This paper discusses the technology for disposal of diesel particulate by catalytic ignition and combustion.
Using the trap-oxidizer concept, the collected soot was catalytically treated to make ignition and combustion more practical under diesel engine exhaust conditions. The catalyzed ignition was examined in a laboratory hot-tube reactor and the information thus obtained was used to design trials under engine exhaust conditions.
Solutions of metal salts such as copper, manganese, or cobalt chlorides, or the corresponding nitrates, have been shown to be effective; most of this study was carried out using solutions of mixtures of copper chloride and sodium chloride. Suitable solvents included methanol, glycol-water mixtures, and distilled water.
Soot-related parameters such as the soluble organic content, degree of compaction, graphitization, and surface area have been examined briefly during the course of the study. To minimize the possibilities of a secondary pollution hazard, most of the tests were conducted using low concentrations of catalytic salts. Thus, 1.18 × 10−4 moles of Cu per gram of soot, added from solution, was found sufficient to lower the ignition temperature of diesel soot as much as 200 C, and reductions of 250 C were obtained when sodium or ammonium salts were included. Higher concentrations of catalytic salts can lower the ignition temperature still further. In the exhaust pipe, repeated ignition and combustion of trapped soot was found to regenerate normal operating back pressure in a porous ceramic trap.