CS252452B2 - Method of industrial gas purifying - Google Patents

Abstract

Method of cleaning industrial gas as hydrogen, carbon monoxide, air, oxygen. Helium, argon, 2 to 5 atom monoolefins carbon in the molecule, diolefins with 4 to 5 atoms carbon in the molecule, paraffins or acetylenes, removing trace amounts of one or several impurities from the group water, hydrogen sulfide, carbon dioxide, carbonyl sulfide, sulfur dioxide, hydrogen chloride, hydrogen cyanide nitric acid in which the purified gas is brought to the temperature 15 to 100 ° C in contact with liquid, anhydrous with a solution containing 0.5 to 15% by weight alkali metal or metal alkaline soil, based on its hydroxide or salt weak acid, in liquid aliphatic a polyhydric alcohol having a carbon atom ratio to oxygen atoms 1 to 5 and at least two oxygen atoms separated by at most two of the following carbon atoms.

Description

(54) Industrial gas purification method

Process for the purification of industrial gas such as hydrogen, carbon monoxide, air, oxygen. Helium, argon, C 2 -C 5 monoolefins, C 4 -C 5 diolefins, paraffins or acetylenes by removing trace amounts of one or more impurities from water, hydrogen sulfide, carbon dioxide, carbonyl sulfide, sulfur dioxide, hydrogen chloride, hydrogen cyanide, nitrocyanic acid, in which the purified gas is contacted at a temperature of up to 100 ° C with a liquid, anhydrous solution containing 0,5 to 15% by weight of alkali or alkaline earth metal, based on its hydroxide or weak acid salt , in a liquid aliphatic polyhydric alcohol having a ratio of carbon atoms to oxygen atoms of 1 to 5 and having at least two oxygen atoms separated by a maximum of two consecutive carbon atoms.

The invention relates to a process for the purification of industrial gases and in particular to the removal of minute amounts of impurities from the purified gases.

The reaction of basic alkali metals or alkaline earth metals as such or in the form of hydroxides or weak acid salts is known in the chemical art. The chemistry of these reactions is the basis of significant operating procedures. For example, in the field of purification of industrial gases such as hydrogen, carbon monoxide, air, oxygen, nitrogen, argon, helium, lower olefins, lower diolefins and the like, layers or suspensions of solid particles of sodium or potassium hydroxide are used to remove large amounts of acid gases. However, these processes are relatively ineffective if trace amounts of impurities such as hydrogen sulfide, carbon dioxide, carbonylsulfide, sulfur dioxide and mercaptans and similar impurities are to be removed from the gases. Alkali metal hydroxides have been considered as suitable absorbent compositions for separating acetylene from ethylene, as shown in U.S. Patent 2,742,517.

U.S. Pat. No. 2,185,332 (issued January 2, 1940) discloses a process for dehydrating and purifying freezing systems by providing alkali metal alkoxide, especially sodium methylolate, to the freezing system. The alcoholate is supplied to the system to remove water by double decomposition to give an alkali metal hydroxide, for example sodium hydroxide. Sodium hydroxide then remains in the system. The consequence is obvious. Sodium hydroxide is a corrosive environment and its presence in the cooling gas cannot be beneficial in long-term operation. In addition, said patent describes the removal of acids as such.

For example, hydrogen chloride, probably in the form of hydrochloric acid, is converted to sodium chloride, but it is certainly not preferable to leave sodium chloride in the cooling gas. Thus, according to said patent, known chemical reactions are used to solve the problem of one, but other problems are created.

U.S. Pat. No. 2,177,068, issued October 24, 1939, describes the treatment of natural gas to remove water and acid gases. Polyhydric alcohols are used together with amines such as alkanolamine to remove water and acid gases. This process is based on the old knowledge of the use of amines to remove acid gases and polyols to remove water.

According to the aforementioned patents, the purified gases are saturated hydrocarbons, the inertness of which is well known. The contaminants removed do not adversely affect the function of these gases, but they do not adversely affect the environment.

The use of amines for the removal of acid gases according to the aforementioned patent has the drawback that the amine systems are corrosive.

The evolution of industrial gas purification is related to the improvement of methods for the determination of impurities in gases. Improved analytical methods for evaluating industrial gases have prompted the need for improved processes for removing newly determined impurities.

As used herein, the term non-reactive and inert gases means industrial gases which can be treated by the process of the invention since they do not react with selected solutions of alkali metal and alkaline earth metal compounds and polyhydric alcohol as defined below.

It is generally known that olefins due to their method of production, storage and / or handling may contain trace amounts of the order of ppm of water vapor, hydrogen sulfide, carbon dioxide, carbonyl sulfide, sulfur dioxide and mercaptan. For many syntheses, an olefin having below 0.5 ppm of each of these impurities is required.

For example, to produce ethylene of suitable quality for the production of certain polyethylenes, the low concentration of carbon dioxide, about 10 to 25 ppm, in the olefin should be reduced to less than 1 ppm. A sodium hydroxide pellet is currently used for this purpose. However, the main problems with this process are that only about 3% of the sodium hydroxide contained in the layer is converted to sodium carbonate according to the equation:

NaOH + CO _2? i = Na ₂ CO ₃ + H ₂ 0 and that after converting the surface of pellets of sodium hydroxide to sodium carbonate takes place by treatment with a loose agglomeration of particles of water for forming channels to solidify the layer.

The fact that the entire layer solidifies is a particularly difficult problem since at present the layer has to be removed manually. As an alternative solution, a sodium hydroxide solution was proposed. The disadvantage, however, is that the water vapor from the solution is introduced into ethylene and it is therefore necessary to use a zeolite layer to absorb water: however, the installation of this layer is expensive and its rageneration expensive.

In the process according to the invention, a substantially water-free liquid is used, which therefore does not increase the water content of the gas to be treated. The treatment liquid has a high ability to receive alkali or alkaline earth metals, a very low vapor pressure, with alkali or alkaline earth metals forms a chemically stable system and has a sufficiently low viscosity to allow good wetting of the treated gas.

According to the invention, an alkali metal or alkaline earth metal compound and a liquid polyvalent alcohol are used in the form of a solution to remove the trace impurities mentioned above and in particular to remove any trace impurities present. Thus, the process of the invention is not directed to the removal of one particular impurity, as has been the case so far.

