Compounding Rubber with Petroleum Products Correlation of Chemical Characteristics with Compounding Properties and Analysis of Petroleum Products Used as Compounding Ingredients in Rubber FRITZ S. ROSTLER, Golden Bear Oil Company, Oildale, Calij. HEINZ W.STERNBERG, Wilmington Chemical Corporation, Wiiilmington, Del. Rubber compounding ingredients from petroleum can be evaluated by chemical analysis of the materials themselves. All petroleum products from higher boiling fractions of crude oil consist of five basic groups of components which have been isolated and tested in compounds of GR-S and natural rubber. Each shows typical behavior, reflected in curing characteristics and physical properties. Results presented show that the performance of a petroleum product in rubber depends on type and proportion of the basic components in the compounding ingredient. The method should prove especially useful for identification of plasticizers, extenders, and process oils. The quantitative method of analysis described consists in principle of stepwise precipitation with sulfuric acid. Analyses show that the variation in compositions is considerable even for products sold under the same label. The method is simple, can easily be handled by laboratory technicians for routine analysis in raw material control, and can replace the present practice of mixing and testing a rubber compound for product evaluation. It is generallq applicable to all petroleum products and bitumens of high boiling range.
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OZIPOUYDIXG ingredients for rubber from petroleum are
rarely defined cheiiiically unless they are well knoivn chemicals first produced from other sources. This is especially true of products derived from the higher boiling fractions of petroleum and sold under trade names as process oils, plasticizers, extenders, reclaiming oils, or merely mineral oils. The compounder as a rule knom the chemical composition of his other materials. He has available all that is known about the composition of the rubbers themselves, Thereas petroleurn products are usually labeled “Composition undisclosed” ( 1 6 ) . One reason for this unsatisfactory condit,ion is that J!-ith fern exceptions the chemical composit,ions are unknown. Physical constants are useful for identification of low boiling petroleum products, the components of Jvhich have been isolated and identified, but cannot be applied correctly to the higher boiling fractions of very complex and unknown composition. The object of the investigations reported here n-as to develop a method of defining these petroleum products by chemical characteristics and chemical reactivity, in the absence of chemical formulas. The investigation was concerned with petroleum products with a n init,ial boiling point of not lower t,han 160” C. at 10 mm. of mercury, existing preformed in petroleum or occurring regularly as component,s of petroleum disti,llates.
same methods. Refining of pet,roleum from various localities differs not in method but in the extent of treatment by the same method. Therefore, it should be possible to devise a method of chemical analysis applicable t o all petroleum product,s which tvould reveal groups of component,s of ident,ical reactivity. This paper shows that a chemical analysis based on the reactivity or affinity of petroleum conet,ituents to selected reagents can be used t o define petroleum products employed as compounding ingredients for rubber, and permits rapid and reliable prediction of performance.
METHOD OF QUALITATIVE ANALYSIS The method defines high boiling petroleum products in terms of chemical reactivity. Alrhough this definition is rather broad, the good correlation obtained between thc chemical characteristics and the behavior in rubber compounding proves its practical usefulness. To go farther than to suggest a general and broad classification would be to overstep the boundaries staked out by facts. However, characterization arid definition of the extremely complex petroleum products of high boiling range by chemiea,lly charact,erized groups of components are steps in the direction of using thepe products as chemicals of predictable performance based on general chemical knowlcdge. The concept of a quantitative chemical an products on the basis of group reactions is n 8, 10, d l ) , although none of the methods defines petroleum product,s as groups of components xvhich govern their behavior in rubber compounding. SCOPE OF METHOD
The groups of components that govern the behavior of petroleum products in rubber are deterniined gravimetrically. One group after another is removed from the sample under analysis and the amounts removed are determiiied by difference. Analytical procedure consists of the follorr-ingst,eps: 1. Separation of asphaltenes by treatment Kith petroleum ether in the cold . 2. Removal of nitrogen bases, Group I, by precipitation with dry hydrogen chloride gas in the cold 3. Removal of nitrogen bases, Group 11, by extraction with cold sulfuric acid of 85% HzSOi content 4. Removal of unsaturated hydrocarbons, Group I, by extraction xith cold sulfuric acid of 97% Has04 content 5. Removal of unsaturated hydrocarbons, Group 11, with cold oleum (fuming sulfuric acid) of 30% SO3 content 6. Weighing of the remaining saturated hydrocarbons consisting of Khite oil and solid paraffin
