Key Takeaways & Executive Findings
- •• Amino-functionalization of TS-1 zeolite enables uniform and stable immobilization of phosphotungstic acid, creating a robust solid acid catalyst. • The catalyst achieves a high tributyl citrate yield of 96.2% and citric acid conversion of 98.1% under optimized conditions (150 °C, 6 h). • The immobilized HPW provides strong Brønsted acid sites, while framework titanium contributes weak Lewis acidity, enhancing catalytic performance. • The catalyst demonstrates good reusability over four cycles, with minor deactivation attributed to leaching of weakly anchored species.
Abstract
The amino-functionalization of TS-1 zeolite followed by immobilization of phosphotungstic acid (HPW) was presented to prepare a strong solid acid catalyst for the synthesis of bio-based tributyl citrate from the esterification of citric acid and n-butanol. g-Aminopropyltriethoxysilane (APTES) was first grafted on the TS-1 zeolite via the condensation reactions with surface hydroxyl groups, and subsequently the HPW was immobilized via the reaction between the amino groups and the protons from HPW-forming strong ionic bonding. The Keggin structure of HPW and MFI topology of TS-1 zeolite were well maintained after the modifications. The amino-functionalization generated abundant uniformly distributed active sites on TS-1 for HPW immobilization, which promoted the dispersity, abundance, as well as the stability of the acid sites. The tetrahedrally coordinated framework titanium and non-framework titania behaved as weak Lewis acid sites, and the protons from the immobilized HPW acted as the moderate or strong Brønsted acid sites. An optimized TBC yield of 96.2% (mol) with a conversion of eCOOH of 98.1% (mol) was achieved at 150 °C for 6 h over the HPW immobilized on amino-functionalized TS-1. The catalyst exhibited good stability after four consecutive reaction runs, where the activity leveled off at still a relatively high level after somewhat deactivation possibly caused by the leaching of a small portion of weakly anchored APTES or HPW.
1. Introduction
Plasticizer is the most widely used chemical additive in the plastics industry with the ability to increase the flexibility and processibility of a polymer, and thus find wide applications, e.g., in toys, food and cosmetics packaging, and medical equipment [1,2]. The ever-increasing concerns over the health and environmental protection have spurred research efforts towards developing bio-based, non-toxic, and environmental benign plasticizers. Citric acid ester, which is synthesized via esterification of the bio-based citric acid and alcohols, represents one kind of such green plasticizers [3,4]. Traditional homogeneous Brønsted acids such as H2SO4, H3PO4 and organic acids (e.g., methanesulfonic acid) are effective catalysts for the esterification of citric acid and alcohols [5e7]. However, heterogeneous catalysts are usually preferred over homogeneous ones due to the ease of catalyst separation and reuse, as well as the less corruption issues and environmental impacts [8e14]. As such, research attention is given to developing solid acid catalysts for the efficient synthesis of citric acid esters, such as zeolites, metal oxides, ion exchange resins, heteropoly acids, functionalized carbon, or their combinations [5,6,15e21].
Esterification reaction is typically catalyzed by Brønsted acid [7,22e24], though Lewis acid has also been reported to be effective [17], it tends to deactivate due to the hydration of Lewis acid sites in the presence of water [9]. Heteropolyacids (HPAs) represent a typical class of solid Brønsted acids with well-defined structure, high acid strength, thermal stability, and desirable catalytic performance in diverse acid-catalyzed reactions such as (trans)esterification, dehydration/hydrolysis, alkylation, acylation as well as redox reactions [25,26]. However, HPAs usually exhibit low surface areas and limited porosity in their native form, which tend to restrict the amount and accessibility of the acid sites. Nevertheless, HPAs tend to dissolve in some polar solvent systems (e.g., aqueous solution) forming homogeneous catalytic system, imposing additional difficulties in catalyst separation and recovery. As such, immobilization of HPAs over high-surface area scaffold with well-defined porosity, such as mesoporous silica, metal-organic frameworks, transition metal oxides, zeolites, and carbon, have been proposed to improve the stability and catalytic performance [25e31]. Among others, zeolite is preferred because of the large surface area, strong adsorption capacity, and abundant active sites. For the supported HPA catalysts, the amount of the immobilized HPAs and the interaction strength between HPAs and the support materials are important factors that are directly related to the acidity, activity, and stability of the catalysts. It is known that the Brønste
Loading authentic research manuscript (Pages 1–5)...
