Steam heated stills

Petroleum products may be treated with various solvents for the removal by selective solubility of undesirable constituents or for the recovery of by-products. The solvent and solute must be separated to yield the desired product and to recover the solvent for reuse. The solvents normally boil at a lower temperature than the products from which they are to be removed and so are generally distilled off as overhead products. The pipe stills used for this service may be single-stage or multi-stage units, depending on the service involved. Some solvents can be removed by the use of steam heated stills. In other cases, the high temperature required necessitates the use of fired heaters and vacuum towers. 

A steam-heated still used to top the crude material exploded... 

Doyle, W. H., Loss. Prev., 1969, 3, 16 A steam-heated still used to top the crude material exploded... 

A saturated liquid mixture of 69.4mole% benzene in toluene is to be continuously distilled at atmospheric pressure to produce a distillate containing 90mole% benzene, with a yield of 25 moles distillate per 100 moles of feed. The feed is sent to a steam-heated still (reboiler), where residue is to be withdrawn continuously. The vapors from the still pass directly to a partial condenser. From a liquid separator following the condenser, reflux is returned to the still. Vapors from the separator, which are in equilibrium with the liquid reflux, are sent to a total condenser and are continuously withdrawn as distillate. At equilibrium the mole... 

In high heat flux (heat transfer rate per unit area) boilers, such as power water tube (WT) boilers, the continued and more rapid convection of a steam bubble-water mixture away from the source of heat (bubbly flow), results in a gradual thinning of the water film at the heat-transfer surface. A point is eventually reached at which most of the flow is principally steam (but still contains entrained water droplets) and surface evaporation occurs. Flow patterns include intermediate flow (churn flow), annular flow, and mist flow (droplet flow). These various steam flow patterns are forms of convective boiling. 

The urea-product solution, leaving the first decomposition stage and still containing some unreacted carbamate and excess NH3, is let down in pressure and steam heated in the second-staged decomposition section, which operates at about 2 atm and 120°C. Practically all of the residual carbamate is decomposed and stripped from the urea-product solution together with the residual excess ammonia. The 74—75 wt % urea solution thus obtained is further processed to solid urea... 

The still used for the oils should be constructed so as to serve for all the distilling operations of the laboratory, and mast, therefore, be sot for use either with the naked fire or steam heat, as may be dosired. Mouxit, In Ms Chemical Manipulations, describes an excellent arrangement, the whole of which is shown. in front view by Fig. 385, just as it appears when in operation. The brickwork In which it is set abuts... 

Recovery from Effluent Water. All condensed mixtures of steam and solvent vapors go to a common solvent-water separator (mentioned above), where solvent overflows the top and water syphons out the bottom. The water, still containing traces of solvent, passes through a steam-heated waste-water stripper, where live steam raises the water temperature well above the boiling point of the solvent, 85°C (185°F) for hexane, which boils at 68.9°C (156°F). The driven-off solvent... 

Among the simple catalysts that have been proposed oxides of zinc,09 cadmium, lead, bismuth, silicon, aluminum, titanium may be mentioned.5,0 Alkaline materials as sodium or calcium carbonates have also been claimed. The zinc oxide catalyst is prepared by spraying a solution of zinc nitrate, alone or with nitrates of other metals, on pumice and then heating the product in air. In practice the phthalic anhydride is simply steam dis-stilled into the reaction chamber and the products separated by fractional condensation or selective solution. 

Digest for six hours at very gentle heat, place in a steam jacketed still, add another 5 gallons water, and distill slowly for 2 hours with partial reflux until all the alcohol is driven over. Rectify the raw distillate to 35% alcohol by volume and filter clear over Kieselguhr to remove terpenes. Clean still and then rectify the filtered distillate to 58 gallons, 60% alcohol by volume. 

The unit shall be built to stand operation under a maximum vacuum of 15 in. Hg, The still pot shall be jacketed for steam heating where pressures will not exceed 150 psig. 

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