CA1036725A - Process for removing the salt of a weak acid and a weak base from solution - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The salt of a weak acid and a weak base is removed from a solution by contacting said solution with an emulsion. Said emulsion comprises an exterior phase which is characterized as immiscible with said solution and permeable to the weak acid and/or weak base in their un-ionized forms.
One of the species which can permeate through said exterior phase reacts with a reactant present in the interior phase of the emulsion which converts said permeating species to a non-permeable form, i.e., by neutralization, thus providing a continuing driving force for the permeation of said permeating species. The other nonreacting or nonpermeating species is stripped from solution by passing an inert gas through said solution.
Preferably, stripping and neutralization in the interior phase of the emulsion are carries out simultaneously. By selection of the reactant present in the interior phase of the emulsion, the process of the instant invention may be designed to remove either the weak acid or the weak base in the interior phase of the emulsion. In a preferred embodiment, ammonium sulfide, dissolved in an aqueous solution, is removed from said aqueous solution by permeating ammonium through the exterior phase of an emulsion and neutralizing said ammonia in the interior phase with an acidic reactant. Simultaneously, hydrogen sulfide is removed by steam stripping or air blowing of the aqueous solution.

Description

J036~25

2 BACKGROUND OF THE INVENTION

3 The salt of a weak acid and a weak base is removed

4 from a solution by contacting s~id solution with an emulsion.
S Said emulsion comprises an exterior phase which is character-6 ized as immiscible with said solution and permeable tothew~k 7 acid and/or weak base in their un-ionized forms. One of the 8 species which can permeate through said exterior phase reacts 9 with a reactant present in the interior phase of the emulsion wh~ch converts said permeating species to a nonpermeable form, tl i.e., by neutralization, thus providing a continuing driving l2 force for the permeation of sa~d permeating species.The other 13 nonreacting or nonpermeating species is stripped from solution 14 by passing an inert gas through said solution. Preferably, stripping and neutralization in the interior phase of the l6 emulsion are carried out simultaneously. By selection of the 17 reactant present in the interior phase of the emulsion, the 18 process of the instant invention may be designed to remove 19 either the weak acid or the weak base in the interior phase of the emulsion. In a preferred embodiment, ammonium sulfide, 21 dissolved in an aqueous solution, is removed from said aque-22 ous solution by permeating ammonia through the exterior phase 23 of an emulsion and neutralizing said ammonia in the interior 24 phase with an acidic reactantO Simultaneously, hydrogen sul-fide is removed by steam stripping or air blowing of the aque-26 solution.
27 DESCRIPTION O~ THE PRIOR ART
28 A process for separating volatile bases, e.g. ammo-29 nia, and weak volatile acids, e~g. H2S, from their salts or the liquid or gaseous dissociation products thereof, which 31 comprises contacting these salts in a first step with a non-32 volatile acid, e.g. benzoic acid, in the presence of at least - 2 ~

