KR900006083B1 - Polymeric alkylene phosphoric acid piperazine derivatives for scale control in flue gas desulfurization - Google Patents

Abstract

A desulphurization of a gas (I) contg. S oxides comprises (a) quenching in a vapour-liq. contacting column with an aq. soln. or slurry (II) contg. a Ca cpd. pref. (pref. CaCO3) to react with S oxides, and (b) treating once or more with additional (II) at below 70 deg.C to remove S oxides. The slurry from (b) then being heatd to above 70 deg.C to ppte. the reaction prod. A threshold agent (III) is added to (II), and (III) inhibits a scale formation at the temp. (III) is pref. phosphonomethylated prod. obtd. by reacting aminoethylpiperazine with (di)haloepoxy organic cpd.

Description

Method to suppress scale formation in flue gas desulfurization

This figure schematically shows the absorption tower of the present invention and its accessories used in a gas desulfurization process.

The present invention relates to a method for inhibiting the formation of scale in flue gas desulfurization processes. In more detail, the present invention utilizes a novel polymer prepared by reacting N-amino ethylpiperazine with a dihalo or epoxyhalo compound and nearly phosphonomethylated as a threshold agent, thereby desulfurization. It relates to a method for inhibiting the formation of a scale consisting of inhibiting the formation of a calcium scale at the contact portion of the process and precipitating the calcium compound in a subsequent step. In power plants that burn carbonaceous raw materials, particularly briquettes, as an energy source, in order to prevent air pollution, the gas must be cleaned from the combustible fuel to remove sulfur oxides. The use of limestone (CaC0 ₃ ) as a liquid slurry has long been used for the purpose of removing sulfur oxides from flue gases. Usually, a countercurrent method of contacting the gas and the calcium carbonate slurry in the column has been used. The sulfur is removed from the gas stream by reacting the liquid slurry of sulfur oxide and calcium carbonate contained in the gas to produce sulfite and calcium precipitates.

One of the problems in the process of removing sulfur oxides by reaction with calcium carbonate or other soluble alkaline earth metal salts is that scale forms on the contact surface when the metal sulphate precipitates. Therefore, it is desirable to prevent the scale from depositing during the mentioned contacting process and then to separate it from the solution by allowing it to settle in a subsequent step. In this way, the solution can be regenerated and the solution can be recycled to the process of removing sulfur dioxide from the flue gas, without recycling most of the scaleant.

Conventionally, various methods have been tried to suppress or prevent the formation of scales. Intermittent cleaning of contact surfaces has been attempted, but this is only useful when the gas volume is low or the sulfur content in the gas is low. The use of chelating agents or thresholding agents prevents the formation of scale during the contacting step, but they do not readily precipitate in the settling tanks unless excess limiting agents or chelating agents are used. In this case, therefore, the scale can be formed in the contacting step and in the settling tank.

In order to avoid the formation of scale in the contacting step, a metal ion is present in the solution, and then precipitated in the next step to remove the sulfate of the metal ion.

In the present invention, in particular, using methylene phosphonate provides a method for the metal ion to be present in solution in the contacting step and to be precipitated in the next step.

In particular, polymethylenephosphonic acid derivatives of N-aminoethylpiperazine polymers are useful for flue gas desulfurization processes. The polymer acts as a limiting agent to control metal ions in the gas-contacting step during the desulfurization process, but in the next step it acts to precipitate these ions as sulfates.

Methylenephosphonate amine polymers useful in the present invention, mainly dimers and trimers of N-aminoethylpiperazine (AEP), are produced after reacting N-aminoethylpiperazine (AEP) with a dihalo or epoxyhalo compound. Prepared polymers are usually prepared by reaction with phosphorous acid and alkanyl (aldehyde) at low pH in the presence of an inorganic acid such as hydrochloric acid. N-aminoethylpiperazine has the following structural formula and may be named 1- (2-aminoethyl) -piperazine.

Hereinafter abbreviated as "AEP".

To prepare a dimer or polymer, AEP can be reacted with a dihalo or epoxyhalo compound. It can be reacted with all suitable epoxyhaloalkanes (epihalohydrin), but 1,2-epoxy-3-chloropropane (epichlorohydrin) is preferred. Generally the epoxyhalo compound has 3 to 10 carbon atoms. Other epichlorohydrin-type compounds include 1,2-epoxy-4-chlorobutane, 1,2-epoxy-5-chloropentane, 2,3-epoxy-5-chloropentane and the like. Typically, the corresponding bromo or iodo compounds can be used, but chloro derivatives are preferred. It is also possible to use mixtures of epoxyhaloalkanes.

