovalent cation or ¹/n of a cation of valency n, X is silicon and or germanium. Y is one or more of aluminium, iron, chromium, vanadium, molybdenum, arsenic, manganese, gallium or boron, and H₂0 is water of hydration additional to water notionally present when R is H, and has an X-ray pattern substantially as set out in Table 4 (as determined by standard technique using copper Kα radiation). Table 4 shows X-ray data for zeolite Nu-5. <tables id="tabl0016" num="0016"><img file="EP0055045B1_D0018.tif" /></tables><tables id="tabl0017" num="0017"><img file="EP0055045B1_D0019.tif" /></tables>

Within the above definition of chemical composition, the number of moles of XO₂ is typically in the range 10 to 5000 and zeolite Nu-5 appears to be most readily formed in a state of high purity when the number of moles of XO₂ is in the range 45 to 100.

Zeolite Nu-5 may be prepared by reacting an aqueous mixture comprising at least one oxide XO₂, at least one oxide Y₂O₃ and at least one compound selected from pentaerythritol, dipentaerythritol and tripentaerythritol.

The reaction mixture preferably has the following molar composition: <tables id="tabl0018" num="0018"><img file="EP0055045B1_D0020.tif" /></tables>wherein X and Y are as above, M is an alkali metal or ammonium, A is the aforesaid pentaerythritol compound and Z- is a strong acid radical present as a salt of M and may be added as a free acid to reduce the free OH- level to a desired value. M can be present as hydroxides or salts of inorganic or organic acids provided the MOH/XO₂ requirement is fulfilled.

The preferred pentaerythritol compound is pentaerythritol, itself.

Zeolite Nu-6(2) has a molar composition expressed by the formula: <ul id="ul0004" list-style="none"><li>0.5 to 1.5 R₂O : Y₂O₃ : at least 10 XO₂ : 0 to 2000 H₂O</li></ul> wherein R is a monovalent cation or ¹/n of a cation of valency n, X is silicon, and/or germanium, Y is one or more of aluminium, iron, chromium, vanadium, molybdenum, antimony, arsenic, manganese, gallium or boron, and H₂0 is water of hydration, additional to water notionally present when R is H, and has an X-ray diffraction pattern substantially as set out in Table 5 (as determined by standard technique using copper Kα radiation). <tables id="tabl0019" num="0019"><img file="EP0055045B1_D0021.tif" /></tables>Within the above definition of chemical composition, the number of moles of XO₂ is typically in the range 10 to 5000 and zeolite Nu-6(2) appears to be most readily formed in a state of high purity when the number of moles of XO₂ is in the range 20 to 1000.

Zeolite Nu-6(2) may be prepared by heating zeolite Nu-6(1) at a temperature in the range 200°C to 750°C, zeolite Nu―6(1) itself being made together with some zeolite Nu―6(2) by reacting an aqueous mixture containing at least one oxide XO₂, at least one oxide Y₂O₃ and a 4,4'-dipyridyl compound.

The reaction mixture preferably has the following molar composition: <tables id="tabl0020" num="0020"><img file="EP0055045B1_D0022.tif" /></tables>wherein X and Y are as above, M is an alkali metal or ammonium, Q is the aforesaid 4,4'-bipyridyl compound and Z^- is a strong acid radical present as a salt of M and may be added as a free acid to reduce the free OH- level to a desired value. M and/or Q can be present as hydroxides or salts of inorganic or organic acids provided the MOH/XO₂ requirement is fulfilled. BOH is an aliphatic or aromatic alcohol, preferably an alkanol. Whilst not essential, an alcohol improves crystallisation in viscous reaction mixtures.

The preferred bipyridyl compound is 4,4'-bipyridyl itself.

The preferred alcohol (BOH) is ethanol.

