Fluidization process for removing total reduced sulfur compounds from industrial gases

A process is disclosed for removing total reduced sulfur compounds (TRS), especially H.sub.2 S and mercaptans, from industrial gases wherein substantially dry activated manganese dioxide absorbent particles are fluidized with the industrial gas at an elevated temperature sufficient to effect oxidation of the total reduced sulfur compounds and the absorption of the oxidized compounds on the absorbent particles. In preferred practice, the dried powder containing areas of the oxidized sulfur compounds is recovered as a particle layer in a bag filter unit through which the industrial gas is caused to flow.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a process for the removal of Total Reduced 
Sulfur compounds (TRS), especially H.sub.2 S and mercaptans, from 
industrial gases. More particularly, the present invention relates to a 
moving or fluid bed absorption process employing particulate manganese 
dioxide as an oxidative absorbent and preferably involves enhanced 
absorption by including a bag filter unit downstream of the absorber. 
2. Description of the Prior Art 
Various processes have been proposed for reducing the content of sulfur 
compounds in industrial waste gases. Most of these processes relate to the 
removal of sulfur oxides. Because of their substantial acidic character, 
these sulfur oxides are readily absorbed by alkaline absorbents. 
Unfortunately, the same absorbents are not generally satisfactory for 
removing a number of important industrial byproduct sulfur compounds such 
as hydrogen sulfide, mercaptans and other organic sulfur containing 
compounds, since the acidic character of these compounds is generally much 
less pronounced. This is particularly true of the mercaptans for which 
there is no effective removal process being used commercially. 
In British Patent Specification No. 1,576,534 a process for removing 
hydrogen sulfide from a hot reducing gas is disclosed. The process uses an 
absorbent comprising a mixture of finely divided manganese oxide, i.e., 
manganese of oxidation state 2, and finely divided aluminum oxide. Both 
the absorption and regeneration steps of the patented process require gas 
temperatures substantially higher than those typically encountered in 
industrial applications, for example, in pulping mills. Furthermore, a hot 
sulfur oxide-containing gas is produced by the disclosed high temperature 
regeneration technique, creating additional disposal problems in many 
cases. Moreover, it does not appear that the absorbent can remove 
mercaptans from gas streams. 
U.S. Pat. No. 3,898,320 to Atsukawa uses a dry, powdered absorbent 
comprising a hydrated manganese oxide to remove sulfur oxides from gas 
streams. As described, the sulfur oxides in the gas react with the 
hydrated manganese oxide absorbent to produce manganese sulfate. The 
manganese sulfate is subsequently solubilized in water, converted to 
manganese hydroxide in the presence of ammonium hydroxide and is 
thereafter reconverted to the hydrated absorbent by oxidation with an 
oxygen-containing gas. The oxidation is conducted by bubbling the 
oxygen-containing gas through an aqueous dispersion of the manganese 
hydroxide. As in the prior process, there is not indication that this 
absorbent can be used to remove H.sub.2 S or reduced organic sulfur 
compounds, particularly mercaptans. 
U.S. Pat. No. 3,492,083 to Lowicki, et al., describes a process for 
removing sulfur containing compounds including H.sub.2 S and organic 
sulfur compounds which employs a complex multicomponent absorbent. This 
absorbent includes a metal oxides, hydrated oxide or hydroxide or 
preferably mixtures thereof, for example, manganese dioxide and magnesium 
oxide, in combination with an alkali metal or alkaline earth metal oxide 
or hydroxide, for example, sodium hydroxide. The absorption process is 
conducted at a relatively low temperature but an oxidic roasting at an 
elevated temperature above at least about 750.degree. C. is required to 
regenerate the absorbent. As in the prior British patent, problems with 
disposing a high temperature regeneration gas containing sulfur dioxide 
are created in many cases. 
It is an object of the present invention to provide a process and apparatus 
for efficiently removing H.sub.2 S and organic sulfur-containing 
compounds, and particularly mercaptans, from industrial gas streams. 
It is another object of this invention to provide a process and apparatus 
for removing the aforementioned sulfur compounds from industrial gas 
streams that permits a smooth and continuous operation suitable for 
automation. 
It is a further object of this invention to provide a process for removing 
these sulfur compounds from industrial gas streams which employs a readily 
available absorbent that can be simply and efficiently regenerated by 
ambient temperature oxidation procedures. 