~036~725 1 one liquid phase at a temperature and pressure at which the 2 volatile acid is evolved in the form of a gas, and then in a 3 second step increasing the temperature or reducing the pres-4 sure to liberate the volatile base and regenerate the acid, is taught in U.S. Patent No. 3,649,l90. This process req-~res 6 two steps since the same reagènt is utilized to remove both 7 the volatile acid, i.e. by neutralization, and the volatile 8 base, i.e. by decomposition. The process further requires 9 two steps since the second step, wherein the base is removed rom its reaction product with said nonvolatile acid, is nec-11 essarily carried out at a higher temperature or lower pressure l2 than the irst step. This process is generally more ineffi-13 cient than a one-step prbcess wherein said weak acid and weak 14 base may be removed simultaneously.
U.S. Patent 3,620,674 teaches the reverse of the a-16 bove process; that is, a two-stage process for regenerating 17 volatile bases and weak volatile acids from the salts which 18 comprises contacting in a first stage the salt with an organic 19 base of low volatility to liberate the volatile base in agas-io eous form and liberating the weak volatile acid in a gaseous 21 form in a second stage while regeneratin8 the base of low 22 volatility in the liquid phase. Once again, it is a two-step 23 process which is taught which is necessarily more inefficient 24 than a one-step process which removes the same weak acids and wèak bases. Furthermore, in both cases it is apparent that 26 the nonvolatile acid or base which is utilized to remove the 27 volatile acid or base from solution is necessarily left be-28 hind and would cause further problems in that the nonvolatile 29 acid or base is a contaminant of the aqueous solution and may have to be separated therefrom. It is apparent from this dis-31 cussion that the processes of U.S. 3,620,674 and 3,649,l90 32 are eminently unsuitable to the treatment of dilute aqueous 1 solutions of said ~ea~ acid/weak base salts, and this is pre-2 cisely the field in which the process of the present applica-~ tion is most applicable, i.e. water pollution abatement.
4 Other processes for the removal of H2S and ammonia from aqueous solutions are known in the art. See, for exam-6 ple, U.S. Patent 3,518,166 which describes the difficulties 7 which are encountered in a process wherein H2S and ammonia 8 are separated by means of the prior art methods. The patentee 9 deals with these difficulties by utilizing a multi-step pro-cess wherein H2S is stripped out of an aqueous solution in a 11 first distillation column to obtain an H2S rich overhead l2 stream and an aqueous bottom stream of reduced H2S content.
13 Ammonia is stripped out of said aqueous bottom stream in a 14 second distillation column to obtain an ammonia-rich vapor overhead which is partially condensed to obtain an ammonia-l6 rich vapor and an ammonia-rich overhead condensate contami-17 nated with some H2S. This ammonia-rich condensate is com-18 bined with the aqueous solution containing H2S and ammonia, 19 which is passed to the first distillation column. This ref-erence is cited to show the difficulties encountered in re-21 movin~ ammonium sulfide from aqueous solution and the compli-22 cated methods employed at presentO
23 - Other processes are known wherein the salts of weak 24 bases with strong acids are separated by precipitation methods.
See, for example, U.S. Patent 3,321,275.
26 In U. S. Patent Serial Number 3,779,907, in the 27 names of N. N. Li, R. P. Cahn and A. L. Shrier, a 28 process for the removal of ammonia and/or sulfide is 29 described which utilizes the liquid membrane technique described in U. S. Patents 3,410,794; 3,454,489; 3,617,546 31 and 3,650,091.
32 Other processes which rely on stripping with inert ~0367Z5 1 gasesto removeammonia and H2S from water aredis~osedinU.S.2,927,075.

