It should be noted that only the usual finished products have been described and that these are not the only ones that can be obtained from the crude naphtha. For instance, in times of peace only small quantities of pure benzene and toluene are produced and those only for the manufacture of dye intermediates. The separation is generally only carried as far as the secondary distillation, and the two fractions 90's benzole and 90's toluol are run together to form motor benzole. Again, many special fractions frequently have to be made to meet special requirements of consumers, such as a mixture of the pure xylenes, distilling within a range say from 135° C. to 145° C.
Specifications of Finished Products
The specifications of the various finished products may be briefly described as follows :Benzole Forerunnings. - This is a by-product and the quantity obtained is kept as low as possible as it does not obtain a ready sale. It is composed chiefly of carbon di-sulphide and only the small quantity of benzole that in practice cannot be profitably extracted. There is no definite specification for it.
The specifications, as laid down by the Government and accepted by the dye-makers, are almost identical for the two products and are as follows :For Pure Benzene.Appearance. - To be a clear water-white liquid, free from suspended solid matter.
The specific gravity is not to be less than 0.883 and not more than 0.887 at 15.5° C.
Must correspond approximately to 80.5° C, corrected.
90 c.c. of benzol shaken with 10 c.c. of 90 per cent sulphuric acid for five minutes should impart only a slight colour in the acid layer.
A fractionating flask of 200 c.c. capacity, fitted with thermometer graduated to read to one-tenth of a degree Centigrade, and so adjusted that the top of the bulb is on a level with the side tube. The flask to be placed on a sheet of asbestos board having a hole one inch in diameter in the centre, in which the bottom of the flask rests, the bulb of the flask being surrounded by a cylinder of wire gauze resting on the asbestos sheet, and of such a height that the top of the cylinder is on a level with the top of the bulb.
100 c.c. of benzole are placed in the fractionating flask exposed to the flame (or source of heat) by the hole in the asbestos sheet, the distillation being conducted at such a rate that about 7 c.c. per minute are collected in the receiver, which is a 100 c.c. graduated cylinder.
The temperature is read when 5 c.c. and again when 95 c.c. have come over. The difference between the two readings must not be greater than 0.5° C.
This specification is exactly similar to the foregoing except that the limits of specific gravity are 0.868 and 0.870 and that the boiling point must correspond approximately to 110° C.
The National Benzole Association, which protects the interests of both the manufacturer and user of motor benzole, has laid down that the most suitable benzole for internal combustion engines is one that passes the following specifications :1. Specific Gravity. - .870 to .885.
2. Distillation Test (by flask). - Benzole shall give a distillate of not less than 75 per cent to 80 per cent up to 100° C.; of not less than 90 per cent up to 120° C.; of not less than 100 per cent up to 125° C.
3. Sulphur. - The total sulphur shall not exceed 0.40 per cent.
4. Water. - The benzole shall be entirely free from water
5. Colour. - Water-white.
6. Rectification Test. - 90 c.c. of the sample shaken with 10 c.c. of
90 per cent sulphuric acid for five minutes shall not give more than a light brown colour to the acid layer.
7. The benzole shall be entirely free from acids, alkalis and sulphuretted hydrogen.
8. The benzole shall not freeze at 25° F. below the freezing point of water.
This material, used chiefly as a solvent for raw rubber, is commercially described as 90/160 or 95/160 solvent, thereby indicating that 90 per cent or 95 per cent distils off between 120° and 160° C. when tested in an ordinary retort. The liquid must be water-white, well washed and not strong smelling. It has a specific gravity of .865 to .875, and the flash point is 60° to 70° F. (Abel's closed test).
This product has a specific gravity of .900 to 910 and flash point of 95° to 105° F. It should be water-white., well washed and fractionated well enough to ensure the presence of only small quantities of naphthalene. Its distilling points are generally 90 per cent off up to 190° C, and when this is the case it is consequently known as 90/190 naphtha. It is used chiefly as a paint-vehicle, particularly for ships' anti-fouling compositions.
Methods of Testing
These are fully described in many of the books referred to at the end of this chapter. The retort test is the one most commonly used for all the naphthas and is very simple. Unfortunately it has not been properly standardised, so that different operators frequently obtain conflicting results. It is purely an empirical test, and consequently entirely dependent upon the method of operation and kind of apparatus employed. It is used., particularly in the case of crude benzole, as a basis of sale and purchase and should be thoroughly standardised.
The test which gives consistent results and is recommended by the author is as follows : - 100 c.c. of light oil or crude benzole are placed in a 250 c.c. retort and attached to a 24-inch condenser, the whole apparatus having been previously rinsed with the oil to be tested. The thermometer is fixed so that the bulb is 3/8 of an inch from the bottom of the retort. The distillation is performed with a small naked flame shielded from draughts, the rate of distillation being 4 c.c. per minute. At 120° C. the flame is removed, the condenser allowed to drain, and the amount of distillate noted. The retort should be of the usual normal shape and the thermometer 15 inches long with a bulb 3/8 inch long, and graduated in one-fifth degrees from 70° to 130° C.
