WO1996030325A1

WO1996030325A1 - Process for the purification of 1,3-diethoxypropane by means of subatmospheric pressure distillation

Info

Publication number: WO1996030325A1
Application number: PCT/GB1996/000593
Authority: WO
Inventors: Simon Frederick Thomas Froom
Original assignee: Bp Chemicals Limited
Priority date: 1995-03-24
Filing date: 1996-03-14
Publication date: 1996-10-03
Also published as: GB9506052D0

Abstract

This invention relates to a process for separating 1,3-diethoxypropane from mixtures thereof with 3-ethoxypropanol by distilling a composition comprising 1,3-diethoxypropane and 3-ethoxypropanol in a distillation zone operated at subatmospheric pressure and removing from said zone a product stream comprising relatively pure 1,3-diethoxypropane. 1,3-diethoxypropane is a valuable solvent and diluent used in the coatings, varnish and paint industry.

Description

PROCESS FOR PURIFICATION OF 1 ,3-DIETH0XYPR0PANE BY MEANS OF SUBATMOSPHERIC PRESSURE DISTILLATION

The present invention relates to a separation process and in particular to the separation of 1,3 -diethoxypropane from 3-ethoxy propanol.

1,3 -diethoxypropane is suitable for use as a solvent in the chemical industry and may be prepared by catalytic hydrogenation of 1 , 1 ,3-triethoxypropane. It is reported in "Acrolein", C W Smith, Editor, John Wiley & Sons (1962) at page 114 that the diethyl acetal of ethoxypropionaldehyde (1, 1,3-triethoxypropane) undergoes hydrogenation in the presence of Raney nickel to form the diethyl ether of 1 ,3-propanediol (1,3-diethoxypropane) and ethanol by-product.

PCT patent application serial number PCT/US94/07517 describes a process for making a 1 ,3-diether compound represented by the formula (I):

ROCH₂CH₂CH₂OR (I) wherein R is an alkyl group having 1 to 4 carbon atoms, the process comprising hydrogenating an acetal of the formula (II):

ROCH₂CH₂CH(OR)₂ (II) wherein R has the same meaning as in formula (I) above, in the presence of a catalyst composition comprising at least one catalytic metal selected from the group consisting of Pd, Ni, Co, Pt, Rh and Ru and a support material, said support material being one or more selected from the group consisting of silica, alumina, silica-alumina, aluminosilicates and carbon. A problem arises when 1,3 -diethoxypropane is prepared by hydrogenation of 1, 1,3-triethoxypropane in that in addition to ethanol by-product, undesirable by¬ products such as 3-ethoxypropanol and ethyl propyl ether are also formed. Ethanol and ethyl propyl ether may be readily separated from 1,3 -diethoxypropane by distillation at atmospheric pressure. However, it has been found that 1,3- diethoxypropane and 3-ethoxypropanol despite having relatively different boiling points of 143°C and 160°C respectively at atmospheric pressure, are difficult to separate by conventional distillation at atmospheric pressure Presumably, this is due to molecular interactions, and hence requires the use of a distillation zone having a large number of theoretical stages to achieve a high recovery of suitably pure 1,3 -diethoxypropane. Since such distillation zones are expensive on an industrial scale, there is a need for a more economic process for separating 1,3- diethoxypropane from 3-ethoxypropanol It is well known that where molecules in a mixture interact, their behaviour under distillation conditions is difficult to predict It has now been unexpectedly found that by operating a distillation zone at sub-atmospheric pressure the separation of 1,3-diethoxypropane from 3- ethoxypropanol is significantly improved over that obtained at atmospheric pressure

According to the present invention there is provided a process for separating 1,3 -diethoxypropane from 3-ethoxypropanol which process comprises distilling a composition comprising 1,3 -diethoxypropane and 3-ethoxypropanol in a distillation zone operated at sub-atmospheric pressure and removing from the distillation zone a product stream comprising 1,3 -diethoxypropane

