1410
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 43, No. 6
SUMMARY
ACKNOWLEDGMENT
The elaetic properties of polymeric materials which are too soft t o test on conventional stress-strain machines can be obtained by elongation at constant stress. 9 simple apparatus has been developed for maintaining constant stress during elongation. Data illustrate the time dependence of the elastic behavior of polymeric materials and demonstrate the usefulness of the constant-stres method in the evaluation of this time dependence. The constant-stress method is useful in the evaluation of plasticizers for gum rubbers. Because of the difficulty of aeparating highly delayed elastic elongation from viscous flow, the method has not been found practical as a tool for measurement of viscosity in the solid state. However, under most test conditions the viscous flow has been a negligible fraction of the total deformation. Several terms for delayed elasticity are required to fit an empirical equation t o the elongation time curves, and it seems probable that these terms are only an approximatioll of a very large number of delayed elastic proresses having different relaxation times.
The authors are indebted to W. E. Lundquist, E. 0..Toesting, and Esther Eastwold for supplying many of the test materials, and t o W. W. Wetzel for assistance in developing the recording mechanism of constant-stress elogation tester. LITERATURE CITED
(1) Alfrey, T., Jr., “Mechanical Behavior of H i g h Polymers,” p, 129, N e w York, Interscience Publishers, 1948. (2) Ibid., p. 145. (3) Hahn, S. H., and Gazdik, I., I n d i r ~Rubber World, 103, KO.5, 515 (1941). (4) Holt, W. L., Knox, E. O., and Roth, F. L., J . Research Nall. Bur. Standards, 4 1 , 9 5 (1948). (5) Press, J. J., and Mark, H., Rayon Testile Monthly, 24, 297, 399, 405 (1943). (6) Roth, F. L.,’and Stiehler, R. D., J . Research Natl. Bzar. Standarda, 41, 87 (1948). (7) Scott, R. L., Carter, W. C., and Magat, M., J . Am. Chem. SOC.. 71, 220 (1949). (8) Sebrell, L. B., and Dinsmore, R . P., India Rubber World, 103, N o . 6 , 3 7 4 0 (1941). (9) Taylor, N. W., J . Phys. Chem., 47, 235 (1943). RECEIVEDM a y 26, 1949. Contribution 20. Central Research Depai tment, Minnesota Mining R: Manufacturing Co.
Ydrogenation of Petroleum Nitrogen Bases K. J. MILLER Culijorniu Research Corp., Richmond, Calif. Hydrogenation by several rne~hodswas investigated in an effort to convert the nitrogen bases extractable froni
thermally cracked petroleurii into poten tially iisefiil intermediates and derivatives. Reduction to secondary amines was accomplished by the use of sodium and alcohol, electrolytic reduction, and catalytic hydrogenation. Yariables of both the electrolytic reduction and catalytic hydrogenation were studied and conditions for maximum conversions and yields established. Derivatives of the hj drogenated petroleum nitrogen bases were found to be of utility as viilcanization accelerators, lubricating oil additives, Diesel fuel additives, flotation reagents, fungicides, insecticides, for removal of sulfur from hydrocarbons, and as dewaxing solwents.
A
LTHOUGH the piwclnce of nitrogen compounds
111 California petroleum has been known for many years (10, 11, 16)only a relatively minor proportion of the potential production has ever been separated for nonfuel uses. The present investigation was undertaken in an effort to convert the nitrogen bases extractable from cracked petroleum into potentially uscful intermediates and derivatives. The primary method of attack employed hydrogenation or reduction by several methods. The composition of the nitrogen bases in California cracked petroleum has been the subject of investigations by at least two groups. Extensive work on the separation and identification of the basic nitrogen compounds in distillates from California petroleum w a carried out under A.P.I. Project 20 at the University of Texas by J. R. Bailey and coworkers. I n one of the resulting papers a n investigation of the composition of the nitrogen bases extracted from thermally cracked gasoline was re-
ported ( 1 ) . Seven homologs of pyridine-namely, %methyl, 4methyl, 2,4-dimethyl, 2,5-dimethyl, 2,6-dimethyl, 3,5-dimethyl, and 2,4,6-tn’methylpyridines as well a8 quinoline and quinaldine were found. I n addition t o these compounds, subsequent investigators (8) found nine other homologs of pyridine, five methyl and dimethylquinoline homologs, isoquinoline, two isoquinoline homologs, four bases of unknown stmcture (probably pyridine homologs), and one unidentified strongly basic compound. The charging stock for all experimental and commercial work was cracked petroleum nitrogen base6 having the properties shown in Table I. These bases were extracted from thermally cracked California petroleum by contacting with 45% aqueous sulfuric acid. The extract was diluted with an equal amount of water and allowed t o stand for 12 t o 24 hours. The tarry oil layer which collected at the top was discarded. The aqueous layer was made alkaline by addition of aqueous sodium hydroxide. The resulting upper layer, comprising crude nitrogen bases, was distilled to remove water, collect a heart cut of nitrogen bases, and reject tarry bottoms
TABLEI.