Accordingly, the present invention provides a process for the purification of an industrial gas such as hydrogen, carbon monoxide, air, oxygen, helium, argon, monoolefins having 2 to 5 carbon atoms per molecule, diolefins having 4 to 5 carbon atoms per molecule, paraffins or acetylenes. a plurality of impurities from water, hydrogen sulfide, carbon dioxide, carbonyl sulfide, sulfur dioxide, hydrogen chloride, hydrogen cyanide, nitric acid and mercaptans, characterized in that the purified gas is contacted at a temperature of 15 to 100 ° C with a liquid, anhydrous solution containing by weight 0,5 to 15% of alkali metal or alkaline earth metal, based on its hydroxide or weak acid salt, in a liquid aliphatic polyhydric alcohol having a carbon to oxygen ratio of 1 to 5 and having at least two oxygen atoms separated by no more than two consecutive carbon atoms.

In the process of the invention, the industrial gas as defined above is continuously introduced into the above described solution of an alkali metal or alkaline earth metal compound and a polyvalent alcohol maintained at about 15-100 ° C and the gas is discharged from the solution into an environment whose partial pressure prevents moisture content of the gas to be treated. In a preferred embodiment of the process according to the invention, the concentration of water in the gas removed from the solution and in the medium into which the gas is introduced is less than the concentration of water in the gas introduced into the solution.

The term alkali metal and alkaline earth metal means here the elements of Groups IA and IIA of the Periodic Table of the Elements; in particular lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, strontium barium. Preferred alkali metals are sodium and potassium, with potassium being particularly preferred for the process of the invention.

For simplicity, the process according to the present invention is described by way of example of removing trace amounts of impurities from ethylene gas.

The alkaline reaction of the polyhydric alcohol solution is formed by hydroxides or salts of weak inorganic acids and alkali or alkaline earth metals.

The polyhydric alcohols include glycerine alkylene glycols such as alkylene glycols of up to 12 carbon atoms, for example ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, 1,2-butylene glycol, di-1,2-butylene glycol and alkylene oxide addition products, with a polyol such as the above-mentioned glycols, glycerin and other trioles such as 1,2,6-hexanetriol, erythritol monomethyl ether and pentaerythritol monomethyl ether. Preferred are the ethylene oxide and propylene oxide polyol addition products, with ethylene oxide addition products alone or reacted with propylene oxide alone being most preferred.

The process according to the invention is suitable for the purification of a gas which contains, as the main component, an inert gas which does not react with a liquid solution of an alkali metal or alkaline earth metal compound and a polyvalent alcohol selected for this purpose. chemically reacts with this liquid solution of an alkali metal or alkaline earth metal compound and a polyhydric alcohol. Examples of the non-reactive component of the purified gas are: hydrogen, carbon monoxide, air, oxygen, nitrogen, helium, argon, lower monoolefins, lower diolefins and derivatives thereof, paraffins such as methane, ethane and similar paraffins and acetylenes. By olefins is meant here olefins selected from the group consisting of monoolefins having 2 to 5 carbon atoms, diolefins having 4 or 5 carbon atoms and derivatives thereof. Typical olefins are ethylene, propylene, butylenes, pentylenes, 1,4-pentadiene, 1,3-butadiene and derivatives thereof.

The reactants of the purified gases are primarily those which form acids in the aqueous solution. These react with the alkali metal or alkaline earth metal compound in the solvent to form inorganic or organic salts removable from the gases.

Examples of acidic or reactive components of the purified gases include hydrogen sulfide, carbon dioxide, carbonylsulfide, sulfur dioxide, mercaptans, hydrogen chloride, hydrogen cyanide, nitric oxide and the like.

In carrying out the process according to the invention, it has been found that water vapor can be simultaneously removed from the gas to be purified, even if it is contained in a greater religion than could be described as trace. Water vapor is removed by treatment with a solution of alkali metal or alkaline earth metal compounds and polyhydric alcohol, probably according to a completely different mechanism than the trace amounts of reactive components of the purified gas. The water vapor removal mechanism is probably based on the ability of polyhydric alcohols to absorb moisture, and the double-decomposition solution's ability to apply additionally may also be applied:

RONa + H ₂ O 'ROH + NaOH a

Na ₂ CO ₃ + H ₂ 0 _s · - * 2 NaOH + CO ₂

Additionally, it has been found that water can be removed with a solution of an alkali metal and an alkaline earth metal and a polyhydric alcohol from industrial gases, and water may be present until the respective gas is saturated (dew point). The hydroscopic capability of the polyhydric alcohol, which induces water uptake by the hydrogen bonding mechanism, does not reduce the capacity of the solution of the alkali metal or alkaline earth metal compound and the polyhydric alcohol to react the solution with other trace impurities mentioned above.

Therefore, any amount of water vapor contained in the non-reactive purge gas introduced into the non-reactive gas prior to or during its production or processing is removed with a polyhydric alcohol and an alkali metal or alkaline earth metal absorption solution. Similarly, all of the reaction water formed in situ is also removed with the components of the alkaline solution.

Therefore, the absorption solution is referred to herein as a substantially non-aqueous solution which, according to the invention, removes trace amounts of reactive impurities from the non-reactive purge gas in the gas purification. It is recalled that the water partial pressure maintained above the absorption solution is lower than the non-reactive purge gas, so that water vapor does not entrain the non-reactive gas.

Generally, the non-aqueous absorption solutions of the invention are prepared by adding an alkali metal or alkaline earth metal compound to a solution of a selected liquid polyhydric alcohol, for example glycerin and the above glycols. This addition to the polyhydric alcohol in the form of a solution may be carried out by direct addition of the alkali metal or alkaline earth metal in the form of their hydroxides, carbonates or bicarbonates or other salts of similar inorganic weak acids. The metal or hydroxide or salt may react to form an alkali metal or alkaline earth metal polyhydric alcoholate. It is possible that the carbonate form is first hydrolyzed with water to hydroxide before formation of the alcoholate.

Solutions of the alkali compound and the polyhydric alcohol are prepared by simply mixing the alkali component with the polyhydric alcohol component until a solution of both components is formed. This mixing can be carried out at room temperature or at elevated temperature, for example at the boiling point of the polyhydric alcohol used. Generally, the two components are mixed at a temperature of about 30 to 250 ° C, preferably at a temperature of about 40 to 220 ° C.

