Deposits in a commercial RFCC reactor were characterized using an analytical approach. Further characterization of deposits on the reactor cyclone, which are one of the primary problems causing abnormal shut-down of RFCC, was carried out in order to understand the formation mechanism of the deposit. The deposits in the reactor consist of hydrocarbon and inorganic matter, compositions of which are well matched with the RFCC catalyst. In a longitudinal analysis of a sample reflecting age, H/C atomic ratio decreases slightly with increased aging time in inner regions and has high value at the surface region, which is a relatively fresh deposit. The particles, surrounded by carbonaceous matter, and amorphous carbonaceous matter are observed through surface micrographs. Aromatic compounds and nano- and microcatalyst fines contribute to the formation of deposits. Micro- and nanostructure of the deposit is amorphous or very weakly ordered. The H/C atomic ratios of samples with different ages, over 90 days, do not change with aging and are matched with a variation of feed API. Possible mechanisms for the deposit formation and its reducing methods are proposed.
Radical reactions of vinyl epoxides have received little attention' despite their synthetic usefulness,2 and we are unaware of any studies of n-Bu3Sn radical addition to vinyl epoxides, which serves as a starting point for the generation of allylic or alkyl radicals via translocation of radical sites.3 We wish to report novel sequential radical reactions of vinyl epoxides utilizing 1 ,5-n-Bu3Sn group or ]$hydrogen atom transfer from carbon to oxygen, depending on the structural nature of vinyl epoxides.Although very little is known on 1,Stransfers of heteroatoms bearing d orbitals3 such as organo~ilicon~ and organotin groups,$ the ease of a 1,5-n-Bu3Sn group transfer to an alkoxy radical is anticipated on the basis of three factors. First, the C-Sn bond is much weaker than the C-H bond and an alkoxy radical would abstract a I,5-n-Bu3Sn group rather than a hydrogen atom. Second, 1,5-n-Bu3Sn abstraction should be facile because of the presence of the a-vinyl group. Third, a favorable geometry for 1,5-n-Bu3Sn transfer is realized with 2. The reaction of the vinyl exo epoxide 1 with n-Bu3SnH occurred smoothly, yielding initially the alkoxy radical 2 bearing allyltin moiety. I,5-n-Bu3Sn transfer in 2 proceeded rapidly and cleanly, yielding the allylic radical 3 which underwent cyclization as shown in Scheme I.The radical reaction of a vinyl exo epoxide6 was carried out by the addition of a 0.05 M benzene solution of n-Bu3SnH (1.2 (1) Huyser, E. S.; Munson, L. R. J . Org. Chem. 1965,30, 1436. Stogryn, E. L.; Gianni. M. H. Tetrahedron Lett. 197O,II, 3025. Suzuki, A.; Miyaura, N.; Itoh, M.; Brown, H. C.; Holland, G. W.; Negishi, EA. J. Am. Chem. Soc. 1971,93,2792. Murphy, J. A.; Patterson, C. W.; Wooster, N. F. Tetrahedron Lett. 1988, 29, 955. (2) For recent reports, see: Trost, B. M.; Sudhakar, A. R. J . Am. Chem. SOC. 1988, 110, 7933. Oshima, M.; Yamazaki, H.; Shimizu, I.; Nisar, M.; Tsuji, J. J . Am. Chem. SOC. 1989, 111, 6280 and references cited therein.(3) Reviews: Beckwith, A. L. J.; Ingold, K. U. Rearrangements in Ground and Excited Stares; de Mayo, P., Ed.; Academic Press: New York, 1980; Vol. 1, Chapter 4. Freidlina, R. Kh.; Terent'ev, A. B. Adu. Free Radical Chem. 1980, 6, 1 . (4) As far as we are aware, 1,5-TMS transfer has not been reported. According to our preliminary experiment (i -ii), 1.5-TMS transfer from benzylic carbon to oxygen did not occur, indicative of a strong preference for 1,s-H transfer over 1,S-TMS transfer, probably due to the stabilizing effect of the TMS group (Miura, K.; Oshima, K.; Utimoto, K. Tetrahedron Lett. 1989,30,4413). A similar phenomenon has been recently observed by Curran (Snieckus, V.; Cuevas, J.-C.; Sloan, C. P.; Liu, H.; Curran, D. P. J. Am. Chem. SOC. 1990, 112, 896). n.BySnD TMS Ph -i OH I/, 68% ( 5 ) For one example of 1,5-n-Bu3Sn transfer from enoxyl oxygen to alkoxy oxygen, see: Davies, A. G.; Tie, M.-W. J. Orgatwmet. Chem. 1978, 155, 25. (6) Vinyl exo epoxides (h,Ib,lc) were prepared from cyclohexanone in seven steps (LDA, allyl bromide/LDA, HCHO MsCl pyridine, DBU/...
Deposits in the cyclone dipleg of a commercial residue fluid catalytic cracking (RFCC) reactor, which are one of the primary problems causing abnormal shut-down of RFCC, were characterized using an analytical approach in order to understand the formation mechanism of the deposit. The main components of the deposits are hydrocarbons and a high portion of inorganic matter, reflecting dipleg conditions with particle flow. The deposit consists of two parts of massive bulk matter which are mainly pure Sb metal and catalyst particles surrounded by filamentous cokes and lumps of carbonaceous matters. Nickel nanopowders on the catalyst surface and from heavy oil in vapor phase catalyze the filament coke, which accelerate the increase in the amount of deposits by filtering heavy oil droplets. The Sb metals, originated from injected Ni passivator in the riser, contribute largely to deposit formation, and this is validated by a simulation of RFCC conditions and a calculation of cyclone collection efficiency. Possible mechanisms for the deposit formation and methods for the reduction of the deposits are proposed.
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