Process for sweetening a sour hydrocarbon fraction

This invention relates to a process for sweetening a sour hydrocarbon fraction containing mercaptans. The process involves contacting the hydrocarbon fraction in the presence of an oxidizing agent with a catalytic composite, ammonium hydroxide and a quaternary ammonium hydroxide. There is a synergistic effect between the ammonium hydroxide and the quaternary ammonium hydroxide. Use of ammonium hydroxide instead of an alkaline hydroxide allows the waste stream to be re-used in other parts of the refinery, and allows for easier disposal of the waste stream.

BACKGROUND OF THE INVENTION 
Processes for the treatment of a sour hydrocarbon fraction where the 
fraction is treated by contacting it with an oxidation catalyst and an 
alkaline agent in the presence of an oxidizing agent at reaction 
conditions have become well known and widely practiced in the petroleum 
refining industry. These processes are typically designed to effect the 
oxidation of offensive mercaptans contained in a sour hydrocarbon fraction 
to innocuous disulfides--a process commonly referred to as sweetening. The 
oxidizing agent is most often air. Gasoline, including natural, straight 
run and cracked gasolines, is the most frequently treated sour hydrocarbon 
fraction. Other sour hydrocarbon fractions which can be treated include 
the normally gaseous petroleum fraction as well as naphtha, kerosene, jet 
fuel, fuel oil, and the like. 
A commonly used continuous process for treating sour hydrocarbon fractions 
entails contacting the fraction with a metal phthalocyanine catalyst 
dispersed in an aqueous caustic solution to yield a doctor sweet product. 
Doctor sweet means a mercaptan content in the product low enough to test 
"sweet" (as opposed to "sour") by the well known doctor test. The sour 
fraction and the catalyst containing aqueous caustic solution provide a 
liquid-liquid system wherein mercaptans are converted to disulfides at the 
interface of the immiscible solutions in the presence of an oxidizing 
agent--usually air. Sour hydrocarbon fractions containing more difficult 
to oxidize mercaptans are more effectively treated in contact with a metal 
chelate catalyst dispersed on a high surface area adsorptive 
support--usually a metal phthalocyanine on an activated charcoal. The 
fraction is treated by contacting it with the supported metal chelate 
catalyst at oxidation conditions in the presence of an alkaline agent. One 
such process is described in U.S. Pat. No. 2,988,500. The oxidizing agent 
is most often air admixed with the fraction to be treated, and the 
alkaline agent is most often an aqueous caustic solution charged 
continuously to the process or intermittently as required to maintain the 
catalyst in the caustic-wetted state. 
The prior art shows that the usual practice of catalytically treating a 
sour hydrocarbon fraction containing mercaptans involves the introduction 
of alkaline agents, usually sodium hydroxide, into the sour hydrocarbon 
fraction prior to or during the treating operation. See U.S. Pat. Nos. 
3,108,081 and 4,156,641. The prior art also discloses that quaternary 
ammonium compounds can improve the activity of these catalytic systems. 
For example, see U.S. Pat. Nos. 4,290,913 and 4,337,147. In these patents 
the catalytic composite comprises a metal chelate, an alkali metal 
hydroxide and a quaternary ammonium hydroxide dispersed on an adsorptive 
support. 
Although the above processes have shown commercial success, there are 
problems associated with the use of alkaline agents. One problem is that 
phenols and cresols present in the hydrocarbon stream are extracted into 
the aqueous alkaline solution. Since phenol is on the EPA list of 
hazardous compounds, the solution containing the phenols is considered a 
hazardous waste and must be disposed of according to EPA procedures. Also 
because of the presence of alkali metals, the aqueous waste stream often 
cannot be re-used in other parts of the refinery owing to possible 
contamination of vessels or catalysts with the alkali metals. 
Applicants have solved the above problems by making the discovery that 
ammonium hydroxide can be effectively substituted for an alkali metal 
hydroxide. By using ammonium hydroxide no alkali metals are present in the 
aqueous waste stream, thereby allowing the waste stream to be re-used in 
other parts of the refinery. More importantly, the disposal is much easier 
due to reduced phenol and cresols content. 
