Mid‐infrared polarization spectroscopy: A tool for in situ measurements of toxic gases in smoke‐laden environments

Infrared polarization spectroscopy (IRPS) was used to detect HCl in an 800 mm long tube furnace. Pieces of a polyvinyl chloride‐carpet were continuously fed into the furnace producing a heavy smoke, which is exemplified by the fact that the smoke completely obscured a red laser beam from a He‐Ne laser. This constitutes a very harsh environment from a diagnostic point of view due to the high smoke density and relatively long path through the furnace. Despite this it was still possible to measure HCl concentrations in the smoke down to a level of ～50ppm using IRPS. The explanation for this success is twofold. First, the IRPS method is inherently almost noise free due to the use of crossed polarizers, creating a virtually zero background. Second, the laser beam attenuation due to non‐resonant absorption and scattering in the smoke, especially with soot particles, decreases with increasing laser wavelength. Therefore, this type of measurements would have been much more difficult to perform in the visible regime (with wavelengths ～0.5µm) than in the infrared regime (with wavelengths ～3µm). Copyright © 2010 John Wiley & Sons, Ltd.     

Determination of the formaldehyde‐to‐phenol molar ratios of resol resins by infrared spectroscopy and multivariate analysis

The formaldehyde/phenol (F/P) ratios of resol resins were successfully predicted by the recording of infrared (IR) spectra of both calibration and analyzed resins and by a multivariate analysis technique. In the creation of applicable models, the best correlating IR spectral areas were found between 1800 and 700 cm^?1. The positive effects of the increasing replicates and the omission of first‐derivative preprocessing on model quality were proven by systematic testing. The characteristic statistical parameters were acceptable when the resin was similar to the calibration resins. Although the calibration samples had narrow F/P molar ratios (2.00–2.40), or a particular urea content or alkalinity, the best calibration model could also successfully predict the F/P molar ratios of resins with greater F/P ratios, higher urea contents, and lower alkalinity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3582–3586, 2003     

In‐line near‐infrared spectroscopy: A tool to monitor the preparation of polymer‐clay nanocomposites in extruders

In‐line diffuse reflectance and on‐line transmission near‐infrared spectroscopy (NIR) measurements are performed at the same location of the barrel of a twin screw extruder during the preparation of a polypropylene/clay nanocomposite. Their performance is evaluated by means of a 7‐parameter chemometric model using off‐line rheological and structural (FTIR) data obtained from samples prepared under different screw speed, compatibilizer content and clay loading, as well as a process‐related thermomechanical index. Despite the higher variability of the diffuse reflectance signal, the two models present analogous high quality indices. The aptness of the reflectance measurements is thus validated, which has direct practical advantages, as this probe can be fixed in any typical melt pressure transducer port. The probe is then used for the real‐time in‐line monitoring of the production of the same nanocomposite but now using different throughputs, and the chemometric‐based predictions are compared with experimental off‐line characterization data. The nonlinear effect of throughput is correctly anticipated. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Ultraviolet curing kinetics of cycloaliphatic epoxide with real‐time fourier transform infrared spectroscopy

The photo‐induced curing kinetics of cycloaliphatic epoxide coatings were investigated with real‐time Fourier transform infrared spectroscopy with an optical fiber ultraviolet curing system. The consumption of epoxy group as a function of time was obtained by monitoring of the oxirane absorbance in the 789–746‐cm^?1 region. The effect of the type of epoxide, hydroxyl equivalent weight, ratio of oxirane to hydroxyl groups (R), photoinitiator, and exposure time on the curing reaction was investigated. In general, the rate of curing was dependent on the hydroxyl equivalent weight, R, type of epoxide, and photoinitiator. For formulations without polyol, both initiator concentration and exposure time had minimal effects on the curing reaction. However, for formulations with polyol, the curing a reaction was dependent on the initiator concentration. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2485–2499, 2003     

In‐line and in situ monitoring of semi‐batch emulsion copolymerizations using near‐infrared spectroscopy