The alkaline component can be introduced into the polyhydric alcohol in the form of hydroxide and in the form of a salt of weak inorganic acids, for example carbonic acid. Preferably, the alkali metal or alkaline earth metal is introduced in the form of hydroxide, carbonate and / or bicarbonate.

As will be discussed below, the highest soil removal efficiency is achieved when the alkali metal or alkaline earth metal is used in the form of hydroxide, but the most stable system is achieved using carbonate. Examples of suitable alkali metal or alkaline earth metal compounds include lithium hydroxide, lithium carbonate or bicarbonate, sodium hydroxide, carbonate or bicarbonate, potassium hydroxide, carbonate or bicarbonate, hydroxide, rubidium carbonate or bicarbonate, cesium hydroxide, carbonate or bicarbonate, magnesium, calcium, strontium or barium carbonate or bicarbonate.

According to the invention, 0.5-15% by weight of an alkali metal or alkaline earth metal is used to form an absorption solution with a sufficient concentration of alcoholate after reaction with a small proportion of polyhydric alcohol, for example glycerol or a selected glycol.

A high-pressure pilot plant unit is constructed to determine the technological values and to study the operating characteristics of the system according to the invention. A glass column having an internal diameter of 28 mm and 20 trays is used for this purpose. The glass column is integrated into a pressure unit for high-pressure operations. The feed gas-ethylene is preheated to the desired column temperature in a shell and tube heat exchanger. Another heat exchanger is used between the circulation pump and the column to control the temperature of the liquid introduced in the column cover.

Sodium hydroxide pellets in glycol are mixed at 50-75 ° C under nitrogen purge: 3 hours are sufficient to dissolve the pellets completely. The solution is then transferred to a reservoir section of a glass column for stripping water. The solution is circulated at a temperature of 50 [deg.] C. and a pressure of 345 kPa over a countercurrent nitrogen line. Stripping is performed until the water concentration in the purge nitrogen has dropped below 10 ppm.

The glass column used has three simple taps to analyze the gas introduced into and out of the column. The carbon dioxide and water vapor content are determined in a coterminal manner in the gas samples. Liquid samples are also taken periodically to determine viscosity.

The column is tested under various technological conditions:

Solvents ethylene glycol

Reagents ⁺ triethylene glycol feed gas (TEG)

2% or 5% sodium hydroxide 2% pyrogallol

2% manganese chloride nitrogen or ethylene

Overpressure in column, kPa Column temperature, ° C 690 to 2 38 to 60 518.5 Liquid to gas mass ratio 0.023 to 0.167 Gas velocity, m / s Concentration of carbon dioxide 0.045 to 0.09 feed gas, ppm Water concentration in the feed gas 1 to 110 nu, ppm Oxygen concentration in the feed 1 to 1,000 gas, ppm Concentration of hydrogen sulphide in feed 0 to 50 gas, ppm 0 to 20

% by weight of the reactant with respect to the weight of the total solution

For good gas-liquid contact and continuous operation, the gas velocity should not exceed the column congestion rate. The bed speed is calculated for 5% sodium hydroxide and triethylene glycol solutions according to Table I:

Table I

Column congestion rate using 5% sodium hydride solution and triethylene glycol, ethylene gas and a column diameter of 28 mm Weight ratio Overpressure in the column Temperature The speed at which the liquid fluid flow in the column has a column against the rising to gas gas ⁺ kPa ° c m / s 0.1 2 070 20 May 0.324 0.2 2 070 20 May 0.291 0.1 2 760 20 May 0.339 0.2 2 760 20 May 0.315 0.1 103.5 75 1,500 0.2 103.5 75 1,350 0.1 793.5 40 0.540 ⁺ Based on the entire cross-sectional area columns For a column operating at an overpressure of 1,725 kPa calculated flooding speed about 0.3 m / s.

This value represents the most common industrial operations with aqueous solutions and therefore the viscosity of the absorption liquid is not included. However, the viscosity of the absorption liquid using sodium hydroxide and glycol must be taken into account.

The results of the carbon dioxide removal tests are shown in Table II.

O

XD

P α

with

XD a

xn e Ό Ci xd CM>

+ + + + k + or> <NCNOOOO + m ^ fOrNOmfNCNi— (CNf) KO <OOi—

OťNrHrHOOOOOOOrHfOiHO

X o

Φ ϋ

«3

P

P (3

Φ

U α

o w

G G XD d Ό rH Xd CM>

o o in in t CO CO t in in cm cn • m * rH o

IT)

Φ> ϋ o

CM

P

Φ

P cd

CM

O O O O O CN <N CN CN o rH i — f

0 'řd 'řd 'řd > < > 1 'íd 'řd '> Ί P X 44 44 44 44 X X 44 44 'řd 'řd 'řd 'íd 'řd 'řd 0 0 0 0 0 0 0 0 0 44 44 44 44 44 44 > « W ω w W W d d d N N N N N N X Řd íd íd íd Řd Řd > 1 > 1 Řd M M M M M M > 1 0 > > ř> > > > > > > (3 G G G G G

Removal of carbon dioxide using a solution of glycol and sodium hydroxide β

> 1 d

p c + &gt; <1) -d +

S H o d CM CM

CMO

Φ

Ch

X d

r — I d

P CM Φ X> P CM

Ό • H ·

X P

'D Q MCE Ό Ό «5> i 0

W W *> Φ

P

Xfl

CM • cp CO 00 cn ^ poococofo ^^ mk ©

M3 cn cn kO k £> k oo o σ> ro in cn m o o o in in m in in in k k k 00 CO σ \ σϊσ> σϊσ> σ \ οοα)

O O O O O O O O O O O O O O O w « w w w w w w w w w W W w ω E-t E-t E-t EH E-t E-t E-t EH Ed E-t E-t

