JPH0557013B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for selectively removing sulfur dioxide gas from a gas stream in the presence of carbon dioxide. The absorbent that removes sulfur dioxide is regenerated, thereby making it possible to reuse the absorbent and allowing continuous operation of the process. Numerous patents and publications exist that describe techniques for removing sulfur compounds from gas streams containing them. The most common techniques to date have been the use of one or more acid gases, hydrogen sulfide ( _H2S ),
Sulfur dioxide (SO ₂ ), carbonyl sulfide (COS)
Natural gas with carbon dioxide (CO ₂ ) and carbon dioxide (CO 2 ) is treated with an aqueous liquid poor (with respect to acid gases) to produce an absorbent-rich stream, and the rich absorbent stream is thermally treated to allow recirculation. It is a technique used to generate scarce flow. A large number of compounds have been suggested and used as absorbents, some of which selectively remove _H2S or _CO2 , and others more generally remove each of the acidic gases present as much as possible. It has the property of removing a lot. There is now renewed interest in coal-fired boilers, etc., as well as greater environmental concerns, and it is becoming increasingly important to remove sulfur dioxide, but not the major component of carbon dioxide, from the flue gases produced in such plants. There is a need to provide a low pressure (atmospheric pressure or below), low temperature selective process. A commercially desirable feature of this absorbent would be the ability to regenerate the absorbent from the absorbed gas so that it can be reused. One method of removing _SO2 that is widely used today is limestone scraping. The disadvantage of this process is the formation of large quantities of solid waste, calcium sulfite-sulfuric acid, which is often contaminated with fire ash, which requires waste. In regions of the country where pulp and paper operations are carried out,
Although waste is often usable, such cases are rare. Other methods that have come to the forefront recently include U.S. Patent No.
The use of potassium or sodium salts of citric acid as disclosed in No. 4366134. Although the absorbent can be regenerated and recycled, the cost of replenishment can be high due to the formation of thermally stable salts.
Additionally, it is necessary to use stainless steel throughout the plant to prevent excessive corrosion of the metal. It would be advantageous to provide a method that satisfies the following requirements: (a) selectively absorbs sulfur dioxide;
excludes other gases, especially carbon dioxide; (b) lower replenishment costs for other gases; (c) lower operating costs;
and (d) allows economical construction of the device to process large volumes of gas streams, such as flue gas, at low pressures to reduce or eliminate the sulfur dioxide content of such gases. Surprisingly, the method of the invention satisfies the aforementioned objectives. This method combines a gas stream containing sulfur dioxide and carbon dioxide with the general formula where X is an oxygen atom or NR', R' is a hydrogen atom or _C1 - _C5 alkyl, and R
sulfur dioxide is selectively removed from the gas stream by contacting with an aqueous solution of the compound, wherein is a hydrogen atom or a _C1 - _C5 alkyl. The gas stream usually also contains one or more hydrocarbons, natural or synthetic and/or other acid gases associated with combustion gases (flue gases), such as H ₂ S or COS. Also, for purposes of the present invention, the gas stream need not contain carbon dioxide. However, when carbon dioxide is present in the gas, the method of the present invention can selectively remove sulfur dioxide. This method uses a lean aqueous absorbent solution of a compound of formula (I), preferably at a concentration of 0.1 molar to the saturation point. A rich absorbent containing most of the SO ₂ and very little CO ₂ is added to the absorption device (contacting device).
and thermally regenerated to produce a lean absorbent solution for recycling to the absorber. The absorber is preferably operated at a temperature of 5 DEG to 95 DEG C. and at about atmospheric pressure. Higher temperatures and pressures will not adversely affect the method, but it may be necessary to modify the equipment to handle higher temperatures and pressures. The concentration of sulfur dioxide in the gas stream can vary from about 10 ppm to about 45% by volume of the gas stream being treated. The regeneration method can be one of the conventional methods used in conventional gas sweetening as well as by steam stripping. An integrated absorber-stripper (contactor-regenerator) as shown in FIG. 1 was constructed by connecting ten tray Oldershaw columns 10 with pipes. The tower has an inner diameter of 2.5cm
(1 inch) and tray spacing of 3.17 cm (1.25 inch), receiving the lean absorbent solution at its upper end 11 and receiving the contaminated gas stream at its lower end 12. The upper part 13 and the lower part 14 were each independently connected by pipes to collect the treated gas in the upper part and the rich absorbent in the lower part, respectively. The rich absorbent was sent to the shell and tube cooler 15. The cooler 15 passed hot lean absorbent to the shell side and cool rich absorbent to the tube side. The next richest absorbent is Stripper 1.
7 to the upper end 16. Stripper 17 is 6.35cm
It was 0.635 m (2 feet 1 inch) inside diameter filled with a 1/4 inch (1/4 inch) Berl saddle.
The sulfur dioxide exits the upper part 18 with some water vapor and is sent to a condenser 19 where the water vapor is condensed and the sulfur dioxide is sent to a deaerator 20 from where it is discharged and the condensate is stripper 17 by pump 20A.
It was returned as reflux to the top of the tank. stripper 1
The liquid collected in the lower part 21 of 7 was substantially poor absorbent and a portion of it was passed through the reboiler 22 and returned below the stripper filling section. The remainder of the lean absorbent collected in the lower part 21 was sent to the cooler 15 where it gave most of its heat to the rich absorbent. The cold absorbent was withdrawn to the intake side of the pump 23, passed through another cooling device 24, and then sent to the poor absorbent feed point of the absorber 10. The following examples illustrate the method of the invention. Example 1 Data collected from several experiments are set forth in the table below. The title "Alphabet" means the flow indicated by "Alphabet" in FIG.