PROPERTIES
OF
CRACKED BASES
Specific gravity 6O0/6Oo F Flash point, cloLed TAG, O ’ F . Color, A.S.T.M. Nitrogen (Dumas method), % Average equivalent weight Average basic dissociation constant D 86, O F.
NITROGEN
PETROLEUM
0.96
172 Black 8.9 4
x
165 10-3
These nitrogen bases may be reduced t o a mixture comprising mainly secondary amines by a number of methods including the following:
OF EXCESSACID IN ELECTROLYTIC TABLE11. EFFECT REDUCTION OF NITROGEN BASES r.--.L:--.a
1. Sodium and alcohol reduction 2. Electrolytic reduction (8) 3. Hydrogenation with a catalyst comprising molybdenum sulfide deposited on active carbon (17) 4. Hyd!rogenation over Raney nickel catalyst (8)
The first three methods were employed in this laboratory for the reduction of nitrogen bases extracted from thermally cracked gasoline and are discussed in the order given. SODIUM AND ALCOHOL REDUCTION
v
The method employed was a simple adaptation of one used for pyridine reduction t o piperidine (7). No difficulties were encountered, and good yields were obtained on a laboratory scale. The process was quite useful for the preparation of samples of the reduced nitrogen bases for preliminary evaluation. However, the process was not considered for commercial adoption because of the cost of sodium and the hazards involved in handling it. ELECTROLYTIC REDUCTION
A thorough investigation of the variables involved in electrolytic reduction of petroleum nitrogen bases was carried out. The cell consisted of electrodes of 1/18-inchcommercial sheet lead placed on both sides of a porous separator in a glass jar of about 1200-ml. capacity. The only difficulty found with the lead cathodes was poisoning which occurred when foreign metal salts such as ferrous sulfate contaminated the catholyte. Attack on the lead anode could be reduced t o a very low point by water cooling and coating the surface exposed above the anolyte with paraffin. Carbon anodes disintegrated rapidly. Three different types of separators were tried in this cell. ' A woven glass separator proved unsatisfactory because of the rapid rate of diffusion through the relatively large openings. Ordinary porcelain separators high in alumina were slowly dissolved by the strong acid and could not be used. The separators which proved most satisfactory were highly fired aluminous porcelain supplied by the Coors Porcelain Co. of Golden, Colo.
-%
*
1411
INDUSTRIAL AND ENGINEERING CHEMISTRY
June 1951
The general experimental procedure was t o use a solution of nitrogen bases in excess sulfuric acid as the catholyte and 50% sulfuric acid as anolyte. The temperature was controlled by a water bath. During passage of current, samples of the catholyte were subjected t o p H titration by which means the change from weak petroleum bases t o strong reduced bases was followed. The product distribution was determined as follows: The final catholyte was made alkaline and steam distilled to remove the reduced and unchanged bases from by-product condensed bases. A measured sample of the distilled bases was dissolved in a slight excess of 0.5 N aqueous sulfuric acid and back-titrated with 0.5 N aqueous sodium hydroxide using a Beckman p H meter with glass and calomel electrodes. Points of inflection were obtained a t pH's of about 3.5 and 9.0. The material titrating between these points was assumed t o be unreduced bases. The material titrating between a p H of 9.0 and the end point calculated from the amount of acid used was considered t o be reduced bases. The neutral oil content was determined by dissolving the distilled bases in aqueous sulfuric acid and measuring the amount of insoluble material. The condensed bases were separated from the residue remaining after steam distillation, and their weight was determined. These condensed bases are probably similar to the di- and polypiperidyls formed in electrolytic reduction of pyridine sulfate with low excess of acid (16). Their properties are: Equivalent weight Dissociation copstant (basic) Boiling range, F.
