DE3205096A1 - Process for the dehydration of alcohols, in particular aliphatic alcohols having not more than three C atoms - Google Patents

Description

STARCCS /; G.m.b.H., Am Alten Bahnhof 5, 3300 Braunschweig

Process for the dehydration of alcohols, in particular aliphatic alcohols with no more than three carbon atoms

The invention relates to a process for dehydrating lower aliphatic alcohols, preferably ethanol, using an entrainer distillation with methylcyclohexane as the solvent to be used. 5

According to claim 1, the energy is supplied in the bottom of the column by condensation of the top product, which was previously pressurized in a vapor compressor. In the case of the ethanol to be dehydrated it is both fermentation alcohol and a synthetic alcohol.

The dehydration of ethanol by entrainer distillation is a technique that has been used in technology for a long time. Benzene has hitherto been used as the solvent, lately mainly because of its greater toxicological harmlessness Use cyclohexane

In addition to ecological and medical aspects, there is also the question of the energy input in the production of ethi.nol, ins- "20 especially when it comes to the absoluteization of ethanol for the purpose of its use as a liquid energy carrier.

Here is a starting point, the energy balance in the xthanol production from agricultural raw materials continues to improve.

The replacement of the cyclohexane by methylcyclohexane enables a fundamental change in the previously known absolutization process.

In the rectification of the three-component system ethanol (1) water (2) - Methylcyclohexane (3) results in a ternary mixture at the top, depending on the number of plates and the reflux ratio the column, which is characterized by a water content that is significantly higher than that of cyclohexane, especially in the overpressure range. This ensures that the amount of substance of the ternary mixture required for dewatering decreases. Simultaneously the boiling temperature of the ternary mixture as a function of the working pressure of the column assumes a value that corresponds to the energy-saving Use of a vapor compressor made possible, whereby a fundamental improvement of the process is achieved.

As is known from practice, the previous way of working with cyclohexane to obtain 1 liter of pure ethanol from an ethanol / water mixture of 94.5% mas Ethanol requires a heat quantity of about 4 MJ. This number refers to a two-column system, consisting of absolute and work-up column.

It is the underlying object of the present invention to provide a method of the aforementioned type, which the continuous production of solvent-free ethanol with a proportion of less than 0.1% by mass water and by a particularly bound to a certain solvent Process sequence enables the energy input to be reduced to 25 - 30% of the above value.

3205Q96

This task is through the characterizing part of the main claim solved.

The method according to the invention is hereinafter referred to as reference to be described on the attached figure.

The figure shows a flow chart showing the principle Circuit of the absolutization rectification column reproduces.

Feed (Z) is made up of ethanol and a certain residual proportion of water, which is usually about 5% by mass H ₃ O, and is fed into the column about 10 to 20 trays below the top. Working pressures between 5 and 15 bar are preferably maintained. The ternary mixture (K) created at the top of the system, which corresponds to the ternary azeotrope with return flow ratios of ν = 4 to ν = 5, is compressed by means of a compressor (V) driven by a motor (M) and transferred to that for heating the system necessary pressure and temperature level brought. In the evaporator (H) the heat of condensation of the top mixture is given off to the bottom product (P), which consists of absolute alcohol. While part of the condensed ternary mixture is fed to the top of the column for reflux generation, an amount necessary for dehydrating the ethanol reaches a decanter (D) ♦ Here the phase separation of the mixture can be carried out either at system pressure or after previous expansion (E) .

During the upper phase, which mainly consists of the solvent exists, is returned directly to the absolutizing column, the lower phase which is rich in ethanol and water is added a work-up column (S).

-T-

This process is based on the fact that rectification is preferred is carried out at system pressures of 5 to 15 bar. Due to the temperature level reached and 'the improved Temperature difference between the boiling points of the top and bottom product, which, depending on the pressure, is 6 to 11 ° C for methylcyclohexane as an entrainer and approximately twice that for cyclohexane, good performance figures of the compressor (V) are achieved.

Example:

A mass flow of 7.86 kg / h of an ethanol / water mixture with a proportion of 94.5 % mass ethanol was fed into a pressure rectification column with a 55 bubble-cap base and a diameter of 100 mm. The system pressure at the top of the column was 8.6 bar and at the bottom 8.8 bar. Adequate insulation and compensation heating jackets contributed to minimizing radiant heat losses.

The production amount of pure ethanol (with 0.1% mass H ₂ O) was 6.15 kg / h with a reflux ratio of ν = 4. To remove the water, 3.72 kg / h of the ternary mixture had to be withdrawn from the column will.

