1290
.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
is added. It therefore appears that a t least one function of hydrogen in increasing the efficiency of the catalyst's action is to maintain some fraction of its surface free from sulfur. I n this connection it is significant that when the naphtha vapor contained added hydrogen the evolution of hydrogen sulfide commenced near the beginning of a run, whereas without hydrogen it appeared only on approach to the steady state. It has been shown that hydrogen is able to remove sulfur from the catalyst surface as hydrogen sulfide. These ideas suggest further that increasing the ratio of hydrogen pressure
Vol. 22, No. 12
to that of the naphtha vapor may increase the efficiency of the catalyst in removing sulfur. I n the present experiments this ratio was only about 1 to 4. Literature Cited (1) Borgstrom and Reid, IND. ENO. CHEM.,Anal. Ed., 1, 186 (1929). (2) Edgar and Caiingaert, Ibid.. 2. 104 (1930). (3) Faragher, Morrell. and Monroe, IND.ENO.CHEM..19, 1281 (1927). (4) I. G. Farbenindustie, A.-G., French Patent 621,434 (1927). Method No. 1. (5) Sabatier and Maihle, Compf. rend., 160, 1569 (1910).
11-Pure Sulfur Compounds in Hydrocarbon Materials in Contact with Nickel Catalysts Joseph C. Elgin FRICK CHEMICAL LABORATORY OF PRINCETON UNIVERSITY, PRINCETON, N. J.
/ '
Naphtha solutions of butyl mercaptan, isobutyl mercaptan, propyl sulfide, isobutyl sulfide, and thiophene, present individually, have been studied in contact with nickel catalysts in continuation of the investigation of the catalytic reactions of organic sulfur compounds in petroleum. The data presented demonstrate differences in the reactivity of sulfur compounds. Mercaptans and sulfides, but not thiophene, undergo a reaction evolving hydrogen sulfide in contact with a nickel catalyst a t the steady state in t h e presence of naphtha vapor. Under the present conditions mercaptans were removed more readily t h a n sulfides, and thiophene was not affected unless hydrogen was added. I n contact with the initially sulfur-free catalyst thiophene sulfur is removed, but the catalyst rapidly loses its activity toward this compound. The
..
I
N Part I it was shown that sulfur compounds present in
high-sulfur naphthas undergo reactions leading to the elimination of sulfur when the vaporized naphtha is passed over nickel or iron catalysts. The addition of hydrogen to the naphtha vapor increased the extent to which such reactions occurred. Differences in behavior with regard to the sulfur removal effected were encountered with different naphthas. These, apparently, were to be attributed to differences in the type and reactivity of the sulfur compounds present. The results presented in this paper confirm this conclusion. The present communication is concerned with preliminary data obtained in a study of the action of contact catalysts on pure sulfur compounds present individually in hydrocarbon material, carried out in extension of the work described in Part I. The investigation is in process of extensive development, and only the initial stages in this general field have been completed. However, certain positive results have been obtained which indicate important differences in the behavior of sulfur compounds in the presence of contact catalysts. Experimental Procedure Except for a few minor improvements, the apparatus and experimental procedure were essentially the same as those employed in Part I. The nickel catalysts were samples of the previously described material obtained from E. I. du Pont de Nemoum and Company. They were reduced in place and were approximately 20 grams in weight with an apparent volume of 25 cc. The sulfur compounds chosen for investigation were butyl mercaptan, isobutyl mercaptan, propyl sulfide, isobutyl sulfide, and thiophene. These were obtained from the
extent to which reaction occurs, and consequently the amount of sulfur removed, depends upon the type of sulfur compound involved. The addition of hydrogen to the naphtha vapor effects partial removal of thiophene i n contact with the catalyst a t the steady state. Increasing the ratio of hydrogen to naphtha increases the amount of sulfur removed. Addition of hydrogen effects the removal of a markedly larger proportion of propyl sulfide sulfur t h a n when no hydrogen is added. These results readily account for the differences in sulfur removal observed with the naphthas presented in Part I. They indicate t h a t the sulfur content of naphthas containing relatively large proportions of thiophene sulfur will be the most difficult to reduce by catalytic methods.
