LaMar process

Kinetic as weU as thermodynamic problems are encountered in fluorination. The rate of reaction must be decelerated so that the energy Hberated may be absorbed or carried away without degrading the molecular stmcture. The most recent advances in direct fluorination ate the LaMar process (18—20) and the Exfluot process (21—24), which is practiced commercially by 3M. 

The typical fluorination apparatus used in the LaMar process for these reactions is simple in design (Fig. 4) (33). It is essential that the materials of constmction are resistant to fluorine (34). The presence of even traces of oxygen or moisture can have a deleterious effect and, therefore, extreme precautions must be taken to eliminate these contaminants. 

There arc a number of other factors that become very important to consider aside from the simple differences in bond strength. The earliest approach to direct fluorination of solid hydrocarbons operated on the principle of very gradual addition of fluorine over a period of time stretching in length from 4 hours to several days as seen in Figure 1. The thermodynamic strategy, the kinetic strategy and the Lamar Process dilution make it much easier to produce a myriad of new fluorocarbon materials which were not accessible by any other fluorination technique. 

Scheme 2.1 Gas-phase perfluorination of a variety of hydrocarbons by the LaMar process. At the top the proposed mechanism of free radical direct fluorination of alkanes is shown [8].

Potentially, this direct fluorination process is a new approach to the synthesis of fluorocarbon polymers. Polyethylene, polypropylene, polystyrene, polyacrylonitrile, polyacrylamide, resor phenol formaldehyde resin, and ethylene propylene copolymer have been fluorinated to produce perf1uorocarbon polymers which are structurally similar to the hydrocarbon starting materials and have physical properties similar to known structurally related fluorocarbon polymers obtained by polymerization of fluorocarbon monomers. High yield of fluorocarbon polymers approaching 100 have been obtained. This direct technique used for fluorination of hydrocarbons and polymers is called the LaMar process and has been previously described in connection with the direct fluorination of Lt ver molecular weight species ". ... 

The LaMar process also holds some physical advantages in certain instances over polymerization. Solid objects may be fluorinated to a depth of at least 0.2 mm (based on a crude weight gain calculation with a polyethylene object). Essentially, a fluorocarbon skin is... 

To achieve the very low initial fluorine concentration in the LaMar fluorination process initially a helium or nitrogen atmosphere is used in the reactor and fluorine is bled slowly into the system. If pure fluorine is used as the incoming gas, a concentration of fluorine may be approached asymptotically over any time period (Fig. 3). It is possible to approach asymptotically any fluorine partial pressure in this manner. The very low initial concentrations of fluorine in the system greatiy decreases the probabiUty of simultaneous fluorine coUisions on the same molecules or on adjacent reaction sites. 

The direct fluorination of inorganic/- organometallic, " and organic compounds, employing the LaMar " and Exfluor-Lagow" methods, has impacted the synthesis of fluorinated compounds over the past 25 years. Among the most important applications of direct fluorination are the synthesis of fluoropolymers Ifom hydrocarbon polymers and the conversion of the surface of the hydrocarbon polymers to fluoropolymer surfaces. The direct fluorination process is an excellent approach to the synthesis of fluoropolymers. 

In the LaMar Fluorination process [11] (referred to as LaMar in the following discussion) the substrates are condensed at low temperature into a tube packed with copper turnings through which fluorine, initially highly diluted in either helium or nitrogen, is passed. The concentration of fluorine and the reaction temperature are slowly increased over a period of several days to permit perfluorination. This is a batch process that requires relatively long reaction times to perfluorinate samples of material. 

The main factors influencing CP remediation include temperature, the properties of the environmental matrix, the toxicity of CPs or other compounds, and the composition of indigenous or added microbial cultures (Crawford Mohn, 1985). Unlike many other xenobiotics, CPs undergo insignificant volatilization (Valo Salkinoja-Salonen, 1986 Lamar et al., 1990b Mueller et al., 1991a). The temperature, the contaminant bioavailability, the possible process amendments and the effects of additional contaminants are discussed below. 

Dozol, J.-F., Lamare, V., Simon, N., Ungaro, R., Casnati, A. 2000. Extraction of cesium by calix[4]arene-crown-6 From synthesis to process. In Calixarene for Separations. Lumetta, G.J., Rogers, R.D., Gopalan, A.S. Eds. ACS Symposium Series No. 757, American Chemical Society, Washington, DC, pp. 12-25. 

Perfluorinations of many ethers [155], cryptands [156], polyethers [119, 157], including the largest perfluoro-macrocycle [158], perfluoro [60]-crown-20 [123, 159], and the first perfluorinated sugar [160], orthocarbonates [161, 162], ketones [163, 164], esters [124, 165], phosphanes [166] and alkyl halides [167, 168] have been successfully accomplished by the LaMar or aerosol processes (Table 2.4). 

Lamar University, Beaumont, Texas / lnvensys Process Systems, Houston, Texas Tabulation Results... 

A modern, improved version of this general method, the LaMar (Lagow-Mar-grave) process, uses a nickel reactor with different temperature zones and silver-... 

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