IE51127B1

IE51127B1 - Process for reducing the water content of ethanol-water mixtures

Info

Publication number: IE51127B1
Application number: IE602/81A
Authority: IE
Original assignee: Snam Progetti
Priority date: 1980-03-31
Filing date: 1981-03-18
Publication date: 1986-10-15
Also published as: SE8101977L; YU82881A; NZ196606A; DD157700A5; YU41038B; SU1034610A3; DK137281A; RO84498B; ES8202776A1; RO84498A; CH648340A5; AU550088B2; PL230427A1; IT1140794B; IE810602L; BR8101872A; DE3112277C2; NO811022L; NL8101594A; GB2072668B

Abstract

An improved process is disclosed for producing petrol-grade C2-C4 alcohols from aqueous mixtures which contain these alcohols. The improvement is that the aqueous mixture is reacted with a tertiary olefin in the presence of a catalyst having an acidic character, preferably at a temperature of from 40 to 90 DEG C and at a space velocity of from 5 to 25 litres of reactants per litre of catalyst per hour. Preferred catalysts are acidic ion-exchange resins, especially those having -SO3H groups. The temperature and space velocity ranges are critical in order to minimize the parasitic ether- forming reaction.

Description

This invention relates to a process for reducing the water content of ethanol-water mixtures, to produce ethanol-water mixtures suitable for adding to petrol without the occurrence of phase separation.

It is known that ethanol has very appreciable octane-number characteristics so that it can be used as such in the formulation of fuel mixtures to reduce the percentage of lead-alkyl additives or to reduce the aromatics content of petrol.

Ethanol is conveniently produced on a commercial scale by the fermentation of carbohydrates. In these procedures, the percentage of alcohol in the fermentation products of sugar-containing juices is below 10%. The subsequent steps directed to recovering alcohol comprise a sequence of distillation steps by which there is obtained a water-ethanol azeotropic mixture which, under atmospheric pressure, has a water content of 4.4% by weight. However, this ethanol still contains too much water for it to be employed directly in fuels, so that further dehydration stages are necessary - 2 51137 The rectification stages and, more particularly, the final dehydration stage, increase the cost of petrol-grade ethanol. This has been conducive to a number of studies dealing with the optimization of heat recovery in conventional systems and also to a number of suggestions for alternative dehydration procedures. Absolute ethanol is obtained at present by azeotropic distillation with benzene. Alternative suggestions have been made recently however, these being based on the stripping of water by the selective absorption on starchy substances, by the preferential absorption on textile fibres, by extraction with solvents in critical phase, by the use of membranes which are impervious to either component, by the absorption on molecular sieves having pore dimensions sufficient to retain water, and by distillation procedures under reduced pressure. All the suggested approaches, however, have the serious drawbacks that they involve a decrease of the liquid product yield and require special apparatus so that the costs are high.

According to the present invention, there is provided a process for reducing the water content of an ethanol-water mixture containing from 4.4 to 7.8% by weight of water to produce an ethanol-water mixture suitable for adding to petrol without the occurrence of phase separation, which process comprises treating the mixture with at least one olefin containing a tertiary carbon atom or with an olefin mixture containing at least one olefin containing a tertiary carbon atom in the presence of an acidic catalyst.

By the process of the invention, the water content of the ethanol-water mixture is reduced since water, by reacting with the olefin concerned, produces a tertiary alcohol. The resultant product, upon stripping the untreated olefins, is a mixture which can be added to fuels in the usual amount without the occurrence of phase separation, even at temperatures below -20°C. - 3 1127 The addition reaction of the olefin containing a tertiary carbon atom to water can be carried out with the aid of conventional catalysts as used for olefin hydrates, such as mineral acids, Lewis acids and ion-exchange resins. In particular, ion-exchange resins comprising polystyrene, di vinyl benzene and polyphenol matrices supporting -SO3H groups are preferred due to their greater simplicity of use.

The working conditions should be carefully selected, inasmuch as too high temperatures or too low spatial velocities worsen the selectivity of the process because the competing reaction, namely the formation of the corresponding ethers, might predominate. The latter reaction should be prevented as far as practicable because it reduces the amount of olefin reacting with the water, the result being that the production of the tertiary alcohol is decreased. The tertiary alcohol is important since it has a solubilizing action on the water residue.