Zeolite Nu-10 has a molar composition expressed by the formula: <ul id="ul0005" list-style="none"><li>0.5 to 1.5 R₂O : Y₂O₃ : at least 60 XO₂ : 0 to 200 H₂O</li></ul> wherein R is a monovalent cation or ¹/n of a cation of valency n, X is silicon, and/or germanium. Y is one or more of aluminium, iron, chromium, vanadium, molybdenum, arsenic, antimony, manganese, gallium or boron, and H₂O is water of hydration additional to water notionally present when R is H, and has an X-ray pattern substantially as set out in Table 6 (as determined by standard technique using copper Kα radiation). <tables id="tabl0021" num="0021"><img file="EP0055045B1_D0023.tif" /></tables>

Within the above definition of chemical composition the number of moles of XO₂ is typically in the range 60 to 500. Zeolite Nu―10 appears to be most readily formed in a state of high purity when the number of moles of XO₂ is in the range 80 to 120.

Zeolite Nu-10 may be prepared by reacting an aqueous mixture containing at least one oxide XO₂, at least one oxide Y₂O₃ and at least one polyalkylene polyamine having the formula: <chemistry id="chem0002" num="0002"><img file="EP0055045B1_D0024.tif" /></chemistry>where x is in the range 2 to 6 and y is in the range from 0 to 10, an amine degradation product thereof. or a precursor thereof. In the polyamine, each of R₁ to R₅, independently, represents hydrogen or a C₁―C₆ alkyl group. when y is from 2 to 6, the R₃ substituents may be the same or different. When y = 0 then x = 2 to 5.

The reaction mixture preferably has the following molar ratios: <ul id="ul0006" list-style="none"><li>XO₂/Y₂O₃ = 60 to 500, preferably 70 to 200, most preferred 80 to 150</li><li>M'OH/XO₂ = 10-⁸ to 1.0, preferably 10-⁶ to 0.25, most preferred 10-⁴ to 0.15 H₂O/XO₂ = 10 to 200, preferably 1 5 to 60, most preferred 30 to 50</li><li>Q/XO₂ = 0.5 to 4, preferably 0.1 to 1.0, most preferred 0.2 to 0.5</li><li>M²Z/XO₂ = 0 to 4.0, preferably 0 to 1.0, most preferred 0 to 0.6</li></ul> wherein X and Y are as above, M' is an alkali metal or ammonium or hydrogen, M² is an alkali metal or ammonium or hydrogen and can be the same as M' and Q is the aforesaid polyalkylene polyamine, amine degradation product thereof or a precursor thereof, or a related compound. Z- is a strong acid radical present as a salt of M² and may be added as a free acid to reduce the free M'OH level to a desired value.

The preferred polyalkylene polyamines are triethylene tetramine and tetraethylene pentamine.

Zeolite EU-1 has a molar composition expressed by the formula: <ul id="ul0007" list-style="none"><li>0.5 to 1.5 R₂O : Y₂O₃ : at least 10 XO₂ : 0 to 100 H₂O</li></ul> wherein R is a monovalent cation or ¹/n of a cation of valency n, X is silicon and/or germanium, Y is one or more of aluminium, iron, gallium or boron, and H₂0 is water of hydration additional to water notionally present when R is H, and has an X-ray pattern substantially as set out in Tables 7 and 8 (as determined by standard technique using copper Kα radiation). Table 7 shows X-ray data for zeolite EU-1 as prepared, and Table 8 shows X-ray data for zeolite EU-1 in the calcined Na-H form. <tables id="tabl0022" num="0022"><img file="EP0055045B1_D0025.tif" /></tables><tables id="tabl0023" num="0023"><img file="EP0055045B1_D0026.tif" /></tables>

Within the above definition of chemical composition, the number of moles of X0₂ is typically in the range 10 to 500 and zeolite EU-1 appears to be most readily formed in a state of high purity when the number of moles of XO₂ is in the range 20 to 300.

