SINGAPORE, June 1 (Reuters) - Top Asian refiner Sinopec Corp said on Tuesday it had started a 5.17 billion yuan ($811 million) refinery upgrade at a subsidiary plant in eastern China that aims to produce cleaner fuels and boost output of higher-value chemicals. The investment in Yangtze Petrochemical Corp, in Nanjing city in the province of Jiangsu, covers eight key facilities, such as a 2.6-million-tonne-per-year residue hydrocracker and a 2.8-million-tpy catalytic cracker. “While maintaining the same crude processing capacity and without increasing emissions of pollutants, the upgrade will raise output of premium quality refined fuel,” the state refiner said on social media. Construction is set to be completed in 2023. ($1=6.3750 Chinese yuan renminbi) (Reporting by Chen Aizhu; Editing by Clarence Fernandez) Our Standards: The Thomson Reuters Trust Principles.