Pre-feasibility study for construction of a unit for styrene extraction from pyrolysis gasoline in the south parts of Iran

فاقد چكيده

Pre-feasibility study and economical evaluation of a unit for extraction of styrene monomer from Pyrolysis Gasoline (PG) is presented in this paper. The location of unit was considered to be in south parts of Iran and the study was done based on the present conditions. Pyrolysis gasoline is a byproduct of olefin plants which contains C5-C10 hydrocarbons but its main compounds are Benzene, Toluene, Styrene and Xylenes. The technical problem in separation of styrene from pyrolysis gasoline is the boiling points of compounds, which are very close to each other especially for styrene and o-xylene. So, separation of these two compounds by traditional processes such as distillation needs huge equipment which makes the process uneconomical. Extractive distillation is one of the useful methods for separation of styrene from pyrolysis gasoline. According to National Petrochemical Company (NPC) reports, there are some deficits for styrene in Iran so construction of new styrene plants seems necessary. Extraction of styrene from pyrolysis gasoline is a suitable process to compensate the styrene demand in Iran. Also, by this process we make a valuable product (styrene) from a lower value material (PG). In this feasibility study, the price of pyrolysis gasoline as feedstock and styrene as product and operating cost of process was needed. So, the average Persian Gulf FOB prices of pyrolysis gasoline and styrene over the last 8 years was considered. Also the STEX process, which was developed by TORAY (a Japanese company) based on extractive distillation, was considered for feasibility study. STEX is the only commercial process for separation of styrene from pyrolysis gasoline. For economical evaluation of process, two alternatives were considered: 1- construction of styrene extraction unit as an individual plant 2- construction of styrene extraction unit in an olefin plant. Feasibility study shows that construction of styrene extraction unit is economical for these two alternatives but the second one is better from economical point of view. Because the feedstock (PG) is supplied from different sources it is better to construct the extraction unit as an individual plant.