Techno-economic, environmental, and exergetic evaluation of a novel isopropyl n-phenylcarbamate production process through non-reductive conversion of CO2

Abstract

The conversion of carbon dioxide (CO2) into valuable chemicals has emerged as a prominent research field. This study attempts to uncover the rigorous design and comprehensive analysis of an innovative process that produces Isopropyl N-phenylcarbamate (IPPhCM) through direct synthesis involving CO2, 2-Propanol (IPA), and phenylamine (PHAM). The reaction system utilizes CeO2 as a catalyst and 2-Cyanopyridine (2-CP) as a chemical dehydrant. In general, this work presents alternative designs in a rigorous manner, with different combinations of conversion and yield. It also evaluates various strategies, such as heat integration, thermal coupling, and the addition of a co-reactant, to enhance the efficiency of the system. Based on the results, the configuration designed with a 92% yield of IPPhCM and incorporating both dividing-wall columns and direct heat integration was determined to be the best scenario. The corresponding minimum required selling price (MRSP) for IPPhCM is 1.996 USD/kg (at a 15% internal rate of return, measured without considering the cost of 2-CP), and the amount of CO2 emission per unit amount of product formed is + 0.075 kg/kg. However, the overall exergy efficiency of this process is only 42.7%. The main reason is the formation of mixtures that are difficult to separate, involving side products such as isopropyl picolinate (IPP), diisopropyl carbonate (DIPC), and others. To enhance the scheme, retrofitting it by adding ammonia to the reaction section enables the conversion of IPP and DIPC into valuable and separable by-products, namely 2-picolinamide (2-PA) and isopropyl carbamate (IPCM). This arrangement significantly enhances the exergy efficiency to 71.8% and reduces the MRSP to 1.759 USD/kg, at the cost of a slight increase in CO2-e to 0.118 kg/kg. With these results, the regeneration of byproducts can make the entire process more appealing and sustainable.