CN1003038B - Process for the removal of dissolved gas from an aqueous solution of ethylene oxide - Google Patents

Abstract

The present invention relates to a method for removing dissolved gas in an oxirane water solution which comprises at most about 15 wt% of oxirane and at most about 0.5 wt% of dissolved gas, wherein the gases are carbon dioxide and at least one kind of other gases. The method comprises the steps that the water solution, water and one kind of other gases except carbon dioxide and oxygen are in contact in a separation tower under the condition that the contact time, the temperature and the pressure are sufficient and basic for removing the dissolved gases completely, wherein the tower comprises an upper section and a lower section; each section at most comprises 15 theoretical plates; the oxirane water solution is added between the two sections; the gases are added from the bottom of the lower section; the water is added from the top of the upper section.

Description

From aqueous solution of ethylene oxide, remove the method for dissolved gas

The present invention touches upon to the processing containing the oxirane dilute aqueous solution of dissolved gas, to remove these gas from this solution.

This class solution has various sources, but mainly carrys out the flow process of the method synthesize epoxyethane of comfortable gas phase catalytic oxidation ethene.In this synthesizing, the oxirane generating must be separated from admixture of gas, this admixture of gas is containing very rare oxirane and unconverted ethene, unconverted oxygen, steam, carbon dioxide, methane, ethane, nitrogen, rare gas and other impurity, impurity is mainly that aldehyde is as formaldehyde and acetaldehyde.

The common method that obtains oxirane from this admixture of gas, comprising:

(a) water absorbs: allow and contact with water from the admixture of gas of conversion zone, obtain the aqueous solution of oxirane, this aqueous solution contains the oxirane of approximately 2～3% (weight), and impurity is as aldehyde and be particularly the CO of dissolved state ₂, methane, ethane, ethene, nitrogen, oxygen and rare gas;

(b) desorb: rare ethylene oxide solution is used steam extraction in tower, at the bottom of tower, remove the current that reality does not contain oxirane, shift out admixture of gas at tower top, this admixture of gas contains steam, the gas that is dissolved at first aqueous solution of ethylene oxide and impurity as the oxirane of aldehyde and 30～60% (weight).

(c) absorb again: said flow is cooling in advance to be contacted with water afterwards, oxirane, CO ₂and most impurity absorbed again, and the most gas existing with solubilised state together with oxirane is at first separated with gas flow.From absorbing again the ethylene oxide solution obtaining, generally contain the oxirane of 5～15% (weight).

(d) distillation: then this solution, through distillation, obtains substantially pure oxirane.In addition, often need to insert additional step in step (c) with (d), to remove CO ₂.Aqueous solution of ethylene oxide after carbon dioxide removal, can be used as manufacturing glycol after treatment, obtains pure ethylene oxide, or obtain the mixture of two products through distillation.

The object of the invention is to process the aqueous solution, as from step (a) and the aqueous solution (c), more generally, all oxirane dilute aqueous solutions that processing contains solubilised state carbon dioxide and at least one other common gas material, this gaseous matter is present in from producing in the solution of oxirane, directly to remove dissolved gases from this class solution, and these gases are after separation, capable of circulation for the synthetic of oxirane without oxirane.If not so,, before these gases are used for circulating, be necessary to add an additional step with eseparation ring oxidative ethane from gas.Clearly, this separation makes the method become complicated, say unsatisfactory from business angle, as United States Patent (USP) 3,729, No. 899 described method is the same, in the method, rare ethylene oxide solution is carried out to flash distillation, separates but only obtain part, be at most be dissolved at first to process in ethylene oxide solution in gas 85%.

The invention provides a kind of method of removing dissolved gas from aqueous solution of ethylene oxide, remove the oxirane of effective dose simultaneously.

