Catalysis of Organic..

290 Hydrogenolysis over Structured CatalystsResults and DiscussionThe present investigation provides a hydrogenolysis method in which sorbitol isreacted with hydrogen, at a temperature of 210°C and 1200psig. The solid catalyst ispresent as a new form of a structured monolith containing Nickel and Rhenium asthe multimetallic catalyst. The study provides a method of improving the catalyticselectivity of sorbitol hydrogenolysis to valued added products. It has beendemonstrated that the total selectivity to glycerol, ethylene glycol, and propyleneglycol can be improved by 20% using such a structured mass transfer reducedcatalyst compared to conventional trickle bed format catalyst. This method can beextendedly applied to hydrogenolysis of other sugar alcohols such as glycerol, xylitoland potentially also to glucose.As shown in Table 1, at the same temperature and pressure, sorbitol conversionand selectivity to value-added products are listed, in which the monolith reactorcovers the liquid hourly space velocity (LHSV) condition of the trickle bed. It wassurprisingly observed that total selectivity to glycerol, ethylene glycol (EG), andpropylene glycol(PG) from the monolith reactor was as 12.5% higher than that ofconventional trickle bed. The PG selectivity is particularly high in the monolithreactor, which gives high C3/C2 ratio in the product mixtures. Such selectivityincrease does sacrifice sorbitol conversion to a certain extent, but the lowerconversion is caused by higher weight hourly space velocity(WHSV) due to lessactive material loading. It is noted that the comparison was made at the similarvolume based LHSV. In the meantime, the monolith reactor was operated at a muchhigher WHSV, as the catalyst loading on the monolith substrate is much less thanthat in the packed bed. This demonstrated the high efficiency of catalyst utilizationwith reduced mass transfer resistance. The reduction of mass transfer limitation is inpart attributed to the decreased mass transfer distances with thin coating as well asthe unique Taylor flow pattern within the tunnel structure of the monolith catalyst.Table 1. Performance comparison between the monolith reactor and theconventional trickle bed reactor.Catalyst Ni/Re/TiO2 T = 210°C P = 1200 psigProduct Polyol SelectivitySorbitolEthylene Propylene Total EG +PG CarbonMonolith # 1 LHSV Conversion Glycerol Glycol Glycol + Glycerol Balance0.38 65.40% 17.90% 11.10% 30.70% 59.70% 96.50%0.76 52.20% 19.30% 12.70% 41.30% 73.30% 97.90%1.52 44.80% 20.20% 13.40% 38.90% 72.50% 96.90%Trickle BedNi/Re/Carbon0.83 89.00% 16.70% 12.60% 31.50% 60.80%