3 The instant invention relates to a process for re-4 moving the salt of a weak acid and a weak base from solution which comprises contacting said solution with an emulsion, 6 said emulsion comprising an exterior phase, said exterior 7 phase being characterized as immiscible with said solution 8 and permeable to either or both said weak base and weak acid, 9 and an interior phase, said interior phase comprising a reac-ta~t which is capable of converting either said permeating 11 weàk base or weak acid to an impermeable form. This provides l2 a continuing driving force for the permeàtion of the species 13 which reacts with said reactant, thus insuring its continued 1~ permeation through said exterior phase. The nonreacting spe-cies is removed by stripping the aqueous solution with an in-l6 ert gas. In order to achieve--efficient and essentia~ycomplete 17 removal of both the weak acid and weak base from the solution, 18 `the process is preferably run so that both the stripping and 19 the permeation are carried out simultaneously.
In a preferred embodiment of the instant invention 21 the salt is present in an aqueous solution and is selected 22 from the group consisting of ammonium salts of volatile weak 23 acids such as ammonium sulfide and bisulfide, sulfites, cya-2~ nide, phenate, aceta`te, and carbonates; and salts of organic bases, e.g. amines and other nitrogen compounds, such as amine 26 sulfidesorcarbonates,especia~yamines h~gfroml ~5,p~eferably l~3, 27 carbonatoms pernitnogen,andpreferablyhav~no more t~an lOcarbon atoms.
28 By the addition of oil soluble cation exchange res-29 ins to the external phase, i.e., sulfonic acid or carboxylic acidgroup containing polymers, many common metal ions canbe al-31 lowed to permeate into the interior phase where they can be 32 reacted with a reagent dissolved in said interior phase to ~Q36!7ZS
1 form a nonpermeating species, i.e. by precipitation. Thus, 2 solution of carbonate,sulfides, sulfites, cyanides, acetates, 3 etc. of many metals, i.e. copper, calcium, iron, can be 4 treated in the manner of this invention.
The process of the instant invention is especially 6 suitable for the removal of ammonium sulfides or carbonates 7 from dilute aqueous solution, and can be used to illustrate 8 the underlying concept which governs this novel method of 9 ~eparation.
When ammonium sulfide is dissolved in water, the lt salt will completely dissociate into ammonium and sulfide l2 ions, which in turn establish a hydrolysis equilibrium with 13 the hydrogen ion and hydroxyl ion present in the aqueous 14 phase to form as hydrolysis products undissociated ammonia, undissociated hydrogen sulfide as well as bisulfide ion.
l6 The resultant mixture has a composition and pH governed by 17 the concentration and dissociation constants of the various 18 species involved.
l9 The vapor pressures of the hydrolysis products, NH3 and H2S, over this solution are a function of (a) the 21 solubility of these gases in water at the given temperature 22 and of (b) the concentration of undissociated NH3 and H2S in 23 ehe solution. Since NH3 and H2S are a weak base and acid, 24 respectively, the concentration of the undissociated species is a strong function of pH. Similarly, the solubility and 26 hence permeability of these materials through the external 27 membrane phase is strongly dependent on the concentration of 28 undissociated species.
29 If we now strip a dilute aqueous solution of ammo-nium sulfide or bisulfide with a gas stream, predominantly 31 H2S, because of its low solubility, will come off initially.
32 As H2S removal proceeds, the pH of the solution rises which 1 has a deleterious effect on the fraction of undissociated 2 H2S in the solution. This, in turn, sharply depresses the 3 partial pressure of H2S over the solution, greatly retarding 4 the removal of H2S. At the same time, the fraction of un-dissociated NH3 rises (due to the increased pH), enhancing 6 the NH3 partial pressure. However, NH3 is so soluble in 7 aqueous solutions that only poor NH3 removal ensues. Conse-8 quently, poor NH3 and H2S removal results when a dilute solu-9 tion is on~y vapor stripped (see Curve 1 in Figures 1 and 2 o the attached drawings. ~y the same token, if this dilute 11 solution is now contacted with an emulsion containing as an I2 internal pllase an aqueous acid solution, andasanexternal 13 phase,a water immiscible oil membrane through which both un-14 dissociated NH3 and H2S,because of their solubility in the oil phase,can permeate, immediately upon contact, both un-l6 dissociated H2S and NH3 will commence to permeate through the 17 oil membrane in order to equalize the concentration of un-18 dissociated species on both sides of the membrane, i.e. in 19 the dilute aqueous solution and in the internal acid solutio~.
This equalization will be rapidly accomplished with H2S and 21 permeation will stop. For the NH3,however, no sooner has 22 undissociated NH3 entered the internal phase, then it will be 23 neutralized by the acid present and converted into non-perme-24 ating ammonium ion. Thus, ammonia transfer would tend to continue from the outside into the emulsion.
26 However, as the outside solution becomes depleted 27 in ammonia, its pH will drop. This, as previously discussed, 28 has a detrimental effect on the fraction of ammonia present 29 as undissociated species, i.e. on the rate of ammonia removal by permeation. Consequently, as evidenced by Curves 2 in 31 Figs. 1 and 2 of the drawings, extraction via liquid mem-32 brane alone is an unsatisfactory method of removing ammonium ~036!725 1 sulfide from dilute aqueous solution.
2 Now, if the two processes described above, H2S re-3 moval by gas stripping and NH3 removal by permeation,are 4 carried out simultaneously, both processes will balance each S other and maintain the pH of the aqueous solution within pro~
6 er bounds. Consequently, neither process will cease and re-7 moval of both NH3 and H2S via their respective routes can be 8 carried to completion and at higher rates. This is illustra-9 ted by Curve 3 in Figures 1 and 2.
tO The mechanism described above will hold equally 11 well with the other salts mentioned above, provided one spe-l2 cies, i.e. the acid or base, is removed via the liquid mem-13 bxane and the other species, i.e. the base or acid, via gas 14 stripping. If it is desirable to remove the weak acid via the liquid membrane, an internal phase comprising a suitable l6 aqueous base solution is employed.
17 The emulsion,which is utilized to remove either the 1~ weak acid or the weak base,is prepared by techniques known in 19 the art so as to allow the permeation of either the weak acid or the wea~ base through the exterior phase into the interior 21 phase wherein a reactant is present to convert the permeating 22 species to a nonpermeable species. The exterior phase of the 23 emulsion must be designed so as to be immiscible with the 24 solution with which it will be contacted. In the case of the preferred embodiment wherein the solution containing the above 26 described salt of a weak acid and a weak base is aqueous, the 27 exterior phase of the emulsion may be conveniently prepared 28 by utilizing a hydrocarbon as the exterior phase. Other water 29 immiscible solvents may likewise be utilized, e.g. halogenated hydrocarbons, fats and oils of animal or vegetable origin, 31 higher molecular weight alcohols and esters, etc. Theinterior 32 phase will be an aqueous solution containing either a reagent 1 capable of reacting with the permeating species or an adsorp-2 tion medium. For example, in the case where ammonia perme-3 ates through the membrane,~aqueous sulfuric acid may be con-~ veniently used as the interior phase. When the permeating

5 species is an organic nitrogen compound such as an amine,

6 activated carbon may be conveniently used as an adsorption

7 medium in the interior phase.

