CONVERSION OF NAPHTHA TO PLASTICS BY STEAM CRACKING & POLYMERIZATION

Abstract

Naphtha’s production on annual basis in Pakistan is approximately 2-million tons which is exported as a low value commodity & in return import plastics annually worth PKR 2.38 billion. Naphtha’s main source in Pakistan is through the fractionation of crude oil in refineries, most of which is left unprocessed. An alternative possible source of Naphtha could be the Hydrothermal liquefaction of waste plastics which will close the whole value chain of Plastics in Pakistan while having positive impact on our environment. Naphtha can be cracked using either steam cracker or fluid catalytic cracker to obtain light olefins (Ethene, Propene, Butene etc.). The demand for plastics such as HDPE (High Density Polyethylene) & Polypropylene in Pakistan is increasing day by day leading to imports which is destabilizing the economic condition of Pakistan. This report involves the details to produce olefins by steam cracking of Naphtha & the slurry polymerization of Ethylene to produce HDPE. This report focuses on the use of Steam cracking of naphtha which requires temperature of 850ºC along with steam, which reduces the coke formation within tubes & yields ethylene as the major product along with many unsaturated products. Ethylene from the Steam Cracking plant is obtained & sent to the Polyethylene plant for the conversion of ethylene to HDPE using the slurry polymerization process at high pressures (i.e., 60 bar) & low temperatures (i.e., 110 Celsius). During the project, great importance has been given to the order of the cryogenic distillation section of the steam cracking to reduce the duty on the compression sections & chilling stages by placing the de-propanizer at the front end of the cryogenic section which mainly removes the heavy fractions from the plant at an earlier stage therefore reducing the load on the compression & chilling stages. The Ethylene to Propylene ratios is higher than that obtained from catalytic cracking, which really booms the economics of the project since the main goal is the production of HDPE. This project also has the capacity of producing suitable quantities of propylene & considering the polypropylene polymerization plant process can add more value to this project