SUMMARY OF THE INVENTION 
These and other objectives which will readily occur to those skilled in the 
art are achieved by the present invention which comprises a process for 
removal of Total Reduced Sulfur compounds from an industrial gas 
comprising the steps of: 
(a) fluidizing substantially dry, activated manganese dioxide absorbent 
particles in a reaction zone with an elevated temperature stream of said 
industrial gas to effect oxidation of said Total Reduced Sulfur compounds 
and absorption of Total Reduced Sulfur compound oxidation products on said 
absorbent particles; 
(b) recovering manganese dioxide absorbent particles containing areas of 
reduced manganous compounds from said reaction zone; 
(c) suspending at least a part of the absorbant particles recovered in step 
(b) in water to produce an aqueous regeneration suspension; 
(d) subjecting at least the aqueous portion of said regeneration suspension 
to liquid phase oxidation to produce an activated manganese dioxide 
absorbent-containing suspension; 
(e) drying the activated manganese dioxide absorbent-containing suspension 
to produce substantially dry, activated manganese dioxide absorbent 
particles; and 
(f) recycling the activated manganese dioxide absorbent to the reaction 
zone. 
The present invention also provides a process for the removal of Total 
Reduced Sulfur compounds from an industrial gas comprising the steps of: 
(a) fluidizing substantially dry, activated manganese dioxide absorbent 
particles in a reaction zone with an elevated temperature stream of said 
industrial gas to effect oxidation of said Total Reduced Sulfur compounds 
and absorption of Total Reduced Sulfur compound oxidation products on said 
absorbent particles; 
(b) recovering from said reaction zone a gas stream containing entrained 
manganese dioxide absorbent particles, said particles containing areas of 
reduced manganous compounds; 
(c) forwarding said gas stream to a bag filter collector and therein 
separating said entrained absorbent particles from said gas stream, said 
particles forming a layer on the filter surface whereby further removal of 
Total Reduced Sulfur compounds from the gas stream is effected; 
(d) recovering said layer of asorbent particles from said bag filter 
collector; 
(e) suspending at least a part of the absorbant particles recovered in step 
(d) in water to produce an aqueous regeneration suspension; 
(f) subjecting at least the aqueous portion of said regeneration suspension 
to liquid phase oxidation to produce an activated manganese dioxide 
absorbent-containing suspension; 
(g) drying the activated manganese dioxide absorbent-containing suspension 
to produce substantially dry, activated manganese dioxide absorbent 
particles; and 
(h) recycling the activated manganese dioxide absorbent to the reaction 
zone. 
In a preferred embodiment of this invention, the manganese dioxide 
absorbent, containing areas of reduced manganeous compounds is regenerated 
(i.e., activated) by: 
(a) providing an aqueous regeneration medium by supplying a flow of 
oxygen-containing gas through said aqueous medium; 
(b) adding to said aqueous regeneration medium at least a part of the 
manganese dioxide absorbent containing areas of reduced manganese 
compounds or an aqueous extract thereof; 
(c) after the oxygen-containing gas flow to step (a) has begun, 
maintaining, by alkaline material addition if necessary, the pH in said 
regenerating medium at an alkaline level sufficient to produce an 
activated manganese absorbent-containing suspension; 
(d) continuing the flow of said oxygen-containing gas through the alkaline 
regenerating medium for a period sufficient to produce an activated 
manganese dioxide absorbent-containing suspension; and 
(e) drying the activated manganese dioxide absorbent-containing suspension 
to produce substantially dry, activated manganese dioxide absorbent 
particles.

DESCRIPTION OF THE INVENTION 
As used in the specification and claims, the term "industrial gas" refers 
to gases produced as products or byproducts in industrial processing 
facilities including, for example, waste gases from pulping mills, 
petroleum refineries, and other chemical manufacturing and refining 
installations. 
The terms "Total Reduced Sulfur compound" herein refers in general to 
sulfur compounds having no substantial acidic character and includes, 
inter alia, H.sub.2 S, mercaptans such as methyl mercaptan, butyl 
mercaptan and the like, organic sulfides such as dimethyl sulfide, 
dimethyl disulfide, dimethyl sulfoxide and similar materials including 
homologs of the foregoing. These Total Reduced Sulfur (TRS) compounds are 
typically toxic and/or ordorous contaminants of various industrial gases 
which must be at least partially removed before releasing the gases into 
the environment or before the gases can be used for other purposes. 