This article shows that near‐infrared spectroscopy (NIRS) can be used efficiently for the simultaneous in‐line and in situ monitoring of monomer (methyl methacrylate, MMA, and butyl acrylate, BuA) and polymer concentrations in the reaction medium during seeded semibatch emulsion copolymerizations. A series of actual reaction experiments was planned to allow the proper obtainment and selection of calibrating samples. Partial least squares (PLS) was used to build three independent calibration equations in the range of 1100–1900 nm, which were used to successfully monitor some disturbed reactions in‐line. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2670–2682, 2002     

Analysis of a crease‐resisting finish on linen fabrics using Fourier transform infrared spectroscopy and visible and near‐infrared spectroscopy

A wide range of chemical reagents are capable of producing a satisfactory crease‐resisting finish for cellulosic fabrics and are currently available on the market. However, these agents do not work as efficiently on linen relative to cotton or rayon. Untreated linen controls and samples treated with a N‐methylol reagent were investigated for physical and chemical changes, and an attempt was made to quantify the crosslinking bonds formed and assess other changes in the treated fabrics using Fourier transform infrared spectroscopy (FTIR) and visible and near‐infrared spectroscopy (NIR). The results were compared with nitrogen analysis data, crease‐recovery angle measurements, and abrasion‐resistance tests in an attempt to assess the effectiveness of the treatment relative to the responses of the instrumental techniques. This study shows correlations between the visible and NIR and FTIR spectra and the crease‐recovery angle and abrasion resistance. The study also indicates that FTIR may be useful in assessing the crosslinking bonding changes associated with the dimethylol urea treatment of linen to achieve improved crease recovery. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1886–1896, 2001     

Denitrifying phosphorus removal with nitrite by a real‐time step feed sequencing batch reactor

BACKGROUND: Nitrite is toxic to anoxic phosphorus uptake when it exceeds a threshold concentration. In this study, denitrifying phosphorus removal with nitrite as electron acceptor was investigated in a sequencing batch reactor (SBR) operated using a real‐time step feed strategy. RESULTS: The nitrite pulse concentration was initially determined by batch experiments. pH increased with use of nitrite for phosphate uptake, and decreased when the nitrite was used up. Nitrite was added promptly after the pH reached the peak value, and phosphate uptake continued, driven by the nitrite addition. The pH was adjusted to 7.50 using HCl with each pulse of nitrite addition. ORP could be used to determine the endpoint of denitrifiying phosphorus removal. However, the variation of second derivative of ORP with time was much more sensitive and should be a more suitable control parameter than ORP itself to determine the endpoint of denitrifying phosphorus removal. CONCLUSION: Compared with denitrifying phosphorus removal with nitrate as electron acceptor, denitrifying phosphorus removal with nitrite using real‐time step feed can save 22.3% of polyhydroxyalkanoate (PHA) for phosphorus removal and 49.4% of PHA for nitrogen removal. In addition, the reaction time could be shortened. Copyright © 2010 Society of Chemical Industry     

Comparison of real‐time methods for maximizing power output in microbial fuel cells

Microbial fuel cells (MFCs) constitute a novel power generation technology that converts organic waste to electrical energy using microbially catalyzed electrochemical reactions. Since the power output of MFCs changes considerably with varying operating conditions, the online optimization of electrical load (i.e., external resistance) is extremely important for maintaining a stable MFC performance. The application of several real‐time optimization methods is presented, such as the perturbation and observation method, the gradient method, and the recently proposed multiunit method, for maximizing power output of MFCs by varying the external resistance. Experiments were carried out in two similar MFCs fed with acetate. Variations in substrate concentration and temperature were introduced to study the performance of each optimization method in the face of disturbances unknown to the algorithms. Experimental results were used to discuss advantages and limitations of each optimization method. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

