Note: Descriptions are shown in the official language in which they were submitted.
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C;AS TREATING PROCESS
FIELD OF INVENTION:
The ~.ese,.l invention relates to a ~rucess for removing water, low
5 II.DI~ ~ weight h~ oca-Lo,.s and/or ca.~on ~ cide in ~d~ ;Gn to hycJr~6..
sulfide from a ~ceol ~s str~am in one pr~-~3ss i. .~ unit, and more particularly, to
such a ~rocess for removing and recovering water, low IIIDI~ wsight
hycl-o~-l,G--s and/or cal~GII dioxids from a ~ses~C stream in a single
~Jrocessing unit wherein hydlo~en sulfide which is initially contained in the
10 DPseo~ls feed stream is also converted to elemental sulfur in the same
pr~csssi. ,~ unit.
DESCRIPTION OF RELATED ART:
Numerous industrial ~,.vcesses, particularly those pertaining to the
petroleum industry, ~e. .e.~le g~-ceo~ ~-s by-products containing hy.lro~en sulfide,
15 either alone or in a mixture with water and/or other gases, such as, methane,carbon dioxide, low mole~ ~ weight hydl uca- L,ons, ~ luyel l, a..,...G"ia etc. In
addition, natural gas which is produced from subterranean ficr.,.dlions often
cc:,. ~l~i. .s similar gases to those D~ses~ ~-s by-products llsted above.
Many ~.uc~sses have been developed to remove these COIII~JUI .~. .ls from
20 such ç~as ~ dlllS prior to tran:,pG. tdliol . and~or further p~ ssi. ~a ll .ereof. For
example, U. S. Patent No. 3,039,251 (Kamlet~ scloses simulld. .eously
removing water, hy.lr~gen sulfide, ..,er~apta..s and CalL~GIl ~ e from gas,
such as natural gas, by conlac~i--g said gas with tetrahydrothiophene-1, 1-
dioxide (s~ ~rul -- .e) or homologues thereof. U. S. Patent No. 4,359,450 (Blytas
25 et al.) ~liscloses the removal of It2S CO2 and COS from ~seo~s slrea...s
d .~ by the r~a~tiGI I of H2S to crystalline or solid sulfur, the abSGI ~,lics. I
of CO2 and COS, the desorption of CO2 and COS, the hydrolysis of COS, and
the recovery of H2S. In acco~a..ce with the first step of the ~,rucess, the
~ceo~ ~-s stream is conla-,tt:d with an absorL,e"L mixture CGI ,la;"ing an oxidizing
30 reactant. The absorbent employed are those absorbents which have a high
degree of selectivity in abso,l,i.,g CO2, COS and H2S, such as propylene
carbonate, N-methyl pyrrolidone, and sulfolane. U. S. Patent No. 3,773,896
(Preusser et al.3 ~iscloses a process or washing the ~seo~ ~s acidic
SUBSTITUTE SHEET (R~JLE 26~
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components such as carbon dioxide, hydrogen sulfide and hydrogen cyanide
from a gas stream by treating the gas stream with a washing agent that absorbs
at least a portion of the gaseous acidic components. The washing agent
includes a carboxylic acid amide of morpholine preferably containing between
1 and 7 carbon atoms in the carboxyiic acid chain. Propylene carbonate and
sulfolane are identified as previously known washing agents. However, all of
these prior art processes require further steps or stages to treat hydrogen
sulfide by converting it to products which have further utility, such as sulfur,hydrogen, or hydrogen peroxide.
~0 Further, many processes relating to the petroleum industry generate
gaseous by-products containing hydrogen sulfide, either alone or in a mixture
with other gases, for example, methane, carbon dioxide, nitrogen, ammonia etc.
For many years, these gaseous by-products were oxidized by common
oxidation processes, such as the Claus process, to obtain sulfur. In accordance
with the Claus process, hydrogen sulfide is oxidized by direct contact with air to
produce sulfur and water. However, several disadvantages of air oxidation of
hydrogen sulfide, including loss of a valuable hydrogen source, precise air ratecontrol, removal of trace sulfur compounds from spent air, and an upper limit onthe ratio of carbon dioxide to hydrogen sulfide, led to the development of
alternative processes for the conversion of hydrogen sulfide in gaseous by-
products to sulfur.
As detailed in U. S. Patent No. 4,592,905 to Plummer et al., one such
alternative process involves contacting within a reactor a feed gas containing
hydrogen sulfide with an anthraquinone which is dissolved in a polar organic
solvent. This polar organic solvent preferably has a polarity greater than about3 Debye units. The resulting reaction between hydrogen sulfide and
anthraquinone yields sulfur and the corresponding anthrahydroquinone. The
sulfur precipitates from the solution in crystalline form and is recovered as a
product while the l ~" ,aini"g solution containing dl Ill 11 dh ydroquinone is thermaliy
or catalytically regenerated producing the initial anthraquinone form and
releasing hydrogen gas. The anthraquinone is recycled back to the reactor and
the hydrogen gas is recovered as a product. A significant disadvantage of this
process is that the reaction between hydrogen sulfide and anthraquinone
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proceeds at a relativeiy slow rate, thereby limiting reactor throughput. Anotherdisadvantage of this process is that the feed gas must be cG~I~pressed to
provide H2S partial pressures of from about 6 to about 200 atmospheres which
significantiy increases the reactor cost. A further disadvantage of this processis that hydrogenolysis by-products, i.e. anthrones and anthranols, produced
during anthrahydroquinone regeneration reduce the selectivity of producing
hydrogen and anthraquinone.
Thus, a need exists for a process for removing water, low molecular weight
hydrocarbons andlor carbon dioxide as products in addition to hydrogen sulfide
from a gaseous stream in a single processing unit while converting hydrogen
sulfide which is initially contained in the g~seous feed stream to a useful product
in the same processing unit. A further need exists for a process for increasing
the rate which hydrogen sulfide reacts with quinone in the ~)rocess for converting
hydrogen sulfide to sulfur and hydrogen as described above, while decreasing
the tl.S partial pressure of such reaction.
Accol d;, Igly, it is an object of the present invention to provide a process for
rernoving water, low molecular weight hy.li oca, bons andlor carbon dioxide as
products in addition to removing hydrogen sulfide from a gaseous stream while
converting hydrogen sulfide which is initially contained in the gaseous feed
stream to elemental sulfur in the same processing unit.
It is another object of the present invention to provide a such a process for
the concurrent removal of hydrogen sulfide from a gaseous stream and
conversion of hydrogen sulfide to sulfur which is economical.