The terms "manganese dioxide" or "MnO.sub.2 " as used in the specification 
and claims refer to both naturally occurring forms, i.e., ores and 
synthetic forms of this compound. In addition, "MnO.sub.2 " materials 
employed as virgin starting material or as regenerated materials can have 
an oxygen content below exact stoichiometric amounts, i.e., slightly less 
than 2. Moreover, it is to be understood that the formula and term also 
cover compounds which may be hydrated. For convenience, all these 
MnO.sub.x materials are simply referred to as MnO.sub.2 or manganese 
dioxide. 
As used herein the terms "moving bed", "fluid bed", "fluidization", 
"fluidizing" and the like pertain generally to those arrangements and 
conditions used in the art for contacting substantially dry solid 
particles with gas wherein the contact causes the particles to exhibit 
quasi-fluid behavior. 
The basic starting material employed in the process of the present 
invention is the MnO.sub.2 absorbent. In order to be useful in the 
absorption process it is necessary that the MnO.sub.2 employed be 
activated. Some sources of MnO.sub.2 by either their nature or their 
method of production possess this activity without special treatment. In 
many cases, however, it is necessary to perform an activation step prior 
to use of the MnO.sub.2 as an absorbent for TRS compounds. According to 
the present invention, this activation is preferably accomplished by 
subjecting the non- or partially-active MnO.sub.2 to at least one 
reduction/oxidation cycle. While this redox cycle treatment can, of 
course, be effected as a separate absorbent preparation step, it is 
preferred to utilize hereinafter-described regeneration steps of the 
present invention to effect or enhance the activation of the absorbent. 
Using this approach, the recycled regenerated material is in effect 
activated by reduction in the moving or fluid bed reaction zone and 
oxidation in the regeneration step. It has also been found that the 
activity of some MnO.sub.2 starting material or unregenerated recycle 
MnO.sub.2 (as described hereinafter) may be increased by merely washing 
the absorbent with water. This may have the effect of removing interfering 
water-soluble salts on the surface of the insoluble MnO.sub.2 materials. 
While initial activities of various MnO.sub.2 materials may vary widely, 
the wet oxidative regeneration step of the present invention results in 
high activity for most MnO.sub.2 materials. This discovery forms an 
important aspect of the present invention. 
In the first step of the process of the present invention substantially dry 
activated MnO.sub.2 particles are fluidized in a reaction zone, e.g., a 
fluid bed 2. The phrase "substantially dry" means that the activated 
MnO.sub.2 particles have a moisture content of less than 10 percent by 
weight. The particles are fluidized by an industrial gas containing Total 
Reduced Sulfur compounds introduced into fluid bed 2 through conduit 1. 
The industrial gas typically can have contaminant levels of TRS compounds 
of at least 10 ppm and preferably at least about 500 and can range up to 
1,000 ppm or more, depending on the source. In addition to the gaseous 
contaminants, many industrial gas streams may also contain particulate 
materials such as alkaline dust or other fly ash type particulates. The 
presence of such materials does not prevent the oxidation and removal of 
TRS compounds but as described later, certain alternative processing steps 
may be required for proper regeneration of an active MnO.sub.2. The 
adsorbent particles are supported above gas introduction point by any 
suitable means, e.g., a screen or perforated plate 4. 
The gas flow rate through the reaction zone can vary depending on the 
nature of the apparatus employed and the conditions of operation. The gase 
flow rates must be sufficient to fluidized the absorbent and is preferably 
high enough to entrain spent adsorbent partices, i.e., manganese dioxide 
absorbent particles containing areas of reduced manganous compounds, for 
collection downsteam thereof, e.g., in a bag house filter. 
In the fluid bed reaction zone, the industrial gas stream and the activated 
manganese dioxide absorbent particles are contacted so that at least a 
part of the TRS compounds are simultaneously removed from the gas by 
MnO.sub.2 oxidation and absorption on the MnO.sub.2 particles. The product 
formed is a dry powder which comprises the MnO.sub.2 absorbent particles 
containing areas of reduced manganous compounds, i.e., the TRS oxidation 
products. The exact nature of all reactions taking place in the fluid bed 
reaction zone is not completely known and will, of course, vary with the 
nature of the industrial gas. In general, however, sulfur containing 
compounds are converted (oxidized) to sulfates or sulfonates while the 
MnO.sub.2 is reduced to a lower valence state, i.e., Mn.sup.++. 