Zeolite EU-1 may be prepared by reacting an aqueous mixture comprising at least one oxide XO₂, at least one oxide Y₂O₃ and at least one alkylated derivative of a polymethylene α-ω diamine having the formula: <chemistry id="chem0003" num="0003"><img file="EP0055045B1_D0027.tif" /></chemistry>an amine degradation product thereof, or a precursor thereof, wherein n is in the range from 3 to 12 and R₁ to R₆ which may be the same or different, can be alkyl or hydroxyalkyl groups, containing from 1 to 8 carbon atoms and up to five of the groups R₁―R₆ can be hydrogen, the mixture having the molar composition: <tables id="tabl0024" num="0024"><img file="EP0055045B1_D0028.tif" /></tables>wherein X and Y are as above, M is an alkali metal or ammonium, and Q is the aforesaid alkylated derivative of a polymethylene diamine, an amine degradation product thereof, or a precursor thereof, or a related compound.

M and/or Q can be present as hydroxides or salts of inorganic or organic acids provided the OH^-/XO₂ requirement is fulfilled.

Preferred alkylated polymethylene diamine starting materials include alylated hexamethylene diamines, especially methylated hexamethylene diamines, for example 1:6-N,N,N,N¹,N¹,N¹-hexamethyl hexamethylene diammonium salts (e.g. halide, hydroxide, sulphate, silicate, aluminate).

Zeolite EU-2 has a molar composition expressed by the formula: <ul id="ul0008" list-style="none"><li>0.5 to 1.5 R₂O : Y₂O₃ : at least 70 XO₂ : 0 to 100 H₂O</li></ul> wherein R is a monovalent cation or ¹/n of a cation of valency n, X is silicon and/or germanium, Y is one or more of aluminium, iron, gallium, or boron, and H₂0 is water of hydration additional to water notionally present when a is H, and has an X-ray pattern substantially as set out in Table 9 (as determined by standard technique using copper Kα radiation). <tables id="tabl0025" num="0025"><img file="EP0055045B1_D0029.tif" /></tables> Within the above definition of chemical composition, the number of moles of XO₂ is typically in the range 100 to 5000 and zeolite EU-2 appears to be most readily formed in a state of high purity when the number of moles of XO₂ is in the range 150 to 3000.

Zeolite EU-2 may be prepared by reacting an aqueous mixture comprising at least one oxide XO₂, at least one oxide Y₂O₃ and at least one alkylated derivative of a polymethylene α-ω diamine having the formula: <chemistry id="chem0004" num="0004"><img file="EP0055045B1_D0030.tif" /></chemistry>which by our definition is Q²⁺ an amine degradation product thereof, or a precursor thereof, wherein n is in the range from 3 to 12, R, to R₆ which may be the same or different, can be alkyl or hydroxyalkyl groups containing from 1 to 8 carbon atoms and up to five of the groups R₁―R₆ can be hydrogen, the mixture having the molar composition: <tables id="tabl0026" num="0026"><img file="EP0055045B1_D0031.tif" /></tables>wherein X and Y are as above, M is an alkali metal or ammonium and Q is the aforesaid alkylated derivative of a polymethylene diamine, an amine degradation product thereof, or a precursor thereof, or a related compound.

M and/or Q can be present as hydroxides or salts of inorganic or organic acids provided that OH^-/XO₂ requirement is fulfilled.

Preferred alkylated polymethylene diamine starting materials include alkylated hexamethylene diamines, especially methylated hexamethylene diamines, for example 1:6-N,N,N,N¹,N¹,N¹-hexamethyl hexane-1,6-diammonium salts (e.g. halide, hydroxide, sulphate, silicate, aluminate).

Zeolite FU-9 has a molar composition expressed by the formula: <ul id="ul0009" list-style="none"><li>0.5 to 1.5 R₁O : Y₂O₃ : 15 to 30 XO₂ : 0 to 500 H₂O</li></ul> wherein R is a monovalent cation or ¹/n of a cation of valency n, X is silicon and/or germanium, Y is one or more of aluminium, iron, chromium, vanadium, molybdenum, arsenic, manganese, gallium or boron, and H₂0 is water of hydration additional to water notionally present when R is H, and having an X-ray. pattern substantially as set out in Table 10 (as determined by standard technique using copper Kα radiation). Table 10 shows X-ray data for zeolite FU-9 as prepared.

