CS206791B1 - Refining method of alcohols,having less than 4 carbon atoms,by alcaline hydroxide solution - Google Patents

Description

The invention relates to an improved process for the refining of alcohols by means of an alkali hydroxide solution, wherein the contact of the refined alcohol vapors with the alcoholic refining agent solution removes impurities affecting the quality of the refined alcohol judged to be KMnO ₄ oxidation resistance.

Alcohols with a carbon number of less than 4, ie methanol, ethanol, n-propanol and isopropyl alcohol, produced by chemical synthesis or by biochemical ie fermentation processes, are usually; Purified by utilizing changes in the relative volatility of the desired alcohol and pollutants as the concentration of water in the solution changes. Therefore, the distillation system used for alcohol purification works first in the so-called ancestor column, which is also called, according to industry practice, also an epuration column or an extractive distillation column so that a high concentration of water is maintained for most of the total column height. . In the said operating mode, the distillate of this; the first columns carry not only substances of lower boiling point than those of the desired alcohol, but also substances of the same or higher boiling point, which, however, are less polar in nature than this alcohol.

In the next distillation step, the alcohol is then separated from the water and the area in the distillation column in which the high alcohol concentration and the low water concentration is high is used to separate other impurities different in nature from those which separate at high water concentration. and

The distillation line for refining alcohols can be equipped with more columns than the two described! however, distillation columns, in which a high water concentration is maintained, alternate with columns which contain a section with a low concentration of water in the passing streams.

In order to maintain a high water concentration in the first column, water separated from the alcohol in the second distillation column is usually used; a water recycle between the columns is introduced.

The described process involves the refining of methanol produced by synthesis from hydrogen and carbon monoxide, ethanol produced either by fermentation or by direct hydration of ethylene, possibly also by refining C ₃ - alcohols.

Even with careful distillation refining, impurities are present in the alcohol produced in trace amounts, the presence of which can be detected, for example, with a permanganate test. The impurities that influence this analytical data are mostly aldehydes or unsaturated hydrocarbons, which are also produced by side reactions in alcohol production.

It is known in ^. ^ ^1, et residual aldehyde content in the alcohol may be reduced by contact with an alkali hydroxide solution practically usually sodium hydroxide.

Described are methods in which a solution of a column in which alcohol is separated from water is described. However, the supply of an alkaline hydroxide solution to the column means that the hydroxide passes into the water leaving the bottom of the column and makes it difficult to use again. One of the most important negative aspects is that when the alkali hydroxide-containing water is circulated to the first (ancestor) distillation column, the aldehydes present may be aldolized in an alkaline environment, making it difficult to separate them in the distillate of this ancestor column. The resulting compounds are thermally labile and decompose in the next distillation step to form substances that impair the quality of the alcohol produced.

Also described are methods in which sodium hydroxide refining is carried out in a separate step, but it does not operate under more favorable conditions than for refining reactions. and for the exchange of matter between the contacting phases. Also; the thermo-technical solution does not guarantee the minimization of: energy consumption for alcohol and alkali refining.

For example, a process has been described in which ethanol is separated from water in two stages:

In the first step, the distillation residue from the ancestor column, i.e. the extractive distillation column, is terminated from an initial concentration of about 8% by weight. 80% by weight. and water which i) is the distillation residue of this first step; concentration of ethanol is used either in the extractive distillation column or in ethanol synthesis. In the second stage, the ethanol concentration is then increased to a final value of up to 94.5% by weight. in a distillate of the column to which a sodium hydroxide solution for the chemical refining of ethanol is fed. The sodium hydroxide which has passed through the column is then discharged in the effluent - the distillation residue of the column. The concentration of sodium hydroxide in the liquid on the distillation trays maintains a maximum of 0.1% by weight. ; The method described, which, while allowing the use of the bulk of the water contained in the feed of the first stage of ethanol concentration, is very energy intensive in separating any of the alcohols to which the invention relates. In the case of the production of ethanol whose equilibrium curve liquid the vapor of the mixture with water has an inflection point, the separation of ethanol from water in two stages at the desired j (product concentration approx. 94.5% by weight is particularly disadvantageous. The second column separates; The heat consumption is due to this specific shape of the equilibrium curve determined by the so-called closed area at tangential contact of the working line with the equilibrium curve in the vicinity of the ethanol concentrations in the liquid equal to 80% mol, and is solely influenced by the composition of the distillate, so that in the second stage of ethanol concentration the same amount of heat is consumed as in the one-stage concentration, all the heat consumed in the first stage of ethanol concentration is added. · '.

