Selective salt separation and resource recovery via nanofiltration in coal-to-ethylene glycol wastewater

Aiming to address the challenges of high treatment cost and low recycling degree in coal-to-ethylene glycol wastewater, this study conducted research on the application of nanofiltration membranes for salt separation in the resource utilization plant of coal-to-ethylene glycol wastewater, and studied the operation parameters of the nanofiltration system in this resource utilization process. First, membrane elements were screened based on the water quality characteristics of the wastewater. Subsequently, systematic characterization of the selected membrane elements was conducted, followed by long-term pilot-scale experiments to determine operational parameters for the project. During 3 months of continuous operation, the rejection rate of Na₂SO₄ was >98 %, and the rejection rate of NaCl was <10 %. Among them, the mass ratio of NaCl and Na₂SO₄ on the permeate side is 30, and the mass ratio of NaCl and Na₂SO₄ on the concentrated water side is 3, which effectively realizes the separation of Na₂SO₄ and NaCl. Through the reverse osmosis + evaporation + crystallization process, Na₂SO₄ products with a purity of 98.4 % and NaCl products with a purity of 98.9 % were finally obtained. This study provides a reasonable process route for the recycling of coal chemical wastewater and verifies the feasibility of salt separation of nanofiltration system in the recycling of coal chemical wastewater, to provide corresponding guidance for the resource utilization of concentrated brine.