It is preferred that the addition reaction be carried out at a temperature of from 40 to 90°C under a pressure which is so selected as to maintain the hydrocarbon stream being processed either in the liquid or the gaseous phase, depending upon whether it is desired to process the stream concerned in the vapour phase or the liquid phase. When working in the liquid phase, the spatial velocity (LHSV) of the reaction, expressed in litres of feed per litre of catalyst per hour, is preferably from 5 to 25.

For a better understanding of the invention, reference will now be made, by my of example, to the drawing. Figure 1 of the drawing illustrates a particular embodiment of the process according to the present invention, relating to the treatment of an aqueous mixture which contains ethanol with an olefin fraction which contains isobutene. The alcoholic mixture 1 and the - 4 Si 127 olefin fraction 3, together with recycled olefins 2, are fed to a reactor R-1.

The reaction product 5 is sent to a rectification column C-1, from the bottom 6 of which ethanol is recovered together with the reaction product and unreacted water. At the column head 7, an olefin fraction is recovered, a portion 2 of this fraction being recycled to the reactor R-1 and a portion 8 of this fraction being removed from the process. Figure 2 shows a process similar to that of Figure 1, without olefin recycling.

The invention will now be illustrated by the following Examples, in which all parts and percentages are by weight.

In Example 1 there is described a process of the invention. As can be seen from Example 1, it is possible to obtain a product which is perfectly miscible with petrol even at low temperatures, while concurrently achieving an improvement in yield, relative to the starting alcohol, of the order of magnitude of 18% at the expense of a gaseous product, namely isobutene (which has not been directly added to petrol as this is not possible).

A comparison between the results of Example 2 and those of Example 3 shows how important it is to limit the conversion of ethanol. As a matter of fact, by working at a lower space velocity, there is obtained a product which, when mixed with petrol, has a higher turbidity temperature.

A comparison between the results of Examples 4, 5 and 6 shows that, for the same spatial velocity, the reaction temperature is critical, the optimum value being 70°C.

EXAMPLE 1.

In a tubular reaction R-1 of Figure 1, which contained a macroporous acid25 form ion-exchange resin such as Amberlyst 15 (RTM), a mixture of 28.20 parts - 5 51127 of ethanol 1 (containing 7% of water), 61.50 parts of a recycled olefin fraction 2 containing 6.4% of isobutene and 10.36 parts of an olefin fraction 3 containing 50% of isobutene was reacted. The composition of the mixture 4 was as follows: Non-reactive butenes ...................... 62.7% Isobutene ................................. 9.1% Ethanol ................................... 26.2% Water ..................................... 2.0%.

The mixture 4, fed into the reactor at a space velocity of 10 litres per hour per litre of catalyst, was reacted at a temperature of 70°C, and the following reaction product 5 was obtained: Unreacted butenes ......................... 62.7% Isobutene ................................. 4.3% Ethyl tert-butyl ether .................... 3.6% Tert-butyl alcohol ........................ 3.8% Ethanol ................................... 24.6% Water ..................................... 1.0% Subsequent fractionation of the reaction product was carried out in the rectification column C-1 to obtain 33.0 parts of a bottom product 6 having the following composition: Ethanol ................................... 74.5% Water ..................................... 3.0% Tert-butyl alcohol ........................ 11.5% Ethyl tert-butyl ether .................... 11.0%.

Also obtained were 67 parts of a head product 7 having the following composition: -651127 Unreacted butenes .............................. 93.6% Isobutene ....................................... 16.4% The head product 7 was separated into two portions 2 and 8, the former (61.5 parts) being recycled and the latter (5.5 parts) being used as a by-product.

The bottom product 6 could be directly mixed with petrol without any demixing problems.

By way of comparison, the values of the turbidity temperature of the ethanol 1 (mixture A) and of the reaction product 6 (mixture B), both mixed in an amount of 10% with a hydrocarbon stream containing 30% of aromatics and 70% of saturated hydrocarbons, were as follows: Mixture A ........................................ above + 20°C Mixture B ........................................ under -20°C.

EXAMPLE 2.

In the tubular reactor R-1 of Figure 2 containing a macroporous acidform ion-exchange resin such as Amberlyst 15, a mixture of 34.1 parts of ethanol 1 (7.3% water) and 65.9 parts of an olefin fraction 2 containing 50.7% of isobutene was reacted. The composition of the mixture 3 was as follows: Non-reactive butenes ............................. 32.5% Isobutene ........................................33.4% Ethanol .......................................... 31 .6% Water ............................................ 2.5%.

