Process for the removal of H.sub.2 S from fluid streams using a water soluble polymeric chelate of an oxidizing polyvalent metal

The present invention relates to a cyclic continuous process and a composition for the removal of hydrogen sulfide from a variety of sour gas streams. The sour gas stream is contacted with an aqueous solution of a water-soluble organic polymeric chelate containing an oxidizing polyvalent metal, e.g., Fe(III). The sulfur in the hydrogen sulfide is converted to elemental sulfur and the iron in the polymeric chelate is reduced. The process includes removal of the elemental sulfur, and an inexpensive method for removing water and excess low molecular weight materials, e.g., materials having molecular weights below 500, preferably using ultrafiltration or dialysis, regeneration and recycle of the reactive polyvalent metal.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a process wherein a fluid stream comprising a 
noxious gas, i.e., hydrogen sulfide (H.sub.2 S), is treated with a 
water-soluble polymeric chelate of a polyvalent metal to oxidize the 
H.sub.2 S, i.e., the sulfur contained in the H.sub.2 S, to elemental 
sulfur. The elemental sulfur is separated and the polymeric chelate of the 
reduced metal in the aqueous solution is concentrated by means, such as 
dialysis or ultrafiltration. The polyvalent metal chelate is then oxidized 
and recycled. More specifically, the present invention relates to a 
process of removing H.sub.2 S from a gas stream using an aqueous solution 
of a water-soluble polymeric chelate of iron in the Fe.sup.+3 state, 
separating the elemental sulfur, concentrating the aqueous solution of the 
chelate of divalent iron using ultrafiltration or dialysis, oxidizing the 
Fe.sup.+2 to Fe.sup.+3, and recycling the polymeric chelate. 
2. Relevant Art 
It has been reported in U.S. Pat. No. 4,123,506 and in U.S. Pat. No. 
4,202,864 that geothermal steam containing H.sub.2 S can be purified by 
contacting the steam with a metal compound that forms insoluble metallic 
sulfides. The subsequent disposal of the metallic sulfides is expensive 
and time consuming. 
In U.S. Pat. Nos. 4,414,817 and 4,468,929, R. T. Jernigan discloses the 
treatment of geothermal steam by condensing it with an aqueous solution of 
a monomeric ferric chelate, such as N-hydroxyethylenediamine triacetic 
acid. The hydrogen sulfide is converted to elemental sulfur and the ferric 
chelate is reduced to ferrous chelate. The ferrous-monomeric chelate is 
subsequently oxidized to monomeric ferric chelate and re-cycled. 
Z. Diaz in U.S. Pat. No. 4,400,368 discloses a cyclic process for the 
removal of hydrogen sulfide and carbon dioxide from a variety of gas 
streams. The "sour gas" stream containing these acidic gases is contacted 
with an aqueous solution of specific monomeric ligands or chelates of 
polyvalent metals or mixtures thereof. Hydrogen sulfide is oxidized to 
elemental sulfur, and the reactive metal monomeric chelate is reduced. The 
process includes sulfur removal and regeneration of the reactive metal 
chelate. Further, no provision is disclosed for removal of low molecular 
weight products or water from the process. 
R. B. Thompson in U.S. Pat. Nos. 4,189,462 and 4,218,342 discloses a 
composition for use in an oxidation-reduction process for effecting the 
catalytic oxidation of hydrogen sulfide gas comprising a monomeric soluble 
ferric ion salt. This reference does not disclose a process using organic 
polymeric chelates of iron. 
F. Engelhardt et al. in U.S. Pat. No. 4,518,745 disclose a number of metal 
chelates of water-soluble copolymers. The copolymers are useful as 
dyestuff auxiliaries and leather retanning agents. 
M. E. Klecka in U.S. Pat. No. 4,518,577 discloses a process for the removal 
of H.sub.2 S from a sour gas stream. The H.sub.2 S is oxidized using 
aqueous solutions of oxidizing polyvalent metal chelates of specified 
monomeric organic acids and by the separation and recovery of the sulfur 
from solutions of specific organic extractants. 
Z. Diaz in U.S. Pat. No. 4,518,576 discloses a cyclic process for the 
removal of hydrogen sulfide from a variety of gas streams. The sour gas 
stream is contacted with an aqueous solution of a monomeric chelate of 
iron (III) and a combination of a crystal modifier of phosphate and 
thiosulfate ions. The H.sub.2 S is oxidized to elemental sulfur and the 
thiosulfate reactant is reduced. The process includes sulfur removal and 
regeneration and recycle of the reactant. 
C. A. Lieder et al. in U.S. Pat. No. 4,332,781 disclose a process for the 
removal of hydrogen sulfide and carbonyl sulfide from a gas stream in a 
staged procedure characterized by conversion of the hydrogen sulfide to 
produce sulfur in aqueous solution or suspension. The reactant materials 
include polyvalent metals bound to monomeric chelates. 
J. O. Porath in U.S. Pat. No. 4,423,158 discloses introducing a 
chelate-forming group into a polymer such as polystyrene. There is 
obtained an adsorbant for bivalent or multivalent metal ions which are 
useful in ion exchange chromatography. The patent does not disclose the 
use of water-soluble polymeric chelates or the process of the present 
invention which are employed to remove H.sub.2 S from fluid streams with 
recovery of the polymeric chelate and active metal ion. 
Additional art of interest includes, for example, U.S. Pat. No. 4,400,361. 
Thus, several techniques are known for treating the exhaust stream from a 
geothermal steam well, or the sour gas or sour water from a refinery 
process with a monomeric organic chelate of iron (III). A problem with 
these processes is that the efficient separation of excess water, products 
and by-products which accumulate in the processes from the monomeric 
organic chelate of iron (II) or iron (III) from the aqueous stream is 
usually difficult and very costly. A portion of the expensive 
iron-monomeric organic chelate is lost during separation of water and the 
low molecular weight materials, and cannot be recovered. It is therefore 
highly desirable to have a process where the expensive organic iron (III) 
or iron (II) polymeric chelate can be separated easily from a waste stream 
originally containing H.sub.2 S, and recycled again and again. This 
invention provides such an improved process and a water-soluble polymeric 
composition for use in the process. 
SUMMARY OF THE INVENTION 
The present invention relates to a process for the removal of H.sub.2 S 
from a fluid stream comprising H.sub.2 S, which process comprises: 
(A) contacting the fluid stream in a contacting zone with an aqueous 
reaction solution at a temperature between about 10.degree. and 90.degree. 