• 3 G M > P P 3 Λ 0 Ό O CM XD G XD τ — l G xd 0 3 rH G 0 • H 43 44 <H P 0 0 G xd > 44 0 44 Řd 44 P 3 rH 0 G rH Cn Řd G Řd 0 G rH Ό rH 44 Φ Φ Φ CM > 1 rH > N • r * i rH Řd > Φ P Cn 43 43 43 d G P ϋ 0 Φ Φ Řd M <H rH • H 44 G 43 Řd Φ > P □ 43 P Xd d Řd P P Ό 0 P 0 G xd XD P xd xd G P 0 G G Φ Φ with <D Φ G P , 2 G WITH d X d d G > Φ φ G G N sa > N N O + + CM O H + CC w Ed

257452

Based on the results shown in the table, it can be concluded that once the ethylene glycol / sodium hydroxide mixture and the triethylene glycol / sodium hydroxide mixture are very effective at removing traces of carbon dioxide: triethylene glycol is, however, preferable for its lower vapor pressure. The concentration of carbon dioxide in ethylene can be reduced to less than 0.5 ppm in a 10 tray column, provided good gas-liquid contact is maintained. Even a low liquid to gas ratio of, for example, 0.05 is sufficient to be effectively removed in treiethylene glycol have good flowability at 40-50 ° C with very good tray performance. The viscosity of this solution at 40 ° C is 110 mPa. After three weeks of continuous operation with a single dose of 5% sodium hydroxide in triethylene glycol, no increase in viscosity is observed even though the solution contains sodium carbonate as a byproduct. No deposition of solid sodium carbonate is evident in the vessel, but some solids remain on the filters after liquid filtration. The deposition rate of sodium carbonate is very low. Removal of carbon dioxide is equally effective both before and after water removal by stripping the solution.

A single dose of 5% solution (percentages are still by weight unless otherwise specified) of sodium hydroxide in triethylene glycol will last for three weeks until the carbon dioxide concentration in the gas from the column increases due to a decrease in the sodium hydroxide content. To determine whether the decrease in carbon dioxide removal efficiency is due to a lack of free water in the system or a decrease in sodium hydroxide content, 0.75 liters of triethylene glycol containing 0.1% water is added to the liquid reservoir and the column is put back into operation. No improvement in the removal of carbon dioxide is observed, demonstrating that the loss of column efficiency is due to a decrease in the sodium hydroxide content.

During the continuous operation, three viscosity fluid samples were taken. No viscosity changes are observed, suggesting that dimerization and oligomerization reactions are insignificant.

The solution is filtered to remove sodium carbonate in solid form, although there is no noticeable settling in the container. The observed settling is in agreement with the settling calculation using the Stokes equation. For example, these calculations give a settling rate of 0.0017 m / day at 40 ° C for sodium carbonate particles with a diameter of one micrometer in a 5% solution of sodium hydroxide in triethylene glycol. A scanning electron microscope implies that the sodium carbonate particles have a size of 1 to 10 microns, with most particles having dimensions at the bottom of this range. Therefore, filtration may be necessary to remove solids.

In addition to the use of sodium and lithium as alkali metals for in situ reaction with a selected glycol to form a non-aqueous absorption solution, tests were conducted to determine the effectiveness of various alkaline earth hydroxides for the glycolate preparation. and a decrease in carbon dioxide and percent theoretical removal of carbon dioxide in the nine-cycle regeneration using these alkaline earth metal hydroxides (Table IV).

Figure 3 is a graph of nonaqueous reversilibate carbon dioxide removal efficiency for barium, calcium, potassium and sodium based systems over a nine cycle regeneration. The sodium-based system is a highly efficient process over all nine cycles.

Table III

Initial carbon dioxide content in various glycolates (% are always by weight)

Solvent Solvent G CO 9 binding 5% solution of SrlOH in diethylene glycol 125 1.95 5% solution of Ba (OH) ₂ in diethylene glycol 125 2.80 5% Ca (OH) 2 solution in diethylene glycol 125 4.50

Conditions: room temperature, carbon dioxide pressure corresponds to ambient pressure

Table IV

Alkaline earth glycollate regeneration (% by weight)

Solvent Regeneration cycle

Decrease in CO 2% theoretical removal of CO 5% Sr (OH) ₂ solution in diethylene glycol

5% solution of Ba (OH) 2 in diethylene glycol

5% Ca (OH) 2 solution in diethylene glycol

G % 0.8 44 0.3 17 0.5 28 0.9 50 0.4 22nd 0.4 22nd 0.4 22nd 0.3 17 0.35 19 Dec 0.5 39 0/5 39 0.35 27 Mar: 0.45 35 0.4 31 0.5 39 0.5 39 0.45 35 0.5 39 1.5 51 1.1 37 1,2 40 1.05 35 1.0 34 1,2 40 1.0 34 0.9 30 0.95 32 at 0, , 1 MPa and per

Conditions: carbon dioxide in the preparation of the test solution introduced at 0.1 MPa at room temperature, regeneration at 200 ° C, solvent weight 125 g.

The method according to the invention is illustrated by the accompanying drawings, which are described in detail below:

FIG. 1 is a simplified flow diagram of the gas purification apparatus of the present invention; FIG. 2 is a flow diagram of a device similar to FIG. 1 having additional means for recovering the non-aqueous absorption solution and recycling the recovered solution to the liquid and gas contactor;

FIG. 3 shows the carbon dioxide removal efficiency curve for the number of heat recovery cycles, where the heat recovery cycles are plotted on the x-axis and the carbon dioxide removal efficiency on the y-axis, and curve 1 is for the 7% potassium carbonate / triethylene glycol system; % by weight sodium hydroxide / diethylene glycol, curve 3 for the 5% by weight calcium hydroxide / diethylene glycol system and curve 4 for the 5% by weight barium hydroxide / diethylene glycol system;

Fig. 4 is a simplified flow diagram of a continuous gas scrubbing facility with no absorbent metal carbonate regeneration; carbonate.

According to FIGS. 1, 2, 4 and 5, the scrubbing gas is introduced via line 2 into the gas and liquid contactor 2, from which the cleaned gas is discharged via line 2 to a device 4 to remove traces of non-aqueous solution from which According to FIGS. 2 and 4, the non-aqueous solution removed ^{from the} gas in line 2 is introduced into line 6 through line 9. 1 and 2, the non-aqueous treatment solution is fed to the contactor 2. For regeneration purposes, the solution used can be discharged from the contactor 2 according to FIGS. 1 and 2 via a pump 7 through a pump 2 to a stripping column 10 to which FIG. 2, nitrogen gas is introduced via line 11, and the solids impurities are discharged from the stripping column 10 via line 12, waste solution is discharged via line 13, gaseous impurity line 14 via line 14 and the purified solution via line 15 via line 15. 1 and 2, the non-aqueous treatment solution is fed to the contactor 2 according to FIGS. 1 and 2. Referring to FIG.

