Highly efficient and recyclable catalysts SnCl 2 – x H 3 PW 12 O 40 /AC with Brønsted and Lewis acid sites for terephthalic acid esterification

An in-depth assessment on the non-isothermal esterification reaction for the di(2-ethylhexyl) terephthalate production: Kinetic modelling considering phase equilibria

UDC 678.674'524'420.03 An investigation of the solution of terephthalic acid (TPA) in ethylene glycol (EG) and their reaction products is of considerable interest because the solution is a necessary precondition for the reaction of direct esterification. It has been established [1] that at high temperatures (->250°C) the esterification proceeds in the diffusion region, i.e. the process rate is limited by the solution process of the TPA. The published information about the influence of the reaction medium on the solubility and esterification of TPA is highly contradictory. Some workers researching the solubility of TPA in organic solvents do not relate the solubility index to the concrete properties of the solvent [2] or relate it to its proton-acceptanc e capacity [ 3]. Krumpole et al. [4] cite data about the solubility of TPA in EG and draw the conclusion that the solubility of TPA does not depend on the presence of reaction products. Other workers [ 5; 6] offer evidence that the presence of diglycol terephthalate (DGT) in the system TPA-EG stimulates the reaction rate but fail to disclose the nature of this effect of the medium. Kodaira et al. [7] also report the favorable influence of DGT on the esterification rate and ascribe it to the entropy effect which increases with the DGT concentration. Other workers [ 8] state, however, that the solubility of TPA is higher in EG than in a mixture of mono- and diesters and show that DGT has an adverse effect on the reaction rate because its basicity characteristics enable it to combine with the TPA over hydrogen bonds resulting in the formation of inactive associated products. In view of these facts it was deemed relevant to investigate the solution of TPA in EG and in their reaction products and the effect of the chemical reaction on the solution process, and to determine the temperature boundary between the purely physical solution process and the onset of the chemical reaction. The experiments were carried out with TPA with a specific surface Ssp of 0.5, 1.5, and 2.9 m2/g (Ssp was determined by the BlOT adsorption method). All experiments were carried out with an EG/TPA ratio of 10 by weight. The COOH groups were determined in specimens from which the solid TPA had first been filtered out. The content of the products of the chemical reaction in the specimens was determined by polarography and thin-film chromatography [9]. To begin with, the influence of the speed of stirring on the rate of TPA solution in EG was investigated. It was found that the solution rate increases with an increase in the stirrer speed to 700 rpm after which it remains unchanged. The influence of the other diffusion factor, viz. Ss_, on the solution rate was therefore investigated at a stirrer speed of 700 rpm. The results are set out in Table 1. According to the theory of diffusion processes, the rate of the solution process described by Shchukarev's equation [ 10] always increases with the specific surface of the substance being dissolved:

A study on the esterification of terephthalic acid

Esterification of terephthalic acid with methanol over mesoporous Al-MCM-41 molecular sieves

The esterification of terephthalic acid (PTA) with methanol to dimethyl terephthalate (DMT) was investigated using commercially available zeolite catalysts as the eco-friendly solid acids. Six typical zeolites (ZSM-5-25, ZSM-5-50, ZSM-5-100, ZSM-35, MOR, and β) were systematically evaluated. Among them, β zeolite showed excellent catalytic performance, achieving nearly 100% PTA conversion and 76.1% DMT selectivity under the conditions of 200 °C, of 0.5 MPa N2 pressure, m(PTA):V(methanol) of 1:40 (g/mL), m(PTA):m(catalyst) of 10:1 over 4 h. The characterization results show that the catalytic efficiency was correlated with acid site strength, specific surface area, and mesoporous structure of the zeolite. After optimization, β zeolite achieved 100% PTA conversion and 94.1% DMT selectivity under the conditions of 200 °C, of 1 MPa N2 pressure, m(PTA)/V(methanol) of 1:30 (g/mL), m(PTA)/m(catalyst) of 8:1 over 8 h. Moreover, β zeolite exhibited superior stability, maintaining over 92% of its initial activity after five cycles, highlighting its potential for sustainable DMT production.

This work studies the chlorine (Cl) release during the esterification of terephthalic acid (TPA) and ethylene glycol (EG) due to the addition of different amounts of polyvinyl chloride (PVC) that emulates its presence as an impurity. With the aim to explore the possible effects of PVC presence and its dehydrochlorination during the syntheses of bis(2‐hydroxyethyl) terephthalate (BHET) and with the aid of a mathematical model, the evolution releasing of Cl during PVC dehydrochlorination is analyzed. Theoretical results present a good correlation with experimental data that indicate the presence of Cl in the composition of the final product because the dehydrochlorination is incomplete. Additionally, the model predicts the temperature in that Cl can be completely released avoiding its presence in BHET. These kinds of studies are of particular interest when products with a high degree of purity are required, and Cl is detrimental to end applications.