The invention provides a kind of method of removing dissolved gas from the aqueous solution, in this solution, contain approximately 15% (weight) oxirane and at the most approximately 0.5% (weight) dissolved gas at the most, this gas is selected from carbon dioxide and at least one other common gas compound, the method comprises described aqueous solution of ethylene oxide is contacted with water, and contact with at least one gas that is selected from one of common gas compound of described dissolving, outside removing carbon dioxide or oxygen, its time temperature and pressure will be enough to effectively, substantially fully remove described dissolved gas, described contact is carried out in knockout tower, this tower divides epimere and hypomere, every section has 15 blocks of theoretical trays at the most, described aqueous solution of ethylene oxide adds between described two sections, described gas adds from the bottom of this hypomere, the gas flow rate of introducing this tower be introduce this tower aqueous solution of ethylene oxide flow velocity 0.05% to 10%, described water adds from the top of this epimere, the flow velocity of introducing the water of this tower is the 5%-15% that introduces the solution flow rate of the epoxyethane water of this tower.

Now explain orally the present invention with example, and with reference to accompanying drawing, this figure is the schematic diagram that is suitable for the device of implementing the inventive method.

Tower used can be any conventional knockout tower of specifying theoretical cam curve that has, and in it, can be the form of column plate or the form of filling, or other device, to guarantee effective gas one liquid contact.

Absolute pressure in this tower is that from 1 to 20 bar is more satisfactory.

Solution to be processed can be containing the oxirane that is at most 15% (weight).Very commonly contain the solution of 2～12% (weight) oxirane.The total amount of dissolved gas is generally lower than 0.5% (weight) of this solution, commonly low hand 0.3% (weight).

Temperature when ethylene oxide solution enters this tower, generally higher than environment temperature lower than 80 ℃.

The water of introducing with tower top can be pure water, or as the water through circulating in oxirane flow process, this water can contain a small amount of oxirane and/or glycol.For example it can be similar in appearance to those gas for always autocatalyzed oxidation section absorb the water of oxirane, its inlet temperature be 10 ℃ to 50 ℃ better.Its flow rate is comparatively ideal is 5 to 15% (weight) of ethylene oxide solution flow rate.

From the bottom of this tower hypomere or below the gas flow introduced, comprise nitrogen, ethene, methane, one of in ethane and argon or more than one are more favourable.Its flow rate is generally to want 0.05% to 10% (weight) of Treatment Solution flow rate.

In accompanying drawing 1, tower 6 comprises two sections of A and B, and these two sections by column plate or media assemblage, and every section has at most 15 theoretical plates.

Oxirane dilute aqueous solution is from 1 introduction, and this place is between the A of tower 6 section and B section.

For carrying the gas flow of this ethylene oxide solution dissolved gas, from 3 introduction towers 6, water is introduced from 2 of this tower.

Substantially by the gas flow of the gas composition that is dissolved at first the gas of ethylene oxide solution and introduce at 3 places, discharged by 4 places.

Processed ethylene oxide solution is discharged at 5 places.

The present invention will be further described with following example.

Example 1

Containing 2.55% (weight) oxirane, 5.22% (weight) ethylene glycol, 0.17% (weight) CO ₂0.032% (weight) ethene, the aqueous solution of ethylene oxide of the mixture of 0.015% (weight) nitrogen and 0.004% (weight) ethane, oxygen and argon gas, introduce device tower 6 as shown in the figure with the speed of 1902kg/h with 72 ℃ time, two sections in this tower respectively have 5 theoretical plates.

Formed by nitrogen for the gas flow that carries ethylene oxide solution dissolved gas, and introduce tower 6 with the flow rate of 1.46kg/h with 25 ℃ time.

Containing the current of 5.5% (weight) ethylene glycol, introduce tower 6 with the flow rate of 131.33kg/h with 25 ℃ time.

Average absolute pressure in tower 6 is 2.5 bar.

The gas flow of discharging with 5.66kg/h speed at this top of tower, containing 99.8%CO ₂be dissolved at first all other gases in the ethylene oxide solution of introducing in this tower.This gas flow is containing the oxirane lower than 0.004% (weight).