On‐line monitoring of wastewater quality: a review

Real‐time monitoring of wastewater quality remains an unresolved problem to the wastewater treatment industry. In order to comply with increasingly stringent environmental regulations, plant operators as well as instrument manufacturers have expressed the need for new standards and improved comparability and reliability of existing techniques. A review of currently available methods for monitoring global organic parameters (BOD, COD, TOC) is given. The study reviews both existing standard techniques and new innovative technologies with the focus on the sensors' potential for on‐line and real‐time monitoring and control. Current developments of biosensors, optical sensors and sensor arrays as well as virtual sensors for the monitoring of wastewater organic load are presented and the interests and limitations of these techniques with respect to their application to the wastewater monitoring are discussed. © 2001 Society of Chemical Industry     

Two‐dimensional fluorescence as a fingerprinting tool for monitoring wastewater treatment systems

BACKGROUND: The use of two‐dimensional (2D) fluorescence for monitoring complex biological systems requires careful assessment of the effect of chemical species present, which may be fluorescent and/or may interfere with the fluorescence response of target fluorophores. Given the complexity of fluorescence data (excitation emission matrices—EEMs), the challenge is how to recover the information embedded into those EEMs that can be related quantitatively with the observed performance of the biological processes under study. RESULTS: This work shows clearly that interference effects (such as quenching and inner filter effects) occur due to the presence of multiple species in complex biological media, such as natural water matrices, wastewaters and activated sludge. A statistical multivariate analysis is proposed to recover quantitative information from 2D fluorescence data, correlating EEMs with the observed performance. A selected case study is discussed, where 2D fluorescence spectra obtained from the effluent of a membrane bioreactor were compressed using PARAFAC and successfully correlated with the effluent chemical oxygen demand, using projection to latent structures modelling. CONCLUSION: This study demonstrates the potential of using 2D fluorescence spectroscopy as a status fingerprint. Additionally, it is shown how statistical multivariate data analysis can be used to correlate EEMs with selected performance parameters for monitoring of biological systems. Copyright © 2011 Society of Chemical Industry     

Central limit theorems for nonparametric estimators with real‐time random variables

In this article, asymptotic theories for nonparametric methods are studied when they are applied to real‐time data. In particular, we derive central limit theorems for nonparametric density and regression estimators. For this we formally introduce a sequence of real‐time random variables indexed by a parameter related to fine gridding of time domain (or fine discretization). Our results show that the impact of fine gridding is greater in the density estimation case in the sense that strong dependence due to fine gridding severely affects the major strength of nonparametric density estimator (or its data‐adaptive property). In addition, we discuss some issues about nonparametric regression model with fine gridding of time domain.     

Study of activation process and active site of co‐based catalyst for 1, 3‐butadiene polymerization using X‐ray absorption spectroscopy and DFT calculations

Activation process and active site of Co‐based Ziegler‐Natta catalysts were studied by using synchrotron X‐ray absorption spectroscopic technique and an optimum model of the cobalt active site was proposed with density functional theory (DFT) calculations. In the X‐ray absorption near edge structure (XANES) spectrum of Co(2‐ethylhexanoate)₂, the preedge peak, 1s → 3d transition at 7707.8 eV and the K‐edge peak, 1s → 4p transition at 7719.2 eV were observed. Both the intense K‐edge and the weak preedge peaks indicate that Co(2‐ethylhexanoate)₂ possesses high O_h symmetry and the cobalt exists in a divalent state. Upon addition of methylaluminoxane (MAO), some changes in peak positions and intensities were observed. The preedge peak was a little shifted to 7708.2 eV with increased intensity, and the K‐edge peak was shifted to a lower energy, 7717.2 eV with decreased intensity. This indicates that the oxidation state of cobalt still mainly remained +2 and the coordination geometry was altered from O_h to T_d resulting from Co 3d and 4p orbital mixing with a loss of O_h symmetry. In the XANES spectrum of a mixture of Co(2‐ethylhexanoate)₂, MAO and t‐BuCl, the K‐edge peak at 7715.7 eV was observed. The orbital mixing of 4p cobalt and 2p chlorine orbitals results in a low energy transition. In 1,3‐butadiene polymerization, this is attributable to the coordination of chlorine to cobalt, which is believed to facilitate cis‐configuration and increasing reactivity. B(C₆F₅)₃ was employed as Lewis acid, but no significant interaction with cobalt was found in the XANES spectrum of a mixture of Co(2‐ethylhexanoate)₂, Al(iBu) and B(C₆F₅)₃, which is similar to the XANES of a mixture of Co(2‐ethylhexanoate)₂ and Al(iBu)₃. B(C₆F₅)₃ as Lewis acid does not greatly disturb the coordination symmetry of cobalt nor influence the oxidation state. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Rapid monitoring of bisphenol‒A diglycidyl ether formation through byproduct estimation: A study by Fourier transform infra‐red spectroscopy