I54 1 x 10-6 Above 5 80
Excess Acid. Table I1 summarizes the results of runs to determine the effect of excess acid on the products of electrolytic reduction. Excess acid increased the yield of reduced bases and suppressed formation of condensed bases.
"UUlUi'lYU
Products Recovered. Wt. o/, (Based on Nitrogen Bases Cha-ed) Reduced Unreduced Condensed Neutral bases bases bases oil 9.0 33.5 7.5 26.0 4 .0 43.0 11.0 21.5 4.5 65.0 18.5 Small 66.0 22.5 Negligible 1.0 22.5 Negligible 2.0 67.5
--a as'u
Free Acid, Equivalents/ Liter 1.02 2.00 3.28 4.5 6.0
Total recovery 76.0 79.5 88.0 89.5 92.0
Constants: Nitrogen bases in catholyte 14.75% by volume; cell temperature, 122' F.; current density, 13 amp./&. dm. (only one side of the cathode included in area); anolyte acid strength, 47% HzS04; time of runs, 6 hours.
Nitrogen Base Concentration. Another series of runs was made to determine the effect of nitrogen base concentration in the catholyte on the products of reduction; results are shown in Table 111. TABLE111. EFFECTOF NITROGENBASE CONCENTRATION ON ELECTROLYTIC REDUCTION
.
-
-. Kecoverea. wt. % ,- Prpducjs, -. Time (Hased on Nitrogen Bases ChdGged) of Run, Reduced Unreduced Condensed Total ' Hours bases bases recovery bases Small 83.5+ 6 65.0 18.5 10.5 96.0 10 62.0 23.5 15.5 83.5 12 56.0 12.0 34.0 79.5 18 40.0 5.5
Combined Nitrocten Basesin Catholyte, % by Vol. 14.8 25.0 37.5 50.0
Constants: Free acid, 2.5 e uivalents/liter; .temperature, 122O F.: ourrent density, 13 amp./sq.%m.; anolyte acid strength, 47% Ht604.
.
An increase in nitrogen base concentration above 14.8% caused an increase in formation of condensed bases even with B constant amount of free acid.. Tn view of the small gain in reduction between 25.0 and 14.8y0nitrogen bases, lower concentrations were not explored. Temperature. A series of runs was made to determine the effect of temperature on the electrolytic reduction with results shown in Table IV. TABLEIv.
op.), 80 122 160
F.
EFFECT OF TEMPERATURE ON ELECTROLYTIC REDUCTION OF NITROGEN BASES
bases 51.5 66.0 59.0
bases 11.o 12.0 25.5
bases 24.0 15.5 Small
recovery 86.5 83.5 84.5
Constants: Nitrogen base strength, 37.5% by vol.; free acid strength, 2.5. equivalents/liter; time, 12 hours; current density, 13 amp./sq. dm.
Although the formation of reduced bases was increased only slightly by raising the temperature, the loss t o condensed bases was reduced markedly. The reason for the latter effect was not determined. Cathode Poisoning. The greatest difficulty anticipated in commercial application of this method of reduction was cathode poisoning. The electrolytic reduction depends on the hydrogen overvoltage on the cathode being sufficientlygreat that reduction of nitrogen bases is the preferred reaction as compared to liberation of hydrogen. Small amounts of some metallic ions tend ta lower the hydrogen overvoltage. Table V and Figure 1 show the effect of adding iron to the catholyte in the form of ferrous sulfate (FeS04.7HzO). Unless special precautions are taken in manufacture and shipment, commercial sulfuric acid may contain sufficient iron to reduce appreciably the rate of reduction. Furthermore, the poisoning effect is probably cumulative so that eventually the cathode would have t o be replaced even with extremely small catholyte iron contents.
