DE1960139B2 - Process for the production of alcohols by hydration of olefins with 2-3 carbon atoms - Google Patents

Description

20th

The invention relates to a process for the preparation of alcohols by hydrating olefins with 2 - 3 carbon atoms on a fixed bed catalyst in the gas or gas-liquid phase.

It is known to produce alcohols by direct gas phase hydration of olefins. The usual one Technology consists in the fact that, due to the unfavorable equilibrium of the to be used Reaction temperatures, except at elevated pressure -io must also work with very large amounts of circulating gas.

In the known method, it is customary to reduce the concentration of the circulating gas to a value of hold about 85% by volume. This is because of the fact that the higher the concentration of circulating gas Although the conversion at the catalyst increases and energy and investment costs are reduced, at the same time, however, the amount of gas to be discharged increases significantly, since the impurities in the Can enrich circulating gas only slightly. If, on the other hand, you work with a lower concentration Olefin in the recycle gas; d. H. with a much higher concentration of impurities in the circulating gas, so the amount of gas to be discharged decreases considerably. The way of working with circulating concentrations is essential - »5 However, below 85% by volume is out of the question because the olefin conversion per pass under otherwise constant conditions practically proportional to the decrease in the olefin concentration in the circulating gas decreases.

The impurities that have to be removed from the cycle gas are, on the one hand, substances that are introduced with the feed olefin and, on the other hand, by-products that occur during hydration arise from olefins. The impurities brought in with the olefin used are substances that in part boil lower than the olefin, with ethylene (ethanol production) z. B. methane, nitrogen, and some boil higher, like ethane and C3 hydrocarbons; in the case of propylene (isopropanol production) in the lower than propylene boiling substances, besides methane and nitrogen, also ethylene and the higher boiling impurities Propane and O-hydrocarbons. The by-products formed during hydration are particular low molecular weight olefin polymers, such as dimers, trimers and tetramers, which during the Reaction on the catalyst can form the corresponding alcohols, and the corresponding saturated

Hydrocarbons.

Separation of these alcohols from the main alcohol product is not easy. The low molecular weight Olefin polymers can also polymerize further to give higher hydrocarbons, which are in the form are carried along by the finest mists with the circulating gas and are extremely difficult to separate. By occupying the catalyst, the latter cause a decrease in its activity and a reduction the service life.

The discharged gas has so far either been burned or in a plant that allows the recovery of Olefins of lower concentration permitted to be used (e.g. alkylation of benzene) or in the Recirculated olefin recovery or worked up on site by distillation.

For example, DE-AS 12 10 768 mentions a work-up of the olefins by distillation. The distillative Work-up is carried out in accordance with the prior art at low to medium pressures and accordingly carried out at a low temperature, d. H. under conditions well below the critical olefin data lie. The disadvantage of this procedure can be seen, among other things, in the fact that multi-stage refrigeration units for the Condensation and columns with a larger radius must be used; besides is because of the higher heat of evaporation of the olefins at lower temperatures a higher energy expenditure for Evaporation and condensation required. According to the distillative separation processes customary in the art up to now (U 11 m a η η, Encyclopedia of Technical Chemistry, 3rd Edition, Volume 10, Pages 150-161) for low boiling olefins are two for the separation of lower and higher boiling impurities Columns required, the low-boiling impurities being separated off in the first column, while in the second column the higher-boiling impurities in the bottom of the column and the concentrated olefin can be drawn off at the top of the column.

According to Asinger, Chemistry and Technology of Monoolefins, 1957, page 576, it is further known to use 97% ethylene in the production of ethyl alcohol. It is also about the use of ethylene, the process belonging to the state of the art on this concentration was brought.

It has now been found that, contrary to the general rules of kinetics, according to which at increased Concentration an increased coincidence of the reaction participants and thus in the present case an increased polymer formation would also have to occur, the formation of the lower polymers with increasing Olefin concentration in the recycle gas decreases.

It has surprisingly been shown that, contrary to the prejudice existing in technology, the low molecular weight olefins, such as ethylene and propylene, with advantage under operating conditions close to the can purify and concentrate critical data of these olefins. This makes it possible to turn off the circulating gas the olefin hydration at higher pressures and temperatures than usual to purify. At this Working method has surprisingly been found that part of the lower than that to be cleaned Olefin-boiling impurities are located in the bottom of the column and are thus already separated here can be.