The corrections for barometric pressure and for inaccuracies of the thermometer may be made before each test by suspending the thermometer in the neck of a flask containing boiling water, taking care that the length of thread immersed in the steam is the same as the height of the retort. This is very important, as pointed out by Wheeler.1 The same difference below or above 100° C. may be taken when stopping the distillation at 120° C, as it may usually be assumed that the error is the same at these two points.
It is most unfortunate that the retort test has grown to be the usual one, and it is very desirable that a test based on fractional distillation or even a distillation from an Engler flask (as used by some makers) be instituted and adopted as a standard.
Much useful work has been done recently on the analysis of the various naphthas but is too comprehensive to be described here. For those interested in this subject reference may be made to the undermentioned papers: 1. H. G. Colman. " Determination of Toluene in Commercial Toluol," J.S.C.I., 1915, 34, 168.
1 J. Soc. Chem. Inct., 1916, 35, 1198.
2. H. M. James. "Determination of Toluene, with a Note on Application of the
Method to Benzene and Toluene," J.S.C.I., 1916, 35, 236.
3. P. E. Spielmann, E. G. Wheeler. "The Analyses of Commercial Benzoles,"
J.8.G.I., 1916, 35, 396.
4. A. Edwards. "The Estimation of Benzene and Toluene in Commercial
Mixtures," J.S.C.I., 1916, 35, 587.
5. D. Wilson, L. Roberts (Gas Record, Chicago). " Determination of Benzene,
Toluene and Solvent Naphtha in Light Oils, etc." J. Gas Lighting, 1916, No. 134, pp. 225-227; Abst. J.S.C.I., 1916, 35, 684.
6. P. E. Spielmann, F. Butler-Jones. " The Analyses of Benzole First Runnings," J.S.C.I., 1916, 35, 911.
7. E. G. Wheeler. "The Stem Correction of Thermometer," J.S.C.I., 1916, 35,
8. G. Harker. " Estimation of Toluene and Benzene in Coal Tar Oils," J. Royal
Soc. N.S.W., 1916, No. 50, pp. 99-105 ; Abst. J.S.C.I., 1917, 36, 950.
9. P. E. Spielmann, G. Campbell-Petrie. " Observations on Crude Benzoles,"
J.S.C.L, 1917, 36, 831.
10. P. E. Spielmann, F. B. Jones. "Estimation of Xylene in Solvent Naphtha," J.S.C.L, 1917, 36, 480.
11. F. Butler-Jones. " Analyses of Commercial ' Pure' Benzole," J.S.C.L,
1918, 37, 324 T.
12. F. W. Sperr. "Method for Boiling Point Test of Benzole," Met. and Ckem. Eng., 1917, No. 017, pp. 586-588 ; Abst. J.S.C.L, 1918, 37, 26a and 50a.
13. W. G. Adam. "Analyses of Crude Benzole," Gas. Journal, 1918, No. 14, p. 65 ; Abst. J.S.C.L, 1918, 37, 50.
14. J. M. Weiss. "Methods of Analysis used in Coal Tar Industry," J. Ind. arid Eng. Chem., 1918, No. 10, pp. 1006-1012; Abst. J.S.C.L, 1919, 38, 68a.
15. W. J. Jones. "Determination of Degree of Purity of Samples of Benzene," J. Soc. Dyers and Col, 1919, No. 35, pp. 45-47 ; Abst. J.S.C.L, 1919, 38, 216a.
16. H. G. Colman, G. W. Yeoman. "Determination of Benzene and Toluene in Coal Tar and Similar Products." J.S:C.L, 1919, 38, 57 T, 136 T, and 152 T.
17. W. J. Jones. " Determination of Benzene in Crude Benzole," J.S.C.L,
1919, 38, 128 T.
18. P. E. Spielmann, F. Butler-Jones. "Estimation of Carbon Di-sulphide,"
J.S.C.L, 1919, 38, 185-188 T.
For further information on this subject the following books may be consulted : Lunge. Coal Tar and Ammonia.
Warnes. Coal Tar Distillation.
Cooper. By-Product Coking.
Christopher and Byrom. Modern Coking Practice.
Malatesta. Coal Tars and their Derivatives.
E. Hausbrand. Die Wirkungsweise der Rektificir- und Destillirapparate, also
Verdampfen, Kondensieren, und Kuhlen. C. Mariller. La Distillation fractionnee. S. E. Whitehead. Benzole : its Recovery, Rectification and Uses.