All required concentration values are listed in the table.

After the subsequent decantation, the upper phase, as shown in the figure, was returned to the rectification while the lower phase containing the water was discarded. The ethanol withdrawn from the process as a result was added to the feed quantity (Z) taken into account. Solvent losses of 0.12 kg / h were compensated for by metering into the upper phase, because the experimental apparatus is not a HilScolonne, which is common in technology to work up the sub-phase.

-T-

The column was heated with the aid of the compressed overhead product vapor.

The power consumption at the motor (M) of the compressor (V) was 0.207 kW, which corresponds to a heat flow of 747 kJ / h, 'respectively. 97 kJ / 1 r.A. or 0.027 kWh / l r.A.

To meet the need for electrical energy with conventional To be able to compare steam heating, the turbine efficiency must be must be included for internal power supply (-9 = 0.7 /,

It turns out that in the production of absolute ethanol according to the method on which the patent claim is based 139 kJ / 1 r.A. in the form of appropriately pre-stressed steam are needed. As in the conventional process in the overpressure range, the work-up column consumes about 670 kJ / 1 r.A. in addition, so that a total heat requirement of 809 kJ / 1 r.a. results.

Tabel

Concentrations of the components (% mas)

Systems K than oil Fathers Methylcyclohexane Phase proportion
% mas ternary
Azeotrope
(Head product) 35.0 11.6 53.4 - Upper phase
Dean
(25 ° C) 3.0 <0.01 97.0 52.5 Sub-phase
Dean
(25 ° C) 69.5 24.4 6.1 47.5

Working pressure of the rectification column = 8.6 bar

GO K) O

OD (T)

LL 2 HlH

"'-' ■ 320509G

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Zur ^ G Judunn hcran7; ii7.iehr.nfici writings

Riedel, K.U .: Branntweinwirtschaft 5 (1976) p.

Sure, M .:

Manufacture of absolute alcohol for use as:

Additives to motor substances ^T. -7. Knapp Verlag, Halle, 1936

3) Leppmann, 0. - Denslow, J. - Ronkainen, P .:

Energy Consumption in the Distillation of Fuel Alcohol (Lecture at the IV. International Symposium on Alcoholfuels Technology, Guaruja, Brazil, 1980.)

4) Tegtmeier, U, - Misselhorn, K, Biotechnology Letters VoI 3, 8 (1981) p.

*) ÜS-PS 4 256 541, 3/1981 Müller et al.

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Claims (1)

ETARCOSA G.m.b.H., Λπ Alten Bahnhof 5, "3300 Braunschweig Claims Γ1.j Process for the dehydration of alcohols, in particular aliphatic alcohols with no more than three carbon atoms, characterized in that methylcyclohexane is used as an entrainer, both the alcohol / water mixture to be separated and a dem Water content of the mixture adjusted amount of methylcyclohex & n a rectification column are fed, with the water. "by thermal separation as a component of the ternary Top product ethanol / water / methylcyclohexane removed quantitatively, obtained as bottom product almost pure alcohol and the top product is used to heat the column after vapor compression. 2. The method according to claim 1, characterized in that ethanol is dehydrated. 3. The method according to claims 1 and 2, characterized in that that the thermal separation is carried out at a pressure higher than atmospheric pressure. k. Process according to one of Claims 1 to 3 »characterized in that alcohol with less than 0.1 % mass of water is drawn off from the bottom of the column. _ 7 - -I- 5. The method according to any one of claims 1 to 4, characterized characterized in that the ternary mixture obtained as the top product of the rectification column has a temperature from 20 to 60 C a decanter for phase separation 5 is fed. 6. The method according to any one of claims 1 to 5, characterized characterized in that a temperature is maintained during phase separation, which is lower than that the boiling point of the ternary mixture belonging to the corresponding column pressure. 7. The method according to any one of claims 1 to 6, characterized in that the water content of the ternary Mixture depending on the working pressure of the rectifying column and the preselected reflux ratio at least 5% mas is set. 8. The method according to any one of claims 1 to 7, characterized in that the aqueous phase of the Decanters are fed quantitatively to a second rectification column for processing and recovery of the components. 9. The method according to any one of claims 1 to 8, characterized characterized in that the inlet at the lower end of the upper third of the column is fed. 10. The method according to any one of claims 1 to 9, characterized in that the alcohol / water mixture is fed to a column with 40 to 70 trays.