Vaporizer, benzene

Pyrolysis. Benzene undergoes thermal dehydrocondensation at high temperatures to produce small amounts of biphenyls and terphenyls (see Biphenyl AND terphenyls). Before the 1970s most commercial biphenyl was produced from benzene pyrolysis. In a typical procedure benzene vapors are passed through a reactor, usually at temperatures above 650°C. The decomposition of benzene iato carbon and hydrogen is a competing reaction at temperatures of about 750°C. Biphenyls are also formed when benzene and ethylene are heated to 130—160°C ia the presence of alkaH metals on activated AI2O3 (33). 

Various types of detector tubes have been devised. The NIOSH standard number S-311 employs a tube filled with 420—840 p.m (20/40 mesh) activated charcoal. A known volume of air is passed through the tube by either a handheld or vacuum pump. Carbon disulfide is used as the desorbing solvent and the solution is then analyzed by gc using a flame-ionization detector (88). Other adsorbents such as siUca gel and desorbents such as acetone have been employed. Passive (diffuse samplers) have also been developed. Passive samplers are useful for determining the time-weighted average (TWA) concentration of benzene vapor (89). Passive dosimeters allow permeation or diffusion-controlled mass transport across a membrane or adsorbent bed, ie, activated charcoal. The activated charcoal is removed, extracted with solvent, and analyzed by gc. Passive dosimeters with instant readout capabiUty have also been devised (85). 

Treatment for acute exposure to benzene vapor involves removing the subject from the affected area, followed by artificial respiration with oxygen intubation and cardiac monitors may be necessary for severe acute exposures (125,127). Because of its low surface tension, benzene poses a significant aspiration hazard if the liquid enters the lungs. Emesis is indicated in alert patients if more than 1 mL of benzene per kg of body weight has been ingested and less than two hours have passed between ingestion and treatment (127). 

Example 37 Estimate the Diffusivity of Benzene Vapor Diffusing... 

Example 37 Estimate the diffusivity of benzene vapor diffusing into air at 30°C and 96.5 kPa total pressure. 

FIG. 12-38 Humidity chart for air-benzene-vapor mixture. To convert British thermal units per pound to joules per kilogram, multiply by 2326 to convert British thermal units per pound dry air-degree Fahrenheit to joules per Idlogram-kelvin, multiply hy 4186.8 and to convert cubic feet per pound to cubic meters per kilogram, multiply by 0.0624. 

Adsorption and ehemieal reaetion type hydrophylie adsorbate (aleohol) - hydrophobie agent (benzene vapor) and hydrophobie adsorbate (benzole aeid) - hydrophilie agent (aleohol vapor) takes plaee in the temperature range ... 

A 6-in. (150-mm) relief valve on a petrochemical plant discharged benzene vapor to atmosphere. It was ignited by a furnace and exploded, rupturing piping, which released more than 100 tons of various flammable liquids. One man was killed, and damage was extensive [5]. 

The capacity of a relief valve for a tank has been calculated to be 50,000 cu ft/hr at 110°F and 1.0 psig, with a benzene vapor. Determine the required free air capacity. For benzene MW = 78.11... 

Benzene, a known carcinogen, was once widely used as a solvent A sample of benzene vapor in a flask of constant volume exerts a pressure of 325 mm Hg at 80°C. The flask is slowly cooled. 

At one time, benzene was widely used as a solvent, both commercially and in research and teaching laboratories. Its use for that purpose has largely been abandoned because of its toxicity. Chronic exposure to benzene vapor leads to various blood disorders and, in extreme cases,... 

Benedict-Webb-Rubin equation 252. 256-7 benzene, vapor pressure 260-1 benzene + I, 4-dimethylbenzene mixture, phase equilbria 420-2, 424... 

A sample of hydrogen chloride gas, HC1, is being collected by bubbling it through liquid benzene into a graduated cylinder. Assume that the molecules pictured as spheres show a representative sample of the mixture of HC1 and benzene vapor ( represents an HCl molecule and O a benzene molecule), (a) Use the figure to determine the mole fractions of HCl and benzene vapor in the gas inside the container, (b) What are the partial pressures of HCl and benzene in the container when the total pressure inside the container is 0.80 atm ... 

Self-Test 7.17B Confirm that liquid benzene and benzene vapor are in equilibrium at the normal boiling point of benzene. 80.1°C, and 1 atm pressure. The enthalpy of vaporization of benzene at its boiling point is 30.8 kj-mol 1 and its entropy of vaporization is 87.2 J-K -mol. ... 

Down-Draft Hood. To protect personnel from benzene vapors, it is recommended that all the pouring, container closing, and final decantation and bottling operations be performed on an efficient down-draft hood (4) To increase efficiency in inserting and removing the bolts on the steel cans, a reversible air-driven screwdriver has been suspended on a counterweight over the down-draft hood. 

The benzene strip or extract solutions are evaporated nearly to dryness in 500-ml. standard-taper Erlenmeyer flasks on 3 units of a 6-unit variable heat extraction apparatus hot plate (see Figure 1). Evaporation is hastened by directing a jet of air at the surface of the benzene, gentle enough to avoid spattering when maintained 0.5 inch above the surface of the liquid. The benzene vapors are removed through a manifold connected to the house vacuum. On this apparatus 250 ml. of sample can be reduced to a volume of about 5 ml. in 10 minutes. 

