CS255017B1 - Process for the production of synthetic ethanol - Google Patents

Abstract

The essence of the method for producing synthetic ethanol by direct hydration of ethylene with the total formation of off-gases containing 90 to 99 % by weight of ethylene and less than 100 kg per 1 ton of ethanol produced is that a stream is separated from the circulating ethylene, which is washed with a mixture of ethanol and water, expanded to a pressure of 0.5 to 3 MPa with a simultaneous decrease in temperature to 0 to -40 °C with subsequent separation of condensed fractions and returned to the circulating ethylene or the pressure of the liquid part of the products is reduced to a value of 0.5 to 3 MPa and the released gas containing ethylene is fed into the circulating ethylene and used in the production of ethanol.

Description

The present invention relates to a process for the production of synthetic ethanol by direct hydration of ethylene while substantially reducing off-gas generation, which is achieved by utilizing a portion of ethylene released from the raw alcohol directly in ethanol synthesis and / or separating undesirable components from circulating ethylene.

The principle of ethanol synthesis by direct hydration of ethylene is its reaction with steam catalyzed by acid, most often phosphoric acid on kieselguhr carrier, □ since the conversion rate of ethylene does not exceed 4%, unreacted ethylene is added after separation of the liquid fractions; pure raw material and reused for ethanol synthesis,

In addition to the main reaction, several side reactions take place to form diethyl ether and then oligomerization of ethylene to form hydrocarbons, in particular t-butene.

Other undesirable impurities enter the system with pure ethylene containing max. 0.1% impurities, especially ethane.

In order to prevent the concentration of undesirable substances in the circulating ethylene system, a part of it is discharged in the form of a so-called high-pressure off-gas in the amount of, for example, 60 kg / t synt, ethanol, corresponding to 8% of the ethylene input.

Further ethylene leaves the system together with the liquid components of the reaction mixture - raw alcohol, the so-called alcoholic condensate, from which it is released during its expansion eg from 7 MPa to 0.45 MPa in the amount of 40 to 90 kg / t.

255 017 synthetic alcohol.

In the case of both offgases, only their energy recovery or reprocessing is currently possible.

At a limit concentration of 0.1% of impurities in the incoming ethylene, a quantity of 40 kg of off-gas per t of synthetic alcohol would be sufficient to remove inert substances from the system, less than 20 kg of off-gas per t of synthetic alcohol.

The production of high-pressure off-gases in the present amount is forced by the need to keep the hydrocarbon content of the circulating ethylene at a level of max. 4% by weight. , the amount of low-pressure off-gas generated is determined by the specific technological conditions of the direct hydration production line.

It has now been found that these disadvantages are substantially eliminated by the process of producing synthetic ethanol by directly hydrating ethylene with water on a phosphorous supported catalyst, which utilizes part of the ethylene leaving the system together with the liquid as a ring gas component.

Process for the production of synthetic ethanol by direct hydration of ethylene with the total formation of off-gases containing 90 to 99 wt. Ethylene lower than 100 kg per 1 ton of ethanol produced according to the invention consists in the fact that from the circulating ethylene a branch stream is washed with a mixture of ethanol and water, expanding to a pressure of 0.5 to 3 MPa with a temperature drop to 0 to -40 ° C followed by separation of the condensed fractions and returned to the circulating ethylene; and / or the pressure of the liquid product portion is reduced to 0.5 to 3 MPa and the released ethylene-containing gas is fed to the circulating ethylene and utilized in ethanol production.

Alcoholic condensate, which separates from the orbital gas at a temperature of about 50 ° C and a pressure of 7 MPa, can be fed to a separator in which the pressure of this aqueous solution is reduced to 2.1 MPa and approximately

255 017% of the ethylene contained in the alcoholic condensate.

This return gas can be fed directly to the intake of fresh ethylene compressors and reused for ethanol synthesis *

It is preferred to treat the return gas after the ethanol scrubbing by cooling and separating the condensed impurities.

The cooling ethylene treated according to the invention can be used.

