Rapid Determination of Water in By-product Sulfur LOUIS SHNIDXIAN, Rochester Gas and Electric Corp., Rochester, N. Y.
By-product sulfur, sometimes known as sulfur paste, recovered during the purification of manufactured, natural, or refinery gases using liquid purification and sulfur recovery processes, is being used extensively as a fungicide. The texture and consistency of the specially milled and creamed sulfur are controlled by its water content during its production. A rapid density method for the determination of water in the byproduct sulfur requires no weighing, but merely comprises liquefying the sulfur
.
paste, deaerating the sample by suction with constant stirring i n a special metal container, counterbalancing a given weight, and reading the moisture content directly from a calibrated flask. Its accuracy has been established by comparison with a distillation procedure previously developed. The rapid density method will give results within 0.5 per cent of the true water content of by-product sulfur. The time required for a determination is 10 minutes.
B
Figure 1 presents a view of the hydrogen sulfide removal system with the two absorbers a t the left, the pressure thioniaer on the right, and the operating building in the center. The plant is capable of handling some 566,300 cubic meters (20,000,000 cubic feet) of gas per day. The sulfur slurry released at the top of the thioniaer flows to R supply tank, thence to a continuous vacuum filter where the by-product sulfur is separated and washed. The nature and general properties of by-product sulfur have been described previously (2, 3, Q, 7, 8). By-product sulfur consists essentially of water, free sulfur, less than 1 per cent of iron oxide, and less than 1 per cent of water-soluble salts. The by-product sulfur as it comes from the filters consists of a yellow-gray sticky paste containing about 45 per cent of nater. To prepare this material for market, the sulfur is milled and creamed in special equipment and the moisture content is raised to 52 to 60 per cent, depending upon the type of product desired. I n this condition, it is being used extensively today as a fungicide not only for apple orchards but for other fruits as well. I n preparing the final milled sulfur a t the plant, it is necessary to keep the water content within definite limits. This requires a rapid and reliable method for determination of the water in the sulfur paste. The author (8) previously described a distillation method for determination of water in by-product sulfur, which was based upon the separation of water from the sulfur by the use of a mixture of light oil and gas oil which aided in distilling over of the water into a calibrated trap using a reflux condenser. This method proved to be accurate and convenient. However, the 2 to 3 hours required for the determination by the distillation procedure were too long when the by-product sulfur was being processed a t the plant, and the mater content was required within a short time in order not to hold up production.
Y-PRODUCT sulfur, sometimes known as sulfur paste, is recovered during the purification of manufactured, natural, or refinery gases which utilize liquid purification and sulfur recovery processes (5, 6, 9, 10). At Rochester, N. Y., an “ammonia-Thylox” liquid purification system is in operation. The details of the process have been described by Bowman (1). The chemistry of the process as studied by Gollmar (5) and in the author’s laboratory can be briefly summarized as follows: Certain thioarsenates are capable of absorbing oxygen from the air, replacing part of the sulfur in the thioarsenate molecule, and precipitating it as elemental sulfur. This lower sulfur thioarsenate molecule can absorb hydrogen sulfide, forming the original thioarsenate, and the cycle can be repeated continuously. In practice theoretical quantities of arsenic trioxide and soda ash are dis5olved in boiling water and added to the system as required to maintain an arsenic trioxide concentration of 6.0 grams per liter. The gas containing some 25.9 grams (400 grains) of hydrogen sulfide per 2.83 cubic meters (100 cubic feet,) is scrubbed by the Thylox (arsenic) liquor containing the thioarsenates as indicated in the reactions that follow: A. Preliminary reactions:
+ 2Ka2COs + H20 +PNa2HAsO3 + 2C02 2SazHAs0g + 5H2S-+- h’a4As2SS + 6H20 SarAs2S; + -+- Na4As2S502
As203
0 2
(1)
(2)
(3)
B. In the hydrogen sulfide absorber the following reactions take place in the ammonia-Thylox process: (NHa)aAszS502 (hTH4)4AsaSeO
+ HzS + (NH4)&860 + Hz0
(4)
( N H J ~ A ~ Z S T Hn0
(5)
+ HnS
-+-
+
Reaction 4 is faster than 5 and represents the main reaction in the absorber. C. I n the thionizer the Thylox liquor is treated with air under pressure, where oxygen is absorbed and sulfur liberated as follows:
+
(NH~)~As&
+
‘/no2 -+- (KH4)4AszSaO
+
S
(6)
Experimental Work
+
At the outset the operating engineers requested that a method be developed nhich would be simple, accurate, and reliable, and have the result available within 10 minutes or less. If such a method could be developed, plant operation and production could proceed normally and without delay. To meet these requirements a number of procedures were studied and some preliminary work was performed. Some
(SHI)&&O ‘/zOz (SHa)rAs&Oz S (7) Reaction 7 is faster than 6 and is believed to be the main reaction taking place in the pressure thionizer.
F h e n the p H of a solution of (XH4)4As2SB0 drops below 7.3, arsenic trisulfide and free sulfur precipitate out, indicating some reduction of pentavalent As+++++ to trivalent As+++.
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ANALYTICA
July 15, 1943
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substances to aid in such separation. Further work showed that
was ahandoned. 5. The determination of the density of the sulfur paste was tried. The density method WBS given further consideration heortuse it showed from the start that results could be obtained that were within 1 to 2 per cent of the true moisture content when ming sulfur from the same hatch. However, when sulfur paste from other hatches was employed, results were erratic. It N&S found that the density of sulfur in the by-product material was close to that of sulfur reported in the literature. ~~~
~~~
From previous work carried out in this laboratory on the properties and behavior of by-product sulfur, it was found that various dispersing agents possessed the pr0pert.y of liquefying the sulfur paste, thereby converting it int.0 a creamy solution that could he readily handled. One of the dispersing agents found best for this purpose was Bindarene flour, made by the International Paper Company. The analysis of this Bindarene flour dispersing agent was as follows: Total solids
Ash Silica and insoluble Oxides of iron e.nd alumina Caloium oxide Magnesium oxide Sulfur trioxide Sulfur dioxide Total sulfur pH (of 10% solution) Organic matter (100% wster ash)
96.90 8.52
0.04
0.11
4.60
1.70
0.36
4.10
3.06 5.7
88.39
One procedure employed early in this study NBS to liquefy the sulfur paste with the Bindarene flour dispersing agent and measure the volume of a known weight of sample. It was observed that the liquefied sulfur paste contained large quan-
431
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