*..... Eastman Kodak Company and were used without further purification. They were added individually to sulfur-free naphtha in amounts sufficient to give solutions containing approximately 0.4 per cent sulfur. The naphtha employed was from Cabin Creek crude. Through the courtesy of C. R. Wagner, of the Pure Oil Company, fractions of this material having boiling ranges of 150" to 200', 200' $0 300', and 300' to 400' F. were supplied. The material employed depended upon the boiling point of the sulfur compound under investigation. The solutions were analyzed for sulfur by the lamp method. Since it is reported in the literature that this method gives low results with mercaptans, the mercaptan solutions were also analyzed for sulfur by the silver nitrate method of Borgstrom and Reid (1). Only a slightly higher value for the sulfur content was obtained by this method, and since it was necessary to employ the lamp method for the material passed over the catalyst, the lamp sulfur value has heen taken w the sulfur content of the solution. The sulfur content of separate 2540. portions of the naphtha condensed after passing the catalyst was determined, and thus indirectly the extent to which the sulfur compound present underwent reaction. It is evident that this method does not detect reactions of the sulfur compounds which do not evolve hydrogen sulfide or otherwise reduce the sulfur content, nor does it distinguish between several reactions which have hydrogen sulfide as a product. Experimental Results
No HYDROGEN ADDED-curves 1 and 11 in Figure 1 show the results obtained when naphthas containing 0.375 per cent sulfur as butyl mercaptan and 0.388 per cent sulfur as thiophene, respectively, are passed in vapor form over an
INDUSTRIAL AND ENGINEERING CHEMISTRY
December, 1930
initially sulfur-free nickel catalyst at 300" C. The rate of passage was 100 cc. (liquid) of naphtha per hour. The sulfur contents of successive 25cc. portions of the condensed product are plotted against the total volume of naphtha which has passed over the catalyst from the start of the run. I t is evident that butyl mercaptan and thiophene behave quite differently in contact with the catalyst. No hydrogen sulfide was evolved during the run with thiophene, while with butyl mercaptan its evolution began a t the 375-cc. point and gradually increased to a large value which remained practically constant after the 525-cc. point. Practically the entire butyl mercaptan content was continuously removed, but no thiophene is decomposed over the catalyst after the initial stages of the run. It is evident from the results obtained that both thiophene sulfur and butyl mercaptan sulfur are at first removed by reaction with the sulfur-free nickel surface, but to a widely different degree. The catalyst reaches a state of constant activity in which it catalyzes a reaction of butyl mercaptan which evolves hydrogen sulfide; thiophene, however, is unaffected in contact with it. (It seems probable that this is a question of equilibrium rather than reaction rate.) Under the present conditions 93 per cent of the mercaptan sulfur was removed at the "steady state." Test showed the residual sulfur to be practically entirely in mercaptan form. Sabatier and Maihle ( 4 ) state that metallic sulfides catalyze the decomposition of mercaptans according to the reaction 2CnHzne1SH +(cnH~n+~hS f HzS
1291
volved. Under the present conditions the mercaptans were removed more readily than the sulfides and thiophene was not affected. It is probable that the various members of each class of sulfur compounds will also differ in the same manner. This question will be studied further. Table I-Removal of Sulfur from Naphtha Solutions of Individual Sulfur Compounds a t 300° C. by a Nickel Catalyst i n Steady State. No Added Hydrogen
NAPHTHA
1 9
2 3 4 10
IN
Butyl mercaptan Butyl mercaptan P r o w l sulfide IsotjGtyl mercaptan Thiophene Isobutylsulfide
100 100 100 100
I
0.375 0.375 0.393 0.374 0 389 0 388
0.038 O.Oi9 0.309 0 105 0 368 0 323
93 79 21 72 0 17
I
Table 11-Effect of Added Hydrogen on Removal of Sulfur from Naphtha Solutions of Thiophene and Propyl Sulfide i n Contact with a Nickel Catalyst
SULFUR COMEXFT.
