The effect of air blowing on paving grade vacuum residue to produce high softening point industrial grade asphalt have been studied in a gas-liquid reactor.
Factors such as reactor design, temperature, air flow rate and time were investigated. Response of different feedstock sot metallic chloride catalysts were examined.
The course of reaction was followed by measuring penetration and softening point of the blown product at regular intervals. It was found that the catalytic activity of metallic chloride could be enhanced by combining the chloride with manganese dioxide. Quantity of chloride catalyst, the amount of blown distillate and acidic gases are considerably reduced, by the addition of manganese dioxide for a given degree of hardness of the blown product.
Chemical changes occurring during asphalt air blowing has been evaluated by adsorption-adsorption chromatography. The amount of asphaltene increases at the expense of saturate, namphthene aromatic and polar aromatic. Identical fractional chemical composition of different asphalts results in identical penetration and softening point. However, high molecular weight hydrocarbons may also be connected with hardening of asphalt.
N.m.r. studies show transformation of straight chain hydrocarbons to cyloparaffins which in turn, are dehydrogenated to form aromatic hydrocarbons during air blowing. Dehydrogenation of asphalt molecules is supported by elemental analysed. U.v spectra show the formation of polycondensed aromatic, while f.t.i.r. spectra indicate incorporation of oxygen and cross linking in blown asphalt.
Structural characterization of asphalt by instrumental methods, suggest that the blown product becomes more complex and condensed leading to increase in molecular weight. These changes are accelerated by active catalysts. The air blowing induces a movement of components from non-polar to more polar fractions. A general transformation mechanism has been proposed.
Quantity and characteristics of the effluents have been found to be dependent on the chemical nature and physical properties of feed as well as on the catalyst used.