4 and 5 have the same meaning as in FIGS. 1 and 2. According to FIG. 4, the solution 17 from the contactor 2 is fed through the pump 2 via the valve 17 to the stripping column 12 into which the 18 is introduced via the valve 18. if necessary, hot steam or cooling water via line 19, both environments, both steam and possibly water being discharged via line 21.

From the stripping column 10, carbon dioxide and water vapor are removed via line 22, whereby an organic liquid such as triethylene glycol is added via line 23 and an alkali line such as potassium carbonate 24 via line 24. The cleaned and added non-aqueous treatment solution is then passed through the pumps 25 through line 26 to the regenerated non-aqueous treatment solution reservoir 27 and returned via line 28 through valve 29 after mixing with the non-aqueous solution from the device 2.

According to FIG. 5, the solution used is withdrawn from the contactor 2 via line T and passed through a filter 30 from which a metal carbonate precipitate is discharged via line 31 and through the valve 32 solids free of the used solution are discharged through a valve 43 to a stripper 10 equipped with a stirrer 34. In this way, steam is passed through line 18, nitrogen is introduced through line 35, and sodium hydroxide and triethylene glycol are added through line 36. The gaseous products are discharged from the stripper column 10 via line 37, while via line 38 via line 40 provided with valve 21 a purified non-aqueous treatment solution is fed via pump 33 via line 42 to gas and liquid contactor 2.

As can be seen, the contactor 2 may be a container filled with sodium hydroxide in the form of an extraction solution into which the purified gas is introduced. In the process according to the invention, the ethylene introduced as impurities contains, for example, carbon dioxide, water, sulfur dioxide, hydrogen sulphide, carbonyl sulphide and mercaptans: it is mixed with a non-aqueous solution in a gas and liquid contactor 2 containing at least one reaction zone. Impurities are removed from the gas by reaction with the components of the absorption solution or by dissolution in the solution. If desired, the cleaned gas leaving the gas and liquid contactor 2 may be further purified, for example by passing through a selective absorption layer in a 2 N &lt;

Depending on the concentration of impurities in the feed gas and the amount of gas to be cleaned, the solution may be regenerated intermittently or continuously by removing solid reaction products, cleaning the solution used and / or separating the solution used and the impurities absorbed from the active solution.

To compensate for losses of the solution: by entrainment or evaporation into the cleaned gas, the treatment nonaqueous solution is added to the process.

At the top of the column may be a device for entraining liquid droplets. Ethylene gas leaves this apparatus and passes through a filter to remove submicrometer glycol particles. The retained liquid may be returned to the stripper or collected at a low flow rate and periodically removed. Downstream of the filter there may be an activated carbon scavenger to remove the last triethylene glycol traces from ethylene. At a temperature of 50 ° C and at a pressure of 3,105 kPa, the triethylene glycol concentration in ethylene will be less than 0.1 ppm.

If removal of triethylene glycol is desired below this limit, adsorption on activated carbon is used. Activated carbon is expected to receive more than 20% triethylene glycol. With this adsorption capacity, 362 kg of activated carbon is sufficient to completely remove all traces of triethylene glycol from ethylene from a column of 18,120 kg.ethylene per year (8,000 hours) of operation. Therefore, the activated carbon used can simply be removed from the process and does not need to be regenerated for economic reasons.

Two filters can be used to remove solid sodium carbonate from the solution. The sodium hydroxide solution in the glycol leaving the filters is divided into two streams. The pressure of approximately 20% of the solution is brought to 130 kPa and introduced into a stripper column and the remaining 80% is returned to the absorber using a circulation pump. For a column processing 18,120 kg / h of ethylene, at least 37.8 l of liquid should be used per minute (liquid to gas ratio is 0.125).

The stripper column operates at an overpressure of 68.7-137.4 kPa at 100 ° C, the column having two main tasks: to reduce the moisture content of fresh solutions of sodium hydroxide in glycol to less than 10 ppm in the gas phase: this is achieved by flushing nitrogen at 100 ° C continuously when sodium hydroxide is added to the system. The second task is to remove the moisture adsorbed by the circulating solution by continuously flushing with nitrogen at 100 ° C. In doing so, it removes the sodium hydroxide solution in the carbon dioxide glycol by chemical reaction and water by physical adsorption.

With a low moisture content in the introduced ethylene (about 5 ppm), only a small portion of the circulating solution must be desorbed. The distillation unit should be sized to 456.6 liters of 10% sodium hydroxide in triethylene glycol.

The stripping column is equipped with a turbine type stirrer to dissolve solid sodium hydroxide in the glycol solution. Once sodium hydroxide has been removed from the system by reaction with carbon dioxide, sodium hydroxide must be added to the system. To add sodium hydroxide, pressurize the column with ambient pressure, flush the column with nitrogen, open, and add sodium hydroxide flakes to contain, for example, 15% sodium hydroxide. When the moisture content of the purge nitrogen is below 10 ppm, the concentrated product is mixed gradually with the circulating solution. During solid sodium hydroxide addition and dehumidification, all of the liquid from the filters is returned to the column and no by-streams are discharged to the stripper.

The heat source for the stripping column may be a low pressure steam guided through the jacket. It must be able to heat the solution to 150 ° C, although 100 ° C is sufficient to remove moisture.

Typical examples of the practice of the present invention using various feed gases, sodium and potassium absorption systems using different flow rates and operating pressures are given in Table V below.

From the examples, it is evident that in the process of the present invention, the glycol and glycolate solution, as the major part of the absorbent, is used for purification, gas, nitrogen or ethylene, by reducing impurities such as carbon dioxide, carbonyl sulfide and hydrogen sulfide from a relatively high concentration of several ppm.