It is still another object of the present invention to provide a process for
increasing the rate of reaction between hydrogen sulfide and a quinone which
is dissolved in a polar organic solvent.
It is a further object of the present invention to provide a process for
increasing the rate of reaction between hydrogen sulfide and a quinone while
significantly decreasing the partial pressure of hydrogen sulfide in the gaseousfeed.
It is a still further object of the present invention to provide a process for
increasing hydrogen production selectivity during dehydrogenation of
hydroquinone.
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SUMMARY OF THE INVENTION
To achieve the foregoing and other obiects, and in accor~la, Ice with the
purposes of the present invention, as embodied and broadiy described herein,
one cha, d~ri~dlio" of the present invention is a ,c rocess of removing hydrogensulfide and other components from a gas. The process coll~p,ises co"La~ g
2 gaseous stream containing hydrogen sulfide with a polar organic solvent
having a quinone dissolved therein. S~ ILidliy all of the h~dluyel) sulfide and
at least a portion of a second component of said gaseous stream which Is
selected from the group consisting of water, low molecular weight hydl~ GI~S,
carbon dioxide or mixtures thereof are dissolved in said polar organic solvent.
In another cl ,a,aclel i~dlion of the present invention, a f~rc cess is providedfor decomposing hydrogen sulfide to sulfur and hydrogen. The process
comprises contacting a gaseous stream containing hydrogen sulfide with a
polar organic solvent having a quinone dissolved therein. Substantially all of the
hydrogen sulfide and at least a portion of a second component of said gaseous
stream which is selected from the group consisting of water, low molecular
weight hydrocarbons, carbon dioxide or mixtures thereof are dissolved in said
polar organic solvent. The hydrogen sulfide is reacted with the quinone to
produce sulfur and a hydroquinone in the solvent. The hydroquinone is
dehydrogenated to the corresponding ~uinone and hydrogen.
BRIEF DES~:RIPTION OF THE DRAWINGS
The ac.;o",,ua"~/ing drawings, which are incorporated in and form a part o~
the specification, illustrate the embodiments of the present invention and,
together with the description, serve to explain the principles of the invention. In the drawings:
FIG. 1 is a graph which depicts the rate constants of the two separate
mechanisms for conversion of t-butyl anthraquinone ~TBAQ) to t-butyl
anthrahydroquinone ~H1TBAQ) as a function of the pKb value of different
complexing agents which are dissolved together with TBAQ into a polar organic
solvent;
,
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FIG. 2 is a graph which depicts the activation energy of the two separ~le
mechanisms for conversion of t-butyl anthraquinone (TBAQ) to t-butyl
anthrahydroquinone (H2TBAQ) as a function of the pKb value of different
complexing agents which are dissolved together with TBAQ into a polar or~~anic
solvent;
FIG. 3 is a graph which depicts the conversion of t-butyl anthraquinone
(TBAQ) to t-butyl anthrahydroquinone (H2TBAQ) as a function of the ratio of
diethylmethylamine (DEMA) complexing agent to TBAQ which are dissolved
together into a polar organic solvent;
FIG. 4 is a graph which depicts the rate constants of the two separate
mechanisms for conversion of t-butyl anthraquinone (TBAQ) to t-butyl
anthrahydroquinone (H2TBAQ) as a function of the partial pressure of hydrogen
sulfide in the reactor for feed gases having varying ratios of hydrogen sulfide to
carbon dioxide;
1~ FIG. 5 is a graph which depicts sulfur recovery achieved in accor~ar,ce
with the process of the present invention as a function of the partial pressure of
hydrogen sulfide in the reactor;
FIG. 6 is a graph which depicts hydrogen production selectivity as a
function of the ratio of complexing a8ent to total quinone, i.e. t-butyl
anthrahydroquinone (H2TBAQ) and t-butyl anthraquinone (TBAQ), during the
dehydrogenation of t-b~tyl anthrahydroquinone in the presence of platinum
catalysts;
FIG. 7 is a graph which depicts hydrogen production selectivity as a
function of the pKb value of different complexing agents which are dissolved
2~ .together with t-butyl anll " al ,ydroquinone ~H2TBAQ) into a polar organic solvent
in dehydrogenation reactor feeds;
FIG. 8 is a graph which depicts the conversion of t-butyl anthraquinone
(TBAQ) to t-butyl anll"ahydroquinone (H2TBAQ) as a function of the number of
injection stages for hydrogen sulfide (H2S) into the ~2S-TBAQ reactor;
FIG. 9 is a graph which depicts sulfur (S~) recovery, as the weight percent
of the total S atoms formed in the conversion of t-butyl anthraquinone (TBAQ)
to t-butyl anthrahydroquinone (H2~BAQ), as a function of the number of injectionstages for hydrogen sulfide (tl2S) into the HzS-TBAQ reactor;
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FIG. 10 is a graph which depicts sulfur (S") recovery as a function of the
molar ratio of water to t-butyl anthraquinone (TBAQ) in the process of the
present invention; and
FIG. 11 is a semi-log~ ill ""ic graph which depicts the hydrogen production
seiectivity as a function of the dehydrogenation temperature for separate
reaction solutions, one of which does not contain water and another of which
contains one mole of water per mole of t-butyl anthraquinone (TBAQ) added
prior to the sulfur production stage of the process of the present invention.
DETAI~ED DESCRIPTION OF THE PREFE~RED EMBOD~NIENTS
The present invention relates to the removal of water, low molBcl ll~r weight
hydrocarbons, for example ethane, propane, butanes, pentanes and hexanes
and/or carbon dioxide in addition to hydrogen sulfide from a gaseous stream in
2 single processing unit wherein hy~ e, I sulfide which is initialiy contained in
the gaseous feed stream is also converted to elemental sulfur in the same
processing unit. Water, iow molecular hydrocarbons, and carbon dioxide which
are removed from the gaseous stream can be recovered as separate products.
In accordance with the process of the present invention, the gaseous feed
conLai, ling hydrogen sulfide ~H2S) is contacted in an H2S absorber with a polarorganic solvent having a quinone and a H2S complexing agent dissolved therein.
