Modeling of PVA Degradation in a Continuous Photochemical Reactor using Experimental Step Testing and Process Identification (original) (raw)
Related papers
Journal of Environmental Chemical Engineering, 2021
In AOP processes, the flow of oxidant must be controlled to minimize the oxidant residuals in a post biological treatment and to maximize the total organic carbon (TOC) removal and degradation. Designing a controller to regulate the hydrogen peroxide (H2O2) begins with a dynamic model determination of a chemical process. Therefore, a step testing technique is employed to construct a dynamic model of the UV/H2O2 degradation of polyvinyl alcohol (PVA) process based on pH and TOC responses to H2O2 step change. The experimental design consists of three different initial PVA concentrations, of 60.0, 280.0, and 500.0 mg PVA/L. Eight experimental tests were conducted for different hydrogen peroxide mass flowrates ranging from 0.336 to 125 mg H2O2/min. For every test, a transfer function was experimentally determined to describe the dynamics of the UV/H2O2 photochemical reactor for the degradation of PVA. System identification toolbox in Matlab software was used to determine first order plus time delay (FOPTD), second order plus time delay (SOPTD) and ARX polynomial models. The transfer functions and ARX models are a good model representation of the pH response data of a specific step change of H2O2 concentration. For example, the standard deviation of the process gain of test # 1 and its replicate was calculated to be 1.18 and standard deviation of the time constant was calculated to be 1.27. The pH response of the first test was fitted with a FOPTD model with a data fitting score of 88.8%. Test # 2 pH response data was fitted with a SOPTD transfer function with data fitting score of 83.6%. Tests # 6 and 7's pH response was fitted with a FOPTD model with a data fitting score of 94.3 and 87.7 % respectively. The different transfer functions obtained for the low, average, and high PVA concentrations indicate the nonlinearity aspect of polymer systems. All quality models are quite reliable estimations of the pH and TOC response data, since they were developed from experimental tests and parameter estimation techniques based on nonlinear regression approach.
Environments, 2021
Polyvinyl alcohol (PVA) is an emerging pollutant commonly found in industrial wastewater, owing to its extensive usage as an additive in the manufacturing industry. PVA’s popularity has made wastewater treatment technologies for PVA degradation a popular research topic in industrial wastewater treatment. Although many PVA degradation technologies are studied in bench-scale processes, recent advancements in process optimization and control of wastewater treatment technologies such as advanced oxidation processes (AOPs) show the feasibility of these processes by monitoring and controlling processes to meet desired regulatory standards. These wastewater treatment technologies exhibit complex reaction mechanisms leading to nonlinear and nonstationary behavior related to variability in operational conditions. Thus, black-box dynamic modeling is a promising tool for designing control schemes since dynamic modeling is more complicated in terms of first principles and reaction mechanisms. T...
Photochemical Kinetic Modeling of Degradation of Aqueous Polyvinyl Alcohol in a UV/H2O2 Photoreactor
Journal of Polymers and the Environment, 2018
This study presents a photochemical kinetics model to describe the degradation of water-soluble PVA (Polyvinyl Alcohol) polymer in a UV/H 2 O 2 batch reactor. Under the effect of UV light, the photolysis of hydrogen peroxide into hydroxyl radicals can generate a series of polymer scission reactions. For a better understanding and analysis of the UV/H 2 O 2 process in the cracking of the PVA macromolecules, a chemical reaction mechanism of the degradation process and a relevant photochemical kinetics model are developed to describe the disintegration of the polymer chains. Taking into account the probabilistic fragmentation of the polymer, the statistical moment approach is used to model the molar population balance of live and dead polymer chains. The model predicts the PVA molecular weight reduction, the acidity of the solution, and hydrogen peroxide residual. In addition to previously published data collected in this laboratory, a new set of experiments were conducted using a 500 mg/L PVA aqueous for different hydrogen peroxide/PVA ratios for model validation. Measurements of average molecular weights of the polymer, hydrogen peroxide concentrations and pH of the PVA solution were determinant factors in constructing a reliable photochemical model of the UV/H 2 O 2 process. Experimental data showed a decrease in the PVA molecular weight and a buildup of the solution acidity. The experimental data also served to determine the kinetics rate constants of the PVA photochemical degradation and validate the model whose predictions are in good agreement with data. The model can provide a comprehensive understanding of the impact of the design and operational variables.
