The petrochemical industry is a foundational sector supporting China's national economic development and is also a key industry within the industrial sector characterized by concentrated energy use and significant emissions. Due to complex feedstock routes and long production chains, the petrochemical industry has long faced challenges such as unclear accounting boundaries for carbon emissions and difficulty in pinpointing key emission reduction nodes. Existing research has largely remained at the national or sectoral scale or focused on assessments of a few products, often relying on foreign generic emission factors and lacking precise emission reduction studies tailored to China's specific conditions.

Addressing these gaps, a research team led by Professor Guan Dabo, Deputy Dean of the Institute for Carbon Neutrality, Tsinghua University, and Professor in the Department of Earth System Science, Tsinghua University, systematically mapped the "feedstock‑process‑product" production chain relationships in China's petrochemical industry. They traced China‑specific energy consumption and material consumption data, unified a multi‑level accounting framework spanning "process‑plant‑chain‑complex," and constructed a carbon emission factor database for China's petrochemical production processes covering 123 chemical products and 185 production processes. The study developed a plant‑level, facility‑specific annual CO₂ emission inventory for China's petrochemical production (the China Petrochemical CO₂ Emission Inventory, CEADs‑CPEI), integrating the product chain relationships within chemical complexes into a unified analytical framework. This systematically revealed the emission structure and key emission reduction nodes in China's petrochemical industry at the product, process, and production chain levels.

Figure 1: CO₂ emissions from China's petrochemical plants in 2021 (by product, emission source, and process)

Figure 2: Carbon emission intensity of key products by detailed production process and emission unit

The results show that total CO₂ emissions from China's petrochemical production processes in 2021 amounted to approximately 814 million tonnes, of which energy‑related emissions accounted for 66.8% and process emissions accounted for 33.2% (Figure 1). Industry emissions are largely concentrated in the production of upstream basic chemicals, which contributed approximately 73% of total industry emissions, with methanol and synthetic ammonia together accounting for about 48% of that share. The analysis revealed that feedstock route, process reaction type, and energy consumption structure significantly influence carbon emission intensity (Figure 2). For example, compared to the natural gas route, the coal‑to‑methanol and coal‑to‑ammonia routes have carbon emission intensities approximately 2.8 and 1.6 t CO₂/t product higher, respectively. In terms of dominant emission sources across different processes, high‑temperature reaction processes are primarily characterized by fuel combustion emissions; some dehydrogenation processes are mainly affected by steam heat consumption; while products such as caustic soda, polypropylene, and polyethylene are primarily influenced by electricity use. This indicates that emission reductions in the petrochemical industry cannot be achieved through a single solution but should instead focus on dominant emission sources, promoting coordinated efforts in feedstock substitution, process optimization, and electrification.

Figure 3: Carbon emissions and intensity along key product production chains in typical chemical complexes

The study traced emissions and cumulative carbon intensity along product chains within typical chemical complexes, revealing significant emission differences for the same end products depending on upstream feedstock configurations and intermediate conversion pathways (Figure 3). Taking the polymer product chains of PET, PBT, PC, and PVC as examples, carbon intensities vary markedly across different product chains. The PC chain has an intensity of approximately 5.1 t CO₂/t product, while the PVC chain has an intensity of approximately 2.7 t CO₂/t product. Significant differences also exist for the same product chain across different complexes. In the PET chain, the coal‑based dimethyl oxalate route has a carbon intensity approximately 1.5 times that of the oil‑based ethylene route; in the PBT chain, the oil‑based butadiene route has a carbon intensity approximately 1.5 times that of the gas‑based maleic anhydride route. This demonstrates that industry emissions are influenced not only by individual processes or products but also by the production networks within complexes and the interplay between upstream and downstream relationships.

The findings were published in Science Advances under the title "China's petrochemical plants CO₂ emissions and high‑impact contributors for carbon‑neutrality production." Chen Xiujing, a 2024‑year PhD student in the Department of Earth System Science, Tsinghua University, is the first author. Lecturer Lei Tianyang from University College London and Professor Guan Dabo from Tsinghua University are the corresponding authors. The research was supported by the Carbon Neutrality and Energy System Transformation (CNEST) multilateral cooperation project, the National Natural Science Foundation of China's Excellent Innovation Group project, and other funding sources.

Link to paper: https://www.science.org/doi/10.1126/sciadv.adx7784