The solvent solubilizes hydrogen sulfide from the feed gas to form a reaction
solution which is transported to and maintained in a polymerization reactor at atemperature and a pressure, as hereinafter discussed, and for a time which is
sufficient to convert the hydrogen sulfide and quinone to sulfur and
hydroquinone. The solvent also solubilizes in the absorber significant portions
of the water, low molecular weight hydrocarbons, i.e. C2 - C6, and/or carbon
dioxide present in the gaseous feed stream. In addition, the feed gas may
conlai,l other sulfur compounds, such as COS, CS2 and mercaptans, which are
dissolved in the polar organic solvent and converted in the process to H2S,
recycled to the absorber andfor reactor, and converted to sulfur. Although
described throughout this description as separate components of a single
processing unit, the absorber and polymerization reactor may be a single
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reaction vessel, for example a s~irred tank, in which both functions are
performed.
In accordance with the present invention, the number of injection stages
utilized to introduce the hydrogen sulfide containing feed gas into the absorberor reactor where the gas is contacted with a polar organic solvent containing a
quinone and a H2S complexing agent is a factor which siyl ,iricanLly increases the
conversion of quinone to hydroquinone and elemental sulfur and to ensure the
desired S" sulfur precipitate is formed. The number of injection stages employedto introduce the hydrogen sulfide feed gas into the reactor or absorber is
preferably 1 to 6, more preferably 2 to 5 and most preferably 4.
Although not completely understood, the conversion of quinone to
hydroquinone in the i-i2S absorber andlor polymerization reactor is believed to
occur in accordance with five overall chemical mechanisms. First, the polar
organic solvent forms a charge-Lt~" ;rer complex with the quinone ("mechanism
1"). Secondly, H2S reacts with a complexing agent ("CA") to form an ion
complex ("mechanism 2") in accordance with the following general reaction:
CA + H2S - CAH+HS- (ion complex)
In the conversion of quinone to hydroquinone in the H2S absorber and/or
polymerization reactor, sulfanes (i.e., H2SX where X generally equals zn integerfrom 2 to 20) may be formed. These sulfanes can also react with the
complexing agent to form ion complexes which have utility in accordance with
the present invention. Next, the ion complex reacts with the solvent-quinone
compiex in two steps to form elemental sulfur and hydroquinone ("mechanism
3a and 3b"). Lastly, a reaction occurs which poiymerizes elemental sulfur (S)
to polymerized sulfur (S~) which then precipitates out of solution ("mechanism
4").
In accordance with the present invention, applicants have discovered that
utilizing a polar organic solvent in conjunction with a complexing agent, which
has been selected in accordance with certain parameters set forth below,
unexpectedly results in very high conversions of quinone to hydroquinone in
extremely short periods of time. Further, these results have been achieved at
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reactor temperatures and H2S partial pressures which unexpectedly are
significantly lower than previously thought to be required.
The polar o,~anic solvent utiiized in the process of the present invention
is chosen to have a high polarity and yet remain stable at dehydrogenation
temperatures Suitable polar organic soivents include N-methyl-2-pyrolidinone,
N,N-dimethylacetamide, N,N-dimethylformamaide, sulfolane
(tetrahydrothiophene-1, 1 -dioxide), acetonitrile, 2-nitropropane, propylene
carbonate and mixtures thereof. The most preferred solvent is N-methyl-2-
pyrrolidinone (NMP).
A complexing agent is also incorporated into the polar organic solvent in
accordance with the present invention. This complexing agent is believed to
react with H2S in accordance with mechanism 2 to form an ion complex
(CAH ' I IS~). Thus, selection of a suitable complexing agent is based in part upon
the ability of the complexing agent to react with H2S to form an ion complex.
The complexing agent must also be chosen upon its ability to increase the rate
consla"~s for mechanisms 3a and 3b while decreasing the activation energies
for mechanisms 3a and 3b. It has been discovered that the basicity of these
complexing agents, as measured in units of pKb, directly correlates to the
increase in rate constants of mechanisms 3a and 3b. In general, employing a
complexing agents of decreasing pKb value in the process of the present
invention will increase the formation of the ion complex and the rate COI ~sLa"l of
mechanism 3a (FIG. 13. In addition, as complexing agent basicity is increased,
i.e. p~ decreased, the activation energies of mechanisms 3a and 3b are
decreased (FIG. 2). "A~tivation ener~y" represents the energy level required to
activate 1 mole of reactants to a state sufficiently above the average energy
level of all molecules such that reaction may occur. Thus, use of a complexing
agent of high basicity results in increased ion complex formation and therefor
increased conversion of quinone. In accor~d~ ~ce with the present invention, thePKb Of complexing agents is less than about 13.0, more preferably less than
about 9.0, and most preferably less than about 6Ø The pKb values are based
on KW (equilibrium constant) of 14.0 for the dissociation of water. Suitable
complexing agents are se~ected from amines, amides, ureas, nitrogen
conlai, ling heterocyclic aru,))dlics, quanidines, imidazoles, and mixtures thereof.
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These complexing agenl:s can also be substituted with alkyl, aryl and organic
alcohol groups. Examples of suitable complexing agents are n-
methylacetamide, pyridine, substituted pyridines, diethylmethylamine, tri-
butylamine, methyldiethanolamine and tetramethylurea. The preferred
complexing agents are diethylmethylamine ~DEMA~, methyldiethanolamine
(MDEA), tri-butylamine, pyridine (PY), and substituted pyridines. Additionally,
it is believed that those complexing agents which contain a hydrogen bonding
proton, for example, methyldielh~nol amine (MDEA), have a greater impact on
increasing the rate of mechanisms 3a and 3b. The ratio of complexing agent to
quinone in the polar orya,-;c solvent is also crucial in yielding an unexpectedly
high conversion of quinone to hydroquinone ~FIG. 3). The molar ratio of
complexing agent to quinone in the polar organic solvent is about ~ :50 to about2:1 and preferably about 1:10 to about 1:1.
In general, the quinone utilized in the process of the present invention is
selected from a"lhla~ inones, benzoquinones, napthaquinones, and mixtures
thereof and are cl~osen to ",axi,l~i~e its reaction with H2S. Choice of the quinone
is based on such properties as the solubility of quinone in the polar organic
solvent. Solubility is a function of the groups substituted on the quinone. For
example, alkyl quinones have much higher sol~ Ihilities than sulr~ aled quinones.
Useful anthraquinones are ethyl, t-butyl, t-amyl and s-amyl anthraquinones and
mixtures thereof because of their relatively high solubilities in most polar organic
solvents.
It has further been discovered that, by utilizing a suitable complexing agent
in coniunction with a polar organic solvent, both of which are selected in
accordance with parameters specified above, that the temperature and tl2S
partial pressure required ~or conversion of quinone can be subst~ntially reducedwhile the percentage of quinone converted to hydroquinone is increased.