8 The internal phase of the emulsion may contain a

9 reactsnt which is regenerable or nonregenerable. By regen-erable it is meant that after contacting with the aqueous 11 801ution the emulsion may be removed to a regenerating zone l2 wherein the emulsion is heated and steam stripped to remove 13 the permeating speciesthen~y regenerating the emulsion for re-1~ use.
Regenerable acids within the scope of the instant invention must have the following general properties:
17 (1) they must be soluble in water at a level of from 18 about 1 to about 5 moles/liter of ammonia capacity;
19 that is, aqueous solutions of the regenerable acids must be able to neutralize from about 1 to S moles/
21 liter of ammonia;
22 (2) the pH of the regenerable acids should vary from 23 about 2 to about 6, preferably from about 3 to a-24 bout 5;
(3) the regenerable acids must be capable of reacting 26 with ammonia at the temperatures at which the in-27 stant process will be run; that is, from 25 to a-28 bout 100C;
29 (4) when the aqueous solutions of these regenerable acids are heated to the regeneration temperature 31 of from about 100 to about 250C, the ammonia par-32 tial pressure, in the case wherein ammonia is re-l moved by neutralization in the membrane, should be 2 at least one-twentieth of the total solution 3 vapor pressure; and 4 (5) thepart~ pressure of the acid at the regeneration temperatures disclosed above should be less than 6 1% of the total vapor pressure.
7 The regenerable acids of the instant invention,of 8 course,must all have at least one hydrogen available for ex-g change with the weak base, e.g. ammonia. Preferred regener-able acids include phosphoric acid and the salts thereof, ll benzene polycarboxylic acid and the salts thereof, e.g. ben-l2 zoic acid, phthalic acid, pyromellitic acid, trimellitic ac-l3 id, trimesic acid and the salts thereof, especially the amm~niun~
1~ s~mand~assium salts; aliphatic polycarboxylic acids and the salts thereof including maleic acid, succ~nic acid,fuma~
l6 acid, 7-carboxydecanoic acid and the salts thereof; sulfo-17 carboxylic acids including both aliphatic and aromatic deriv-18 atives, e.g. 5-sulfoisophthalic acid, 5-sulfopentanoic acid 19 and the salts thereof; monocarboxy acids having sufficient functional groups to decrease their oil solubility, for exam-21 ple salicylic acid, and the varioùs other hydroxy aliphatic 22 acids, etc. As can be seen from the above list of regener-23 able acids which are preferred for use in the instant inven-2~ tion, high solubility in water is desirable. Regenerable ac-ids having lower water solubility may be substantially taken 26 up by the nonaqueous exterior phase of the emulsion and thus 2~ result in ineffective systems.
28 When it is desired to separate a weak acid in the 29 interior phase of the emulsion, a regenerable base may be utilized. Examples of regenerable bases, which functionally 31 should meet the same requirements as described abo~e for re-32 generable acids (except for the pH, which in the case of re-

- 10 -1 generative bases shouldvaryfrom about~ to about 10.5),are thevar-2 ious aminesand hydroxyamines, e.g., ethanolamine, die~oL~ne, 3 triethanolamine, 5-carboxypentamine; various polyamines, e.g., 4 ethylenediamine etc.; alkaline and alkaline earth carbonates, phosphates, borates, etc., e.g. K2C03, KHC03, K3PO4, etc.
6 Regenerationcanbeachieved at230-450F and 5-300 psig.
7 In theembodimentoftheinstantinvention whereinregenerable 8 emulsions are utilized, the regeneration can be effected after 9 breaking the emulsion, or without breaking the emulsion. The emul~don which is utilized in the instant process may also be of ll a nonregerable nature.For e~ample, in one embodiment wherein l2 ammonia is removed through the exterior phase of the emulsion 13 while H2S is steam stripped, the ammonia may be neutralized 1~ with sulfuric acid or phosphoric acid in the internal phase of the emulsion whereby the ammonia is converted to the ammo-6 nium ion, a nonpermeable form of ammonia. The emulsion is 17 then sent to a de-emulsification zone wherein the emulsion is 18 broken and the exterior phase, along with surfactants present 1~ therein, cycled to a stage wherein fresh emulsion is prepared.
The internal phase, which will now contain aqueous ammonium 21 sulfate or ammonium phosphate, may be utilized in a manner 22 which will be known to the skilled artisan.
23 The aqueous solution of the weak acid/weak base 2~ salt is stripped with an inert gas in the presence of the emulsion in order to remove the nonpermeating species. Strip-26 ping may be accomplished at temperatures ranging from ambient 27 (75F) to about 220F, at pressures ranging from 5-50 psia.
28 The stripping gas rate is a group function of pressure, tem-29 perature and solution pH, and, of course, the specific spe-cies to be stripped out, but is eas~ly calculable by conven-31 tional chemical engineering techniques once these variables 32 are known. For stripping H2S out of ammoniacal sour waters, 1 these stripping rates can be computed as described in M. R.
2 Beychok "Aqueous Wastes from Petroleum and Petrochemical 3 Plants," J. Wiley and Sons, N. Y. 1967, pages 158-196. While 4 conventional steam stripping towers operate under 5-25 psig pressure and with stripping steam rates of 1-2 lb/gal of 6 sour water feed, the process of this invention can operate 7 conveniently at, say, 5-10 psia, and steam rates of 0.05-8 0.~5 lb/gal. Inert gas or airinpLa~ oforin ~dition to steam 9 can also be used. Stripping is preferably carried out in a countercurrent multista~e tower.