For identification and quantification of desired and undesired products during epoxy resin formation, polymerization of bisphenol‐A with the stoichiometric excess of epichlorohydrin is carried out using catalytic excess of alkali. The reaction is monitored using Fourier transform infra‐red (FT‐IR) spectroscopy technique. Major undesired products are unreacted monomers (bisphenol‐A and epichlorohydrin) and byproducts (chlorine and α‐glycol substituted diglycidal ether of bisphenol‐A), whereas the desired product is only diglycidal ether of bisphenol‐A. Molar concentrations of epichlorohydrin, bisphenol‐A, diglycidal ether of bisphenol‐A, chlorine substituted resin, and α‐glycol substituted resin in the polymerization mixture are analyzed and quantified using FT‐IR characteristic frequency bands at 925, 3448, 1344, 773, and 3641 cm^?1, respectively. For optimal determination of process parameters on polymerization, effect of temperature and alkali loading on epoxy polymerization is carried to maximize the yield of diglycidal ether of bisphenol‐A with simultaneous minimizing the byproducts formation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Near infrared (NIR) spectroscopy compared with thermogravimetric analysis as a tool for on‐line prediction of water diffusion in polyamide 6,6

NIR spectroscopy in the transmission mode and thermogravimetric analysis were used to predict diffusion of water into polyamide 6,6 samples immersed in water at 40, 60, 75 and 90 °C for different periods of time. The sorption curves between 40 and 75 were sigmoidal indicating that the surface concentration was time dependent. The sorption curves were readily fitted by the use of a time‐dependent surface concentration and a water‐concentration‐dependent diffusivity. The zero‐concentration water diffusivity decreased non‐linearly and the activation energy of diffusion increased from 24 to 58 kJ mol^?1, with decreasing temperature. The surface concentration relaxation time decreased rapidly. The sorption of water in thick polyamide samples was readily characterized by FT‐NIR spectroscopy. The accuracy and feasibility of this method was similar to conventional thermogravimetric methods. The greatest advantage of FT‐NIR, however, is the possibility of detecting and monitoring the moisture concentration on‐line and in a non‐destructive way. © 2002 Society of Chemical Industry     

In‐line monitoring of hydrogen peroxide in two‐phase reactions using raman spectroscopy

Hydrogen peroxide is an environment‐friendly oxidizer, which is used in several chemical processes. However, safety necessitates the determination and control of the concentration of hydrogen peroxide during oxidation reactions. We propose a methodology to monitor hydrogen peroxide in disperse two‐phase reaction mixtures based on in‐line Raman spectroscopy. We compare indirect hard modeling (IHM), peak integration (PI), and partial least squares (PLS). Building predictive PLS and PI calibration models is challenging, whereas the IHM calibration is easy to develop. These methods show good accuracy for known samples (root mean square error of cross validation [RMSECV] of 0.3–0.7 wt %) compared to the classic titration method (RMSECV of 0.4 wt %). After calibration, inline monitoring during reaction is performed demonstrating that the concentration of hydrogen peroxide can be successfully monitored in a fast and reliable way by Raman spectroscopy. The IHM seems to give slightly better inline predictions. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3994–4002, 2017