Preparation and purification of gases

Reactions in nitromethane should be carried out at temperatures below 100°, in order to avoid the explosions that have been reported from time to time.45 Noteworthy is that nitromethane is an excellent solvent for aluminum chloride and has given excellent service in Friedel-Crafts alkylations46 and acylations 47 it is to be preferred to carbon disulfide for such reactions because of its greater safety. 

Nitrobenzene, obtained by nitration of benzene, may contain very small amounts of the nitration products of the toluene or thiophen present in the benzene. 

Purification and drying of nitrobenzene Nitrobenzene (11) is dried by periodic shaking with sodium hydroxide (50 g), decantation, and fractionation in a vacuum. 

Water may be removed by drying over calcium chloride or phosphoric oxide. Anhydrous nitrobenzene can also be obtained by fractional distillation if the forerun is discarded. 

For safety, mixtures of nitrobenzene with aluminum chloride or alkali hydroxide should not be heated above 100°. 

---

N20 emission at chemical plants and the methods of its abatement have been considered in several reviews [185-187]. The major emission is related to the preparation of nitric add and its use in oxidation processes, like those involved in the production of adipic acid, caprolactam, glyoxal, acrylonitrile, and so forth. Of them, the biggest emission is the offgases of adipic acid about 1 M MT N 20 per year with a concentration of 30-40%. Recovery and purification of N20 from these offgases for use in the oxidation of benzene to phenol are described by Uriarte [188], Some companies use these off-gases to obtain medical-grade nitrous oxide. 

B. Generation Of Dry Gases. Directions are given below for the preparation and/or purification of several useful gases. 

The catalytic activity of the SHS ceramic catalysts in the processes of incineration was found to be virtually identical to that of widespread precious metal catalysts. The ceramic catalysts prepared by promising SHS technique may be a challenge to conventional catalysts for purification of engine exhaust and other waste gases. 

Based on the above mentioned data the paper shows the results of research performed for a Cu-ZSM-5 catalyst production to the purpose of purification of vehicle engines exhaust gases. The influence of the ion exchange level in ZSM-5 upon the catalytic performances is also studied. The catalysts used were Cu-ZSM-5 granules or Cu-ZSM-5 coating on a ceramic monolith. The trials of correlation between the catalysts performances and the state of copper in catalysts prepared is also showed. 

Hydrides, for example, CuH [16], ZnHg [15], CeHg [5], UHg [8] and so forth these are decomposed in high vacuum at relatively low temperatures. Active uranium prepared from UHg has the remarkable ability to absorb large quantities of Hg, Og, Ng, CO, COg and other base gases it can thus be used for the purification of inert gases, especially in closed systems [4],... 

After the actual reaction, a separation process to obtain a pol mier of a certain purity and state follows. Usually, thermal and mechanical imit operations are applied. Pol miers may include residual monomer and solvents which are often difficult to remove. Special consideration has to be given to this subject in the polymers industry in a perspective of life-cycle impact of the products. In the context of the IPPC Directive, the focus is on the minimisation of the emissions of monomers at the industrial site [27, TWGComments, 2004]. Separated monomers, mostly as gases, can be directly returned to the process, returned to the monomer unit to be prepared for purification, transmitted to a special purification unit, or flared off Other separated liquids and solids are sent to a centralised clean-up or recycling unit. Additives needed for processing or for protection may be added to the polymer at this point. 

---