The only prior art reference known to applicants which mentions the use of 
ammonia is U.S. Pat. No. 4,502,949. This patent discloses a process for 
sweetening a sour hydrocarbon fraction using a metal chelate catalyst and 
anhydrous ammonia in the absence of an aqueous phase. There are several 
differences between the present invention and the '949 reference. First, 
the '949 specifically states that the ammonia is present in an anhydrous 
form and is used in the absence of an aqueous phase. In contrast to this, 
applicants use ammonium hydroxide in an aqueous form. There is no 
indication in the '949 reference that aqueous ammonium hydroxide would be 
a good promoter for mercaptan sweetening. 
Second, the stability of the catalyst when ammonia is used is only about 60 
hours. Although the '949 reference states that this stability is improved 
versus a process without ammonia, the stability is very poor when compared 
to a conventional process using an alkali metal hydroxide. In contrast, 
applicants' data show that the stability of the catalyst in the instant 
process is several hundred hours (see details infra), i.e., comparable to 
a conventional commercial process. 
The stability and efficiency of a process using ammonium hydroxide is also 
unexpected based on the knowledge that alkali metal hydroxides are needed 
to successfully promote mercaptan sweetening. The reason for this is that 
ammonium hydroxide and alkali metal hydroxides have vastly different base 
properties. Whereas ammonium hydroxide is a weak base with a K.sub.b 
(dissociation constant) of 1.79.times.10.sup.-5, alkali metal hydroxides 
are strong bases which are 100% dissociated, K.sub.b..apprxeq.1. Since the 
first step in the oxidation of mercaptans is to form a mercaptide ion by 
abstracting a proton using a strong base, it would not be expected that a 
weak base such as ammonium hydroxide would adequately promote mercaptan 
sweetening. 
The inadequacy of using ammonium hydroxide is shown by U.S. Pat. No. 
4,207,173. The object of the '173 patent is the use of a tetra-alkyl 
guanidine as a promoter for mercaptan oxidation (no alkaline base 
present). However, in Table I, column 8, there is presented data comparing 
sodium and ammonium hydroxide. The data clearly show that using ammonium 
hydroxide would not provide an acceptable, i.e., sweet, product. Thus, 
based on the prior art there is no incentive to substitute ammonium 
hydroxide for sodium hydroxide. 
SUMMARY OF THE INVENTION 
It is a broad objective of this invention to present an improved process 
for treating a sour hydrocarbon fraction containing mercaptans. Thus, one 
broad embodiment of the invention is a process for sweetening a sour 
hydrocarbon fraction containing mercaptans comprising contacting the 
hydrocarbon fraction in the presence of an oxidizing agent with a 
catalytic composite effective in oxidizing said mercaptans to disulfides, 
ammonium hydroxide and a quaternary ammonium hydroxide having the 
structural formula 
##STR1## 
where R is a hydrocarbon group containing up to about 20 carbon atoms and 
selected from the group consisting of alkyl, cycloalkyl, alkaryl, and 
aralkyl; R.sub.1 is a straight chain alkyl group containing from about 5 
to about 20 carbon atoms; and R.sub.2 is a hydrocarbon group selected from 
the group consisting of aryl, alkaryl and aralkyl and said catalytic 
composite comprises a metal chelate dispersed on an adsorbent support. 
Other objects and embodiments of this invention will become apparent in the 
following detailed description. 
DETAILED DESCRIPTION OF THE INVENTION 
As stated, the process of this invention comprises contacting a sour 
hydrocarbon fraction in the presence of an oxidizing agent with a 
catalytic composite, ammonium hydroxide and a quaternary ammonium 
hydroxide. The catalytic composite comprises a metal chelate dispersed on 
an adsorbent support. The adsorbent support which may be used in the 
practice of this invention can be any of the well known adsorbent 
materials generally utilized as a catalyst support or carrier material. 
Preferred adsorbent materials include the various charcoals produced by 
the destructive distillation of wood, peat, lignite, nutshells, bones, and 
other carbonaceous matter, and preferably such charcoals as have been 
heat-treated or chemically treated or both, to form a highly porous 
particle structure of increased adsorbent capacity, and generally defined 
as activated carbon or charcoal. Said adsorbent materials also include the 
naturally occurring clays and silicates, e.g., diatomaceous earth, 
fuller's earth, kieselguhr, attapulgus clay, feldspar, montorillonite, 
halloysite, kaolin, and the like, and also the naturally occurring or 
synthetically prepared refractory inorganic oxides such as alumina, 
silica, zirconia, thoria, boria, etc., or combinations thereof like 
silica-alumina, silica-zirconia, alumina-zirconia, etc. Any particular 
solid adsorbent material is selected with regard to its stability under 
conditions of its intended use. For example, in the treatment of a sour 
petroleum distillate, the adsorbent support should be insoluble in, and 
otherwise inert to, the hydrocarbon fraction at the alkaline reaction 
conditions existing in the treating zone. Charcoal, and particularly 
activated charcoal, is preferred because of its capacity for metal 
chelates, and because of its stability under treating conditions. 