I n practice it is convenient to determine the five main groups on one sample (omitting Step 2) and to determine the Group I nitrogen bases on a separate and larger sample. The procedure of determining the five main groups of component3 is shown sche, matically in Figure 1. The determination of asphaltencs by difference tlirough’t h e 2 insolubilit,yin petroleum et,her was fi
BACKGROUND AND BASIS OF INVESTIGATION
The investigation n-as based on the consideration that petroleum fractions, especially those of the higher boiling range, respond Kith remarkable uniformity to certain chemicals independent of the crude oil from which they are derived. This fact has found practical application in the refining Of all petroleum by the
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were found to dissolve, reproducibly to f1%, all the other constituents of the materials except this group. Fifty volumes of this petroleum ether are consequently specified. Petroleum ether of this boiling range is commercially available from chemical supply houses. n-Pentane is preferable to petroleum ether, as cyclic hydrocarbons present in some petroleum ethers dissolve asphaltenes, but all data used in this paper are derived from tests made with petroleum ether; each lot was checked in a blank test to be sure it did not react with the reagents. Precipitation of the total nitrogen bases is based on tests on a wide variety of high boiling petroleum products, which showed by elementary analysis that the nitrogen content of the portion of the sample not precipitated was in no case more than 0.1% if the concentration of the sulfuric acid used was not less than 85%. The distinction between Group I and I1 nitrogen bases can be supported by the fact that dry hydrogen chloride did not remove all the nitrogen-containing components, regardless of how long or how often the treatment was repeated. How much these twonitrogen-containing fractions actually differ has not yet been clearly established. For rubber-compounding purposes, however, their effect appears to be alike.
Eickmann (14) who mixed bitumens with sand and extracted them with petroleum ether. A modification has recently been suggested by Fernandez (6). The precipitation of asphaltenes with hydrocarbons of low molecular weight has found large scale application in the propane deasphalting process (17). The principle of removing unsaturated hydrocarbons with sulfuric acid has also been utilized in a number of analytical methods, although the action of the sulfuric acid is not well understood and is sometimes described as coagulation of colloidal suspensions, sulfonation, oxidation, or other chemical reaction. Early methods of analysis by precipitation with sulfuric acid which found practical use are discussed by Holde (11). The action of sulfuric acid on reactive components of petroleum is the basis of the classic and still widely used method of refining with sulfuric acid (9). The action of fuming sulfuric acid is utilized in the manufacture of white oils. A commercial method of manufacturing white oils, similar to the steps described in the analytical procegure suggested, has been given by Nugey (18). The originality of the method reported in the present paper consists in the proper selection of reagents and in the sequence of their use. The method defines petroleum products of unknown composition in terms of percentages of materials which can be isolated as well as quantitatively determined. This feature provides the possibility of correlating composition with performance on the basis of tests carried out with the actual components besides giving numerical expressions for writing specifications. The method has been thoroughly tested on hundreds of products and found dependable, giving reproducible results with an accuracy within a fraction of 1yo.
Example. Exactly 10.0 grams of a petroleum product, prepared in the laboratory by neutralizing an acid sludge from lubricating oil refining and by distilling the organic material under vacuum, were dissolved in 100 ml. of petroleum ether. By repeated precipitation with dry hydrogen chloride gas and decomposition of the precipitate with potassium hydroxide, the mixture was split into 6.10 grams not precipitable with hydrogen chloride gas, having a nitrogen content of 0.37%, and 3.65 grams entirely precipitable with hydrogen chloride gas, having a nitrogen content of 3.35%. By treatment with 85% sulfuric acid, the 6.10 grams containing 0.37% nitrogen gave 5.40 grams of a product practically free of nitrogen (0.05%).
SELECTION O F TEST CONDITIONS
Because the reliability of every analytical method described in the literature is questioned by other investigators, all steps used in the analysis reported in this paper were worked out without preformed opinion. The asphaltene determination is based on the fact that 40 to 60 volumes of petroleum ether of boiling range 35" to 60" C.
The two concentrations of sulfuric acid specified in the analyses for the determination of unsaturated hydrocarbons, 97 to 98% for the removal of Group I, and oleum (27 to 30% sulfur trioxide) for Group 11, was suggested by similar tests. The method is based in principle on the fact that in treatment wkh
Loo0 g. Sample 50 m l . Petroleum ether
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R. I R1 Waporate to dryaess AITROQEN AITROQA BASES BASES IJXSATLTORBTED EYDROCARBONS SATURATED RYDROCARBORS 20 ml. Petroleum ether