In addition to active MnO.sub.2, the absorbent particles may also include 
alkaline material such as sodium carbonate, sodium hydrogen carbonate, 
sodium hydroxide, or the like, including mixtures thereof. It has been 
found that the oxidation/absorption step proceeds more efficiently when an 
alkaline material is present in the particles. In general, the alkaline 
material can be added in an amount of from about 1% to 10% by weight based 
on the total weight of the absorbent. Preferred are alkaline additions of 
from abut 1% to 3%. As described below, certain industrial gases may have 
significant quantities of alkaline particulates entrained therein. 
The next step of the process is the recovery of spend absorbent particles, 
i.e., the MnO.sub.2 absorbent particles containing areas of reduced 
manganous compounds produced in the fluid or moving bed reaction zone. In 
the broad practice of this invention, this can be accomplished in several 
ways. For example, in the embodiment shown in FIG. 1, a portion of the 
particles is removed directly from the bottom of the fluid bed reaction 
zone. The remaining portion of the particles is carried out of the fluid 
bed as entrained particles in the scrubbed gas stream 5. This stream is 
fed to a collector unit 6 described below. In the collector unit, the 
remainder of the particles is separated from the gas stream, the former 
being recovered from the collector unit (line 7) and the latter being 
forwarded to stack 8 for discharge to the atmosphere. In the preferred 
manner of operation, all the particles are entrained in the gas and are 
recovered from the collector unit. 
While collector unit 6 may broadly comprise a cyclone, an electrostatic 
precipitator or a bag filter unit or baghouse, a bag filter or baghouse is 
preferred. In the bag filter unit the absorbent particles form a layer on 
the upstream surface of a gas permeable filter fabric through which layer 
all the gas that enters the unit is constrained to pass. As will be more 
particularly illustrated in the examples hereafter, this arrangement 
provides an extremely efficient contact between the gas and the manganese 
dioxide absorbent particles due to lower void volume in the filter fabric 
than in the fluid bed. As a result, surprisingly substantial further 
absorption of TRS compounds takes place in the bag filter unit. 
As noted above, it is preferred to remove all of the spent absorbent from 
the reaction zone 2 via entrainment in the fluidizing gas. This can be 
accomplished by using a flash duct or fast fluid bed for reaction 2. In 
these arrangements, the gas velocity is high enough to entrain all of the 
absorbent particles in the gas to the collection device 6. 
The spent absorbent material collected in the bag filter collector unit 6 
and removed therefrom through outlet 7, possibly together with absorbent 
material recovered through outlet 3, may be divided into two portions; the 
first of which is recycled through conduit 9 for directly re-introducing 
it into fluid bed reaction zone 2. The remaining portion of the absorbent 
material is passed through conduit 10 to an oxidative regeneration section 
11, which, within the scope of the present invention, may comprises 
various operations. Alternatively, the total amount of absorbent material 
recovered through outlets 3 and 7 may be passed to the regeneration 
section. 
Regeneration generally is effected by liquid phase oxidation of Mn.sup.++ 
compounds resulting from the reactions taking place in the fluid bed 
reaction zone. The products of regeneration include an insoluble 
reactivated MnO.sub.2 -containing stream 12 and stream 13 containing 
soluble sulfur-containing compounds which can be removed (bled) from the 
system by separating all or a part of the aqueous regeneration products. 
Among the suitable liquid phase oxidation techniques are electrolytic 
oxidation (i.e., oxidation by nascent oxygen) and treatment with various 
oxidizing agents such as oxygen-containing gases (e.g., air), ozone, 
peroxides, persulfates, permanganates, hypochlorites, perchlorates, 
hypochlorates, and the like. Preferably, these techniques are carried out 
at ambient temperatures although somewhat higher or lower temperatures may 
be employed as long as the liquid system is not adversely affected, e.g., 
by boiling or freezing. 
