Molecular distillation, also known as short-path distillation, is a novel and unique separation and purification technique. Unlike conventional distillation, which relies on differences in boiling points, it achieves separation at lower pressures and temperatures far below boiling points by utilizing the differences in the mean free path of molecular motion of different substances. It is a gentle distillation method for separating and purifying complex and heat-sensitive substances.
Molecular distillation has become the mainstream purification route for food-grade and pharmaceutical-grade diacylglycerol (DAG). Compared with supercritical CO₂ and solvent crystallization, molecular distillation has the advantages of "low temperature, short time, and high vacuum". It can increase the purity of DAG from 40-44% crude product to over 92% in one step under conditions of 1–10 Pa and 150–220 °C, reduce the acid value to 0.97 mg KOH/g, and significantly reduce the color and peroxide value.
Core Steps
① First-stage light phase evaporation: Removes FFA and MAG, DAG purity ≈ 72%;
② Second-stage heavy phase evaporation: Redistills with the same parameters to separate TAG, final product DAG ≥ 92%, overall yield 60–77%;
③ High vacuum system: Roots + diffusion pump, limit ≤ 0.1 Pa, ensuring thermistor DAG is heated < 60 s;
④ Online detection: Real-time measurement of DAG content using near-infrared or Raman probes, with closed-loop control of reflux ratio/temperature, achieving batch-to-batch variation ≤ 1%.
Molecular distillation, with its advantages of high vacuum, short heating time, and low pollution, has moved from the laboratory to a multi-ton-scale industry. It is currently the most mature and economical industrialization path for DAG purification and will be integrated with membrane separation and nano-adsorption technology to promote the upgrading of the functional oil industry.
