Pressure increase

Proteins are best removed from sample before injection, and various techniques will be described in the sample preparation section for doing so (Chapter 12). If you must shoot crude sample-containing protein, use a guard column and change it often. A new guard column might be less expensive than your time needed to clean it and, certainly, will be less expensive than a new column. 

The first step is to locate the point of the pressure increase. Since most problems are column problems, we can simplify our task by eating the elephant one bite at a time. Remove the column from the system and turn on the pump. If the pressure problem goes away, it was in the column. If not, it s in the system leading up to the column. I ll deal here only with the column pressure problems, the system problems will be dealt with in Chapter 10 on troubleshooting. 

There are three areas in a column where pressure increase can occur the inlet frit, the outlet frit, and the column bed. The most likely source of 

In either case, if the frit is plugged it can usually be fixed. Open the end-cap and carefully remove the frit with the column in an upright position. (If you point it the wrong way you end up with white powder on your shoes.) Put the frit in a covered flask with 20% nitric acid (6N) and sonicate it for 1-2 min. Carefully discard the acid, add distilled water, and resonicate. Keep washing with water until the water s pH reaches lab neutral. Replace the frit, blow the end-cap thread clean with a pipette to remove silica particles that can score column treads, and retighten the endcap. 

If you reconnect the column and start the pump and the pressure persists, then you need to remove the outlet end frit in the same way. (Remember the white packing on the shoes ) Outlet pressure is due to fines in the column collecting in this filter usually only a problem if you are using the original irregular-shaped microporous columns. Sonicating with 10% sodium hydroxide can clean them since they are silica. Wash the base out repeatedly with water, replace the frit, and run the column. 

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In the case of a liquid recycle, the cost of this pressure increase is usually small. Pumps usually have low capital and operating costs relative to other plant items. On the other hand, to increase the pressure of material in the vapor phase for recycle requires a compressor. Compressors tend to have a high capital cost and large power requirements giving higher operating costs. 

The error of this method is about 10% at atmospheric pressure. The accuracy becomes lower as the pressure increases. 

Density is the most commonly measured property of a gas, and is obtained experimentally by measuring the specific gravity of the gas (density of the gas relative to air = 1). As pressure increases, so does gas density, but the relationship is non-linear since the dimensionless gas compressibility (z-factor) also varies with pressure. The gas density (pg) can be calculated at any pressure and temperature using the real gas law ... 

Unlike gases, liquid viscosity decreases as temperature increases, as the molecules move further apart and decrease their internal friction. Like gases, oil viscosity increases as the pressure increases, at least above the bubble point. Below the bubble point, when the solution gas is liberated, oil viscosity increases because the lighter oil components of the oil (which lower the viscosity of oil) are the ones which transfer to the gas phase. 

Formation water density is a function of its salinity (which ranges from 0 to 300,000 ppm), amount of dissolved gas, and the reservoir temperature and pressure. As pressure increases, so does water density, though the compressibility is small... 

After passing through several stages of processing, gas pressure may need to be increased before it can be evacuated, used for gas lift or re-injected. Inter-stage pressure increases may also be required for further processing, particularly where wellhead pressure is low. Gas is compressed to increase its pressure. 

Application of 150 MPa pressure increases the interfacial tension for w-hex-ane-water from 50.5 to 53.0 mN/m at 25°C. Calculate AV. What is AV for that area corresponding to a molecular size (take a representative molecular area to be 20 A ) Convert this to cm /cm mol. 

If an ionic surfactant is present, the potentials should vary as shown in Fig. XIV-5c, or similarly to the case with nonsurfactant electrolytes. In addition, however, surfactant adsorption decreases the interfacial tension and thus contributes to the stability of the emulsion. As discussed in connection with charged monolayers (see Section XV-6), the mutual repulsion of the charged polar groups tends to make such films expanded and hence of relatively low rr value. Added electrolyte reduces such repulsion by increasing the counterion concentration the film becomes more condensed and its film pressure increases. It thus is possible to explain qualitatively the role of added electrolyte in reducing the interfacial tension and thereby stabilizing emulsions. 

