Department of Chemical Engineering

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Release of lead (Pb) in drinking water from lead service lines has been extensively studied in single pipes, and the importance of water chemistry has been reported. However, the impact of variations in water chemistry parameters during water supply from the treatment plant to the downstream distribution network is crucial to understand toward minimizing lead release rates and has not yet been researched. This study proposes a comprehensive framework for investigating the changes in dissolved lead concentrations resulting from variations in the concentration of water chemistry parameters (such as pH, orthophosphate, free chlorine disinfectant residual, dissolved inorganic carbon and natural organic matter). The framework accounts for changes in the chemistry as water flows in a typical, full-scale water distribution network from the treatment plant to the homes through iron distribution mains and lead service lines under dynamic hydraulic conditions. The approach comprises the development of a multispecies reactive transport model for simulating important water chemistry reactions in distribution mains using EPANET-MSX. This water chemistry model is coupled in the framework with a mass transfer-based model for lead release from service lines. The resulting trends of water chemistry parameters variations with water age are qualitatively verified with general trends from experimental and field studies. The influence of complex water chemistry on the spatial and temporal profile of lead levels are analyzed by generating holistic simulations for a full-scale water distribution network case study. Three relevant treatment scenarios of pH adjustment, disinfectant dosage, and orthophosphate addition are presented to reflect the importance of the causal relationship between water chemistry variations in distribution mains and dissolved lead release from service lines. A strong correlation is observed between % change in dissolved lead levels and variations in pH, free chlorine residual, and orthophosphate residual in distribution mains. Further, practical implications for the use of the proposed framework to identify lead release hotspots, suggest potential sampling locations, and optimize remedial treatment measures to control lead dissolution for safe water supply are discussed. © 2020 American Society of Civil Engineers.

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Journal of Environmental Engineering (United States)

Framework for Evaluating the Impact of Water Chemistry Changes in Full-Scale Drinking Water Distribution Networks on Lead Concentrations at the Tap

The present work delineates the hydrodynamics and thermal characteristics due to mixed convection in the lid-driven semi-circular cavity affected by the presence of the adiabatic block at its geometric center for two-dimensional, steady-state, laminar and for non-Newtonian power-law fluids. The semi-circular cavity has a diameter of D. The horizontal wall/lid is sliding with a uniform horizontal velocity (u = U) and is subjugated to the ambient thermal condition; while the curved surface is subjugated to a higher isothermal temperature. The convective characteristics inside the system is explored for the broad range of Richardson number (0.1 ≤ Ri ≤ 10), Prandtl number (1 ≤ Pr ≤ 100) and non-Newtonian power-law index (0.5 ≤ n ≤ 1.5) at a constant Grashof number of 104. Apart from this, the effect of shape (cross-section) of the inserted block, i.e., circular, square and triangular on heat transfer characteristics has also been explored. It is observed that the shear thickening fluids display better cooling characteristics. Besides, the cavity with immersed triangular block shows better heat transfer results than the circular and square blocks. The deviations observed in the flow and heat transfer characteristics in the cavity by inserting an adiabatic block as compared with cavity without block have been ascertained by calculating normalized Nusselt number (NuN). The presence of the block was found to have a diminishing effect on the heat transfer due to convection in the cavity. In the end, the results of the study are summarized in the form of a predictive correlation exhibiting the functional dependence of average Nusselt number with Prandtl number, power-law index, and Richardson number. © 2020 Elsevier B.V.

Chinese Journal of Chemical Engineering

Mixed convection in the heated semi-circular lid-driven cavity for non-Newtonian power-law fluids: Effect of presence and shape of the block

Subspace identification methods using Generalized Poisson Moment Functionals (GPMF) have been proposed previously to tackle the problem of derivative estimation in continuous time (CT) systems. In this paper, a convergence result underpinning the GPMF methods for continuous time identification is detailed. Based on this, a CT-MOESP method is proposed to estimate the system matrices in state–space models. Since these results hold in the asymptotic case where the number of data points tend to infinity, Nuclear Norm Minimization (NNM) is used to integrate the low rank approximation step in subspace identification with a goodness of fit criterion. This paper extends these existing discrete time methods to continuous time by formulating the NNM optimization into the framework of the Alternating Direction Method of Multipliers (ADMM) algorithm. On the numerical front, the accuracy of the proposed method is demonstrated with the help of simulations on two systems frequently cited in literature. An industrial dryer application is considered in order to demonstrate the practical applicability of proposed method. © 2019 Elsevier Ltd

Control Engineering Practice

Nuclear norm subspace identification of continuous time state–space models with missing outputs

