Dynan ters

The height equivalent to a theoretical plate (HETP) for a chromatographic column is approximated by the van Deem ter equation (107)  [c.303]

Theory. Most theoretical models of gas chromatographic processes are based on analogy to processes such as distillation (qv) or countercurrent extraction experiments (6). The separation process is viewed as a type of successive partitioning of the components of a mixture between the stationary and mobile phases similar to the partitioning that occurs ki distillation columns. In those experiments an important parameter is the number of theoretical plates of which the column may be considered to be composed the greater the number of theoretical plates, the greater the efficiency of the column for achieving separations of similar components. In gas chromatography, the equivalent measure of efficacy is the height equivalent to theoretical plates (HETP), which measures the ultimate abiUty of the column to separate like components. This quantity depends on many kistmmental parameters such as wall or particle diameter, type of carrier gas, flow rate, Hquid-phase thickness, etc. The theoretical expression relating these various parameters is called the van Deem ter equation, which relates the change ki efficiency to the flow.  [c.108]

The expanded version of the van Deem ter equation is used to help understand the relationships between the packing parameters and the gas flow.  [c.108]

The polypeptide chain of Src tyrosine kinase, and related family members, comprises an N-terminal "unique" region, which directs membrane association and other as yet unknown functions, followed by a SH3 domain, a SH2 domain, and the two lobes of the protein kinase. Members of this family can be phosphorylated at two important tyrosine residues—one in the "activation loop" of the kinase domain (Tyr 419 in c-Src), the other in a short  [c.275]

The basically correct equation appears to be that of Giddings but, over the range of mobile phase velocities normally employed i.e., velocities in the neighborhood of the optimum velocity), the Van Deem ter equation is the simplest and most appropriate to use.  [c.332]

The Van Deem ter equation appears to be a special case of the Giddings equation. The form of the Van Deemter equation and, in particular, the individual functions contained in it are well substantiated by experiment. The Knox equation is obtained  [c.332]

Reiterating the Van Deem ter equation,  [c.343]

From the Van Deem ter equation, H = A + — + Cu  [c.368]

Tn this approach the domain of the solution is first divided into a number of large sub-domains without leaving any gaps or overlapping. I liis division provides a very coarse unstruetured mesh which is used as the basis tor the generation of structured grids in each of its zones. The union of these local grids gives a computational grid for the entire domain, called a block-structured (or a multi-block) mesh. The flexibility gained by this approach can be used to handle complicated domains having multiply connected boundaries, problems involving heterogeneous physical phenomena and mathematical non-uniformity. Figure 6.1 shows representative examples of block-structured grids with different forms of linking or communication interface between adjacent sub-regions.  [c.193]

The top of the bench should always be kept clean and dry this can easily be done if a wet and a dry rag are kept at hand. Apparatus not immediately required (a) should be kept as far as possible in a cupboard beneath the bench if it must be placed on the bench, it should be arranged in a neat and orderly manner. All apparatus should be washed immediately after use and placed in a position to drain at the first opportunity, the apparatus should be dried. It must be emphasised that as a general rule a deposit of dirt or tar is more easily removed when it is freshly formed a suitable cleaning agent can usually be found while one still remembers the nature of the material or the circumstances attending its formation. It is hardly necessary to add that sohd waste and filter papers must not be thrown into the sink, and that all operations requiring the handhng of unpleasant and noxious materials sliould be carried out in the fume cupboard ( hood ).  [c.205]

This is my version, but may be better done. First one, evaporate methanol, better with vacuum. Then we have two layers similar in volume, we add 100 of solvent and 50 cc of basic solution (sodium carbonate, bicarbonate or 10 % NaOH ). We shake it and may be we will have little more precipitate or tar. Also may be we can t see separation, then w/e add a bit more solvent without shaking to see separation. We make two more extractions with 50 cc of solvent. Even if we can t see separation, we can add enough HCI and shake, this will forme some tar and layers will be distincts, so we can separate and make a basic wash. Sometimes I ve done first an acid wash, but I can t sure it s better. I m thinking now may be is better to do all extraction as Strike s top 3. Add acid solution, like 250 cc (less PdClz and no CuCI) 15% HCI, extract and make a basic wash.  [c.86]

In the simplest form of the method, heavy organic or inorganic Hquids, the latter usually dissolved salts in water, of appropriate (1.5—5) specific gravities are used (2,10). Higher density minerals are collected in a sink product lower density minerals are collected in a float product. A third middlings product is also sometimes collected. Examples of heavy Hquids are tri- and tetrachloroethane, tri- and tetrabromoethane, di- and triio dome thane, and aqueous solutions of sodium polytungstate, and thallium formate—malonate. The specific gravities of the medium can be varied by mixing in Hquids of lower specific gravities such as carbon tetrachloride or triethyl orthophosphate. In view of the toxicity and high cost of most of these Hquids, use is restricted to laboratory testing of ore to assess suitabiHty of ores for gravity concentration and to determine the economic separation density and minerals Hberation.  [c.406]