Another necessary component of the catalytic composite used in this 
invention is a metal chelate which is dispersed on an adsorptive support. 
The metal chelate employed in the practice of this invention can be any of 
the various metal chelates known to the art as effective in catalyzing the 
oxidation of mercaptans contained in a sour petroleum distillate to 
disulfides. The metal chelates include the metal compounds of 
tetrapyridinoporphyrazine described in U.S. Pat. No. 3,980,582, e.g., 
cobalt tetrapyridinoporphyrazine; porphyrin and metaloporphyrin catalysts 
as described in U.S. Pat. No. 2,966,453, e.g., cobalt tetraphenylporphyrin 
sulfonate; corrinoid catalysts as described in U.S. Pat. No. 3,252,892, 
e.g., cobalt corrin sulfonate; chelate organometallic catalysts such as 
described in U.S. Pat. No. 2,918,426, e.g., the condensation product of an 
aminophenol and a metal of Group VIII; and the metal phthalocyanines as 
described in U.S. Pat. No. 4,290,913, etc. As stated in U.S. Pat. No. 
4,290,913, metal phthalocyanines are a preferred class of metal chelates. 
The metal phthalocyanines which can be employed to catalyze the oxidation 
of mercaptans generally include magnesium phthalocyanine, titanium 
phthalocyanine, hafnium phthalocyanine, vanadium phthalocyanine, tantalum 
phthalocyanine, molybdenum phthalocyanine, manganese phthalocyanine, iron 
phthalocyanine, cobalt phthalocyanine, platinum phthalocyanine, palladium 
phthalocyanine, copper phthalocyanine, silver phthalocyanine, zinc 
phthalocyanine, tin phthalocyanine, and the like. Cobalt phthalocyanine 
and vanadium phthalocyanine are particularly preferred. The ring 
substituted metal phthalocyanines are generally employed in preference to 
the unsubstituted metal phthalocyanine (see U.S. Pat. No. 4,290,913), with 
the sulfonated metal phthalocyanine being especially preferred, e.g., 
cobalt phthalocyanine monosulfate, cobalt phthalocyanine disulfonate, etc. 
The sulfonated derivatives may be prepared, for example, by reacting 
cobalt, vanadium or other metal phthalocyanine with fuming sulfuric acid. 
While the sulfonated derivatives are preferred, it is understood that 
other derivatives, particularly the carboxylated derivatives, may be 
employed. The carboxylated derivatives are readily prepared by the action 
of trichloroacetic acid on the metal phthalocyanine. 
An optional component of the catalytic composite useful for this invention 
is an onium compound dispersed on the adsorptive support. Onium compounds 
are ionic compounds in which the positively charged (cationic) atom is a 
nonmetallic element, other than carbon, not bonded to hydrogen. The onium 
compounds which can be used in this invention are selected from the group 
consisting of phosphonium, ammoniun, arsonium, stibonium, oxonium and 
sulfonium compounds, i.e., the cationic atom is phosphorus, nitrogen, 
arsenic, antimony, oxygen and sulfur, respectively. Table 1 presents the 
general formula of these onium compounds, and the cationic element. 
TABLE 1 
______________________________________ 
Name and Formula of Onium Compounds 
Formula Name Cationic Element 
______________________________________ 
R.sub.4 N.sup.+ 
quaternary ammonium 
nitrogen 
R.sub.4 P.sup.+ 
phosphonium phosphorous 
R.sub.4 As.sup.+ 
arsonium arsenic 
R.sub.4 Sb.sup.+ 
stibonium antimony 
R.sub.3 O.sup.+ 
oxonium oxygen 
R.sub.3 S.sup.+ 
sulfonium sulfur 
______________________________________ 
*R is a hydrocarbon radical. 
For the practice of this invention it is desirable that the onium compounds 
have the general formula [R'(R).sub.y M].sup.+ X.sup.-. In said formula, R 
is a hydrocarbon group containing up to about 20 carbon atoms and selected 
from the group consisting of alkyl, cycloalkyl, aryl, alkaryl and aralkyl. 