ARX-PID/NARX-PID Modelling and Control of UV/H2O2 Tubular Photoreactor for PVA Degradation in Water
International Conference of Recent Trends in Environmental Science and Engineering, 2021
Various industries rely on water-soluble polymers as additives, therefore, it is imperative to treat them so that they do not enter our environment as persistent pollutants. Though used as a leading method for degradation of organic pollutants, biological treatment can only treat wastewater that is readily degradable by living organisms. If that is not possible, researchers mainly focused on the oxidation of polyvinyl alcohol (PVA) in an Advanced Oxidation Process (AOP) such as UV/H2O2 process as an easy process owing to its relatively developed kinetics, non-selective degradation, low cost, and ease in operation at large-scale [1-3]. In particular, the UV/H2O2 process requires modelling to establish a control system that prevents adverse effects of PVA and residual hydrogen peroxide (H2O2) to the aquatic system and subsequent biological processes by maintaining H2O2 residuals in the treated effluent within a safe level. During this study, the performance of black-box methods was examined in determining the dynamics of polyvinyl alcohol degradation in various UV/H2O2 systems, where process inputs and responses involved hydrogen peroxide concentration and acidity, respectively. The complete data analysis and model fitting is undertaken with MATLAB R2019b software. Models including the linear AutoRegressive with eXogenous Input (ARX), the nonlinear ARX (NARX), and the Hammerstein-Wiener model are compared for their success in providing an accurate representation of statistical dynamics. Comparatively, the sigmoidnetwork-based NARX was better at representing the process dynamics when compared to others. The study also explores the design of PID controllers via ARX and sigmoid-network-based NARX models and analyzes controller performance for set-point tracking and disturbance rejection. The ARX-P, ARX-PI, NARX-P, and NARX-PI controllers were not adequate for a good control design as they exhibit higher offset from set-point, higher overshoot, and longer settling time. The ARX-PID and NARX-PID provide adequate closed-loop responses, while NARX-PID seems better suited for the studied process. However, the ARX-PID has a higher IAE and produces a more robust output response against disturbances as it is adequate for processing disturbances but less useful in tracking process set-points. As a result, to compensate for the complexity in generating models and tuning the parameters with the NARX model, an approximation based on the ARX model is appropriate when its implementation will be followed by another setup for H2O2 elimination. Although feasibility of linear control scheme was presented, it is suggested that similar scenarios should be considered in future designs, validations, and performance evaluations of the entire controlled system, especially for improving controller robustness by implementing multivariate adaptive controls and linear or non-linear predictive controls [4-9].
Kinetic Modeling of Photodegradation of Water-Soluble Polymers in Batch Photochemical Reactor
Kinetic Modeling for Environmental Systems [Working Title]
Synthetic water-soluble polymers, well-known refractory pollutants, are abundant in wastewater effluents since they are extensively used in industry in a wide range of applications. These polymers can be effectively degraded by advanced oxidation processes (AOPs). This entry thoroughly covers the development of the photochemical kinetic model of the polyvinyl alcohol (PVA) degradation in UV/ H 2 O 2 advanced oxidation batch process that describes the disintegration of the polymer chains in which the statistical moment approach is considered. The reaction mechanism used to describe the photo-degradation of polymers comprises photolysis, polymer chain scission, and mineralization reactions. The impact of operating conditions on the process performance is evaluated. Characterization of the polymer average molecular weights, total organic carbon, and hydrogen peroxide concentrations as essential factors in developing a reliable photochemical model of the UV/H 2 O 2 process is discussed. The statistical moment approach is applied to model the molar population balance of live and dead polymer chains taking into account the probabilistic chain scissions of the polymer. The photochemical kinetic model provides a comprehensive understanding of the impact of the design and operational variables.
