Abstract

ABSTRACT

Mixed Petroleum Hydrocarbons and Biomass Derived Compounds Used in the Thermal Catalytic Steam Cracking (TCSC) Process for the Production of Light Olefins

HaiTao Yan

Light olefins and diolefins such as ethylene, propylene, butenes and 1,3-butadiene are considered as the backbone of the petrochemical industry as they are precursors of numerous plastic materials, synthetic fibers, and rubbers. The most prevalent technologies for producing these precursors are steam cracking and fluid catalytic cracking using petroleum-based feedstock like light naphtha and gas oil. However, petroleum based feeds have several problems in terms of limited reserves, environmental pollution and economic and geopolitical problems. Therefore, it is imperative to find an alternative source, which may be able to overcome the limitation of petroleum oil.
In the current work, hydrocarbons-alcohol mixed feeds have been used in the Thermal-Catalytic/Steam-Cracking (TCSC) process for the production of propylene and ethylene. Alcohols like methanol and ethanol can be obtained from biomass, a potential sustainable and renewable source, through gasification and/or fermentation, and they can also be produced from natural gas and coal which are longer lasting fossil fuels than petroleum. The results from on-stream cracking of mixed feedstocks indicated difference in behaviors of ethanol and methanol. While ethanol undergoes predominantly dehydration into ethylene, methanol predominantly intervenes directly on reactions involving hydrocarbons (reactants and their intermediates). Moreover, the addition of methanol to hydrocarbons feedstock significantly increased the product yield of C2-C4 olefins, particularly that of ethylene and propylene. However, there was a maximum limit of efficiency for the methanol content in the mixed feed. Over 25wt% of methanol, the beneficial effect was not as important as expected. In addition, the increasing presence of methanol in the feed significantly accelerated the kinetics of the catalytic cracking. The gradual and significant decrease of the apparent activation energy with increasing methanol concentration in the mixed feed was attributed to the effect of intensive interactions between the hydrocarbons and methanol. These results demonstrated the possibility of partial replacement of petroleum based feedstocks by methanol for the production of propylene and ethylene. In the last part of this work, co-processing biomass derived glycerol with hydrocarbon feedstock over TCSC process was studied. It was found that glycerol as an additive to hydrocarbon feed, can be beneficial till a content of 30 wt%. However, the main concern is the rapid catalyst decay caused by formation of coke. Therefore, there is a need for a more advanced hybrid catalyst having higher hydrogen spillover activity.