Process for removing elemental sulfur from fluids

A process for removing elemental sulfur from fluids such as refined petroleum products transported through pipelines for the transportation of sour hydrocarbon streams. The fluids are contacted with an aqueous solution containing caustic, sulfide and optionally elemental sulfur to produce an aqueous layer containing metal polysulfides and a clear fluid layer having a reduced elemental sulfur level. Organo mercaptans may also be mixed with the fluid to accelerate the removal of elemental sulfur.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a process for removing elemental sulfur from 
fluids, particularly fuels such as gasoline transported in a pipeline for 
the transportation of sour hydrocarbon streams. The fluids are contacted 
with caustic, water, sulfide and optionally elemental sulfur to form an 
aqueous layer containing polysulfides and a fluid layer having a reduced 
elemental sulfur level. 
2. Description of Related Art 
It is well known that elemental sulfur and other sulfur compounds contained 
in hydrocarbon streams is corrosive and damaging to metal equipment, 
particularly copper and copper alloys. Sulfur and sulfur compounds may be 
present in varying concentrations in the refined fuels and additional 
contamination may take place as a consequence of transporting the refined 
fuel through pipelines containing sulfur contaminants resulting from the 
transportation of sour hydrocarbon streams such as petroleum crudes. The 
sulfur has a particularly corrosive effect on equipment such as brass 
valves, gauges and in-tank fuel pump copper commutators. 
Various techniques have been reported for removing elemental sulfur from 
petroleum products. For example U.S. Pat. No. 4,149,966 discloses a method 
for removing elemental sulfur from refined hydrocarbon fuels by adding an 
organo-mercaptan compound and a copper compound capable of forming a 
soluble complex with said mercaptan and said sulfur and contacting said 
fuel with an adsorbent material to remove the resulting copper complex and 
substantially all the elemental sulfur. 
U.S. Pat. No. 4,908,122 discloses a process for sweetening a sour 
hydrocarbon fraction containing mercaptans by contacting the hydrocarbon 
fraction in the presence of an oxidizing agent with a catalytic composite, 
ammonium hydroxide and a quaternary ammonium salt other than hydroxide. 
U.S. Pat. No. 3,185,641 describes a method for removing elemental sulfur 
from a liquid hydrocarbon which comprises contacting with solid sodium 
hydroxide a hydrocarbon stream having dissolved therein at least 7.6 parts 
by weight of water per part of sulfur contained therein to yield both a 
hydrocarbon phase and an aqueous phase. The method is claimed to be 
effective and convenient for treating gasoline containing from trace to 
more than 25 ppm sulfur employing temperatures as high as about 
140.degree. F. (60.degree. C.). 
U.S. Pat. No. 4,011,882 discloses a method for reducing sulfur 
contamination of refined hydrocarbon fluids transported in a pipeline for 
the transportation of sweet and sour hydrocarbon fluids by washing the 
pipeline with a wash solution containing a mixture of light and heavy 
amines, a corrosion inhibitor, a surfactant and an alkanol containing from 
1 to 6 carbon atoms. 
SUMMARY OF THE INVENTION 
The present invention provides a process for removing elemental sulfur from 
fluids such as hydrocarbon fuels, fuel blending components such as octane 
improvers, liquified petroleum gas (LPG), solvents and other petroleum 
streams transported in a pipeline for the transportation of sour 
hydrocarbon streams, comprising contacting the sulfur-containing fluid 
with an inorganic caustic material, water, sulfide, and optionally 
elemental sulfur to form an aqueous layer containing polysulfides and a 
fluid layer having a reduced elemental sulfur level. The fluid layer is 
decanted from the aqueous layer leaving a treated product having a low 
residual elemental sulfur content. The fluid may additionally be contacted 
with an organo mercaptan to accelerate removal of elemental sulfur.

DETAILED DESCRIPTION OF THE INVENTION 
The inorganic caustic material which is employed in this invention includes 
alkali metal or ammonium hydroxides having the formula MOH wherein M is 
selected from the group consisting of lithium, sodium, potassium, NH.sub.4 
or mixtures thereof. M is preferably sodium or potassium. 
The sulfide which is employed in this invention includes sulfides of metals 
from Groups I and II of the Periodic Table. Examples of sulfides include 
Na.sub.2 S, K.sub.2 S, Li.sub.2 S, NaHS, (NH.sub.4).sub.2 S, H.sub.2 S 
(the fluid itself could provide the source of H.sub.2 S) and the like. 