POUNDIN
TEMP.
NAPHTHA
HYDROOEN
NAPHTHA
C.
cc./
hour
c:./
man.
E$;:uNRT
initial
1
Per cent
Final
Per cent
1
RED''TION IN
SULFUR
I
P@
cent
CATALYST CARRIED TO STEADY STATE WITH BUTYL MERCAPTAN
7
S
Thiophene Thiophene Thiophene Propyl sulfide
11
ThioDhene
5
6
300
100
0.389 0.389 0.349 0.393
0.360 0.322 0.345 0,137
CATALYST INITIALLY SULFUR-FREE
and effect less readily the decomposition of sulfides, according to the reaction,
300
100
100
I 0.368
0.350
I
7.4 17.2 11.3 65.1
9.8
Comparison of experiments 1and 9, in which the rate of ffow of the naphtha was doubled, shows that the amount of reaction occurring is also dependent upon the space velocity, at least in the case of the mercaptans. It is probable that
( C ~ H I ~ + I+ ) Z S 2CnH~nf HzS
It is evident that, if this is the mechanism by which butyl mercaptan is decomposed in the present case, the rate of decomposition of butyl sulfide must be nearly equal to that of the mercaptan. I n view of the above statement and of the writer's results with propyl sulfide, this appears unlikely. Decomposition of the mercaptan according to the equation C4HoSH +GHs HIS would not involve this difficulty. The nickel catalyst which had been carried to the state of constant activity with butyl mercaptan was then employed with the naphtha solutions of I I 1 I I I I each of the other sulfur compounds. The results are recorded in Table I. The exnerimental conditions were identical in each run except in 9, where the rate of flow of the naphtha wasdoubled. Thevaluegiveninthefifth w o 75 I50 225 300 375 450 525 600 675 700 Volume ofNaphfha Passed over Cuialysf- CC. column represents the average sulfur content of Figure 1-Effect of Contact with Initially Sulfur-Free Nickel Catalysts In Vapor the entire volume of naphtha pLqsed Over the cata- Phase on Sulfur Content of Naphtha Containing Butyl Mercaptan or Thiophene lyst* Independent Curve I-Naphtha solution of butyl mercaptan, initial sulfur content 0 375 per cent. made on each 25 CC. of product. Small amounts of Curve 11-Naphtha solution of thiophene initial sulfur content 0.388 per cent. Curve dissolved hydrogen sulfide were present in the con- ~ ~ ! , ' , ~ ~ ~ " , ~ 3 ~ l ~ ~ 4 n o finitiai e t ~ sulfur ~ p c h content a ~ ~ ,0.386 e , per cent, hydrogen added. densate, but the differences in lamp sulfur after cadmium chloride washing were generally inappreciable. the quantity of sulfur removed in the case of the sulfides More than 70 per cent of the residual sulfur in the case of would be increased by a reduction of the space velocity. isobutyl mercaptan was in mercaptan form. Hydrogen sulIt should be noted that experiment 4 in Table I, in which fide was continuously evolved during the run in every case the catalyst employed had been previously carried to the but that of thiophene. steady state with butyl mercaptan, and the independent It is evident from the table that mercaptans and sulfides, experiment plotted in curve I1 of Figure I check quite defibut not thiophene, undergo a reaction evolving hydrogen nitely the conclusion that thiophene is not affected by the sulfide in contact with the catalyst in the presence of naphtha catalyst a t the steady state. vapor. It is also apparent that the extent to which such As previously discussed in the case of butyl mercaptan, reaction occurs, and consequently the amount of sulfur the reaction by which isobutyl mercaptan is decomposed removed, depends upon the type of sulfur compound in- would appear to be largely:
+
I
l . - L ? ! ~ - W ~ - - f U = i
1292
INDUSTRIAL AND ENGINEERING CHEMISTRY GHsSH +GHs
+ HzS