It is preferred that one R group be an alkyl group containing from about 
10 to about 18 carbon atoms. The other R group(s) is (are) preferably 
methyl, ethyl, propyl, butyl, benzyl, phenyl and naphthyl groups. R' is a 
straight chain alkyl group containing from about 5 to about 20 carbon 
atoms and preferably an alkyl radical containing about 10 to about 18 
carbon atoms, X is hydroxide and y is 2 when M is oxygen or sulfur and y 
is 3 when M is phosphorous, nitrogen, arsenic or antimony. The preferred 
cationic elements are phosphorous, nitrogen, sulfur and oxygen. 
Illustrative examples of onium compounds which can be used to practice this 
invention, but which are not intended to limit the scope of this invention 
are: benzyldiethyldodecylphosphonium hydroxide, 
phenyldimethyldecylphosphonium hydroxide, benzyldibutyldecylphosphonium 
hydroxide, benzyldimethylhexadecylphosphonium hydroxide, 
trimethyldodecylphosphonium hydroxide, 
naphthyldimethylhexadecylphosphonium hydroxide, 
tributylhexadecylphosphonium hydroxide, benzylmethylhexadecyloxonium 
hydroxide, benzylethyldodecyloxonium hydroxide, naphthylpropyldecyloxonium 
hydroxide, dibutyldodecyloxonium hydroxide, phenylmethyldodecyloxonium 
hydroxide, dipropylhexadecyloxonium hydroxide, dibutylhexadecyloxonium 
hydroxide, benzylmethylhexadecylsulfonium hydroxide, 
diethyldodecylsulfonium hydroxide, naphthylpropylhexadecylsulfonium 
hydroxide, phenylmethylhexadecylsulfonium hydroxide, 
dimethylhexadecylsulfonium hydroxide, benzylbutyldodecylsulfonium 
hydroxide, benzyldiethyldodecylarsonium hydroxide, 
benzyldiethyldodecylstibonium hydroxide, trimethyldodecylarsonium 
hydroxide,trimethyldodecylstibonium hydroxide, benzyldibutyldecylarsonium 
hydroxide, benzyldibutyldecylstibonium hydroxide, 
tributylhexadecylarsonium hydroxide, tributylhexadecylstibonium hydroxide, 
naphthylpropyldecylarsonium hydroxide, naphthylpropyldecylstibonium 
hydroxide, benzylmethylhexadecylarsonium hydroxide, 
benzylmethylhexadecylstibonium hydroxide, benzylbutyldodecylarsonium 
hydroxide, benzylbutyldodecylstibonium hydroxide, 
benzyldimethyldodecylammonium hydroxide, benzyldimethyltetradecylammonium 
hydroxide, benzyldimethylhexadecylammonium hydroxide, 
benzyldimethyloctadecylammonium hydroxide, dimethylcyclohexyloctylammonium 
hydroxide, diethylcyclohexyloctylammonium hydroxide, 
dipropylcyclohexyloctylammonium hydroxide, dimethylcyclohexyldecylammonium 
hydroxide, diethylcyclohexyldecylammonium hydroxide, 
dipropylcyclohexyldecylammonium hydroxide, 
dimethylcyclohexyldodecylammonium hydroxide, 
diethylcyclohexyldodecylammonium hydroxide, 
dipropylcyclohexyldodecylammonium hydroxide, 
dimethylcyclohexyltetradecylammonium hydroxide, 
diethylcyclohexyltetradecylammonium hydroxide, 
dipropylcyclohexyltetradecylammonium hydroxide, 
dimethylcyclohexylhexadecylammonium hydroxide, 
diethylcyclohexylhexadecylammonium hydroxide, 
dipropylcyclohexylhexadecylammonium hydroxide, 
dimethylcyclohexyloctadecylammnium hydroxide, 
diethylcyclohexyloctadecylammonium hydroxide, 
dipropylcyclohexyloctadecylammonium hydroxide, and the like. Other 
suitable quaternary ammonium hydroxides are described in U.S. Pat. No. 
4,156,641. 
The metal chelate component and optional onium compound can be dispersed on 
the adsorbent support in any conventional or otherwise convenient manner. 
