Vapor pressure isobutane

Hydroca.rbons. Hydrocarbonsn such as propane, butane, and isobutane, which find use as propellants, are assigned numbers based upon their vapor pressure in psia at 21°C. For example, as shown in Table 2, aerosol-grade propane is known as A-108, / -butane as A-17. Blends of hydrocarbons, eg, A-46, and blends of hydrocarbons and hydrochlorocarbons orHCFCs are also used. The chief problem associated with hydrocarbon propellants is their flammabihty. 

Propane and light ends are rejected by touting a portion of the compressor discharge to the depropanizer column. The reactor effluent is treated prior to debutanization to remove residual esters by means of acid and alkaline water washes. The deisobutanizer is designed to provide a high purity isobutane stream for recycle to the reactor, a sidecut normal butane stream, and a low vapor pressure alkylate product. 

Fig. 1. Vapor-pressure ratios of the alkanes, alkenes, and dienes with respect to / -butane A, isobutane B, isobutylene C, 1-butene D, 1,3-butadiene E,...

Like propane, butanes are obtained from natural gas liquids and from refinery gas streams. The C4 acyclic paraffin consists of two isomers n-butane and isobutane (2-methylpropane). The physical as well as the chemical properties of the two isomers are quite different due to structural differences, for example, the vapor pressure (Reid method) for n-butane is 52 Ib/in., while it is 71 Ib/in. for isobutane. This makes the former a more favorable gasoline additive to adjust its vapor pressure. However, this use is declining in the United States due to new regulations that reduce the volatility of gasolines to 9 psi, primarily by removing butane. ... 

Like propane, n-hutane is mainly obtained from natural gas liquids. It is also a hy-product from different refinery operations. Currently, the major use of n-hutane is to control the vapor pressure of product gasoline. Due to new regulations restricting the vapor pressure of gasolines, this use is expected to he substantially reduced. Surplus n-butane could be isomerized to isobutane, which is currently in high demand for producing isobutene. Isobutene is a precursor for methyl and ethyl tertiary butyl ethers, which are important octane number boosters. Another alternative outlet for surplus n-butane is its oxidation to maleic anhydride. Almost all new maleic anhydride processes are based on butane oxidation. 

Alkylation, where the olefins are reacted with isobutane to make a very desirable gasoline blending stock. Alkylate is an attractive blending component because it has no aromatics or sulfur, low vapor pressure, low end point, and high research and motor octane ratings,... 

Reported vapor pressures of isobutane (2-methylpropane) at various temperatures and the coefficients for the vapor pressure equations... 

FIGURE 2.1.1.1.1.1 Logarithm of vapor pressure versus reciprocal temperature for isobutane. 

A clear example of the possible use of acid and/or superacid solids as catalysts is the alkylation of isobutane with butenes. Isobutane alkylation with low-molecular-weight olefins is one of the most important refining process for the production of high-octane number (RON and MON), low red vapor pressure (RVP) gasoline. Currently, the reaction is carried out using H2SO4 or HF (Table 13.1), although several catalytic systems have been studied in the last few years. 

The use of thermal and catalytic cracking processes for the production of high-octane motor gasolines is accompanied by the production of quantities of light hydrocarbons such as ethylene, propylene, butene, and isobutane. These materials are satisfactory gasoline components octane-wise, but their vapor pressures are so high that only a portion of butanes can actually be blended into gasoline. Alkylation is one of several processes available for the utilization of these excess hydrocarbons. 

The vapor pressure of a light component at a given temperature, divided by the vapor pressure of a heavier component at the same temperature, is called the relative volatility. For practice, calculate the relative volatility of isobutanes and normal pentane at 140°F (answer 4.0). Next, calculate their relative volatility at 110°F (answer 4.9).1... 

Figure 4.2b shows the equivalent of Figure 4.2a to be slightly more complex for systems such as ethane + water, propane + water, isobutane + water, or water with the two common noncombustibles, carbon dioxide or hydrogen sulfide. These systems have a three-phase (Lw-V-Lhc) line at the upper right in the diagram. This line is very similar to the vapor pressure ( V-Lhc) line of the pure hydrocarbon, because the presence of the almost pure water phase adds a very low vapor pressure (a few mmHg at ambient conditions) to the system. 