Pr~e, ably, the reaction solution, i.e. the polar organic solvent having a suitable
quinone, complexing agent and hydrogen sulfide dissolved therein, is
maintained in the H2S absorber and/or polymerization reactor at a temperature
of from about 0~ C. to about 70~ C., and more preferably about 20~ C. to about
60~ C., and at a H2S partial pressure of from about 0.05 to about 4.0
atmospheres, more preferably about 0.1 to about 3.0 atmospheres, and most
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preferably about 0.5 to about 2.0 a~, I)ospl .eres. These lower temperatures andpressures reduce the design requirements for the H2S ai so~er andlor
polyme, i~aLio" reactor which results in significant cost savings. In addition, the
cost of co" ,uressing the feed gas to obtain the requisite H;!S partiar pressure is
significantly reduced. At these conditions, some unreacted ff2S in addition to
C02, water and/or low moiecular weight hydrocarbons may be rernoved from
the pol~"~eri ~lion reactor, separated and recovered by any suita~ie means as
will be evident to a skilled artisan, sudl as by means of a three phase se,va~or.
Aithough disr~ssed throughout this s,ueciri~Lioi, as being two se~Jaral~ and
distinct compound~;, it is within the scope of the present invention to utilize one
cor,,,uound as both the polar organic solvent and the complexing agent as long
as one compound can satisfy the criteria for both polar organic solvent and
complexin~ agent specified herein, i.e. have a high polarity, remain stable at
dehydrogenation temperatures, and have a pi~ value of less than about 13Ø
Applicants have further discovered that, by including a S--r~ci~, IL amount
of carbon dioxide in the gaseous feed col~laining h~dl uyen sulfide to ensure that
a predetermined amount of carbon dioxide is dissolved in the polar organic
solvent together with hydrogen sulfide, ti~e rate of reaction between hydrogen
sulfide and quinone can be significantly increased over the reaction rate
obtained when carbon dioxide is not included in the gaseous feed to the
absorber andlor reactor. While it is not exactly understood why carbon dioxide
increases this l~a- lio-, rate, it is believed that the presence of carbon dioxide in
the gaseous hydro~en sulfide containing reaction solution within the absorber
and/or polymerization reactor alters the structure of the quinone, thereby
resulting in an increased rate of quinone conversion. In accordance with the
process of the present invention, the amount of carbon dioxide present in the
gaseous feed should be sufficient to ensure that at least 0.05 mole of carbon
dioxide are absorbed into the polar organic solvent per mole of quinone
contained therein, more preferably 0.10 moie of carbon dioxide per mole of
quinone, and most ~,~rt:r~bly 0.25 mole of carbon dioxide per mole of quinone.
Carbon dioxide may be present in the gaseous stream to be treated in
accordance with the present invention or carbon dioxide may be added to the
gaseous stream from any readily available source so as to ensure that the
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1 1
amount of carbon dioxide specified above is absorbed from the gaseous stream
into the polar organic solvent containing quinone.
The presence of water which is dissolved from the feed gas into the
reaction solution also results in an unexpected increase in the recovery of sulfur
formed during the conversion of hydrogen sulfide and quinone to sulfur and
hydroquinone. While it is not exactly understood wi~y the addition of water to
the reaction solution increases the amount of sulfur which can be recovered
from the reaction solution, it is believed that the addition of a small amount of
water to the reaction soiution likely limits the total solution solubility and water
is selectively solubilized over sulfur, i.e. S~.
The treated feed gas is removed from the absorber and/or rea~lor and
lranspo, led for further treatment or for use. The insoluble sulfur, e.g. S~ or other
forms of polymerized sulfur, is withdrawn from the polymerization reactor as a
precipitate in the reaction solution, is separated from solution by filtration,
centrifugation or other means known in the art, is washed to remove the polar
organic solvent, dissolved hydroquinone, any unreacted ~uinone and
complexing agent, and is dried and may be subsequently melted to a liquid
form. In accorda, Ice with the present invention, the insoluble sulfur is washedwith a wash solvent. The wash solvent is any liquid hydrocarbon which
solubilizes the reaction solution, i.e. the polar organic solvent having quinone,
hydroquinone, and complexing agent dissolved therein. This wash solvent has
a boiling point of at least about 50~ C, preferably at least about 100~ C, and
most preferably at least about 150~ C below that of the polar organic solvent.
Preferred wash solvents are oxygenated hydrocarbons, such as, acetone, 3-
pentanone, or mixtures thereof. The reaction solution which is remaining after
sulfur removal and which contains hydroquinone, any unreacted quinone,
complexing agent, solvent, and unreacted compounds from the feed gas, such
as H2S, COS, CS2, CO2, me,ca,utalls and unrecovered sulfur, is heated to and
maintained at a temperature of from about 70 C. to about 220 C. and at a
pressure of from about 0.01 to about 2.0 atmospheres to convert COS, CS2.
mel w~lans and unrecovered sulfur to H2S. The reaction solution is then fed to
a flash tank or fractionator where substantially all unreacted feed gas
constituents, including water, C02 and/or low molecular weight hydrocarbons,
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WO 97/18028 12 PCT~US96/1~314
are removed from solution, separated, and recovered as products. The
separation of unreacted feed gas conslil.lents which have been removed from
the reaction solution via the fiash tank or r, a~io- Iator can be effect~l~te~ by any
suitable means as will be evident to a skilled artisan. For exampleS a three
phase sepa,~i.or can be utiiized wherein water having C02 dissolved therein is
removed from the bottom of the separator while liquid low molecular weight
hydrocan~ons having C02 dissolved therein are also removed from the
separator. The remaining gas which consists primarily of unreacted H2S is
recycled to the absorber and/or poly",eri~aLion reactor with the incoming feed
gas. The reaction solution which is withdrawn from the flash tank or fractionator
is further heated to from about 220~ C. to about 3~0~ C. at a pressure sufficient
to prevent solvent boiling. The heated solution is then fed to a dehydrogenationreactor where the hydroquinone is catalytically or thermally converted to
quinone and hydrogen gas (H2) under the temperature pressure conditions
stated above. Quinone in its initial forin is withdrawn from the dehydrogenationreactor dissolved with the complexing agent in the polar organic solvent and is
recycled to the H2S-quinone absorber, while the H g~s is recovered as a
commercial product.
