Comprehensive Study of Ethylene Oxide Production in Gas-Expanded Liquid Phase

摘要

Every year about 3.4 million tons of carbon dioxide (CO2) is emitted to atmosphere by ethylene oxide (C2H4O) conventional gas phase process as byproduct. Also, the C2H4O process is considered as one of the most hazardous chemical operating plant due to presence of very flammable gas like C2H4O and oxygen in high pressure and temperature reactor. The following work illustrates alternative synthesis to produce C2H4O in gas-expanded liquid phase with zero CO2 emission in an operation that consider safer and more secure than the old conventional gas phase process.;The alternative process depends on ethylene epoxidation over methyltrioxorhenium (MTO) catalyst. Unlike the conventional gas epoxidation reaction with oxygen, this reaction takes place in the (ethylene) gas-expanded liquid solvent phase (methanol) while the reaction oxidant is hydrogen peroxide. The reaction takes place at temperatures and pressures close to the ethylene critical point (Pc = 50.42 bar; Tc = 48.56 °F)1. At the Laboratory of Integrated Systems Engineering at Lamar University, an optimized steady state design process was created by using the simulation program Aspen Plus version 8.8 and its economic and energy-analyzing associate packages. The synthesized design has two reactors for ethylene epoxidation and hydrogen peroxide decomposition, one flash drum, and three distillation columns for product and recycled material purification. The design has secured the safety of the operation by not presenting oxygen and flammable vapor mixtures in any of the process equipment. The model could produce up to 200,000 tons of ethylene oxide per year at purity of 99.9%. Ethylene oxide manufacturing costs $0.52 per pound, and the fixed capital investment of the project is $66,240,000, which is estimated to be paid back after 7.3 years, while the net present value is $56,900,000.;In the second chapter of this work, a further study on safety, controllability, and stability of the MTO catalyst process is introduced. Therefore, a dynamic plant wide simulation model is built in Aspen Dynamic Plus version 8.8 simulation program. Starting with a base case model that is consists of the steady state model with simple control schemes. The base case controllers are tuned to run the simulation with small disturbance rejection and small setpoint change. But, the target of this work is to build a success model that can rejects 10% feed flowrate disturbances and 10% setpoint changes for all model controllers. Also, the model's controllers must reject all disturbances within 5% deviation of their setpoint. Therefore, the base case model was updated several times by adding new composition, temperature, and pressure controllers. Also, ratio controls and cascade controls schemes strategies are implemented to the model to improve its performance. In addition, new pumps, heat exchangers, and buffer drums are added to the model to respond to flowrate disturbances and utilities shortage. Finally, liquid levels in several equipment are updated to increase safety of the process.