The process according to which ethanol vapors obtained by evaporating a chemically unrefined product of the desired final concentration through a layer of a refining agent solution has also been described. The disadvantage of this process is, in particular, poor contact between ethanol vapors and the refining agent solution, as well as heat consumption for re-evaporation of the refined product. ,,

It has now been found that optimum results in refining alcohols with less than 4 carbon atoms; with an alkaline hydroxide solution is obtained by the process according to the invention, which consists in that:. with alcohol vapors of a concentration greater than. 80% by weight, are brought into intensive contact with an alkali hydroxide solution in countercurrent. tangent in a vertical direction, the alkali hydroxide solution being circulated from below during refining;

; and its concentration in the liquid stream contacting the vapor of the refined alcohol is in the range of 0.1 to 5.0% by weight, preferably 0.1 to 1.0% by weight. In order to save the energy required to carry out the refining, it is advantageous to remove the alcohol to be refined with the alkali hydroxide from the previous stage of the distillation treatment in the form of vapors without being condensed to a liquid state. Another possibility of saving heat is that although the alcohol to be refined with the alkali hydroxide is introduced into the column apparatus in the liquid phase and evaporated in the reboiler associated with the apparatus, the refining is carried out at elevated pressure and correspondingly elevated temperature, whereas the heat of condensation collected when the alcohol vapors are returned to the liquid phase can be usefully used in the purification and concentration thereof in the preceding; stages of the production line. The increased pressure and temperature favorably influence the refining process. Practically, pressures up to 2.0 MPa can be used. ^;

The advantages of this method of refining alcohols are, in particular, the energy savings that result in a reduction in refining heat consumption. This results in a high purity of the alcohol produced. and

The refining of the alcohols according to the invention can be carried out; in a device, the principle of which is illustrated in the attached diagram. The main apparatus of the refining plant is a column 1 equipped with a built-in 2, which may be a layer of loose filling, several distillation trays, or other similar device. Do the bottom! of the column 1 is fed the alcohol to be refined via line 3 from the distillation column 4 in which it was concentrated. The alcohol is withdrawn from the column 4 in the form of vapors, either from below the head of the distillation column, as shown in the diagram, or from the top of the column. Likewise, alcohol can be withdrawn from column 4 or reflux tank 5

L in liquid form and conveyed to the refining column 1 by means of a pump installed along the pipeline; 3, e.g. at the location indicated by A. j

The refining column 1 is equipped with a boiler 6, which supplies the heat necessary to cover the heat losses and possibly also for the evaporation of alcohol when introduced into the column 1 in a liquid state. Preferably, the apparent heat of the distillation residue from the distillation column 4 (liters water) can be used to heat the digester 6. The alkaline hydroxide solution used for refining is circulated from the bottom of the column 1 by means of a pump 7 through a line 8 above the installation of the column 2. A part of the spent alkaline hydroxide solution is discharged from the circuit via a line.

and is used, for example, to produce a second-quality alcohol or to neutralize the reaction products of direct hydration. The required amount of fresh alkaline hydroxide is added to the circuit via line 10 in the form of an aqueous or alcoholic solution having a concentration of 5 to 50% by weight, preferably 15 to 20% by weight. By selecting the ratio of the supply and exhaust flow rate of the caustic alkali solution lines 10 and 9 is maintained at the optimum concentration of the circulating stream kappa ^lin · ^s; y ^U 7 refined alcohol vapors that passed internals layer 2 pass prior to exiting the column internals one auxiliary layer, optionally a separating nezaplněným space 11 serving to separate the droplets of alkali metal hydroxide stricken. This auxiliary filling of the cartridge may be sprinkled with a small stream of alcohol through line 12 by means of a pump 13 to improve the efficiency of the entrainment of entrained drops. The refined alcohol vapor then condenses in the heat exchanger 14 and flows to the intermediate storage 15. When the alcohol refining column 11 is operated at elevated pressure, a reboiler or heater of the preceding stages of refining and alcohol concentration serves as condenser 14. Refined alcohol is removed from the plant via line 16 for reuse or shipping.