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
1412
Vol. 43, No. 6
nicrsed in an electrically heated lead bath. il sulfactive catalyst, TABLE\-. EFFECTOF IRON IK CATHOLYTE ON ELECTROLYTIC molybdenum sulfide deposited on active charcoal, was used beREDUCTION OF XITROGEK RASES cause of poisoning of ordinary hydrogenation catalysts by sulfurReduced Iron in containing impurities in the nitrogen bases. To prevent deCatholyte, % Bases, % X t . sulfuiization of the catalyst and maintain its activity, carbon di0.0000 54 46 0.0043 sulfide was added to the feed. The procedure for determining 22 0.0225 the product distribution was similar to that for the products from 0 0.335 electrolytic reduction with the exceptions of omission of the steps Constants: Xitrogen bases, 37.59' b . 1.01.; free acid, 2.5 equiralentsiliter; temperat,ure, 122" F.; current d e h s y , 13 am p.isq. din.: time, 10 hours; of adding alkali and steam distilling. KO condensed bases were anolyte acid strength -17Ls; HtSOa. detected in the products of hydrogenation. Catalyst Temperatures. The effect of catalyst temperature is indirated in Table VI and Figure 2. 60 The reduced base content of the liquid product did not appear I t o be very sensitive to changes in reaction temperature within the range studied. However, destructive hydrogenation to ammonia and neutral oil increased Kith temperature a t the expense niainly of unreduced bases. The data suggest use of lower space rate or recycle operation in the lower temperature range in ordcr to obtain higher conversion t o reduced bases without cxccvivc loss to neutral oil. Pressure. The effect of piessure on the reaction is shown i n Table T'11
I 1
T.iE3L.E
T;II.
IhFECT OF
Q4
0. I
0.
%
IRON IN CATHOLYTE
43
Figure 1. Effect of Iron in Catholytc on Electrolytic Redaction of Nitrogen Bases
*
~Product Composition,
Maximum
F.
Reduced
Average
basr-
Unreduced bases
OS
Vol o/oSeutrxl oil
Other conditions; Pressure, 3000 Ib./sq. inch; hydrogen recycle rate 22 t o 33 moles/mole nltrogen bases; carbon disulfide feed, 0.5 to 1% by bel. in . catalyst/hour. nitrogen base feed; space rate, 0.3 to 0.5 ~ o l liquid/vol.
90NEUTRAL OIL
ao-
M w 702
?
z 0
UNREDUCED
BASES
eo: E . 0
,of50 a I JO0 V 20-
2100
2600 3000
TABLE171. EFFECTO F CATALYST TEIIPER.1TURE H Y D R U G E N A T I O K O F NITROGEN BASES _Catalyst _ _ T e m~ p,
Oren I'rcssure. Lh /Sq, Inch 1450 1800
REDUCED
BASES
' O i
AVERAGE CATALYST TEMPERATURE - O F
Figure 2. Effect of Catalyst Temperature on Hydrogenation of Nitrogen Bases CATALYTIC HYDROGENATION
I n view of the disadvantages of the two processes discussed previously, it was decided t o try high pressure catalytic hydrogenation in a pilot continuous hydrogenation unit having a 500-ml. catalyst chamber. The catalyst chamber and preheater were im-
PRESSURE
ON
NITI~OGEN BASES
HYDROGENhTIOS
OR'
-~ Product Composition, Vol. % Reduced bases Unreduced basen Neutral oil
33 33 38
39 48
Other conditions: iliaximuin oven temoerature. 535' F.: ai-esaac oven temperature 505' F ' hydrogen recycle ;ate 22 moles/mole nitroge; bases, carbon disulfide feed,'O.l t o 1.07 b vol. of 'nitrogen base feed; space rate: 0.29 vol. liq%dyvol. catalyst/hour.