Na.sub.2 S is preferred. 
Elemental sulfur may also be added with the caustic and sulfide. The 
sulfide in caustic reacts with the elemental sulfur in the fluid to be 
treated to form polysulfides in caustic. Elemental sulfur may be added for 
promoting the reaction or if it is present in a convenient source of 
caustic such as white liquor from paper pulp mills. 
Organo mercaptans may also be employed in the process of the invention. The 
organo mercaptan forms a soluble sulfur complex with the elemental sulfur, 
thereby accelerating its removal. The organo mercaptans which may be used 
include a wide variety of compounds having the general formula RSH, where 
R represents an organic radical which may be alkyl, alkenyl, cycloalkyl, 
cycloalkenyl, aryl of arylalkyl having from 1 to about 16 carbon atoms. 
Thus, the radical may be, for example methyl, ethyl, n-propyl, i-propyl, 
n-butyl, i-butyl, sec-butyl, t-butyl, amyl, n-octyl, decyl, dodecyl, 
octadecyl, phenyl, benzyl and the like. Most preferably, RSH is an alkyl 
mercaptan containing 2 to 5 carbon atoms. 
Alcohols such as methanol, ethanol, propanol, ethylene glycol, propylene 
glycol and the like may also be added to the mixture which is contacted 
with the fluid to be treated. The amount of alcohol used may vary within 
wide limits. In the case of methanol, for example, from 0 to about 90 
volume percent of the water may be replaced with alcohol. 
The fluids which are treated in accordance with the invention include 
fluids containing elemental sulfur where the elemental sulfur is 
detrimental to the performance of the fluid. The invention is particularly 
applicable to those liquid products which have become contaminated with 
elemental sulfur as a result of being transported in a pipeline previously 
used to transport sour hydrocarbon streams such as petroleum crudes. 
The fluids treated in accordance with the invention include a wide variety 
of petroleum fuels and particularly refined hydrocarbon fuels such as 
gasoline, jet fuel, diesel fuel and kerosene. 
Other fluids include ethers used to improve the octane ratings of gasoline. 
These ethers are typically dialkyl ethers having 1 to 7 carbon atoms in 
each alkyl group. Illustrative ethers are methyl tertiary-butyl ether, 
methyl tertiary-amyl ether, methyl tertiary-hexyl ether, ethyl 
tertiary-butyl ether, n-propyl tertiary-butyl ether, isopropyl 
tertiary-amyl ether. Mixtures of these ethers and hydrocarbons may be 
treated in accordance with the invention. 
Fluids containing quantities of elemental sulfur as high as 100 mg, or 
higher, sulfur per liter, more usually from about 10 to about 60 mg per 
liter, can be effectively treated in accordance with this invention to 
reduce the sulfur contamination to about 5 mg sulfur per liter or lower. 
In general, the process of the invention involves the addition to the fluid 
to be treated of effective amounts of caustic, water, sulfide, and 
optionally organo mercaptan, elemental sulfur and/or alcohol. The mixture 
is allowed to settle so as to form an aqueous layer containing metal 
polysulfides and a clear fluid layer having a reduced elemental sulfur 
level. Contact with the mercaptan would result in a clear fluid layer 
having a reduced elemental sulfur level and containing soluble polysulfide 
reaction products which are relatively non-corrosive. The treated fluid 
may be recovered by decantation. The recovered aqueous layer may be 
recycled back to the mixing zone for contact with the fluid to be treated 
or it may be discarded or used, for example, as a feedstock to sulfite 
pulping paper mills. 
The treating conditions which may be used to carry out the present 
invention are conventional. Contacting of the fluid to be treated is 
effected at ambient temperature conditions, although higher temperatures 
up to 100.degree. C. or higher may be employed. Substantially atmospheric 
pressures are suitable, although pressures may, for example, range up to 
1,000 psig. Contact times may vary widely depending on the fluid to be 
treated, the amount of elemental sulfur therein and the treating materials 
used. The contact time will be chosen to effect the desired degree of 
elemental sulfur conversion. The reaction proceeds relatively fast, 
usually within several minutes, depending on solution strengths and 
compositions. Contact times from 30 seconds to a few hours may be 
employed. 
The reactants may be dispersed within the fluid to be treated using any 
suitable mixing device which will provide adequate mixing with the fluid. 