In Section XVII-16C there is mention of S-shaped isotherms being obtained. That is, as pressure increased, the amount adsorbed increased, then decreased, then increased again. If this is equilibrium behavior, explain whether a violation of the second law of thermodynamics is implied. A sketch of such an isotherm is shown for nitrogen adsorbed on a microporous carbon (see Ref. 226). 

If the triple point pressure of a solid is below one atmosphere, it will melt if the heating is conducted rapidly so that the vajiour pressure can exceed that at the triple point. If camphor is heated in a closed space, the vapour pressure increases and when the value of 360 mm. is reached, the solid will melt further heating results in an increase in the vapour pressure and the camphor will boil when the vapour pressure is 760 mm. 

The evidence obtained in compaction experiments is of particular interest in the present context. Figure 3.22 shows the results obtained by Avery and Ramsay for the isotherms of nitrogen on compacts of silica powder. The hysteresis loop moved progressively to the left as the compacting pressure increased, but the lower closure point did not fall below a relative pressure of 0-40. Similar results were obtained in the compaction of zirconia powder both by Avery and Ramsay (cf. Fig. 4.5), and by Gregg and Langford, where the lower closure point moved down to 0-42-0-45p° but not below. With a mesoporous magnesia (prepared by thermal decomposition of the hydrated carbonate) the position of the closure point... 

In many applications of mass spectrometry, it is necessary to obtain a mass spectrum from a sample dissolved in a solvent. The solution cannot be passed directly into the mass spectrometer because, in the high vacuum, the rapidly vaporizing solvent would entail a large pressure increase, causing the instrument to shut down. 

Increases in the appHed static pressure increase the acoustic intensity necessary for cavitation, but if equal number of cavitation events occur, the coUapse should be more intense. In contrast, as the ambient pressure is reduced, eventuaUy the gas-fiUed crevices of particulate matter which serve as nucleation sites for the formation of cavitation in even "pure" Hquids, wiU be deactivated, and therefore the observed sonochemistry wiU be diminished. 

The heat of reaction is approximately 147 kj/mol (35.1 kcal/mol) (23). Optimum yields of ketene [463-51-4] require a temperature of about 730—750°C. Low pressure increases the yield, but not the efficiency of the process. Competitive reactions are... 

The typical operating pressure of filter presses is 600 or 700 kPa, although some manufacturers offer presses for 2000 kPa or higher. As the pressure increases during filtration, it forces the plates apart this maybe offset by a pressure compensation faciHty offered with some large mechanized presses. 

Most small Hquid helium containers are unpressurized heat leak slowly bods away the Hquid, and the vapor is vented to the atmosphere. To prevent plugging of the vent lines with solidified air, check valves of some sort are included in the vent system. Containers used for air transportation are equipped with automatic venting valves that maintain a constant absolute pressure with the helium container in order to prevent Hquid flash losses at the lower pressures of flight altitudes and to prevent the inhalation of air as the pressure increases during the aircraft s descent. Improved super insulation has removed the need for Hquid nitrogen shielding from almost all small containers. 

Increasing pressure increases yields of methanol and ethanol, increases the C2H 0H CH20H ratio, and reduces yields of acetaldehyde and formaldehyde (96,97,130). Ethylene is insignificant at 790 kPa (7.8 atm) even at 460°C (96). 

Heats of adsorption for hydrocarbons typically range from —20 to —70 kJ/mol (—4.8 to —16.7 kcal/mol ). Equations 1 and 4 both indicate that vapor pressures increase exponentially with increasing temperature. 

It foUows from these two equations that the water flux is proportional to the appHed pressure, but the salt flux is iadependent of pressure. This means the membrane becomes more selective as the pressure increases. Selectivity can be measured ia a number of ways, but conventionally, it is measured as the salt rejection coefficient, R, defined ia equation 6. 

Ru(1PP)2(00)2, at 2000 ppm mthenium and 1-hexene as substrate, gives only an 86% conversion and a 2.4 1 linear-to-branched aldehyde isomer ratio. At higher temperatures reduced conversions occur. High hydrogen partial pressures increase the reaction rate, but at the expense of increased hydrogenation to hexane. Excess triphenylphosphine improves the selectivity to linear aldehyde, but at the expense of a drastic decrease in rate. 

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