On-line Fourier Transform Infrared Research Articles

Monitoring and investigating reactive extraction of (di–)carboxylic acids using online FTIR – Part II: Reaction equilibria, reaction kinetics and competition within the complex formation between itaconic acid and several amine extractants

The downstream processing of biocatalytically produced (di–)carboxylic acids still is a challenging task. One innovative approach, demonstrating industrial applicability, applies an initial reactive extraction (RE) using hydrophobic amine extractants into an organic solvent, followed by a subsequent back-extraction (BE) using water soluble amine extractants into a (fresh) aqueous solution. Although showing promising results in terms of yield and selectivity, state-of-the-art amine extractant selection is only based on trial-and-error screening approaches. Thus, to enable an optimized process design and thereby optimized downstream processing, a deeper understanding of RE and BE on a molecular level is crucial.Within this work, we successfully applied an experimental setup incorporating online Fourier Transform Infrared (FTIR) spectroscopy to elucidate influencing factors on RE and BE as well as to provide a guideline for an optimized selection of amine extractants. Investigations on the kinetics of complex formation between itaconic acid (IA) and tri-n-octylamine (TNOA) in 1-decanol revealed the reaction order to be zero in TNOA, indicating that mass transfer is the rate limiting step in RE. Reaction equilibrium investigations revealed that for all IA - amine extractants combinations in 1-decanol reaction equilibrium was almost completely on the product (complex) side. The strength of the acid-extractant complexes was evaluated using FTIR experiments, providing a novel approach / methodology to efficiently select an optimal combination of amine extractants for RE and BE. Applying the novel online FTIR spectroscopy setup allowed to monitor a complete process sequence of RE and BE of IA with selected amine extractants, validating the proposed guidelines for an optimized selection of amine extractants. The results of this work will facilitate the definition of appropriate RE and BE systems for biocatalytically produced (di–)carboxylic acids.

Monitoring and investigating reactive extraction of (di–)carboxylic acids using online FTIR – Part I: Characterization of the complex formed between itaconic acid and tri-n-octylamine

Reactive extraction (RE) using amine extractants in an organic solvent has been proven a promising downstream strategy for (di–)carboxylic acids of biocatalytic origin. Available analytical techniques allow for observation of the acid depletion in the aqueous phase and thus an indirect link to the course of the RE as well as concentration of the complex.In order to further optimize RE performance in these systems, a direct information on the complex concentration as well as its stoichiometry (amine extractant to (di–)carboxylic acid ratio in the complex) in the organic phase is crucial.Within this work, we successfully applied Fourier Transform Infrared (FTIR) spectroscopy for the detection and quantification of the acid-extractant complex formed between itaconic acid (IA) and tri-n-octylamine (TNOA) in 1-decanol. A newly developed experimental setup incorporating FTIR spectroscopy and a systematic procedure for the characterization of the acid-extractant complex allow clarifying the structure of the acid-extractant complex. Our investigations revealed the complex formation between IA and TNOA to be based on the ion-pair mechanism whereas the stoichiometry was identified to be 2:1 (TNOA:IA) when TNOA is available in excess. Applying the experimental setup enables online monitoring of the IA concentration simultaneously in both phases during extraction of IA using 1-decanol as organic extraction phase. The mechanistic understanding of the complex formation on a molecular basis gained from the results of this study as well as the possibility to online monitor RE enables the optimization of RE as downstream strategy for (di–)carboxylic acids.

Infrared Spectroscopy for Online Measurement of Tars, Water, and Permanent Gases in Biomass Gasification.

Online measurements of the raw gas composition, including tars and water, during biomass gasification provide valuable information in fundamental investigations and for process control. Mainly consisting of hydrocarbons, tars can, in principle, be measured using Fourier transform infrared (FT-IR) spectroscopy. However, an instrument subjected to raw gas runs the risk of condensation of tars on optical components and subsequent malfunction. Therefore, an external cell, heated to at least 400 ℃, has been designed to ensure that tars remain in the gas phase during FT-IR measurements. The cell was used for on-line FT-IR measurements of permanent gases (CO, CO2, CH4), water, and tars during the operation of a lab-scale downdraft gasifier using wood pellets, bark pellets, and char chips. Based on calibration, the measurement error of permanent gases was estimated to be 0.2%. Concentrations evaluated from spectral signatures of hydrocarbons in tar are in good agreement with results from solid-phase adsorption measurements and correlated well with operational changes in the gasifier.

