I,VDUSTRIAL Ah7D ESGISEERISG CHEUISTR Y
March, 1930
Table I-Mercaptan Sulfur Remaining i n Naphtha after Steam Distillation from Caustic Soda and Copper Solutions MERCAPTAN SULFURAFTER DISTILLATION FROM: hfERCAPT.4N
2: %-Butyl sec-Butyl n-Amyl NAPHTH.4 3 . Ethl-1 n-Propyl Isopropyl %-APHTHA 4 Isopropyl n-Butvl sec-Bityl sec-Amyl h-APHTHA 6 n-Propyl Isopropyl n-Butyl Isobutyl sec-Butvl n-.kmyi Isoamyl sec-Amyl
H?O
cuso4 NaOH
CI /O
5
%
0.0792 0.0434 0.0557
0 083 0 044 0 058
0.083 0.041 0.057
0.0363 0,0882 0.0592
0 048 0 086 0 058
0.060 0 087 0.060
0.0798 0.0796 0,0462 0,0582
0 074 0.080
2.5
5.0
%
%
10.0
%
%
R
S.4PHTH.4
0.0543 0.0530 0.0477 0.0528 0.0491 0 . 0500 0.0487 0 0470
0.053
0.056 0.047 0.049 0.056 0.046 0.052
0.050 0.042
0 030 0 028 S“ S 0.038
0.040
S
0.045
0.017
0.020 0.004 0 007
s
0.037
0.004 0.006
0.045 0.049 0.043 0.045 0.050 0.049 0.046 0.048
S S
S S
0 , 0 1 1 0 , 0 0 5 Trb 0 . 0 2 5 0.020 0 . 0 1 3
0,005
0.017 0 . 0 2 4 0 . 0 1 4 0.009
S
S
S
0.019
a S means sweet b Trace means 0 002 per cent or less.
more completely renioved than the correspondirig secondary mercaptans. and that the higher mercaptans TVere removed less than the lower ones, emphasizing again the fact that all mercaptans do not behave alike. Three distillations were made with 10 equivalents of copper sulfate arid 8 equivalents of caustic soda to find out if the alkali content would help in the removal of mercaptans. This was tried because
249
copper oxide is used for the removal of sulfur compounds such as mercaptans in refining. K i t h steam distillation it had no effect; in fact, the amount of mercaptan in the distillate vvas slightly greater with alkali than without it. The column labeled “CuAcZ)’ in Table I gives the result with steam distillation in which 10 equivalents of copper acetate \\-ere used to 1 of mercaptan (same as for the preceding experiments). I n all cases the resulting naphtha was sweet. It v a s necessary to mix the naphtha and the copper acetate solutions thoroughly before distillation; otherwise the first of the distillate contained a trace of mercaptan. Conclusion
From the evidence in this paper, the mercaptans studied are volatile with steam and the mercaptan contmt of all the naphthas except 4 remains constant after distillation from water or alkali. On steam distillation from a copper sulfate solution the mercaptan content in the distillate is decreased with increased amounts of copper sulfate. The addition of caustic soda to the copper sulfate does not asqist in reducing the amount of mercaptan in the distillate. Copper acetate gives a sweet distillate. Whether these copper salts remove the mercaptans or change them to other forms is not known from these data. Thiq will be discusqed in another paper (page 253 this isiue). L i t e r a t u r e Cited (1) Borgstrom and Reid, I \ c E v c CHEM., Anal E d ( 2 ) Frasch, I \ D . Exo CHEY, 4, 134 (1912) (3) IVood, Lowy, and Faragher, I b i d , 16, 1116 (1924)
1, IS6 (1929)
Behavior of Mercaptans in Naphtha’ I-Naph thas Used2a3 P. Borgstrom KAVAL RESEARCH LABORATORY, WASHIKGTON, D . C.
