Pretreatment beds

The idea of integrating the pretreatment beds in PSA has also been used in hydrogen purification, in which an inefficient sorbent in the pretreatment beds adsorbs pentane and heavier compounds, whereas the main beds adsorb methane, ethane, and propane (Alexis, 1967). This idea should be useful in many multi-component separations. 

The pretreatment bed can be combined with the main bed that is, two sorbents are packed in the same bed with the desiccant (alumina or silica gel) placed near the feed end followed by the zeolite bed. This arrangement is widely used in the production of oxygen from air (Armond, 1979), as well as other separations. 

This volnme reviews many details about tools available to the individual for protection from arthropod bites. New prodncts come on the market constantly and some represent real improvements to old capabilities. Over the years, a few products have been innovative additions to the kinds of protection available, for example, pretreated bed nets and clothing. More recently, effective spatial repellents that can be carried by an individual have provided protection in a way that ineffective products attempted to achieve for many years. ... 

Adsorption (qv) of gases has been reviewed (40,50) (see also Adsorption, gas separation). Adsorption, used alone or in combination with other removal methods, is excellent for removing pollutant gases to extremely low concentrations, eg, 1 ppmv. When used in combination, it is typically the final step. Adsorption, always exothermic, is even more attractive when very large gas volumes must be made almost pollutant free. Because granular adsorbent beds ate difficult to cool because of poor heat transfer, gas precooling is often practiced to minimize adsorption capacity loss toward the end of the bed. Pretreatment to remove or reduce adsorbable molecules, such as water, competing for adsorption sites should also be considered (41). 

Neither rapid sand nor mixed-media filters remove appreciable quantities of coUoidal particles without adequate pretreatment. Although it is widely beheved that filters are an effective barrier against unsafe water, the effluent may be as colored, as turbid, or as bacteriologicaHy unsafe as the water appHed. In contrast, slow sand filters requite no pretreatment, as the slow passage through the bed allows the particles to contact and attach to the schmut ecke. 

Liquid-liquid extraction is used primarily when distillation is imprac-tic or too costly to use. It may be more practical than distillation when the relative volatility for two components falls between 1.0 and 1.2. Likewise, liquid-liquid extraction may be more economical than distillation or steam-stripping a dissolved impurity from wastewater when the relative volatility or the solute to water is less than 4. In one case discussed by Robbins [Chem. Eng. Prog., 76 (10), 58 (1980)], liquid-liquid extraction was economically more attractive than carbon-bed or resin-bed adsorption as a pretreatment process for wastewater detoxification before biotreatment. 

Other Considerations In situations where waste gas contains both particulates and gases to be controlled, venturi scrubbers are sometimes used as a pretreatment device, removing PM to prevent clogging of a downstream device, such as a packed bed scrubber, which is designed to collect primarily gaseous pollutants. 

Typically, for any given pressure, industrial packaged boilers operate at higher heat-flux rates than field-erected boilers, This requires that the package boiler FW quality should be substantially better (i.e., lower overall TDS and lower levels of silica and sodium). Appropriate MU water pretreatment may, for example, necessitate the use of twin bed and mixed bed demineralization ion exchange, or RO and mixed bed (in addition to mechanical deaeration and other processes). 

Ultrafiltration is particularly useful as a pretreatment roughing filter for the type of ion-exchange resin beds and EDR technologies... 

In the feed pretreatment section oil and water are removed from the recovered or converted CCI2F2. The reactor type will be a multi-tubular fixed bed reactor because of the exothermic reaction (standard heat of reaction -150 kJ/mol). After the reactor the acids are selectively removed and collected as products of the reaction. In the light removal section the CFCs are condensed and the excess hydrogen is separated and recycled. The product CH2F2 is separated from the waste such as other CFCs produced and unconverted CCI2F2. The waste will be catalytically converted or incinerated. A preliminary process design has shown that such a CFC-destruction process would be both technically and economically feasible. 

Resids HDT is carried out at temperatures between 360°C and 450°C, pressures from about 1500 to 3000psig, and 0.2 to lh-1 of space velocity. Graded catalyst beds combining CoMo and NiMo catalysts can be adapted to the quality of the feedstock and depending on whether atmospheric or vacuum residues are going to be treated. HDT of resids is seen as a feedstock pretreatment for preparing feedstock for either mixed with ordinary FCC feeds or for HCK (mixed with VGO or to a resid HCK). The advantages... 

Products Company and Davison (W.R. Grace) Catalysts) and Hydrocarbon Technologies, Inc. ART provides non-zeolitic catalysts for ebullating residue hydrocracking and fixed bed pretreating HDT [140], A nanoscale iron based, slurry catalyst is recommended for coal liquefaction, while a molecule-sized and chemically in situ generated catalyst is employed for the high conversion of asphaltenic fractions or heavy oils [141],... 

Curran, G. P., Pasek, B., Pell, M., and Gorin, E., Pretreatment of Bituminous Coals for Pressure Gasification, paper presented at the Fluidized Bed Combustion Symposium, American Chemical Society Meeting, Chicago (1973)... 

The MDA experiments were performed in a continuous down-flow fixed bed reactor at 700°C, atmospheric pressure, and a space velocity of 1500 em3/(gcat h). Catalysts were pretreated in He flow at 700°C for 30 min before feeding a CH4 N2 mixture in a 9 1 voEvol ratio (N2 used as internal standard). Unreacted methane, the reference N2, and the reaction products were analyzed on line in a gas chromatograph (HP-GC6890) as detailed in [6]. Product selectivities are given on a carbon basis. The use of N2 as internal standard allows to obtain the amount of carbonaceous residues as the amount of carbon required to close the mass carbon balances to 100%. 

OptiCAT-plus A process for regenerating hydrotreating catalysts. It uses a fluidized-bed pretreatment to control the initial exotherms found in regeneration, followed by a moderate heat soak to eliminate sulfur and carbon. Developed in the 1990s by the Criterion Catalyst Company. 

Carbon electrodes are commercially available in many forms. These include plates, foams, felts, cloths, fibers, spherical and other particles suitable for beds or powders. Graphite or amorphous carbons exhibit quite different performances. Porosity, surface area and pretreatment are important variables to be considered in designing carbon electrodes. 

In this cell, mechanical vibration is applied to the cell housing to enhance the transfer in the parallel plate tank cell [248]. The vibrations are transfered to the electrolyte resulting in an increase of the mass-transfer coefficient. The cell is extensively used in industry for the pretreatment of higher and high metal concentrations which is finally purified by a packed bed electrolysor if the required conversion is not too high [247],... 

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