Aqueous solution of ethylene oxide, draws with the flow rate of 2,029kg/h from this tower bottom, the CO only dissolving containing 0.003%-(weight) ₂.CO ₂removal efficiency more than 98%.

With the methane displacement nitrogen of identical mole, obtain similar result.

Example 2

Operate by example 1, but the ethylene stream that is 1.91kg/h by speed replaces nitrogen stream.The ethylene oxide solution of leaving from this tower bottom, only containing being dissolved at first CO in the ethylene oxide solution of introducing this tower ₂1% and 0.01% (weight) ethene.

The gas flow of drawing with this top of tower is only containing 0.005% (weight) oxirane.

Example 3

Operate by example 2, but in tower, hypomere only has 2 theoretical plates, ethene flow rate is 3.76kg/h, CO ₂removal degree reaches 99%, is dissolved at first other gas in the ethylene oxide solution of introducing this tower, is removed completely.With the gas flow of the gas of removing from ethylene oxide solution, containing the oxirane lower than 0.005% (weight).

Example 4

Containing 2.5% (weight) oxirane, 0.17% (weight) CO ₂with the aqueous solution of 0.32% (weight) ethene, with 1902kg/h speed and 80 ℃ of importing towers 6, two sections of each own 5 theoretical plates of this tower, operation under average absolute 15 bar.19.4kg/h nitrogen respectively from the bottom of hypomere and the top of epimere is introduced tower 6 with 131kg/h water at 25 ℃ at 25 ℃.

By processing of the present invention, can obtain only containing initial CO ₂1% CO ₂ethylene oxide solution, the removal degree that is dissolved at first the gas of this solution is 94%, the gas flow of drawing from this top of tower, ethylene oxide content is only 0.0005%.

Example 5

Containing 11.73% (weight) oxirane, 0.031% (weight) CO ₂with the aqueous solution of 0.0014% (weight) ethene, 42 ℃, introduce with the speed of 1971kg/h in the tower of example 4, at this tower, this aqueous solution with 25 ℃, introduce nitrogen in tower with the rate that hastens of 3.83kg/h and flow and contact.

Water is introduced from this top of tower with 25 ℃, the flow rate of 131kg/h.

The average absolute of this tower is 2.5 bar.

The ethylene oxide solution extracting from this tower, containing CO ₂amount lower than the initial contained CO of this solution ₂1% of amount, other dissolved gases is virtually completely removed.

The gas flow taking out from this top of tower is only containing 0.0003% (weight) oxirane.

Claims (5)

1. remove the method for dissolved gas in the aqueous solution for one kind, this solution is containing 15% (weight) oxirane and at the most approximately 0.5% (weight) dissolved gas at the most, this gas comprises carbon dioxide and at least one other common gas, it is characterized by this aqueous solution and water and remove oxygen, at least one common gas contact outside carbon dioxide, time of contact, temperature and pressure is enough to effectively remove described dissolved gas, knockout tower used has an epimere and a hypomere, every section has 15 blocks of theoretical trays at the most, described aqueous solution of ethylene oxide adds between these two sections, described gas adds from the bottom of this hypomere, the flow velocity of introducing the gas of this tower be introduce this tower aqueous solution of ethylene oxide flow velocity 0.05% to 10%, described water adds from the top of this epimere, the flow velocity of introducing the water of this tower be introduce this tower aqueous solution of ethylene oxide flow velocity 5% to 15%.

2. by a method for claim 1, the gas that it is characterized by this tower of introducing is nitrogen, argon gas, methane, ethane or ethene.

3. by the method for claim 1, it is characterized by, the temperature of aqueous solution of ethylene oxide is from higher than environment temperature to 80 ℃.

4. by a method for claim 1, it is characterized by, the temperature of introducing the water of this tower is 10 ℃ to 50 ℃.

5. by a method for claim 1, it is characterized by, the average absolute pressure of this tower is I to 20 bar.