Zeolite FU-9 may be prepared by reacting an aqueous mixture comprising at least one oxide X0₂, at least one oxide Y₂0₃ and at least one tetramethylammonium compound.

The reaction mixture preferably has the following molar composition: <tables id="tabl0027" num="0027"><img file="EP0055045B1_D0032.tif" /></tables>wherein X and Y are as above, M is an alkali metal or ammonium, and Q is a mixture of TMA the tetramethylammonium compound, amine degradation product thereof or a precursor thereof, or a related compound, and A which is a trialkylamine and/or an alkanolamine or salt thereof, where x is equal to 0.2 to 2.0 moles and A preferably contains 1 to 12 carbon atoms. Z- is a strong acid radical present as a salt of M and may be added as a free acid to reduce the free M₂O level to a desired value. M and/or Q can be present as hydroxides or salts of inorganic acids provided the M₂O/XO₂ requirement is fulfilled.

The preferred quaternary compound is a tetramethyl ammonium hydroxide.

For the efficient use of the reactants in methyl t-butyl ether production, it is important that any catalyst for the vapour phase reaction does not promote by-product formation. By virtue of its unique crystal structure, the channel system in our preferred zeolite, <tables id="tabl0028" num="0028"><img file="EP0055045B1_D0033.tif" /></tables>Nu-10, limits the formation of oligomers of isobutene. Thus, a very high proportion of isobutene is converted to methyl t-butyl ether.

The invention is illustrated by the following Examples.

Examples 1-7

These examples illustrate the preparation of zeolite Nu-2 and its use as a catalyst in the production of methyl t-butyl ether (MTBE) from isobutene and methanol.

The synthesis mixture for the preparation of zeolite Nu-2 had the following molar composition: <ul id="ul0010" list-style="none"><li>1.35 Na₂O, 3.14 Q₂O, Al₂O₃, 29 SiO₂, 311 H₂O</li></ul> 8.7 g solid sodium hydroxide were dissolved in 250 g tetraethyl ammonium hydroxide (40% aqueous solution) followed by 16.4 g Kaiser SA alumina powder. Next 649 g colloidal silica were added with stirring. The resulting gel/slurry was crystallised to zeolite Nu-2 in a stirred autoclave after 6 days at 150°C. The washed dried product had the molar composition: <ul id="ul0011" list-style="none"><li>0.6 Na₂O, 2.2 Q₂O, Al₂O₃, 20 SiO₂, 6 H₂O</li></ul>

The product thus obtained was calcined at 450°C for 48 hours, followed by treating with normal hydrochloric acid for 24 hours, washing thoroughly with deionised water and calcined for 24 hours at 450°C. The product was zeolite H-Nu-2.

20 ml of methanol (0.5 mole) and 1 g of Nu-2 zeolite (prepared as above) were added to a glass flask in a stream of nitrogen. 20 ml (0.21 mole) of isobutene was condensed into the cooled flask. The mixture was put into an autoclave then heated with stirring at 90°C for one hour. After the reaction the autoclave was cooled to 0°C and the reaction mixture was analysed by gas chromatography. <tables id="tabl0029" num="0029"><img file="EP0055045B1_D0034.tif" /></tables><tables id="tabl0030" num="0030"><img file="EP0055045B1_D0035.tif" /></tables>

Referring to Table 11, Examples 1-7 illustrate the use of zeolite Nu-2 as catalyst for the production of MTBE from isobutene and methanol.

Example 1 shows the high conversion and selectivity to MTBE in a short reaction time (1 hour) and at 90°C.

Example 2 demonstrates that a lower concentration of catalyst can be used without adversely affecting conversion and selectivity.

Example 3 shows that the reaction can be carried out under high pressure in the presence of an inert diluent (carbon dioxide), with only slight reduction in conversion and selectivity.

Example 4 shows that the reaction can be carried out in the presence of an inert solvent (hexane) with only slight reduction in conversion and selectivity.

Examples 5-7 show the reaction can be carried out at much lower temperature, although the reaction time is increased.

