Refrigerator recycling

Composition, Properties and Economic Study of Recycled Refrigerators, American Plastics Council, Arlington, VA, April 1994. 

Sometimes it is extremely difficult to avoid vapor recycles without using very high pressures or very low levels of refrigeration, in which case we must accept the expense of a recycle compressor. However, when synthesizing the separation and recycle configuration, vapor recycles should be avoided, if possible, and liquid recycles used instead. 

Compounds having low vapor pressures at room temperature are treated in water-cooled or air-cooled condensers, but more volatile materials often requite two-stage condensation, usually water cooling followed by refrigeration. Minimising noncondensable gases reduces the need to cool to extremely low dew points. Partial condensation may suffice if the carrier gas can be recycled to the process. Condensation can be especially helpful for primary recovery before another method such as adsorption or gas incineration. Both surface condensers, often of the finned coil type, and direct-contact condensers are used. Direct-contact condensers usually atomize a cooled, recirculated, low vapor pressure Hquid such as water into the gas. The recycle hquid is often cooled in an external exchanger. 

A simplified flow diagram of a modern H2SO4 alkylation unit is shown in Eigure 1. Excess isobutane is suppHed as recycle to the reactor section to suppress polymerization and other undesirable side reactions. The isobutane is suppHed both by fractionation and by the return of flashed reactor effluent from the refrigeration cycle. 

Polypropylene-derived branched alkyl (0 2) benzene (BAB) has been batch sulfonated using 60—70% oleum in Hquid SO2 solvent at temperatures of — 1 to —8°C, with SO2 serving as a self-refrigerant and viscosity reducer in the process. After sulfonation and digestion, SO2 is stripped, recovered, and recycled (256). 

External refrigeration with gas recycle External refrigeration with NGL recycle 8.800 20.200 36 29.000 +850... 

Gas recirculation in the anunonia synthesis section is necessary because only 9-30% conversion is obtained per pass over tlie catalyst." There are two tj pes of synthesis loops. One type recovers anunonia product before recycle compression. Inerts entering witli tlie makeup gas are removed with a purge stream. The ammonia is recovered by condensation, which requires refrigeration. Since airliydrous anunonia is readily available, it is normally used as tlie refrigerant. 

The gas leaving the catalyst beds contains about 15% NH3 this is condensed by refrigeration and the remaining gas mixed with more incoming synthesis gas and recycled. Variables in the final reaction are the s)mthesis pressure. 

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