The treated recycle gas can be expanded at adiabeticky ^Ο Θ Ο to about - 1O ° C and a pressure of 2 MPa at a pressure from 0.2 to 0.3 MPa, and after the separation of impurities vykondenzovaných used for chemical processing, e.g., for the synthesis of ethylbenzene.

Ethylene losses can further be reduced by suppressing the formation of high pressure off-gas, but this would mean an increase in the concentration of impurities in the orbital gas, especially if the amount of impurities is increased by reducing the formation of low pressure off-gas as proposed by the present invention.

It has now been found that the concentration of the dominant component of an orbital gas admixture, i-butane, can be reduced as follows:

From the orbital gas, the stream is washed with ethyl alcohol at operating pressure, cooled to 30 to 40 ° C and, after liquid separation, allowed to expand adiabetically when the temperature drops to -20 ° C to -25 ° C to condense some of the impurities such as water ethanol, diethyl ether and butene.

After the liquid separation, the gaseous portion, after compression, together with fresh ethylene and the return gas released from the spirits condensate, is fed to a ring gas system for ethanol synthesis. Preheating of the cold gas can advantageously be used in a tube heat exchanger, the return gas released from the alcohol condensate, as mentioned previously.

The liquid fractions from the separators can be treated together with the alcoholic condensate and ethanol and / or diethyl ether, the gaseous components which are liberated during this treatment, i.e. in particular ethylene and butene, can be used as an addition to the fuel gas.

- 4,255,017

The advantage of this shirring is not only to reduce ethylene consumption by reducing low-pressure and high-pressure off-gas, but also to reduce the concentration of some impurities in the orbital gas below present values, resulting in, for example, suppressing catalyst deactivation in ethanol synthesis;

The method of modification of the technological process is illustrated in the attached diagram:

The reaction mixture 2 from the ethanol synthesis line by direct hydration of ethylene 1 in the scrubber 3 is divided into a part by liquid 15 and a gas 4, a so-called orbital gas, under which a stream 5 in the heat exchanger 6 is cooled with water; ethanol? J from a common feed. The scrubbed gas is fed to a separator 11 via a throttle 10 at which pressure is reduced while the temperature decreases, where it is separated from the condensed parts. The treated gas 21 is supplied to the compressor suction via a heat exchanger 13 where it is heated to the required temperature. 27 and after compression adds to the orbital gas 4.

The distillate condensate 15 from the scrubber 3 is fed to a separator 14 where the return gas 16 is separated and the separated distillate condensate 28 is further processed in a conventional manner on a distillation line.

The return gas 16 is scrubbed in a scrubber 18 with ethanol 17 from a common inlet and cooled in a heat exchanger 13. The condensed liquid fractions are separated in a separator 24 and the treated return gas 26 is passed to the compressor suction 27 together. and used to synthesize ethanol.

The liquid fractions 9, 12, 19 and 25 are treated together with the distillation condensate 28.

Installation of the washer 18 and possibly the separator 24 is not necessary. In this case, the heat exchanger 13 was designed for

255 017 steam heating of 0.25 MPa and the return gas 16 would be supplied to the intake of the compressor 27 without prior treatment.

The method of production of synthetic alcohol and degassing can be illustrated by the following examples:

Example i:

In the production of synthetic ethanol, 138 kg / h is eliminated as a by-product. high-pressure off-gas and the same amount of low-pressure off-gas.

From the orbital gas, at a pressure of 7 MPa, it is branched and treated by cooling to 35 ° C, scrubbing with ethanol and cooling by adiabetic expansion to a pressure of 2.1 MPa while reducing the temperature to -20 ° C and separating the liquid at 400 kg / h.

381.7 kg of treated ring gas are obtained • 18.3 kg of liquid fractions, except for scrubbing liquid

The current composition is shown in Table 1.

The treated off gas, after compression, together with fresh ethylene, is returned to the system and used for the synthesis of ethanol.

Liquid fractions containing 5.9 kg of butene and 10.8 kg of ethylene are added to the distillation condensate, where the pressure is reduced to 0.45 MPa to release ethylene and butene, which can be further processed together with the low-pressure off-gas.