EFFECTO F ADDINGHYDROGEN-Experiments were carried out with the naphtha containing thiophene and the propyl sulfide-naphtha solution, in which hydrogen was added to the naphtha vapor. The results obtained using the same catalyst employed for the experiments without added hydrogen are recorded in Table 11. Curve I11 of Figure 1 shows the results obtained when hydrogen was added to the naphtha vapor containing thiophene passed in contact with an initially sulfur-free catalyst. I n each experiment 300 to 500 cc. of naphtha were passed over the catalyst and the sulfur contents of successive 25-cc. portions of the product independently determined. The sulfur contents were practically constant throughout the run except in the case of propyl sulfide. I n this run, which followed that with thiophene a t 400" C., the sulfur content of the first portions of the product was low, gradually increasing to a constant value. The value recorded in column 7 is the average value of the total volume of naphtha passed over the catalyst after the steady state was attained. Hydrogen sul6de was evolved in each run. As will be seen subsequently, however, when hydrogen is added the evolution of hydrogen need not necessarily indicate decomposition of the sulfur compound, in the case of a previously used cataiL-it,since hydroqen removes sulfur from the catalyst surface &s hydrogen sulfide. The results of Table I1 show definitely that the addition of hydrogen to the naphtha vapor effects the removal of thiophene in contact with the catalyst at the steady state. At 300" C. the amount of thiophene which underwent reaction at the steady state, in contact with the catalyst previously carried to this state with butyl mercaptan, was closely the same as that with an initially sulfur-free catalyst. Increasing the temperature to 400' C . increased the amount of thiophene sulfur removed only 1.5 times. Increasing the ratio of hydrogen to naphtha increases the amount of sulfur removed. (A study of the effect of increased pressure is in progress.) In no case, however, was a major portion of the thiophene sulfur removed under the present experimental conditions. Note-in attempting a run a t 400' C. with added hydrogen with an idtially sulfur-free ratalvat. complete carbonization of the naphtha took place in contact with the catalyst, no liquid coming through the reaction
tube.
It will be seen from a comparison of the results of experiment 8 in Table 111 with those of experiment 2, Table I, that the addition of hydrogen effects the removal of a larger perrenhge of propyl sulfide sulfur than is effected when no hydrogen is added. Whether the increase in amoiint of propyl sulfide reacting is to be attributed to catalywd reaction with hydrogen or to removal of sulfur from t,he catalyst surface hy hydrogen cannot at present be decided. EFFECTO F HEATINGCATALY5T IN HYnRoaEN-Heating the nickel cat,alyst which had been in use for some time in hydrogen at 400°C. produced a very large evolution of hydrogen sulfide, which continued for about 4 hours. It appears, therefore, that hydrogen is able to reduce the nickel sulfide surface. I t is significant that in experiment 9 with butyl mercaptan, recorded in Table I, and which immediately followed this treatment, the first portions of the product passing the catalyst contained only about 0.01.5 per cent of sulfur. The succeeding fractions rapidly increased in sulfur content until the steady-state value of 0.079 per cent was attained. It should also he noted in this connection that in experiment 8 with propyl sulfide, which followed immediately a run a t 400" C. with hydrogen and naphtha containing thiophene, the first 25 cc. of naphtha passing the catalyst contained only 0.041 per cent sulfur as compared with the steady-
VOl. 22, No. 12
state value of 0.137 per cent. It appears, therefore. that in the case of mercaptans and sulfides heating the nickel catalyst in hydrogen after it has attained the state of constant activity restores to a certain degree its activity toward these compounds. There was no such effect in the case of thiophene. ADSORPTION FROM LIQUID PHAsE-The adsorption of butyl mercaptan, isobutyl mercaptan, propyl sulfide, and thiophene from naphtha solution a t room temperature by the nickel catalyst was determined. The results are given in Table 111. Table 111-Adsorption of Sulfur from the Liquid Phase Weight of catalyst, 25 grams: volume of naphtha, 100 cc. \
