1. Upgrading Petroleum Residues and Heavy Oils;Gray,1994
2. West, T. H. and Thompson, J. A., US Patent No. 4,432,866, 1984.
3. Bitter, J. G. A. and Haan, J. P., US Patent No. 4,810,366, 1989.
4. Black, L. E., Miasek, P. G. and Adriaens, G., US Patent No. 4,532,029, 1985.