Here, we use molecular dynamics simulations to evaluate the behavior of toluene (TOL) and p-xylene (XYL) within three different solvents: n-hexane (HEX), n-heptane (HEP), and a thermally-robust ionic liquid (triphenyl-p-phenyl sulfonyl phenyl phosphonium + bis(trifluoromethylsulfonyl)imide (TPSP + Tf2N)). Several different temperatures are explored, while the solvation structures, energetics, and dynamics of TOL and XYL are evaluated. The solvation free energy (ΔGsolv) and transfer free energy (ΔGtransfer) of TOL and XYL are calculated using thermodynamic integration (TI). The transfer free energy of XYL from HEP/HEX to TPSP + Tf2N is more favorable than that of TOL over the entire temperature range, while the transfer of both TOL and XYL becomes less favorable as the temperature increases. The diffusion rates of TOL and XYL are lower in the ionic liquid when compared to HEP and HEX, but the thermal stability of TPSP + Tf2N may allow for higher operating temperatures and accelerated mass transport rates. © 2020 Elsevier Ltd

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Chemical Engineering Science

Molecular simulation of the separation of toluene and p-xylene with the thermally-robust ionic liquid triphenyl-p-phenyl sulfonyl phenyl phosphonium

Molecular dynamics simulations are performed to study the separation of CO2 from flue gas using carbon and boron nitride nanotube membranes. Flue gas is considered as a binary mixture of CO2 and N2 with CO2 molar concentrations of 25 and 50%. Nanotubes of boron nitride and carbon with three different chiralities of (10,0), (14,0), and (18,0) are considered for the investigation of the effect of pore size on gas separation. The permeance of CO2 is found to be higher in the boron nitride nanotube (BNNT) membrane compared to that in the carbon nanotube (CNT) membrane. The estimated CO2 permeance is of the order of 107 GPU in both types of membranes at an initial applied pressure of 50 bar. The gas permeance decreases with a decrease in membrane pore size. The optimum pore size is determined on the basis of gas permeance and the corresponding selectivity data. The free-energy changes for N2 molecules to pass through from the gas phase to the BNNT and CNT membranes are 19.36 and 9.06 kJ/mol, respectively, indicative of a significant barrier for N2 permeance in the case of BNNT. Selectivity analysis also shows that the performance of boron nitride is better than that of carbon nanotube under same conditions. This work suggests that the direct use of boron nitride nanotube as a membrane can be useful for separating CO2 from flue gas with high permeance. Copyright © 2020 American Chemical Society.

Energy and Fuels

Selective Separation of CO2from Flue Gas Using Carbon and Boron Nitride Nanotubes as a Membrane

Synthesis of methyl pentenone (MPO) using the aldol condensation reaction of methyl ethyl ketone (MEK) and acetaldehyde (AcH) in the presence of mineral acid is a commercially practiced process. The reaction is associated with the formation of a number of side products. We propose an environment-friendly, commercially available heterogeneous cation exchange resin (e.g., Ambelryst-15) catalyst for this reaction and examine its efficacy under optimized conditions. Amberlyst-15 offers better yield as compared to its homogeneous counterpart. The selectivity of the desired product was found to be increasing with the conversion of acetaldehyde, which prompted us to explore the detailed chemistry of the process. The major side products include the oligomers of acetaldehyde of different molecular weights formed by various self- and repeated aldol condensation reactions. The reaction kinetics is studied by performing experiments in batch mode in the presence of Ambelryst-15 (average diameter of 600 μm) at 600 RPM to avoid effects of external mass transfer resistances. The effect of different parameters such as particle size, stirrer speed, temperature, composition, and catalyst loading on the reaction performance is investigated. A detailed kinetic model is proposed based on the Langmuir-Hinshelwood-Hougen-Watson (LHHW) mechanism, which explains the progress of main and side reactions satisfactorily. The proposed route that uses cation exchange resin catalyst holds a potential to make the process more compact and environment-friendly. ©

Industrial \& Engineering Chemistry Research

A Greener Alternative for the Synthesis of Methyl Pentenone Using Reusable Cation Exchange Resin

Diglycolamine (DGA), one of the alkanolamine solvent used in natural gas sweetening unit, produces total organic acid (TOA) anions as degraded products that has detrimental effects over the operational units. In this study, calcium alginate carbon (CAC) adsorbents were used to remove TOA anions from industrial lean DGA solvent. The adsorbents were characterized by TGA, DSC, Raman, FTIR, and SEM analysis. Effects of different parameters such as the adsorption time, adsorbent dosage, and solution temperature were examined in the batch adsorption experiments. The kinetic data were best fitted to the pseudo-second-order model, highlighting chemisorption as the rate-limiting step. This was also validated using molecular modeling by predicting the intermolecular hydrogen bond formation between the organic acid anions and the calcium alginate molecules. The TOA uptake increased with the increase in the solution temperature from 49.9 mg/g at 25 °C to 72.5 mg/g at 55 °C. The CAC beads were regenerated effectively for six adsorption–desorption cycles in a fixed-bed column. The environmentally friendly CAC adsorbent exhibited significant application potential for the removal of TOA anions from lean DGA solvents. © 2020 Elsevier B.V.

