Operation under pressure

Continuous processes have been developed for the alcohols, operating under pressure with Hquid ammonia as solvent. Potassium hydroxide (206) or anion exchange resins (207) are suitable catalysts. However, the relatively small manufacturing volumes militate against continuous production. For a while a continuous catalytic plant operated in Raveima, Italy, designed to produce about 40,000 t/yr of methylbutynol for conversion to isoprene (208,209). 

Another option available with rotary vacuum dmm filters is fiiU enclosure. This enables operation under nitrogen or other atmospheres, for reasons such as safety, prevention of vapor loss, etc. Enclosure may also be used to prevent contamination of the material being filtered or to confine the spray from washing nozzles. The rotary dmm filter also can be enclosed in a pressure vessel and operated under pressure. 

The relatively low capital cost of the simple batch reactor is its most enticing feature. The inabiUty to operate under pressure typically limits the simple batch reactor to use with the higher alkenes ie, octenes, nonenes, and dodecenes. For mainly economic reasons, these reactors are usually mn at phenol to alkene mole ratios of between 0.9 and 1.1 to 1. 

The predominant process for manufacture of aniline is the catalytic reduction of nitroben2ene [98-95-3] ixh. hydrogen. The reduction is carried out in the vapor phase (50—55) or Hquid phase (56—60). A fixed-bed reactor is commonly used for the vapor-phase process and the reactor is operated under pressure. A number of catalysts have been cited and include copper, copper on siHca, copper oxide, sulfides of nickel, molybdenum, tungsten, and palladium—vanadium on alumina or Htbium—aluminum spinels. Catalysts cited for the Hquid-phase processes include nickel, copper or cobalt supported on a suitable inert carrier, and palladium or platinum or their mixtures supported on carbon. 

Batch Percolators The batch tank is not unlike a big nutsche filter it is a large circiilar or rectangiilar tank with a false bottom. The solids to be leached are dumped into the tank to a uniform depth. They are sprayed with solvent until their solute content is reduced to an economic minimum and are then excavated. Countercurrent flow of the solvent through a series of tanks is common, with fresh solvent entering the tank containing most nearly exhausted material. In a typical ore-dressing operation the tanks are 53 by 20 by 5.5 m (175 by 67 by 18 ft) and extract about 8200 Mg (9000 U.S. tons) of ore on a 13-day cycle. Some tanks operate under pressure, to contain volatile solvents or increase the percolation rate. A series of pressure tanks operating with countercurrent solvent flow is called a diffusion battery. 

Since most batch-type filters operate under pressure rather than vacuum, the following discussion will apply primarily to pressure filtration and the various types of pressure filters. 

Some disintegrators are available for operation under pressure. 

Carbon should be prewetted prior to being placed in the test columns. Backwashing the carbon at low rates (2.5 m/hr) does not remove the air. Rates that would expand the bed 50 percent or 15-30 m/hr, are required. The liquid used for prewetting can either be water, if it is compatible with the liquid to be treated, or a batch of the liquid to be treated which has been purified previously. There are three types of carbon systems (1) fixed beds, (2) pulse beds, and (3) fluidized beds, and these can be used singly, in parallel, or in combination. The majority of systems are either fixed or pulse beds. The two basic types of adsorbers which can be designed to operate under pressure or at atmospheric pressure are the moving or pulse bed and the fixed bed. Either can be operated as packed or expanded beds. 

Natural circulation reboilers are effective and convenient units for process systems operating under pressure. They are usable in vacuum applications but must be applied with care, because the effect of pressure head (liquid leg) on the boiling point of the fluid must be considered. The temperature difference between the heating medium and boiling point of the fluid may be so small as to be impractical, regardless of the tube length in a vertical unit. 

The reactor is equipped with magnetic stirrer, microwave power and temperature control by computer and can operate under pressure. Even though it was developed for homogeneous organic synthetic reactions, it can be used also for heterogeneous catalytic reactions in the liquid phase. 

Alphabutol Also called IFP-SABIC. A process for dimerizing ethylene to 1-butene. It operates under pressure at 80°C, using a complex Ziegler-Natta catalyst, a titanium alkoxide. Developed by the Institut Frangais du Petrole. First operated in Thailand in 1987. Seven plants had been licensed by 1993, of which three were operating. 

Fischer-Tropsch A process for converting synthesis gas (a mixture of carbon monoxide and hydrogen) to liquid fuels. Modified versions were known as the Synol and Synthol processes. The process is operated under pressure at 200 to 350°C, over a catalyst. Several different catalyst systems have been used at different periods, notably iron-zinc oxide, nickel-thoria on kieselgtihr, cobalt-thoria on kieselgiihr, and cemented iron oxide. The main products are C5-Cn aliphatic hydrocarbons the aromatics content can be varied by varying the process conditions. The basic reaction was discovered in 1923 by F. Fischer and... 

A cyclone will operate equally well on the suction or pressure side of a fan if the dust receiver is airtight. Probably the greatest single cause of poor cyclone performance, however, is the leakage of air into the dust outlet of the cyclone. A slight air leak at this point can result in a tremendous drop in collection efficiency, particularly with fine dusts. For a cyclone operating under pressure, air leakage at this point is objectionable primarily because of the local dust nuisance created. 

Figure 11.21 Axial pressure profile for the barrier screw after the screw modification. All sections of the screw are filled and operating under pressure. The solid line in this figure was calculated using the methods described previously, and the dashed line represents the expected pressure profile and was not calculated...

Exposure limits Potential occupational carcinogen. Given that no standards have been established, NIOSH (1997) recommends the most reliable and protective respirators be used, i.e., a self-contained breathing apparatus that has a full facepiece and is operated under positive-pressure or a supplied-air respirator that has a full facepiece and is operated under pressure-demand or under positive-pressure in combination with a self-contained breathing apparatus operated under... 

Deep-sea divers routinely operate under pressures of multiple atmospheres. One malady these divers must be concerned with is the bends, a dangerous condition that occurs when divers rise too quickly from the depths, resulting in the rapid release of gas from blood and tissues. Why does the bends occur ... 

A temperature control system. Although operating under pressure, temperature is the controlling factor in steam sterilization. The modern temperature controller is made up of several key elements to sense, record, and react. These are discussed in a later section. 

This reaction is catalysed by a Pt-Ru catalyst with activated carbon support at 35°C and it is considered to be pseudo-first order with respect to phenol under the condition of 02 excess (Atwater et al., 1997). The reaction was studied in a trickle-bed microreactor of 1.27 cm diameter and volume of 4.8 cm3. The bed porosity is 0.28, while the ratio of bed length-to-particle size is about 30. The reactor was operated under pressure enough to keep a single-phase flow, while the liquid feed was saturated with oxygen. Under these conditions, we can assume complete wetting of the catalyst particles. 

Tubular reactors are operated under pressures of 250 - 330 MPa measured at the reactor inlet. When a pressure drop of 0.01 - 0.03 MPa/m is taken into account the pressure at the reactor outlet is lower by 30 - 60 MPa. 

Continuous Saponification. Fat stocks, plus caustic and salt solutions, are fed continuously into an autoclave operating under pressure at typically about 250°F (120°C). A recycle stream provides sufficient soap concentration to solubilize the fat stream for good contacting with the caustic. The soap-lye-glycerin mix moves to a mixer/cooler to complete saponification. The cooler temperature reduces the solubility of soap in the lye and aids separation. See also Saponification. 

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