Pei Li, Bianfang Shi, Junyao Shen, Ran Cui, Wenze Guo, Ling Zhao, Zhenhao Xi (2024). Phosphotungstic acid immobilized on amino-functionalized TS-1 zeolite as a solid acid catalyst for the synthesis of tributyl citrate. Chinese Journal of Chemical Engineering. https://doi.org/10.1016/j_cjche_1448
Research & Educational Purpose Only:The translations, structured abstracts, analytical annotations, and data reports provided by SinoTechIntel are intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
Copyright & Intellectual Property Notice: Original copyright of the underlying source articles and experimental data remains with the respective authors, institutions, and original publishing journals. SinoTechIntel claims intellectual property only over its proprietary translations, analytical syntheses, and AEO structured enhancements in accordance with international fair use and academic citation principles.
Frequently Asked Questions
What is the main innovation of this study?
The study presents a novel method to immobilize phosphotungstic acid (HPW) on amino-functionalized TS-1 zeolite, creating a strong solid acid catalyst for the synthesis of tributyl citrate. The amino-functionalization enhances the dispersion and stability of HPW, leading to high catalytic activity and reusability.
What are the optimal reaction conditions for tributyl citrate synthesis?
The optimized conditions are a temperature of 150 °C and a reaction time of 6 hours, achieving a tributyl citrate yield of 96.2% and a citric acid conversion of 98.1%.
Why is the immobilization of HPW on TS-1 zeolite beneficial?
Immobilization prevents the dissolution of HPW in polar solvents, improves the accessibility of acid sites, and enhances the stability and reusability of the catalyst, making it a more sustainable and efficient alternative to homogeneous acid catalysts.
What types of acid sites are present in the catalyst?
The catalyst contains both Brønsted acid sites from the immobilized HPW and weak Lewis acid sites from the framework titanium and non-framework titania in the TS-1 zeolite, which together contribute to its high catalytic performance.
How stable is the catalyst over multiple reaction cycles?
The catalyst shows good stability over four consecutive runs, with only slight deactivation attributed to the leaching of weakly anchored APTES or HPW, indicating its potential for industrial application.
Related Technical Papers & Translations
Design and optimization of a high-efficiency distillation process for cellulosic fuel ethanol integrated with thermal coupling and molecular sieve adsorption
To address the challenges of high energy consumption and prominent costs in the traditional three-columns distillation process for cellulosic fuel ethanol, a distillation—molecular sieve coupling separation process is proposed. This process integrates a three-column (crude distillation column, first distillation column, second distillation column) system with a 3A molecular sieve adsorption deep dehydration unit. A thermal coupling network is constructed via differential pressure design (steam from medium/high-pressure columns as mutual heat sources, reboiler liquid waste heat for feed preheating), and molecular sieve adsorption conditions are optimized. The study first performs a thermodynamic consistency test on the ethanol—water system, determines optimal non-random two-liquid (NRTL) model binary interaction parameters via experimental data regression for Aspen Plus simulation. Aiming at minimum total annual cost (TAC), Aspen Plus is used to optimize process parameters (theoretical tray number, feed location, reflux ratio, side-draw position, etc.). Economic analysis shows this process reduces CO2 emission costs by 27.56%, TAC by 15.58% (to 5.123 × 106 USD·a-1), and increases ethanol purity to ＞99.6%, providing an effective solution for green, efficient separation.
A cohesion loss model for determining residual strength of deep bedded sandstone
Rock residual strength, as an important input parameter, plays an indispensable role in proposing the reasonable and scientific scheme about stope design, underground tunnel excavation and stability evaluation of deep chambers. Therefore, previous residual strength models of rocks established were reviewed. And corresponding related problems were stated. Subsequently, starting from the effects of bedding and whole life-cycle evolution process, series of triaxial mechanical tests of deep bedded s
Federated model with contrastive learning and adaptive control variates for human activity recognition
Recent attention to privacy issues demands a communication-safe method for training human activity recognition (HAR) models on client activity data. Federated learning (FL) has become a compelling technique to facilitate model training between the server and clients while preserving data privacy. However, classical FL methods often assume independent and identically distributed (IID) data among clients. This assumption does not hold true in practical scenarios. Human activity in real-world scena