Conversion of Olefins in LPG through hydrogenation

Abstract

The objective is to remove undesirable components namely olefins present in the Liquefied petroleum gas (LPG) stream in order to match the quality pertaining to environmental aspects and safety requirements which are achieved by processing the unsaturated hydrocarbons to the saturated hydrocarbon product. The principal reason for removing the olefins is that it certainly produces significant smoke based on the mole percent of olefin content when the fuel is burnt and that which is not desirable when it is being utilized by the end users inorder to provide a smoke free environment. Hence a detailed study and analysis which was carried out for hydrogenating the olefins to produce saturates have been discussed here. The complete analyses have been modelled and simulated using process modelling software hysys. The efficiency in terms of the final achievable product with respect to the throughput plays a vital role in the quality of saturated LPG product. The results are analyzed with respect to the feedstock composition of unsaturated LPG to the obtained saturated LPG product composition. This gas processing method of treating unsaturated LPG provides us a cleaner and safe environment by reducing the emission / smoke intensity levels while burning the fuel. Description of the model In order to mitigate the olefins in the LPG and achieve desired specification, it is intended to go for a Hydrogenation facility to saturate olefins. The feedstock comprises of known composition of the liquefied petroleum gas with identified mole percent of the unsaturated hydrocarbons. The complete model is carried out in the process modelling software, Hysys. Peng-robinson property package is used as the simulation basis. Olefins in LPG entering into the feed vessel at a pressure of 26 bar and 40°C (Refer to Figure 1 for the schematic representation of the hydrogenation facility), is then pumped via feed pump to the equalizer. Fresh hydrogen stream is mixed at the equalizer for hydrogenation reaction to occur in the Hydrogenation reactor. Mixer upstream of the reactor ensures that proper mixing takes place for enhancing the reactivity of this two phase flow. The reaction is input for 98% conversion of the base components which are fed as input with appropriate stoichiometric coefficients. Hydrogenation reactor is loaded with specific metal based catalysts which have ability to convert olefins to saturated hydrocarbons. The exothermicity causes an increased temperature in the product. The flow in the reactor to be taken care to avoid channelling effects for more efficient conversion. There are two beds of reactor considered in the reactor. Each reaction continues until the specified conversion is attained or until a limiting reactant is depleted.