Indicator Scale for Determining the Color of Dark Petroleum Products
Abstract Generated abstract
This paper proposes a simple indicator scale for visually determining the color intensity of dark petroleum products, a task not adequately served by existing colorimeters or solution standards designed mainly for light-colored products. The authors describe a ten-standard scale made from sodium salts of humic acids dissolved in 2 percent sodium hydroxide, with concentrations selected to provide a gradual range from light yellow to nearly black. They report that the scale matches common petroleum-product color tones, is stable, inexpensive, and easy to prepare in modest laboratory conditions. The paper also discusses reproducibility, noting that humic acids should be prepared from materials of comparable origin and age, or preferably supplied as a centralized standard preparation.
Full Text
Indicator Scale for Determining the Color of Dark Petroleum Products
I. V. Gebler, S. I. Smolyaninov, D. A. Popov, D. D. Yodvorov
In practice one often has to determine the color, or more precisely the intensity of coloration, of various petroleum products and similar substances. For these purposes there are several designs of colorimeters and chromometers in which the intensity of coloration of the product under test is compared with the intensity of coloration of a colored solution of a definite concentration or with standard glasses possessing quite definite spectrometric properties [1]. As colored solutions, solutions of potassium dichromate in sulfuric acid are usually used.
Sometimes, in order to simplify determinations, instead of comparatively expensive optical instruments an “indicator scale” is used, consisting of a set of test tubes with colored solutions of different concentrations. In this way, for example, the degree of purification of crude-benzene fractions is determined [2].
All these methods, however, are intended chiefly for determining the intensity of coloration of light-colored products. When working with dark products, on some colorimeters it is proposed to carry out preliminary dilution of the substance under test with some light-colored product. An indicator scale for darker petroleum products, similar to the one mentioned above, has not been proposed.
After a number of experiments with various dyes we succeeded in preparing such a scale, convenient to use and simple to manufacture, from solutions of sodium salts of humic acids.
The indicator scale proposed by us has ten standards, which are solutions of humic acids of different concentrations in 2-percent sodium hydroxide. In order of increasing color intensity, these solutions have the following concentrations, in grams of dry ash-free acids per liter of 2-percent caustic-soda solution: No. 1—0.5; 2—0.75; 3—1.0; 4—1.5; 5—2.0; 6—3.0; 7—4.0; 8—5.0; 9—7.5; 10—15.
The humic acids were prepared from upper transitional peat by treating it with a one-percent solution of caustic soda, followed by dilution of the extract with a 20% solution of hydrochloric acid and repeated washing to complete peptization (the direct method for determining humic acids [3]). The yield of humic acids from the peats we used is 25–28% on dry peat.
This scale has a smooth change in color intensity from a light-yellow tone to dark brown, almost black, only slightly transparent in diffuse daylight, and covers all practically encountered colors of petroleum products. The scale may be extended in both directions; in addition, any intermediate number can be prepared. In its color tone it corresponds well to the usual colors of petroleum products. The humate solutions proved, as we verified, to have sufficient stability. Preparation of the solutions is not difficult and is accessible as a method, in terms of the starting materials, to any even primitively equipped laboratory.
reproducibility. The instructions available in the literature for the colorimetric determination of humic acids [3] may cast doubt on the possibility of accurately reproducing such a scale under different conditions.
The difference in the coloration of solutions of identical concentrations, but prepared from humic acids of different peats or coals, is due to the presence in their composition of “young” caustobioliths that are insoluble in water and organic solvents, but that pass into solution under the action of alkalis and salts of dark-colored acids. In this case, for reproducibility of the scale it is necessary to take the starting substance of one and the same origin and age. Thus, the scales we prepared from two high-moor sphagnum peats from different deposits, with yields of humic acids by the direct method of 25.5 and 28.5%, were absolutely identical, whereas a scale prepared from humic acids of woody peat (yield 26%) proved to be, on average, one number darker.
Thus, taking the above-mentioned factors into account eliminates the difficulty in reproducing the scales. This difficulty is still more readily eliminated when humic acids for these purposes are manufactured centrally. Thus, for example, a standard preparation was produced and used as a reference standard for the colorimetric determination of humic acids [3].
LITERATURE
- Kusakov M. M. Methods for determining the physicochemical characteristics of petroleum products. ONTI, 1932.
- Gluzman L. D., Edelman I. I. Control of coke-chemical production. Metallurgizdat, 1946.
- Stadnikov G. L. Analysis and investigation of coals. Publishing House of the Academy of Sciences of the USSR, 1936.