Preferably, the distillation zone of the present invention is operated at a head pressure in the range from 0 006 (0 6 KPa) to 0 8 bara (80 Kpa) and most preferably in the range from 0 01 bara ( 10 KPa) to 0 8 bara (80 KPa)

Preferably, the 1 ,3 -diethoxypropane product stream has a purity of at least 98 5% by weight Preferably, the 1,3 -diethoxypropane product contains less than 0 5% by weight, preferably less than 0 3% by weight total alcohols Preferably, the 1,3-diethoxypropane product contains less than 0 5% by weight, preferably less than 0 3% by weight 3-ethoxypιopanol and high boiling impurities

The process of the present invention may be operated as a batch or continuous process, preferably as a continuous process

When operated as a batch process the process comprises charging to a kettle having a distillation zone, the composition comprising 1,3 -diethoxypropane and 3-ethoxypropanol, operating the distillation zone at sub-atmospheric pressure and removing from the distillation zone a product stream comprising 1,3- diethoxypropane whilst the 3-ethoxypropanol remains in the kettle

When operated as a continuous process, the process comprises feeding the composition compπsing 1 ,3 -diethoxypropane and 3-ethoxypropanol to the feed point of the distillation zone; operating the distillation zone at sub-atmospheric pressure and removing from the distillation zone, at a point above the feed point a product stream comprising 1,3 -diethoxypropane and removing from the distillation zone at a point below the feed point a co-product stream comprising 3- ethoxypropanol.

Preferably, the 1,3-diethoxypropane product stream is removed from the head of the distillation zone in both batch and continuous operation. Preferably, the 3 -ethoxypropanol co-product stream is removed from the base of the distillation zone in continuous operation. The 1,3 -diethoxypropane product stream may be removed from the distillation zone as a vapour or liquid. In continuous operation, the 3- ethoxypropanol co-product stream may be removed from the distillation zone as a vapour or a liquid, preferably as a liquid.

Suitably, the distillation zone used in the process of the present invention has up to 50 theoretical stages. However, the number of theoretical stages will depend on such factors as feed composition, purity of product required, the temperature and pressure at which the column is operated and the reflux ratio. The distillation zone is operated with suitable reflux to the head of the distillation zone. Preferably a reflux ratio of 0 : 1 to 25 : 1 is employed. The reflux ratio is the ratio of the reflux which is returned to the distillation zone and the amount of material which is removed from the head of the distillation zone.

The weight ratio of 1 ,3-diethoxyρropane: 3 -ethoxypropanol in the feed composition is suitably in the range from 1 : 3 to 10000 : 1 preferably in the range from 20 : 1 to 10000 : 1 The feed composition comprising 1,3 -diethoxypropane and 3- ethoxypropanol may be derived by hydrogenation of 1, 1,3-triethoxypropane, for example, as described in PCT patent application serial number PCT US94/07517. The composition when derived from such processes may contain, in addition to 1,3 -diethoxypropane and 3 -ethoxypropanol, low boiling components such as ethanol and ethyl propyl ether and high boiling components such as unreacted

1, 1,3-triethoxypropane and l-ethoxy-3-(3-ethoxypropoxy)propane. By low boiling components is meant components having a boiling point below that of 1,3- diethoxypropane. By high boiling components is meant components having a boiling point above that of 1,3 -diethoxypropane. Preferably, such a composition derived from such hydrogenation processes is fed to a distillation zone preferably operated at atmospheric pressure where the low boiling components are removed from above the feed point, preferably the head of the distillation zone and a composition comprising 1,3 -diethoxypropane, 3- ethoxypropanol and any high boiling components is removed from below the feed point, preferably from the base of the distillation zone. The composition removed from the base of the distillation zone is then used in the process of the present invention.