The invention is therefore a method for

Production of alcohols by hydration of olefins with 2-3C-atoms on a fixed bed catalyst in the gas or gas-liquid phase, thereby characterized in that the unreacted olefin gas leaving the reactor with the reaction mixture after condensation of water and alcohol and separation of the same partly distilh'.iv under conditions concentrated near the critical point of olefins, except for those higher than olefin boiling impurities and the higher polymeric ι υ the lower boiling than the olefin impurities via the sump of the hydrocarbons Distillation column are separated.

In the corresponding procedure according to the invention, the column for separating off these low-boiling impurities is omitted. Another surprising advantage of the procedure under distillation conditions close to the critical point of the olefin is to be seen in the fact that the column can be increased to a multiple of the design load without having to increase the energy consumption. Despite the reflux being reduced in this way, the separating effect of the column is still very good. The products that were previously not or only extremely imperfectly separated by the separation devices for oil mist customary in technology can be separated easily and completely from the circulating gas. As a result, these oil mists are now present in the olefin used again for hydration in a smaller amount corresponding to the stress of the concentration; the hydration catalyst is protected accordingly. The distillative concentration according to the invention under conditions close to the critical point of the olefins thus takes place in the presence of oils formed during hydration. In the case of ^r in 3> of hydration resulting oils are next ether and lesser amounts of higher alcohols predominantly hydrocarbons having a boiling range up to 350 ⁰ C. As a method foreign substances washing z come. B. paraffin oils similar boiling > o situation into consideration.

It is believed that in the process of the invention for olefin purification of the distillation Washing extraction by the oil mist in the circulating gas, which mainly consists of higher molecular weight Hydrocarbons exist, is superimposed, whereby the excellent separation effects are achieved. These The exception is supported by experiments in which a synthetic mixture of pure gases is appropriate the composition of the cycle gas once with and once without the oil from the distillation being injected is subjected. It can be seen that the amount of impurities drawn off at the bottom of the column when injecting oil is 8 times greater than when distilling without the addition of oil.

The advantages of the measures according to the invention are considerable. In this way, the lower-boiling impurities that are always in the feed olefin can no longer accumulate in the circulating gas. They are easily removed together with the higher boiling w impurities and hydrocarbon oils via the bottom of the distillation column, thereby eliminating special columns for the separation of the low boilers. Ether and other alcohols hj can also be obtained from the mixture obtained in the bottom of the column. It is also possible to dimension the concentration columns considerably smaller, the energy consumption is significantly lower because of the lower heat of evaporation in the vicinity of the critical point, the liquefaction takes place relatively easily by low heat extraction at a relatively high temperature, so that cheaper coolants can be used. For the recycling of the purified olefin, if it is withdrawn in gaseous form at the top of the column, to the operating pressure of the hydration system, only a correspondingly lower energy is required, likewise because of the higher operating pressure of the separating column. In addition, the water content of the olefin to be distilled does not have to meet too high requirements, since the risk of the formation of solid hydrates, which lead to blockages, is correspondingly lower at a higher temperature.

When using the procedure according to the invention, the hydration process is also more advantageous, because with the same olefin content in the cycle gas when applying the measures according to the invention there is a much lower content of oil mist. Because this oil mist is partly on the catalytic converter precipitate and thus block its active centers, the decrease in the activity of the Catalyst prevented to a large extent. Due to the increased separation of oil mist from the circulating gas its density decreases. The advantage of this for the hydration process is that the energy requirement is reduced reduced for both the circulation compressor and the superheater.

Example 1 (comparison)

Hydration of ethylene
(State of the art, see scheme)

