Microencapsulation of oxalic acid (OA) via coacervation induced by polydimethylsiloxane (PDMS) for the sustained release performance

Abstract Acid catalyst with sustained release performance is the key to the exothermic reaction between ammonium chloride (NH 4 Cl) and sodium nitrite (NaNO 2 ) in the in-situ heat system for hydraulic gel fracturing. For the sustained release performance, oxalic acid (OA) was microencapsulated with the shell of acrylonitrile butadiene styrene (ABS) via coacervation induced by polydimethylsiloxane (PDMS), and all the reagents during the preparation could be recycled for reuse to lower production cost. The micro-morphology, structure, catalytic performance of product, and factors affecting on the products were investigated. The results show that the OA loaded microcapsules coated with ABS (OA/ABS microcapsules) were micron-grade microspheres with core-shell structure, sustained-release properties, and benign catalytic performances for the in-situ heat system for the hydraulic gel fracturing, and the content of OA loaded in the microcapsules, particle size, and release property were affected by the core/shell ratio, viscosity of the PDMS, and recycled reagents. Moreover, the OA content of microcapsule could reach to 86.7 wt%, and the time to reach the temperature peak of the in-situ heat system was delayed by 80 min. Therefore, the microencapsulation via coacervation of ABS induced by PDMS is an economical and feasible method to confer a sustained release for the OA.