The presence of a complexing agent in the remaining reaction solution, i.e.
that solution which is withdrawn from the polymerization reactor, which has had
sulfur removed therefrom, and which co"lai"s hydroquinone, any unreacted
quinone, complexing agent, solvent, and unreacted compounds from the feed
gas, is also desirable. As previously mentioned, after being heated to from
about 70~ C. to about 220~ C., flashed, and further heated to from about 220~
C. to about 350~ C., the heated solution is then fed to a dehydrogenation
reactor where the hydroquinone is catalytically or thermally converted to
quinone and hydrogen gas (H2~ under the temperature pressure conditions
stated above Dehydrogenation of hydroquinones using metal supported
catalysts may cause hydrogenoiysis which results in the undesirable production
of water and by-products. In the case of a, llh~ unones, these by-products are
a"U ~, o"es and/or a"li " anols. Applicants have discovered that the presence ofa complexing agent in the reaction solution fed to the dehydrogenation reactor
results in an unexpected and mariced increase in the seiectivity of hydroquinone
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13
to quinone and hyd, ~en product, and thus, the all~ndal1l decrease in unwanted
hydrogenolysis by-products. The molar ratio of complexing agent to total
quinones, i.e. hydroquinone and any unreacted quinone, in the remaining
reaction solution within the dehydrogenation reactor is about 1:50 to about 2:1,and more preferably about 1:10 to about 1:1.
Further, the addition of water to the polar organic solvent prior to the sulfur
production stage of the process of the present invention results in increased
hydrogen product selecl:ivity in the dehydrogenation stage of the process.
Although not completely u".le, ~ od, it is believed that water ~d~ition prior to the
sulfur production stage substantially eliminates the production of the free
radicals at this stage which are necess~ry for al)Lll~anol production in the later
dehydrogenation stage. Anthrone production is effectively eliminated by
operating at temperatures less than about 265~ C.
The following example ~le,no, l~ les the practice and utility of the present
1~ invention, but are not to be construed as limiting the scope thereof.
Example 1
A solution of N,N-dimethylacetamide ~DMAC) having 1~ wt% t-butyl
anthraquinone (TBAQ) dissolved therein has a complexing agent further
incorporated therein at a complexing agent/TBAQ molar ratio of 1:8. Several
complexing agents having differing piCb values are incorporated into separate
solutions of DMAC and TBAQ and are contacted with a hydrogen sulfide
containing gas in a suitable reactor at a temperature of 70~ C. and at a H2S
partial pressure of about 3.~ atmospheres. The complexing agents utilized
2~ are methylacetamide (MAC~, pyridine (PY), diethylmethylamine (i~EMA), N-
methyl-2-pyrrolidinone (NMP) and methyldiethanolamine (MDEA). Mechanism
3a occurs in about 10 to 20 minutes and mechanism 3b then follows and
continues up to about 60 minutes of reaction time. The rate constants for
mechanisms 3a and 3b are calculated and the results are illustrated in FIG. 1.
The rate constant for mechanism 3a exponentially increases with decreasing
compiexing agent pi~, value.
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14
Example 2
T-butyl a"Ll1ra~-linone (TBAQ) is added to dimethylacetamide (OMAC) in
an amount of 15 wt%. Diethylmethyiamine (DEMA), pyridine (PY) or
dimethylacetamide (DMAC) are also added to the solution as a complexing
a~ent in a moiar ratio of complexing agent to TBAQ of 1/8. The separate
solutions are maintained in suitable reactors at different temperatures of from
0~ C. to 70~ C. and at a H2S partial pressure of 3.55 atmospheres. Reaction
rate constants are c;~ir~ te~ at each reaction temperature for mechanisms 3a
and 3b assuming first order kinetics in TBAQ conversion. The calculated rate
constants are correlated to reaction temperature accordi.,g to the Arrhenius
model from which activation energies are calculated. As graphically
represented in FiG. 2, these results illustrate that as complexing agent pK
decreases from the base case where DMAC is both the solvent and complexing
agent, the activation energies for mechanisms 3a and 3b linearly ~lecrease.
This decrease is slightly more pronounced for mechanism 3b than for
mechanism 3a.
Example 3
Varying amounts of diethylmethylamine (DEMA) complexing agent are
added to N,N dimethylace~,tlide (DMAC) solvent which contains 15 wt% t-butyl
anthraquinone (TBAQ). The resuitant solutions are maintained in a suitable
reactor at a temperature of 20~ C. and at a H2S partial pressure of 3.55
atmospheres. Total ~8AQ conversion after the end of conversion mechanism
3a, i.e., 6-11 minutes or after 11 minutes of total reaction time is measured. As
illustrated in FIG. 3, these results indicate that the conversion of t-butyl
a, Ill Irc4uinone (TBAQ) to t-butyl anthrahydroquinone (H2TBAQ) increases with
increasing complexing agent/TBAQ ratio. Extrapolation of the data depicted in
FIG. 3 indicates that a 100% conversion of TBAQ to H2TBAQ will occur in 6-11
minutes for a ~EMA/~BAQ molar ratio of about 0.75.
Example 4
A gaseous mixture of hydrogen sulfide and carbon dioxide is introduced
into a laboratory reactor together with 15 wt% t-butyl anthraquinone (TBAQ) in
,
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a N,N-dimethylacetamide (DMAC) solution. This solution also contains
diethylmethylamine (DEMA) as a co",plexi"g agent in a ratio of 1 m~l~ of DEi~A
per 8 moles of TBAQ. The reactor is operated at a constant te~perature of
about 20~ C. and at a total pressure of from about 0 85 to 3.5~ atm~spheres.
Three gaseous feeds having varying H2S/CO;! molar ratios of 10010, 4~.5\50.5
and 19.8/80.2 are introduced separately into the reactor and the reaction rate
constants for mechanisms 3a and 3b are calculated using a rea~tion model
which is first order in TBAQ conce~ lion. The results are illustrated 9l a~JI ,;cally
in Fig. 4 and indicate that the reaction rate constants using a mixture of
hydrogen suifide and carbon dioxide in the reactor are about twice the rate
constants achieved with a pure hydrogen sulfide feed. This result is valid for
carbon dioxide/anthraquinone molar ratios in excess of 0.05. This result is alsoachieved at relatively low partial pressures of hydrogen sulfide, e.g. 0.68
atmospheres, thereby reducing cost of gas compression.