C. for a time effective to oxidize S.sup.= to elemental sulfur, the 
reaction solution itself comprising an effective amount of water-soluble 
organic polymeric chelate containing an oxidizing polyvalent metal; 
(B) separating the treated fluid stream and chelate-containing aqueous 
phase produced in step (A); 
(C) removing the elemental sulfur from the aqueous phase separated in step 
(B); 
(D) treating the organic polymeric chelate-containing aqueous solution of 
step (C) by separation means effective to remove water and low molecular 
weight impurities; 
(E) contacting the concentrated and purified aqueous solution of the 
chelate with an effective amount of an oxidizing agent to oxidize the 
polyvalent metal; and 
(F) recycling the concentrated aqueous chelate solution of step (E) to the 
contacting zone of step (A). 
In another embodiment, the organic polymeric chelate of reduced polyvalent 
metal is oxidized before separation from the elemental sulfur. That is, in 
the above process sequence, step (C) and step (E) are interchanged. 
In another embodiment the invention relates to a process for the removal of 
H.sub.2 S from a gas stream comprising H.sub.2 S, which process comprises: 
(A) contacting the gas stream in a contacting zone with an aqueous solution 
at a temperature between about 10.degree. and 90.degree. C. for a time 
effective to oxidize S.sup.= to elemental sulfur, said solution comprising 
an effective amount of a water-soluble organic polymeric chelate 
containing an oxidizing polyvalent metal and an oxidizing agent effective 
to continuously reoxidize the reduced polyvalent metal; 
(B) separating the gas stream and the resulting aqueous phase produced in 
step (A); 
(C) removing the elemental sulfur from the aqueous solution of step (B); 
(D) treating the organic polymeric chelate-containing aqueous solution of 
step (C) by separation means effective to remove water and low molecular 
weight materials; and 
(E) recycling the concentrated and purified aqueous solution of step (D) to 
the contacting zone of step (A).

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS 
With reference to the present application, the following definitions are to 
be used: 
Fluid Stream 
In the present invention "fluid stream" refers to any gaseous, liquid or 
combination gaseous-liquid stream. These fluid streams include, for 
example, geothermal steam, "sour" gas streams from a petroleum refinery, 
natural gas containing H.sub.2 S, and aqueous H.sub.2 S solutions, and the 
like. 
The Water-Soluble Polymeric Chelates 
Any otherwise inert water-soluble polymeric chelate capable of chelating an 
oxidizing polyvalent metal is suitable in the present process. "Inert", in 
this context, is defined as not detrimentally reactive in the reaction to 
an intolerable extent. Polymeric chelates having a molecular weight 
between about 500 and 1,000,000 are preferred in the present process. 
Polymeric chelates having a molecular weight between about 1000 and 
500,000 are more preferred. 
Chelates are discussed in general by A. L. McCrary et al. in "Chelating 
Agents", Kirk-Othmer: Encyclopedia of Chemical Technology, Volume 5, pp. 
339-368 (1979), which is incorporated herein by reference. 
Polymeric chelates having the following structures are preferred: 
(i) 
##STR1## 
wherein X.sub.1 in each polymer unit is independently selected from --H 
or from a substituent R-- selected from --CH.sub.2 COOH, --CH.sub.2 
CH.sub.2 COOH, --CH.sub.2 --P(.dbd.O)(OH).sub.2, or 
##STR2## 
wherein R.sub.1 and R.sub.2 are each independently --CH.sub.3, --SO.sub.3 
H, --Cl, --H, or --COOH and n is an integer between about 5 and 20,000; 
(ii) 
##STR3## 
wherein X.sub.2 in each polymer unit is selected from --H or a 
substituent selected from --CH.sub.2 CH(OH)CH.sub.2 OH, --CH.sub.2 
CH(OH)CH.sub.2 Cl or 
##STR4## 
wherein R.sub.3, R.sub.4 and R.sub.5 are each independently selected from 
R as defined hereinabove, p is an integer between about 5 and 20,000; and 
q is an integer selected from 0, 1, 2, 3 or 4; 
(iii) 
##STR5## 
wherein X.sub.3 in each polymer unit is independently selected from --OH, 
--Cl or a substituent: 
##STR6## 
wherein R.sub.3, R.sub.4 and R.sub.5 are as defined hereinabove; r is an 
integer between about 10 and 20,000, and s is an integer between about 1 
and 4; 
(iv) 
##STR7## 
wherein X.sub.4 in each polymer unit is independently selected from --OH, 
--OCH.sub.3, --OCH.sub.2 CH.sub.3 or a substituent: 
##STR8## 
wherein R.sub.3, R.sub.4 and R.sub.5 are as defined hereinabove, t is an 
integer between about 10 and 20,000; and x is an integer between 1 and 4; 
(v) 
##STR9## 
wherein X.sub.5 in each polymer unit is independently selected from --OH, 
--Cl or a substituent: 
##STR10## 
wherein R.sub.3, R.sub.4 and R.sub.5 are as defined hereinabove; y is an 
integer between about 10 and 20,000, and z is an integer between about 1 
and 4; 
(vi) 
##STR11## 
wherein X.sub.6 in each polymer unit is independently selected from --H 
or a substituent --CH.sub.2 CH(OH)CH.sub.2 OH, --CH.sub.2 CH(OH)CH.sub.2 
Cl, or 
##STR12## 
wherein v is between about 10 to 10,000, a is 6, b is 1 to 4, c is 1 to 
4; and R.sub.3, R.sub.4 and R.sub.5 are as defined hereinabove; 
(vii) 
##STR13## 
wherein X.sub.7 in each polymer unit is independently selected from --H 
or a substituent selected from --CH.sub.2 CH(OH)CH.sub.2 OH, --CH.sub.2 
CH(OH)CH.sub.2 Cl, or 
##STR14## 
wherein m is an integer from 1 to 4, g is between 10 and 10,000, q and 
R.sub.3, R.sub.4 and R.sub.5 are as defined hereinabove; or 
(viii) 
##STR15## 
wherein X.sub.8, X.sub.9 and X.sub.10 in each polymer unit are each 
independently selected from --H or a substituent selected from --CH.sub.2 
CH(OH)CH.sub.2 Cl, --CH.sub.2 CH(OH)CH.sub.2 OH, or 
##STR16## 
q, R.sub.3, R.sub.4 and R.sub.5 are as defined hereinabove, w is between 
about 10 and 10,000; or 
(ix) mixtures of polymeric chelates (i) to (viii); with the proviso that 
the overall ratio of --H, --OCH.sub.3, --OCH.sub.2 CH.sub.3, --Cl, or --OH 
to substituent in each of X.sub.1, X.sub.2, X.sub.3, X.sub.4, X.sub.5, 
X.sub.6, X.sub.7, X.sub.8, X.sub.9 or X.sub.10 in each polymeric chelant 
(i to viii) hereinabove is between about 10/90 and 90/10. 