Thus, in a preferred embodiment of the present invention there is provided a process for the preparation of 1,3-diethoxypropane which process comprises the steps of:

(a) hydrogenating 1 , 1 ,3-triethoxypropane in the presence of a suitable hydrogenation catalyst to produce a composition comprising 1,3- diethoxypropane, 3 -ethoxypropanol, low boiling and high boiling components; (b) feeding the composition produced in step (a) to a first distillation zone preferably operated at atmospheric pressure;

(c) removing the low boiling components from above the feed point, preferably from the head of the first distillation zone;

(d) removing a composition comprising 1,3 -diethoxypropane, 3- ethoxypropanol and high boiling components from below the feed point, preferably from the base of the first distillation zone;

(e) feeding the composition obtained in step (d) to a second distillation zone operated at sub-atmospheric pressure;

(f) removing a product stream comprising 1,3-diethoxypropane and containing less than 0.5% by weight 3 -ethoxypropanol from above the feed point of the second distillation zone, preferably from the head of the distillation zone; and

(g) removing a second co-product stream comprising 3 -ethoxypropanol and high boiling components from below the feed point of the second distillation zone, preferably from the base of the second distillation zone.

The invention was initially tried out in practice on a laboratory scale by operating the process under conditions of reduced pressure in a packed column. Surprisingly, this appeared to provide a better separation of the offending component, 3 -ethoxypropanol, than was found under atmospheric pressure. The activity coefficients of the components in the impure product, which were hitherto unknown in the literature, were calculated using an ASPEN® programme and a computer model developed based on these calculations. Thus, in order to evaluate this concept of using reduced pressure, the laboratory scale experiment was extrapolated using this computerised model. The results of this extrapolation of the laboratory experiments are represented graphically in Figure 1 which shows the relationship between reflux ratio and the number of theoretical stages required to separate 1,3-diethoxypropane from 3 -ethoxypropanol at three different distillation zone head pressures (0.006, 0.5 and 0.8 bara). These results form the basis of the following examples. Example 1

A batch distillation apparatus was used to separate 1,3 -diethoxypropane and 3 -ethoxypropanol.

The batch distillation apparatus comprised a 5 litre kettle equipped with a thermometer, nitrogen bleed and a packed distillation column. The packed distillation column comprised a 35 x 3.4 cm section and a 95 x 4.0 cm section, both sections containing Pro-Pak® column packing material (6mm x 6mm). The packed distillation column was well lagged with Rockwool®. To the top of the distillation column was fitted a condenser, a vapour reflux divider, a thermometer and a distillate fraction collector. A trial distillation using a mixture of ethanol and iso-propanol showed that the distillation column had the equivalent of about 28 theoretical stages for the separation of ethanol and propanol, at both atmospheric and sub-atmospheric head pressure (22.6 KPa).

The kettle was charged with 3252g of a product composition derived by hydrogenation of 1,1,3-triethoxypropane in the presence of a palladium catalyst. The composition was estimated from gas chromatography analysis to contain (by weight) 23.6% ethanol, 2.2% ethyl propyl ether, 1.4% 3 -ethoxypropanol, 65.4% 1,3-diethoxypropane and 3.3% 1, 1,3-triethoxypropane (i.e. a 1,3 -diethoxypropane 3 -ethoxypropanol weight ratio of 46.7: 1 ). Distillation was then commenced at atmospheric pressure. A first distillate fraction comprising low boiling components (ethanol and ethyl propyl ether) was removed at a temperature in the range 49 to 81 °C. A second distillate fraction comprising 1,3 -diethoxypropane, amounting to 523g, was then collected using a reflux ratio of 4: 1 and was found to contain by weight about 99.6% 1,3- diethoxypropane and 0. 15% 3-ethoxypropanol by gas chromatography. The amount of 1,3 -diethoxypropane recovered in the second vapour fraction was thus only 25% of the total amount of 1,3-diethoxypropane in the composition charged to the kettle

