Front-end volatility

This expression is known as the vapor lock index (VLI) or the front-end volatility index (EEVI). The value of n for U.S. cars is generally reported as 9 when RVP is in kPa (0.13 when pressure is in psi) (23). The maximum level of VLI is set by month and by region according to the ninetieth percentile daily maximum temperature. 

Specifications for fuel oil may include limits on the temperatures at which 10% and 90% of the fuel are distilled by the standard procedure (ASTM D-396). For kerosene-type fuel oil (ASTM D-1) these values control the volatility at both ends of the distillation range, whereas for gas oil (ASTM D-1, ASTM D-2), where the front-end volatility is not so critical, only the 90% distillation temperature is normally specified. This ensures that high-boiling-point components, which are less likely to burn and which can cause carbon deposition, are excluded from the fuel. 

Usually 100 to 400 degrees F, ASTM containing sufficient front end volatility-usually as butane—for suitable ignition but not so much as to produce vapor locking. Ten to 12 psia is a good target vapor pressure for the finished product. 

When the sample solvent evaporates at the front end of the liquid, volatile compounds co-evaporate with the solvent and start moving through the main column. In this way, volatile components can be lost through the early vapour exit or, if venting is delayed, the most volatile compounds reach the detector even before the end of... 

With respect to ETBE, ethanol has, however, some disadvantages such as volatility and water solubility. Its RVP is more four times that of ETBE and it adversely affects the gasoline volatility in fact, ethanol addition causes a significant reduction in temperature for the front end evaporation and, as a consequence, the light cheap gasoline components, such as butanes and pentanes, have to be removed to meet the volatility specification limit. 

Volatility This has emerged as a significant factor in automotive lubricant products from environmental and operational standpoints and again pertains predominantly to the distillation front end. Low volatility... 

One method for ethanol dehydration is heterogeneous azeotropic distillation, which has been used for many decades. A suitable light entrainer component (benzene, cyclohexane, isooctane, ethylene glycol, and so on) is added to modify the relative volatilities. The water is driven overhead with the entrainer and a high-piu ity ethanol bottoms stream is produced in the azeotropic column. The overhead vapor is condensed and fed to a decanter. The organic phase is refluxed back to the column. The aqueous phase is fed to another column that produces a bottoms product of high-purity water and a distillate that is recycled back to the azeotropic column. A third column in the front end of the process is used to preconcentrate the low-concentration stream from the fermenter up to a concentration closer to the azeotrope before feeding this into the azeotropic column. 

The net gas output from the sinter machine is at a temperature of 200 to 500°C and contains a significant load of dusts, fumes and volatile materials, including compounds of lead, cadmium, mercury, chlorine and fluorine. The SO2 content can be variable from 2.5 per cent to 6.5 per cent, depending on measures taken to raise its concentration such as tip end gas recirculation. Gas may also be separated from the front end and tip end, giving relatively high SO2 concentrations from the front end and low concentrations from the tip end. 

Lube oil volatility is a measure of oil loss due to evaporation. Noack volatility measures the actual evaporative loss which is grade dependent, and a function of molecular composition and the efficiency of the distillation step. The volatility is generally lower for higher viscosity and higher VI base stocks. The gas chromatographic distillation (GCD) can be used to measure the front end of the boiling point curve and may be used as an indication of volatility, e.g. 10% off at 375°C. 

A key objective of the VPS is to set the viscosity of the final product. This basic product property is set in the distillation by setting the cut points of the product streams. Volatility, another key product specification is the amount of material removed at a certain temperature and is controlled in the distillation by cut point targets and front-end fractionation. It affects engine oil... 

Oil in the solvent results from incomplete solvent-oil separation and may be due to entrainment from flash vessels, volatilization or stripper flooding. Characterization of the solvent contamination by GCD can be used to determine if contamination is occurring by light or heavy oil fractions. A light oil contamination suggests that the accumulation of distillate in the front end. Presence of heavy oil suggests entrainment oil in the solvent, which can reduce raffinate yield and increase the treat rate required. 

Process condensate collected from the front end of the plant is condensed steam and therefore quite clean except for traces of soKds and a small amount of dissolved gases. The process condensate is stripped with steam and then sent to a demineralizer unit, where the solids are removed from the water so it can be recycled as boiler feedwater. The volatile by-products are carried with the steam into the reformer, where they are reprocessed. 

Note 23—If the concentrations of propane and butane in the calibration mixture are known, differences noted between the observed and calculated response factors indicate loss of front-end components. If a fresh calibration mixture is used, these differences can be indicative of sampling problems. Deviation of the response factors of the heavier components from the straight-line relationship could indicate problems in volatilizing the sample. Possible reasons include injection port temperature being too low, insufficient carrier gas flow, or lack of homogeneity in sampling. Figure 6 illustrates these effects. 

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