There appeared to be a trend toward higher conversion as the pressure was increased. Ratio of Hydrogen to Nitrogen Bases. The effect of the ratio of hydrogen t o nitrogen bases fed is shon-n in Table VI11 arid Figure 3. Increasing the ratio of hydrogen to nitrogen bases improved the conversion t o reduced bases. It also decreased the loss to neutral oil, probably because of a decrsase in the true contact time. Even the lowest ratio tried was considerably higher than the theoretical of 3 moles of hydrogen for saturation of a pyridine nucleus or 5 moles for saturation of a quinoline nucleus. The combination of conditions employed in the last run shown in Table VI11 gave the best results obtained in any of the series. Maintenance of Catalyst Activity. Previous experience on gasoline polymer hydrogenation had indicated that it was desirable t o maintain a minimum hydrogen sulfide concentration of 1 grain per cubic foot of hydrogen in order t o maintain the sulfur content and activity of the catalyst. The pilot plant work on hydrogenation of nitrogen bases indicated that this could be accomplished by addition of 0.7 to 1.0% by volume of carbon disulfide to the nitrogen bases fed. Previous experience on gasoline polymer hydrogenation had also indicated the desirability of keeping the ammonia content of the hydrogen low. This might be accomplished by scrubbing any recvcle gas with water to remove the ammonia. PROPERTIES OF HYDROGENATED BASES
The process of reduction changed the material from weak bases of poor color stability to strong bases having a stable lightstraw color. A qualitative test by the Hinsberg method (19) indicated that before reduction the bases were tertiary amines and after reduction mainly secondary amines. Typical inspections of the reduced bases are presented in Table 13.
INDUSTRIAL AND ENGINEERING CHEMISTRY
June 1951
Evaluations of the reduced bases and particularly derivatives were carried out in a number of fields.
TABLEVIII. EFFECTOF RATIOOF HYDROGEN TO NITROGEN BASESFED
VULCANIZATION ACCELERATION TESTS.The first four derivatives listed in Figure 4 were tested as vulcanization accelerators. Properties of the vulcanized rubber samples were comparable to those obtained with similar types of accelerators now on the market and some properties, particularly flexing of carbon black filled rubber, were better than usual for commercial accelerators. LUBRICATING OIL ADDITIVES. The potassium, zinc, calcium, and tin salts of the reduced nitrogen bases dithiocarbamic acid were found t o be oxidation inhibitors for lubricating oil. The zinc salt was further tested and found t o be beneficial for corrosion inhibition and anti-ring-sticking tendency in lubricating oils ( l a ) . Furthermore, the addition of the zinc salt t o compounded lubricants containing metal phenate was found to decrease the corrosivity of the lubricant ( I S ) . The reduced nitrogen base dithiocarbamates have also been found to be beneficial in other compounded lubricants (3-5). DIESELFUELADDITIVES. The reduced nitrogen base thiuram disulfide and the nitroso derivative of reduced nitrogen bases have been found to be effective in improving the cetane number of Diesel fuel (80). One per cent of the former gave an 11-point rise in cetane number and 1% of the latter gave 9 points rise.
Hydrogen Feed Rate, Product Composition, Vol. % Moles/Mole Nitrogen Bases Reduced bases Unreduced bases Neutral oil 11 38 36 27 22 48 45 7 36 8 56 33 Other conditions: Maximum oven temperature 530" F.: average oven temperature, 501e F.; pressure, 3COO lb./sq. in;?h. carbon disulfide feed, 0.5 to 0.7% by vol. of nitrogen bases. space rate, 6.3 vol. liquid/vol. catalyst/hour. I
a
707
BASES
UNREDUCED
REDUCED
zol
I
0ASLS
OF REDUCED SITROGEN BASES TABLEIX. PROPERTIES
Specific gravity 6Oo/6O0 F. Flash point, closed T A G , F. Color. A.S.T.M. Average e uivalent weight Nitrogen &urnas method), % Average basic dissociation constant
IO 0
15
2s
20
30
Distillat.ion, A.S.T.M. D 86, Start 5% 10%
HYDROGEN FEED RATE-MOLE I MOLE NITROGEN BASES Effect of Ratio of Hydrogen to Nitrogen Bases Fed
Figure 3.
Derivatives and Their Utilization. A number of derivatives of the hydrogenated nitrogen bases were prepared by procedures similar to those revealed for hexamethylene imine ( 2 1 ) . Equations for the reactions and analyses of the products are shown in Figure 4. Sodium cyanide was used as reagent for the thiuram monosulfide preparation rather than phosgene as shown in the patent. All the reactions shown occurred readily, giving good yields. Because of the heterogeneous nature of the reduced bases, the products were either viscous liquids or amorphous solids.
C
j
H
+ CS2 + KOH
=
R ___