In one plant, the circulation ^{compressor 3 drives 45,000 Nm 3 of} ethylene (85%) together with 2100 NmVh of fresh ethylene (99.9%) from the fresh ethylene compressor 1 via line 10 into the heat exchanger 4 via line 12. With the process water pump 2, 16mVh of degassed deionized water are fed in via line 11. The reactants are heated and evaporated in the heat exchangers 4 in countercurrent by the products leaving the reactor 6, then brought to the reaction temperature of 265 ° C. in the superheater 5 and then fed to the reactor 6 via line 13. The pressure at the reactor inlet is 70 atm. The reactor is ^{filled with 38 m 3 of} catalyst, which was produced by leaching a spherical cracking catalyst of approx. 5 mm 0 based on bentonite with hydrochloric acid and subsequent impregnation with phosphoric acid so that the Al ₂ O ₃ content was 3.7% The pore volume is 0.85 ml / g of the catalyst and the inner surface area is 185 m ² / g of the catalyst and the HsPOi content after impregnation and drying is 41.5%, based on the total weight. The reaction products are fed via line 14 to the heat exchangers 4, where they warm up the reactants with cooling and partial condensation. The gas-liquid mixture is separated in the sump of the washer 7, the rising gas is ^{freed from alcohol by washing with 4.5 m 3} / h of water in countercurrent at a temperature of 60 ° C. and then fed to the circulation compressor 3 via line 15 . The liquid that accumulates in the sump of the washer 7 is expanded in line 17 and stored in the raw alcohol storage tank 8. From here it is fed to the distillation via line 19. The gas released during the expansion 18 - approx. 75 NmVh -

is fed to the incineration.

In 8 there are 23.0 t of raw alcohol per hour with the following composition:

17.40% ethanol

0.32% diethyl ether

0.03% acetaldehyde

0.05% butanols

0.09% hydrocarbons

Rest water

The raw alcohol contains 195 ppm of phosphoric acid, which before entry 14 into the washer 7 by adding Sodium hydroxide solution is neutralized. As a substitute, 4.5 kg of phosphoric acid (calculated 100%) per hour are added in sprayed the free space of the reactor above the catalyst.

From the raw alcohol 19 4.0 t / h of ethanol are obtained by distillation, which is a yield of 95.0%.

The density of the circulating gas on the pressure side of the circulation compressor 3 is 168 g / l (75 atmospheres and 76 ° C.). Per ton of alcohol produced (calculated 100%) the energy requirement for superheater 5 is 1.725 · 10 ⁶ kcal and for driving the circulation compressor is 0.11 · 10 * kcal.

Example 2 (comparison)

Hydration of propylene

(State of the art)

In the plant described in Example 1, per hour over the catalyst in the reactor the following quantities:

37,000 Nm ³
2 000Nm ³
8.5 m ³
36 atü
178 ° C

Propylene (85%) in the circuit 15 Fresh propylene (99.6%) 10 Degassed deionized process water 11 Pressure at reactor inlet 13 Temperature at reactor inlet 13

Energy consumption for the driving of the circulation compressor 3 is 0.09 x 10 ⁶ kcal and (calculated 100%) on the superheater 5 0.86 ■ 10 ⁶ kcal per ton produced isopropanol. The density of the circulating gas on the pressure side of the circulation compressor 3 was ^{measured at 45.6 atmospheres and 106 °} C. to be 128 g / l.

Example 3

a) hydration of ethylene
with purified circulating gas (invention)

As described in Example 1, 75 NmVh of circulating gas are not discharged from the system via line 18, but this amount is compressed with the fresh ethylene compressor 1 and thus returned to the system via line 11. ^{For this purpose, 400 Nm 3} per hour are fed to the distillation column 9 from the circulating gas downstream of the washer 7 via line 16. The concentrated top product is added to the cycle ^{gas again via line 20, while 10 Nm 3 of} a gas of the following composition is obtained in the sump:

40

38 m ^{3 of} catalyst are used. The phosphoric acid content of the catalyst is 26.3% by weight.

The by cooling in 4 partially freed from the formed isopropanol recycle gas is at a temperature of 95 ⁰ C in the scrubber 7 in countercurrent with 24.5 m ³ of water with a temperature of 98 ° C washed. A portion of the water obtained in the sump of the rectification column during the distillation of the crude isopropyl alcohol is used as washing water.

The gas 18 released during the expansion of the alcohol formed in 8 is partly returned to the process; ^{120 Nm 3} are discharged per hour and fed to the incineration.

By distillation, 19 4.91 isopropyl alcohol is obtained from the crude isopropyl alcohol, which is a Yield of 95.8% corresponds.

In 8, about 36.6 tons of crude isopropyl alcohol fall per hour the following composition: t> o

13.45% isopropyl alcohol

0.15% diisopropyl ether

0.005% acetone

0.08% n-propanol

0.04% hexanols

0.03% hydrocarbons

Rest water

0.2% by volume

0.4% by volume

19.5% by volume

47.1% by volume

15.6% by volume

nitrogen
methane
Ethane
Ethylene
Isobutane )
η-butane J.

