1. (to Shell Internationale Research Matschappij N. V.), Netherlands Patent 6 604 094, 1966;
2. , (to Shell Internationale Research Matschappij N. V.), US Patent 3,400,163, 1968.
3. , , (to Shell Internationale Research Matschappij N. V.), German Patent 1,909,620, 1969;
4. (to Shell Oil Co.), U.S. Patent 4,472,534, 1984,