Roles of decalin as hydrogen donor in visbreaking of heavy oil

The effect of the timing of adding 1 wt% decalin as a hydrogen donor on heavy oil visbreaking was studied. Experiments show that either premixing decalin with heavy oil or adding decalin during the reaction accelerates the formation of light distillates and improves the efficiency of viscosity reduction. Premixing with heavy oil is an appropriate way to add decalin. After 10 min of reaction at 400 ℃, the viscosity reduction rate of the product reaches 90% and the asphaltene content of the product is 1.8 wt% lower than that of the raw heavy oil. According to theoretical calculations, the active hydrogens of decalin preferentially saturate the aromatic C radicals that are critical for condensation. The equilibrium constant of the H-donation reaches the order of 105, while the activation energy of the reaction is only about 26 kJ/mol. The thermal cracking of decalin itself releases active and small-sized radicals, which accelerate visbreaking by participating in the dealkylation network of heavy oil molecules.