Extruded Rigid Foa.m. In addition to low temperature thermal insulation, foamed PSs are used for insulation against ambient temperatures in the form of perimeter insulation and insulation under floors and in walls and roofs. The upside-down roof system has been patented (256), in which foamed plastic such as Styrofoam (Dow) plastic foam is appHed above the tar-paper vapor seal, thereby protecting the tar paper from extreme thermal stresses that cause cracking. The foam is covered with gravel or some other wear-resistant topping (see Roofing materials).  [c.527]

Sulfur constitutes about 0.052 wt % of the earth s cmst. The forms in which it is ordinarily found include elemental or native sulfur in unconsohdated volcanic rocks, in anhydrite over salt-dome stmctures, and in bedded anhydrite or gypsum evaporate basin formations combined sulfur in metal sulfide ores and mineral sulfates hydrogen sulfide in natural gas organic sulfur compounds in petroleum and tar sands and a combination of both pyritic and organic sulfur compounds in coal (qv).  [c.115]

The nature of the secondary reactions is uncertain. Some beheve that the primary tar components are broken down to small free radicals that recombine as they travel toward the retort exit others suggest that some components remain relatively intact except for the removal of peripheral substituent groups and that the higher molecular weight components of coal tar are, in effect, slightly altered fragments of the original coal stmcture.  [c.343]

Steam can also be injected into one or more weUs, with production coming from other weUs (steam drive). This technique is effective in heavy oil formations but has found Httle success during appHcation to tar sand deposits because of the difficulty in connecting injection and production weUs. However, once the flow path has been heated, the steam pressure is cycled, alternately moving steam up into the oil zone, then allowing oil to drain down into the heated flow channel to be swept to the production weUs.  [c.356]

Direct coking of tar sand usiag a fluid-bed technique has also been tested. In this process, tar sand is fed to a coker or stiU, where the tar sand is heated to ca 480°C by contact with a fluid bed of clean sand from which the coke has been removed by burning. Volatile portions of the bitumen are distilled, whereas nonvolatile material is thermally cracked, resulting ia the production of more Hquid products and the deposition of a layer of coke around each sand grain. Coked soflds are withdrawn down a standpipe, fluidized with air, and transferred to a burner or regenerator, operating at ca 800°C where most of the coke is burned off the sand grains. The clean, hot sand is withdrawn through a standpipe. Part (20—40%) is rejected and the remainder is recirculated to the coker to provide the heat for the coking reaction. The products leave the coker as a vapor, which is condensed ia a receiver. Reaction off-gases from the receiver are recirculated to fluidize the clean, hot sand, which is returned to the coker.  [c.360]

Goal Tar. In roofing, coal tar is used as mopping bitumen in between 15 and 20% of the BUR roofs installed. Coal-tar pitch and asphalt are considered incompatible and should not be mixed. If mixed, an oily exudate is formed that plasticizes the bitumen, and the mixture remains soft and does not weather well. For this reason, if coal tar is used in BUR systems the felts must be coal-tar saturated. There has been some success using asphalt-coated fiber-glass mat felts with coal-tar pitch. However, this has only been done for a limited number of years so the actual compatibiHty is not fully known.  [c.321]

At about the same time a thorough study was undertaken by the Department of Agriculture to determine which dyes, if any, were safe for use in foods and what restrictions should be placed on thek use. This monumental task eventually included a study of the chemistry and physiology of the then nearly 700 extant coal-tar dyes as well as the laws of various countries and states regarding thek use in food products. Most of this investigation was done under the guidance of Dr. Bernard C. Hesse, a German dye expert (17).  [c.432]

The simplest unit employing vacuum fractionation is that designed by Canadian Badger for Dominion Tar and Chemical Company (now Rttgers VFT Inc.) at Hamilton, Ontario (13). In this plant, the tar is dehydrated in the usual manner by heat exchange and injection into a dehydrator. The dry tar is then heated under pressure in an oil-fired hehcal-tube heater and injected directly into the vacuum fractionating column from which a benzole fraction, overhead fraction, various oil fractions as side streams, and a pitch base product are taken. Some alterations were made to the plant in 1991, which allows some pitch properties to be controlled because pitch is the only product the distillate oils are used as fuel.  [c.336]

The Van Deem ter equation was confidently used to describe the peak dispersion that took place in a packed column until about 1961 when, by the use of small particles and high pressures, very high efficiency LC columns were produced. As a result of the very narrow peaks produced by these columns, it was found that, when the Van Deemter equation was tested against experimental data obtained at high linear mobile phase velocities, very poor agreement was realized. This poor agreement between theory and experiment was eventually shown to be due to the presence of experimental artifacts arising from extra-columm dispersion generated in the detector sensor, detector electronics, sample valve and connecting tubes. At the time, however, the importance of extra-column dispersion was not appreciated and certainly not fully understood. As a consequence, the apparent failure of the Van Deemter equation provoked the development of alternative HETP equations in the hope that a more exact relationship between HETP and linear mobile phase velocity could be obtained that would agree well with experimental data. As it turned out, much of this work was futile as, when appropriate precautions were taken to eliminate extra-column dispersion, it was found (and the data will be discussed in a later chapter) that the Van Deemter equation described dispersion in packed columns very accurately.  [c.261]