Example 5
Gamma-butyrolactone (GBL) having 15 wt% t-butyl ~ uinone (TBAQ)
dissolved therein is contacted with a hydrogen sulfide conlai,~ 9 gas in a
suitable reactor at a tel "perdlure of 20~ C. and at a H2S partial pressure of 3.17
atmospheres. Gamma-butyroiactone has a polarity of 4.17 Debye units. The
reaction is allowed to proceed for one hour and the amount of t-butyl
anthraquinone (TBAQ) which is converted to t-butyl a~ Ill ,ral1ydroquinone
(HzTBAQ) is measured. TBAQ conversion was zero. This result indicates that
utilizing a solvent having a polarity above 3.0 Debye units in the absence of a
complexing agent does not necessarily result in acceptable TBAQ conversion.
Example 6
T-~utyl anthraquinone (TBAQ) is added to N,N-dimethylacetamide (DMAC)
in an amount of 15 wt%. Diethylmethylamine (DEMA) is also added to the
solution as a complexing agent in a molar ratio of complexing agent to TBAQ
of 118. The solution is separately maintained in suitable reactors at a
temperature of 20~ C. and at varying H2S partial pressures. The results are
iliustrated in FIG. 5. S~ recovery is essentially constant for H~S partial pressures
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16
above about 1.52 atmospheres while S" recovery increases for ~ S partial
pressures below about 1.52 atmospheres to 100% at a H2S partial pressure of
0.68 dllllOSpl ,e,es. Thus, the reduced H2S partial pressure at which the process
of the present invention can be operated results in increased S, recovery.
Example 7
Varying amounts of pyridine complexing agent are added to se~rale
dehydrogenation feeds containing t-butyl ~I~U ,r~li ,ydroquinone and introduced
to a reactor wherein the al~U ,~ ydroquinone is dehydrogenated to
anthraquinone and hydrogen in the presence of a platinum catalyst.
Dehydrogenation is carried out in the reactor at a total pressure of about 4.35
to about 5.71 atmospheres and at a temperature of 265~ C. when the SiO2
catalyst support is used and 285~ C. when the quartz catalyst support is used.
Each feed is reacted for approximately 1.05 minutes. The results are illustratedgraphically in Fig. 6 and i,~.ii~le that the presence of a complexing agent in the
reaction solution feed to the dehydrogenation reactor in a ratio of complexing
agent to total quinones, i.e. anthrahydroquinone and any unreacted
al 1~111 a-~uinone, of about 1:50 to about 2: 1 and p, é:r~, ably about 1: 10 to about 1:1
results in an unexpected and marked increase in the selectivity of
anthrahydroquinone to anthraquinone and hydrogen. Thus, unwanted
hydrogenolysis by-products, such as anthrones andlor anll)r~,)ols, are also
decreased.
Example 8
Pyridine, 2,4 lutidine, and diethylmethylamine ~DEMA~ are each added to
separate dehydrogenation feeds which contain 18.7~ wt% t-butyl
~n~h, ~hydroquinone (~2TE3AQ) as complexing agents in the amount of 1 mole
of complexing agent per 8 moles of total anthraquinones, i.e. t-butyl
a"ll ,rd4uinone (TBAQ) and t-~utyl anthrahydroquinone. Pyridine, 2,4 lutidine,
and DEMA have p~ values of 8.8, 7.0 and 3.6, respectively. Each
dehydrogenation feed is introduced to a reactor wherein the
anthrahydroquinone is dehydrogenated to anthraquinone and hydrogen in the
presence of a platinum catalyst on a SiO2 support. Dehydrogenation is carried
out in the reactor at a total pressure of about 4.21 atmospheres and at a
temperature of 265~ C. Each feed is reacted for approximately a 1 minute
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residence time. The selectivity of t-butyl a, ~ rdhydroquinone to hydrogen and
t-butyl ar,ll"~4uinone is 74 %, 88%, and 100% when pyridine, 2,4 lutidine, and
DEMA, respectively, are used as the complexing agent in the feed to the
deh~d, u~enalion reactor. These results which are illustrated graphically in Fig.
7 indicate that the pK~ of the complexing agent in the reaction solution feed tothe dehydroge, laliorl reactor has an siy"iricanL effect in increasing the selectivity
of anthrahydroquinone to anthraquinone and hydrogen. Thus, unwanted
hydrogenolysis by-products, such as al~li,rones and/or anthranols, are also
decreased.
Example 9
A solution is formed from 24.50 wt% t-butyl anthraquinone (TBAQ), 73.51
wt% n-methyl-2-pyrrolidinone (NMP), 1.67 wt% water and 0.32 wt%
diethylmethylamine (DEMA) and is pumped into the bottom of a reactor
containing four HzS injection points equally spaced along the height of the
reactor. A separate updraft turbine mixer which rotates at 200 rpm is positionedwithin the reactor at each injection point. Three separate tests are conducted
in which the total amount of H2S introduced into the reactor is sufficient to
convert 90% of the TBAQ into t-butyl a"li "ai ,ydroquinone (HzTBAQ) and sulfur
The entire amount of H2S is introduced into the reactor soleiy via the first
injection point in the first test. In the second test, one haif of the total amount
of H2S is introduced into the reactor via each of the first and third injection
points, while in the third test, one fourth of the total amount of H2S is introduced
into the reactor via each of the four injection points. In each test, the solution
is pumped at a rate sufficient to create a 10 minute residence time within the
reactor prior to the solution exiting the top thereof. The temperature and
pressure of the reactor is maintained at 6!~ C. and 1.5 atmospheres in all testsIn all three tests, the effluent solution from the reactor is fed to a second
reactor where the effluent is completely back mixed, held at 20 C. and 1.0
atmosphere for a residence time of 20 minutes. Sulfur (S") crystaliization and
precipitation occurs in this second reactor. The reaction solution is removed
from the second reactor and filtered to remove sulfur. The amount of S~, thus
removed is compared to the total amount of S atoms formed in the reaction of
TBAQ and H.S. These results indicate that the use of 4 injection stages or
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points for introduction of HzS into the first reactor was critical for significantly
increasing the amount of TBAQ converted into H2TBAQ in the first, eaclor ~FIG.
8) and the amount of S atoms converted into S" for precipitation in the second
reactor (FIG. 9).
Example 10
A solution of 2.47 wt% benzoquinone, 24.13 wt% t-butyl
anthraquinone(TBAQ), 1.01 wt% diethylmethylamine (DEMA) and 72.39 wt%
N-methyi-2-pyrrolidinone (NMP) is introduced into a reactor and maintained
therein at a temperature of 21 C. and a pressure of 1.5 al.,)ospheres. ~EMA
is present in the solution as a complexing agent in a ratio of ().1 moles of DEMA
per mole of total quinones. While in the reactor, the solution is contacted witha hydrogen sulfide containing gas for 0.3 minutes and the temperature
in.;reases to 46.7' C. in the reactor. The solution is cooled within the reactor to
20' C. in 8.7 minutes. This reaction results in a 83% conversion of TBAQ to t-
1~ butyl anlt " dh ydroquinone and a 67% conversion of benzoquinone to
benzohydroquinone.
