GB2116546A - Production of t-butyl alkyl ethers - Google Patents

Abstract

In producing t-butyl alkyl ethers by etherifying with aliphatic alcohols isobutene in a hydrocarbon feedstock containing butadiene in addition to the isobutene, the increase in the pressure drop in the etherification reactor(s) that is due to the butadiene is eliminated by feeding the reactants from the bottom upwards. The reactors preferably contain an acidic ion-exchange resin catalyst.

Description

SPECIFICATION Production of t-butyl alkyl ethers This invention relates to a process for producing t-butyl alkyl ethers in the presence of butadiene.

The addition reaction of alcohols to tertiary olefins such as isobutene to produce t-butyl alkyl ethers is an exothermic reaction which is acid catalysed. In the presence of suitable catalysts, such as macroporous ion-exchange resins, the reaction proceeds to equilibrium in times which are of industrial interest, even at relatively low temperatures (40-500C).

It is known that it is not necessary to operate with high purity isobutene; instead, any cut which contains it is suitable, as the alcohol addition takes place selectively at the double bonds which are bonded to a tertiary carbon atom. Cuts from catalytic cracking and cuts from steam cracking, the latter either before or after extraction of butadiene, are particularly suitable.

When using as olefin feedstock the C4 fraction from catalytic cracking or from steam cracking afte extraction of butadiene, and using methanol or ethanol as the alcohol and a sulphonic macroporous resin type catalyst, namely Amberlyst (RTM) 1 5 or lewatit (RTM) SPC 108, the reaction can be carried out industrially in a wide range of reactor designs and under a wide range of operating conditions, directed towards optimising the conversion of one or other of the reactants. In these cases, a high selectivity is obtained, together with good performance of the catalyst both in terms of catalytic activity and life.

When operating with an olefin cut with a high butadiene content, such as the C4 cut from steam cracking before extraction of butadiene, the operating conditions must be accurately defined in order to obtain a butadiene recovery exceeding 9899%. In particular, it is necessary to maintain a strict relationship between the temperature and spacial velocity, as described in US-A-4039590.

It has however been noted that when carrying out the isobutene etherification reaction in the presence of butadiene in a tubular reactor containing a macroporous resin, and feeding the reactants from the top downwards in the normal manner, an increase in the pressure drop takes place with time, even when operating under conditions which allow a high butadiene recovery of 99% or more, and in addition a slight conversion fall-off takes place with time.

However, an identical test carried out with a butadiene-free cut shows neither a pressure drop increase not a conversion reduction. It has been surprisingly found, in accordance with the present invention, that by feeding the butadiene-containing feedstock so that it flows from the bottom upwards, under slight bed expansion conditions, the pressure drop remains constant with time.

The process according to the present invention comprises producing one or more t-butyl alkyl ethers, by reacting isobutene of a hydrocarbon feedstock, which feedstock contains butadiene in an amount of from 10 to 70% by weight, with one or more aliphatic alcohols, preferably methanol or ethanol, in one, two or more reactors, preferably in series. The process is characterised in that the reactants (i.e. the hydrocarbon feedstock containing butadiene and the alcohol or alcohols) and the reaction products flow through the reactor or reactors, which preferably contain a macroporous acidic ion-exchange resin catalyst, from the bottom upwards.

The linear velocity of the reactants through the reactor or reactors is preferably from 0.5 to 2 cm/sec. The temperature in the reactor or reactors is preferably from 50 to 600 C, more preferably from 50 to 550C.

The invention will now be illustrated by the following Example and Comparative Examples, wherein the abbreviation "MTBE" means "methyl t-butyl ether".