11 PREFERRED EMBODIMENT
l~ A refinery sour water stream containing from 500 to 13 15,000 ppm ammonium sulfide in water is contacted with an e-14 mulsion comprising a hydrocarbon exterior phase and an inte-rior phase containing the monoammonium salt of succinic acid l6 in water. The emulsion is prepared by mixing at high shear 17 conditions, 50 parts of a hydrocarbon mi~ture, e.g.
18 Solvent 100 Neutral, an isoparaffinic solvent available from 19 Exxon Chemical, containing 5 wt % of Span*80,with 50 parts of a 30% solution of the succinic acid salt in water. The emul-21 sion is mixed with said refinery sour water stream and the 22 two streams are fed together to the top of a stripping tower 23 at a temperature of 185F. Simultaneously, steam is passed 24 into the bottom of the tower. The steam and the refinery sour water stream are contacted countercurrently. The liquid 26 residence time in the stripping tower is from ~ to 3 minutes.
27 As described, the aqueous sour water stream together with 28 the emulsion is brought in at the top of the tower and travels 29 down the tower to the bottom where it is removed. The aque-ous sour water stream leaving the bottom of the tower will 31 now be depleted in ammonium sulfide. The stream may be cir-32 culated to a second tower for further contacting. The emul-* Trade Mark - 12 -, . . .

~036~25 1 sion, which will now be depleted in free succinic acid by 2 virtue of neutralization with the permeating ammonia, is 3 separated from the effluent aqueous stream and sent to a 4 regeneration zone. The spent emulsion is heated to about 400F and sent to the regeneration zone where steam is con-6 tacted countercurrently with the spent emulsion at a temper-7 flture from 230 to 450F and a pressure of 5 - 300 psig, but 8 preferably between 375-425F and 200-275 psi~. The steam is 9 blown through the emulsion at a rate of 0.5 to l.0 lb/gal of water being treated in the stripper tower with the emulsion.
11 In the same water stripping tower, the emulsion is spent by l2 virtue of the permeating ammonia, neutralizing the internal 13 aqueous acid solution from the monoammonium salt to substan-14 tially the diammonium salt of succinic acid. In the regener-ator the emulsion is now substantiaIly regenerated by driving 16 off the absorbed ammonia so that the diammonium salt reverts 17 back to substantially the monoammonium succinate~ from 30 to 17A 70% neutralization.
18 The regenerated ammonia plus accompanying steam 19 are taken overhead for subsequent fractionation to high pu-rity, substantially anhydrous ammonia.
21 In an alternate embodiment of the instant invention 22 the emulsion will contain sulfuric acid. The emulsion, after 23 contacting with the sour water stream, will be depleted in 24 free sulfuric acid by means of neutralization with the per-mea~ing ammonia species. The internal phase, which will con-26 tain from 25-40% ammonium sulfate, is cycled to a de-emulsi-27 fication zone wherein the emulsion is broken, the surfactant 28 containing hydrocarbon layer is separated for reuse in forming 29 fresh emulsions with fresh acid, and the aqueous ammonium sul-fate solution i8 fed to an appropriate unit for recovery of 31 ammonium sulfate.
32 The process of this invention will be made clear by - 13 ~