Abstract. The Conformational Free Energy Thermodynamic Integration (CFTI) method, a new multidimensional approach for conformational free energy simulations, is presented. The method is applied to two problems of biochemical interest exploration of the free energy surfaces of helical alanine (Ala) and a-methylalanine (Aib) homopeptides in vacuum and the cost of pre-organization of the opioid peptide Tyr-D-Pen-Gly-Phe-D-Pen (DPDPE) peptide for disulfide bond formation. In the CFTI approach a single molecular dynamics simulation with all rj) and dihedrals kept fixed yields the complete conformational free energy gradient for the studied peptides. For regular structures of model peptides (Ala) and (Aib)n where 11=6,8,10 and Aib is o-methylalanine in vacuum, free energy maps in the helical region of — space are calculated, and used to roughly locate stable states. The locations of the free energy minima are further refined by the novel procedure of free energy optimization by steepest descent down the gradient, leading to structures in excellent agreement with experimental data. The stability of the minima with respect to deformations is studied by analysis of second derivatives of the free energy surface. Analysis of free energy components and molecular structures uncovers the molecular mechanism for the propensity of Aib peptides for the 3ia-helix structure ill the interplay between the quality and quantity of hydrogen bonds. For the linear form of the DPDPE peptide in solution, free energy differences are calculated between four conformers Cyc, representing the structure adopted by the linear peptide prior to disulfide bond formation, 0c and /3e, two slightly different /3-turns previously identified as representative, stable structures of the peptide, and Ext, an extended structure. The simulations indicate that 0e is the most stable of the studied conformers of linear DPDPE in aqueous solution, with 0c, Cyc and Ext having free energies higher by 2.3, 6.3, and 28.2 kcal/mol, respectively. The free energy differences of 4.0 kcal/mol between 0c and Cyc, and 6.3 kcal/mol between 0R and Cyc, reflect the cost of pre-organizing the linear peptide into a conformation conducive for disulfide bond formation. Such a conformational change is a pre-requisite for the chemical reaction of S-S bond formation to proceed.  [c.163]

Instead of washing the reactants with water, extracting the product with ether, removing the ether then hydrolyzing, why couldn t one just hydrolyze right off the bat in the original reaction pot As it so happens this can be done. The chemist can put 200mL of 30% aqueous NaOH or 200mL 30% HCI right into the flask and reflux for 5 hours. Using NaOH to hydrolyze has two advantages it is gentler on the methylenedioxy ring structure of the X molecule and it is faster to process. After hydrolysis is over and the solution has cooled all one needs to do is extract with ether to obtain the MDA oil because using NaOH means that the MDA stays as an oil throughout. A really frugal chemist can do one extra thing to help herself out. She can take that ether/MDA layer and mix it with a few hundred mLs of 3N HCI. This, as usual, will cause the MDA to go into the water layer but what is going to be left behind in the ether besides tar is going to be a lot of unreacted, valuable P2P. The chemist saves that layer to deal with its P2P payload at another time. Meanwhile, all that remains is for the chemist to release the MDA from the water/HCI by basifying and extracting with ether.  [c.113]

Coal feedstocks dominated the chemical industry up until the 1950s. However, the volume of chemicals available from this source was not sufficient to meet wartime demands or keep up with a rapidly expanding chemical industry after the war. The emergence of the petrochemical industry provided the requited quantities, and petroleum rapidly became a more economical feedstock for chemical production (see Feedstocks, petrochemical). In Germany, petroleum did not surpass coal as a chemical feedstock until after 1961 (2). Even in the 1990s some aromatic and heterocycHc chemicals are most easily obtained from coal tar. Since the oil supply dismption problems of the 1970s, much work has been done to develop conversion processes that can transform coal economically to Hquid and gaseous fuels and chemical products. Methods to accomplish this goal include gasification, direct coal Hquefaction, and indirect Hquefaction.  [c.161]

One key step in the PBCF process is the conversion of an isotropic petroleum or coal-tar pitch to a mesophase pitch by separating or converting the low molecular weight components from the planar aromatic molecules that tend to orient under proper conditions. A simplified phase diagram for the complex pitch composition (Fig. 7) (49) shows that conversion can be done by thermally treating the pitch at elevated temperatures (typically from 350—500°C) under inert atmosphere. Alternatively solvents can be used to dissolve the low molecular weight disordering components leaving an insoluble fraction of more aromatic species that will form mesophase (50). In other processes (51), a coal-tar or petroleum pitch is hydrogenated, then heat treated to thermally strip the low molecular weight species. The partial hydrogenation of the aromatic molecules helps avoid the formation of particulate graphitic defects during carbonization that limit strength development.  [c.6]

See pages that mention the term Dynan ters : [c.284]    [c.322]    [c.18]    [c.44]    [c.319]    [c.283]    [c.134]    [c.317]    [c.56]    [c.77]    [c.147]    [c.220]    [c.139]    [c.1035]    [c.412]    [c.41]    [c.190]    [c.17]    [c.407]    [c.484]    [c.340]    [c.358]    [c.66]    [c.292]    [c.276]   
Compressors selections and sizing (1997) -- [ c.4 ]