Design, Implementation, and Evaluation of a Green Solvent System for Industrial Esterification Processes

Thesis Abstract

The increasing environmental and safety concerns surrounding traditional organic solvents in industrial esterification demand scalable alternatives that combine efficiency with sustainability. This study addresses the core problem of high solvent hazard profiles, volatile organic compound emissions, and energy-intensive recovery processes in large-scale esterification plants. The aim is to design, implement, and evaluate a green solvent system that enables equal or superior reaction performance while reducing environmental impact and lifecycle costs. Specific objectives include (i) selecting and optimizing a green solvent system compatible with common esterification catalysts (e.g., acid catalysts) and substrates (carboxylic acids and alcohols), (ii) establishing a sustainable process design that minimizes energy use and solvent losses through process intensification, (iii) validating solvent performance through pilot-scale experiments, and (iv) evaluating environmental and economic benefits using a cradle-to-gate assessment and a multi-criteria decision analysis framework. A mixed-methods approach integrates experimental, process-design, and lifecycle assessment components. The research adopts a design, implementation, and evaluation framework underpinned by the Theory of Ecological Modernization and the Green Chemistry Principles. The population comprises industrial esterification processes using traditional solvents, while the sample includes three representative reaction systems acyl chlorides converted to esters, fatty acid esters for biodiesel production, and pharmaceutical-grade esterifications. Laboratory-scale screening (n=12 solvent candidates) informs a pilot-scale validation (flow reactor trials at 5–20 L/h) using a 1.0–2.5 M substrate concentration and standard acid catalysts. Data collection instruments include high-performance liquid chromatography (HPLC) for product purity, gas chromatography–mass spectrometry (GC-MS) for solvent and by-product profiling, Karl Fischer titration for trace water content, and in-situ infrared spectroscopy for real-time monitoring. Instrumental calibration, method validation, and blind sample analyses ensure data integrity. Process performance metrics encompass reaction conversion, selectivity, solvent recovery yields, energy consumption, and waste generation. Data analysis employs Design of Experiments (DoE) to optimize solvent–catalyst–temperature–stoichiometry interactions, followed by regression analysis to model response surfaces; ANOVA tests determine statistical significance (p<0.05). A techno-economic analysis evaluates capital and operating expenditures, while a cradle-to-gate lifecycle assessment quantifies environmental impacts across global warming potential, ozone depletion potential, and aquatic toxicity categories. A simplified conceptual model links solvent properties (polarity, hydrogen-bonding capacity, boiling point, miscibility) to esterification kinetics and mass-transfer performance, guiding the selection of the optimal green solvent system. Expected findings include identification of a non-volatile, recyclable solvent blend or solventless eutectic system that delivers equal or higher esterification conversion and selectivity compared with conventional solvents, while reducing energy intensity by 15–25% and solvent losses by 40–60%. It is anticipated that the green system will enable smoother heat integration and lower boiling point requirements, facilitating easier solvent recovery and reduced downstream purification costs. Environmental analyses are expected to show substantial reductions in global warming potential and human health hazards, with cost savings driven by lower solvent consumption and enhanced catalyst life. The study contributes to knowledge by providing a transferable design framework for green solvent adoption in esterification, validated at pilot scale and accompanied by robust economic and environmental justifications. It advances the application of Green Chemistry in industrial reaction engineering and offers a decision-support toolkit for process engineers and managers. The main conclusion anticipates that a carefully designed green solvent system can meet or exceed performance targets of traditional systems while delivering meaningful sustainability benefits, enabling a scalable pathway for industry adoption. Recommendations include extending the framework to other carbonyl-activation chemistries, exploring solvent-free or continuous-flow configurations for high-throughput esterifications, and developing industry guidelines for lifecycle benchmarking and regulatory compliance.