Desorption hydrocarbons

Fig. 11. Adsorption isotherms for hydrocarbons on activated coconut-sheU carbon at 25°C (46). 0> Adsorption A, desorption. To convert kPa to mm Hg,...

However, ia some cases, the answer is not clear. A variety of factors need to be taken iato consideration before a clear choice emerges. Eor example, UOP s Molex and IsoSiv processes are used to separate normal paraffins from non-normals and aromatics ia feedstocks containing C —C2Q hydrocarbons, and both processes use molecular sieve adsorbents. However, Molex operates ia simulated moving-bed mode ia Hquid phase, and IsoSiv operates ia gas phase, with temperature swiag desorption by a displacement fluid. The foUowiag comparison of UOP s Molex and IsoSiv processes iadicates some of the primary factors that are often used ia decision making ... 

For adsorbed hydrocarbons, the adsorption—desorption process can be thought of as a reaction and the adsorption isotherm as a description of the reaction at equihbtium. For the Langmuir isotherm,... 

The desorptive process may be analyzed before boiling. The key assumption is that the vapor and adsorbed phases are ia equiUbrium ia the bulk of the bed. This assumption eliminates iatraparticle resistances from further consideration and is reasonable for rotary kiln appHcations. The two remaining resistances are associated with hydrocarbon diffusion out of the bed and with convection from the bed surface to the bulk gases. The flux of species Fi from the desorbiag bed becomes... 

A wide variety of guest molecules may be trapped by the Wemer-type crystalline host lattice, ranging, eg, from noble gases to condensed aromatic hydrocarbons. These clathrates may be formed from solution or by sorption. Kinetics of sorption—desorption have been studied (83). 

Separation of Norma/ and Isoparaffins. The recovery of normal paraffins from mixed refinery streams was one of the first commercial appHcations of molecular sieves. Using Type 5A molecular sieve, the / -paraffins can be adsorbed and the branched and cycHc hydrocarbons rejected. During the adsorption step, the effluent contains isoparaffins. During the desorption step, the / -paraffins are recovered. Isothermal operation is typical. 

Chlorinated hydrocarbon solvent vapours in air Lab method using pumped charcoal adsorption tubes, solvent desorption and gas chromatography 28... 

Hydrocarbons (mixed C3-C,q) Lab method using pumped porous polymer and carbon sorbent tubes, thermal desorption and gas chromatography 60... 

Chlorinated hydrocarbon Charcoal tube, solvent desorption... 

As the spent catalyst falls into the stripper, hydrocarbons are adsorbed on the catalyst surface, hydrocarbon vapors fill the catalyst pores, and the vapors entrained with the catalyst also fall into the stripper. Stripping steam, at a rate of 2 to 5 lbs per 1,000 lbs (2 kg to 5 kg per 1,000 kg,) is primarily used to remove the entrained hydrocarbons between catalyst particles. Stripping steam does not address hydrocarbon desorption and hydrocarbons filling the catalyst pores. However, reactions continue to occur in the stripper. These reactions are... 

The desorption using a nonadsorbing medium such as nitrogen equals a pressure swing process because the purge gas reduces the partial pressure of the n-alkane and works as a vacuum. This variant also is only suitable for the isolation of n-alkanes from low molecular weight hydrocarbon mixtures like gasoline fractions. 

The partial oxidation of propylene occurs via a similar mechanism, although the surface structure of the bismuth-molybdenum oxide is much more complicated than in Fig. 9.17. As Fig. 9.18 shows, crystallographically different oxygen atoms play different roles. Bridging O atoms between Bi and Mo are believed to be responsible for C-H activation and H abstraction from the methyl group, after which the propylene adsorbs in the form of an allyl group (H2C=CH-CH2). This is most likely the rate-determining step of the mechanism. Terminal O atoms bound to Mo are considered to be those that insert in the hydrocarbon. Sites located on bismuth activate and dissociate the O2 which fills the vacancies left in the coordination of molybdenum after acrolein desorption. 

PE/PP (25 %), rubbers (including EVA) (20 %) and other thermoplastics (5 %). Physical blowing agents (PBAs) liberate gases as a result of physical processes (evaporation, desorption) at elevated temperatures or reduced pressures. PBAs are mostly volatile liquids, freons, aliphatic hydrocarbons or solid blowing agents. 

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