NAPHTHA
Initial
Final
Per cent 0.385 0.374 0 406 0 388
Per cent 0 234 0 242 0 327 0.322
I Butyl mercaptan Isobutyl mercaptan Propyl sulfide Thiophene
PERCENT
SULFUR CONTENT
SULFURCOMPOUND IN
OF
I
TOTAL
SULFUR A~~~~~~~
Per cent 39 35 19 17
They show that the mercaptans are adsorbed to ahout the same extent and that propyl sulfide and thiophene are adsorbed to approximately the same degree. The amount of mercaptan sulfur adsorbed is, however, approximately twice that adsorbed in the case of propyl sulfide or thiophene. The differences in the degree to which these siilfur compounds are adsorbed is not nearly so marked as the differences in reactivity exhibited in the vapor phase. On shaking the naphtha solutions of butyl and isobutyl mercaptans with the reduced nickel catalyst. a deep red color developed after about a IO-minute interval. This color completely disappeared after 10 days' standing, leaving the solutions completely colorless. Reid and co-workers (3) have obtained this red color in the case of secondary mercaptans in experiments directed toward the determination of the adsorption of mercaptans on cupric sulfide. They do not state whether or not the normal and isomercaptans exhilit the phenomena. It appears, however, that it is specific neither for secondary mercaptans nor for cupric sulfide. Discussion
The preliminary results given above show definitely that the different classes of sulfur compounds occurring in petroleum exhihit marked differences in reactivity in contact with reduced nickel catalysts in the vapor phase. The mercaptans react most readily to eliminate suli u r as hydrogen sulfide, a large percentage of this type of sulfur being removed from naphtha even in the absence of added hydrogen. Thiophene is the most stable of the compounds studied, while the sulfides apparently occupy an intermediate pnsition. The derivatives of thiophene most probably will parallel the behavior of thiophene in this respect. Differences in catalytic reactivity also exist between isomers and also, undoiihtedly, will be found to exist between lower and higher members of the same series. The thiophanes and disulfides remain to be investigated. The results of the present study explain readily the differences in sulfur removal effected in the case of different highsulfur naphthas in contact with nickel catalysts obtained in Part I. Comparison of curve I11 in Figure I with curve I11 of Figure 2 of Part I, ohtained with a high-sulfur cracked naphtha. leads to the conclusion that the failiire to reduce the sulfur content of thie naphtha materially was due largely to the presence of sulfiir in thiophene form. Since it is known (2) that the thermal decomposition of mercaptans and siilfides results in the formation of thiophene. it appears that in general the sulfur content of cracked naphthas will
December, 1930
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
be more difficult to reduce by the present method than will that of straight-run naphthas. It is obvious that, when sulfur Occurs largely in thiophene form, Operating conditions have to be those necessary to effect the msximum removal of this type.
1293
Literature Cited (1) Borgstrom and Reid, IND. END.CHBH.,Anal. Ed., 1, 186 (1929). (2) Faragher, Morrell, and Comay, IND. ENO.CHEW,, 20, 537 (1928). (3) Reid et al.. Am. P C ~ ~ Inst. C U Bull.. ~ . , 11 (1930). . 11.. N ~ 53. . (4) Sabatier and Maihle, Compt. rcnd., 160, 1569 (1910).
The Acid Treatment of Lubricating Distillates‘ H. M. Weir, W. F. Houghton, and F. M. Majewski THEATL.4KTIC REFINIKG COMPANY, PHILADELPHIA, PA.