In industrial practice, two liquid acids are employed as catalysts for isobutane/ butene alkylation, namely sulfuric acid and hydrofluoric acid [3, 19, 20]. Both processes deliver a high-quality gasoline component. The catalyst consumption in the H2S04 process is high, typically 70-100kg/t The spent sulfuric acid contains tarry hydrocarbons and water and has to be processed externally. On the other hand, corrosiveness and toxicity of HF are reasons of concern that require use of additives that lower the HF vapor pressure and minimize the amount of HF released in the case of an accident. However, in many industrialized countries, new HF alkylation processes are no longer approved by authorities. 

What is the vapor pressure of a 60 40 w/w mixture of propane (MW = 44.1) and isobutane (MW = 58.1) Assume an ideal solution. The vapor pressures of propane and isobutane are 110 and 30.4 psig at 70°F, respectively. If the vessel is large enough, what is the vapor pressure and composition of the liquid mixture when the last drop of the liquid mixture vaporizes ... 

Figure 3.10 shows the vapor pressure/composition curve at a given temperature for an ideal solution. The three dotted straight lines represent the partial pressures of each constituent volatile liquid and the total vapor pressure. This linear relationship is derived from the mixture of two similar liquids (e.g., propane and isobutane). However, a dissimilar binary mixture will deviate from ideal behavior because the vaporization of the molecules A from the mixture is highly dependent on the interaction between the molecules A with the molecules B. If the attraction between the molecules A and B is much less than the attraction among the molecules A with each other, the A molecules will readily escape from the mixture of A and B. This results in a higher partial vapor pressure of A than expected from Raoult s law, and such a system is known to exhibit positive deviation from ideal behavior, as shown in Figure 3.10. When one constituent (i.e., A) of a binary mixture shows positive deviation from the ideal law, the other constituent must exhibit the same behavior and the whole system exhibits positive deviation from Raoult s law. If the two components of a binary mixture are extremely different [i.e., A is a polar compound (ethanol) and B is a nonpolar compound (n-hexane)], the positive deviations from ideal behavior are great. On the other hand, if the two liquids are both nonpolar (carbon tetrachloride/n-hexane), a smaller positive deviation is expected.

The vapor pressure of isobutane is given in the preceding problem. 

Other Isobutane-Based Chemicals. Isobutane can be directly dehydrogenated to isobutylene by a modification of the Houdry process. This can then be converted to MTBE. The estimated use is over 1 billion lb of isobutane. Because of their inertness and higher vapor pressures, high-purity propane and butanes have become the important substitutes for fluorocarbons as aerosol propellants. Isobutane can also be used as a solvent in polymer processing, and as a blowing agent for foamed polystyrene. 

This process is quite important in the petroleum industry because isobutane is usually more valuable as a chemical feedstock than normal butane. The typical amount of iC.s contained in crude oil and produced in refinery operations such as catalytic cracking is sometimes not enough to satisfy the demand. On the other hand the supply of nC4 sometimes exceeds the demand, particularly in the summer when less nCi can be blended into gasoline because of vapor pressure limitations. 

Various blends of hydrocarbon propellants that have a range of physical properties suitable for different applications are commercially available, e.g., CAP30 (Calor Gas Ltd.) is a mixture of 11% propane, 29% isobutane, and 60% butane. A-46 (Aeropres) is a commonly used mixture for aerosol foams and consists of about 85% isobutane and 15% propane. The number following the letter denotes the approximate vapor pressure of the blend or mixture. 

The hydrocarbon yields shown represent those expected averaged over the useful life of the ZSM-5 catalyst. Finished gasoline contains C4 s for vapor pressure control. For an 82.7 kPa (12 psi) RVP (Reid Vapor Pressure) finished gasoline, the yield is 86 wt% of hydrocarbons and the clear Research octane number is 93. Additional gasoline could be made by alkylating the propene and butenes produced with isobutane. As the amount of alkylate would be low, its manufacture would most likely be considered only for very large plants. 

Note Error in Problem statement in 1st printing vapor pressure of isobutane is 490.9 kPa not 4.909 kPa. 

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