In this way, at least 65% of the butene formed is removed from the system and the high-pressure off-gas amount can be reduced from 138 kg / h to 46 kg / h, the low-pressure off-gas generation increases by ethylene and butene leaving to 138 kg / h ' 154.7 kg / h, which means a total ethylene reduction of 75.3 kg / h.

255 017

Table 1

The composition of the streams during the treatment of the orbital gas (% by weight) before the treatment of the orbital gas and after the treatment the liquid fractions of ethane, ethylene butene ethanol diethyl ether water

96.28

3.34

0.16

0.20

0.02

98.0

2,0

0.0

0.0

0.0

59.2

32.5

3.5

4.4

0.4

Example 2

In the production of 1000 tonnes of 100% ethanol, 60 tonnes of high-pressure off-gas and 60 tonnes of low-pressure off-gas are eliminated as by-products,

By separating the return gas at a pressure of 2.1 MPa, the formation of low-pressure off-gas decreases to 15 t and 45 t of the gas of the composition given in Table 2, the so-called fresh ethylene compressors are sucked in and used together with the orbital gas.

In order to ensure a constant concentration of C ₄ hydrocarbons in the system, it is necessary to increase the amount of high-pressure vent to 85 tons, which means a total reduction of 20 tons of input ethylene consumption,

Table 2

The composition of the return gas separated from the alcoholic condensate (% by weight) ethylene, ethane 95.9 butene 1.7 ethanol 0.8 water 0.5 diethyl ether 1.1

Example 3 ^{zss 017}

In the production of synthetic alcohol producing 138 kg / h of low and high pressure off-gases, the return gas is separated from the alcoholic condensate and further utilizes the return gas as shown in Example 2 at 103.5 kg / h.

Further, 520 kg / h of the orbital gas is treated and processed according to Example 1, of which 496.2 kg / h are returned to the orbital gas and 23.8 kg / h of liquid fractions containing 21.7 kg after treatment. of ethylene and butene are treated together with the alcoholic condensate according to Example 1.

The amount of off-gases is then: high-pressure off-gas 46 kg / h low-pressure off-gas 56.2 kg / h

The amount of ethylene input therefore decreases by 173.8 kg / h while maintaining the butene concentration.

The concentration of inert, which is predominantly ethane, increases with an average concentration of impurities in ethylene of 600 ppm by weight. to 1.4 wt. at a concentration of 1100 ppm by weight. on

2.2 wt.%, Which is not adversely affected by the ethanol synthesis.

Example 4

In the production of synthetic ethanol, with the formation of 138 kg / h of low pressure and high pressure off-gases, the return gas is removed from the spirits condensate as shown in Example 2 in an amount of 103.5 kg / h.

Further, from the orbital gas of the industry and according to Example 1, a quantity of 1000 kg / h of orbital gas is treated and processed.

958.2 kg / h of treated orbital gas is obtained

41.8 kg / h liquid fractions except washing liquid

The liquid fractions are treated with alcoholic condensate and the liberated ethylene and butene are utilized by low-pressure off-gas.

Number of outgoing offgases:

295 017 high-pressure off-gas low-pressure off-gas kg / h 67,9 kg / h

Ethylene consumption is thus reduced by 162.1 kg / h. Furthermore, the butene concentration in the orbital ethylene at the outlet of the direct hydration line before enrichment with pure ethylene is reduced from 3.3 wt% to 2.6 wt%.

Claims (1)

Process for the production of synthetic ethanol by direct hydration of ethylene with the total formation of off-gases containing 90 to 99 wt. of ethylene less than 100 kg per tonne of ethanol produced _f, characterized in that / from the circulating ethylene, a sector stream which is washed with a mixture of ethanol and water is expanded to a pressure of 0.5 to 3 MPa with a temperature drop of 0 to -40 ° C followed by separation of the condensed fractions and returned to the circulating ethylene and / or the pressure of the liquid product portion is reduced to 0.5 to 3 MPa and the liberated ethylene-containing gas is added to the circulating ethylene and used in ethanol production.