Applications of computer difference spectroscopy in ion-exchange resins analysis

Infrared spectra demonstrate the use of computer difference spectroscopy and other dataprocessing routines to derive and enhance the difference spectra that relates the concentration of a resin to the concentration of other resins in the mixture. Therefore, a simple quantitative treatment accounting for the resin concentration has been determined. © 1995 John Wiley & Sons, Inc.     

Ion-exchange equilibria of amino acids on strong-acid resins: Theory

Equations describing equilibrium uptake of neutral, acidic, and basic amino acids by strong-acid cation exchangers as a function of pH and concentrations of amino acid and added electrolyte or buffer are derived.     

Determination of formaldehyde/urea molar ratio in amino resins by near‐infrared spectroscopy

New processes for synthesis of urea‐formaldehyde (UF) and melamine‐fortified urea‐formaldehyde (mUF) resins have been developed in the last years, motivated by the current concerns about the effects of formaldehyde on human health. All these formulations are quite susceptible to possible operation error, which can significantly influence the characteristics of the final product. The main objective of this work was to implement chemometric techniques for off‐line monitoring of the product's formaldehyde/urea (F/U) molar ratio using near infrared (NIR) spectroscopy. This allows the timely implementation of the necessary corrections in case the product is off‐specification. Calibration models for F/U molar ratio were developed taking into account the most relevant spectral regions for these resins, individually or in combination (7502–6098 cm^?1 and 5000–4246 cm^?1) and using different preprocessing methods. When the appropriate spectral range and preprocessing methods are selected, it is possible to obtain calibration models with high correlation values for these resins. The best preprocessing methods were identified for three cases: UF resin (produced by strongly‐acid process), mUF resin (alkaline‐acid process), and a combined model that involves both UF and mUF resins. It was concluded that significantly better accuracy is obtained when a new model is developed for each particular resin system. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Esterification of free fatty acids in waste cooking oils (WCO): Role of ion-exchange resins

Although WCO plays a crucial role for the economical production of biodiesel, free fatty acid (FFA) level in the nature of WCO cause saponification problems during transesterification. Acidic ion-exchange resins can be used to decrease WCO free fatty acid level. In this study, activities of resins (Amberlyst-15 (A-15), Amberlyst-35 (A-35), Amberlyst-16 (A-16) and Dowex HCR-W2) in direct FFA esterification were examined in the temperature range of 50–60 °C and the effect of catalyst amount (1–2 wt%) on FFA conversion was also analyzed. FFA conversion increased with increasing reaction temperature and catalyst amount. Order of catalytic activities was found as A-15 > A-35 > A-16 > Dowex HCR-W2. This was related to the size of average pore diameters and magnitude of BET surface area.     

Infrared spectroscopy of single-wiain KNbO3 in the tetragonal phase

Owing to the development of an original technique of crystal growth and thermal gradient poling, large single-domain samples of KNbO₃ have been prepared at high temperature in the tetragonal phase. Infrared reflection spectra are reported for the first time in this phase and compared with similar data previously obtained in isomorphous BaTiO₃.     

Fast determination of fatty acids in oil-utilizing resins by NMR spectroscopy

This work describes the determination of oil either as such or in oil-utilizing resins such as alkyds and urethanes, by means of NMR techniques. Both the qualitative and quantitative analyses are demonstrated and the accuracy is assessed. Typically, the complete analysis of an alkyd resin takes less than 1 hr.     

Immobilization of spent ion-exchange resins in the urea-formaldehyde matrix

Studies have been carried out on the immobilization of spent ion-exchange resins produced in nuclear power plants in urea-formaldehyde matrix. The matrices were prepared by incorporating different types of ion-exchange resins in the pH range of 4.5 to 5.0, using boric acid as a catalyst. Characterization of the matrices was carried out with respect to dimensional changes, compressive strength, and leach resistance. The cumulative percentage weight loss and volume change were observed to decrease with the increase in boric acid concentration before attaining a plateau. The diffusion coefficients were in the order of 10^?16 M/s, and the compressive strengths were in the range of 0.83 to 12 MPa. Infrared spectral studies on the urea-formaldehyde matrices revealed that the rate and the extent of cure depended on the type of resin. © 1994 John Wiley & Sons, Inc.     