The mixture 3, fed into the reactor at a space velocity of 1.5 litres per hour per litre of catalyst, was reacted at a temperature of 60°C to obtain a reaction product 4 having the following composition: Unreacted butenes ............................... 32.5% Isobutene ....................................... 2.5% Ethyl tert-butyl ether .......................... 45.7% Tert-butyl alcohol .............................. 7.9% Ethanol ......................................... 10.7% Water ........................................... 0.7%.

Subsequent fractionation of the reaction product 4 was carried out in the rectification column C-1 to obtain 65 parts of a bottom product 5 having the following composition: Ethyl tert-butyl ether .......................... 70.4% Tert-butyl alcohol .............................. 12.1% Ethanol ......................................... 16.4% Water ........................................... 1.1%.

The water content of the product 5, based on the sum of the alcohols present, was 3.7%.

The column head product 6 consisted of 35.0 parts of an olefin fraction having the following composition: Unreacted butenes ............................... 92.9% Isobutene ....................................... 7.1%.

The turbidity temperature of a mixture of 10% of the bottom product 5 and 90% of a hydrocarbon fraction (70% of saturated hydrocarbons and 30% of aromatics) was -12°C. - 8 51127 EXAMPLE 3.

In the tubular reactor R-1 of Figure 2, containing a macroporous acid-form ion-exchange resin such as Amberlyst 15, a mixture of 34.2 parts of ethanol 1 (7.8% water content) and 65.8 parts of an olefin fraction 2 containing 48.2% of isobutene was reacted. The composition of the mixture 3 was as follows: Non-reactive butenes ................................ 34.1% Isobutene ........................................... 31.7% Ethanol ............................................. 31.5% Water............................................... 2.7%.

The mixture 3, fed into the reactor at a space velocity of 16 litres per litre of catalyst per hour, was reacted at a temperature of 60°C, and the following reaction product 4 was obtained: Unreacted butenes ................................... 34.1% Isobutene ........................................... 22.9% Ethyl tert-butyl ether .............................. 5.5% Tert-butyl alcohol .................................. 7.9% Ethanol ............................................. 28.9% Water ............................................... 0.7%.

Subsequent fractionation of the reaction product 4 was carried out in the rectification column C-1 to obtain 43.0 parts of bottom product 5 having the following composition: Ethyl tert-butyl ether .............................. 12.8% Tert-butyl alcohol .................................. 18.4% Ethanol ............................................. 67.2% Water .................................................1.6%.

The water content of the product 5, based on the sum of the alcohols present, was 1.8%. - 9 51127 The column head product 6 consisted of 57.0 parts of an olefin fraction having the following composition: Unreacted butenes ................................. 59.8% Isobutene ......................................... 40.2%.

The turbidity temperature of a mixture of 10% of the column bottom product 5 with 90% of a hydrocarbon fraction (70% of saturated hydrocarbons and 30% of aromatics) was under -20°C.

EXAMPLE 4.

In the tubular reactor R-1 of Figure 2, containing a macroporous acidform ion-exchange resin such as Amberlyst 15, a mixture of 31.5 parts of ethanol t (7.5% water content) and 68 .5 parts of an olefin fraction 2 containing 50.8% of isobutene was reacted. The composition of the mixture 3 was as follows: Non-reactive butenes ............................... 33.7% Isobutene .......................................... 34.8% Ethanol ............................................ 29.1% Water .............................................. 2.4%.

The mixture 3, fed into the reactor at a space velocity of 20 litres per litre of catalyst per hour, was reacted at a temperature of 60°C, and the following reaction product 4 was obtained: Unreacted butenes .................................. 33.7% Isobutene .......................................... 25.7% Ethyl tert-butyl ether ............................. 6.5% Tert-butyl alcohol ................................. 7.2% Ethanol ............................................ 26.2% Water .............................................. 0.7%. - 10 51127 Subsequent fractionation of the reaction product 4 was carried out in the rectification column C-1 to obtain 40.6 parts of a bottom product 5 having the following composition: Ethyl tert-butyl ether........................... 16.0% Tert-butyl alcohol ......................... 17.7% Ethanol ............................................. 64.6% Water ............................................... 1.7%.

The water content of the product 4, based on the sum of the alcohols present, was 2.0%.

The column head product 6 consisted of 59.4 parts of an olefin fraction having the following composition: Unreacted butenes ................................... 56.7% Isobutene ........................................... 43.3%.

EXAMPLE 5.