In the above polymeric chelants (i to viii) in R.sub.3, R.sub.4 and 
R.sub.5, the preferred groups are each --CH.sub.2 COOH and --CH.sub.2 
CH.sub.2 COOH, especially --CH.sub.2 COOH. 
It is also contemplated that mixtures of the water-soluble organic 
polymeric chelates are useful in the present invention. 
The concentration of the polymer should be at a level so as to provide up 
to about 1 gram equivalent weight of the chelating group per liter of 
solution. A preferred range is between about 0.05 and 1 gram equivalent. 
The polymeric chelates described herein are prepared as is described 
hereinbelow. Some polyamines and polyethers used in the synthesis are 
described in Table I. 
TABLE I 
______________________________________ 
POLYAMINES AND POLYETHERS 
USED AS STARTING MATERIALS 
FOR SYNTHESIS OF POLYMERIC CHELATORS 
Degree of Molecular 
Polymerizaton 
Weight Nature of 
Amine (D.P.) Range Chain 
______________________________________ 
E-100.sup.a 6 250-300 Branched 
PEI-6.sup.b 15 600 Branched 
Hydrolyzed PEOx 
50.sup.c 2000 Linear 
Purifloc C-31.sup.d 
500.sup.e 10,000-30,000 
Branched 
Hydrolyzed PEOx 
500.sup.f 20,000 Linear 
PEI-600 1500 60,000 Branched 
Hydrolyzed PEOx 
5000.sup.g 500,000 Linear 
______________________________________ 
.sup.a E100 is a byproduct of ethylenediamine manufacture and is a low 
molecular weight branched polymer containing about six ethyleneamine 
groups. 
.sup.b PEI = polyethyleneimine; PEOx, polyethyloxazoline. PEI is a polyme 
of molecular weight 60,000 (CORCAT 600) and is obtained from Cordova 
Chemical Company. The nitrogen content is detemined by drying a sample, 
and elemental analysis of the solid. 
.sup.c 100% hydrolyzed 
.sup.d Purifloc C31 is a polyethyleneamine produced by the Dow Chemical 
Company, Midland, Michigan. 
.sup.e Probably also partially crosslinked. 
.sup.f 85% hydrolyzed 
.sup.g 97% hydrolyzed 
In the synthesis of the pendant polymeric chelants (i to viii), the 
procedure usually includes the addition of the pendant group to an 
available polymeric backbone. However, under the reaction conditions not 
all of the possible chelant additions occur on each repeating polymer 
;unit of the polymer backbone. Thus, in chelate (i) where the repeating 
unit is: 
##STR17## 
some of the pendent groups X.sub.1 are --H and others are, for example, 
--CH.sub.2 COOH, e.g.: 
##STR18## 
This type of random pattern of addition occurs for the pendent chelant 
groups in the polymeric chelants (i to viii). If the polymer backbone 
contains a pendant epoxide group, e.g.: 
##STR19## 
then after addition, if all epoxide groups do not react further, then the 
chemical groups --CH.sub.2 CH(OH)CH.sub.2 OH (hydrolysis), or CH.sub.2 
CH(OH)CH.sub.2 Cl are pendant groups on the polymer backbone. 
One embodiment of the chelate designated (i) 
##STR20## 
where X.sub.1 is --H or --CH.sub.2 COOH (CHELATE A) is prepared by 
dissolving polyethyleneimine (PEI 150 or PEI 600, available from the Dow 
Chemical Company) in water followed by reaction with excess sodium 
chloroacetate in the presence of strong base. 
Another embodiment of the polymeric chelate designated (i) --[CH.sub.2 
--CH.sub.2 --N(X.sub.1)].sub.n --, where X.sub.1 is --H or --CH.sub.2 
P(.dbd.O)(OH).sub.2 (CHELATE B) is prepared by dissolving 
polyethyleneimine in water and reaction with phosphoric acid and 
formaldehyde. The process described by R. S. Mitchell in U.S. Pat. No. 
3,974,090 for the monomer may be adapted using the polymeric imine. 
A further embodiment of the polymeric chelate (i) designated 
##STR21## 
where X.sub.1 is --H or 
##STR22## 
and R.sub.1 and R.sub.2 are each methyl (CHELATE C), is obtained by 
dissolving polyethyleneimine in water followed by treatment with 
2,4-dimethylphenol and formaldehyde. The general procedure described by G. 
Grillot and W. Gormley, Jr., J. Amer. Chem. Soc., Vol. 67, pp. 1968 ff 
(1945) for the monomer is adapted using the polymeric imine, and is 
incorporated herein by reference. 
One embodiment of the polymeric chelate designated (ii) where X.sub.2 is 
--H or --CH.sub.2 CH(OH)CH.sub.2 N(CH.sub.2 COOH)CH.sub.2 CH.sub.2 
N(CH.sub.2 COOH).sub.2 and p is 2000 (CHELATE D), is obtained by first 
reacting epichlorohydrin, 
##STR23## 
with ethylenediamine-triacetic acid to produce Cl--CH.sub.2 
--CH(OH)CH.sub.2 --N--(CH.sub.2 COOH)CH.sub.2 CH.sub.2 N(CH.sub.2 
COOH).sub.2, followed by reaction with polyethyleneimine. The procedure 
described above for CHELATE A may also be adapted. For those polymers 
where q is 2, 3, or 4, the ethylenediamine is replaced with the 
corresponding diethylenetriamine, triethylenetetraamine and 
tetraethylene-pentamine, respectively. 
Another embodiment is of the polymeric chelate designated (ii) wherein 
X.sub.2 is --H or --CH.sub.2 CH(OH)CH.sub.2 [N(R.sub.3)CH.sub.2 CH.sub.2 
].sub.q N(R.sub.4)(R.sub.5), p is about 2,000, q is 0, and R.sub.4 and 
R.sub.5 are each --CH.sub.2 COOH. (CHELATE D-1), Iminodiacetic acid is 
dissolved in water and epichlorhydrin, about a 20% excess is added. The 
product is extracted with a chlorinated hydrocarbon such as methylene 
chloride to remove the unreacted epichlorhydrin. To this aqueous solution 
is added a 33% aqueous solution of polyethyleneimine e.g., CORCAT 600, 
heated and further treated with sodium hydroxide at a pH of 9-10. The 
chelate solution is used without further purification. 