氨基膦酸型含氟螯合树脂用于离子膜二次盐水精制

对D-412氨基膦酸型螯合树脂进行共聚改性,在聚合中引入含氟单体,在树脂骨架上引入氟元素制得氨基膦酸型含氟螯合树脂。最佳反应条件为:聚合配方中含氟单体选用甲基丙烯酸八氟戊酯(质量分数为0.8%),再经过氯甲基化、胺化、膦酸化反应。试验证明:该改性螯合树脂用于离子膜法烧碱盐水的二次精制,吸附性能得到提高,力学性能也得到提高,树脂破碎率远低于未处理的D-412螯合树脂。     

Removal of amino acids from water by adsorption on polystyrene resins

The adsorption of eight amino acids, L ‐asparagine, D,L ‐threonine, L ‐lysine, L ‐leucine D,L ‐methionine, L ‐tyrosine, L ‐phenylalanine and D,L ‐tryptophan, on the non‐polar macroporous adsorbents Amberlite XAD‐2 and XAD‐4 (polystyrene–divinylbenzene copolymers) was studied. Equilibrium adsorption experiments were conducted to estimate the types of isotherm and their parameters. The effect the chemical composition and structure of the amino acids on the efficiency of adsorption was evaluated. The influence of pH and ionic strength was also studied. The data of adsorption isotherms of the examined amino acids seemed generally to approach the Freundlich isotherm model. Tryptophan isotherm adsorption data could match in some cases the Langmuir model. The majority of the adsorption isotherms were almost linear. In terms of adsorbed amino acid on both resin surfaces, the amino acids can be ranked thus: D,L ‐tryptophan > L ‐phenylalanine > D,L ‐methionine, L ‐tyrosine > L ‐leucine > L ‐lysine > D,L ‐threonine > L ‐asparagine. In low pH solution, adsorption was generally higher than that at intermediate and high pH values. Generally, as the ionic strength increases, the adsorption of the amino acids increases. © 2001 Society of Chemical Industry     

Nonionic adsorption of aromatic amino acids on a cation-exchange resin

Nonionic adsorption of aromatic amino acids on a cation-exchange resin (Dowex 50W-X8) was studied. At low concentrations, phenylalanine and tyrosine were adsorbed on the resin by monovalent ion-exchange process. Deviation from stoichiometric ion exchange became large as phenylalanine and tyrosine concentrations increased. On the other hand, aliphatic amino acids, glycine and alanine, were adsorbed on the resin by monovalent ion-exchange process. In column breakthrough experiments, the bed capacities for phenylalanine and tyrosine were higher than those for metal ions (Na⁺, Pb²⁺, and Ni²⁺) and the aliphatic amino acids. The increased capacities may be due to nonionic interaction between the aromatic amino acids and the polystyrene resin matrix. The nonionic interaction could be suppressed in 25% ethanol solution.     

Infrared spectroscopy study of powder celluloses modified by Lewis acids

It is shown that modified powder celluloses distinguish from microcrystal cellulose produced by a hydrolytic method by the presence of the modification of cellulose II and by a low index of crystallinity. © 1994 John Wiley & Sons, Inc.     

Industrial utilization of spent ion-exchange resin in the coke battery

Experimental coking with spent ion-exchange resins as an additive in the coal batch is considered; rammed batch is employed. Both box coking and large-scale coking are considered; the resin content in the batch is 1–5 wt %. The influence of the resins on coke quality is assessed. The coal blend used in industrial coke production is employed. Adding small quantities of resin (<5 wt %) to the batch improves the coke’s cold strength M ₈₀ and M ₄₀, without impairment of CRI and CSR. The quality of the coal tar and the organized gas emission remains unchanged. Hence, spent ion-exchange resins may be recycled by adding small quantities (3%) to the coal batch in coke production.     