Dihalide having 1 to 20 carbon atoms can be used. Saturated dihalide of the following general formula can be used.

Wherein X is chlorine, bromine, iodine or mixed radicals thereof, n is an integer from 1 to 10, preferably an integer from 2 to 6. Thus, for example, dichloromethane (methylene chloride), 1,2-dichloroethane (ethylenedichloride), 1,2- or 1,3-dichloropropane, 1,4- or 1,2-dibromobutane and the like Can be used.

이고, R은 수소, 할로겐, 탄소수 1 내지 4의 알킬, 하이드록시 및 탄소수 1 내지 4의 하이드록시알킬이며, X는 할로겐 원자이다.Where Ar is

R is hydrogen, halogen, alkyl having 1 to 4 carbon atoms, hydroxy and hydroxyalkyl having 1 to 4 carbon atoms, and X is a halogen atom.

Dihaloalkylene ethers such as bis (chloromethyl) ether or bis (chloroethyl) ether can also be used. General formulas of the ethers mentioned include the followings:

Wherein n is 1 to 3 and X is a halogen atom.

The dihalides mentioned may be unsaturated. Thus, 1,2-dichloroethene, 1,4-dichloro-2-butene and the like can be used.

The polymer preparation conditions are to use about 0.2 to about 1.0 mole, preferably about 0.25 to about 0.6 mole, of a chain extender compound, i.e., a diepoxy-, dihalo- or epoxyhalo- compound, per mole of AEP as a reactant. . The reaction temperature is about 50 to 100 ° C., preferably 70 to 80 ° C. under pressure sufficient to keep the reactants in the liquid phase.

The Mannich reaction is then carried out on the reactants in the presence of a strong acid capable of maintaining a pH of less than one.

The reaction is carried out over a wide range of temperatures, ie, 85 to 150 ° C. and it is preferred to keep the reaction medium under reflux. If desired, the reactions mentioned may be carried out under subatmospheric superatmospheric pressure, but are preferably carried out under atmospheric pressure. The reaction time varies depending on a number of factors, but is preferably 1 to 5 hours, most preferably 2 to 4 hours.

Phosphorous acid and alkanal may be added to the reaction mixture in any order together or separately, but it is preferred to add phosphorous acid to the polyamine and then slowly add alkanal under reflux.

Almost equimolar amounts of alkanal and phosphorous acid are used for the phosphonomethylation mentioned. The alkanal or acid mentioned can be used in excess, but many excesses are uneconomical. A preferred process is to use an amount of alkanal corresponding to the available amine hydrogen and slightly excess phosphorous acid than the stoichiometric amount.

Although methanal (formaldehyde) is preferable, other alkanal (aldehyde) may be used instead of methanal such as ethanal (acetaldehyde) or propane (propionaldehyde), and the alkanal mentioned is a straight chain having 10 or less carbon atoms. Or side chains.

Thus, the compounds of the present nickname can be represented by the following structural formula:

또는

[여기서, Z는 수소, 하이드록시에틸, 하이드록시프로필,

또는 BA(여기서, M은, 수소, 알칼리금속 또는 암모늄이다)이며, Z그룹의 50%이상은

그룹이다]의 유리 라디칼이고, B는, 일반식 -(CH₂)_n-, -(CH₂)_n'-O-(CH₂)_n'

또는

[여기서, Ar은

또는

이고, n은 1내지 10이며, n'는 1 내지 3이고, R은 수소 또는 메틸이고, R'는 수소, 탄소수 1 내지 4의 알킬라디칼 또는 하이드록시알킬 라디칼, 하이드록시라디칼 또는 할로겐원자이다]의 디할로, 디에폭시 또는 할로에폭시 유기 화합물로부터 유도된 2가 라디칼이며, m은 1 내지 10이다.Wherein A is a general formula

or

[Where Z is hydrogen, hydroxyethyl, hydroxypropyl,

Or BA (wherein M is hydrogen, an alkali metal or ammonium) and at least 50% of the Z group

Group is a free radical, and B is a general formula-(CH ₂ ) _n -,-(CH ₂ ) _n '-O- (CH ₂ ) _n '

or

[Where Ar is

or

N is 1 to 10, n 'is 1 to 3, R is hydrogen or methyl, R' is hydrogen, an alkyl radical or hydroxyalkyl radical of 1 to 4 carbon atoms, hydroxy radical or halogen atom. Dihalo, is a divalent radical derived from a diepoxy or a haloepoxy organic compound, m is 1 to 10.