A solution of 8.7~ wt% benzoquinone, 0.73 wt% diethylmethylamine
(DEMA) and 90.52 wt% N-methyl-2-pyrrolidinone (NMP) is introduced into a
reactor under conditions which are identical to those set forth above in this
Example. DEMA is present in the solution as a complexing agent in a ratio of
0.25 moles of D~MA per mole of benzoquinone. The solution is contacted with
a hydrogen sulfide containing gas in the reactor for 0.3 minutes and the
temperatL~re increases to 46.7 C. in the reactor. The solution is cooled in the
reactor to 20~ C. in 8.7 minutes. This reaction results in a 78% conversion of
benzoquinone to benzohydroquinone.
A solution of 18.03 wt% 1,4 napthaquinone, 1.24 wt% diethylmethylamine
(DEMA) and 80.73 vvt% N-methyl-2-pyrrolidinone (NMP) is introduced into a
reactor under conditions which are identical to those set forth above in this
Example. DEMA is present in the solution as a complexing agent in a ratio of
0.125 moles of DFMA per mole of 1,4 napthaquinone. The solution is contacted
with a hydrogen sulfide containing gas in the reactor for 0.3 minutes and the
temperature increases to 46.7- C. in the reactor. The solution is cooled in the
.
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reactor to 20~ C. in 8.7 minutes. This r~acliG, I results in a 70% conversion of 1,4
napthaquinone to 1,4 napthahydroquinone.
The foregoing examples demo, IsL- ate that benzoquinones and
napthaquinones are equally as suitable as anthraquinones for use in the
process of the present invention.
Example 1 1
A natural gas feed stream containing 90.41 mole % ",eLl)dne, 2.51 mole
% H2S, 1.81 mole % C02, 4.92 mole % natural gas liquid (NGL) and 0.3~ mole
% water is introduced into the bottom of an absorber operating at 49 ~ C and 43
atmospheres. The composition of the NGL is 61.94 mole % ethane, 1~.67 moie
% propane, 15.95 mole % butanes, 5.69 mole % pentanes and 0.75 moie %
hexanes. Also, a recycle gas stream with a composition of 60.49 mole %
methane, 8.38 mole % H2S, 10.03 mole % C ~2~ 20.79 mole % NGL, and 0.31
mole % water is introduced into the bottom of the absorber. The molar ratio of
the recycle gas stream to the feed gas stream is 0.0444.
A recycle absorbent having a composition of 77.91 mole % N-methyl-2-
pyrrolidinone(NMP), 7.05 pyridine(PY), 7.27 mole % t-amyl anthraquinone
(TAAQ), 0.18 mole % t-amyl a"ll"dl"/droquinone (H2TAAQ), 7.45 mole %
water, 0.0~ mole % H2, and 0.09 mole % H2S is introduced into the top of the
absorber in an amount such that 1 mole of TAAQ plus H2TAAQ is introduced
per mole of total H2S in the feed gas plus the H2S in two recycle gas streams.
The H2S in the ~eed gas reacts with a portion of the TAAQ to produce H2TAAQ
and sutfur atoms.
A product gas is withdrawn from the top of the absorber. This stream
contains 93.40 mole % methane, 0.05 mole % NMP plus PY, 0.04 mole %
water, 0.03 mole % H2, 1.77 moie % CO2, and 4.71 mole % NGL. Essentially
all of the methane in the feed gas is recovered to the product gas, and
essentialiy all of the H2S is removed from the feed gas and is converted into
sulfur.
Recycle absorbent is removed from the absorber and introduced into
polymerization reactor where addili~,"al reaction between H2S and TAAQ occurs
and sulfur atoms are poiymerized into insoluble S8. This reactor operates at 30~C and 1.7 atmospheres. The resulting slurry of S8 and recycle absorbent is
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removed from the polymerization reactor and introduced into a fi~ter where
essentially all of the H2S in the feed gas is recovered as S8.
Also, a gas phase is removed from the poly" ,e~ i~dlion reactor by a ccmpressor.In this step, the gas phase is cor,l~ sse~ to 42 atmospheres and cooied to 49~
C. A liquid NGL product is then removed from this co" ,prsssed gas phase. ~he
amount of this NGL product is 7.18 mole% of the total NGL in the feed gas.
Also, CO2 is removed in this step at 5.1 mole% of that in the feed gas. The
remaining gas is then recycled back to the absorber. As discussed above, tne
molar ratio of this gas to the feed gas is 0.0444.
The recycle absorbent from the above ril~l dliOI ~ step is then introd~ ~c~ intoa rl aCLjG~ ldlion unit ope~liny at 2.0 atmospheres and temperatures fr~m 149 to210~ C. A water and acid gas mixture is removed from the top of this
fractionation unit. The water, which equals 90 mole% of the water in the feed
gas, is then recovered from this acid gas as a product. The acid gas is then
recycled to the polymerization resctor. The molar ratio of this gas to the feed
gas is 0.0366. The co"~position of this acid gas is 2.01 mole % methane, 0.13
mole % NMP, 10.6~ mole % water, 58.39 mole % H2S, 3.38 mole % CO2, 25.44
mole % NGL.
Recycle absorbent essentially free of any unreacted H2S is removed from
the bottom of the fractionation unit and introduced into a dehy~,ogel,dLio~)
reactor where the H2TAAQ is converted back into TAAQ and H2 product. This
reaction occurs at 250~ C and 4.7 atmospheres. The ratalyst used contains Pt
on a SiO2 support. The H plus re~ycle absorbent is removed from the
dehydrogenation reactor and cooled to 49~ C. H2 is then recovered from the
recycle absorbent as a product at molar ratio of 0.9214 to the H2S in the feed
gas. The absorbent is then cooled to 49~ C and recycled back to the absorber
to start its cycle over again.
