Vapor pressure unit conversion

The water-vapor transmission rate (WVTR) is another descriptor of barrier polymers. Strictly, it is not a permeabihty coefficient. The dimensions are quantity times thickness in the numerator and area times a time interval in the denominator. These dimensions do not have a pressure dimension in the denominator as does the permeabihty. Common commercial units for WVTR are (gmil)/(100 in. d). Table 2 contains conversion factors for several common units for WVTR. This text uses the preferred nmol/(m-s). The WVTR describes the rate that water molecules move through a film when one side has a humid environment and the other side is dry. The WVTR is a strong function of temperature because both the water content of the air and the permeabihty are direcdy related to temperature. Eor the WVTR to be useful, the water-vapor pressure difference for the value must be reported. Both these facts are recognized by specifying the relative humidity and temperature for the WVTR value. This enables the user to calculate the water-vapor pressure difference. Eor example, the common conditions are 90% relative humidity (rh) at 37.8°C, which means the pressure difference is 5.89 kPa (44 mm Hg). 

Residue Curve Maps for Reactive Mixtures 461 Heat-Exchanger Design 474 Materials of Construction 483 Saturated Steam Properties 487 Vapor Pressure of Some Hydrocarbons 489 Vapor Pressure of Some Organic Components 490 Conversion Factors to SI Units 491... 

The book is completed with Annexes on the analysis of reactive mixtures by residue curve maps, design of heat exchangers, selection of construction materials, steam tables, vapor pressure of typical chemical components and conversion table for the common physical units. 

Vapor pressures are quite temperature dependent, and can vary appreciably over as little as 5 or 10°C. For example, the vapor pressure of trichloroethene increases by approximately 27% over less than 5°C the vapor pressure at 25.50°C is approximately 9.546 kilopascals (kPa), compared with 7.506 kPa at 20.99°C (Boublik et al., 1984). Therefore, it is extremely important to note the temperature at which a vapor pressure was measured or estimated. (See the Appendix for conversions between kilopascal and other units of pressure.) Over narrow temperature ranges, the Antoine equation is commonly used to predict vapor pressure of a liquid at a particular temperature,... 

The vapor pressure of petroleum or a petroleum product is the force exerted on the walls of a closed container by the vaporized portion of a liquid. Conversely, it is the force that must be applied to the liquid to prevent it vaporizing further. The vapor pressure increases with increase in temperature and is variously expressed in terms of millimeters of mercury, pounds per square inch, or other equivalent units of pressure depending on common usage. Gasoline vapor pressure depends critically on its butane content, and in the refinery the final adjustment of vapor pressure of a gasoline to meet the specification is often made by butane injection. 

The barometric pressure reading must be corrected for the change in the density of the mercury column between 0 C and the operating temperature and converted to the same units of pressure as the vapor pressure apparatus display. After making the denaty correction, the conversion for the height of a mercury column at 0 C to kPa or psia is made as follows 1 in. (25 mm) Hg at 0 C = 3.3865 kPa or — 0.49116 psia. 

Both vapor-phase and Hquid-phase processes are employed to nitrate paraffins, using either HNO or NO2. The nitrations occur by means of free-radical steps, and sufftciendy high temperatures are required to produce free radicals to initiate the reaction steps. For Hquid-phase nitrations, temperatures of about 150—200°C are usually required, whereas gas-phase nitrations fall in the 200—440°C range. Sufficient pressures are needed for the Hquid-phase processes to maintain the reactants and products as Hquids. Residence times of several minutes are commonly required to obtain acceptable conversions. Gas-phase nitrations occur at atmospheric pressure, but pressures of 0.8—1.2 MPa (8—12 atm) are frequentiy employed in industrial units. The higher pressures expedite the condensation and recovery of the nitroparaffin products when cooling water is employed to cool the product gas stream leaving the reactor (see Nitroparaffins). 

Most of the vinyl acetate produced in the United States is made by the vapor-phase ethylene process. In this process, a vapor-phase mixture of ethylene, acetic acid, and oxygen is passed at elevated temperature and pressures over a fixed-bed catalyst consisting of supported palladium (85). Less than 70% oxygen, acetic acid, and ethylene conversion is realized per pass. Therefore, these components have to be recovered and returned to the reaction zone. The vinyl acetate yield using this process is typically in the 91—95% range (86). Vinyl acetate can be manufactured also from acetylene, acetaldehyde, and the hquid-phase ethylene process (see Vinyl polymers). 

Selective tertiary-huimoX (tBA) dehydration to isobutylene has been demonstrated using a pressurized reactive distillation unit under mild conditions, wherein the reactive distillation section includes a bed of formed solid acid catalyst. Quantitative tBA conversion levels (>99%) have been achieved at significantly lower temperatures (50-120°C) than are normally necessary using vapor-phase, fixed-bed, reactors (ca. 300°C) or CSTR configurations. Substantially anhydrous isobutylene is thereby separated from the aqueous co-product, as a light distillation fraction. Even when employing crude tBA feedstocks, the isobutylene product is recovered in ca. 94% purity and 95 mole% selectivity. 

Butane from natural gas is cheap and abundant in the United States, where it is used as an important feedstock for the synthesis of acetic acid. Since acetic acid is the most stable oxidation product from butane, the transformation is carried out at high butane conversions. In the industrial processes (Celanese, Hills), butane is oxidized by air in an acetic acid solution containing a cobalt catalyst (stearate, naphthenate) at 180-190 °C and 50-70 atm.361,557 The AcOH yield is about 40-45% for ca. 30% butane conversion. By-products include C02 and formic, propionic and succinic acids, which are vaporized. The other by-products are recycled for acetic acid synthesis. Light naphthas can be used instead of butane as acetic adic feedstock, and are oxidized under similar conditions in Europe where natural gas is less abundant (Distillers and BP processes). Acetic acid can also be obtained with much higher selectivity (95-97%) from the oxidation of acetaldehyde by air at 60 °C and atmospheric pressure in an acetic acid solution and in the presence of cobalt acetate.361,558... 

A thermal cracking unit for waxes consists of a furnace, a primary separation column, a stabilization column and a distillation section. The feedstock-is vaporized, mixed with steam to 40 per cent weight, and enters a tubular furnace in which the residence time is a few seconds (2 to 10 s) at 500 to 600° . Once-throucb conversion is relatively low (15 to 30 per cent) to avoid side reactions. Operation is at atmospheric pressure or slightly above. Direct quench, or quench with a heat transfer fluid, generates steam. Primary fractionation allows the recycling of the unconverted part of the feedstock. 

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