Multi-objective optimization of VOCs and NOx co-reduction strategies under carbon emission constraints: A petrochemical case study in China

As a key contributor to atmospheric pollution, the petrochemical industry emits substantial quantities of volatile organic compounds (VOCs), nitrogen oxides (NO_x), and carbon dioxide (CO₂) emissions. This study develops a novel multi-objective optimization model for a local petrochemical facility (based on 2022 operational data), simultaneously addressing VOCs and NO_x emissions, carbon intensity, and economic expenditures. By quantifying the cost-carbon nexus,it enables policy-relevant, priority-specific reduction pathways. Employing the weighted sum method under carbon emission constraints, this approach achieves >10 % reduction in individual emission (VOCs and NO_x), with an overall emission decrease exceeding 30 % compared to baseline levels. Through the multi-objective optimization, we determine technologically optimal portfolios corresponding to three strategic scenarios: multi-pollutant control prioritization (VOCs-NO_x co-reduction), cost-minimization orientation, and carbon-constrained operation. The optimized results demonstrate: (i) Annual emissions are minimized at 2,112.94 tons, representing a 66.52 % reduction versus baseline; (ii) Total costs are reduced to 1.549 billion CNY (16.45 % decrease compared to reference levels); (iii) Carbon emissions achieve a 9.83 % reduction, reaching 653,200 tons annually. Key sector-specific reduction potentials are quantified as: 9.99 % from VOCs emissions in circulating water systems, 4.53 % from equipment sealing point VOCs, and 88.9 % of total NO_x treatment attributable to organized emission sources. These findings demonstrate that the proposed model offers considerable practical value in supporting the development of coordinated VOCs and NO_x treatment strategies for carbon-regulated industrial facilities.