91 



COLLOID CHEMISTRY OF PETROLEUM. 



By Dr. A. E. Dunstan. 



A considerable body of evidence is available concerning the 

 colloidal nature of crude petroleum and some of its distillates. Crude 

 oil of the paraffin base type [i.e., oil which on distillation yields solid 

 paraffins in the high boiling fractions) usually contains colloidal 

 amorphous matter which only assumes the crystaUine state after 

 distillation. It is probable that the effect of heat in this case is 

 physical, bringing about a change of state whereby the was is no 

 longer in the dispersed condition characteristic of the original oil. 

 Such oils and their residues after the removal of benzine and kerosene 

 are frequently highly viscous, particularly at low temperatures, 

 owing to the " setting " of the paraffin sol. This phenomenon may 

 be demonstrated by immersion of a suitable residual oil in ice for 

 several hours when the mass appears to be quite solid. A sudden 

 jerk or violent shaking will destroy the quasi-soUd mass and a thick 

 clotted semi-fluid material will be formed. 



The black or dark coloured " asphaltic base " oils contain 

 bituminous matter which is to be regarded as being derived from 

 the petroleum hydrocarbons by oxidation (and sulphuration) and 

 condensation. 



These oils are optically heterogeneous, although in most cases 

 the degree of dispersion is very high (see Holde, Koll. Zeits., 1908, 3, 

 270; Schneider and Just, Zeit. f. Wiss. MikrosJc, 1905, 22, 561). 



The colloidal asphalts may readily be coagulated by means of 

 strong sulphuric acid (Schultz, Petroleum, 5, 205, 446). The 

 chemistry of the well known " acid treatment " has been 

 investigated by B. T. Brooks and I. Humphrey {Jour. Amer. Chem. 

 Soc, 1918, 40, 822). The usually accej)ted view that olefines are 

 polymerised to tar and removed as sludge is erroneous, for pure 

 olefines (up to the Cio member) do not give tars with acid up to 

 100 per cent, strength at 15° C. The formation of " acid tar " is 

 probably a dual phenomenon — firstly, the acid coagulates the colloidal 

 matter present in the oU; and, secondly, it brings about polymerisa- 

 tion of olefines and diolefines, sulphonation of aromatic derivatives, 

 together with oxidation of primary materials and products. 



Pyhala {Zeits. Chem. Ind. Koll., 1911, 9, 209) considers that crude 

 oils are sols of which the disperse phases are solid gels such as asphalt, 

 together with liquid particles. Separation may be achieved by means 

 of centrifuging or the addition of electrolytes. When the disperse 

 phase exceeds 60 per cent, the phenomenon of gelattnisation makes 

 its appearance. 



In the discussion on a paper by Glazebrook, Higgins and Pannell 

 {Jour. Inst. Petr. Techn., 1915, 2, 54 et seq) the A\Titer brought forward 

 the peculiar hj^steresis effect in the viscosity of fuel oils and showed 

 that by a suitable alteration in the previous history of a given oil, 

 wide variations in its viscosity may be effected. The corresponding 

 behaviour in aqueous gelatine sols is well kno\vn and affords an 

 interesting parallel, 



