EXERGY DISSIPATIONAND POTENTIAL PROFITS COMPARISON FOR SUSTAINABILITY ASSESSMENT OF VINYL CHLORIDE SYNTHETIC ROUTES GENERATED FROM ‘CREATE-REACTIONSET’ SOFTWARE THAT RUNS ON MATLB (original) (raw)
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In this work, fourteen synthetic routes of vinyl chloride are generated from 'create-reactionset' software that runs on MATLAB using the molar constraints of all the molecules of the reactants, products and the by-products involved in the manufacture of one unit of vinyl chloride. In order to quantitatively evaluate the energy performance and the potential profits of the process routes, comparison of the fourteen synthetic routes showed that eight synthetic routes is heat absorbing reactions requiring energy input, while six are heat generating reactions resulting to negative energy quality. Route , with synthetic reaction Cl 2 +HCl+O 2 + C 2 H 4->2H 2 O + 3C 2 H 3 Cl, and with exergy dissipation of-1370.1563Kcal/g-mol and a potential profit of 51c/lb is considered as being sustainable. The comparison rendered it possible to rapidly screen out synthetic routes that are highly unlikely to be sustainable at the earliest possible stage thereby preventing the enormous expenditure required for developing such processes. Definitions and calculation formulas of exergy and potential profits of a substance, a mixture, a stream, and a unit (process) are illustrated. INTRODUCTION Limiting energy utilization and achieving economically viable processes is one of the main challenges of chemical engineering at present for sustainable chemical process route development. To develop and design a less energy consuming processes and cost effective alternative to replace or retrofit a current inefficient process, it is essential to establish a method for quantitatively evaluating and comparing the energy performance and the potential profits of chemical processes.
A case study for reactor network synthesis: the vinyl chloride process
A key objective of the integrated reactor network synthesis approach is the development of waste minimizing process flowsheets (Lakshmanan & Biegler, 1995). With increasing environmental concerns in process design, there is a particularly strong need to maximize conversion to product and avoid generation of wasteful byproducts within the reactor network. This also avoids expensive treatment and separation costs downstream in the process. In this study, we present an application of the mixed integer nonlinear programming (MINLP)-based reactor network synthesis strategy developed by Lakshmanan and Biegler (1996a). Here we focus on applying these reactor network synthesis concepts to the vinyl chloride monomer production process. Vinyl chloride is currently produced by a balanced production process from ethylene, chlorine and oxygen with three separate reaction sections: oxychlorination of ethylene; direct chlorination of ethylene; and pyrolysis of ethylene dichloride. The hydrogen chloride produced in the pyrolysis reactor is used completely in the oxychlorination reactor. Byproducts such as chlorinated hydrocarbons and carbon oxides are generated by these reaction sections. These are studied using reaction kinetic models for the three reaction sections. The case study results in optimal reactor networks that improve the conversion of ethylene to vinyl chloride and minimize the formation of byproducts. These results are used to generate an improved flowsheet for the production of vinyl chloride monomer. Moreover, an overall profit maximization, that includes the effect of heat integration, is presented and a set of recommendations that improve the selectivity of vinyl chloride production are outlined. Finally, the optimal reactor structures, overall conversion and annual profit are shown to be only mildly sensitive with respect to small changes in the kinetic parameters.
Cleaner Production of Vinyl Chloride Monomer (VCM
Cleaner production eliminates pollution throughout the entire production process. It is a way of reducing pollution damage to both the environment and the human population by increasing the efficiency of resource use – decreasing pollution discharge by improving management and technology. Cleaner production is implemented at the factory level. The factories get both economic and environmental benefits from implementing cleaner production. The implementation of cleaner production involves a combination of reorganization, improved technology in the factories, power saving and decreasing consumption, improved management and competent resource use. The eventual goal of clean production is to achieve a 'closed loop' operation in which all excess materials are recycled back into the process, which is utmost necessary in today's world. ..Here we have included a case study of vinyl chloride monomer (VCM) production using cleaner production (CP), which includes Material Balance, Energy Balance, Cost Estimation and Simulation.