242453 + J

O + J tn • H> O

0) a

cl

CL

O

O ϋ

X4 (0 μ

O

4J

0 >% rH rH Η I 43 CL 43 υ cn > 1 3 e 2 34 2

and 3 3 3 3 3 O 0 0 0 O 0 34 44 44 £ 44 34 34 > N XM > N OF > N > N > N XQ xd xd and and and and and xd Xd xd CL > 1 CL > 1 CL ί> 1 and 43 43 43 43 43 CL > 1 CL & H CL φ cj φ tí Φ and 43 10 it it it 10 Φ and Φ and Φ > M r— | > μ rH > μ 1—1 » μ μ μ μ μ > μ ι — 1 > μ rH > μ & > CL > CL > Φ + Φ + Φ Φ + Φ + <u + CL > CL fc> CL Ό + Ό + Ό Ό + Ό + Ό + tn xu tn XI) tn Xl, r-1 + Η -Ι- rH rH + rH + rH -Ι- tn XI) <n xp tn > > > O M Ο J HIM μ O μ O μ Ο μ > t> Φ O Φ O Φ 0 Φ < AT Φ φ φ φ Φ 0 Φ 0 Φ at rH υ i — 1 at rH and -P and μ a + » and 44 and 4J and -Μ at rH ϋ rH υ * rl in • r | 0 • rl here and a a and a and and and and and and a • rl Φ • rl Φ • r | jq at 43 ϋ 43 at O CL O CL o CL O CL O Λ O CL 43 O 43 O 43 O 3 0 fl 0 r — 1 rH rH rH rH rH 3 0 3 0 3 μ μ μ 0 o 0 O 0 O O O 0 O O o μ μ μ 44 N 44 N 44 N 34 CM rH 44 rH 34 CM 34 CM 34 rH • μ N P N 44

tn o

> N (0

CM

O

O> N a

CM

O tn o

> N <0

O rH rH ι-Η fO

V v v tn tn

CM rH rH

V «v

Γ *> 1 a

XU>

o rH

Φ

O

O o

in tn o in γμ in rtn rtn rtn tn

CM CM CM

CM VO r> tn vo>

o o

XT in tn cn o x * vo in n t ·· o o

> 1 rH ** xr xr CL CM CM CM CM CM CM CM CM 2 2 2 2 2 2 2 2 2 2 2 CM CM CM '3ί 3 •"IN \ •with. ***. i.e AT O 3 > 1 CM CM CM CM CM CM CM CM - * » ***. with. > Φ rH O O O O O O O O CM tn tn Ό CL at at at O υ O υ AT O O CM xd \ O O 2 > G xí « xr O O O O O cn rn cn and 2j O O O O O O O O O O O N CL rH rH rH tn tn tn m m rH rH rH

rH 0 34 > x rH 0 » t — 1 and 0 rH rH φ 34 0 0 rH > 1 34 34 > 1 rH > 1 ►i 43 θ ' rH rH 44 and 0 and 0> Cn Φ φ > rH • r | and and • r | rH • H * 3 μ - φ φ μ > 1 X XI) φ rH rH 44 43 0 H4 υ > t > X ‘'-, 44 and μ XO řn 43 43 + Φ * α 3 H • P P + ’ • H 34 > 1 0 3 » Φ Φ 2 μ 43 CL O 44 rH N 2 2 2 and ’, 0 O O O 2 2 3 and μ and and and O 6 -p 2 2 2 <*> and 4) XI, 0 S> i 2 p i and <* OP OP xr and tn λ »3 O OP > » O O O O EH tn <#> and rH rH CM tn tn

rH i-tI rH 0 0 0 34 34 34 > 1 >% >, rH rH rH rH rH rH 0 0 0 tn tp θ ' 34 34 34 and and and > 1 > 1 > 1 φ Φ φ rH rH iH rH H rH 3 » Q. 0 » > 1 > 1 > 1 • a and and 43 43 43 φ φ φ 44 44 44 rH rH rH Φ Φ Φ > 1 > 1 > 1 • rl • H • rl 43 43 43 μ μ μ 44 44 44 44 44 44 Φ Φ Φ \ 'IN. 2 2 2 2 2 2 O O O O O O and and and 2 w 2 2 2 0P OP OP OP OP OP O O O tn CM CM CM CM CM

ambient gas introduced; ⁺⁺⁺ 100 gh ⁺⁺ column flow added as 2.9% sodium metal

In the pilot plant of FIG. 5, another embodiment of the cleaning method according to the invention is illustrated.

The pre-purified ethylene from the ethylene production plant is passed through a non-aqueous absorption solution containing 6% sodium hydroxide and 94% water for 56 days. triethylene glycol. The temperature in the scrubber is maintained at 30 ° C and the ethylene feed pressure is 30 psig. The carbon dioxide content of the feed gas is 1 to 6 ppm and the exhaust gas is 0.05 to 0.15 ppm. 13.6 kg of ethylene per hour are introduced and the gas velocity in the scrubber is 0.18 m / min. On the last day of operation, the scrubber reduces the carbon dioxide content of the feed gas from 5.35 ppm to 0.10 ppm.

In the first tests of the process of the invention, a sodium-based system was investigated, wherein the absorption solution was prepared by adding sodium or sodium or sodium metal carbonate or carbonate to an excess glycol or glycerin solution to form the desired sodium glycol or glycerin sodium in unreacted glycol or glycerin as solvent.

This sodium-based system does not have to be a problem during operation. When using absorbent solutions based on sodium hydroxide and liquid polymorphic alcohol, filtration of the solution used may be necessary to remove very fine sodium carbonate particles of 1 to 40 microns, which are formed in the presence of moisture. The sodium-based system can operate intermittently and not cotinuously.

A potassium-based absorption system does not have this drawback. The non-aqueous absorption solution is potassium glycolate or glycerate formed either by reacting elemental potassium or potassium hydroxide or potassium carbonate with a polyol, for example, glycol and / or glycerin. When the preferred potassium carbonate is used as a potassium source, it is necessary to convert it to a hydroxide at about 200 ° C to optimize the formation of the alcoholate.