A simplified mathematical model to predict PVC photodegradation in photobioreactors
Polymer Testing, 2012
A simplified mathematical model to predict transparent poly(vinyl chloride) (PVC) degradation in photobioreactors under the incidence of sunlight is proposed. The model is based on the widely accepted theory of photochemistry degradation, which states that HCl is produced as an intermediate compound yielded in a propagation reaction, taking into account the entire dehydrochlorination process. A system of ordinary differential equations for concentrations and energy with respect to time results from the application of the principles of species and energy conservation, which is integrated explicitly and accurately with low computational time. Previously published experimental data were used to validate the numerical simulation results obtained with the model, with good quantitative and qualitative agreement. The developed model is expected to be a useful tool for simulation, design, and optimization of PVC for minimum photodegradation.
Industrial & Engineering Chemistry Research, 2012
The advanced oxidation of aqueous polyethylene oxide (PEO) is studied using the UV/H 2 O 2 process in a batch recirculation photoreactor. The response surface methodology (RSM), combined with quadratic programming, is used for the experimental design, statistical analysis, and optimization of the process. In the second part, a detailed mathematical model is developed to predict the total organic carbon (TOC) removal as a function of time. Continuous distribution kinetics is applied to establish the kinetic model for the photodegradation of PEO. The model is validated at different influential operating conditions using experimental data obtained by a recirculating batch photoreactor. An excellent agreement between the model predictions and the experimental data is confirmed for all experimental conditions. Also, the intrinsic rate constants are estimated using an optimization algorithm. The model provides a good insight into the free-radical-induced degradation mechanisms and kinetics that could be considered for the process optimization.
Photoreactor design and CFD modelling of a UV/H2O2 process for distillery wastewater treatment
The Canadian Journal of Chemical Engineering, 2012
A pseudo-kinetic model for the treatment of a distillery wastewater by the ultraviolet irradiation and hydrogen peroxide process in a continuous tubular photoreactor is developed. There is a scarcity of information on modelling of organic degradation rates based on chemical oxygen demand (COD) and total organic carbon (TOC) in advanced oxidation technologies (AOTs). In this study, the COD and TOC are used as surrogate parameters to design a photoreactor instead of individual concentrations of species. The rate constants for the reaction between COD and TOC with hydroxyl radicals were determined to be 4.9 × 10 9 and 5.0 × 10 6 M −1 s −1 , respectively. A laminar flow model was simulated to estimate the velocity and residence time of the medium in a cylindrical photoreactor. The model was validated by the experimental data published in the open literature for different concentrations of H 2 O 2 (1, 10, and 100 mM), COD (589, 709, and 850 mg O 2 L −1 ), and TOC (190, 200, and 192 mg C L −1 ). The optimal value of the inlet hydrogen peroxide concentration was predicted to be 400 mg L −1 . Axial and radial concentration distributions of species in the photoreactor were also obtained. At different photoreactor radii (from 50 to 200 mm), the values of radial local volumetric rate of energy absorption (LVREA) were estimated. It was found that a higher LVREA was achieved in the photoreactor space at smaller radii.
Photoreactor scale-up for degradation of aqueous poly(vinyl alcohol) using UV/H2O2 process
Chemical Engineering Journal, 2014
A scale-up methodology for binary degradation of PVA by UV/H 2 O 2 is proposed. Intrinsic kinetic parameters are determined by kinetic parameter estimation. Obtained kinetic parameters are independent of the photoreactor geometry. Methodology enables direct photoreactor scale-up of lab-scale to pilot-scale. CFD model development for scale-up methodology is validated experimentally.
Polymer Degradation and Stability, 2014
The present study investigates the degradation of poly(acrylic acid) in aqueous solution by a photo-Fenton-like process. Batch experiments are carried out to model and optimize the process. The effects of the initial concentration of poly(acrylic acid), the initial concentration of Fe 3þ , and the H 2 O 2 dosage as independent variables on the total organic carbon (TOC) removal as the response function are studied using response surface methodology (RSM). The significance of the independent variables and their interactions are tested by means of analysis of variance (ANOVA) with 95% confidence level. The statistical analysis of the results indicated satisfactory prediction of the system behavior by the developed model. The optimum operating conditions to achieve maximum TOC removal are also determined. The model prediction for maximum TOC removal is compared to the experimental result at optimal operating conditions. A good agreement between the model prediction and experimental results confirms the reliability of the developed model.