In the tubular reactor R-1 of Figure 2, containing a macroporous acid-form ion-exchange resin such as Amberlyst 15, a mixture of 31.5 parts of ethanol 1 (7.5% water content) and 68.5 parts of an olefin fraction 2 containing 50.8% of isobutene was reacted. The composition of the mixture 3 was as follows: Non-reactive butenes ................................ 33.7% Isobutene ........................................... 34.8% Ethanol ............................................. 29.1% Water............................................... 2.4%.

The mixture 3, fed into the reactor at a space velocity of 20 litres per litre of catalyst per hour, was reacted at a temperature of 70°C, whereby the following reaction product 4 was obtained: - 11 51127 Unreaeted butenes .................................... 33.7% Isobutene ............................................ 14.0% Ethyl tert-butyl ether ............................... 27.3% Tert-butyl alcohol ................................... 8.1% Ethanol .............................................. 16.5% Water ................................................ 0.4%.

Subsequent fractionation of the reaction product was carried out in the rectification column C-1 to obtain 52.3 parts of a bottom product having the following composition: Ethyl tert-butyl ether ............................... 52.2% Tert-butyl alcohol ................................... 15.5% Ethanol .............................................. 31.5% Water ................................................ 0.8%.

The water content of the product 5, based on the sum of the alcohols present, 15 was 1.7%.

The column head product 6 consisted of 47.7 parts of an olefin fraction having the following composition: Unreaeted butenes ..................................... 70.6% Isobutene ............................................. 29.4%.

EXAMPLE 6.

In the tubular reactor R-1 of Figure 2, containing a macroporous ion-exchange resin of acid -form such as Amberlyst 15, a mixture of 31.5 parts of ethanol 1 (7.5% water content) and 68.5 parts of an olefin fraction 2 containing 50.8% of isobutene was reacted. The composition of the mixture 3 was as follows: - 12 S1127 Non-reactive butenes ................................. 33.7% Isobutene ............................................ 34.8% Ethanol .............................................. 29.1% Water ................................................ 2.4%.

The mixture 3, fed into the reactor at a space velocity of 20 litres per litre of catalyst per hour, was reacted at a temperature of 80°C, whereby the following reaction product 4 was obtained: Unreacted butenes .................................... 33.7% Isobutene ............................................ 9.0% Ethyl tert-butyl ether ............................... 37.1% Tert-butyl alcohol ................................... 7.2% Ethanol .............................................. 12.4% Water ................................................ 0.6%.

Subsequent fractionation of the reaction product 4 was carried out in the rectification column C-1 to obtain 57.3 parts of a bottom product 5 having the following composition: Ethyl tert-butyl ether ............................... 64.7% Tert-butyl alcohol ................................... 12.6% Ethanol .............................................. 21.6% Water ................................................ 1.1%.

The water content of the product 5, based on the sum of the alcohols present, was 3.1%.

The column head product 6 consisted of 42.7 parts of an olefin fraction having the following composition: Unreacted butenes ..................................... 78.9% Isobutene ............................................. 21.1%. - 13 51127

Claims

1. A process for reducing the water content of an ethanol-water mixture containing from 4.4 to 7.8% by weight of water to produce an ethanol-water mixture suitable for adding to petrol without the occurrence of phase separation, which process comprises treating the mixture with at least one olefin containing a tertiary carbon atom or with an olefin mixture containing at least one olefin containing a tertiary carbon atom in the presence of an acidic catalyst.

2. A process according to Claim 1, wherein the acidic catalyst is a mineral acid, a Lewis acid or an acidic ion-exchange resin.

3. A process according to Claim 2, wherein the acidic catalyst is an ion-exchange resin comprising a polystyrene, divinyl benzene or polyphenol matrix supporting -SO 3 H groups.

4. A process according to any of Claims 1 to 3, wherein the treatment is carried out at a temperature of from 40 to 90°C.

5. A process according to any of Claims 1 to 4, wherein the treatment is carried out at a space velocity, LHSV, of from 5 to 25 litres per litre of catalyst per hour.

6. A process according to any of Claims 1 to 5, wherein the olefin is isobutene.

7. A process for reducing the water content of an ethanol-water mixture, substantially as described with reference to Figure 1 or Figure 2.

8. A process for reducing the water content of an ethanol-water mixture, substantially as described in any of the foregoing Examples.

9. An ethanol-water mixture whose water content has been reduced by a - 14 51127 process according to any of Claims 1 to 8.

10. A mixture as claimed in Claim 9, from which olefin(s) have been removed.

11. Petrol containing, in an additive, a mixture as claimed in 5 Claim 10.