The continuous system is characterized by the thermal regeneration of a solution containing potassium glycolate or glycerate, which is used to remove carbon dioxide from various gases. Potassium carbonate, soluble in glycol solutions, has been found to be well soluble up to a concentration of 10% at ambient temperature or at a slightly elevated temperature of 20-25 ° C. It has also been found that by heating these potassium carbonate containing solutions to a temperature of about 160 ° C to 200 ° C, the potassium carbonate decomposes to release carbon dioxide while forming the glycolate potassium salt. The reaction is probably as follows:

N ₂

K, CO, + ROH - = -> 2 YE + H, O + CO, (A) ^J '(180-200 ° C) where ROH is any glycol.

Thus, the potassium glycolate salt of formula ROK is of the same kind as produced from potassium hydroxide according to the equation:

N,

ROH + KOH - = - YE + H, 0 (B) (125 ° C) ^-2

When the potassium glycolate of formula ROK is prepared in the presence of water, to use potassium hydroxide as an alkali metal source (see equation Β), water is displaced from the system in the regenerator using nitrogen gas.

In displacing carbon dioxide in the absence of water, the reaction is likely to follow the following equation C:

II

YEAR + CO, -RO - C - OK (25 to 100 ° C)

The produced substance of the general formula

242452

O

II

RO-C-OK is also soluble in excess glycol as a solvent and also decomposes at 180 to 200 ° C to carbon dioxide and to a salt of formula ROK for reuse. If trace amounts of water are introduced into the scrubber along with the feed gas, organic potassium carbonate is likely to form, but unlike sodium carbonate, which is contained in solid form, potassium carbonate remains in solution and can be recovered by heat recovery. An advantage of this embodiment of the process of the invention is that no precipitate is formed under the conditions and all carbonate formed can decompose thermally, again forming a carbon dioxide removal solution after cooling.

Thus, in this embodiment, the method according to the invention is a heat-regenerable carbon dioxide removal system that does not need any filter device.

The potassium hydroxide or carbonate based process and the glycol for carbon dioxide removal is based on the use of a fixed non-aqueous solvent such as triethylene glycol, with low vapor pressure and high dissolution capability.

The chemistry of potassium hydroxide and potassium carbonate solutions and glycol is currently not entirely clear. Potassium carbonate is not expected to be simply physically dissolved in glycols. Most likely, certain reactions occur between the alkali and, for example, triethylene glycol; partial alcoholisation is likely to occur.

Commercially available triethylene glycol (TEG) contains about 0.1% by weight of water. In addition, water is formed by the reaction of potassium hydroxide and triethylene glycol. Therefore, in the preparation of the glycolate or glycerate, the mixture contains some water after preparation. This water is generally removed by stripping before using the solution to remove the impurities mentioned above. During stripping, the equilibrium is continuously shifted in a direction favorable to the formation of the alcoholate as the water is removed from the system. If the bulk of the water is removed from the system, the solution contains potassium glycolate, unreacted glycol and small amounts of free, unreacted potassium hydroxide and / or potassium carbonate (if used as starting materials).

Potassium hydroxide and glycol solutions are extremely hygroscopic and always contain some condensed water and bound with excess glycol, leaving the water in the system even after drying. This water is removed from the system by heating and purging with an inert gas or similar, since it must not accumulate in the system. However, such removal of water is not the essence of the invention. Potassium hydroxide and glycol solutions can therefore also serve to remove water.

Table V above shows typical examples of the practice of the present invention using various feed gases, various sodium and potassium hydroxide systems, and solvent, various flow rates and operating temperatures.

From these examples, it is apparent that a large amount of an absorbent glycol / glycolate solution system is used in the process of the invention to purify gases such as nitrogen or ethylene to reduce impurities such as carbon dioxide, carbonylsulfide and hydrogen sulfide from relatively high to a concentration corresponding to several ppm.

The use of a potassium-based system improves the ability of the system to simultaneously remove water while removing carbon dioxide without forming solids. In the case of ethylene gas, which also contains traces of water, the system eliminates the need for absorbents to remove water or at least substantially reduces their volume. The process of the invention is ideally applicable to removing atmospheric carbon dioxide from the air used to produce nitrogen and oxygen by cryogenic air separation. As mentioned above, spent non-aqueous absorption solution is recovered in a cyclic process as shown in Figure 2.

For regenerating the solution, nitrogen purging is used together with heating to 180 to 200 ° C to decompose the carbonate formed in the solution to form carbon dioxide, removing the carbon dioxide along with water vapor and other gaseous impurities that are released and removed from the process system.

As noted above, Figure 4 is a simplified flow diagram of a pilot plant for continuous ethylene purification using a potassium-based system or any other system in which a solid carbonate precipitate does not form in the absorption solution. As shown, valves V1 and V2 open only to interrupt the daily continuous operation. The cycle allows a continuous or continuous regeneration operation. In the case of a continuous operation, it is necessary to include a cooler in the piping between the conditioners and the recovery and storage vessel. It is also noted that the solution in the recovery vessel is cooled before being introduced into the container. The embodiment of FIG. 4 is for purifying ethylene using a 6% by weight solution of potassium carbonate in a solution of triethylene glycol. The use of nitrogen scrubbing to remove carbon dioxide is an optional measure for a nitrogen based system.

The use of a non-aqueous sodium-based absorption system for prolonged periods of time can result in the formation of a fine precipitate of sodium carbonate particles of 1 to 40 microns in diameter, and removal of such a precipitate using a filtration step is difficult. It has been found that such fine particles can be agglomerated to larger particles with a diameter of 200 to 400 microns in various ways. Such larger particles can then be removed from the solution using a simple direct filtration as shown in the embodiment of Figure 5.

Such agglomeration can be achieved in one of a number of ways, such as: adding up to 15% by weight of water prior to heat treatment at a temperature of about 150 ° C; and adding up to 2% by weight of a conventional ionic additive, such as sodium chloride for chloride ions, with or without the addition of about 5% by weight of water. Such cycle additives affect the agglomeration and are shown in the simplified flow diagram of FIG. 5, but are used together with the use of a heater in the pipeline immediately upstream of the filter press.

In a sodium hydroxide scrubber, sodium carbonate may accumulate under certain operating conditions. However, a washing machine with a non-aqueous sodium hydroxide solution is still more attractive than with a sodium hydroxide pellet as an absorption system. The use of a washing machine with a non-aqueous potassium carbonate solution results in a thermally regenerable system. A potassium carbonate system has two advantages over a sodium hydroxide system: no precipitation occurs in cyclic carbon dioxide removal, and the system is thermally regenerated. However, potassium carbonate has only half the chemical activity compared to sodium hydroxide to remove carbon dioxide. Sodium hydroxide systems can remove approximately 42% of theoretically contained carbon dioxide, while potassium carbonate systems separate about 20% of carbon dioxide.