alcohol prevention avoids. The alcohols are separated from the alcohols in the distillation column 4 with an alkali hydroxide and allow its use to which it is discharged via line 17. 7 7 'J ·. 1 'b7 · y 7' U advantages (described refining process ijiop alcohol with alkali hydroxides in the following examples. ^'': '7 ΊΝΓ 7f R 7 7 7 ¹ I- <7

Described method of water pollution, which "".

________206791

Example i

Consumption of ethanol-two-mode ethanol raffinate solution is compared. In the first one, the ethanol concentration is increased from 8% by weight in the first column. to 80% by weight, the column is operated at a reflux ratio R _x = 2.34 at; minimum reflux ratio (Ri) min. ⁼ 1.56. In a further column, the top of which is fed with sodium hydroxide solution, the ethanol concentration is increased from 80% by weight. The value of the manganese test according to ČSN ¹ 66 0805 rises to 94.5% by weight by the refining effect of sodium hydroxide for 35 minutes. This second column operates with a reflux ratio R ₂ = 3.9 when the value of | the minimum reflux ratio equal to (Ø ₂ µ _min = = = 2.6. The vapor flow in the heads of both columns, which is proportional to the heat consumption for distillation, is about 8.24 t / t 'of ethanol produced.

In the second case, ethanol is concentrated to 8% by weight in one step. up to a final concentration of 94.5 wt. and steam withdrawn from the upper portion (column are refined according to the invention. In the refining column at an upper portion thereof for improving the function of the separation of drops applied reflux ^oranges! ru R = 0.1, the concentration column operating with a reflux ratio R = 3.9 at a minimum reflux ratio equal to (R 1) _min = 2.6 The vapor flow, comparable to the previous case, is 5.0 t / t of ethanol produced, which means about 40% heat savings.

Example 2

On a laboratory scale, the influence of the concentration of both sodium hydroxide and sodium hydroxide solution on the permanganate test value of refined ethanol is monitored at atmospheric pressure.

With the addition of a 20% strength alcoholic solution and sodium hydroxide to the refining column in amounts such that the concentration of NaOH in the liquid (stream contacting ethanol vapors is in the range of from 0.05 to 5% by weight) permanganate test:

permanganate concentration test

NaOH (minutes) (wt.%) 20

35

0,05 45

0,1 53

0,5 55

Claims (4)

Process for refining alcohols with less than 4 carbon atomic alkali hydroxide solution, characterized in that the alcohol vapors with a concentration even higher than 80 wt. are introduced into intensive contact with an alkaline hydroxide solution in a three-stream flow in a vertical direction, wherein the alkaline hydroxide solution during refining? it circulates from the bottom of the sweep and its concentration in the liquid stream contacting the vapors of the refined alcohol is in the range of 0.1 to 5.0 wt%, preferably 0.1 to 1.0 wt%. 2. The method according to claim 1, wherein the ²⁰⁶⁷⁹¹ ... the alcohol to be refined with the alkali hydroxide is withdrawn from the previous stage of the distillation treatment in the form of vapors without prior concentration to the liquid state and is thus introduced into the process. 3. A process according to claim 1, characterized in that _{: the} refining is carried out at a pressure of more than 0.1 MPa and less than 2 MPa, and that the condensation heat of the refined alcohol vapor is used for purification and concentration in the preceding stages of the technology. system. 4. A process as claimed in claim 1, wherein the alkali hydroxide is introduced into the circulation circuit. it is supplied in the form of an aqueous or alcoholic solution at a concentration of 5 to 50% by weight, wherein: the concentration of the alkali hydroxide in the liquid; ; contacting the vapors of the refined alcohol is governed by the ratio between the amount of feed solution; and the amount of liquid drained.