Examples 8-18

These examples illustrate the production of methyl t-butyl ether (MTBE) from isobutene and methanol using a range of zeolites as catalysts. The preparation of the zeolites is described in the relevent patent specifications (to which reference has already been made). The as-made zeolites were calcined and exchanged and calcined as described in Example 1.

The results, shown in Table 11, illustrate that zeolite beta (Example 16) and zeolite Nu-(2) (Examples 1-7) are the most effective catalysts.

Example 19

This example illustrates the production of ethyl t-butyl ether (ETBE) from isobutene and ethanol. 20 ml of ethanol (0.5 mole) and 1 g of Nu-2 zeolite were added to a glass flask in a stream of nitrogen. 20 ml (0.21 mole) of isobutene was condensed into the cooled flask. The mixture was put into an autoclave then heated with stirring at 90°C for one hour. After the reaction the autoclave was cooled to 0°C and the reaction mixture was analysed by gas chromatography.

The results were as follows:- <tables id="tabl0031" num="0031"><img file="EP0055045B1_D0036.tif" /></tables>

Example 20

This example illustrates the production of methyl 3-methylpentyl ether (M3MPE) from 3-methyl- pent-2-ene and methanol using zeolite Nu-2 as catalyst.

10 ml of methanol (0.25 mole), 10 ml of 3-methylpent-2-ene (0.082 mole) and 1 g Nu-2 zeolite were added to a glass flask in a stream of nitrogen. The mixture was put into an autoclave then heated to 90°C for one hour. After the reaction the autoclave was cooled to 20°C and the reaction mixture was analysed by gas chromatography.

The results were as follows:

<tables id="tabl0032" num="0032"><img file="EP0055045B1_D0037.tif" /></tables>

Example 21

This example illustrates the production of ethylene glycol methyl t-butyl ether (EGMTBE) from isobutene and 2-methoxyethanol using zeolite Nu-2 as catalyst.

20 ml of 2-methoxyethanol (0.25 mole), 20 ml of isobutene (0.21 mole) and 0.25 g Nu-2 zeolite were added to a glass flask in a stream of nitrogen. The mixture was put into an autoclave then heated to 90°C for one hour. After the reaction, the mixture was analysed by gas chromatography.

The results were as follows:

<tables id="tabl0033" num="0033"><img file="EP0055045B1_D0038.tif" /></tables>

Examples 22-24

1 gm of Nu-2 zeolite was powdered and packed into a glass tube. The tube and contents were heated by a furnace to 90°C whilst passing a continuous stream of methanol vapour and isobutene over the zeolite bed (mole ratio 2:1 ). The products from the reaction were collected at hourly intervals and analysed by gas chromatography.

The results, shown as Example 22 in Table 12, are as follows:

<tables id="tabl0034" num="0034"><img file="EP0055045B1_D0039.tif" /></tables>

The procedure described for Example 22 was used in Examples 23 and 24 except that the temperature was lowered to 70°C then 50°C as shown in Table 12. Examples 22-24 demonstrate that selectivity to MTBE increases as the temperature is lowered.

Example 25

1 g of zeolite Nu-2 prepared as described in Example 1 was soaked in the bulky amine phenanthridine (20 ml) for 24 hours then filtered, washed well with hexane and dried on a vacuum line at 100°C. The amine treated zeolite was then packed into a glass tube as described in Example 22 and evaluated for the synthesis of MTBE in a flow reactor at 90°C.

The results are shown in Table 12 and demonstrate that at 90°C the bulky amine ion-exchanged onto the surface of the zeolite inhibits the formation of di-isobutene and improves the overall selectivity to MTBE without loss in catalyst activity.

Examples 26-30

These examples illustrate the production of methyl tertiary butyl ether from isobutene and methanol using a range of zeolites in the flow reactor. The preparation of the zeolites is described in the relevant patent specification (to which reference has already been made). The as-made zeolites were calcined and exchanged and calcined as described in Example 1. <tables id="tabl0035" num="0035"><img file="EP0055045B1_D0040.tif" /></tables>

The results, as shown in Table 12, illustrate that zeolites Nu-4 and Nu-10 are particularly effective catalysts.