In general, there are two basic procedures for effecting this liquid phase 
oxidative regeneration. As indicated above, the spent absorbent material 
contains areas of reduced Mn values, possibly as Mn.sup.++ salts. The 
first and most preferred approach is to suspend this material in water and 
subject the entire suspension to oxidation. While not wishing to be bound 
to any particular theory, applicants believe that oxidation of Mn.sup.++ 
values may take place at or on the surface of the spent absorbent 
particles and/or in the aqueous phase due to solubilization (extraction) 
of these values. In any event, the regeneration of MnO.sub.2 from 
Mn.sup.++ values is best accomplished by oxidizing the complete aqueous 
suspension (possibly containing both absorbed and extracted Mn.sup.++ 
values). In an alternative embodiment, it is possible to rely solely on 
extraction to provide Mn.sup.++ values for regeneration, in which case, 
the aqueous suspension can be separated (e.g., by filtration decantation, 
etc.) into a solid unreacted MnO.sub.2 fraction and an aqueous fraction 
and only the aqueous fraction subject to oxidation of the type described 
above. Generally, the particle size of the regenerated material produced 
using this alternate option is too small for optimum operation of the 
fluid bed reaction zone. In either case, the solubilized sulfur containing 
salts can be removed from the system by bleeding out all or a portion of 
the aqueous phase. 
An important advantage of the process of the present invention is the 
ability to bleed off the soluble oxidation products (i.e., sulfates, 
sulfonates, sulfinates and the like) and the resulting elimination of the 
counterproductive need to regenerate the oxide by high temperature 
heating. In the context of paper mill gas effluent treatment, some part of 
the bleed-off solution from the regeneration of manganese dioxide can be 
sent to the recovery boiler where it will be converted into sodium sulfate 
suitable for reuse in the pulping process. Generally, sodium ions will 
also be present in the aqueous phase (bleed-off) removed from the system. 
This bleeding or partial dewatering can be effected by a number of 
techniques which include, inter alia, sedimentation, wet cycloning, 
centrifuging, filter pressing and the like. 
Both of the above-described approaches will now be described in connection 
with the preferred type of oxidative regeneration--that employing an 
oxygen-containing gas (e.g., air) as the oxidizing agent. 
The preferred embodiment of this procedure is illustrated in FIG. 2. An 
oxidizing vessel 14 is provided with means for aerating the contents 
thereof with an oxygen-containing gas. Air will generally be used because 
of economic considerations. Although nozzles 15 are illustrated as the 
means for introducing the gas into vessel 14, other means including 
aerators of the surface or submerged variety may also be used. Such 
aerating means are well known to one skilled in the art. 
The next step involves adding the spent absorbent material 10 to this 
aerated aqueous medium (i.e., suspending the powder). An important feature 
of this preferred regeneration procedure is the establishment of a 
well-aerated aqueous medium in vessel 14 before the absorbent material to 
be regenerated is introduced thereto. 
Another parameter which appears important in this preferred regeneration 
scheme is the pH of the aerated aqueous medium. The oxidative regeneration 
is based primarily on the following overall reacton: 
EQU 2Mn.sup.++ +O.sub.2 +4OH.sup.- .fwdarw.2MnO.sub.2 +2H.sub.2 O 
While not wishing to be bound to any particular therory, it is believed 
that this overall rection actually proceeds via the precipitation of an 
intermediate Mn(OH).sub.2 which in turn is oxidized to MnO.sub.2. This 
reaction via Mn(OH).sub.2 proceeds most efficiently under alkaline pH 
conditions. While the exact pH necessary to effect production of an 
activated MnO.sub.2 absorbent (e.g., by Mn(OH).sub.2 precipitation) can 
vary widely dependent on the nature of the absorbent and its concentration 
in the slurry, in general, the slurry pH should be adjusted (unless 
already alkaline) to a value of at least 7 or above and preferably in the 
range of from about 9 to 12.5. The proper pH for any particular 
regeneration system can be determined experimentally. If the pH is too low 
or too high, an active MnO.sub.2 is not produced. 
Since the above reaction indicates a consumption of hydroxide ions, it may 
be necessary to provide for a continuous addition of alkali to the vessel 
10 as indicated by the dotted line 16. However, since a sufficient amount 
of alkali will often be present in the material to be regenerated through 
line 10, the addition of further alkaline material may not be necessary. 
The proposed Mn(OH).sub.2 intermediate reaction route is also primarily 
responsible for the requirement of starting the flow of oxygen-containing 
gas at the very beginning of the regeneration process. It has been found 
that sufficient oxygen must be present at the very moment of formation of 
insoluble Mn(OH).sub.2 precipitate so it can be immediately oxidized to 
MnO.sub.2. If Mn(OH).sub.2 is allowed to age before oxidation takes place, 
crystallization of the hydroxide will occur making oxidation to an active 
form of MnO.sub.2 difficult or impossible. 