A fast progressive spectrum denoising combined with partial least squares algorithm and its application in online Fourier transform infrared quantitative analysis

Fourier transform infrared (FTIR) spectroscopy is an important method in analytical chemistry. A material can be qualitatively and quantitatively analyzed from its FTIR spectrum. Spectrum denoising is commonly performed before online FTIR quantitative analysis. The average method requires a long time to collect spectra, which weakens real-time online analysis. The Savitzky-Golay smoothing method makes peaks smoother with the increase of window width, causing useful information to be lost. The sparse representation method is a common denoising method, that is used to reconstruct spectrum. However, for the randomness of noise, we can't achieve the sparse representation of noise. Traditional sparse representation algorithms only perform denoising once, and the noise can not be removed completely. FTIR spectrum denoising should therefore be performed in a progressive way. However, it is difficult to determine to what degree of denoising is required. Here, a fast progressive spectrum denoising combined with partial least squares method was developed for online FTIR quantitative analysis. Two real sample data sets were used to test the performance of the proposed method. The experimental results indicated that the progressive spectrum denoising method combined with the partial least squares method performed markedly better than other methods in terms of root mean squared error of prediction and coefficient of determination in the FTIR quantitative analysis.

Development of on-line FTIR spectroscopy for siloxane detection in biogas to enhance carbon contactor management

Activated carbon filters are used to limit engine damage by siloxanes when biogas is utilised to provide electricity. However, carbon filter siloxane removal performance is poorly understood as until recently, it had not been possible to measure siloxanes on-line. In this study, on-line Fourier Transform Infrared (FTIR) spectroscopy was developed to measure siloxane concentration in real biogas both upstream (86.1–157.5mgm−3) and downstream (2.2–4.3mgm−3) of activated carbon filters. The FTIR provided reasonable precision upstream of the carbon vessel with a root mean square error of 10% using partial least squares analysis. However, positive interference from volatile organic carbons was observed in downstream gas measurements limiting precision at the outlet to an RMSE of 1.5mgm−3 (47.8%). Importantly, a limit of detection of 3.2mgm−3 was identified which is below the recommended siloxane limit and evidences the applicability of on-line FTIR for this application.

Combination of mid-infrared spectroscopy and chemometric factorization tools to study the oxidation of lubricating base oils

The effect of the presence of iron as a catalyst during base oil oxidation has been studied. Fourier transform infrared (FTIR) spectroscopy was combined to Principal Component Analysis (PCA) in order to extract chemical information during oil oxidation process. After 8 h, the presence of iron did not lead to significant change in the global chemical composition as revealed by the first principal component. However, the second principal component indicated clearly that the initial formation of alcohols and esters was favoured by the presence of iron. The influence of iron was highlighted by PCA analysis of on-line FTIR data.

Characterization of Styrene Copolymers Using Size-Exclusion Chromatography with On-line FT-IR Viscometer Detectors

Size-exclusion chromatography (SEC) provides a rapid method for determining molar mass distributions of macromolecules. In this article, we demonstrate the method of SEC coupled with an on-line Fourier-transform infrared (FT-IR) detector and an on-line differential viscometer developed for copolymer characterization. Using a chemometric technique to analyze the FT-IR spectra allows for determining copolymer concentration and composition. The combination of the FT-IR concentration detector and the viscometer allows the universal calibration method to be used for measuring copolymer molar mass. Molar mass distribution and compositional distribution are described and the method's application demonstrated using several types of styrene copolymers.

An On‐Line Approach To Monitor Ethanol Fermentation Using FTIR Spectroscopy

Fermentation process control is currently limited by its inability to measure parameters such as substrate, product, and biomass concentrations rapidly for consistent on-line feedback. Physical and chemical parameters, such as temperature and pH, currently can be obtained on-line using appropriate sensors. However, to obtain information on the concentration of the substrate, product, and biomass, samples must be taken off-line for measurement. With the use of spectroscopic techniques, real-time monitoring of process constituents such as product and substrate is possible. Spectroscopic techniques are rapid and nondestructive, require minimal or no sample preparation, and can be used to simultaneously assess several constituents in complex matrices. The production of ethanol is the largest fermentation process in terms of production volume and economic value as a result of its prominence in the food, agricultural, and fuel industries. This study attempts to develop an on-line ethanol fermentation monitoring technique using Fourier transform infrared (FTIR) spectroscopy with a flow-through ATR capability. Models developed using multivariate statistics, employed to obtain on-line FTIR measurements, were successfully validated by off-line HPLC analysis and spectrophotometry data. Standard errors of prediction (SEP) values of 0.985 g/L (R2 = 0.996), 1.386 g/L (R2 = 0.998), and 0.546 (R2 = 0.972) were obtained for ethanol, glucose, and OD, respectively. This work demonstrates that FTIR spectroscopy could be used for rapid on-line monitoring of fermentation.

