Wiped-film evaporator

Alcohol autoxidation is carried out in the range of 70—160°C and 1000—2000 kPa (10—20 atm). These conditions maintain the product and reactants as Hquids and are near optimum for practical hydrogen peroxide production rates. Several additives including acids, nitriles, stabHizers, and sequestered transition-metal oxides reportedly improve process economics. The product mixture, containing hydrogen peroxide, water, acetone, and residual isopropyl alcohol, is separated in a wiped film evaporator. The organics and water are taken overhead and further refined to recover by-product acetone and the... 

A naphthalene sulfonation product that is rich in the 2,6-isomer and low in sulfuric acid is formed by the reaction of naphthalene with excess sulfuric acid at 125°C and by passing the resultant solution through a continuous wiped-film evaporator at 245°C at 400 Pa (3 mm Hg) (26). The separation in high yield of 99% pure 2,6-naphthalenedisulfonate, as its anilinium salt from a cmde sulfonation product, has been claimed (27). A process has been patented for the separation of 2,6-naphthalenedisulfonic acid from its isomers by treatment with phenylenediarnine (28). 

Methods for isolation of the product polycarbonate remain trade secrets. Feasible methods for polymer isolation include antisolvent precipitation, removal of solvent in boiling water, spray drying, and melt devolatization using a wiped film evaporator. Regardless of the technique, the polymer must be isolated dry, to avoid hydrolysis, and essentially be devoid of methylene chloride. Most polycarbonate is extmded, at which point stabiUzers and colors may be added, and sold as pellets. 

Consider wiped-film evaporator (WEE) (external condenser) when pressure must be in 0.6—0.013 kPa (5—0.1 torr) range. 

The second type of thin-film evaporator, termed a wiped-film evaporator, introduces feed material on a heated waU of a cylinder. Rotating wiper blades continuously spread the feed along the inner waU of the cylinder to maintain uniformity of thickness and to ensure contact with the heated surface. The volatile components are driven off and coUected on an internal chilled condenser surface. The condensate or distUlate is removed continuously. At the end of the process, the residual becomes dry and heavy and drops to the bottom of the unit for removal. The wiped-film evaporator is best suited for treatment of viscous or high-solids content feed. 

The clay-cataly2ed iatermolecular condensation of oleic and/or linoleic acid mixtures on a commercial scale produces approximately a 60 40 mixture of dimer acids and higher polycarboxyUc acids) and monomer acids (C g isomerized fatty acids). The polycarboxyUc acid and monomer fractions are usually separated by wiped-film evaporation. The monomer fraction, after hydrogenation, can be fed to a solvent separative process that produces commercial isostearic acid, a complex mixture of saturated fatty acids that is Hquid at 10°C. Dimer acids can be further separated, also by wiped-film evaporation, iato distilled dimer acids and trimer acids. A review of dimerization gives a comprehensive discussion of the subject (10). 

Independent of the specific duty, the Dryex system is based on the use of a specially designed wiped-film evaporator characterized by... 

In this design a thin layer of solution is spread on the heating surface by mechanical means. Wiped-film evaporators are used for very viscous materials and for producing solid products. The design and applications of this type of evaporator are discussed by Mutzenburg (1965), Parker (1965) and Fischer (1965). 

Wiped-Film Evaporator/02 Reactivation of Catalyst. In this technology [38], spent or-ganophosphine-modified rhodium catalyst is first concentrated in a wiped-film evaporator where most of the organophosphine is removed. The rhodium concentrate is contacted with air to break down phosphido bridges in rhodium clusters. This air treated concentrate may then be used as a catalyst precursor. This procedure is suitable in circumstances where most of the aldehyde dimers, trimers and tetramers are sufficiently volatile to be removed in a wiped-film evaporator. 

Catalyst Reactivation Using Propargyl Acetate. The Wiped-Film Evaporator/02 reactivation procedure and the Capture of Active Catalyst Using Solid Acidic Support with FI2 Elution procedure (see above) both involve the separation of uncomplexed phosphine from rhodium complex. Since the value of the uncomplexed phosphine is significant, technology that does not require separation of phosphine during catalyst reactivation is desirable. 

In one such procedure a rhodium complex concentrate prepared from a 400 ppm rhodium containing hydroformylation catalyst solution, for which catalytic activity had declined to about 30 percent of its initial value, was concentrated in a wiped-film evaporator to about 27,700 ppm rhodium. This concentrate was oxygenated with tertbu-tylhydroperoxide. After isolation and treatment with triphenylphosphine, a 70% yield of [HRh(CO)(PPh3)3] was obtained.[41]... 

Winterization, 70 813 of corn oil, 26 289 Winter wheats, 26 276-277 Wiped-film evaporator... 

Solvent mixtures that contain heat-sensitive compounds, are viscous, or have high boihng points can be separated using wiped-film evaporators (WFE) [57, 58]. A WFE operates by receiving a liquid feed into a column that contains several wiper blades. The walls of the WFE are heated at a constant temperature in order to vaporize the solvent film. As the solvent vapors migrate to the center of the WFE, they come into contact with a coohng unit that condenses the vapors, allowing them to flow down the condenser to the outlet receiver. The thin solvent film and reduced system pressure (in the case of vacuum operation) allows the solvents to be separated slowly at lower temperatures [57-59]. 

Finally, the product (3) was purified using a three-stage continuous distillation process using Hastelloy wiped-film evaporators (WFEs). The key distillation, employing a WFE equipped with a fractionating column, required only a single pass to remove all process impurities with minimal product loss. The final Hastelloy WFE product distillation was required for product decolorization. 

PROCESS DESIGN SECTION WIPED FILM EVAPORATOR ... 

There are three basic types of devolatilization equipment that have been used for the commercial manufacture of polystyrene wiped film evaporators, devolatilizing extruders and flash evaporators. In wiped film evaporators, the polymer solution is fed into a vessel under vacuum. The solution is moved into thin films along the vessel walls by a set of rotating blades. These blades continue to move the polymer through the vessel while continually renewing the surface area. The tank walls are heated to supply the required energy for devolatilization. These units are typically mounted vertically with the polymer solution fed at the top. At the bottom is a melt pool where a gear pump transfers the melt to the next unit operation, typically pelletization. 

Wiped film evaporators are more effective at removal of components with lower diffusion constants such as styrene dimer and trimer. 

Although there are clearly some specific advantages with the wiped film evaporators, they have not been widely applied for commercial polystyrene production. Reasons for this are most likely the high equipment and maintenance costs associated with these types of units. 

---