Chemical engineering Do number one, answer all parts a to d (c) Ch 3-Section 3.0

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Chemical engineering

Do number one, answer all parts a to d

(c) Ch 3-Section 3.0 through 3.2.1 (pgs. 85-91) Mass Transfer (Fick's Law, Diffusivity) 1) Separation Techniques: Molecular and Transport Properties & Factors for Feasible Separations For each of the following systems suggest two (different) viable separation techniques. Clearly state the general separation technique and provide an explanation for why each may be feasible. Hint: Approaches to the problem-One separation method is likely to be easily found (the industrial approach) while a second may be discovered as a laboratory scale method. Alternatively examining the molecular, thermodynamic and selected transport properties (requires considering additional materials, e.g. solvents, filters/membranes, adsorbents, etc.) and determining feasible separation approaches. a) Toluene - Xylene b) Propylene Glycol-Water c) Argon - Nitrogen d) Thorium: Isotope 232 from other isotopes t lible (a tymed solution is not required but is

Explanation / Answer

a) In any petroleum refinery, naptha cracking is the most preferred or the steam cracking of hydrocarbons for the production of BTX. The steam cracking produces cracked naptha typically called as pygas, a source of BTX mixture. However, industrially Advanced pygas upgradation (APU) (a catalytic process technology) is integrated in the treatment process for the isolation of BTX mixture which produces pure benzene cut, toulene cut and xylene cut with low ethyl benzene content.

In general, toulene-xylene mixture can be separated either through liquid-liquid extraction or extractive distillation using different kinds of solvents. However, the individual cut from the extraction should be further processed for the isolation of toulene/benzene from the extract/raffinite which has economical constraints.

b) Propylene-glycol can be separated through simple distillation as the water can be removed as distillate since the propylene glycol BP is 188 degrees Celsius. Reactive distillation is more followed in the industrial sector for the above said compounds separation. However, reactive disitillation is more feasible and economical since the separation of products from the reaction mixture does not require a separate distillation step which saves energy (for heating).

c) The simple technique for the separation of argon nitrogen mixture is adsorption using any adosrbents like molecular seives. However, pressure swing adsorption (PSA) or vaccum swing adsorption (VSA) are the commercially available methods for the production of pure nitrogen/oxygen/argon from the air. Cryogenic air separation units are often used for nitrogen/oxygen, which co-produce argon.

Among the cryogenic distillation separation of gas separation and PSA, VSA may be considered as best because it operates at near-ambient temperatures and pressures.

d) Th 232 can be separated via adsorption technique using different kinds of adsorbents. Laboratory equipment could be a simple batch reactor, where the Th solution and the adsorbent can be mixed well untill equillibrium occurs and then chelated/eluted using eluting agents for the isolation of Th from loaded adsorbent. Industrially, a sequence of adsorption columns are used for the isolation of Th. The separation technique could be the same either in labaratory/industrail scale, but the mode of operation (batch/continues) differs since the batch mode is an cumbersome operation for commercial scale units.  

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