The components can be dispersed on the support simultaneously from a 
common aqueous or alcoholic solution and/or dispersion thereof or 
separately and in any desired sequence. The dispersion process can be 
effected utilizing conventional techniques whereby the support in the form 
of spheres, pills, pellets, granules or other particles of uniform or 
irregular size or shape, is soaked, suspended, dipped one or more times, 
or otherwise immersed in an aqueous or alcoholic solution and/or 
dispersion to disperse a given quantity of the metal chelate and optional 
onium compound. Typically, the onium compound will be present in a 
concentration of about 0.1 to about 10 weight percent of the composite. In 
general, the amount of metal phthalocyanine which can be adsorbed on the 
solid adsorbent support and still form a stable catalytic composite is up 
to about 25 weight percent of the composite. A lesser amount in the range 
of from about 0.1 to about 10 weight percent of the composite generally 
forms a suitably active catalytic composite. 
One preferred method of preparation involves the use of a steam-jacketed 
rotary dryer. The adsorbent support is immersed in the impregnating 
solution and/or dispersion containing the desired components contained in 
the dryer and the support is tumbled therein by the rotating motion of the 
dryer. Evaporation of the solution in contact with the tumbling support is 
expedited by applying steam to the dryer jacket. In any case, the 
resulting composite is allowed to dry under ambient temperature 
conditions, or dried at an elevated temperature in an oven, or in a flow 
of hot gases, or in any other suitable manner. 
An alternative and convenient method for dispersing the metal chelate and 
optional onium compound on the solid adsorbent support comprises 
predisposing the support in a sour hydrocarbon fraction treating zone or 
chamber as a fixed bed and passing a metal chelate and optional onium 
compound solution and/or dispersion through the bed in order to form the 
catalytic composite in situ. This method allows the solution and/or 
dispersion to be recycled one or more times to achieve a desired 
concentration of the metal chelate and optional onium compound on the 
adsorbent support. In still another alternative method, the adsorbent may 
be predisposed in said treating zone or chamber, and the zone or chamber 
thereafter filled with the solution and/or dispersion to soak the support 
for a predetermined period. 
Typically, the sour hydrocarbon fraction is contacted with the catalytic 
composite which is in the form of a fixed bed. The contacting is thus 
carried out in a continuous manner. An oxidizing agent such as oxygen or 
air, with air being preferred, is contacted with the fraction and the 
catalytic composite to provide at least the stoichiometric amount of 
oxygen required to oxidize the mercaptan content of the fraction to 
disulfides. 
Another essential feature of the process of this invention is that the 
hydrocarbon fraction be contacted with an aqueous solution containing 
ammonium hydroxide and a quaternary ammonium hydroxide. The amount of 
ammonium hydroxide which may be employed varies considerably but is 
conveniently chosen to be from about 0.1 to about 200 wppm and preferably 
from about 1 wppm to about 100 wppm based on hydrocarbon. The quaternary 
ammonium hydroxide has the formula 
##STR2## 
where R is a hydrocarbon group containing up to about 20 carbon atoms and 
selected from the group consisting of alkyl, cycloalkyl, aryl, alkaryl, 
and aralkyl; and R.sub.1 is a straight chain alkyl group containing from 
about 5 to about 20 carbon atoms; R.sub.2 is a hydrocarbon group selected 
from the group consisting of aryl, alkaryl and aralkyl. Illustrative 
examples of the quaternary ammonium hydroxides which can be used are those 
enumerated above. The quaternary ammonium hydroxide should be present in a 
concentration from about 0.05 to about 500 wppm and preferably from about 
0.5 wppm to about 100 wppm based on hydrocarbon. The aqueous solution may 
further contain a solubilizer to promote mercaptan solubility, e.g., 
alcohols and especially methanol, ethanol, n-propanol, isopropanol, etc. 
The solubilizer, when employed, is preferably methanol, and the aqueous 
solution may suitably contain from about 2 to about 10 volume percent 
thereof. 
The treating conditions which may be used to carry out the present 
invention are those that have been disclosed in the prior art. The process 
is usually effected at ambient temperature conditions, although higher 
temperatures up to about 105.degree. C. are suitably employed. Pressures 
of up to about 1,000 psi or more are operable although atmospheric or 
substantially atmospheric pressures are suitable. Contact times equivalent 
to a liquid hourly space velocity of from about 0.5 to about 10 or more 
are effective to achieve a desired reduction in the mercaptan content of a 
sour petroleum distillate, an optimum contact time being dependent on the 
size of the treating zone, the quantity of catalyst contained therein, and 
the character of the fraction being treated. 