~ 03U6~ Z 5 1 ` reference to Figure 3 which illustrates the technique for 2 stripping refinery sour water containing ammonia and hydrog~n 3 sulfide with the use of a regenerable liquid membrane emul-4 sion-The emulsion comprises an external oil phase and 6 an internal aqueous monoammonium succinate phas~ as discussed 7 before~and is capable of drawing ammonia selectively out of 8 dilute aqueous solution also containing a weak acid, such as 9 hydrogen sulfide.
The refinery sour water containing up to 15,000 ppm monium sulfide is introduced via line 1, preheated in heater ~2 2 to about 180F and mixed with fr~sh or regenerated acid 13 emulsion coming through line 3 and introduced into stripper 14 tower 5 via line 4. This tower may operate under a vacuum of lS S-10 psia when steam is introduced via line 6 at the bottom l6 of the tower. Alternatively, it can operate under atmospher-17 ic or elevated pressure when an inert gas or air is admitted t8 with or without steam via line 6. The simultaneous stripping 19 ~permeation process occurs while `the sour water/emulsion mix-ture descends through the tower countercurrent to the ascend-21 ing gas. Water, essentially free of both ammonia and hydro-22 gen sulfide, is taken off, admixed with the spent emulsion 23 via line 7, and allowed to settle in drum 8. Treated water 24 is removed via 9, while the spent acid emulsion is sent to further processing via line 10.
26 The hydrogen sulfide together with the inert gas, 27 such as steam, is taken of~ the tower in line 11, cooled in 28 condenser 12 and any water settled out in distillate drum 29 13 and refluxed back to the tower 5 through line 14. Essen-tially pure hydrogen sulfide gas, possibly mixed with inertgas 31 or air (but not ammonia) is taken overhead through line 15 32 to its proper disposal, such as a Claus plant for sulfur re-1~036~725 1 covery.
2 The spent emulsion is pumped by pump 16 through 3 preheater 17 into regenerator tower 18, where the spent emul-4 sion is decomposed into ammonia rich overhead gas leaving via line 19 and a regenerated acidic emulsion via line 24. A re-6 boiler 23 provides the necessary heat and stripping vapor 7 for this regeneration.
8 The ammonia rich ammonia/steam mixture taken over-9 head through line l9 can be fed directly to a conventional ammonia/water fractionator 20 which, with proper reflux and 11 reboil, separates the feed into an ammonia overhead 21 and l2 water bottoms 22.
13 The regenerated emulsion is cooled in exchanger 25 14 ` and fed to an emulsion make-up and maintenance system 26 be-fore recycling back into the stripping tower via line 3. The 16 facilities in system 26 may include an emulsifier to repair 17 that part of the emulsion which may have broken during the 18 high temperature regeneration step, fresh emulsion make-up 19 facilities and disposal facilities for discard emulsion which may have undergone undesirable chemical change.
21 If, in place of the regenerable emulsion, a non-22 regenerable emulsion is used, i.e. the interior phase is a 23 sulfuric or phosphoric acid solution, all the regeneration 24 equipment from items 17 through 25 can be deleted. However, system 26 now is expanded to include emulsion breaking, com-26 plete emulsion make-up, and, if necessary, ammonium salt solu-27 tion handling or drying facilities.

1 The following experiments were designed to demon-2 strate that simultaneous gas stripping to remove H2S and 3 liquid membrane extraction to remove N~3 by permeation can 4 effectively reduce the ammonium sulfide content of a dilute aqueous solution.
6 In all cases about 1,450 g o the dilute aqueous 7 solution containing about 1,500-2,000 ppm by weight each of 8 ammonia and hydrogen sulfide ~as contacted with the treating 9 a~ent at a temperature o~ 185F. A vacuum was applied during tO the operation as required to achieve the necessary boil up 11 to simulate steam stripping in a column. The two-phase mix-l2 ture was stirred with a mechanical agitator in the e~fective-13 ly single-stage batch treater.
14 The emulsion was prepared by adding the aqueous succinic acid(monoammonium salt) solution with vigorous stir-l6 ring slowly to the oil phase (Solvent 100 Neutral, an iso-17 paraffinic solvent) having detergent/thickener (Lubrizol*
18 3702,a styrene-maleic anhydride copolymer wherein 95% o~ the 18~ groups are esterified with Clo-Clgalcohols)dissolved in it.
19 The actual e~periments were carried out by sampling the aqueous phase initially, stirring the emulsion/aqueous 21 phase mixture for the length of time indicated with the boil-2~ up rate shown by applying a vacuum, and allowing to settle.
23 The concentrations of both ammonia and hydrogen sulfide were 2~ me&sured after each stirring period and are reported in Table I and Table II and illustrated in Figs. 1 and 2.
26 Experiment 1 (EX-20) 27 In this experiment only the aqueous phase was 28 treated in the manner described above, no emulsion being ad-29 ded. Very incomplete ammonia removal by the stripping steam is evident. Hydrogen sulfide is taken out, but quite slowly.
31 Experiment 2 (EX-27) 32 No vacuum was applied while the emulsion was agi-* Trade Mark - lG -A

~C~36 7 Z S
1 tated with the aqueous phase to be treated. Hydrogen sulfide 2 could not leave the solution to any extent since there was 3 no stripping action. Consequently, ammonia removal by perme-4 ation into the emulsion was severely retarded.
Experiment 3 (EX-16) 6 ` Both extraction and stripping were carried out si-7 multaneously, and rapid removal of both contaminants was 8 achieved.
9 Experiment 4 ~EX-17) Another simultaneous extraction/stripping experi-11 ment showed good removal of both contaminants. Since the l2 boil-up rate was somewhat slower in this run than the pre-13 vious experiment, the decrease of concentrations was some-14 what slower.
Experiment 5 (EX-21) 16 Experiment 4 was repeated, but instead of the acid 17 containing emulsion, only an oil-detergent/thickener mixture 18 was contacted with the aqueous phase during the stripping.
19 Very poor contaminant removal resulted.