One embodiment of the polymeric chelate designated (iii) wherein X.sub.3, 
is Cl, --OH or --[N(R.sub.3)CH.sub.2 CH.sub.2 ].sub.s N(R.sub.4)(R.sub.5), 
s is 1, r is about 100 and R.sub.3, R.sub.4 and R.sub.5 are each 
--CH.sub.2 COOH (CHELATE E) is prepared by treating polyepichlorohydrin 
with ethylenediamine in the presence of base followed by treatment with 
excess sodium chloroacetate. 
One embodiment of the chelate designated (iv) where X.sub.4 is --OH or 
NH--[CH.sub.2 CH.sub.2 N(R.sub.3)].sub.x CH.sub.2 CH.sub.2 
N(R.sub.4)(R.sub.5), t is 100, x is 1 and R.sub.3, R.sub.4 and R.sub.5 are 
each --CH.sub.2 COOH (CHELATE F) is prepared by the treatment of 
poly(ethylacrylate) with diethylenetriamine followed by treatment with 
sodium chloroacetate in the presence of a strong base. 
One embodiment of the chelate designated (v) X.sub.5 is --Cl, --OH or 
--[N(R.sub.3)CH.sub.2 CH.sub.2 ].sub.z N(R.sub.4)(R.sub.5) where R.sub.3, 
R.sub.4 and R.sub.5 are each --CH.sub.2 COOH, y is 100 and z is 1 (CHELATE 
G) is the treatment of poly(vinylbenzylchloride) with ethylenediamine in 
the presence of strong base. The product in the presence of base, is next 
treated with excess sodium chloroacetate. By replacement of 
ethylenediamine with diethylenetriamine, triethylene tetraamine, and the 
like, the higher homologues are produced. 
One embodiment of the chelate designated as (vi) where --X.sub.6 is 
--CH.sub.2 CH(OH)CH.sub.2 OH or --CH.sub.2 CH(OH)CH.sub.2 
[N(R.sub.3)CH.sub.2 CH.sub.2 ].sub.c N(R.sub.4)(R.sub.5) where R.sub.3, 
R.sub.4 and R.sub.5 are each --CH.sub.2 COOH and c is 1 (CHELATE H) is 
obtained by the treatment of the commercial polymer KYMENE 557H which is 
obtained from the Hercules Corporation of Wilmington, Del., with 
ethylenediamine triacetic acid. 
One embodiment of the chelate designated as (vii) where X.sub.7 is --H or 
--CH.sub.2 CH(OH)CH.sub.2 ]N(R.sub.3)--CH.sub.2 CH.sub.2 ].sub.c 
N(R.sub.4)(R.sub.5) where m is 1, g is about 1,000, q is 1 and R.sub.3, 
R.sub.4 and R.sub.5 are each --CH.sub.2 COOH and n is 1 (CHELATE J), is 
obtained by reacting the polymer of methacrylic acid and ethylenediamine 
with ethylene diamine triacetic acid. 
In one embodiment of the chelate designated (vii) X.sub.8, X.sub.9 and 
X.sub.10 are each --H or --CH.sub.2 CH(OH)CH.sub.2 OH or --CH.sub.2 
CH(OH)CH.sub.2 --N(R.sub.3)CH.sub.2 CH.sub.2 N(R.sub.4)(R.sub.5), where 
R.sub.3, R.sub.4 and R.sub.5 are each --CH.sub.2 COOH. The pendant adduct 
is obtained by reacting the commercially available FIBRABON 35 from the 
Diamond Shamrock Co., with ethylenediaminetriacetic acid in the presence 
of base (CHELATE K). 
Generally in polymeric chelants (i) to (viii), the ratio of --H (or 
OCH.sub.3, OCH.sub.2 CH.sub.3, OH or Cl) to substituent in each of X.sub.1 
to X.sub.10 is between about 10/90 to 90/10, more preferably the ratio is 
between about 10/90 and 40/60. 
A more detailed description of the preparation for these organic polymeric 
chelates is provided below as part of the Examples. 
The Polyvalent Metals 
Generally, any polyvalent metal chelatable in both oxidized and reduced 
states can be used in the present invention as the metal component of 
polymeric chelate, but iron, copper and manganese are preferred. Iron is 
particularly preferred. The polyvalent metal chelate should be capable of 
oxidizing hydrogen sulfide while being reduced itself to the corresponding 
chelate of the metal in a lower valence state, and should then be 
oxidizable by oxygen or similar oxidation means to a chelate of the metal 
in a higher valence state, in typical redox reactions. Other polyvalent 
metals which can be used include tin, lead, platinum, tungsten, nickel, 
palladium, chromium, cobalt, vanadium, titanium, tantalum, zirconium and 
molybdenum. 
Separation Means for Water and Low Molecular Weight Materials 
The separation means to separate the organic polymeric chelate from the 
water and water-soluble low molecular weight products and materials can 
employ any single or combination of techniques suitable for this purpose. 
Preferably membrane separation, e.g., ultrafiltration and/or dialysis are 
used. More preferably, ultrafiltration is employed using a membrane 
consisting of any of a variety of synthetic polymers, in the shape of a 
film, hollow fiber or the like. Particularly useful for the removal of 
water and low molecular weight materials while retaining the water-soluble 
polymeric chelate are membranes such as: UM05, UM2, PM10 available from 
Amicon Company of Danvers, Mass. 
Ultrafiltration is described by R. R. Klinkowski in Kirk Othmer: 
Encyclopedia of Chemical Technology, Vol. 23, pp. 439-461 (1983) and 
dialysis procedures and technology are described by E. F. Leonard in the 
same source, Vol. 7, pp. 564-579 (1979). 