As previously stated, sweetening of the sour hydrocarbon fraction is 
effected by oxidizing the mercaptans to disulfides. Accordingly, the 
process is effected in the presence of an oxidizing agent, preferably air, 
although oxygen or other oxygen-containing gases may be employed. In fixed 
bed treating operations, the sour hydrocarbon fraction may be passed 
upwardly or downwardly through the catalytic composite. The sour 
hydrocarbon fraction may contain sufficient entrained air, but generally 
added air is admixed with the fraction and charged to the treating zone 
concurrently therewith. In some cases, it may be advantageous to charge 
the air separately to the treating zone and countercurrent to the fraction 
separately charged thereto. Examples of specific arrangements to carry out 
the treating process may be found in U.S. Pat. Nos. 4,490,246 and 
4,753,722 which are incorporated by reference. 
As stated, the improvement in the process of treating a sour hydrocarbon 
fraction of this invention is the replacement of ammonium hydroxide for an 
alkali metal hydroxide such as sodium hydroxide. Applicants have 
unexpectedly discovered that ammonium hydroxide, which is a weak base, can 
effectively be substituted for strong bases such as sodium hydroxide. All 
indications from the prior art are that ammonium hydroxide would not be an 
effective substitute for an alkali metal hydroxide. Finally, applicants' 
invention solves an important environmental problem associated with alkali 
metal hydroxide disposal of the waste stream.

The following examples are presented in illustration of this invention and 
are not intended as undue limitations on the generally broad scope of the 
invention as set out in the appended claims. 
EXAMPLE 1 
A sour FCC gasoline feedstock boiling in the 48.degree.-228.degree. C. 
range and containing about 85 wppm mercaptan sulfur was processed downflow 
through a catalytic composite at a liquid hourly space velocity of about 
10, an inlet temperature of 38.degree. C. and a pressure of 70 psig. The 
catalytic composite was present as a fixed bed in a tubular reactor and 
consisted of a sulfonated cobalt phthalocyanine on carbon. The catalytic 
composite was prepared by filling the reactor bed with activated carbon 
(obtained from Norit Co.) in the form of 10-20 mesh granules and then 
downflowing an aqueous ammoniacal solution of sulfonated cobalt 
phthalocyanine (the sulfonated cobalt phthalocyanine (CoPC) was obtained 
from GAF Co.) to give a concentration of 0.15 g CoPC per 100 cc of carbon 
support. 
The feedstock was charged under sufficient air pressure to provide about 
1.2 times the stoichiometric amount of oxygen required to oxidize the 
mercaptans. Varying amounts of ammonium hydroxide and quaternary ammonium 
hydroxide were added as shown in Table 2. The quaternary ammonium 
hydroxide was prepared by ion exchanging a quaternary ammonium chloride 
using an anion exchange resin. The quaternary ammonium chloride was 
obtained from Mason Chemical Co. and consisted of a mixture of 
benzyldimethylalkylammonium chloride and benzylmethyldialkylammonium 
chloride. The alkyl groups are nominally C.sub.14 straight chain alkyl 
groups. An aqueous solution containing 2 weight percent of NH.sub.3 (as 
NH.sub.4 OH) and 1 weight percent quaternary ammonium hydroxide was added 
at such a rate to give the concentrations presented in Table 2. 
The catalytic composite which was used in this example had been previously 
used for other experiments unrelated to this invention. The catalyst had 
been run for 1,200 hours on these other experiments. Therefore, the zero 
hour point (for time on stream) for this example was 1,200. Samples of the 
product were periodically removed and analyzed for mercaptan sulfur. These 
results are presented in Table 2. 
TABLE 2 
______________________________________ 
Effect of NH.sub.4 OH and Quaternary Ammonium Hydroxide 
on Mercaptan Oxidation 
Time on Product 
Stream Mercaptan NH.sub.4 OH 
Quaternary Ammonium 
(Hrs) Sulfur (WPPM) 
(WPPM) Hydroxide (WPPM) 
______________________________________ 
1260 5 5 2.5 
1680 35 0 0 
1850 5 10 5 
1970 4 10 5 
2100 5 10 5 
2200 20 0 5 
2300 3 10 5 
______________________________________ 
The data presented in Table 2 shows the synergistic effect between ammonium 
hydroxide and quaternary ammonium hydroxide. Additionally, the data show 
that using ammonium hydroxide provides a durable process with no catalyst 
deterioration in over 300 hours of operation.