10367~5 ---- I O ~

~D rl O O O ~r o ~1 Q, 1~ 0 Z ~ 11 D O N r` ~
0 ~ o t~ ~ ~ U~ U~ ~ V
X P ~ ~ + o ~ o o ~
~ ~01 ~

._ ~` ~ I OOO~CO
O n ` Z N 11 ~ 00 0 1~ 'r I
I ~ J O O N O ~ U~ r--u~) ~ o ~X) 9? X ~ I o ~ O ~ ~ l )~ ~ o ~1 U) o ~ ~ a~

E~ ~1 ~¦ ~ ~ N
~ .. ~ .
H ~ ~1 ~ a~ ~ ~ ~ ~ U) e~ N~ O 10 N ~r ~:

~ O
C' _ ~ `

R

~0; ~ P~ O
3 dP to ~ Q, 3 E~ o ~ 3~ ~ ~
~ O ~ U~ ~ ~
~ ~ ~ 0 0 0 Z U~ Z ~ .~ J~
o ~ o Q t-w m w ~q H 11~ dP ~ Id ~0 10 ~1N ~ ~ ~ ~ o ~ D t` ~ o O _~ N ~ ~ u~ ~

10367~S
~ ~ ~ ,, ~ ~ U~
o ,, ~ .....
~ c~ d~ dP ~ a~
J~ ~
_~ 3 ~---- ~ Xl Q~O ~ o o o ~ ~~ _I ~ Z ~ ~ 11 o x ~ o o o ~ u~ O ~D
,~ ~ o r~
~ ~o ~ ~
p~ 1 0 ~ ~O O a~ o Q. O ~ a~ Q. Z
h Id p ~ + ooooo U _I .4 ~ ~ ~ o~ ~ ~
X ~ O ~ t~ ~D ~ ~ O
W ~ ~ ~ r ~ z ,~ ~ I a~ o~ ~ o a~
a~ ~ " ~ _ ~: I
Q O ~ U dP d~ ~1 a> r` t~ ~ 1`
H P. 1 U t~ ~ Q~
~s S~ ~ ~ r~ O U~ O ~D O ~ CO 0 Q a) I ~ J ~52: ~ 11 ~D 1` ~ o ~
113 1~ X rl ~a ~ ~ ~ o o ~ o ~ ~q o~ N
E-~ ~ 113 D~ 1 O r` ~1 1:1 rl ~ ~ U) O ~
1~ ~ 1 UlO 1~ ~ D CO O
D ul ~ Z; ~ ~ co a~
tl~ ~O P~ + ooooo P~ :E: X U ,~ Q ~, t~
o ~ m r~
Z _~
~ U~
~r H E~ t`~
H D
O ~ .
~i3 ~ 1~

. _. .
~;4 S~
:~ 3 X ~ ~
H O o dP .
~ ~ Ul P. ` ~O o E~ C~
X o ' tO
u~
: ~0 ~ ~
Q
O oY ~ _~
~0 ~ ~ `
~ P ~ ~ 3 ~ 'I
o ` ~ o 3 ff~ tn ~
Sl ` ~ M 3 ~ O O
~r~
~ ~ a~ .
o ~ ~ d . ~ O D. O E~ ~
Q O rl ~ 1 ~ rl U ~ 3: 1~ 0 ~Z; ~~ ~ o ~ ~
o o ~ ~ ~ Z ~ .
a ~ ~ m 1~ o H ~ OP ~ ~ ~ ~

10367A~S
The following experiments were carr~ed out to demon-2 strate that ammonium succinate solutions and emuIsions con-3 taining such solutions could be regenerated.
4 Experiment 6 An aqueous solution containing 3.384 g mol of 6 ammonia and 1.716 g mol NH3/g mol succinic acid was found 7 to have a pH of 6. This solution was heated to 400F at 8 245-255 psig and a vapor sample taken. The ammonia concen-9 tration in this vapor was 10.2 mol %.
10 Experiment 7 11 The procedure of Experiment 6 was repeated except

