Refrigerant recycling

Investigations at Cornell University are based on process concepts in which an ice slurry is produced from saline water by evaporation of a suitable immiscible refrigerant. After washing, the ice crystals are melted by direct condensation on the ice of the compressed refrigerant vapors. Potable water is the product, and the immiscible refrigerant recycles to the process. 

To control an operating plant for minimum acid make-up, the Isobutane concentration in the reactor must be maintained at the maximum possible level. This means operating both the depropanizer and the deisobutanizer under optimum conditions. The operator should adjust tower feed rates and operating conditions, always using the isobutane concentration in either the total effluent hydrocarbon or the net effluent hydrocarbon from the reactor as his primary reference. Isobutane-to-olefin ratio, deisobutanizer overhead purity, depropanizer recycle purity, and refrigerant recycle purity are significant only as they relate to reaction zone isobutane concentration. 

The alkylate released from the acid phase, will be absorbed by the Isobutane liquid and removed from the crystallizer. Without this removal of alkylate, crystal size growth control is difficult. A portion of the alkylation reactor auto-refrigerant recycle from the bottom of the depropanizer tower is used for this purpose. 

A different approach to making open cell foam slabs has been proposed recently [11], which is based on the use of the PU fluff obtained from the recycling of used refrigerators (Recycled Urethane Fluff, or RUF panel). 

F. Herzog, J. Busse, S. Terkatz, Refrigerator recycling - how to deal with CFCs and pentane, Focus on gas 13, Company booklet, Messer Griesheim GmbH, D-47805 Krefeld, Germany. 

Many alkylation units use auto refrigeration to cool their reactors. Effluent refrigeration commonly used on Stratco units also falls within this classification. To maximize isobutane purity in the refrigerant recycle stream, circulating refrigerant is depropanized. 

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). 

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