Solvent preheating

Figure 6. Light gases produced during solvent preheat methane (O) ethane (A) propane (X) propene ( /) ethylene O).

In plants with a vapor contactor, solvent is pumped from the work tank at 55°C temperature to a steam-heated solvent heater to increase its temperature to 60° C prior to entering the extractor. In plants with a solvent preheater rather than a vapor contactor, solvent is pumped from the work tank at 45°C temperature to a solvent preheater where its temperature is increased to 55°C. The solvent is then further heated in a steam-heated solvent heater from 55°C to 60°C in temperature prior to returning to the extractor. 

Operation. Typical operating conditions for butadiene recovery plants have been described by Buell and Boatright (I). These data were used as a guide for setting the conditions used in this study. At the start of a run, the column was preheated electrically to the desired column temperature profile. The C4 feed was pumped into the column until the pressure reached 30-35 psig. Solvent (preheated to 130°F) was then circulated through the column, and the reboiler temperature increased to about 275°F. The hydrocarbon feed was pumped in at a rate which gave the desired solvent-to-hydrocarbon feed ratio. A portion of the butene stream was returned to the column to provide reflux. Temperature of the solvent feed tray was used to control the amount of reflux. Only that portion of C4 s which dissolved in the solvent could be carried down the column. The excess C4 s were revaporized to the hydrocarbon trays. 

Besides the constraints on instrumental design and the requirement of solvent preheating, one major disadvantage of operating at high temperatures is that faster dissolution of the silica matrix occurs, and column lifetime will inevitably become shorter (72). 

The insoluble residue of diphenylurea from the original filtration is chemically almost pure. It may be recrystallised from hot rectified spirit or ethanol, a process which will be necessary if the material contains fragments of porcelain. When using either of these solvents, however, the hot solution should be filtered at the pump using a small Buchner funnel and flask which again have been preheated by the filtration of some of the hot solvent, as the solution when cooled rapidly deposits the diphenylurea. iSym-Diphenylurea (or carbanilide) is thus obtained as fine colourless crystals, m.p. 237° yield, 1-1 5 S ... 

For purification, transfer the acid to a 150 ml. flask containing 60 ml. of water, boil the mixture under reflux, and then add acetic acid in 5 ml. portions down the condenser until almost all the solid has dissolved avoid an excess of acetic acid by ensuring that the solvent action of each addition is complete before the next portion is added. A small suspension of insoluble impurity may remain. Add 2 g. of animal charcoal, boil the solution again for 10-15 minutes, and then filter it through a preheated Buchner funnel. Cool and stir the filtrate, which will deposit pale cream-coloured crystals of the acid. Collect as before and if necessary repeat the recrystallisation. Yield of pure acid, 9 g. m.p. 227-229°. 

Recrystallise from methylated spirit, using animal charcoal for this purpose, use about twice the minimum quantity of methylated spirit required to obtain a clear solution, and filter through a funnel preheated by the filtration of some boiling solvent, as the tribromobenzene separates very rapidly as the solution cools. The 1,3,5-tribromobenzene is thus obtained as colourless crystals, m.p. 122° yield, 3 g. 

Recrystallise the remaining half of the crude anthraquinone from boiling acetic acid, using animal charcoal filter the hot solution through a Buchner funnel which has been preheated by the filtration of some of the boiling solvent, as the anthraquinone crystallises rapidly as the solution cools. Cool the filtrate in cold water and then filter at the pump, drain, wash with methylated spirit and dry. Yield, 4-5 g. 

Dissolve 5 g. of phenol in 75 ml. of 10 per cent, sodium hydroxide solution contained in a wide-mouthed reagent bottle or conical flask of about 200 ml. capacity. Add 11 g. (9 ml.) of redistilled benzoyl chloride, cork the vessel securely, and shake the mixture vigorously for 15-20 minutes. At the end of this period the reaction is usually practically complete and a sohd product is obtained. Filter oflf the soUd ester with suction, break up any lumps on the filter, wash thoroughly with water and drain well. RecrystaUise the crude ester from rectified (or methylated) spirit use a quantity of hot solvent approximately twice the minimum volume required for complete solution in order to ensure that the ester does not separate until the temperature of the solution has fallen below the melting point of phenyl benzoate. Filter the hot solution, if necessary, through a hot water funnel or through a Buchner funnel preheated by the filtration of some boiling solvent. Colourless crystals of phenyl benzoate, m.p. 69°, are thus obtained. The yield is 8 g. 

Heat/Solvent Recovery. The primary appHcation of heat pipes in the chemical industry is for combustion air preheat on various types of process furnaces which simultaneously increases furnace efficiency and throughput and conserves fuel. Advantages include modular design, isothermal tube temperature eliminating cold corner corrosion, high thermal effectiveness, high reHabiHty and options for removable tubes, alternative materials and arrangements, and replacement or add-on sections for increased performance (see Furnaces, fuel-FIREd). 

The coating technique starts by applying a solvent-based adhesive on to a previously pretreated metal substrate. The item is then preheated to 200-250°C, the exact time and temperature depending on the metal thickness. It is then dipped in the plastisol which partly gels owing to the... 

The polyurethane lining systems in use today are normally of the 100% solids type without solvents. The individual components, prepolymer and isocyanate are preheated and pumped to the mix/dispenser for metering and mixing. After mixing, the material is pumped through an orifice where it is... 

The hexane solvent was removed from a solution of DIB AL (22 mmol, 1 Min hexane) at reduced pressure and at ambient temperature, and ether (10 ml) was introduced. l-Cyclohexyl-2-trimethylsilylethyne (20 mmol) was added at such a rate as to maintain ambient temperature within the reaction, and. after 15 min, the reaction flask was placed in a preheated (40 °C) bath for I h. The resulting clear solution was transferred by means of a double-ended syringe to a vigorously stirred cold solution of HC1 (50 ml, 10%). The flask was rinsed with ether (20 ml), and the mixture was stirred until the resulting phases were almost clear. The layers were separated, and the aqueous layer was extracted with ether (40 ml). The combined organic extracts were washed successively with dilute HC1 (20%), saturated sodium hydrogen carbonate solution and brine, and dried. 

Photolysis Procedure. The solvent-cleaned Kevlar-29 fabric swatch (2.5 cm x 18 cm) was placed around the outside quartz tube inside the photolysis chamber, which was subsequently evacuated, before - - 02 (99%) was introduced to 0.2 atm. The photolysis chamber was preheated to the specified photooxidation temperature, before the Hg-Xe lamp was turned on. The temperature, which was held constant in the chamber by adjusting the air flow around the lamp, was monitored by a thermocouple placed next to the fabric sample inside the chamber. After the photooxidation had continued for the specified... 

Reaction rate experiments were conducted in NMR tubes sealed with Teflon valves. In an inert atmospere glovebox, catalysts and internal standard, TMS4C, were weighed into the tube, followed by addition of solvents and reactants. The tube was immediately inserted in the preheated (50 °C) probe of a 500 MHz Varian Unitylnova spectrometer. To acquire spectra the sample was irradiated twice with a 30° pulse, 5 sec acquisition time, and 120 sec delay. 

The experimental apparatus consisted of a 1-liter, stirred autoclave (AC1), used to preheat the solvent-coal slurry, connected to a 2-liter, stirred autoclave (AC2), equipped with an internal heating coil to bring the solvent-coal slurry rapidly to a constant reaction temperature, and a third autoclave (AC3), equipped with a cooling coil to act as a quench vessel (Figure 1). This allowed direct determination of the material lost in... 

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