Table VI summarizes the results of the cyclic removal of carbon dioxide by using solutions containing 3% lithium hydroxide in diethylene glycol, triethylene glycol and dipropylene glycol · ¹ ·. Theoretically, 5.5 g of carbon dioxide can be removed using 100 g of a 3% solution of lithium hydroxide in these solvents. Using 5.5 g as a numerical value of total carbon dioxide absorption, the theoretical percentage of carbon dioxide removed at each carbon dioxide absorption / desorption cycle can be calculated.

In five cycles of absorption / desorption of carbon dioxide 3% lithium hydroxide in diethylene glycol theoretically removes an average of 14.7% of the theoretical amount of carbon dioxide per cycle, while using lithium hydroxide in dipropylene glycol or triethylene glycol removes 15.7 and 14 as the mean amount, 3% of the theoretical amount of carbon dioxide per cycle.

The use of certain glycol and lithium hydroxide is of minor importance for the removal of carbon dioxide. It is also evident from Table VI that the chemical carbon dioxide removal efficiency decreases significantly with each subsequent carbon dioxide absorption / desorption cycle regardless of glycol choice. For comparative purposes, Table VII shows the results for non-aqueous solutions of diethylene glycol and sodium hydroxide, potassium carbonate and hydroxide lithium.

Table VII shows the highest chemical efficiency of a washer with a non-aqueous solution of sodium hydroxide compared to a washer with a non-aqueous solution of potassium carbonate and lithium hydroxide. This conclusion is supported by the fact that after five cycles of carbon dioxide removal, the average value of the theoretical amount of carbon dioxide removed using sodium hydroxide is the average.

42.0% per cycle, while for potassium carbonate or lithium hydroxide 19.9 and 17.4% carbon dioxide per cycle.

ιϋηί carbon dioxide elution using a 3% by weight solution of lithium hydroxide in glycol as an ileal solvent of 20 0 ° C /

Ol

Λ

XU

G> 0)

G <0

O

Λ

XU

P

XJ

Ρ

Ρ • Η

X ο

Ρ

Ό • Η 0 X Χί 0 XU

4->

Φ · Η μ Κ> χθ -Η Μ Η Μ Χί Ν Ρ

G tr <u

P 0 CL

Ό 0 • h x: X x O O G

XU op G d

XU G> α υ • rM r-ί Ll) ρ 2 &

Ρ Ό Ο Ή *ί * xU Ο G

XU OP G d

XU Μ Λ * -Ρ ϋ W

τί IX • id O 4-> 0 » X! <U X! ’Γ 0 0 μ 0 ϋ rd XJ 0) 0 XJ <u AND) '0 rd <u XU rd + j A4 Ε- » 4-1 Oh IX

tO ο Ο

Ο Ο Ο to <*> rd ΙΛ η «η © ο

flj μ Xí <U Ή 0 řh rd x > G rd rd cn <U > υ Ό tP G rd μ fO XU G <U μ 4-1 0) rd p XU 0 XO rd > 1 G G P Řd XJ XJ Ό <u O XJ 4-1 0 CL X » Φ (0 > <u N <u • H <u μ O • rl μ Ex of OJ Q EH

To σ to to to it to ο

Ο ΚΟ Γ 'σ \ σ. to ιη to σ »xr and m •• τ m to t-» oo

ToχηοσίΓ ^ ο oo σ ο oo σ σποοίΛωοιη f-tojm ^ mtor ^ co

O> 1 i — I

Cn

G (U

I— <> 1 Λ O M CL i i d 'Φ Li P P -H i W> 0 IX Ό -H

H d P P to 3 O q 0 3 -úío 0 'Φ -H o o Μ -H fi 4-1 O d φλ φ Li XI)> L O fi Ρ φ> φ

Comparison of Non-aqueous Reversible Flushing Efficiency for Carbon Dioxide Systems of Sodium, Potassium and Lithium Systems

O

Λ

KU

P <#> O · Η rd> □ 'φ' φ -H λ: ch υ> φ λ • h q 3 ρ d Φ Li 3 L Pd o w · Η Q) d X H O O

T3 • H O 54 rC O 'Φ CP

P d · η P> u d -H Li Ρ Λ n q> □ d

Li φ ω q 3 Φ H tP44 Φ> í P □

Tř O Tř

Ol O 04

OJ Ol 04 Ol 04 oj <n incl. M

O 44 ►H r-i tp q φ q

P o

E

P

W cw O d tn Z <0 O O Ch o r-i oi m o

> 1 rH

3 »q

φ o

> 1 r — I tn

Φ i

Claims (6)

SUBJECT OF THE INVENTION A process for the purification of an industrial gas such as hydrogen, carbon monoxide, air, oxygen, helium, argon, monoolefins having 2 to 5 carbon atoms per molecule, diolefins having 4 to 5 carbon atoms per molecule, paraffins or acetylenes, by removing trace amounts of one or a plurality of impurities selected from water, hydrogen sulfide, carbon dioxide, carbon sulfide, sulfur dioxide, hydrogen cyanide, nitric acid and mercaptans, characterized in that the purified gas is contacted at a temperature of 15 to 100 ° C with a liquid, anhydrous solution containing 0, 5 to 15% by weight of an alkali metal or alkaline earth metal, based on its hydroxide or weak acid salt, in a liquid aliphatic polyhydric alcohol having an oxygen atom ratio of 1 to 5 and having at least two oxygen atoms separated by at most two successive carbon atoms. 2. Process according to claim 1, characterized in that 1 to 10% by weight. 3. Method according to claim 1, characterized by. in the form of hydroxide. 4. A process according to claim 3, wherein sodium hydroxide is used. 5. The process of claim 1, wherein the carbonate or hydroxide form. 6. The process of claim 1 wherein the triethylene glycol. alkali metal is used alkali metal, sodium or potassium is used alkali metal hydroxide, and alkali metal is used, and potassium in polyfunctional alcohol is used 5 drawings