Study Of Autocatalytic Esterification For Dimethyl Oxalate And Diethyl Oxalate Syntheses

Oxalic acid esters are widely used as the most important intermediates to produceethylene glycol. With the sharp increase of market demand of ethylene glycol inpresent years, more and more attention has been attached to the fast production ofoxalic acid esters. At present, the traditional catalytic esterification process usingoxalic acid and monohydric alcohol is still the most widely used method forproducing oxalic acid esters.In this work, autocatalytic esterification processes using batch reactor to producedimethyl oxalate and diethyl oxalate were studied. Firstly, we established a reliablemethod to detect reaction products by using high performance liquid chromatography(HPLC). With consideration of the effects of mobile phase ratio, pH, flow rate andother conditions on the detection results, the optimal analysis conditions for the HPLCwere determined. Secondly, the effects of several factors such as reaction temperature,initial feed molar ratio of alcohol to oxalic acid and reaction time on the conversionrate of oxalic acid and the yield of oxalate esters were investigated in depth. Theexperimental results indicates that both of the oxalic acid conversion rate and the yieldof oxalate esters increase gradually with the rising of reaction temperature and initialmolar ratio of alcohol to oxalic acid.Meanwhile, the kinetics of oxalic acid self-catalyzed esterification with alcoholwere studied in this paper. According to the test results we found that the oxalatemonoester exists during the period of esterification, which act as an intermediateproduct. Consequently, the reaction path of autocatalytic esterification was confirmedand appropriate reaction kinetic models were established. The reaction kineticequations were obtained in two steps. Firstly, the reaction kinetic models wereproperly simplified and the reaction kinetic equations parameters were fitted using theexperiment data with the help of mathematic tools. Then, a comparison of thecalculated and experimental data was made and the autocatalytic reaction kineticequations were determined finally.In this paper, batch and semi-continuous reaction experiments for the synthesis ofdimethyl oxalate and diethyl oxalate were carried out. For the synthesis of dimethyl oxalate, the results of the batch and semi-continuous reaction processes are nearly thesame. While, for the synthesis of diethyl oxalate, the semi-continuous results weremuch better. Thus, a continuous autocatalytic esterification process for the synthesisof diethyl oxalate using ethanol and oxalic acid can be achieved in a reactivedistillation configuration.