Thereafter the mixture is allowed to settle to produce the aqueous and 
fluid layers. 
While the reactants employed in the invention may be contacted with the 
fluid to be treated in accordance with known techniques, it is convenient 
to prepare an aqueous mixture of caustic metal sulfide and elemental 
sulfur. The mixture is then contacted with the fluid to be treated. The 
organo mercaptan may also be employed, usually as a separate stream which 
may be mixed with the fluid to be treated. 
The proportion of water, caustic, sulfide and elemental sulfur to be mixed 
may vary within wide limits. Typically, the aqueous treating solution 
contains caustic in the range of 0.01 to 20M, the sulfide concentration is 
from 0.1 to 20M and the elemental sulfur concentration is from 0 to 10% by 
weight. The amount of organo mercaptan which may be optionally added may 
range from 0 to about 2 moles of organo mercaptan per mole of elemental 
sulfur present in the fluid to be treated. The relative amount of aqueous 
treating solution containing caustic, metal sulfide and optionally 
elemental sulfur and the fluid to be treated may also vary within wide 
limits. Usually about 0.05 to 10, more usually, 0.25 to 0.5 volumes of 
aqueous treating solution will be used per volume of fluid to be treated. 
The following examples are illustrative of the invention. 
EXAMPLE 1 
In this Example the following solutions were prepared. 
Solution A: 20 g sodium hydroxide+24 g sodium sulfide (9H.sub.2 O)+0.53 g 
elemental sulfur in 100 ml water (5M NaOH, 10M Na.sub.2 S, 0.53 wt % S) 
Solution B: 20 g sodium hydroxide+24 g sodium sulfide (9H.sub.2 O) in 100 
ml water (5M NaOH, 10M Na.sub.2 S). 
Solution C: 20 g sodium hydroxide in 100 ml water (5M NaOH) 
Solution D: 50 ml saturated sodium hydroxide in water+12 g of sodium 
sulfide (9H.sub.2 O). 
EXAMPLE 2 
Into a beaker were added 100 ml of pipelined gasoline having an elemental 
sulfur level of 30 mg/L elemental sulfur (Mercury Number Method; UOP 
Method 286-59). The gasoline was stirred for 1 hour with 50 ml of 
Solution A, allowed to settle and thereafter decanted to produce a treated 
gasoline having an elemental sulfur level of 7 mg/L. 
EXAMPLE 3 
Into a beaker were added 100 ml of pipelined gasoline having an elemental 
sulfur level of 44 mg/L elemental sulfur. The gasoline was stirred for 1 
hour with 25 ml of Solution A and 25 ml of Solution B, allowed to settle 
and thereafter decanted to produce a treated gasoline having an elemental 
sulfur level of 4 mg/L. The treated gasoline was treated again as above in 
this example to produce a gasoline having an elemental sulfur level of 3 
mg/L. 
EXAMPLE 4 
100 ml of the pipelined gasoline of Example 3, 25 ml of Solution A and 25 
ml of Solution C were mixed for 1 hour. The mixture was then allowed to 
settle and the gasoline removed by decantation. The treated gasoline had 
an elemental sulfur level of 3 mg/L, showing that dilution with caustic 
still achieved significant sulfur removal. 
EXAMPLE 5 
100 ml of the gasoline of Example 3 and 50 ml of Solution C were mixed for 
1 hour. The mixture was then allowed to settle and the treated gasoline 
removed by decantation. The treated gasoline has an elemental sulfur level 
of 41 mg/L, showing that caustic alone does not remove significant amounts 
of elemental sulfur. 
EXAMPLE 6 
100 ml of the gasoline of Example 3 and 50 ml of aqueous solution 
containing 12 g of sodium sulfide (9H.sub.2 O) (10M) were mixed for 1 
hour. The mixture was then allowed to settle and then the treated gasoline 
removed by decantation. The treated gasoline had an elemental sulfur level 
of 30 mg/L, showing that sulfide alone is not very effective for removing 
elemental sulfur. 
EXAMPLE 7 
100 ml of the gasoline of Example 3 and 50 ml of solution D were mixed for 
24 hours. The mixture was then allowed to settle and then the treated 
gasoline removed by decantation. The treated gasoline had an elemental 
sulphur of 3 mg/L, showing that addition of elemental sulphur in the 
aqueous phase is not essential to remove the elemental sulphur from the 
gasoline.