Cooling pressure reduction

In a chemical process, the transformation of raw materials into desired chemical products usually cannot be achieved in a single step. Instead, the overall transformation is broken down into a number of steps that provide intermediate transformations. These are carried out through reaction, separation, mixing, heating, cooling, pressure change, particle size reduction or enlargement. Once individual steps have been selected, they must be interconnected to carry out the... 

Most applications use a combination of pressure- and temperature change. After pressure-reduction the extraction gas is heated so that it reaches the gaseous state. In this phase, no solvent-power of the extraction gas is present for any substances and therefore complete separation of extracted substances takes place. In cycling the extraction gas after separation, it has to be condensed, under-cooled to prevent cavitation of the pump, and recompressed and heated up to extraction temperature. 

When any vapor expands, due to a pressure reduction (other than H2 and C02), it cools off. This is called a Joule-Thompson expansion. The reduction in temperature of the steam is called a reduction in sensible-heat content. The sensible heat of the steam is converted to latent heat of condensation. Does this mean that the latent heat of condensation of 10-psig steam is much higher than that of 450 psig steam Let s see ... 

Sulfuric acid alkylation also is used. In addition to the type of acid catalyst used, the processes differ in the way of producing the emulsion, increasing the interfacial surface for the reaction. There also are important differences in the manner in which the heat of reaction is removed. Often, a refrigerated cascade reactor is used. In other designs, a portion of the reactor effluent is vaporized by pressure reduction to provide cooling for the reactor. 

Pressure reduction is accompanied at the hydrate interface by a temperature decrease to the equilibrium temperature. Normally the pipeline cannot be depressured sufficiently rapidly for Joule-Thomson (isenthalpic) cooling to lower the temperature this would occur through a restriction such as a valve. If the pressure is reduced slowly, a vertical isothermal depressurization (AT = 0) results. Usually an intermediate pressure reduction rate causes the hydrate interfacial temperature to be significantly less than the surroundings, causing heat influx from the surroundings to melt hydrates from the pipe boundary inward. 

Experimentally nucleation rates can be determined in expansion chambers [35], The vapor is expanded in a fast and practically adiabatic process. Then it cools down. Since at low temperatures, the equilibrium vapor pressure is much lower, supersaturation is reached. Partially, this is compensated for by the pressure reduction during the expansion, but the temperature effect dominates. The density of nuclei can be measured by light scattering. 

Extraction time 6, 12 or 24 h Reduced time compared to Soxhlet, i.e. 2-4 h Typically 5-15 min, but repeated for up to three times Should be possible in under 30 min 30 min-1 h 20 min (plus 30 min cooling and pressure reduction) 12 min... 

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