Benzene Specifications

Some processes use only one reactor (57) or a combination of liquid- and vapor-phase reactors (58). The goal of these schemes is to reduce energy consumption and capital cost. Hydrogenation normally is carried out at 2—3 MPa (20—30 atm). Temperature is maintained at 300—350°C to meet a typical specification of less than 500 ppm benzene in the product at higher temperatures, thermodynamic equiUbrium shifts to favor benzene and the benzene specification is impossible to attain. Also, at higher temperatures, isomerization of cyclohexane to methylcyclopentane occurs typically there is a 200 ppm specification limit on methylcyclopentane content. 

A tank of benzene (specific gravity 0.88) pressurized to 2 bar (1 bar above atmospheric) is damaged causing a 10 cm sharp opening located 2 m below the liquid level. What is the discharge rate... 

In a countercurrent-flow heat exchanger, 1.25 kg/s of benzene (specific heat 1.9 kJ/kg K and specific gravity 0.88) is to be cooled front 350 to 300 K with water at 290 K. In the heat exchanger, tubes of 25 mm external and 22 mm internal diameter are employed and the water passes through the tubes. If the film coefficients for the water and benzene are 0.85 and 1.70 kW/nr K respectively and the scale resistance can be neglected, what total length of tube will be required if the minimum quantity of water is to be used and its temperature is not to be allowed to rise above 320 K ... 

Logarithms of retention indices of alkyl benzenes specific retention volumes of esters, aldehydes and alcohols and retention times of alkanes and alkanes have been correlated with Equations 13 snd 15 or relationships derived from them (l3.). Logarithms of retention times of allyl alkyl ethers on various column packings have also been successfully correlated with Equation 15 (lA). 

XH and 13C NMR Measurements. In order to confirm these 129Xe NMR results obtained indirectly from the co-adsorbed xenon, we performed separate NMR experiments on the adsorbed benzene. Specifically, the and 13C NMR of benzene were measured with the same samples used in the 129Xe... 

In vitro experiments using human skin support the fact that benzene can be absorbed dermally. An experiment on the permeability of excised human skin with regard to benzene (specific activity 99.8 mCi/mmol total volume of applied benzene not reported) resulted in the absorption of 0.17 mg/cm2 after 0.5 hours and 1.92 mg/cm2 after 13.5 hours (Loden 1986). Following application of 5, 120,270, and 520 pL/cm2 of benzene to human skin, total absorption was found to be 0.01, 0.24, 0.56, and 0.9 pL/cm2, respectively. Thus, the total amount absorbed appears to increase linearly with dose. When exposure time (i.e., the time to complete evaporation) at each dose was measured and plotted as the ordinate of absorption, total absorption was found to increase linearly with exposure time. The percentage of the applied dose absorbed at each concentration was constant at about 0.2% (Franz 1984). 

Li G-L, Yin S-N, Watanabe T, et al. 1986. Benzene-specific increase in leukocyte alkaline phosphatase activity in rats exposed to vapors of various organic solvents. J Toxicol Environ Health 19 581-589. 

As shown in Scheme 2, diphenylalkyllithium ([1]) formed from the reaction of ADPE with n-butyllithium revealed the absorption maximum at = 455 nm in benzene/THF mixture and at = 422 nm in pure benzene. Specifically, the cross-over reaction was finished in benzene/THF mixture within at least 2 h, which will be discussed in more detail later. The addition of styrene renders the absorption band at = 455 nm disappeared rapidly and simultaneously new absorption... 

C-radiolabeled benzene was obtained dissolved in distilled H2O from Mew England Nuclear. Each sealed ampule contained 0.10 mCi of uniformly labeled benzene (specific activity of 54.0 mCi/m mol) mixed with 20 ml H2O. New England Nuclear analyzed this mixture after we had stored some of the solutions for over one year and found no deterioration of the benzene. 

In 1866, August Kekul used his recently published structural theory of matter to propose a structure for benzene. Specifically, he proposed a ring comprised of alternating double and single bonds. 

Since buckyballs are comprised of interlocking aromatic rings, we might expect C q to function as if it were one large aromatic compound. However, this is not the case, because the curvature of the sphere prevents all of the p orbitals from overlapping with each other, so the first criterion for aromaticity is not met. This explains why C q does not exhibit the same stability as benzene. Specifically, C q readily undergoes addition reactions, much like alkenes. 

In the previous chapter, we explored the remarkable stabiUty of benzene. Specifically, we saw that while alkenes undergo an addition reaction when treated with bromine, benzene is inert under the same conditions. 

Pure benzene, CgHg, freezes at 5.45°C. A solution containing 7.24 g C2CI4H2 in 115 g of benzene (specific gravity = 0.879) freezes at 3.55°C. Based on these data, what is the molal freezing-point constant for benzene ... 

