An Investigation of Antioxidant Properties of Zinc and Molybdenum Dithiocarbamates in Hydrocarbons

The oxidation and degradation of hydrocarbons at high temperature and pressure in the presence of oxygen is one of the common oil product problems. There are many antioxidants to prevent or inhibit oxidation processes; molybdenum and zinc dithiocarbamates are known as powerful antioxidants. In this paper, the oxidation inhibition time of cumene has been investigated using zinc and molybdenum dithiocarbamate substituted with different alkyl groups as antioxidants and azobisisobutyronitrile (AIBN) as the initiator. The best result obtained for molybdenum dibutyldithiocarbamate was about 210 min, while zinc dialkyldithiophosphate (ZDDP), a well known commercial antioxidant, showed an oxidation inhibition time of about 14 min under the same conditions. It was shown that antioxidancy properties decreased with increasing the chain length of the substituted alkyl groups. This can be explained by the fact that alkyl groups participate in the oxidation process and thus increasing the alkyl chain length reduces antioxidancy effect. The synergism effect of molybdenum dibenzyl dithiocarbamate on ZDDP was also investigated and the oxidation inhibition time of about 110 min was obtained, which was greater than that of any individual antioxidant.