“If equations are trains threading the landscape of numbers, then no train stops at pi.” - Richard Preston, IN: "The Mountains of Pi," New Yorker (1992)
HOW TO GET AN OVERVIEW OF A TECHNICAL TOPIC
If you’re like me, you don’t know everything. Sometimes you run across a term that you are not quite sure of. But because it is in a field related to your area of expertise, you want to learn something about it. Where do you start?
Begin with an overview of the topic. Let’s take, as an example, the topic of “π complexation.” Now, you may already know everything you need to know about π complexation, but bear with me … the general principal is the same, no matter what topic you are investigating.
1) Look for reference "books" like Encyclopedia of Chemical Processing (Many libraries carry this whether in hard copy or via online subscription; check with your librarian)
2) Look for review articles (see below)
3) Google and browse (this can be very tedious, but can yield unexpected results)
Here are examples illustrating points (1) and (2)
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Sorbent Technology (Shuguang Deng) 2006
Chemical Engineering Department, New Mexico State University, Las Cruces, New Mexico, U.S.A.
IN: Encyclopedia of Chemical Processing DOI: 10.1081/E-ECHP-120007963 Copyright # 2006 by Taylor & Francis. All rights reserved.
Π-complexation Sorbents and Composite Sorbents
A very good review article based on a panel study of status, future research needs, and opportunities for porous sorbent materials was published several years a go. It was pointed out that very significant advances have been made in tailoring the porosity of porous sorbent materials in terms of size and shape selectivity. Relatively little progress has been achieved in terms of chemoselectivity of sorbents based on specific interactions between adsorbate molecules and functional groups in the sorbents. Incorporation of active sites into sorbents is of high priority in the development of sorbents.
The π-complexation bond is a weak chemical bond that is slightly stronger than van der Waals interaction , which governs physical sorption processes. Sorbents with π-complexation capability tend to have higher selectivity than other physical sorbents for certain adsorbate molecules. Several different types of π-complexation sorbents with Cuþ or Agþ ions supported on different supports (SiO, g -Al2O2,TiO, variety of zeolites , polymer resin, and activated carbon) were synthesized using different methods including thermal dispersion, wet-impregnation, sol–gel, microwave heating, ion exchange zeolite, and ion-exchange resin. It was found that the CO adsorption capacity increases with Cuþ loading in an activated alumina supported sorbent.
To achieve the highest sorption capacity, the active species should be dispersed as a monolayer form. The potential applications of these π-complexation sorbents include:
• Desulfurization of gasoline and diesel fuels;
• Separation of olefins and paraffins;
• CO separation from synthesis gases;
• CO removal from hydrogen;
• Removal of aromatics ; and
• Removal of volatile organic compounds (VOC s).
A π-complexation sorbent can also be viewed as a composite sorbent especially when the sorbent support contributes significantly to the adsorption. Composite sorbents are typically made by physically mixing the powders of constituent sorbents with different sorption properties; they tend to have multiple sorption sites for different adsorbate molecules. One example of a composite sorbent is a mixture of activated alumina and zeolites for removing moisture, carbon dioxide, and other trace components from air in an air-purification process prior to cryogenic air separation.
Conventionally, moisture is removed by activated alumina, carbon dioxide by zeolite 13X, and hydrocarbons by zeolite 5A. Traditional air-purification processes employ multiple layers consisting of activated alumina, zeolite 13X, and optional zeolite 5A sorbents in a single vessel to achieve significant removal of moisture, carbon dioxide, and hydrocarbons from air. The major disadvantages of layered bed are nonuniform sorbent packing for a short sorbent layer, very significant temperature variation ( > 30C, sometimes called cold spots) between the zeolite and the activated alumina sorbent layers. The large temperature difference could upset the sorption process operation if it is designed to be operated isothermally. It is beneficial to have a single sorbent with multiple sorption features for different impurities and eliminate sorbent layering and temperature variations .
source: http://lib.nmsu.edu/accreditation/resources/FSA/DengArticle8.pdf
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Example of a review article:
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Desulfurization of Transportation Fuels by Adsorption
Authors: Arturo J. Hernndez-Maldonado(a); Ralph T. Yang(Department of Chemical Engineering, University of Michigan, Ann Arbor, MI
*To whom correspondence should be addressed. E-mail: yang@umich.edu
Abstract
This paper is a review on sorbents for desulfurization of transportation fuels (gasoline, diesel, and jet fuel). Since the π-complexation sorbents are the most promising, they are the focus of the discussion. During π-complexation, the thiophenic compounds can bind selectively to the sorbents, especially the substituted ones. The later remain highly unreacted in hydrodesulfurization (HDS) (i.e., “refractory” sulfur). Molecular orbital (MO) calculations and experiments have shown that these refractory compounds [(e.g., 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene (DMDBT)] bind strongly with the π-complexation sorbents because of a better electron donation/back-donation ability. The sorbents reviewed include Ag-Y, Cu(I)-Y, Ni(II)-Y, and Ni(II)-X zeolites prepared using various ion-exchange techniques. The techniques included vapor and solid-state ion exchanges, which are suitable for obtaining high loadings of transition metals. The best sorbent, Cu(I)-Y [vapor-phase ion-exchanged (VPIE)], is capable of producing almost 38 cm3 of desulfurized fuel per g of sorbent with a sulfur concentration of less than 0.2 ppmw. Using these π-complexation sorbents in layered bed matrices further increases the desulfurization capacity.
Keywords: Desulfurization; Transportation fuels; Dibenzothiophenes; Pi-complexation; Zeolite
source: http://www.informaworld.com/smpp/content~content=a713625088~db=all~jumptype=rss
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Follow the Desulfurization Blog (http://www.desulf.blogspot.com/) for an ongoing review of tips and tricks to help maximize your online research effectiveness.
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