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Ethylene is a bulk petrochemical product used for producing polymers, chemical agents, textiles and household chemicals. The most common sources for receiving ethylene are ethane (one of the natural gas components) and naphtha (one of the oil refining products). Bioethanol is an alternative for these types of feedstock, it is received from husk and haulm of such cereal crops as oat, wheat and rice. However, bioethanol contains alcohol impurities, which are fermentation products used for producing perfumes, dyes and detergents (butanol, iso-butanol, iso-propanol).
Removing impurities from butanol is a rather energy-intensive process accounting for 20% of all the energy consumed during its production. That is why future producers of green ethylene need to understand: if they use bioethanol without preliminary deep purification, how it will impact the process economics. To answer this question, scientists from the Catalysis Institute of the RAS Siberian branch simulated receiving ethylene from 92% pure bioethanol containing from 0.003% to 0.3% iso-propanol. This simulation showed that such impurities impede the formation of by-products and thus increase the ethylene output.
“In the process of the reaction we receive by-products, e.g., butylene and acetic aldehyde. Iso-propanol make all the reactions slower, especially the formation of acetic aldehyde. The cumulative selectivity for all the products is 100 %, and if the selectivity of by-products goes down, the selectivity of the target product — ethylene — goes up. We identified that formation of acetic aldehyde becomes 7 times slower than formation of all other products. We believe that this makes the process more economically profitable because deep purification of ethanol is not required”, the Catalysis Institute of the RAS Siberian branch is citing Elena Ovchinnikova, one of the authors of the research.
In the opinion of scientists, bioethanol is better to use for low-tonnage production of ethylene in tubular reactors containing thousands tubes used for loading special aluminium oxide catalyst – the Catalysis Institute of the RAS Siberian branch patented the environmentally safe method of receiving this catalyst.
