Hydrocracking of long-chain alkanes and polyolefins over dual-functional strong solid acid catalysts.

摘要

This dissertation deals with the hydrocracking and hydroisomerization of long-chain alkanes and polyolefins over metal-promoted, anion-modified transition metal oxides as catalysts. The main objective is to study and develop novel pathways for producing high quality gasoline-range (C{dollar}sb5{dollar}-C{dollar}sb{lcub}12{rcub}){dollar} alkanes and related chemicals by the catalytic hydrocracking and hydroisomerization of long-chain alkanes. The research focused on studying various anion-modified metal oxides as catalysts for low-value feedstocks such as waste polyolefins.; n-Hexadecane was chosen as a suitable model compound for the polyolefins in evaluating the various catalysts synthesized. Zirconium oxide was found to be most active metal oxide component and modification of ZrO{dollar}sb2{dollar} by either the SO{dollar}sb4{dollar} Or WO{dollar}sb3{dollar} (but not MoO{dollar}sb3){dollar} anion-derived group resulted in active catalysts for n-hexadecane hydrocracking. In addition to platinum, nickel was also effective in stabilizing the activity of the anion-modified zirconium oxides (AZO's). Among the catalysts studied, a Pt/ZrO{dollar}sb2{dollar}/WO{dollar}sb3{dollar} catalyst containing 0.509 mmol W/g ZrO{dollar}sb2{dollar} calcined at 700{dollar}spcirc{dollar}C had the highest n-hexadecane cracking activity. Higher tungsten contents favored cracking while lower tungsten contents favored skeletal isomerization of n-hexadecane.; Metal-promoted AZO's were found to be effective for the complete conversion of high density polyethylene (HDPE), polypropylene (PP) and polystyrene (PS) at 300-375{dollar}spcirc{dollar}C and 750-1200 psig (cold) H{dollar}sb2.{dollar} The products obtained from HDPE and PP hydrocracking over these catalysts were of superior fuel quality in terms of iso/normal alkane ratios, boiling point distributions and anti-knock characteristics. By varying reaction time, either high yields of C{dollar}sb5{dollar}-C{dollar}sb{lcub}12{rcub}{dollar} isoalkanes or gases rich in isobutane and isopentane could be obtained.; Characterization of catalysts recovered from polyolefin hydrocracking revealed that the sulfated zirconium oxides lost sulfur during reaction whereas Pt/ZrO{dollar}sb2{dollar}/WO{dollar}sb3{dollar} catalysts were found to be both active and stable for polyolefin hydrocracking as no loss of tungsten or change in its oxidation state were observed on the recovered catalysts. The metal-promoted AZO's do not sinter or agglomerate during reaction. Platinum exists as Pt{dollar}sp0{dollar} on the surface of AZO's while nickel exists as NiO and must be reduced to Ni{dollar}sp0{dollar} before providing an active hydrogenation function.