Chemical and kinetic study of acetophenone hydrogenation over Pt/Al 2O 3: Application of BTEM and other multivariate techniques to quantitative on-line FTIR measurements

The heterogeneous catalytic hydrogenation of acetophenone (Aceph) over Pt/Al 2O 3 in d 8 -toluene/ h 8 -toluene at 273 K was performed in semibatch mode, using a recycle configuration and on-line quantitative Fourier transform infrared (FTIR) spectroscopy measurements. Based on the d 8 -toluene solvent used and the multivariate analysis applied, further details of the reaction chemistry were elucidated, including the following: (i) Solvent activation occurred during reaction, leading to observable hydrogenation and H–D exchange, and (ii) 1-phenylethanol (Phel), cyclohexyl methyl ketone (CMK), and cyclohexylethanol (Che) were observable products, and little H–D exchange occurred. The on-line FTIR measurements, with sensitivity on the order of 10 −5 mol / L , also lead to the following kinetic observations: (i) Water had a strong inhibiting effect on the hydrogenation rates, and (ii) very interesting short time-scale kinetic behavior occurred after some perturbations. The latter included rapid initial hydrogenations on fresh catalyst (due to the presence of spillover hydrogen) and observable adsorption–desorption of other reactants. The reaction rates obtained from the well-defined experiments in h 8 -toluene were fit to a number of Langmuir–Hinshelwood–Hougen–Watson (LHHW) models, in which the effects of solvent and water were included. A model involving a pairwise addition of adsorbed dissociated hydrogen to the adsorbed substrate provided the best fit of the data. The regression of the kinetic data suggested that water made a statistically significant contribution to the competitive adsorption on the catalyst surface. In more general terms, the present contribution suggests the utility of detailed on-line liquid-phase spectroscopy together with multivariate techniques for exploratory studies of heterogeneous catalytic systems.

A versatile and compact experimental apparatus for the on-line spectroscopic study of liquid-phase heterogeneous catalytic systems

A versatile and compact experimental system is described for the study of fine-chemistry liquid-phase heterogeneous catalysis. The general experimental system consists of a stirred tank (25–100 mL), pump, tubular reactor, spectrometer(s), and injection block for liquid-phase perturbations, all in a closed-recycling configuration. The basic designs of the in-house-constructed components are provided. The system was characterized with respect to gas–liquid mass transfer, mixing, liquid–solid mass transfer, and intraparticle diffusion. The utility of the system is demonstrated with a heterogeneous catalytic reaction—the racemic hydrogenation of acetophenone over Pt/Al 2O 3—using on-line Fourier transform infrared (FTIR) analytics. Liquid–solid mass transfer and intraparticle diffusion were studied by varying the liquid hourly space velocity (LHSV) as well as the catalyst particle sizes used. The reaction rates based on the instantaneous reagent concentrations were precisely evaluated using on-line FTIR measurements. The rather novel inclusion of an injection/sampling block was particularly useful for performing multiple perturbations of reagents, a situation neither normally available nor convenient for the experimentalist, thus facilitating outstanding spectral deconvolution using band-target entropy minimization. The small total liquid-phase volume involved (≈15 ml) would facilitate the frugal use of chiral reagents/auxiliaries as well as isotopically labeled components.

