Stoichiometric technology

Examples of replacement of classical stoichiometric technologies with cleaner catalytic alternatives will be delineated in the following sections. 

The fine chemicals industry, with its roots in coal-tar chemistry, positively abounds with processes involving classical, stoichiometric technologies, e.g. sulfonation, nitration, chlorination, bromination, diazotization, Friedel-Crafts... 

The solution to this waste problem is evident the widespread substitution of antiquated stoichiometric technologies with cleaner catalytic alternatives. But if the solution is so obvious why has it not been widely applied in the past We suggest several reasons. Firstly, because of the smaller quantities compared with bulk chemicals, the need for a reduction in waste in fine chemicals production was not fully appreciated in the past. 

Germanium difluoride can be prepared by reduction (2,4) of GeF by metallic germanium, by reaction (1) of stoichiometric amounts of Ge and HF in a sealed vessel at 225°C, by Ge powder and HgF2 (5), and by GeS and PbF2 (6). Gep2 has been used in plasma chemical vapor deposition of amorphous film (see Plasma TECHNOLOGY Thin films) (7). 

FIG. 26-30 Siipp ression of explosions, Pressures in an ethylene explosion and a sodium bicarbonate suppressed ethylene explosion, Tests conducted by Fike Corp, in a 1-m vessel. Ethylene concentration = 1,2 times stoichiometric concentration for combustion, (dp/dt)e = 169 bar/s (2451 psi/s), = reduced explosion pressure = 0,4 bar gauge (5,8 psig), (F/om Chatrathi, Explosion Testing, Safety and Technology News, vol. 3, issue 1, Pike Cotp., 1.98.9, hy permission. )... 

Most LAB is sulfonated using thin-film S03 technology. In this process no spent acid is produced because the S03 reacts almost stoichiometrically with LAB. High-quality LAS slurry with low color and a low level of Na2S04 can be produced. Sulfonation of LAB yields predominantly the para isomer [14]. 

Examples for necessary process improvements through catalyst research are the development of one-step processes for a number of bulk products like acetaldehyde and acetic acid (from ethane), phenol (from benzene), acrolein (from propane), or allyl alcohol (from acrolein). For example, allyl alcohol, a chemical which is used in the production of plasticizers, flame resistors and fungicides, can be manufactured via gas-phase acetoxylation of propene in the Hoechst [1] or Bayer process [2], isomerization of propene oxide (BASF-Wyandotte), or by technologies involving the alkaline hydrolysis of allyl chloride (Dow and Shell) thereby producing stoichiometric amounts of unavoidable by-products. However, if there is a catalyst... 

For similar motivations, there are limited incentives to develop an alternative SCR process for stationary sources based on methane (CH4-SCR) or other HCs, or based on NTP technologies, if not for specific, better applications. The situation is instead quite different for mobile sources, and in particular for diesel engine emissions. The catalytic removal of NO under lean conditions, e.g. when 02 during the combustion is in excess with respect to the stoichiometric one (diesel and lean-burn engines, natural gas or LPG-powered engines), is still a relevant target in catalysis research and an open problem to meet future exhaust emission regulations. 

The oxidation of ethylene to acetaldehyde by dioxygen catalyzed by palladium and cupric salts found important technological application. The systematic study of this process was started by Smidt [245] and Moiseev [246]. The process includes the following stoichiometric stages [247,248] ... 

This cycle, often referred to as the Shilov-cycle converts methane into methanol and chloromethane in homogeneous aqueous solution at mild temperatures of 100-120 °C (11). However, while Pt(II) (added to the reaction as PtCl ) serves as the catalyst, the system also requires Pt(IV) (in the form of PtCle-) as a stoichiometric oxidant. Clearly, this system impressively demonstrates functionalization of methane under mild homogeneous conditions, but is impractical due to the high cost of the stoichiometric oxidant used. A recent development by Catalytica Advanced Technology Inc., often referred to as the Catalytica system used platinum(II) complexes as catalysts to convert methane into methyl-bisulfate (12). The stoichiometric oxidant in this case is S03, dissolved in concentrated H2S04 solvent. This cycle is depicted in Scheme 3. 

Degner [194] and Couper et al. [75] have recently critisized the technology as it unavoidably produces, after the separation of the products, aqueous solutions containing stoichiometric amounts of salts of metals used as anodes. Solutions to this problem are possible as demonstrated in the case of Mg and Zn [177] electrodes. Al and Mg can easily be precipitated as hydroxides, recovered by filtration and dehydrated to the corresponding oxides, whereas Zn is recycled electrochemically. 

Stoichiometric combustion air requirement, 72 322t Stoichiometric concentration, 27 840 Stoichiometric organic synthesis, metal carbonyls in, 76 72 Stoichiometric parameters, in reactor technology, 27 337-338 Stoichiometric ratios, epoxy/curing agent, 70 418-420... 

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