Clear time (tcl), the time required for the turbid mixture of terephthalic acid (TPA) and ethylene glycol (EG) to be clear, was measured to examine the effect of poly(ethylene terephthalate) (PET) prepolymer (DP of 1–5) on the kinetics of dissolution and/or ester-ification of TPA with EG. The tcl of the mixture of TPA/EG (1 : 1.5 in molar ratio) was reduced to 1 : 2.2 or 1 : 3.5 by addition of 30 wt % of PET prepolymer or bis-(2-hydroxyl ethyl) terephthalate (BHET), respectively. Diethyl terephthalate (DET) as an addititive was used as a model compound to examine the effects of the —OH group on the esterification reaction of TPA/EG. The tcl value increased with addition of DET. The effect of the carbonyl group was also examined by determining esterification rates of benzoic acid (BA) with either ethylene glycol monobezoate (EGMB) as a compound with carbonyl group, or 2-penoxyethanol (2-PhE) as a compound without the carbonyl group. The reaction rate of BA with EGMB was much higher than that of BA with 2-PhE, which indicates that the carbonyl group gave an increasing effect of the esterification rate. Fourier transform infrared spectra showed that the —OH group in both BHET and EGMB formed intramolecular hydrogen bonding with the ester carbonyl group. On the basis of these observations, we concluded that the electron density of oxygen in the hydroxyl group increased through the formation of the intramolecular hydrogen bond. The increased electron density gave the —OH group easier access to the carbonyl carbon in BA, leading to an increase in the esterification rate. © 1996 John Wiley & Sons, Inc.

Efficient and stable Ni-Cu catalysts for ex situ catalytic pyrolysis vapor upgrading of oleic acid into hydrocarbon: Effect of catalyst support, process parameters and Ni-to-Cu mixed ratio

The present work considers the relationship between the acidic properties and catalytic activity of non‐zeolitic oxides and zeolites in glycerol dehydration. The acidic properties of the catalysts were characterized by a method of NH 3 infrared‐mass spectroscopy/temperature‐programmed desorption. This revealed the amounts of Brønsted and Lewis acid sites and the Brønsted acid strength. Brønsted acid sites are more active in glycerol dehydration than Lewis acid sites. The acid strength generally increased with glycerol conversion, but the acid sites on mordenite zeolite were so strong that the activity declined. The selectivity to acrolein showed more improvement on Brønsted acid sites than on Lewis acid sites. Lewis acid sites were moderately effective active sites in the formation of acrolein and acetol. Sodium cations deactivated Brønsted acid sites but did not influence the catalytic performance of Lewis acid sites in this reaction. In this study, high‐silica ZSM‐5 zeolite exhibited considerably higher catalytic activity and acrolein selectivity than non‐zeolitic oxides and other zeolites.

Some physico-chemical properties and catalytic activity of sulfate ion supported on WO3/SnO2 catalyst

A procedure was developed for preparing composites of nanocrystalline cellulose (NCC) with poly(ethylene terephthalate) (PET). Poly(ethylene terephthalate) and PET/NCC composites were prepared by a continuous procedure in two steps: esterification of terephthalic acid with ethylene glycol and polycondensation. The morphological, thermal, sorption, and mechanical properties of the synthesized PET/NCC composites were studied using a set of modern physicochemical methods. Introduction of a small amount of nanocrystalline cellulose (about 0.1%) in the course of poly(ethylene terephthalate) synthesis does not lead to changes in the molecular mass composition of the polymer but appreciably increases the degree of crystallinity and improves the mechanical properties of the composite.

Copolyester (CP)-titanium dioxide (TiO2) (CPT) nanocomposites with low melting point were synthesized by esterification of terephthalic acid, isophthalic acid, ethylene glycol and 1,4-butanediol monomers in the presence of tetrabutyl orthotitanate (TBOT). TBOT hydrolysis caused the TiO2 nanoparticles to act as catalysts for polymerization. Transmission electron micrographs showed that the TiO2 nanoparticles with the content ranging from 0.2 wt% to 0.4 wt% were well dispersed in the copolyester matrix. The thermal properties of the nanocomposites were assessed by differential scanning calorimetry. The melting point of CPT nanocomposite with 1.2 wt% TiO2 was 201.9°C, significantly lower than that of pure polyethylene terephthalate (above 260°C). Therefore, the obtained CPT nanocomposites with low melting point are potentially better for industrial applications than the commercial product.

Pseudo-homogeneous kinetic modeling of dioctyl terephthalate (DOTP) production by esterification of terephthalic acid and 2-ethylhexanol over tetrabutyl titanate catalyst

Abstractγ‐Valerolactone (GVL) is a renewable and versatile platform chemical derived from sustainable carbon feedstocks. The cascade conversion of levulinic acid into GVL requires Brønsted and Lewis acid catalysed reactions. Here, a dual‐catalyst bed configuration is demonstrated that promotes synergy between Brønsted acid sites in sulfated zirconia (SZ) and Lewis acid sites in ZrO2/SBA‐15 for the liquid phase, continuous flow esterification and subsequent catalytic transfer hydrogenation (CTH) of levulinic acid to GVL. A saturated surface sulfate monolayer, possessing a high density of strong Brønsted acid sites, was optimal for levulinic acid esterification to isopropyl levulinate over SZ (>80 % conversion). A conformal ZrO2 bilayer, deposited over a SBA‐15 mesoporous silica and possessing mixed Brønsted:Lewis acidity, catalysed CTH of the levulinate ester and subsequent dealcoholisation/cyclisation to GVL (>60 % selectivity). Maximum stable productivity for the dual‐bed was 2.2 mmolGVL.gcat.h−1 at 150 °C, significantly outperforming either catalyst alone or a physical mixture of both. Flow chemistry is a versatile approach to achieve spatial control over cascade transformations involving distinct catalytically active sites.

Theoretical exploration of novel compounds in Sr(B,C)x (x = 7,8) at high pressure