DETAILED DESCRIPTION OF THE FIGURES 
In FIG. 1, the sour gas stream for example, spent geothermal steam or 
natural gas containing about 1.0 percent by volume of H.sub.2 S, or a 
refinery stream containing up to about 1.0 percent by volume of H.sub.2 S 
in line 1 enters column 2 which contains an admixture comprising an 
aqueous solution (about 1 molar), of a water-soluble polymeric chelate as 
described herein containing a polyvalent metal in oxidized form. Fe.sup.+3 
is preferred and will be used hereafter. It is to be understood that 
Fe.sup.+3 (oxidized form) and Fe.sup.+2 (reduced form) as used herein will 
be representative of any comparable polyvalent metal. The pressure of the 
feed gas is generally not critical and may vary from between about 10 and 
1000 pounds per square inch gauge (psig). A preferred pressure range is 
between about 15 and 100 psig. The temperature of the aqueous admixture is 
between about 10.degree. and 90.degree. C., with between 20.degree. and 
80.degree. C. being preferred. A more preferred temperature range is 
between about 20.degree. and 50.degree. C. A suitable contact time between 
the aqueous admixture and the sour gas is usually between about 1 sec and 
5 min, with between about 2 sec and 1 min being preferred. This time 
period is normally sufficient to oxidize substantially all of the sulfide 
ions to elemental sulfur (S.degree.). The purified or sweetened gas stream 
then leaves zone 2 via line 3. Generally, the purified gas exiting in line 
3 meets standard environmental emission standards for H.sub.2 S. 
In the aqueous admixture, the H.sub.2 S has been converted by the 
Fe(III)-containing polymeric chelate to elemental sulfur particles. The 
Fe(III) is simultaneously reduced to Fe(II) in the polymeric chelate. The 
aqueous mixture containing solid sulfur particles and water-soluble 
polymeric chelate of Fe(II) is removed in a continuous manner through line 
4, optionally to a degassing and depressurization unit 5. Additional gases 
are evolved through line 6. 
Sulfur separation and removal are accomplished by any conventional means, 
e.g., precipitation, centrifugation. The crude aqueous mixture is conveyed 
by line 7 to separation unit 8. Preferably, unit 8 is a filtration unit. 
It is not necessary that all sulfur be removed at this stage via line 9. 
Those skilled in the art will know to adjust conditions to achieve the 
appropriate rates of withdrawal of the liquid and gas streams. 
The polymeric chelate containing aqueous solution now free of elemental 
sulfur is conveyed via line 10 to a second separator unit 11. This 
separator uses means to separate excess water and low molecular weight 
products and byproducts. Generally, the means used are ultrafiltration or 
dialysis, with ultrafiltration being preferred. The water and low 
molecular weight materials, such as EDTA, etc. having a molecular weight 
of less than 1000, preferably less than 500, are separated and conveyed 
away through line 12 and disposed of in an environmentally acceptable 
manner. The concentrated aqueous polymeric chelate is then conveyed 
through line 13 to regeneration zone 14. 
In the regeneration zone or column 14, the mixture is contacted with an 
oxidizing agent, such as, excess air or oxygen, entering through line 15 
to convert the Fe(II)-polymeric chelate to the Fe(III)-polymeric chelate. 
The temperature of the column may vary between 0.degree. and 50.degree. 
C., preferably between 20.degree. and 40.degree. C. and the pressure is 
between about 10 and 100 psig, more preferably 20 and 50 psig. 
The polymeric chelate containing the oxidized metal [Fe(III)] is then 
conveyed through line 16 to contacting zone 2 to begin the reaction 
process cycle again. As needed, make-up water, polymeric chelate and 
polyvalent metal are added to the process through line 17. 
Some variations in the sequence of the process shown in FIG. 1 are 
contemplated within this invention. These include interchanging the 
positions of separator 8 for the elemental sulfur and separator 11 for 
removal of the water and low molecular weight materials. Thus, a portion 
of the wat4er and low molecular weight materials may be separated with the 
elemental sulfur particles produced still present, although the elemental 
sulfur might tend to clog the pores of an ultrafiltration or dialysis 
membrane. 
An additional variation of the present process described in FIG. 1 is the 
removal of separation unit 11, the combination of lines 10 and 13, and the 
insertion of unit 11 into line 16 between regeneration unit 14 and the 
point where makeup line 17 combines with recycle line 16. A difficulty 
encountered in this configuration is that large volumes of aqueous liquid 
are subject to processing through unit 14. 
In FIG. 2, a number of the apparatus elements, i.e., 1 to 12 correspond to 
similarly numbered elements in FIG. 1 and have essentially the same 
function. In this embodiment an oxidizing agent, e.g., oxygen, is added to 
contactor unit 2 through line 1A at the same time that the aqueous organic 
polymeric chelate of Fe(III) is added through line 1. In this embodiment 
the Fe(III) is reduced to Fe(II) as the H.sub.2 S present is oxidized to 
elemental sulfur, and concurrently the Fe(II) produced is simultaneously 
oxidized to Fe(III) by the oxygen present. The following equations are 
illustrative: 
##STR24## 
Combining these equations, the overall reaction is represented by the 
following equation: 
EQU H.sub.2 S.sub.(gas) +1/2O.sub.2 (gas).fwdarw.S.degree.+H.sub.2 O 
Iron levels in a number of polymeric chelates were in the range of 0.03M as 
shown in Table II. The ratio of chelate to iron is not greatly dependent 
upon the total iron level because of the stability of the chelate. As can 
be seen from Table II, value W is important because it is the mole ratio 
of nitrogen in the chelator (polymeric chelator) to iron at the point of 
incipient precipitation at room temperature. This value represents 
essentially the maximum amount of iron in the chelate. 
TABLE II 
______________________________________ 
CHELATION OF IRON (III) BY POLYCHELATORS 
Ratio W is the mole ratio of nitrogen in chelating monomer 
or polymer to iron at point of incipient precipitation at room 
temperature. pH in all test is 7 .+-. 0.5. 
