Compared with conventional crude oil, the elemental composition of heavy oil asphalt is characterized by low hydrogen content and low hydrogen-carbon ratio, mostly below 1.7. Except for crude oil from Gudao, Bamianhe and Caoqiao, the sulfur content in Shengli Oilfield is generally low, less than 1% (Table 12-4). The sulfur content in heavy oil asphalt from Venezuela, Canada and Iraq is obviously higher, and most of them contain more than 3% sulfur, among which the sulfur content in heavy oil asphalt from Kajala, Iraq is as high as 8.4% (table 12-5). As for the nitrogen content, it is relatively high in China.
Table 12-4 Element Composition of China Heavy Oil
Table 12-5 Chemical Composition of Heavy Oil and Asphalt Abroad
Heavy oil asphalt in China, like conventional crude oil, contains more nickel and less vanadium (Table 12-6). The nickel content of Liaohe Goldman Sachs heavy oil asphalt is the highest, reaching 122.5μg/g, and most of the rest are tens of micrograms /g. The vanadium content is very low, generally only about 1μg/g, so the mass ratio of nickel to vanadium is greater than 1. This is just the opposite of foreign heavy oil asphalt. They are characterized by less nickel and more vanadium, and the vanadium content is mostly several hundred micrograms per gram. Among them, the vanadium content of frankincense heavy oil asphalt is as high as 1220μg/g, and the mass ratio of nickel to vanadium is generally less than 1. Some scholars regard the mass ratio of nickel and vanadium as geochemical indicators, and consider that crude oil with the mass ratio of nickel and vanadium greater than 1 is terrestrial oil, while crude oil with the mass ratio of nickel and vanadium less than 1 is marine oil. It can be seen that the heavy oil asphalt in China is terrigenous. In addition, it must be pointed out that the calcium content in some heavy oil asphalts in China is high, which has adverse effects on further processing and often needs to be removed by measures.
Table 12-6 Contents of Trace Elements in China Heavy Oil
Table 12-7 Contents and Acid Values of Wax, Gum and Heptane Asphaltene in China Heavy Oil
① Adsorption method.
It can also be seen from tables 12-7 and 12-5 that the gum content of China heavy oil asphalt is obviously lower than that of foreign heavy oil asphalt. The difference in asphaltene content of heptane is even greater. The content of heptane asphaltene in China heavy oil asphalt is generally less than 1% and only 2% at most, while that in Venezuelan and Canadian heavy oil asphalt is mostly around 10%, and that in Kajala heavy oil asphalt in Iraq is as high as 20.4%.
Because most heavy oil asphalts belong to cycloalkyl and cycloalkyl-intermediate groups, their wax content is generally not high, but their acid value is relatively high, indicating that they are rich in naphthenic acid-based petroleum acids.
The chemical composition of China heavy oil asphalt is obviously different from that of foreign countries. Similar to most conventional crude oils, the chemical composition of China heavy oil asphalt is characterized by low sulfur content, high nitrogen content, high nickel content, low vanadium content and low heptane asphaltene content.