Butene 12.1% by volume

Butadiene 0.2% by volume

Unknown 5.0 vol%

(for further details see example 3b)

This procedure results in a circulating gas concentration of 95.1% by volume of ethylene. The ethylene conversion on the catalyst increases to 2400 NmVh and the ethylene yield, based on the converted ethylene, to 97.4%. The density of the circulating gas on the pressure side of the circulating compressor 3 is now 106 g / l (75 atmospheres and 76 ° C.). The energy consumption for the rotary compressor 3 has decreased to 0.06 · 10 * kcal and for the superheater 5 has ^{decreased to 0.56 · 10 6} kcal per ton of ethanol produced (calculated at 100%).

Under the conditions of Example 3, the catalyst only worked in a period of 5 months 12.7% of the activity that the catalyst has lost under the conditions of Example 1 is lost.

b) Separation of the impurities

from the catalytic hydration recycle gas

of ethylene (invention)

In a sieve tray column 9, 380 mm inner diameter, 78 trays, bottom stand 160 mm, with a reflux condenser flanged to the column and the ethanol synthesis through line 16 per hour 400 Nm ^{3 of} circulating gas with an ethanol content of 95.1 vol .-% together with 0.5 1 ethylene glycol - to prevent hydrate formation - fed in at the 44th floor. The operating pressure is atü the top of column 42, the head temperature +2 ⁰ C and the bottom temperature 116 ° C. The steam consumption is 0.048 · 10 ⁶ kcal / h. At the top of the cooler 20, 390 Nm ³ per hour are withdrawn in gaseous form and fed via the fresh ethylene compressor 1 to the circulating gas. The ethylene concentration at the head is 96.3%. The liquid withdrawn from the bottom of the column 9 via line 21 is separated into gas and liquid after the expansion. The resulting gas -

10 NmVh, composition see example 3 - is burned. The liquid is separated into two layers in the decanter. The water is separated from the lower layer by distillation; the ethylene glycol returns to column 9. The upper layer, about 40 l / h, can be worked up to diethyl ether by distillation. The upper layer contains approx. 38% diethyl ether, 5.5% C ₂ -C ₄ hydrocarbons, 0.3% ethanol and 2.7% butanols. The remainder are higher alcohols and hydrocarbons with a boiling range of up to 315 ° C. Elemental analysis was used to determine the _{empirical formula for the mixture boiling above 115 ° C. Ct 3} H _{26 O.}

Example 4

Hydration of propylene
with purified circulating gas (invention)

The plant is operated as in Example 2. By discharging 400Nm ³ circulating gas from the pressure

ropes of the circulation compressor 3, before process water 11 and fresh propylene 10 are fed into a sieve tray column of 100 trays, which is operated at a pressure of 22 atmospheres, a level of 96.2% is set in the circulation gas. The gas released during the expansion of the crude isopropanol in 8, on the other hand, is completely returned to the cycle gas via the compressor 1. The propylene conversion increases to 2250 Nm ³ / h and the yield of isopropanol, based on converted propylene, to 97.6%. The density of the circulating gas is now on the pressure side of the circulation compressor 3 at 45.6 atmospheres and 106 ^c C 120.5 g / l. The energy consumption measured for the compressor is 3 0.05 · 10 ⁶ kcal, for the superheater 5 0.48 · ΙΟ ⁶ kcal per ton of alcohol produced (calculated at 100%). The decrease in activity of the catalyst over the period of 7 months was only 27.3% of the decrease in activity of the catalyst in Example 2.

1 sheet of drawings

809 540/51

Claims (1)

Claim: Process for the production of alcohols by hydration of olefins with 2-3 carbon atoms a fixed bed catalyst in the gas or gas-liquid phase, characterized in that, that the unreacted olefin gas leaving the reactor with the reaction mixture is replenished Condensation of water and alcohol and separation of the same partly by distillation Conditions near the critical point of the olefins concentrated, except for those higher than olefin boiling impurities and the higher polymerized hydrocarbons also the lower than the olefin-boiling impurities are separated off via the bottom of the distillation column.