Chelator (Fe), M W 
______________________________________ 
EDTA 0.03 2.0 
MBEDTA 0.03 2.2 
Sym. EDDA 0.03 &gt;10 
DTDA 0.015 &gt;9 
DTPA 0.03 2.5 
TTHA 0.05 2.3 
CM E-100 0.04 3.4 
CM PEI 6 0.045 3.2 
CM PEOx, DP-50 0.025 5 
CM PEOx, DP-1000 0.025 4 
CM PEOx, DP-10,000 0.015 4.2 
CM C-31 (Purifloc C-31) 
0.04 5 
(Dow) 
______________________________________ 
EDTA -- Ethylenediamine tetracetic acid 
MBEDTA -- Methylp-benzylethylenediaminetriacetic acid 
Sym. EDDA -- Sym. Ethylenediaminediacetic acid 
DTDA -- Diethylenetriaminediacetic acid 
DTPA -- Diethylenetetraaminepentaacetic acid 
TTHA -- Triethylenetetraaminehexaacetic acid 
CM -- Carboxymethyl 
PEI -- Polyethyleneimine 
PEOx -- Polyethyleneoxazoline 
The following Examples are to be construed as being illustrative and are 
not limiting in any way. For X.sub.1 to X.sub.10 in the Examples, the 
pendant group in each polymer unit of the polymer is selected from those 
designated. It is also to be understood that from the description herein 
that when complete or partial addition of the pendant chelating group on 
the polymer backbone is desired the experimental synthesis conditions need 
only to be adjusted. That is, if only partial substitution is required, 
adjustment to shorter reaction times, lower concentrations of reactants, 
lower reaction temperatures and those techniques known in the art are 
used. For more complete or complete additions of the pendant chelating 
groups to the polymer backbone is desired, longer reaction times, higher 
concentration of reactants and higher reaction temperatures are used. The 
molecular weight of the polymers described herein are usually expressed as 
the weight average molecular weight. 
EXAMPLE 1 
Organic Polymeric Chelate (i) Based on Polyethyleneimine (PEI) 
[CHELATE A; X.sub.1 is --H or --CH.sub.2 COOH] 
(a) Polyethyleneimine 11 g [degree of polymerization (DP) 1500] is 
dissolved in water (200 ml) to produce a solution of 1.25 molar (in amine 
nitrogen). To the aqueous solution is added sodium chloroacetate (31 g, a 
5% excess) with stirring while maintaining the reaction mixture at about 
60.degree. C. A pH electrode is used to monitor the reaction and 50% 
sodium hydroxide is added to maintain the pH above about 10. After 40 
minutes of reaction the reaction is complete, and the reaction mixture is 
allowed to cool. The aqueous solution is diluted to 1.0M (amine nitrogen) 
and used without further purification. 
EXAMPLE 1A 
Preparation of Polymeric Chelate (i) 
[CHELATE B: X.sub.1 is --H or --CH.sub.2 P(.dbd.O)(OH).sub.2 ] 
To a 500 ml flask equipped with a water condenser and dropping funnel are 
added 99 g (0.6 mole) of 49.9% orthophosphorous acid (which also contains 
9.4 g of hydrogen chloride) and 5.2 g of 37% hydrochloric acid. The total 
mole of hydrogen chloride used is 0.4. The resultant mixture is then 
allowed to heat by the addition of 14 g of CORCAT 150 (Cordova Chemical 
Co.) as a 33% aqueous solution of polyethyleneimine containing 0.1 mole of 
amine nitrogen. The polyamine is added over a period of 8 to 10 minutes 
while the reaction mixture achieves a temperature of about 
70.degree.-75.degree. C. The reaction mixture is then heated for about 20 
minutes to the boiling temperature thereby producing a homogenous clear 
solutionhaving a boiling point of between 110.degree.-115.degree. C. The 
resulting clear aqueous solution is maintained at boiling for about 2 
hrs., and 22 g (0.66 mole) of paraformaldehyde is added. After the 2-hr. 
period, the clear reaction mixture is kept boiling for an additional 30 
min and cooled to about 25.degree.-30.degree. C. The clear solution has an 
amber color, and contains about 50% by weight of the polyethyleneimine 
phosphonate which is used without further purification. 
EXAMPLE 1B 
Preparation of Polymeric Chelate (i) 
[CHELATE C: X.sub.1 is --H or 6-methylene-2,4-dimethylphenol] 
To a 13 g aqueous solution (33%) of polyethyleneimine CORCAT 150 (from 
Cordova Chemical Company) containing 0.1 mole of available amine nitrogen 
is added 10.8 g of 2,4-dimethylphenol(0.1 mole). The solution was 
maintained below 20.degree. C., while a 37% aqueous formaldehyde solution 
(0.11 mole) was added slowly with stirring. The solution was allowed to 
stand for an hour at ambient temperature and then warmed to 80.degree. C. 
for 2 hrs. The aqueous solution was used without purification in 
subsequent experiments. 
EXAMPLE 2 
Preparation of Polymeric Chelate (ii) 
[CHELATE D: X.sub.2 =--H or --CH.sub.2 CH(OH)CH.sub.2 N(CH.sub.2 
COOH)--CH.sub.2 CH.sub.2 N(CH.sub.2 COOH).sub.2 
This preparation was performed in two steps: (1) attachment of 
ethylenediamine to the polymer; and (2) conversion of the amine of the 
ED3A. 
Step 1: 23.5 Grams of polyepichlorhydrin (0.25 Mole monomer unit) and 94 
grams of 85% ethylenediamine (1.3 moles) were dissolved in 50 ml 
isopropanol and 25 ml of toluene and refluxed (about 100.degree. C.) for 
six hrs. As the reaction proceeded additional isopropanol was added to 
maintain homogeneity, with the final system being about 75/25 
isopropanol/toluene. The reaction was followed by titrating aliquots for 
chloride ion with silver nitrate. Next, 20 grams of 50% NaOH (0.25 mole) 
was added, the solid NaCl which formed was filtered, washed with ethanol, 
and the liquid was removed in a vacuum evaporator at 55.degree. C. 
Although some NaCl remained in the product, the elemental analysis gave a 
C:H:N mole ratio of 4.6:12.1:2.00 (Expected mole ratio was 5:12:2). 
Step 2: This intermediate was taken up in about 200 ml of water, to which 
3.3 moles of sodium chloroacetate was added per mole of nitrogen. The 
system was kept at about 60.degree. C. and a pH of about 10 for about one 
hr. At this point a white precipitate (presumably NaCl) was filtered off, 
the pH was adjusted to about 2 (the expected isoelectric point), at which 
point considerable white solid formed. This solid was filtered and found 
to be EDTA, presumably formed because all of the unreacted ethylenediamine 
had not been removed during the vacuum evaporation. The filtrate was 
dialyzed against about 4 liters of water. 
An estimate of the EDTA content of the dialyzed (polymeric) material was 
made by titrating an aliquot with iron (III). About one-third of the 
expected chelant groups were found in the polymer fraction. 