Example 9.1 A process involves the use of benzene as a liquid under pressure. The temperature can be varied over a range. Compare the fire and explosion hazards of operating with a liquid process inventory of 1000 kmol at 100 and 150°C based on the theoretical combustion energy resulting from catastrophic failure of the equipment. The normal boiling point of benzene is 80°C, the latent heat of vaporization is 31,000 kJ kmol the specific heat capacity is 150 kJkmoh °C , and the heat of combustion is 3.2 x 10 kJkmok. ... 

The specific nature of UV absorption for certain structures when combined with the high sensitivity of the method enables trace quantities (— 1 ppm) of molecules in a matrix transparent to UV beams to be analyzed. Benzene in cyclohexane is an example. 

For the refiner, the reduction in benzene concentration to 3% is not a major problem it is achieved by adjusting the initial point of the feed to the catalytic reformers and thereby limiting the amount of benzene precursors such as cyclohexane and Cg paraffins. Further than 3% benzene, the constraints become very severe and can even imply using specific processes alkylation of benzene to substituted aromatics, separation, etc. 

Table 5.24 shows that these specific pollutants are present only in small proportions (about 8%) of the total organic compounds emitted by the motor, but they are particularly feared because of their incontestable toxicity. Prominent among them is benzene. 

Chemical composition does not generally come into play, except for the case where it is necessary to establish maximum specifications for undesirable compounds such as sulfur, nitrogen, and metals, or even more unusually, certain compounds or families of compounds such as benzene in premium gasolines. By tradition, the refiner supposedly possesses numerous degrees of freedom to generate products for which the properties but not the composition are specified. 

For adsorption on Spheron 6 from benzene-cyclohexane solutions, the plot of N N2/noAN2 versus N2 (cyclohexane being component 2) has a slope of 2.3 and an intercept of 0.4. (a) Calculate K. (b) Taking the area per molecule to be 40 A, calculate the specific surface area of the spheron 6. (c) Plot the isotherm of composition change. Note Assume that is in millimoles per gram. 

Placing the 5-Iine control block above the geometry specification block of Exercise 5-4 gives the complete minimal input file for benzene, which we can call miubeuz.inniS (or anything else you like with the extension. mm3). Aside from the geometry block, there are two important differences between miubenz.mm3 and the file miuimal.mm3 for ethylene in File 4-la. One is the switch in column 61 of the first line, the other is the set of switches (hat constitutes the entire second line. The first switch tells the system... 

Let us consider a specific example, viz., the extraction of a solution of 4 Og. of n-butyric acid in 100 ml. of water at 15° with 100 ml. of benzene at 15°. The partition coefficient of the acid between benzene and water may be taken as 3 (or J between water and benzene) at 15°. For a single extraction with benzene, we have ... 

For ammonium surfactants there is evidence for the existence of an additional specific interaction between the headgroups of the surfactant and the aromatic solubilisate . This is in line with the observation that partition coefficients for benzene in CTAB solutions are much higher than those for... 

The prefix ortho signifies a 1 2 disubstituted benzene ring meta signifies 1 3 disubstitu tion and para signifies 1 4 disubstitution The prefixes o m and p can be used when a substance is named as a benzene derivative or when a specific base name (such as ace tophenone) is used For example... 

Now that we ve outlined the general mechanism for electrophilic aromatic substitution we need only identify the specific electrophile m the nitration of benzene to have a fairly clear idea of how the reaction occurs... 

One of the factors responsible for the rather wide variation in a values for benzene is the presence of ji-clectrons in the molecule, which can cause its adsorption to acquire a specific character if the adsorbent is polar (Chapter 1, p. 11). On hydroxylated silica, for example, the heat of adsorption is much higher than on the dehydroxylated material - on the latter solid indeed the interaction is so weak that a Type HI isotherm results (Fig. 2.19). Unfortunately c-values are rarely quoted in the literature, but... 

As discussed earlier in Section lOC.l, ultraviolet, visible and infrared absorption bands result from the absorption of electromagnetic radiation by specific valence electrons or bonds. The energy at which the absorption occurs, as well as the intensity of the absorption, is determined by the chemical environment of the absorbing moiety. Eor example, benzene has several ultraviolet absorption bands due to 7t —> 71 transitions. The position and intensity of two of these bands, 203.5 nm (8 = 7400) and 254 nm (8 = 204), are very sensitive to substitution. Eor benzoic acid, in which a carboxylic acid group replaces one of the aromatic hydrogens, the... 

The reaction rate is increased by using an entraining agent such as hexane, benzene, toluene, or cyclohexane, depending on the reactant alcohol, to remove the water formed. The concentration of water in the reaction medium can be measured, either by means of the Kad-Eischer reagent, or automatically by specific conductance and used as a control of the rate. The specific electrical conductance of acetic acid containing small amounts of water is given in Table 6. 

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