The effect of temperature on the stability of ion-exchange resins in aqueous medium

The effect on ion-exchange resins of the polystyrene type of a thermal treatment has been studied by heating strong cation and strong anion resins in water at 95°C and 250°C and obtaining the IR spectra of the remaining resins as well as those of the decomposition products extracted by the water. The degradation of the resins is highly dependent on their ionic form. The ? (OH^?) and the ? (H⁺) forms are more labile, losing completely their exchange capacity at 250°C, while the ? (Li⁺) form retains considerable ion-exchange capacity. On the other hand, the hydrothermal process affects differently the backbone of the anion and the cation resins. There are similarities in the type of decomposition products found after hydrothermal treatment with those observed after radiolytic exposure of the resins. Heating the resins in water reduces the crosslinking of the polystyrene matrix.     

The use of modified divinylbenzene-polystyrene resins in the separation of fermentation products. A case study utilizing amino acids and a dipeptide

The adsorption of phenylalanine, aspartic acid, asparagine and aspartame from phosphate-buffered aqueous solutions with modified divinyl-benzene-polystyrene resins has been investigated using high pressure liquid chromatography (HPLC). The pH studied was 2.8, the temperature range was 293-313 K and the ionic strength was maintained at 1.0 mol dm^?3. Over the range of variables investigated, the adsorption isotherms are linear and may be characterized by temperature and pH-dependent apparent adsorption equilibrium constants, characteristic of the resin-adsorbate system. By studying the dependence on temperature of this adsorption constant, heats of adsorption and entropy of adsorption have been estimated. In terms of the heat liberated on adsorption, the amino acids and a dipeptide can be ranked thus: aspartame > phenylalanine > aspartic acid > asparagine.     

Determination of the structural configuration of cresol–novolak resins by 13C NMR spectroscopy

¹³C NMR spectroscopy was used to investigate the structures of a series of pure isomeric cresylic novolak resins. Chemical shifts were measured and assigned, and end groups were distinguished from the central repeat units of the chains. Based on these measurements, the number average molecular weight of the para-cresylic oligomer was determined. A comparison of the ¹³C decoupled and coupled spectra of the three isomeric resins indicates that the para isomer has a linear, ordered structure in which the aromatic rings are linked only by ortho–ortho′ methylene-bridging groups. The structures of the ortho and meta isomers are more complex and contain ortho–ortho′, ortho–para′, and para–para′ methylene bridges.     

Synthesis of bifunctional ion-exchange resins through the Arbusov reaction: Effect on selectivity and kinetics

Bifunctional ion-exchange resins are synthesized from vinylbenzyl chloride—styrne copolymers. The two types of functional groups are introduced by an Arbusov reaction followed by sulfonation. The effect of ligand ratios, macroporosity, and matrix rigidity on the complexation of Eu (III) from solutions of low pH is quantified. It is found that ion complexation kinetics and selectivity are maximized with resins having both sulfonic and phosphonic acid ligands. Maximum metal ion complexation rates depend on a balance between chemical interactions (i.e., a bifunctional network interacting with a given substrate through an access and a recognition mechanism) and physical parameters (i.e., matrix porosity and rigidity). Structural integrity must be maintained through an appropriate crosslink level in order for the advantage of bifunctionality to be maintained in low-pH solutions. © 1994 John Wiley & Sons, Inc.     

Analysis of functional groups in amino resins

Aiming at establishing recommended methods for the analysis of functional groups in amino resins, four tentative methods have been tested in an international cooperative exercise. The methods were employed on four model compounds and three commercial amino resin solutions. ¹³C-NMR spectroscopy was additionally employed by two of the participants.

The inter-laboratory analytical study has resulted in four recommended methods: 1. Solvent removal from amino resins, 2. Proton-NMR spectroscopy, 3. Alkoxy group analysis by transetherification plus G.L.C., 4. Alkoxy group analysis by Zeisel/Merz cleavage plus G.L.C. The recommended methods are improved versions of the tentative methods applied in the round robin and possible future inter-laboratory exercises will probably show a reduced variation between laboratories as far as quantitative results are concerned. As to qualitative analysis of amino resins, ¹³C-NMR spectroscopy has been shown to be a powerful technique.