The chemical structure and the caking capacity of fractions in the pitches prepared from Murban vacuum residue were investigated. The pitch was fractionated by n-pentane, benzene and quinoline into four fractions of PS, PI•BS, BI•QS and QI. The NMR spectra, molecular weight and elementary analysis were measured on the fractions, and the structural parameters were estimated. The caking capacity for each fraction was measured by means of the Roga test.
The following results were obtained.
(1) The structural parameters, molecular weight and the Roga index of each fraction were changing in the early stage of heat-treatment when the decomposition reaction mainly occurred, however these values became nearly constant in the latter stage when the polymerization-condensation reaction became predominant.
(2) The degree of condensation was considered to have a tendency to increase in the order of PS, PI•BS, BI•QS, QI. An average number of condensed aromatic rings of each fraction was estimated to be PS: 2-3, PI•BS: 6-7 and BI•QS: 11 and over, respectively. The Roga index of each fraction was PS: 11-22, PI•BS: 60-80, BI•QS: 74-90 and QI: 0, respectively. These results suggest that to obtain the pitch of high caking capacity, vacuum residue must be converted at least into the PI•BS fraction having 6-7 condensed aromatic rings and the aromaticity above 0.7.
(3) QI which has no caking capacity by itself showed a high caking capacity when coexisting with the fraction of high fluidity such as PS, PI•BS and BI•QS.