이고, M이 H, Na 또는 NH₄인 것이다.Preferred compounds useful in the present invention are those in which the B residue is derived from 1,2-epoxy-3-chloropropane (epichlorohydrin) or 1,2-dichloride, m is 1 or 2, and the Z residue is

And M is H, Na or NH ₄ .

Threshold agents active compound used in the present invention, a water-soluble compound containing the metal such as Ca, when used in an aqueous purifying solution used to purify the oxides from the flue gas generated from the combustion of sulfur-containing hydrocarbon fuel, Ca ^{+ It} is effective to prevent metal ions such as ² from being deposited as the scale.

Compounds useful in the present invention are effective in preventing metal ion precipitation at temperatures below about 70 ° C. At temperatures above about 70 [deg.] C., these compounds will diminish the effect such that CaSO ₄ will precipitate in solutions containing SO ₄ ⁼ and Ca ⁺⁺ ions.

Such unexpected properties include contacting flue gas with an aqueous solution or slurry of a calcium compound, such as CaCO ₃ or Ca (OH) ₂ , or other metal compounds that remove SO ₂ and SO ₃ from the gas stream in contact with it. It is useful in the above-described flue gas desulfurization process for contacting. After such contact, these ions do not precipitate as metal sulphates during the contacting step due to the limiting agents used according to the present invention, circulating a portion of the aqueous solution into the quench tank, and at a temperature sufficient to reduce the activity of the limiting agents, usually By heating to a temperature of about 70 ° C. or more, the metal ions precipitate into sulfates. The side stream containing the precipitated sulfate is recovered and transferred to a thickener and then discharged.

The amount of limiting agent commonly used, i.e., the phosphonomethylated AEP polymerization product, is about 0.5 to about 500 rpm, depending on the type of agent and the amount of metal ions present in the solution, which amounts to sulfur oxide concentration and gas capacity in these solutions. Depends on.

In the accompanying drawings, the absorption tower 10 and the supply tank 11 are shown. The supply tank 11 is equipped with the stirring apparatus 23 driven by the motor m. The inside of the absorption tower 10 is provided with a filling part 21 for contacting the gas and a liquid, and a second filling part 22 for demisting the gas before passing through the outlet pipe 27. The gas to be desulfurized is introduced into absorption tower 10 through inlet pipe 26. Conduits 31 and 33 for liquid circulation are connected from the supply tank 11 to the absorption tower 10 and a conduit 35 for recycling the liquid from the quench sump 51 is connected to the absorption tower 10. Liquid dispersers such as spray nozzles 41, 42, 43 and 44 are connected to conduits 31, 37, 33 and 35, respectively. Dispersers 41 and 43 feed absorber (slurry) to fill 21 to reach collector 52, contacting the gas introduced into column 10 through pipe 26. The dispersing device 42 supplies water to the filling section 22 to remove atomized moisture before the gas flowing upwards is discharged through the pipe 27. Dispersing device 44 sprays the slurry from quench tank 51 to contact and cool the gas introduced through pipe 26 to the bottom of the tower. Collector 52 collects almost all of the absorbent solution introduced into column 10 through conduits 31 and 33 and transfers it to feed tank 11 through conduit 34. The overflow conduit 38 transfers the solution from the supply tank 11 to the quench tank 51 by the amount required when transferring from the quench tank bottom through conduit 36 to a thickener (not shown). The pumps in the system are all shown with the letter P.

During operation of the flue gas desulfurization process in the apparatus described above, the limiting agents of the present invention are added to the aqueous feedstock in tank 11 or to the feedstock in conduit pipes 31 and 33 at a position just prior to the inlet of the top 10. . The aqueous solution and / or slurry of CaCO ₃ mentioned is introduced from feed tank 11 via conduits 31 and 33 to the top of column 10 via dispersion devices 41 and 43. The gas stream to be desulfurized is introduced into the bottom of the top 10 through pipe 26 at a temperature of about 85 ° C., where the introduced gas is quenched from the quench flow tank 51 introduced into the dispersing device 44 via conduit 35. Make primary contact. The gas then flows upwards and contacts the sprayed liquid from the dispersers 43 and 41. The flue gas from which almost all the sulfur oxides have been removed then reaches the second packed bed 22 and contacts the sprayed water through the disperser 42. This step is effective to remove all slurry and all atomized moisture remaining in the gas stream. The flue gas is then evacuated to atmosphere through pipe 27 at the top of the tower. Absorbent liquid in contact with the gas stream falls down the tower, but almost all of it is collected by the collecting device 52 and retracted to feed tank 11 through conduit 34.