As noted before, a particularly advantageous feature of the present 
invention is that the oxidative regeneration can be performed at ambient 
temperatures and at average residence times on the order of a few hours. 
The regeneration may be performed in a batchwise fashion or as a 
continuous process. 
When substantially all of the manganous compounds have been converted into 
an activated manganese dioxide, the resulting suspension may be passed to 
a separator 17, for example, a sedimentation vessel, a centrifuge, or a 
filter. In the separator, most or all of the aqueous solution is removed 
through conduit 18. A primary purpose of this separator is to bleed off 
soluble sulfur containing compounds. 
The manganese dioxide recovered from the separator 17 is then generally 
recycled to the fluid bed reaction zone 2. The activated absorbent can 
normally be introduced into the reaction zone as an aqueous suspension, 
having about 10 to about 50% solids by weight, and is dehydrated therein 
to produce substantially dry, activated MnO.sub.2 absorbent particles. The 
absorbent suspension is introduced into the fluid bed reaction zone 
through an appropriate device, e.g., a rotary disc, to facilitate the 
fluidization of the moist material. Consequently, the fluid bed reaction 
zone typically consists of a heterogeneous mass of particles; some 
particles having little or no aqueous material, and others having a small 
amount of an aqueous phase. The manganese dioxide produced in the 
regeneration step by oxidation of manganese ions possesses an activity for 
the absorption of TRS compounds on the same level as the most efficient 
manganese dioxide materials commercially available. 
An alternative approach to regeneration is illustrated in FIGS. 3 and 4. 
This approach is based generally on the regeneration of an aqueous extract 
of the dry powder produced in the spray dryer. The differences between the 
embodiments of FIGS. 3 and 4 are to accommodate different types of feed 
materials. When the spent absorbent material resulting from the fluid bed 
reaction zone has only a low content of highly basic components, the 
scheme of FIG. 3 can be used. However, when the gas to be treated has 
substantial amounts of entrained alkaline dust or the aqueous feed 
suspension contains highly basic additives, e.g., NaOH, the embodiment of 
FIG. 4 should be used. 
Referring to FIG. 3, the material to be regenerated 10 is mixed with water 
in tank 19, i.e., the dry absorbent articles are suspended to form an 
aqueous regeneration suspension. The suspension is forwarded to a 
separator 20, e.g., a centrifuge setting vessel or cyclone, in which the 
solids (MnO.sub.2) are recovered for direct recycling to fluid bed 
reaction zone 2 (FIG. 1). The aqueous extract solution 21 is then added to 
an aerated aqueous medium in vessel 14 as described above. Thereafter, a 
basic solution, such as an aqueous sodium carbonate solution, is added to 
the aeration vessel through line 22. This results in simultaneous 
precipitation and oxidation of the manganous ions to give an active 
MnO.sub.2 product. The remainder of the regeneration process proceeds as 
described in connection with FIG. 2. 
If the TRS compound-containing gas also contains considerable amounts of 
alkaline materials, as might be the case when the gas is a waste gas 
originating from the regeneration furnaces of a pulping mill, the 
embodiment of FIG. 4 can be used for regeneration of the spent absorbent. 
The waste gases from pulping mills generally contain sodium carbonate and 
sodium sulfate as fine particles, which are not easily removed before the 
gas is subjected to the cleaning procedures according to this invention. 
This means that a substantial amount of sodium carbonate and other 
alkaline materials will be present in the spent absorbent material 
delivered through conduit 10. If such a material is subject to the 
regeneration treatment described in connection with FIG. 2, it appears 
that the formation of such manganous compounds as manganous hydroxide and 
manganous carbonate takes place before the oxidation required to yield 
active manganese dioxide can occur. Indeed, even prolonged contact with 
the oxygen-containing gas will not transform these compounds into a 
product having sufficient activity in the absorption process. Therefore, 
regeneration of spent absorbent having a high alkali content preferably 
takes place as illustrated in FIG. 4. 
