Upflow fixed beds

Hydrotreating was carried out at 3.1 MPa (450 psig) and 613 K (340 °C) in a three-phase upflow fixed-bed reactor (Figure 1). The feed liquid was prepared by combining different quantities of 1.0 wt% tetralin (Aldrich, 99%), 0.02 wt% N as quinoline (Aldrich, 99%), 0.05 wt% S as 4,6-dimethyldibenzothiophene (4,6-DMDBT, Fisher, 95%), 0.3 wt% S as dimethyldisulfide (DMDS, Aldrich, 99%), n-octane (Aldrich, 99%), and balance n-tridecane (Alfa Aesar, 99%). Liquid product compositions were determined with a Hewlett-Packard 5890A chromatograph equipped with a 50 m dimethylsiloxane colunm (Chrompack, CPSil 5B) of 0.32 mm i.d. Reaction products were identified by matching retention times with commercially available standards. 

Scale-up is limited by several factors, such as maximum working velocity in the case of adsorption/ion-exchange upflow fixed beds, and maximum allowable temperature in cases where microorganisms are involved in the process, for example, in the packed bed bioreactors (Michell et al., 1999). 

The residence-time distribution in the liquid phase of a cocurrent-upflow fixed-bed column was measured at two different flow rates. The column diameter was 5.1 cm and the packing diameter was 0.38 cm. The bed void fraction was 0.354 and the mass flow rate was 50.4 g s l. The RTD data at two axial positions (which were 91 cm apart in Run 1 and 152 cm apart in Run 2) are summarized in Table 3-2. Using the method of moments, estimate the mean residence time and the Peclet number for these two runs. If one assumes that the backmixing characteristics are independent of the distance between two measuring points, what is the effect of gas flow rate on the mean residence time of liquid and the Peclet number Hovv does the measured and the predicted RTD at the downstream positions compare in both cases ... 

Ultrafiltration, 631 applications, 633 membranes, 637-639 Underwood minimum reflux binaty, 387 multicomponent, 397 Units, conversion of, 671, 672 UMQUAC equation, 475 Upflow fixed beds, 609 Uranium recovery, 515 Utilities, typical characteristics, 15... 

Upflow fixed beds. The liquid phase is continuous and the gas phase dispersed. This mode of operation has the advantages of better mixing, higher rates of mass and heat transfer, better distribution of liquid flow across the cross section, and better... 

Stuber F, Delmas H (2003) Partial hydrogenation in an upflow fixed-bed reactor a multistage operation for experimental optimization of selectivity. Ind Eng Chem Res 42 6... 

Studies on a sequential oxidative reductive process of degradation of chloro-aliphatics and chloroaromatics have been under investigation since 1995. Anaerobic breakdown of o -chlorophenol (100 mg 1 1) and 2,4-dichlorophenol (100 mg H) into catechol acclimatized upflow fixed bed biroeactor is reported to have reached 75% and 55 % respectively [61,62]. 

Upflow fixed bed reactors or submerged biofilters (SBF) have upward groundwater flow, the packing material is submerged under water and no bed expansion is obtained [45,94-97]. 

Mergaeit, J Boley, A., Cnockaert, M.C., Muller, W., Swings, J., 2001. Identity and potential functions of heterotrophic bacterial isolates from a continuous-upflow fixed-bed reactor for denitrification of drinking water with bacterial polyester as source of carbon and electron donor. Systematic and Applied Microbiology 24 (2), 303—310. 

In two-phase downflow and upflow fixed-bed reactors, gas-liquid mass transfer resistance can be detrimental to the overall reactor performance [14, 32]. Therefore, accurate estimation of gas-liquid mass transfer parameters is important for achieving successful reactor design or scale-up. The overall gas-liquid mass transfer coefficient may be expressed, according to the two-film concept, in terms of the liquid-side and the gas-side mass transfer coefficients ... 

In spite of the extensive studies on the gas-liquid mass transfer in two-phase upflow fixed-bed reactors, summarized by Shah [27], Ramachandran and Chaudhari [64], Gianetto and Silveston [65], and Molga and Westerterp [62], only few correlations are reported in the Uterature to evaluate gas-Uquid mass transfer parameters under low and high pressure conditions [59, 66]. 

---