Spectroscopic study on sorption of hydrogen sulfide by means of red soil

This paper reports the results of the characterization of red soils in relation to the sorption of H 2S from coal gas at 500 °C by spectroscopic techniques in order to provide more information on red soils’ structural change both before and after reaction. In addition, by-products analysis has also been studied using Fourier transform infrared (FTIR) spectroscopy. Before and after the experiments the red soils were characterized with X-ray powder diffraction (XRPD), energy dispersion spectrum (EDS), X-ray photoelectron spectroscopy (XPS) and FTIR spectroscopy. XRPD results indicate that iron oxide species disappear from the original to reacted red soil. EDS analysis shows that a significant amount of sulfur is present in the reacted red soil, which is in agreement with the results of the elemental analysis and the calculated value based on breakthrough curve. XPS regression fitting results further indicate that sulfur retention may be associated with the iron oxides. S 2p XPS fittings point out that the major sulfur species present in the reacted red soil are composed of S −2, elemental sulfur, polysulfide, sulfite and sulfate. Additionally, the binding energy of iron shifts to a lower position for the reacted red soil, which indicates that iron oxides in the original red soil have been converted into iron sulfide. Appreciable amounts of the by-products CO 2, SO 2 and COS are detected by on-line FTIR spectroscopy during the initial and later stages of the sorption process. The formation of CO 2 is related to the water-shift reaction, and SO 2 is probably attributable to the reaction of organic matters and H 2S. The concentration of COS is quantified by GC/FPD and found it to be about 350 ppm, which is close to the equilibrium concentration of the reaction of inlet CO and H 2S at a temperature of 500 °C.

In Situ 50°C FTIR Spectroscopy of Pt and PtRu Direct Methanol Fuel Cell Membrane Electrode Assembly Anodes

A tandem surface-transmission Fourier transform infrared (FTIR) method permits the simultaneous investigation of adsorbed and desorbed species formed at the electrode surface of direct methanol fuel cell (DMFC) membrane electrode assemblies (MEAs). Potential dependent, in situ specular reflectance spectra and on-line transmission FTIR spectroscopy of adsorbed and desorbed species on working fuel cell electrode surfaces, confirm that linear bound CO, the primary intermediate on unsupported Pt and PtRu surfaces of fuel cell MEAs, have lower Stark tuning rates than the corresponding on arc-melted alloys. Two peaks corresponding to CO stretching modes were observed on a PtRu fuel cell anode surface prepared with Johnson Matthey catalysts. The higher frequency peak is ascribed to a Pt-rich alloy and the low frequency peak is ascribed to either pure Ru or an Ru-rich phase. The tandem technique confirms that a peak easily misassigned as a linear bound CO stretching mode is a methanol overtone peak. In addition to methylformate is a major product of a gas fed DMFC, which is detected at the anode exhaust by on-line FTIR. © 2002 The Electrochemical Society. All rights reserved.

On-line ATR FTIR measurement of supersaturation during solution crystallization processes. Calibration and applications on three solute/solvent systems

Recently, fourier transform infraRed (FTIR) spectroscopy was reported as a promising technique for in situ measurement of supersaturation during solution crystallization processes. The attenuated total reflection (ATR) probes appeared to be particularly suited to the chemical and physical complexity of industrial suspensions. However, to be used in an industrial context, the technique must be easily and quickly adaptable to different systems. In order to achieve such an aim, a calibration procedure to monitor supersaturation from FTIR measurements is presented. General comments and recommendations about important technical aspects of the technique are also given. Then the technique is used to develop efficient procedures for the determination of solubility and metastability curves. The crystallization of three fine chemical products is studied, thanks to on-line FTIR measurements of supersaturation and off-line CSD determinations. It is shown that the monitoring of supersaturation is a valuable tool for an improved analysis of key phenomena involved during crystallization processes (primary and secondary nucleation, agglomeration, phase transition, seeding, etc.).

Determination of carbonates in waters by on-line vapor generation FTIR

An electrically heated gas-permeation unit (GPU) has been employed for the vapor-generation Fourier transform infrared (FTIR) determination of total carbonate in waters. The developed method is based on the simultaneous injection of 100 μl sample and 100 μl nitric acid in a two-channel manifold with a merging zone, which provides the generation of CO 2 through the GPU, heated at 90°C, from which CO 2 is swept by a stream of N 2 to a long-path infrared gas cell. Absorbance measurements were made in the range from 2500 to 2150 cm −1 and the corresponding flow injection recordings were obtained as a function of time. The areas of these peaks are interpolated in a calibration equation obtained from aqueous standards of Na 2CO 3 treated in the same way as samples. The method provides a limit of detection of 4.6 ppm (expressed as mg of HCO 3 − l −1) and a sampling frequency of 30 h −1. Results obtained for a series of natural waters compare well with those obtained by a titrimetric reference method.