In FIG. 4 is shown a mixing tank 23 into which the absorbent material to be 
regenerated is introduced through line 10 and is mixed with water to form 
an aqueous regeneration suspension therein. The suspension 24 is conducted 
to a separator 25 and separated into an aqueous phase 26 and a thickened 
slurry of the absorbent material 27. At this point the slurry may have a 
pH exceeding 10. 
The thickened slurry of absorbent material 27 is fed to a treatment tank 28 
in which it is treated with a diluted acid, preferably sulfuric acid, 
introduced through conduit 29 to effect dissolution (extraction) of 
manganous values not extracted in the aqueous resuspension step. Adjusting 
the slurry to a pH of generally less than about 4 has been found to be 
suitable to accomplish this result. Since minor amounts of hydrogen 
sulfide may be generated by this procedure, venting means 39 are provided 
for venting any gases released in tank 28 to a location upstream of the 
fluid bed reactor 2. 
The acidified slurry 30 containing undissolved MnO.sub.2 is forwarded to 
separator 31 where MnO.sub.2 is recovered. The aqueous Mn.sup.++ acid 
extract 32 is thereafter supplied to oxidation vessel 14 operation as 
described in connection with FIG. 2. The alkaline extract medium from 
separator 25 is added to oxidizing tank 14 via conduit 33, after partial 
purge of this line, if desired, shown at 34. 
The activated MnO.sub.2 suspension produced in oxidation vessel 14 can be 
recycled via line 35 to conduit 24 resulting in recovery of MnO.sub.2 from 
separator 31. In this scheme any insoluble manganous compounds not 
oxidized in vessel 14 will be dissolved in tank 28 and thereby recycled to 
oxidation tank 14. 
In an illustrated alternative embodiment shown in dotted lines on FIG. 4, 
the acidified slurry from tank 28 is fed directly to vessel 14 via line 
36. In this approach the MnO.sub.2 solids are fed to the oxidizer along 
with the alkaline and acidic extract products. Instead of using recycle 
line 35, the MnO.sub.2 solids can be recovered in separator 37. 
The recovered aqueous phase 38 may be purged or used as a supplemental 
alkaline material for addition to oxidation vessel 14. In addition to the 
alkaline solution introduced through line 33 (or 38), the oxidation tank 
14 may also receive basic materials from other sources (not shown) if 
required for adjusting the alkalinity. 
The following examples are intended to illustrate more fully the nature of 
the present invention without acting as a limitation on its scope. 
EXAMPLE 1 
An amount of MnO.sub.2 was prepared by spraying a solution of MnSO.sub.4 
(10%) into a container which was aerated by means of nozzles. The pH of 
the solution in the container was continuously adjusted to 9 by addition 
of aqueous sodium hydroxide. Aeration was continued for one hour after the 
addition of the MnSO.sub.4 solution was completed. The precipitated 
MnO.sub.2 was washed several times, filtered and dried in an oven at 
105.degree. C. A sample of the prepared MnO.sub.2 was analyzed by the 
oxalate method and the composition found to be MnO.sub.1.70. 
A synthetic effluent gas mixture containing on a dry basis 250 ppm (by 
volume) H.sub.2 S, 2% by volume O.sub.2, the rest being N.sub.2 was 
treated in a laboratory fluid bed with recycling of particles entrained by 
the gas as illustrated by the dotted line in FIG. 1. 
The gas has a temperature of 150.degree. C. and a relative humidity of 0.05 
and was fed to the fluidized bed reaction zone previously charged with 
manganese dioxide prepared as described above. 
The fluidizing velocity of the gas was 0.3 m/s corresponding to a residence 
time for the gas in the fluid bed of 3-4 s. 
A substantial 100% absorption of H.sub.2 S was observed until the MnO.sub.2 
in the fluid bed had absorbed 25 g H.sub.2 S per kg MnO.sub.2. Continuing 
the test after such an amount of H.sub.2 S had been absorbed, the 
absorption efficiency decreased slowly and reached 60% when about 70 g 
H.sub.2 S per kg MnO.sub.2 had been absorbed. 
The reacted MnO.sub.2 was analyzed for SO.sub.4.sup.-2 using an ion 
chromatograph by the following 3 methods: Method 1: The material was 
extracted with water (stirring for 30 minutes) and the filtrate analyzed 
for SO.sub.4.sup.-2 ; method 2: same as method 1 except that the 
extraction was done with 0.5 N HCl; method 3: same as method 1 except that 
the extraction was done with a mixture of 0.5 N HCl and 3% H.sub.2 
O.sub.2. Methods 1 and 2 gave identical results while method 3 showed a 
small increase in SO.sub.4.sup.2- content per gram of sample compared to 
the other methods, showing that about 98% of sulphur was in the form of 
sulphate and the rest as free sulphur. 