Example 12
A natural gas feed stream cc" IL~i. ,i, lg 71.92 mole % methane, ~ 9.95 mole
% H2S, 1.43 mole % CO2, 3.91 mole % natural gas liquid (NGL) and 2.79 mole
% water is introduced into the bottom of an absorber operating at 36 ~ C and 42
atmospheres The composition of the NGL is 61.86 mole % ethane, 15.72 mole
% propane, 15.98 mole % butanes, 5.67 mole % pentanes and 0.77 mole %
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hexanes. Also, a recycle gas stream with a composition of 29.54 mols %
methane, 3.59 mole % H2S, 35.63 mole % CO2, 30.90 mole % NGL, and a.34
mole % water is introd~ ~ce~l into the bottom of the absorber. The molar ratio of
the recycle gas stream to the feed gas stream is 1.008.
A recycle absorbent having a co-."~osilion of 80.50 mole % N-methyl-2-
pyrrolidinone(NMP), 7.30 pyridine(PY), 7.49 mole % t-amyl anthraquinone
(TAAQ), 0.14 mole % t-amyl anthrahydroquinone (It2TAAQ), 4.43 mole %
water, 0.05 mole % H2, and 0.09 mole % H2S is introduced into the top of the
absorber in an amount such that 1.34 moles of TMQ plus H2TAAC~ is
intro~uced per mole of total H2S in the feed gas plus the H2S in two recycle gasstreams. The H2S in the feed gas reacts with a portion of the TAAQ to produce
H2TAAQ and sulfur atoms.
A product gas is withdrawn from the top of the absorber. This stream
contains 9~.77 mole % methane, 0.04 mole % NMP, plus PY, 0.04 mole %
water, 0.48 mole % H2, 0.53 moie % C02, and 3.14 mole % NGL. Esse,.Lially
all of the methane in ~he feed gas is recovered to the product gas, and
essentially all of the H2S is removed from the feed gas and is converted into
sulfur.
Recycle absorbent is removed from the absorber and introduced into a
poly"1eri~dlion reactor where adc~ilio"al reaction between H2S and TAAQ occurs
and sulfur atoms are pol~r" ,eri~ed into insoluble S8. This rea~ol operates at 30~
C and 1.7 atmospheres. The resulting slurry of S8 and recycle absorbent is
removed from the polyrnerization reactor and introduced into a fiiter where
essentially all of the H2S in the feed gas is recovered as S8.
Also, a gas phase is removed from the polymerization reactor by a
colt,plessor. In this step, the gas phase is compressed to 42 atmospheres and
cooled to 49~ C. A liquid NGL product is then removed from this compressed
gas phase. The amount of this NGL product is 91.7 mole% of the propane
through hexane components initially present in the feed gas. Also, CO2 is
removed in this step ~t 27.4 mole% of that in the feed gas. The remaining gas
is then recycled back to the absorber. As discussed above, the molar ratio of
this gas to the feed gas is 1.008.
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The recycle absorbent from the above filtration step is then introd~lGP~i into
a fractionation unit operating at 2.0 atmospheres and temperatures from 71~ C
to 210~ C. A water and acid gas mixture is removed from the top of tt~is
fractionation unit. ~he water, which equals 99 mole% of the water in the feed
gas, is then recovered from this acid gas as a product. The acid gas is then
recycied to the polymerization reactor. The molar ratio of this acid gas to the
feed gas is 0.4241. The acid gas co. ~sisls of 1.26 mole% methane, 0.08 mt~le%
NMP, 9.37 mole% water, 54.48 mole% H2S, 15.41 mole% C02, 19.40 mole~h
NGL.
Recycle absol be, IL essentially free of any unreacted H2S is removed from
the bottoms of tne fractionator and introduced into a dehydrogenation reactor
where the H2TAAQ is converted back into TAAQ and H2 product. This reaction
occurs at 250~ C and 4.7 ~ os,ul ,er~s. The cataiyst used contains Pt on a Si(:)2
support. The H2 plus recycle absorbent is removed from the dehydrogenation
reactor and cooled to 49~ C. H2 is then recovered from the recycle absorbent
as a product at molar ratio of 0.921~ to the H2S in the feed gas. The absorbent
is then cooled to 49~ C and recycled back to the absorber.
Example 13
T-butyl anLI ,ra.~uinone (TBAQ) is added to N-methyl-2-pyrrolidinone ~NMP)
in an amount of 25 wt%. Pyridine (PY) is also added to the solution as a
complexing agent in a molar ratio of complexing agent to TBAQ of 1/1 . Varying
amounts of water are added to separate portions of the solution. Each portion
of the solution is contacted with hydrogen sulfide containing gas in a suitable
reactor at a temperature of 20~ C and at a H2S partial pressure of 1.5
2~ atmospheres for 2 hours. The amount of S" recovered is determined by
weighing the sulfur which is precipitated out of the solution removed from the
reactor. The results are graphically illustrated in FiG. 10. As illustrated in FiG.
10, the amount of S~ recovered, which is expressed as the weight % of total
sulfur formed in the reactor, increases with increasing amounts of water which
are absorbed into the solution prior to or during the sulfur production stage ofthe process, i.e. during the conversion of hydrogen sulfide and anthraquinone
to sulfur and anthrahydroquinone.
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23
Example 14
A dehydrogel ~lion ~eed of N-methyl-2-pyrrolidinone ~NMP) COI ,lai, lil ~9 2
wt% t-butyl anthrahydroquinone (H2TBAQ) is introduced to a reactor wherein
the t-butyl anthrahydroquinone is dehydrogenated to t-butyl arllll.~4~1inone
(TBAQ) and hydl ~~yen in the presence of a platinum catalyst. Dehydlu~e, laliol)is carried out in the reactor at varying hydrogen pressures of about 2.31 to about
6.12 atmospheres to prevent solution boiling at the varying dehyd,u~er,ation
temperatures of from about 220~ C to about 290~ C. Two separaLe feeds are
reacted under these pé;,rdi"elers. Water is not added to one feed and is added
to another feed prior to sulfur production in an amount of about 1 mole of waterper mole of TBAQ. Pyridine (PY) is added as a complexing agent to the latter
feed in the amount of one mole of pyridine per mole of TBAQ. Each feed is
reacted for approximately 1 minute. The results which are illustrated graphically
in Fig. 11 indicate that H2TBAQ selectivity to hydrogen and TBAQ can be
increased to 100% below 225~ C if water is added to the NMP solvent prior to
the sulfur production stage of the process or absorbed from a gaseous feed
stream containing H2S. l~hus, unwanted hydrogenolysis by-products, such as
anthrones and/or anll ,ranols, can be effectively eliminated.
While the foregoing preferred embodiments of the invention have been
described and shown, it is understood that the alternatives and modifications,
such as those suggested and others, may be made thereto and fall within the
scope of the invention.