I
S STCDYISG the behavior of sulfur compounds in a
The constants of the naphthas are given in Table I.4 The solvents were supplied by commercial laboratories. Naphthas 1 and 2 were obtained from natural gas by use of an oil scrubber. The crude naphtha was agitated in turn d h sulfuric acid, fuming sulfuric acid, water, and sodium (1) Boiling point of the naphtha in relation to the sulfur carbonate solution, and finally allowed to stand over solid compound studied. ( 2 ) Does the naphtha contain aliphatic, naphthenic, or aro- potassium carbonate. It was then separated into two matic hydrocarbons, and if so what are the percentages? fractions by distillation as given. The other naphthas (3) Are the hydrocarbons unsaturated or saturated? were used as supplied by the oil companies. Xaphthas 5 , (4) Are there any impurities such as sulfur compounds, 6, and 7 were very similar and were supplied by the same and if so to what extent? (5) Xvailability of the naphtha and if choser. will it be a company as needed in the work in order to eliminate any typical solvent met v i t h in the industry? effect of aging that might occur if one sample had been used (6) Nature of the sulfur compound to be studied, especially throughout. when dealing with refining reagents. The sulfur content of the naphthas was det’ermined by Considering these factors the solvents were chosen with J. C. McIntire in this laboratory by the A. S. T. 31. lamp boiling points such that the mercaptans studied could possibly method. The bromine number was determined by the method of occur naturally in one or more of them. The mercaptans first to be studied are aliphatic, the majority being straight- Francis (1). I t will be noted that it’ is small, especially for chain with the mercaptan group on the first or second carbon. naphthas 1 and 2. From this value and the molecrilar weight (as determined by the freezing point method in benzene as a solvent) the per cent unsaturates mas calculated. 1 Several papers dealing with this subject are t o appear in IXDUSTRIAL A N D ESGINEERIA-G CHEMISTRYfrom time t o time. T h e siudy was begun The effect of the naphtha itself on the ease of removal of under t h e auspices of t h e American Petroleum Institute Project 28, of sulfur compounds is not fully known. With certain refining hydrocarbon solution the choice of the hydrocarbon to be used as solvent is very important. Some of the factors that may influence the choice of the solvent are:
which E E. Reid is director, a t t h e Johns Hopkins University and continued a t t h e Naval Research Laboratory. * Received January 20, 1930. Published by permission of t h e S a v y Department. a Appreciation is expressed t o t h e American Petroleum Institute and t o E . E. Reid for these solutions.
4 T h e naphthas used in studying t h e “Action of Refining s e a g e n t s on Pentamethylene Sulfide in N a p h t h a Solution,” IND.ENG. CHEM., 22, 87 (19301, are numbered t h e same as in this work. I n Table 111, page 88, t h e boiling points for t h e “per cent” under assay distillation should be Centigrade for naphthas 3 and 7 instead o i Fahrenheit a s given.
250 .
Gravity, 'A. P. I. a t 60' F. Color, Saybolt Sulfur, per cent
I.VDUSTRIAL ALVDENGINEERING CHEMISTRY NAPHTHA 1 78.3
T a b l e I-Physical KAPHTHA 2
66.3 ... 0.010
...
0.005
C h a r a c t e r i s t i c s of N a p h t h a s &-APHTHA 3 NAPHTHA 4 54.8 56.8 28 30 0.026 0.010
Vol. 22, No. 3 5 50.0 26 0.016
NAPHTHA
+
NAPHTHA
+
6
h-APHTHA
+
49.9 26 0.012a
7
49.3
25+
0.036
ASSAY DISTILLATION
Over, F. Dry, F.
170 332
130 216
202 390
226 333
OC.
%
OC.
%
OC.
%
OC.
60 65 70 .~
5 28 83 89
7 40 62 73 79 84 88
122 124 127 130 132 138 143
..
...
..
120 130 140 150 160 170 180 190 200
14
75
80 90 100 110 120 130 140
80
67 ..
..
31 57 66 79 88 94 96 98
... ...
296 410
so 10
30
50
70 80 90 95
.. ..
O C .
%
295 414 "C.
150 160 170 180 190 200 210
2 27 60 82 92 95 97
150 160 170 180 190 200 210
...
...
.. ..
...
...
293 404
5%
OC.
2 35 69
150 160 170 180 190 200
S5 93 96
98
.. ..
... .. ..
53 3 34 65 86 93.5 96.7
..