In order t o control plant acid treatments a laboratory N SPITE of the length of On this basis alone color acid-treating procedure has been developed which is time that sulfuric acid was selected as the primary capable of operating under a variety of combinations. has been employed in revariable in studying acidThe method enables one t o determine quickly for any fining petroleum lubricating treating phenomena. oil t h e amount and concentration of acid and t h e best distillates, the mechanism of Though it was believed highly conditions necessary for optimum color and oil yield. the reactions and the effects desirable to retain as much The samples employed are small although large enough produced are still in dispute. standard practice as possible, t o allow further study on such details as bloom, color The need for more knowledge the use of any standard color stability, gravity, viscosity, filter yield, etc. The reon this subject is obvious, scale and colorimetric method sults are reproducible and directly related t o plant especially since acid treating was immediately ruled out. practice. It seemed very unwise to atoccupies a place of primary A complete study of t h e treatment of Solar reduced importance in refinery operatempt to clarify the relationwith acids of concentrations varying from 75 to 98 per tion. During 1929 sulfuric ships in an admittedly coincent was made which revealed interesting data on color acid having a value of more plicated series of reactions removal, gravity, viscosity, index of refraction, oil loss, than 8 million dollars was while hampered by units of acid loss, and*the heat of t h e acid treating reaction. applied to about 34 million measurement which of themOn t h e basis of the results of this investigation, some barrels of lubricating oil in the selves bear no simple relationdiscussion of t h e generally accepted theories of acid United States. Fully 40 per ship one to the other. treating is introduced. The method of measuring cent of this acid was irrecoverablv lost in the oDeration. and expressing the colors of I n aidition, at leasc3 million barrels of lubricating distillate oils which was selected is an adaption of asystem first published were degraded to fuel oil value. by Parson and Wilson (13). This system was first used These figures indicate that appreciable savings might be by one of the authors in 1924 in unpublished work on the effected through a more scientific knowledge of the phe- value of adsorbents in decolorizing oils, work which paralleled nomena of acid treatment. During the past few years much to some extent the later work of Rogers, Grimm, and Lemmon advance has been made in the design of more efficient equip- (15). Lack of space precludes additional discussion of this ment and in improved methods of control. However, very work further than to state that the system is based on a little literature has appeared which offers any basis for under- definition of color similar to the concept of concentration of standing what better acid treating is and how it may be ac- solutions. Thus, a suitable oil is arbitrarily assigned a complished. standard color figure, say 10. By definition the color which No doubt the extreme complexity of heavy oil mixtures is results by mixing S volume parts of the standard oil with W largely responsible for this situation, but tacit agreement volume parts of a white oil is taken as - 10. The on the part of many prospective workers with the old axiom S S W that practical treating results cannot be obtained in laboratory colorimetric scale and method is so arranged that this conapparatus has greatly hampered serious research work in the cept of color concentration is retained over the whole range field. This paper presents a method of acid-treating oils of colors-from the darkest distillate to a white oil itself. This color scale meets two requirements which are deemed in the laboratory and of analyzing the results so that the conclusions can be directly applied to plant procedures with- absolutely fundamental: (1) a simple mathematical relationship between readings; (2) the system makes it possible to out any factors other than the inefficiency of the latter. The first logical step in the improvement of a procedure assign color to the darkest distillate-a “black” oil in common is to measure its efficiency in terms of factors which bear a parlance-in terms of the same units of color as those used to mathematical relationship to the effects produced. Finished express the color of highly refined products. The adoption of a simple and straightforward definition is lubricating oils are held to rigid specifications for gravity, viscosity, color, color stability, pour, bloom, steam emulsion, no guarantee of simple physical relatiomhips, but the charand acidity. The first three factors are capable of accurate acter of the results which will be presented apparently justimeasurement; the others are, in the present state of the art, fies the original assumption that such would be the case. At highly artificial stipulations rather than determinations. all events the ability to measure the color of very dark (dirty) Of the three factors which thus might offer a basis for study, oils gives a criterion of the quality of the raw material which the only one which seemed, a t the beginning of this work, apparently has not previously been used in studying acid to stand in the relationship of cause and effect with respect treatment despite the fact that it would appear to be fundamental to any serious study. to acid treating was the color of the oil. Colors taken on this scale were termed “true colors” 1 Received October 20, 1930. From a paper presented before the (T. C.) and a method of acid treatment was devised which Meeting of the American Petroleum Institute, Chicago, Ill., November 10 used the smallest possible amount of sample consistent with to 13. 1930.
I