Example 10.1 A hydrocarbon gas stream containing benzene vapor is to have the benzene separated by absorption in a... 

Few studies have been made of benzene chemisorption by the volumetric method. Zettlemoyer et al. (8) have examined the adsorption of benzene vapor at 0°C on powders of nickel and of copper. First, the monolayer coverage of argon (vm) A, was measured. The argon was then removed by pumping and the amount of benzene required to form a monolayer, (vmi) Bz, was measured. Weakly adsorbed benzene was then removed by pumping, after which further benzene adsorption provided the value (vm2) Bz. Some results are reproduced in Table I. On the assumption that the same extent of surface is accessible both for argon and for benzene adsorption, it is clear that complete monolayers of benzene were not achieved, that some (Ni) or all (Cu) of the benzene was adsorbed reversibly. It was considered that only the irreversibly adsorbed benzene was chemisorbed, the remainder being physically adsorbed. Thus chemisorption of benzene on copper appeared not to occur. The heat of adsorption of benzene on nickel at zero... 

The experimental procedure is outlined schematically in Fig. 13 a detailed description was given by Hartog et al. 37). Benzene vapor and deuterium gas, in the molar ratio of 1 18, were passed through a catalyst bed and then through a cold trap immersed in liquid nitrogen in which the hydrocarbons were frozen out. The temperature of the catalyst bed was... 

Zhu LZ, Su YH (2002) Benzene vapor sorption by organobentonites from ambient air. Clays Clay Miner 50 421-427... 

Overberger, J.E., Steele, W.A., Aston, J.G. (1969) The vapor pressure of hexamethylbenzene. The standard entropy of hexamethyl-benzene vapor and the barrier to internal rotation. J. Chem. Thermodyn. 1, 535-542. 

The gaseous atmosphere was then vented through a trap at -78° (to remove most of the benzene vapor) into an evacuated vessel. Samples were removed by gas-tight syringe and injected into a Hewlett-Packard 5790 gas chromatograph, equipped with a U ft, 1/8 in Porapak P column and a flame ionization detector. Use of known samples of hydrocarbons (methane and ethane) established that the minimum detectable amounts of product by this procedure were about 0.5-1 0 % (based on starting Nb complex). Several of the reactions (Mo(CO)g, W(C0)g and Ru (CO) p) gave small amounts (around 1-2 %) of these alkanes only with Cr(C0)g was a substantial yield of hydrocarbon product consistently observed (see below). 

A storage vessel contains liquid benzene at 100°F. The vessel vapor space is inerted with pure nitrogen to a total pressure of 1/2-in of water gauge. Assume that the vapor space is saturated with benzene vapor. 

Tyrer A process for making phenol by first sulfonating benzene. Benzene vapor was passed through hot sulfuric acid the excess of benzene served to remove the water formed in the reaction. The benzene sulfonic acid was then hydrolyzed by fusion with sodium hydroxide. Invented by D. Tyrer in 1916. See also Dennis-Bull. 

Titanium dioxide suspended in an aqueous solution and irradiated with UV light X = 365 nm) converted benzene to carbon dioxide at a significant rate (Matthews, 1986). Irradiation of benzene in an aqueous solution yields mucondialdehyde. Photolysis of benzene vapor at 1849-2000 A yields ethylene, hydrogen, methane, ethane, toluene, and a polymer resembling cuprene. Other photolysis products reported under different conditions include fulvene, acetylene, substituted trienes (Howard, 1990), phenol, 2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol, 2,6-dinitro-phenol, nitrobenzene, formic acid, and peroxyacetyl nitrate (Calvert and Pitts, 1966). Under atmospheric conditions, the gas-phase reaction with OH radicals and nitrogen oxides resulted in the formation of phenol and nitrobenzene (Atkinson, 1990). Schwarz and Wasik (1976) reported a fluorescence quantum yield of 5.3 x 10" for benzene in water. 

The amount of cyanogen chloride formed was inversely proportional to the pH of the solution. At pH 6, the greatest amount of cyanogen chloride was formed when the reaction mixture contained ammonium ion and hypochlorous acid at a ratio of 2 3 (Kanno et al., 1982). Benzene vapor reacted with nitrate radicals in purified air forming nitrobenzene (Chiodini et al., 1993). 

In a typical experiment, benzene vapor was admitted into the evacuated balance chamber by means of stopcock D. After achieving the desired pressure, stopcock D was closed. The maximum uncertainty in p/p during the course of any one experiment was 0.008 units. Equilibrium was judged to be established when there was less than a 1 percent change in weight over a 12 hour period. Total sorption values were reproducible to within 1%. 

SORPTION EXPERIMENTS. The extracts were exposed to benzene vapor at several relative vapor pressures (p/p )- Two types of sorption experiments were conducted. Experiments in which the benzene vapor pressure is raised from zero to a higher value are termed integral sorptions. Sorption experiments starting with the extract and vapor in equilibrium at a finite, nonzero pressure, and proceeding to a higher pressure, are termed incremental sorptions. 

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