EXAMPLE 2A 
Preparation of Polymeric Chelate (ii) 
[CHELATE D-1: p=2,000, X.sub.2 is --H or --CH.sub.2 CH(OH)CH.sub.2 
N(CH.sub.2 COOH).sub.2 
14.3 Grams (0.1 mole) of iminodiacetic acid was dissolved in 100 ml of 
water. To this solution was added 0.12 mole epichlorhydrin, about a 20% 
excess. After allowing the solution to stand for an hour at ambient 
temperature it was extracted with 50 ml of methylene chloride to remove 
the unreacted epichlorhydrin. To the aqueous phase from this extraction 
was added 14.7 grams of a 33% solution of polyethyleneimine CORCAT 600 
(Cordova Chem. Co., Muskegon, Mich.), an amount determined to contain 0.1 
mole of nitrogen. The solution was heated to 60.degree. C., while sodium 
hydroxide solution (10N) was added at a rate sufficient to maintain the pH 
in the range of 9-10. After about 30 minutes the reaction was complete and 
the resulting solution, which now contained the polyethyleneimine with 
iminodiacetic acid groups attached to it, was used without purification in 
subsequent experiments. 
EXAMPLE 3 
Preparation of Polymeric Chelate (iii) 
[CHELATE E: X.sub.3 is --OH, --Cl or --[N(CH.sub.2 COOH)CH.sub.2 CH.sub.2 
]N(CH.sub.2 COOH).sub.2 
224 Grams (0.1 mole) of ethylenediamine triacetic acid is dissolved in 100 
ml of water. To this solution is added 0.12 mole of polyepichlorohydrin, 
about a 20% excess [HYDRIN 10.times.1 (DP.about.40)], from B. F. Goodrich 
Co., Cleveland, Ohio, is dissolved in toluene/methylene chloride (50/50; 
v/v). Tetrabutylammonium chloride (0.01 mole) is added as a phase transfer 
catalyst. The solution is stirred for about an hour at ambient 
temperature. The HCl produced is taken up by the addition of sodium 
hydroxide. The aqueous polymeric chelate is subsequently used without 
purification. 
EXAMPLE 4 
Preparation of Polymeric Chelate (iv) 
[CHELATE F: X.sub.4 is --OH or --NH[CH.sub.2 CH.sub.2 N(CH.sub.2 N(CH.sub.2 
COOH)]CH.sub.2 CH.sub.2 N(CH.sub.2 COOH).sub.2 
Poly(methylacrylate) (86 g., equivalent to one mole of formula weight of 
the monomeric methyl acrylate) is dissolved in about 300 ml of toluene, 
and 520 g of diethylenetriamine (5 moles) are added. The solution is 
heated to 40.degree.-50.degree. C. for an hour and the excess amine and 
toluene are evaporated under vacuum. The residue is taken up in 500 ml of 
water and 348 g. of sodium chloroacetate (3.0 mol) are added to the 
solution, and heated to about 60.degree. C. for about 30 minutes while 
sodium hydroxide is added at a rate sufficient to maintain the pH at 9-10. 
This solution, which had the desired structure is used without further 
purification in subsequent experiments. 
EXAMPLE 5 
Preparation of Polymeric Chelate (v) 
[CHELATE G: X.sub.5 is --OH or --N(CH.sub.2 COOH)CH.sub.2 CH.sub.2 
N(CH.sub.2 COOH).sub.2 and y is 100 
Polyvinylbenzyl chloride (15 g., equivalent to 0.1 mole of monomer units) 
is dissolved in 100 ml of methylene chloride, and 30 g of ethylenediamine 
(0.5 mole) were added. The solution is warmed to 40.degree. C. and stirred 
for 2 hours. The excess amine and methylene chloride are evaporated under 
vacuum. The resulting polymer is taken up in 200 ml of water and 
carboxymethylated as in the preceding example. The resulting polymer has 
the desired structure and is used further without purification. 
EXAMPLE 6 
Preparation of Polymeric Chelate (vi) 
[CHELATE H: X.sub.6 is --H or --CH.sub.2 CH(OH)CH.sub.2 N(CH.sub.2 
COOH)CH.sub.2 CH.sub.2 N(CH.sub.2 COOH).sub.2 
Eighty grams of the polymer KYMENE 557H (0.1 mole monomer equivalent) 
(Hercules Corporation, Wilmington, Del.), which is a copolymer of adipic 
acid, diethylenetriamine and epichlorhydrin was added to a solution of 46 
g of ethylenediaminetriacetic acid in about 200 ml of water (a twofold 
excess). The solution was heated to 80.degree. C. for two hours. The 
resulting solution which contained the desired polymer (vi) was used 
without further purification in subsequent experiments. 
EXAMPLE 7 
Preparation of Polymeric Chelate (vii) 
[CHELATE J; X.sub.7 is --H or --CH.sub.2 CH(OH)CH.sub.2 N(CH.sub.2 
COOH)--CH.sub.2 CH.sub.2 N(CH.sub.2 COOH).sub.2, m is 1, and g is about 
100. 
A solution of an adduct of epichlorhydrin and iminodiacetic acid, as 
prepared in Example 2A, was added to an equimolar quantity of a polymer 
solution made by reacting equimolar quantities of methyl acrylate and 
ethylenediamine. The solution was heated to 80.degree. C. for 2 hours, and 
the resulting polymer was used in subsequent experiments. 
EXAMPLE 8 
Preparation of Polymeric Chelate (viii) 
[CHELATE K; X.sub.8, X.sub.9 and X.sub.10 are --H, --CH.sub.2 
CH(OH)CH.sub.2 OH or --CH.sub.2 CH(OH)CH.sub.2 N(CH.sub.2 COOH)CH.sub.2 
CH.sub.2 N(CH.sub.2 COOH).sub.2 
Fifty four grams of the commercial polymer Fibrabon 35 (Diamond Shamrock 
Corporation, Cleveland, Ohio) which contained 100 millimoles of active 
epichlorhydrin groups, was mixed with a solution of 46 grams of 
ethylenediaminetriacetic acid (0.2 mole), the solution was heated to 
60.degree. C. and sodium hydroxide was added at a rate sufficient to 
maintain the pH at about 9-10. After about 2 hours, the reaction was over 
and the solution was used in subsequent experiments. About 1 of X.sub.8, 
X.sub.9 and X.sub.10 in each polymer unit is a pendant chelating group. 
EXAMPLE 9 
Dialysis of Iron Polychelates 
In the dialysis, 100 ml of iron organic chelate, made up to be about 0.1 
molar in iron, was dialyzed into two liters of deionized water overnight. 