The material from the fluid bed absorption experiment was washed carefully. 
A sample of this washed material was analyzed by the oxalate method and 
the composition found to be MnO.sub.1.70. The rest of the washed material 
was used for fluid bed absorption and was found to have regained 
efficiency and capacity for absorbing H.sub.2 S. 
The washing, which contained MnSO.sub.4 formed by the absorption, was 
subjected to an oxidation as described in the first paragraph of this 
Example. A black powder corresponding to the formula MnO.sub.1.7 was 
produced The activity as to absorption of H.sub.2 S was as high as the 
activity of the originally produced material. 
EXAMPLE 2 
This example was performed as described in Example 1 except that CH.sub.3 
SH was substituted as an impurity for the H.sub.2 S. In this case the 
absorption was 100% until 5 g of CH.sub.3 SH per kg MnO.sub.2 had reacted. 
Again ion chromatography showed that the reaction product consisted almost 
entirely of MnSO.sub.4. The reaction material regained its activity by 
washing, and oxidation as described above in connection with Example 1. 
EXAMPLE 3 
This example demonstrates the use of an oxidizing agent such as sodium 
hypochlorite in the ambient temperature, liquid phase oxidative 
regeneration of spent MnO.sub.2 absorbent. The spent MnO.sub.2 was 
resuspended in water and was activated (oxidized) by treatment with 10% 
(W/W) of a sodium hypochlorite solution containing 12.3% (W/W) active 
chlorine. The recovered precipitate exhibits the desired activity for TRS 
compounds. 
EXAMPLE 4 
This example demonstrates the regeneration of spent MnO.sub.2 absorbent 
employing the embodiment of FIG. 2. The spent MnO.sub.2 was resuspended 
in water at a concentration of 10% solids. After mixing for thirty 
minutes, stirring was discontinued and the MnO.sub.2 was allowed to settle 
over a three hour period. Thereafter, the clear supernatant solution 
containing soluble manganous ions was treated with 2% (W/W) sodium 
hypochlorite solution containing 15% (W/W) active chlorine. The resulting 
slurry was then mixed for about two hours, during which time a fine 
precipitate of MnO.sub.2 formed. The resulting slurry was washed three 
times with water; the slurry was allowed to settle after each washing. The 
recovered precipitate exhibits excellent activity for mercaptan removal. 
EXAMPLE 5 
This example demonstrates the regeneration of spent MnO.sub.2 absorbent 
employing the embodiment of FIG. 3. Dry powder produced in the spray dryer 
absorber (see Example 1) and recovered from the bag filter was washed with 
water to form an aqueous extract solution containing soluble Mn.sup.++ 
values. This extract solution was placed in an aerating vessel and the 
flow of air bubling through was started. The pH of the aerated aqueous 
medium was then adjusted to a valve above 10-11. After about 16 hours the 
reaction was stopped, the mixture filtered. The black filter cake 
(MnO.sub.2) was as active as the original material employed. 
EXAMPLE 6 
This example demonstrates the regeneration of spent MnO.sub.2 absorpbent 
employing the embodiment of FIG. 4. Dry powder (4.9 g) from the spray 
dryer absorber produced using an MnO.sub.2 absorbent containing 
NaHCO.sub.3 was treated with 100 ml. of a 10% (W/W) solution of H.sub.2 
SO.sub.4 at 50.degree.-60.degree. C. The suspension was filtered and the 
aqueous acid extract containing Mn.sup.++ was diluted to 300 ml. and 
placed in an aerating vessel. After the flow of air was established, 150 
ml. of 1.2M NaOH were slowly added while stirring and a brown precipitate 
formed. After one hour the reaction was stopped and the mixture was 
filtered to recover a MnO.sub.2 absorbent which proved to be as active as 
the original one. 
While certain specific embodiments of the invention have been described 
with particularity herein, it will be recognized that various 
modifications thereof will occur to those skilled in the art. Therefore, 
the scope of the invention is to be limited solely by the scope of the 
appended claims.