The apparatus was then shut down and a sample of the composition in the kettle was removed. Gas chromatography showed that the ratio of 1,3- diethoxypropanol to 3 -ethoxypropanol in the sample was 33.9: 1 (by weight) The pressure in the distillation apparatus was then reduced to 23.3 KPa and the contents were allowed to regain equilibrium A third distillate fraction 50 lg was then collected, again using a reflux ratio of 4.1 as for the second vapour fraction. Analysis of this fraction by gas chromatography showed that it contained by weight about 99.6% 1,3 -diethoxypropane and only 0 02% 3 -ethoxypropanol. This shows that by operating at sub-atmospheric pressure a distillate fraction having less 3- ethoxypropanol is obtained than that obtained at atmospheric pressure in the second distillate fraction, despite the ratio of 1,3 -diethoxypropane 3- ethoxypropanol being less in the kettle

The pressure in the distillation column was then raised to 59.7 KPa and distillation was continued using a reflux ratio of 4: 1 This allowed the collection of virtually all the remaining 1,3 -diethoxypropane as a fourth fraction which contained by weight 99 2% 1,3 -diethoxypropane and 0 1% 3-ethoxypropanol At the end of the experiment the residual composition in the kettle was analysed, by gas chromatography, to have a 1,3 -diethoxypropane to 3 -ethoxypropanol ratio of 0 85 1 by weight This shows that despite continuing decrease in the ratio of 1,3- diethoxypropane 3 -ethoxypropanol, in the composition in the kettle, operation at sub-atmospheric pressure still produces 1 ,3 -diethoxypropane product of acceptable purity

This experiment showed that the first 1,3 -diethoxypropane fraction which was collected at atmospheric pressure contained higher levels of 3 -ethoxypropanol impurity than the two fractions collected at sub-atmospheric pressure, despite the relatively favourable kettle composition compared to the later fractions Thus, this experiment demonstrates the benefit of separating 1,3 -diethoxypropane and 3- ethoxypropanol by distillation at sub-atmospheric pressure Example 2

The feed composition used for this Example was as follows Table 1 - Feed Composition:

Component Mass Fraction

Ethanol 0.0004

1 ,3 -Diethoxypropane 0.9584

Ethyl propyl ether 0.0001

3 -Ethoxypropanol 0.0411

Computer simulation of the distillation process using an ASPEN® computer model showed that at atmospheric pressure, it was not possible to separate a 1,3-diethoxypropane product of at least 99.5 weight % purity (with the remaining 0.5 weight % being alcohols such as 3-ethoxypropanol) even with a distillation zone having 100 theoretical stages.

Figure 1 represents in graphical form the computer simulated relationship between reflux ratio and the number of theoretical stages required to separate 1,3- ethoxypropane from 3 -ethoxypropanol at three different distillation zone head pressures. When a distillation zone having 100 theoretical stages was simulated using a head pressure of 0.8 bara (80 Kpa) a reflux ratio of about 9 was required to separate a 1,3 -diethoxypropane product of at least 99.5 weight % purity . When the number of theoretical stages was decreased to 70 the reflux ratio required to achieve the same separation increased to 1 1. As the number of theoretical stages was decreased further, the reflux ratio required to achieve the same separation increased more rapidly. A similar relationship was observed using a head pressure of 0.5 bara (50 KPa). With a head pressure of 0.006 bara (0.6 KPa) only a very low reflux ratio was required even for a distillation zone having 25 theoretical stages.

When the distillation zone is operated at a pressure below about 0.006 bara (0.6 KPa), the simulated temperature at the head of the distillation zone is low, making condensation of vapour removed from the head of the distillation zone more difficult because of the need to use chilled condensers. Example 3

The distillation process was simulated (ASPEN® computer model) using a feed having the composition given in Table 2 and with the distillation zone operated using the conditions given Table 3. The calculated compositions of the heads product stream and the base co-product stream are shown in Tables 4 and 5 respectively. This example is according to the present invention and shows that under these simulated conditions a 1,3 -diethoxypropane product of at least 99.5% purity would be obtained.

