ABSTRACT
Heavy crude oils are known to contain significant amount of high molecular-weight substances such as asphalthenes and resins hence, when refined, produce low amount of lightends (gasoline, kerosene and diesel fractions). Compared with light crude oils, as a refinery feed stock this singular reason coupled with difficulty of processing has made heavy crude oil business unattractive at local and global levels. In this work, enhancement of light-ends recovery by joint atmospheric distillation of Venezuela, Mixed (50% Venezuela and 50% Antan wt./wt.) and Antan heavy crude oils blended with used engine oil (UEO) was investigated. This was carried out by subjecting these blends to spectrophotometric analysis for optimal feed choice and subsequently acted as basis for true boiling point (TBP) distillation process. The results show that blended Venezuela heavy crude with 1% UEO which corresponded to maximum particle size of blend and 12% UEO corresponding to minimum particle size of the blend enhanced the recovery of light-ends by extra 1.8% and 0.74% respectively. Similarly, blended Mixed heavy crude with 16% UEO (max. particle size of blend) and 4% UEO (min. particle size of blend) enhanced the recovery of the light-ends by 2.32% and 2.25% respectively. Finally, blended Antan heavy crude with 19% UEO (max. particle size of blend) and 7% UEO (max. particle size of blend) enhanced the recovery of the light-ends by 7.42% and 1.76% respectively. All these confirm that on the average, the larger the particle size of the blend the higher the chance of enhancement of the recovery of the light-ends. However, the undefined pattern (i.e. positive and negative enhancements) of the product slates of the fractional cuts prompted the need for further AAS analyses to check for the presence of freed 3d-metals (V, Ni, Co, Fe.) from their complexes in the residues of the blends. This was to confirm whether the enhancement was partially as a result of light cracking of the vii resin/asphalthenes (preferably porphyrins and porphins) and other organometallic compounds that could have been originally present in the crude. The sequence of probable mechanism of the light cracking is presented thus: Since this type of cracking is of uncontrollable mechanism it underscored the reason why the pattern of the distribution of the products was difficult to establish. While the free radicals formed may recombine to yield gaseous product (methane, ethane, etc.) or light distillate like naphtha/ kerosene fraction, it may as well yield heavier fractional cuts like vacuum distillate. Used engine oil must have only provided enabling environment for these transformations to take place because it must have reduced the energy of the bonding of crude oil micelle, hence enhanced the recovery of the light-ends.