EXAMPLE 1 There was used a C4 cut having the following composition: Propylene 0.46% by weight Isobutane 6.87% by weight n-Butane 11.80% by weight Butene-1 1 1.39% by weight Isobutene 30.19% by weight Butene-2 + 3.2 5% by weight Cis-butene-2 1.55% by weight Butadiene 34.43% by weight The cut was mixed with methanol such that the isobutene:methanol molar ratio was 0.85:1. The mixture was fed at a throughput of 14 litres/hour and a temperature of 500C through two reactors connected in series, having a total capacity of 4.5 litres and filled with 4 litres of catalyst. The catalyst was a macroporous sulphonic resin with an exchange capacity of 4.8 meq H+/g dry. The reactants flowed from the bottom upwards. The linear velocity was 1 cm/sec.

The conversion and pressure drops with respect to time were as given in the following Table 1.

TABLE 1

Time (hours) 24 500 2000 Pressure drop in 1 sot reactor (kg/cm2) 0.2 0.2 0.2 Pressure drop in 2nd reactor (kg/cm2) 0.2 0.2 0.2 MTBE (% by weight) 38.1 38 38 Dimers and codimers (% by weight) 0.05 0.05 0.05 Butenyl ethers (% by weight) 0.2 0.15 0.2 Isobutene conversion 96.6 96.4 96.4 Butadiene recovery > 99 > 99 > 99 EXAMPLE 2 (comparative) The feedstock described in the preceding Example was fed under the same temperature and spacial velocity conditions to the two reactors connected in series, but in such a manner that the flow direction of the reactants was from the top downwards.

At the beginning of the test, the results were analogous to those of the preceding Example, but as time passed a progressive pressure drop increase and a slight conversion fall-off were observed, as can be seen from the following Table 2.

TABLE 2

Time (hours) 24 500 2000 Pressure drop in 1 st reactor (kg/cm2) 0.3 0.4 1.5 Pressure drop in 2nd reactor (kg/cm2) 0.3 0.5 1.8 MTBE (% by weight) 38 37.9 36 Dimers and codimers (% by weight) 0.1 0.1 0.05 Butenyl ethers (% by weight) 0.2 0.2 0.2 isobutene conversion 96.4 96.1 91.3 Butadiene recovery > 99 > 99 > 99 EXAMPLE 3 (comparative) Methanol was added to an olefin cut containing 35% by weight of isobutene and 0.2% by weight of butadiene, such that the isobutene:methanol molar ratio was 0.85:1. The mixture was fed at a throughput of 1 4 litres/hour and a temperature of 500C to the two reactors connected in series, the flow direction being from the top downwards. In the absence of butadiene, no pressure drop increase or conversion fall-off with time were observed, as can be seen from the following table 3.

TABLE 3

Time (hours) 24 500 2000 Pressure drop in 1 sot reactor (kg/cm2) 0.3 0.3 0.3 Pressure drop in 2nd reactor (kg/cm2) 0.3 0.3 0.3 MTBE (% by weight) 43.1 42.9 43 Dimers and codimers (% by weight) 0.3 0.3 0.2 Isobutene conversion 96.8 96.6 96.6

Claims (9)

1. A process for producing one or more t-butyl alkyl ethers, which comprises reacting isobutene of a hydrocarbon feedstock, which feedstock contains butadiene in an amount of from 10 to 70% by weight, with one or more aliphatic alcohols in one or more reactors, the reactants and the reaction products being made to flow from the bottom upwards through the reactor or reactors.

2. A process according to claim 1 , wherein the reactants have a linear velocity of from 0.5 to 2 cm/sec.

3. A process according to claim 1 or 2, wherein the temperature in the reactor or reactors is from 50 to 600C.

4. A process according to claim 3, wherein the temperature in the reactor or reactors is from 50 to 550C.

5. A process according to any of claims 1 to 4, wherein the alcohol is methanol or ethanol.

6. A process according to any of claims 1 to 5, wherein the reaction is carried out in two or more reactors in series.

7. A process according to any of claims 1 to 6, wherein the reactor or reactors contain a catalyst comprising a macroporous acidic ion-exchange resin.

8. A process according to claim 1, substantially as described in the foregoing Example 1.

9. A t-butyl alkyl ether produced by a process according to any of claims 1 to 8.