IAYDU8TRIAL AND ENGINEERIA’G CHE.VISTRY
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Vol. 22. No. 3
Distillation of Naphthas Containing Mercaptans by Steam, with and without Reagents’ P. Borgstrom,z R. Roseman, and E. Emmet Reid3 THEJ O H N S HOPKIWS UNIVERSITY, BALTIMORE, MD.
the distillation of naphthas containing mercaptans by with and without the use of reagents. Materials and Procedure
‘”
Naphthas 2, 3, 4J and described in another paper (page 249 this were used. The mercaptans studied were and isopropyl; normal, iso-, and secondary butyl; and normal, iso-, and secondary
7
This paper describes some experiments on the effect on the mercaptan content of several naphthas of distillation by steam, without reagents, and in the presence of caustic soda and copper salts. The results show that simple steam distillation and distillation from alkaline solution do not appreciably change the mercaptan content, although all mercaptans do not behave alike in this respect. With copper sulfate and copper acetate solutions, however, the mercaptan content of the distillate was decreased. Caustic soda did not aid in removing the mercaptan in these solutions.
more mercaptan than the last owing to theirvolatility. T h e column headed “KaOH” gives the results of steam distillation of the naphtha containing mercaptan from an solution. To 100 cc. of naphtha having 0.05 per cent added sulfur or approximately 0.0012 mol mercaptan were added 5 0 c c . o r 0 . 0 5 m o l of sodium hydroxide. This gave a mol ratio of RSH:-
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
S.4PHTH.4
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
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
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.