The CM PEI 150 and CM PEI 600 polychelators were dialyzed through 
SPECTROPOR 1, from Van Waters & Rogers, San Francisco, Calif. which has a 
nominal molecular weight cut-off of about 6000-8000. In both cases, about 
3-5% of the iron was lost. The CM PEI 6 solution was dialyzed through 
SPECTROPOR 6 (Van Waters & Rogers) which has a cut-off of about 2000. In 
this case about 10% of the iron was lost. 
EXAMPLE 10 
Ultrafiltration of Iron Polychelates 
The ultrafiltration tests were performed in an Amicon Model 52 cell which 
is a cylindrical chamber with a 43 mm diameter (12.5 cm) membrane as the 
bottom surface. The cell volume is about 60 ml and the cell contains a 
suspended magnetic stirring bar to reduce polarization effects. In a run, 
a 25-ml volume of solution was placed in the cell and the gas space was 
connected to an air line maintained at 15 psig. 
Three membranes were used for this study, all obtained from the Amicon 
Corporation of Danvers, Mass. They were designated as UM 05, UM 2 and PM 
10 having nominal molecular weight cutoffs of 500, 1000 and 10,000, 
respectively. The iron was determined by the standard thiocyanate method. 
The results are shown below in Table III. 
TABLE III 
______________________________________ 
ULTRAFILTRATION AND DIALYSIS 
OF IRON POLYCHELATES 
Membrane 
UM 05 UM 2 PM 10 
Rejection 
Rejection 
Flow Rejection 
Flow 
Polychelator 
% % gsfd* % gsfd* 
______________________________________ 
CM PEI 600 
89 98 1.3 91 6 
CM PEI 600 99 2.8 95 16 
(dialyzed) 
CM PEI 150 95 1.4 97 9 
(dialyzed) 
CM PEI 6 80-90 0.8 25 28 
CM PEI 6 61 90 &gt;0.3 
(dialyzed) 
CM E-100 84 92 0.6 27 40 
EDTA 23 10 1 
Deionized 5 100 
H.sub.2 O only 
______________________________________ 
[CM PEI -- Carboxymethyl polyethyleneimine, 
Rejection % values are averages over steady state portion of run. 
Flow values are interpolated or extrapolated to 0.10 M Fe. 
Rejection %the amount of chelate (or material) which did not pass through 
the membrane. 
*gsfd = gal/ft.sup.2 .times. day 
As can be seen from Table III, polychelates based on carboxymethylated 
polyethyleneimine 6 (CM PEI 6, about 15 monomer units) or larger polymers 
are fairly well rejected by ultrafiltration membranes having cut-offs in 
the molecular weight range of 1000-10,000. CM PEI 6 is strongly rejected 
(80-90%) by Amicon UM 2 membrane (having a cut-off value of 1000), but 
poorly (20-30%) by PM 10 (cut-off 10,000). Higher polymers CM PEI 150 and 
CM PEI 600 are both strongly rejected 95-99% by both membranes. 
At a concentration of 0.1M chelated iron (III) output from an Amicon UM 2 
membrane is about 1 gallon per square foot per day (gsfd) with the 
polychelators of Table III at a pressure of 15 psig. For the PM 10 
membrane, the output is 6-30 gsfd. Output was strongly dependent upon iron 
concentration. 
EXAMPLE 11 
Removal of Sulfide Ion 
One hundred ml of a solution of sodium sulfide (30 ppm of S.sup.=, 0.00094 
Molar) was buffered at a pH of 7.8 using 0.01M triethanolamine. Air was 
bubbled through the solutions at 200 ml/min and samples were removed 
periodically to determine sulfide ion level. The disappearance of S.sup.= 
is shown in FIG. 3. An identical experiment was run in which an iron (III) 
chelate was present at a concentration of 0.000188 Molar, i.e., one-tenth 
of the stoichiometric concentration for the direct oxidation of the 
sulfide by iron to sulfur. The disappearance of sulfide is shown also in 
FIG. 3 and is considerably more rapid in the presence of the chelate. The 
polymeric chelate was carboxymethylpolyethyleneimine PEI 150 --[CH.sub.2 
CH.sub.2 --N(CH.sub.2 COOH)].sub.dp where the degree of polymerization 
(dp) is about 300. 
As can be seen from FIG. 3, the S.sup.= level decreases only slightly 
slower for the polymeric iron (III) chelate as with the monomeric iron 
(III) chelate. 
FIG. 4 compares the oxidation of sulfide by Fe (III) chelates generally 
using the conditions described above. As can be seen both of the polymeric 
chelates CM PEI 6 and CM PEI 150 are as effective as the monomeric 
chelates within 2 to 3 minutes. 
EXAMPLE 12 
Removal of H.sub.2 S with Recycle 
A gas stream from a geothermal steam well having a H.sub.2 S concentration 
of 0.99 weight % enters a contact vessel into which also enters an aqueous 
mixture containing 1.0 percent by weight of Fe (based on the total weight 
of the mixture) as Fe (III) polymeric chelate of carboxymethyl 
polyethyleneimine (CM PEI 6). The chelate is supplied in a 10 percent 
molar excess based on iron and the pH of the system is 6. The pressure of 
the feed gas is about 15 psig and the temperature of the mixture is about 
35.degree. C. A contact time of about 60 seconds is used. The H.sub.2 S is 
converted to elemental sulfur by the Fe (III) polymeric chelate which is 
reduced to Fe (III) polymeric chelate. The sulfur produced is fine 
particles and is separated by filtration. The aqueous solution is treated 
by ultrafiltration using an Amicon UM 2 membrane and apparatus. The CM PEI 
6 is retained in the aqueous system while the lower molecular weight 
material (below 1000) are removed. The aqueous solution containing the CM 
PEI 6 Fe (II) is treated with oxygen to reoxize the iron (II) to iron 
(III) and recycled to the contact vessel. 
EXAMPLE 13 
Removal of H.sub.2 S with Simultaneous Oxidation of Iron (II) Chelate 
The H.sub.2 S gas stream of Example 12 is treated as is shown in FIG. 2 
with a simultaneous oxygen flow to the contact chamber of 2 ml/min. The 
H.sub.2 S is oxidized and removed as elemental sulfur and the aqueous 
solution containing the CM PEI 6 Fe (III) is recycled and reused. 
While only a few embodiments of the invention have been shown and described 
herein, it will become apparent to those skilled in the art that various 
modifications and changes can be made in the process to remove H.sub.2 S 
and S.sup.= from fluid streams using a polymeric metal chelate without 
departing from the spirit and scope of the present invention. All such 
modifications and changes coming within the scope of the appended claims 
are intended to be covered thereby.