Table 2 - Feed Composition:

Component Mass Fraction

Ethanol 0.0008

1 ,3 -Diethoxypropane 0.9589

3 -Ethoxypropanol 0.041 1

Table 3 - Distillation Zone:

Head Pressure (KPa) 5

Number of Theoretical Stages 28

Reflux Ratio 1.2

Feed Stage 16

Mass Ratio of Heads Product Stream to 0.951 Feed numbered from the top of the distillation zone

Table 4 - Heads Product Stream:

Component Mass Fraction

Ethanol 0.0008

1 , 3 -Diethoxypropane 0.9976

3 -Ethoxypropanol 0.0024

Table 5 - Base Co-product Stream:

Component Mass Fraction

1 ,3 -Diethoxypropane 0.2031

3 -Ethoxypropanol 0.7969

Claims

Claims:

1. A process for separating 1,3 -diethoxypropane from 3-ethoxypropanol which process comprises distilling a composition comprising 1,3 -diethoxypropane and 3 -ethoxypropanol in a distillation zone operated at sub-atmospheric pressure and removing from the distillation zone a product stream comprising 1,3- diethoxypropane.

2. A process according to Claim 1 wherein the distillation zone is operated at a head pressure in the range from 0.006 bara (0.6 Kpa) to 0.8 bara (80 KPa).

3. A process according to Claim 1 or 2 wherein the distillation zone is operated at a head pressure in the range from 0.01 (10 Kpa) to 0.8 bara (80 KPa).

4. A process according to any one of the preceding Claims wherein the 1,3- diethoxypropane product stream has a purity of at least 98.5% by weight.

5. A process according to any one of the preceding Claims wherein the 1,3- diethoxypropane product stream contains less than 0.5% by weight of total alcohols.

6 A process according to any one of the preceding Claims wherein the 1,3- diethoxypropane product stream contains less than 0.5% by weight of 3- ethoxypropanol and high boiling impurities.

7. A process according to any one of the preceding Claims wherein said process is operated as a continuous process by a. feeding the composition comprising 1,3-diethoxypropane and 3- ethoxypropanol to a feed point of the distillation zone, b. operating the distillation zone at sub-atmospheric pressure and c removing from the distillation zone as a vapour or a liquid i. at a point above the feed point a product stream comprising 1,3- diethoxypropane and ii. at a point below the feed point a co-product stream comprising 3- ethoxypropanol 8 A process according to any one of the preceding Claims wherein the distillation zone has up to 50 theoretical stages 9 A process according to any one of the preceding Claims wherein the distillation zone is operated at a reflux ratio of 0 1 to 25 1

10 A process according to any one of the preceding Claims wherein the weight ratio of 1,3 -diethoxypropane 3 -ethoxypropanol in the feed composition is in the range from 1 3 to 10000 1 11 A process for the preparation of 1 ,3 -diethoxypropane which process comprises the steps of

(a) hydrogenating 1 , 1 ,3-triethoxypropane in the presence of a hydrogenation catalyst to produce a composition comprising 1,3 -diethoxypropane, 3- ethoxypropanol, low boiling and high boiling components, (b) feeding the composition produced in step (a) to a first distillation zone operated at atmospheπc pressure,

(c) removing the low boiling components from above the feed point from the head of the first distillation zone,

(d) removing a composition comprising 1,3 -diethoxypropane, 3- ethoxypropanol and high boiling components from below the feed point from the base of the first distillation zone,

(e) feeding the composition obtained in step (d) to a second distillation zone operated at sub-atmospheric pressure,

(f) removing a product stream comprising 1 ,3-dιethoxγpropane and containing less than 0 5% by weight 3 -ethoxypropanol from above the feed point of the second distillation zone, and

(g) removing a second co-product stream comprising 3 -ethoxypropanol and high boiling components from below the feed point of the second distillation zone