Total 96 92 98'0 Residue 1.4 4 1 1 1 1.6 Loss A 2.6 1 4.5 2 1 0.4 Doctor test Seg. Seg. Keg. Neg. Neg. Seg. Seg 2'' Bromine number 0.05 0.3 2.5 3.8 2.4 1 4 Molecular weight 84 98 128 121 147 143 141 Unsaturates, per cent Trace 0.2 2.0 2.9 2.2 1.3 1 9 a The sulfur content of this naphtha was determined by one operator as 0.028. another found i t t o be 0.019, and t h e third t o be 0.012, The value given i n a previous paper [ I N D . E N G . C H E M . , Anal. E d . 1 186 (1929)l was 0.028, hhile later data show t h a t 0.012 is much nearer t h e true value. This value was found as the blank on t h e solvent itself and aiso'with sulfur compounds dissolved in it.
reagents the influence of the solvent may be very small when dealing with one sulfur compound and very great when working with another. Therefore, in these papers the role of the solvent will be emphasized and in some cases there is not sufficient evidence to explain fully the variations.
Whether the conclusions drawn will hold for other naphthas can only be told by further work. Literature Cited (1) Franct-,
IND
EVG
C H E V ,is, 821
(1926).
11-Effect of Inorganic Salts, Caustic Soda, and the Doctor Solution on Mercaptan Sulfur in Naphtha' P. Borgstrom
-
NAVAL RESEARCH LABORATORY, WASHINGTON, D. C.
HE inorganic salts used in a previous paper (page 246 this issue) that showed a promise of sweetening naphthas were further studied in this work. The naphtha used was number 7, the constants of which are given in Part I.
T
Materials Used
This is a continuation of the work described in a previous paper (page 245 this issue) using a single naphtha and fourteen mercaptans. The naphtha was treated with those reagents which showed some promise of sweetening and also with caustic soda and the doctor solution. The only salt which gave a definitely sweet naphtha after treatment with the reagents was mercuric acetate, although copper chloride and copper acetate gave this indication at first. The doctor solution gave a precipitate with the primary mercaptans immediately. With the secondary mercaptans there was a soluble substance in which the ratio of mercaptan and lead was 1 to 1. The substance precipitated on standing, the time being dependent on the mercaptan.
The mercaptans were the thiols 1 and 2 from three to nine carbon, or fourteen mercaptans in all. The constants of these mercaptans will be published later. The solutions were prepared a5 described in another paper (page 245 this issue). The following reagents were used in 0.3 molar concentration: copper sulfate, ammoniacal copper sulfate, copper oxalate, copper acetate, cupric dichloride, cupric chromate, sodium dichromate, potassium permanganate, mercuric acetate, and potassium ferricyanide. If the substance did not go into solution but remained as a suspension, the bottle was thoroughly shaken before the necessary amount was taken. The sodium zincate was made by mixing 1000 cc. of water, 125 grams of sodium hydroxide, and 22 grams of zinc oxide, allowing to stand and then decanting the clear portion. It was analyzed and gave the following composition: 3.0 N NaOH and 0.15 M zinc. .?iote-silver nitrate solution (0.05 M ) gave a sweet naphtha after treatmegt. The per cent sulfur found by t h e lamp method after this wash was 0 0 % 0037, 0034, 0033, 0.029, 0.039. and 0044 for n-hexyl, sec-
Received January 22, 1930. Department.
Published by permission of the Navy
hexyl, n-heptyl, n-actyl, sec-actyl, n-nonyl, and sec-nonyl mercaptans, respectively. The blank was 0.036 per cent. The results with the nonyl mercaptans show some disulfide formation. The naphtha after the silver nitrate titration should not be used for further work owing t o the emulsion formed and probable loss of other sulfur compounds in the emulsion.
Experimental Procedure T R E A T M E K T WITH RE.4-
GENTS-TO 1 yoluine
of each of the reagents 2 volumes of naphtha were added and there was approximately 1 volume of air in the separatory funnel. The mixtures were vigorously shaken by hand for 10 minutes, allowed to separate into two layers, if possible, and the lower aqueous layer drawn off. If the emulsion formed would not separate, water or dilute acetic acid was added. The primary mercaptans gave naphthas that were especially hard t o separate, giving a very stable emulsion. With the sodium zincate wash of primary hexyl, heptyl, and nonyl it was necessary to add a considerable amount of acetic acid to break the emulsion, and therefore these values may be i n error. CAUSTIC SODA\vASH-For the caustic soda wash the ratio was 1 volume of caustic soda, 2 volumes of naphtha and 1 volume of air, placed in a glass-stoppered flask. The mixtures were vigorously shaken by hand for 5 minutes, allowed to separate, and samples taken. No attempt was made to wash the naphtha, for all samples of the naphtha after the alkali washes showed negative tests for alkali with a small amount of water and phenolphthalein. One sample.
