Multiple Objective Optimization of Industrial Naphtha Cracking Process by Box-Behnken Response Surface Methodology

Abstract

Naphtha in presence of steam is cracked to produce ethylene, propylene, and 1,3-butadiene which are important feedstocks in the petrochemical industry. It is important to optimize industrial process conditions to maximize the yield of 16 desired products individually as well as a combination of those based on the market demand. The parameters influencing the naphtha cracking product yield are feed composition, coil-outlet temperature (COT), coil-inlet pressure, residence time/feed flow rate, and steam to hydrocarbon feed ratio (SHFR). In this research, Box-Behnken response surface design has been used to evaluate the effects and interactions among three factors such as COT, SHFR, feed flow rate on product yields by carrying out 15 experimental test runs. The SHFR, COT, flow rates were varied in the range from 0.38−0.5, 810−824 °C, 14.8−17.2 tons per hour (tph), respectively. Models for three different naphtha feeds having different heavier hydrocarbon content (C8+) have been developed. Another model has been developed considering 27 experimental test runs with C8+ composition (3.74 wt.%, 6.81 wt.%, and 9.88 wt.% ) as the fourth factor. These model results have been validated with Industrial process data on ethylene and propylene yields for ten case studies. The model predicted yields match excellently well with that of industrial reactor yield. Response optimizer has been developed to optimize process conditions to maximize yields of ethylene, propylene separately, and also combined yield of ethylene+propylene+1,3-butadiene. It has been found that the higher COT has a favorable impact on Ethylene and 1,3-Butadiene yield. The Increased C8+ content results in a lower yield of Ethylene, Propylene, and 1,3-Butadiene. Increased SHFR and feed flow rate reduces the Ethylene yield. The optimized condition has been reported. The optimum was found at COT of 824°C, SHFR of 0.4919 kg-steam/kg-naphtha, the flow of 14.8 tph, and C8+ content in a feed of 3.74 wt.%.