The water level in the oil tank 51 is adjusted by adding the absorbing liquid supplied from the feed tank 11 through the conduit 38. Such a facility is necessary because some of the liquid recycled through conduit 35 is continuously or intermittently transferred to the settling tank or thickener so that the calcium sulfate is removed and water is recycled to the system via conduit 37.

In the above gas desulfurization process, the temperature during the contacting step at the top of the column is usually 55 to 60 ° C., while the quench water flow part temperature is 70 to 80 ° C. An ideal inhibitor would prevent deposition at the tom (fill) of the tom, but would cause precipitation at the runoff.

The following examples illustrate the use of phosphonomethylated amines as limiting agents and methods for their preparation, as well as control examples using products known in the art for this purpose.

Example 1

[Manufacture of Limiting Agents] `

In a 500 ml round bottom flask equipped with a water-reflux cooler, a mechanical stirrer, a thermometer with a thermostat and an introduction funnel, 22.7 g (0.176 mole) N-aminoethyl piperazine, 1,2-dichloroethane (DCE) N-aminoethylpiperazine (AEP) -based amine was prepared by reacting 9.8 g (0.099 mole) and 17.5 g deionized water (DCE / AEP molar ratio = 0.56). Approximately 75 g of concentrated hydrochloric acid and 32.6 g (0.40 mol) of phosphorous acid are added to the aqueous amine solution to phosphonomethylate the reaction product, and the reaction mixture is then heated to reflux for 1 hour. 28.1 g (0.35 mole) of 37% aqueous methanol (formaldehyde) solution are added over an introduction funnel over 1.5 hours, and then the reaction mixture is heated for an additional 3 hours and cooled.

The product is evaluated in the laboratory using the following circulator.

Example A (Control)

The desulfurization process conditions described above are tested in the laboratory in the following simulation apparatus: The packed column is conduited to the top and bottom of the vessel containing the supersaturated solution of calcium sulfate (initial pH 3.5-4). The mentioned solution is injected at the top and circulated through the column by returning through a tube connected to the bottom of the vessel. The column is filled with a piece of polyethylene tube 0.30 "long by 0.375" diameter (0.95 cm by 0.95 cm). The precipitation of the calcium sulfate scale on the filler is measured over time; Calcium remaining in the solution is measured by filtering the solution sample through a Millipore filter (4 to 5.5 mu m opening diameter) and titrating with standard disodium ethylenediamine tetraacetate. During circulating at 54 ° C. without using a scale inhibitor, almost half of the calcium sulfate present precipitated while forming scale within 30 minutes to 1 hour. At the start of the test, the amount of CaSO ₄ present in the solution was 3989 ppm, only 2162 ppm remained after 30 minutes of circulation, and 2067 ppm (approximate value in CaSO ₄ labeled solution at 54 ° C.) after 70 minutes.

Example 2

The product of Example 1 is evaluated using the test apparatus in Example A at 10 ppm (active acid) at temperatures of 54 ° C, 75 ° C and 90 ° C. The data is summarized in Table I. The data shows the efficiency of DCE / AEP phosphonate inhibitors. The product of Example 1 prevented the deposition of scale at 54 ° C. (at the contact) but did not measure the dashed line so that calcium sulfate precipitated (at the flowing water) upon heating.

TABLE I

Example B (Control)

A supersaturated solution of calcium sulfate containing 10 ppm of amino trimethylenephosphonic acid (ATMPA), a commercially available organophosphonic acid inhibitor, is prepared. The solution mentioned is circulated at 54 ° C. and periodically concerned with soluble calcium. A commercially available aminomethylene phosphonic acid / diethylene triaminepenta methylene phosphonic acid (DETA-MPA) is used in the same manner as above using an amount of 10 ppm by weight of the solution. The results are listed in Table II.

TABLE II

A significant amount of calcium sulfate accumulates in the filler with ATMPA after 1-2 hours.

The data show that the inhibitor used is inefficient in maintaining calcium in solution, i.e. preventing scale formation at the filling contact of the desulfurization process. It should be noted that when DETA-MPA is used at 54 ° C or 75 ° C, very little calcium sulfate scale is formed on the filler. This fact shows that diethylene triamine pentamethylene phosphonic acid is effective for controlling scale formation at 54 ° C. of the same fill contact, but no precipitation is produced by heating to 75 ° C. as in the flowing part of the process. It can be seen that. When repeated at 90 ° C., calcium sulfate was not deposited.