Table: Example 2 A series of tests were conducted to screen compounds known to absorb SO ₂ for their CO ₂ absorption properties. device, a valve is attached to a part of a steel cylinder filled with glass bulbs, through which
CO ₂ and absorbent could be added. Additionally, a pressure sensor was attached to this cylinder.
The bomb was pressurized to 760 mmHg with CO ₂ and filled with a measured amount of a 1 molar solution of a particular absorbent. The cylinders were then left at ambient temperature (approximately 24°C) or heated as indicated in the table below, and the pressure drop was measured over a 10 minute period for each condition.
The results were as below.

[Table] Perazinone
75 None

Table: Example 3 Various compounds were tested for their CO ₂ and SO ₂ absorption properties using the 10 treley Olderschau column described above. Synthesis of the compositions listed in the table below
A N ₂ /CO ₂ /SO ₂ mixture was fed to the bottom of the column at 55° C. and 4/5 l/min. The top liquid flow was approximately 10 c.c./min. The incoming and outgoing gases were analyzed and the weight percent of CO ₂ and/or SO ₂ absorbed was calculated. The results are listed below.

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[Table] Zu

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[Table] As established by these two experiments,
SO ₂ is CO ₂ at temperatures above 50°C, normal water/gas cleaning temperatures, 5% concentrations as well as 20% concentrations.
selectively absorbed against. Example 4 A 10% aqueous solution of 1-methyl-2-morpholinone in deionized water was prepared in a 1.27 cm x 0.61 m (1/2"
feet) in an excellent (low) packed absorption tower -5
Pass downwards at a normal speed of cc/min, during which time 3.17l/
A mixture of N ₂ /min, 1.2 t/min air, 750 c.c./min CO ₂ and 70 c.c./min CO ₂ (1% by weight CO ₂ ) was fed to the bottom of the column. Liquid extracted from the bottom of the tower
0.6cm of 1.27cm x 0.61m (1/2″ x 2 feet)
(1/4") Berl saddle and fed to a stripper column equipped with a heated bath reboiler. The gas leaving the absorber contains 0.45% by weight of CO ₂ and the absorber liquid contains 0.63% by weight. wt% _CO2
, and 96.8% of the CO ₂ was stripped from the absorbent in the stripper column. This is 1-methyl-2-morpholinone for a 10% solution.
It represents the absorption of 1/2 mole per mole and the ability to regenerate the absorbent for recycling.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the essential components of the method used to treat gases according to the present invention.

Claims (1)

[Claims] 1. A gas stream containing sulfur dioxide and carbon dioxide is defined by the general formula where X is an oxygen atom or NR', R' is a hydrogen atom or _C1 - _C5 alkyl, and R
is a hydrogen atom or a _C1 - _C5 alkyl. 2. The method according to claim 1, wherein X is oxygen. 3. The method according to claim 1, wherein X is NR'. 4. The method of claim 3, wherein R and R' are both _C1 - _C5 alkyl. 5. The method according to claim 1 or 4, wherein the compound of formula (I) is 1,4-dimethylpiperazinone. 6. The method according to claim 1, wherein the compound of formula (I) is 1-methyl-2-morpholinone. 7. The method of claim 1, wherein the method is continuous. 8. A method according to claim 1 or claim 7, comprising an additional step of regenerating the aqueous solution of the compound of formula (I). 9. The method of claim 1 or claim 7, including the additional step of recovering the gas substantially free of sulfur dioxide from the aqueous solution.