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A model is developed for predicting the performance of a partially wetted trickle-bed reactor for a gas-limiting reaction of order less than or equal to one. The model indicates that under certain conditions the liquid reactant may affect the reaction rate due to its inability to rapidly diffuse to catalyst areas that are in direct contact with the gas. This model is the first to explain and predict on a rational basis the experimental results for the hydrogenation of diluted a-methylstyrene and aqueous maleic acid reported in the literature. A criterion that determines when liquid reactant effects can be expected is developed and reported. IntroductionReactions occurring in trickle-bed reactors, where gas and liquid reactants flow cocurrently downward over a packed bed of catalyst, can often be classified into liquid-reactant limited and gas-reactant limited (Mills and DudukoviC, 1980). The former are frequently encountered in high-pressure operations in petroleum processing. The latter occur when there is a nonvolatile liquid reactant and a slightly soluble gas, as in some oxidations and partial hydrogenations of chemicals at low and moderate pressures. Here we concern ourselves only with such gas-limited reactions.It has been well established that at low liquid mass velocities, below 3 to 5 kg/m2 ' s, the trickling liquid does not actively wet the entire external catalyst surface in the bed. The pertinent literature was summarized by DudukoviC and Mills (1986). For such conditions of partial external catalyst wetting, several models have been proposed for evaluation of the catalyst effectiveness factor (DudukoviC and Mills, 1978;Herskowitz et al., 1979;Ramachandran and Smith, 1979;Mills and DudukoviC, 1980;Levec et al., 1980;Tan and Smith, 1980;Martinez et al., 1981;Herskowitz, 1981;Goto et al., 1981;Capra et al., 1982;Sakornwimon and Sylvester, 1982; Ring and Missen, 1984). All of these models predict that the observed reaction rate increases as catalyst contacting efficiency decreases for a nonvolatile liquid in a gas-limited reaction. Here the contacting efficiency is defined to be the fraction of external catalyst area actively wetted by liquid. The above is intuitively acceptable based on the following argument. Since the liquid reactant is nonvolatile, reaction can occur only in the wetted interior of catalyst pellets. The gas reactant must overcome both the gas-liquid and liquidsolid mass transfer resistances of the flowing liquid film to penetrate into a completely wetted catalyst pellet. A pellet with a partially dry surface provides a much smaller resistance at the dry surface for the gas to access the liquid-filled pore volume and react. At higher Thiele moduli, when the reaction rate is large compared to the internal diffusion rate, external mass transfer effects greatly affect the observed reaction rate. The reduction of the mass transfer resistance for the rate-limiting gaseous reactant on partially wetted pellets leads to higher observed reaction rates. These model predictions have been found to...

Raspberries were processed into juice and concentrated to 45 "Brix by two processes: Osmotek's cold, direct-osmotic concentration process and conventional evaporative technology. Compositional analyses included pH, titratable acidity, form01 value, total anthocyanin pigment, polymeric color, and nonvolatile acid, sugar and anthocyanin pigment profiles. Concentration by either process resulted in small anthocyanin pigment losses and formation of fumaric acid and small increases of polymerized pigment. The aroma and flavor of the experimental samples and nine commercial concentrates were evaluated in a raspberry drink formulation by a trained descriptive flavor panel. Principal component analysis revealed no significant flavor differences between the single-strength juice, the concentrates and three of the commercial samples.

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