(383af) Techno-Economic Optimization and Process Modeling of Upcycling of Microwave-Assisted Plastics Wastes and Microwave-Assisted Methane Dehydroaromatization Process

Research Interests: Kinetic Modeling, Dynamic Data Reconciliation, Parameter Estimation, Dynamic Optimization, Techno Economic Optimization, Process System Engineering.

Software skills: MATLAB, JMP, Aspen Hysys, Aspen Plus, Aspen Custom Modeler, Pro II, Aspen Process Economic Analyzer, ChemCad.

Plastic waste is one of the pollutions which requires the attention of the world to look after at presents so that the future generations can sustain their habitat. Polyethylene is one the major contribution to the plastic waste, especially a “polyethylene film” which is hard to recycle in a conventional pathway. Microwave-assisted technology is one of the promising technology to convert the plastic waste into value-added product.

Another alarming issue right now is the rise of greenhouse gas emissions (GHG) such as methane, carbon dioxide, nitrous oxide, water vapor and fluorinated gases. As per the Environmental Protection Agency (EPA) methane gas is the second most abundant anthropogenic GHG after carbon dioxide. To address this issue microwave-assisted methane dehydroaromatization technology will not only eliminate the GHG but also convert it into the value-added product such as ethylene and benzene.

Dynamic Data Reconciliation

I have developed a dynamic data reconciliation model based on the experimental in-house data for a batch lab reactor. While implementing the dynamic data reconciliation a challenge was to maintain the hydrogen to carbon ratio 0.5 overall during the entire duration of the experiment. To address this challenge dynamic data optimization is developed in the MATAB program and successfully achieved it. The above dynamic data optimization is solved for three different temperatures, 250 °C, 300 °C and 350 °C.

A modified catalyst is designed to run a low temperature experiment for methane dehydroaromatization reaction in fixed bed microwave assisted reactor in the lab. A dynamic data reconciliation technique is executed to maintain the carbon to hydrogen ratio since it can affect evaluating further process of the parameter estimation of key parameters. Added to that one of the reactions is also producing coke as product, so it became essential to ensure the maintain the hydrogen to carbon ratio. Dynamic data reconciliation optimization is solved using the extent of reaction as decision variable in MATLAB.

Parameter Estimation

A parameter estimation model is developed in the MATLAB as an optimization problem which is solved to minimize the error between the model and experimental data to estimate the key parameters such as pre-exponential factor, activation energy and power factor. A fmincon is utilized to solve the parameter optimization problem with the aid of ode15s solver to solve the ordinary differential equation at each instant of time for the different set of temperatures. Further, a kinetic model is developed in the Aspen Custom Modeler (ACM) to validate the estimated parameter with a yield model implementation.

In ACM a parameter estimation problem is set up considering gaseous species conservation equations and the catalyst deactivation rate with the boundary conditions. A least square method is implemented in the estimation tool of the ACM to estimate the parameter of the reactions. Total seven parameters are estimated as per the three reactions which are as follows, three pre-exponential factor, three activation energy and the last one is alpha the catalyst activity parameter.

Modeling in Aspen Custom Modeler

A non-isothermal three region model for a bubbling fluidized bed reactor is developed in the ACM including the detailed representation of microwave absorption by the catalyst particles and other energy transfer mechanism. Mass and energy balance are modeled for each region. The model is utilized to study various key parameters such as yield, desired conversion and operating conditions.

A multi scale dynamic heterogenous fixed bed reactor model has been developed for the MW-enhanced reactor.[1] A detailed inter and intra-particle mass transfer model and a reaction kinetic model that includes coke formation and catalyst deactivation have been studied with the updated parameters for the modified catalyst and low temperature. A comprehensive heat transfer model has been developed that considers heat transfer between metal sites, support sites and the gas with the catalyst particles and between the bulk and catalyst particles. MW absorption by both metal and support sites area is taken into consideration. Maxwell’s equations have been used for modeling MW penetration into the catalyst particle.[1]

Plantwide Model in Aspen Plus

A plant-wide model for the upcycling of microwave-assisted plastics is developed in Aspen Plus to produce value-added products with 99.9% purity. A refrigeration cycle is developed to maintain the lower temperature downstream during the separation process of the product. A heat exchanger design is implemented using the Aspen Energy Analyzer to recover the excess heat from the plant-wide plant. Scheduling of the batch reactor and an estimation of minimum number of reactors is established to obtain acceptable time-varying deviation in product flowrate for the downstream.

A plant-wide model is developed for the direct non-oxidative methane dehydroaromatization process with the microwave assisted and thermo-catalytic. A plant-wide model adapted from the [2,3] is studied with updated yield for the products at the lower temperature. As coke gets formed, catalysts need to be regenerated by oxidizing the coke and therefore a schedule of reactor operation is developed to ensure that certain number of reactors is available for reaction while others are undergoing regeneration and the combined products from all reactors have acceptable temporal variabilities.

Techno-Economic Analysis

To have a fair comparison of the market and the products, a conventional ethane-propane mixture cracking plant is developed in the Aspen plus. Ethylene is the key product in both the plant-wide model flow sheet and point of comparison. An economic model is developed for both the plant-wide model in the Aspen Economic Analyzer and economics are evaluated with investment parameter such as contingency, tax rate, desired rate of return and may more.

A model for the balance of the plant has been developed producing final products at their desired specification. Economic analysis of the process has been undertaken by exporting the plantwide model developed in Aspen Plus to Aspen Process Economic Analyzer. Economic analysis is done for the updated available data.

References

1. Mevawala C, Bai X, Bhattacharyya D, Hu J. Dynamic data reconciliation, parameter estimation, and multi-scale, multi-physics modeling of the microwave-assisted methane dehydroaromatization process. Chemical Engineering Science 2021;239:116624. https://doi.org/10.1016/j.ces.2021.116624.
2. Mevawala C, Bai X, Kotamreddy G, Bhattacharyya D, Hu J. Multiscale Modeling of a Direct Nonoxidative Methane Dehydroaromatization Reactor with a Validated Model for Catalyst Deactivation. Ind Eng Chem Res 2021;60:4903–18. https://doi.org/10.1021/acs.iecr.0c05493.
3. Mevawala C, Bai X, Hu J, Bhattacharyya D. Plant-wide modeling and techno-economic analysis of a direct non-oxidative methane dehydroaromatization process via conventional and microwave-assisted catalysis. Applied Energy 2023;336:120795. https://doi.org/10.1016/j.apenergy.2023.120795.