12 that the a~nnonia level in the starting solution was reduced

13 to 1.45 g mol NH3/g mol succinic acid. The a~nonia concen-

14 tration in the vapor sample was 5.6 mol %, the remainder

15 water.
l6 ExPeriment 8 17 The procedure of the previous two experiments was 18 repeated, except that the starting material was an emulsion 19 of the succinic acid salt solution in oil. 440 g of the oil phase (88% Solvent 600 Neutral, 12% Lubrizol 3702 additive) 21 were used to emulsify 250 g of aqueous solution. The aqueous 22 solution contained 2.35 g mol/l of succinic acid and an ammon-23 ia/succinic acid ratio of 1.82 mol/mol. Three vapor samples 24 were taken, containing 6.2, 13.2 and 6.1 mol % of ammonia, respectively, at 405-410F, 250-270 psig.
26 After the heating period, about 60% of the emulsion 27 had broken. It could easily be reemulsified and was found 28 to be a satisfactory treating agent for addit:ional ammonia 29 removal.

~ ~0 ~

Claims (22)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE
IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for removing the salt of a volatile weak acid and a weak base from aqueous solution which comprises contacting said solution with an emulsion under conditions of agitation, sufficient to maintain the emulsion dispersed in said aqueous solution, said emulsion comprising an exterior phase, said exterior phase being characterized as immiscible with solution and permeable to said weak base, and an interior phase, said interior phase comprising a reactant which is capable of converting said weak base to an impermeable form whereby said weak base permeates through said exterior phase into said interior phase wherein it is converted to a non-permeable form, and simultaneously removing said volatile weak acid by passing an inert gas through said solution.

2. The process of claim 1 wherein said inert gas is steam.

3. The process of claim 1 wherein said weak acid is selected from the group consisting of H2S, SO2, CO2, HCN, and phenol.

4. The process of claim 1 wherein said weak base is selected from the group consisting of ammonia and amines.

5. The process of claim 1 wherein said salt is ammonium sulfide.

6. The process of claim 5 wherein said inert gas is steam.

7. The process of claim 6 wherein said removal is carried out at a temperature of from 75 to 220°F and a pressure of from 5 to 50 psia.

8. The process of claim 7 wherein said ammonium sulfide comprises from 100 to 10,000 ppm by weight of said solution.

9. The process of claim 8 wherein said reactant comprises an acid selected from the group consisting of phosphoric acid, sulfuric acid, ant hydrochloric acid.

10. The process of claim 8 wherein said reactant comprises an acid selected from the group consisting of benzene polycarboxylic acids, aliphatic polycarboxylic acids, sulfo carboxylic acids and salts thereof.

11. The process of claim 10 wherein said emulsion is separated from said solution after the acid is substantially neutralized and conveyed to a regeneration zone wherein said emulsion is contacted with steam at a temperature of from 230 to 450°F and at a pressure of from 5 to 300 psig for a period sufficiently to convert said acid substantially back to a less neutralized form.

12. A process for removing the salt of a weak acid and a volatile weak base from aqueous solution which comprises contacting said solution with an emulsion under conditions of agitation, sufficient to maintain the emulsion dispersed in said aqueous solution, said emulsion comprising an exterior phase, said exterior phase being characterized as immiscible with said solution and permeable to said weak acid, and an interior phase, said interior phase comprising a reactant which is capable of converting said weak acid to an impermeable form whereby said weak acid permeates through said exterior phase into said interior phase wherein it is converted to a nonpermeable form, and simultaneously removing said volatile weak base by passing an inert gas through said solution.

13. The process of claim 12 wherein said inert gas is steam.

14. The process of claim 12 wherein said weak acid is selected from the group consisting of H2S, SO2, acetic acid, CO2, HCN and phenol.

15. The process of claim 12 wherein said weak base is selected from the group consisting of ammonia and amines.

16. The process of claim 12 wherein said salt is ammonium sulfide.

17. The process of claim 16 wherein said inert gas is steam.

18. The process of claim 17 wherein said removal is carried out at a temperature of from 75 to 220°F and a pressure of from 5 to 50 psia.

19. The process of claim 18 wherein said ammonium sulfide comprises from 100 to 10,000 ppm by weight of said solution.

20. The process of claim 19 wherein said reactant comprises a base selected from the group consisting of NaOH and KOH.

21. The process of claim 19 wherein said reactant comprises a base selected from the group consisting of alkaline and alkaline earth carbonates, phosphates, and' borates; and amines and hydroxyamines.

22. The process of claim 21 wherein said emulsion is separated from said solution after the base is subtan-tially neutralized and conveyed to a regeneration zone wherein said emulsion is contacted with steam at a temper-ature of from 230 to 450°F and at a pressure of from 5 to 300 psig for a period sufficiently to convert said base substantially back to a less neutralized form.