Journal of Natural Gas Science and Engineering

Removal of the total organic acid anions from an industrial lean diglycolamine solvent using a calcium alginate carbon adsorbent, and molecular modeling studies

We report, for the first time, the development of gamma radiation resistant polysulfone (Psf)-nanodiamond (ND) composite membranes with varying concentrations of NDs, ranging up to 2 wt% of Psf. Radiation stability of the synthesized membranes was tested up to a dose of 1000 kGy. To understand the structure-property correlationship of these membranes, multiple characterization techniques were used, including field-emission scanning electron microscopy, atomic force microscopy, drop shape analysis, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, gel permeation chromatography, positron annihilation spectroscopy, and small angle X-ray scattering. All the composite membranes exhibited enhanced radiation resistance properties, with 0.5% loading of NDs as the optimum. Compared to the radiation stability of Psf membranes up to a dose of 100 kGy, the optimum composite membranes are found to be stable up to a radiation dose of 500 kGy, owing to the unique surface chemistry of NDs and interfacial chemistry of Psf-ND composites. Experimental findings along with the Monte Carlo simulation studies confirmed a five times enhanced life-span of the composite membranes in an environment of the intermediate level radioactive waste, compared to the control Psf membrane. This journal is © The Royal Society of Chemistry.

Nanoscale Advances

Nanodiamonds as a state-of-the-art material for enhancing the gamma radiation resistance properties of polymeric membranes

Nanodiamond (ND) particles of different size (10, 250, and 500 nm) were used as filler materials for preparation of polysulfone-nanodiamond (Psf-ND) mixed-matrix membranes (MMMs), with loading of each ND particle varying from 0.1 to 2 wt% of polymer. Control Psf and MMMs were irradiated up to a γ-radiation dose of 1000 kGy. The effect of ND size was investigated on morphology, surface and mechanical properties, and performance of membranes in γ-radiation environment. The membranes were characterized by surface and cross-section SEM images, AFM, water contact angle studies, GPC, UTM, pure water permeability, and solute (PEO, 100 kDa) rejection measurements. The 10 nm sized ND enhanced the stability and performance of MMM up to 0.5% loading, while higher loading of it led to agglomeration of ND, and in-turn the deterioration of membrane performance. ND with larger particle size (250 and 500 nm), though dispersed homogeneously in the membrane matrix, but resulted in interfacial defects between ND and Psf host membrane matrix. The MMM with an optimum 0.5% loading of ND10 particles offered ~5 times enhanced radiation stability, as compared to that of control Psf membrane. This is the first of its kind study reported herein that provides an insight into the effect of ND particle size in altering the radiation resistance behaviour of MMMs. © 2020 Elsevier B.V.

Diamond and Related Materials

Effect of nanodiamond size on γ-radiation resistance property of polysulfone-nanodiamond mixed-matrix membranes

Drinking water utilities are increasingly facing the challenges of maintaining water quality, and simultaneously complying with conflicting regulatory standards. One such challenge is the dosage of chlorine-based disinfectants which is typically regulated to prevent microbial growth in the water distribution systems, while limiting disinfection by-products (DBPs). On the other hand, chlorine residuals also influence the dissolution of lead into drinking water from corrosion scales in the pipe internals, as has been shown by previous studies. Hence, it is important to consider water lead levels (WLLs) while determining the appropriate chlorine dosage. This study proposes a multi-objective optimization framework to understand and balance the trade-offs between (i) minimizing total disinfectant dosage to reduce DBPs formation potential, and (ii) maximizing the volume of safe drinking water supply with respect to both WLLs and residual free chlorine concentrations. The approach comprises of the development of a dynamic simulation-optimization framework to account for the impact of spatial and temporal variations of network hydraulics and water chemistry on WLLs and residual free chlorine. The framework couples dynamic multi-species water quality simulations (pH, residual free chlorine, dissolved inorganic carbon, and orthophosphate concentration) with a multi-objective genetic optimization algorithm in an integrated MATLAB-EPANET-MSX platform. The application of the optimization formulation is demonstrated on a real-world distribution network case study. The resulting optimal solution set on pareto-plots are discussed for sensitivity of the trade-offs between the two objective functions, under various water chemistry conditions that have been suggested in earlier studies for minimizing lead release from plattnerite (PbO2) corrosion scales in lead service lines. The resulting optimal disinfectant dosage schedule, for pumping and booster station nodes in each case, provided insights on maintaining disinfectant residuals throughout the distribution system so as to prevent microbial growth as well as lead contamination events while limiting DBPs formation. Further, environmental implications related to the use of the proposed framework are also discussed. © 2020 Elsevier Ltd