Guest Editor’s Note: Green Chemical Engineering
Rangsit University, 2016
________________________________________________________________________________________________ Green Chemical Engineering will lead us to a bright, sustainable future. Designers must strive to ensure that all materials and energy inputs and outputs are as inherently nonhazardous as possible. Use your chemical knowledge of properties like boiling point, melting point, freezing point, vapor pressure, and water solubility. In addition chemical engineers must note flammability, explosivity, compressibility, viscosity, and properties that affect heat and mass transfer. These are the starting points when we are designing a new chemical process. We have to do more. Most of us are less familiar with properties related to toxicity to environmental organisms and humans. The engineer must have a systems perspective: i.e., the ability to do mass and energy balances. Don't just look at your laboratory bench or pilot plant process. Look at your systems-factory scale-whole industrial park scale. Designers need to select chemicals or materials whose properties will not cause harm to the environment or to people. With the right choice of chemicals and materials, a designer can control how much energy is required and the form of that energy; e.g., heating, cooling, light, microwave, pressure, etc. In terms of putting toxics into the environment energy matters as much as the choice of chemicals. It is better to prevent waste than to treat or clean up waste after it is formed. A central tenets of green technologies is to make only the amount that is needed for a process. From a business perspective, this makes absolute sense. Think out the new process or procedure that you want to try. How much of everything goes into making your product? Do you need all of these things? If you have to heat the reaction, a large pot of solvent is going to need a lot of heat. Less solvent would need less heat. The engineer might design a process in which the reaction is run to low conversion, a separation is achieved to recover the product, and the unused reactant is recycled back to the reactor, allowing higher overall conversion. Separation and purification operations should be designed to minimize energy consumption and materials use. Industrial separation processes are very energy intensive. Historically, for liquid and condensable gases, multistage distillation has been the workhorse process. Many bulk organic chemicals involve distillation, which adds significantly to their production CO 2 footprints. Thus, avoiding distillation, making distillation more efficient, and searching for alternatives to distillation are very important. One technology that has broken the hold of distillation in a large scale application is reverse osmosis membrane separation for water desalination. Reverse osmosis uses mechanical pressure to overcome the osmotic pressure exerted by the salt solution and thereby push the water through a selective skin. As calculated by the change of free energy of mixing, the theoretical energy to de-mix water and salt is approximately 1 kWh/m 3 of water, the current best membrane technologies have a real energy cost of 4.0 kWh/m 3 and thermal "distillation" type technologies use on the order of 50 kWh/m 3. When you see caparisons like this, you know the old, familiar technologies may need updating. Products, processes and systems should be designed to maximize mass, energy, space, and time efficiency. It is simplicity that will allow us, as a society, to become more sustainable. In the past, there was no consideration regarding the complexity of the reaction, and material, energy and production requirements that will be needed to take this chemical reaction from the bench to the pilot plant to production. As
Sustainability Assessment of Chemical Processes: Evaluation of Three Synthesis Routes of DMC
Journal of Chemistry, 2015
This paper suggested multicriteria based evaluation tool to assess the sustainability of three different reaction routes to dimethyl carbonate: direct synthesis from carbon dioxide and methanol, transesterification of methanol and propylene carbonate, and oxidative carbonylation of methanol. The first two routes are CO2-based and in a research and development phase, whereas the last one is a commercial process. The set of environmental, social, and economic indicators selected were renewability of feedstock, energy intensity, waste generation, CO2balance, yield, feedstock price, process costs, health and safety issues of feedstock, process conditions, and innovation potential. The performance in these indicators was evaluated with the normalized scores from 0 to +1; 0 for detrimental and 1 for favorable impacts. The assessment showed that the transesterification route had the best potential toward sustainability, although there is still much development needed to improve yield. Furt...