Accordingly, in order to produce high quality asphalt cement, one must use a specially selected crude oil which can be transported to a manufacturing plant without the crude oil being intermingled with other crude oils. Alternately, one must utilize polymers and other expensive additives which will dramatically increase the price of the resultant asphalt mixture. In either case, the number of crude oils which may be selected for producing a high quality asphalt cement is limited.Catalytic oxidation of asphaltic residuum is known in the art. Catalytic oxidation, which can be used to produce an asphalt cement having a higher penetration at a given softening point, has been generally used only in the production of roofing asphalt where increased flexibility at lower temperatures is required.The earliest reference to catalytic oxidation of which the applicant is aware is US-A-1 782 186, which discloses incorporating a non-alkaline earth metal salt (such as chloride of iron) in a petroleum residuum prior to blowing the residuum. It is reported that the blown product had an increased penetration with a corresponding decrease in brittleness.
Since that time, catalytic oxidation has become widely utilized in the roofing industry to prepare roofing bitumen 110/30. Catalytic oxidation is advantageous in the roofing industry since asphalt roof shingles are typically very thin and subjected to large daily temperatures fluctuations. Due to these conditions of use, asphalt shingles must have a high viscosity (a high softening point) while maintaining their flexibility (a high penetration). By catalytically oxidizing a roofing asphalt cement, an asphalt cement is obtained which has increased flexibility at a given softening point. Furthermore, catalytic oxidation results in a shortening of the oxidation time.Catalytic oxidation of asphalt cements is discussed in greater detail in US-A- 4 338 137 which discloses a process for air-blowing asphalts in the presence of ferrous chloride. As is described at column 1, lines 12 – 16 of that patent, air-blowing raises the penetration of an asphalt cement at a given softening point.
Until recently, little attention has been paid to the use of catalytic oxidation in the preparation of road asphalts. In the early 1980’s, the use of catalytically oxidized bituminous material to prepare paving asphalts has been considered. See for example J.S. Bahl, and Himmat Singh, Air-blowing of Bitumens: Process Variables and Structural Parameters, Revue de l’Institute Francais du Petrole, volume 38, no. 3 May – June 1983; and, L.N. Shabalin et al Pilot Plant Oxidation of Petroleum Tar in the Presence of Iron Chloride, Nefterpererab, Nefterkhyng, Moscow, 1979.More recently, US-A- 4 456 523 and US-A- 4 456 524 disclose a process for producing a high grade asphaltic material which process comprises blowing a bituminous material to the desired grade in the presence of a catalytic amount of an inorganic carbonate salt or an organic carbonate salt as the oxidation catalyst. At column 1, lines 15 -17, US-A- 4 456 523 discloses that the invention is concerned in one specific embodiment with chemically producing paving grade asphalt cements. The thrust of this patent is the use of new non-corrosive inexpensive readily available catalysts. These catalysts are to be used in preference of Lewis acid catalysts, such as ferric chloride and ferrous chloride, which are very corrosive (column 2, lines 57-65).It is desirable to provide premium paving asphalts. These paving asphalt cements have performance characteristics which are equal to or superior than those of high quality paving asphalt cements without requiring the use of polymers or additives.
It is also desirable to provide a method of upgrading crude oil residues so as to obtain paving asphalt cements from crude oils which would not otherwise render high or low quality paving asphalt cements.It is further desirable to provide means for increasing the number of crude oils which may be utilized to prepare paving asphalt cements having good performance characteristics.