Example C (Control)

Amino ethyl piperazine, a compound required to prepare the methylene phosphonate of the present invention, is reacted with formaldehyde and phosphorous acid to produce trimethylenephosphonic acid derivatives.

This is used at 10 ppm (active acid) as in Control Example B. Calcium sulfate scale at 54 or 75 ° C., although present, is rarely observed. As in Comparative Example B, the aminoethylpiperazine trimethylenephosphonic acid inhibitor is not suitable for the desulfurization process because it does not precipitate calcium sulfate at 75 ° C. and remains in solution at the two temperatures mentioned.

Example 3

Aminoethyl piperazine and 1,2-dichloroethane were reacted at a DCE / AEP molar ratio of 0.80 to prepare aminoethyl piperazine derivative-amine. This product is phosphonomethylated with phosphorous acid and methanal (formaldehyde) in the presence of hydrochloric acid to give a methylenephosphonic acid derivative.

As in Example 2, the product was evaluated at 10 ppm (active acid) at temperatures of 54 ° C and 75 ° C.

The results are shown in Table III.

TABLE III

Compounds that have been shown to be effective in this process are methylene phosphonic acids derived from phosphonomethylation of the N-aminoethylpiperazine-1,2-dichloroethane reaction product. In addition to acid derivatives, it is also possible to use various metal and alkali metal salts, ammonium and amine salts, partial salts of methylene phosphonic acid, and mixtures thereof.

Preferred products are those having aminohydrogens fully substituted with methylenephosphonic acid groups. However, in some cases, some aminohydrogen can be left unreacted. It is preferred to react at least 50% amino hydrogen. Moreover, functional groups other than a methylene phosphonic acid group can also be given to a compound. Representative groups are hydroxyalkyl, methylenesulfonate, hydroxypropylsulfonate, carboxymethyl and the like.

Accordingly, the present invention provides an improved gas desulfurization process in which the gas is contacted with an aqueous solution or slurry of calcium salt or hydroxide to remove sulfur oxides contained in the gas. Such contact results in the formation of calcium sulfate deposited as a scale on the contact surface. The present invention provides a desulfurization method using special limiting agents that inhibit scale formation on the contact surface but allow other parts of the system.

In the system described herein, since the contact is made at a lower temperature than the quench section, it can be seen that certain limiting agents effective at such a contact temperature are diminished at higher temperatures than the quench section. In conclusion, the agents of the present invention are useful agents in preventing the formation of scale on the contact surface, as they allow deposition of the scale in subsequent steps so that the scale can be satisfactorily removed and processed.

Claims (6)

The oxidized sulfur-containing hot gas is quenched by contact with a calcium compound-containing aqueous solution or an aqueous slurry, and the mentioned gas is introduced into a vapor-liquid contact column that recovers the reaction product of the sulfur oxide mentioned with the calcium compound mentioned. In a gas desulfurization process, a phosphonomethylated product of a reaction product of aminoethylpiperazine with a dihalo or haloepoxy organic compound (the molar ratio of dihalo or haloepoxy to amine compound is about 0.20 to about 0.80) Adding to the mentioned aqueous solution or aqueous slurry, wherein the recovery step mentioned consists in heating the mentioned aqueous solution or aqueous slurry to precipitate the sulfur-calcium reaction product. The method of claim 1 wherein the calcium compound mentioned is calcium carbonate. The process according to claim 1, wherein the mentioned dihalo compound is a compound having 1 to 20 carbon atoms and the mentioned haloepoxy compound is a compound having 3 to 10 carbon atoms. The process of claim 1 wherein the phosphonomethylated product mentioned is a compound having the general formula:

In the above formula, A is a general formula

or

[Where Z is hydrogen, hydroxyethyl, hydroxypropyl,

Or BA, wherein M is hydrogen, an alkali metal or ammonium, and at least 50% of the Z group

Group is an organic radical, and B is a general formula

or

[Where Ar is

or

N is 1 to 10, n 'is 1 to 3, R is hydrogen or methyl, and R' is hydrogen, an alkyl radical or hydroxyalkyl radical having 1 to 4 carbon atoms, a hydroxy radical or a halogen atom. Is a divalent radical derived from a dihalo or haloepoxy organic compound of which m is from 1 to 10. The compound of claim 6, wherein Z is

And m is 1-3. 4. The process of claim 3 wherein B is a divalent radical derived from 1,2-dichloroethane and m is 1-4.

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