Downflow reactor

Tubular Fixed-Bed Reactors. Bundles of downflow reactor tubes filled with catalyst and surrounded by heat-transfer media are tubular fixed-bed reactors. Such reactors are used most notably in steam reforming and phthaUc anhydride manufacture. Steam reforming is the reaction of light hydrocarbons, preferably natural gas or naphthas, with steam over a nickel-supported catalyst to form synthesis gas, which is primarily and CO with some CO2 and CH. Additional conversion to the primary products can be obtained by iron oxide-catalyzed water gas shift reactions, but these are carried out ia large-diameter, fixed-bed reactors rather than ia small-diameter tubes (65). The physical arrangement of a multitubular steam reformer ia a box-shaped furnace has been described (1). 

Low pressure-drop and no flooding (at least for cocurrent, downflow reactors). 

The basic elements of each process are similar (Figure 9-9) and consist of a once-through operation of the feedstock coming into contact with hydrogen and the catalyst in a downflow reactor which is designed to maintain activity... 

Fresh, filtered feedstock is heated together with hydrogen and recycle gas and charged to the downflow reactor from which the liquid product goes to fractionation after flashing to produce the various product streams. Each process type is basically similar to its predecessor (Figure 9-11) but will differ in the number of reactors. For example, modifications necessary to convert the Type II to the Type III process consist of the addition of a reactor and related equipment, while the Type III process can be modified to a Type IV process by the addition of a... 

The process centers on a fixed-bed downflow reactor that allows catalyst replacement without causing any interruption in the operation of the unit (Figure 9-28). Feedstock is introduced to the process via a filter (backwash, automatic) after which hydrogen and recycle gas are added to the feedstock stream which is then heated to reactor temperature by means of feed-effluent heat exchangers whereupon the feed stream passes down through the reactor in trickle flow. Sulfur removal is excellent (Table 9-18), and substantial reductions in the vanadium content and asphaltenes content are also noted. In addition, a marked increase occurs in the API gravity, and the viscosity is reduced considerably. 

Downflow reactor a reactor in which the feedstock flows in a downward direction over the catalyst bed. 

The model was developed from experiments conducted in a downflow reactor, where gas residence times are greater than solid residence times. The model may not be able to predict residence time effect in a fluid bed or upflow reactor where solid residence times are greater than gas residence times. But it does give useful information for pressure and temperature effects in these reactors. 

In the once-through studies reported in the literature, a downflow reactor scheme was used for catalytic hydrocracking (9) in contrast to an upflow reactor scheme used in this study. It has been reported in the literature that an upflow reactor scheme is superior to the usual trickle-bed operation for residual feedstocks (18,19). Desulfurization, denitrogena-tion, and demetallization conversions were better in an upflow reactor. 

Experimental apparatus used in this study consisted of a 12.5 mm internal diameter stainless steel tubular reactor with a length of 864 mm (34 in). It was originally constructed and used as a trickle bed downflow reactor. With proper modification of the plumbing it was used to regenerate the catalyst in either an upflow or downflow mode. 

At low liquid flow rates, upflow will provide better distribution of liquid and, thus, in many cases, better performance of the reactor than the downflow reactor under similar operating conditions. 

In an upflow reactor, the catalyst must be kept in place by suitable mechanical methods, otherwise the bed will be fluidized. In a downflow reactor, the catalyst is held in place tightly by the flow. This may cause undesired cementation of the soft catalyst particles. 

In an upflow reactor, the catalyst pores are more likely to fill completely with liquid than in a downflow reactor. The catalyst effectiveness factor is lower when the catalyst pores are completely filled with liquid compared to the case when they are only partially filled with liquid. 

Figure 5-9 Multiple-sphere cocurrent-downflow reactor (simulation of irickle-bcd reactor) lifter Satterfield et al.i0)...

Airlift reactors are an alternative bioreactor in which the agitation is accomplished by a clear cyclic pattern of air flow through both a riser and a downflow reactor compartment. Stirred tank and airlift reactors are most often used for aerobic cell cultures. Airlift reactors are often utilized to culture plant and animal cells because they typically have lower shear levels. ... 

Figure 13 shows the set-up used for a corrosion study at high acid levels, with specimens mounted in a chamber in a vertical downflow reactor configuration. The chamber was nominally divided into five equal-length zones, with each zone being defined by the presence of a thermocouple. Oxidation of organic... 

OD x 12" long Vycor, downflow reactor that contained a... 

ZSM-5 zeolifes modified by inclusion of mefal cafions show higher acfivify than the starting materials in the acylation of phenol wifh AAN. Reactions are carried out using a tubular downflow reactor heated at 250°C. The most promising catalyst is CeZSM-5, showing 75% phenol conversion with a 32.33 ortho/para acylation ratio. An increase in the SAR value results in an increase of O-acylafion, suggesfing fhaf C-acylafion requires more Bronsted acidify. 

These reactions take place normally in a trickle bed downflow reactor at high hydrogen pressures (1500 to 4000 psi) and temperatures in excess of 600°F. The catalyst is frequently referred to as dual function since it promotes both cracking and hydrogenation. The catalyst base material is usually silica-alumina with metal oxides from groups VI and VIII (nickel, cobalt, molybdenum, tungsten). The active forms are the metal sulfides. Fractionation provides the waxy lubes cuts which are subsequently dewaxed and hydrofinished. 

Both powder and monolithic catalysts were evaluated for their activity and selectivity for PTA offgas destmction. For powder catalyst screening, a total of 1 ml of catalyst powder was placed on a quartz frit in a U-shaped, downflow reactor. A reactant mixture, which included carbon monoxide, methyl bromide, benzene, and methyl acetate, was used to represent an industrial PTA offgas. The concentrations of these compounds were 3500 ppm CO, 35 ppm CHjBr, 9 ppm and 410 ppm CH3CO2CH3, respectively. TTie gas hourly space velocity (GHSV) was... 

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