Dibutyl Citrate Synthesis, Physicochemical Characterization, and Px Data in Mixtures with Butanol

Abstract

Dibutyl citrate (DBC) was synthesized via partial esterification of citric acid (CA) with n-butanol (BuOH) and characterized for the first time. Then, the monoacid diester was isolated from the reactive mixture by using a pH-controlled solvent extraction procedure. The identity of the obtained product was verified by NMR spectroscopy, finding that it corresponds to a mixture of asymmetric and symmetric isomers. The obtained product was characterized by thermogravimetric and differential scanning calorimetry analysis and by density and viscosity measurements. As per the calorimetric analysis, DBC exhibited a crystallization point below 213 K, a decomposition temperature of 541 K, and an average heat capacity of 2.461 kJ/kg K in the evaluated temperature range (320–375 K). The average liquid density and viscosity in the studied temperature interval (298–313 K) were 1.122 g/cm3 and 2.03 Pa·s, respectively. Additionally, isothermal vapor–liquid equilibrium data (P–x) in mixtures containing the obtained DBC and BuOH were measured at 313, 323, and 333 K. Experimental data were used to fit UNIQUAC interaction parameters for the binary DBC–BuOH. The regressed model showed good agreement with experimental results, making it suitable for further process design and simulation. The obtained data can be used in the development of processes for citrate plasticizer production and in the development of separation processes for DBC.

Tributyl Citrate Production via Reactive Distillation—Conceptual Design and Pilot-Scale Validation

“…In addition, there is immiscibility in the mixtures of BuOH and water, and TBC and water, distributing the remaining components differently between both liquid phases. Finally, both intermediate esters MBC and DBC have not been commercially isolated, and therefore, there is none or few data available on their physicochemical properties . Taking into account the abovementioned discussion, the UNIQUAC activity coefficient model was selected to model the nonidealities of the mixture.…”

“…In addition to the nonidealities in phase equilibria, there is a thermal decomposition of CA above 426 K, generating different organic acids (e.g., itaconic and aconitic). , This thermal degradation has also been observed with the intermediate citrate esters (MBC and DBC) . Because of the low volatility of these components and their thermal sensitivity, determination of vapor pressure of such pure components is problematic.…”

“…Mass and citrate species balance average error were 8.0 and 13.9%, respectively. Besides HPLC uncertainties caused by the absence of specific response factors for intermediate citrates, , the mass flow measurements were estimated from volumetric or gravimetric data along time. As a time average was necessary, this might involve additional uncertainties to the experimental measurements, mainly when operating at low flow rates.…”

“…Finally, both intermediate esters MBC and DBC have not been commercially isolated, and therefore, there is none or few data available on their physicochemical properties. 11 Taking into account the abovementioned discussion, the UNIQUAC activity coefficient model was selected to model the nonidealities of the mixture. The CA/H 2 O binary parameters were obtained from previous work on CA esterification by RD 18 and other available parameters from the literature 12 and the missing ones were predicted with UNIFAC.…”

“…In this regard, this work deals with the fundamentals of the production of TBC via RD. Initially, the conceptual design of the process was accomplished based on validated kinetic and thermodynamic models. − This was done using novel reactive residue curve maps (RRCMs) applied to mixtures of six components. Then, a computer-aided RD model was developed and implemented in Aspen Plus, exploring different operating configurations that help to guide a further experimental exploration of the process.…”