摘要:

Dense (supercritical) gas chromatography and the related rapidly growing field of dense gas extraction are reviewed and an extensive compilation detailing the dense gas systems (solvent gases, solutes, temperatures, pressures) that have been studied is presented. Furthermore, dense gas chromatography is compared to both gas and high performance liquid chromatographies with emphasis on mass spectrometric detection in all three. “It is concluded that a dense gas chromatograph/mass spectrometer, a new instrument, is both a complement to existing techniques and a timely development for use with dense (supercritical) gas systems.”

ISSN:0149-6395    

DOI:10.1080/01496398208058142

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The potential scope and possible areas of application of gas extraction as a separation technique are outlined. Some problems to be overcome are discussed and the need for accurate physical data determinations and also operating experience at pilot plant level are stressed. Some work directed towards fulfilling these needs is described. Reliable economic, appraisal is essential before large scale design can be contemplated but is probably not practicable with sufficient accuracy until the above needs have been met.

ISSN:0149-6395    

DOI:10.1080/01496398208058143

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The supercritical gas extraction of South African coals was carried out using semi-continuous reactors. The conversion (to liquid and gaseous products) increases as the volatile matter yield or the H/C atomic ratio of the coal increases and as the critical temperature or the Hildebrand solubility parameter of the solvent increases. The effect of pressure and temperature on the conversion is discussed. The chemical nature of the oils (hexane soluble product) from supercritical gas extraction at 350°C and 450°C is also reported.

ISSN:0149-6395    

DOI:10.1080/01496398208058144

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

In the separation by silica-gel chromatography of the. total-alkane fractions of supercritical-gas (SCG) extracts of Turkish lignites, and in the subsequent 5Å-molecular-sieve adsorption to yield the branched/cyclic alkane subfraction, progress may be monitored by gas-liquid chromatography (GLC) and1H nuclear-magnetic-resonance (NMR) spectroscopy. Saturated aliphatic hydrocarbons identified by gas chromatography/mass spectrometry from one lignite include normals n-C13to n-C33inclusive, acyclic isoprenoids C18, C19, and C20, and two C31pentacyclic (triterpane) and one (C15) dicyclic cycloalkanes. The distributions of n-alkanes depend more on extraction conditions than do the distributions of acyclic isoprenoids and cycloalkanes. Overall, batchwise SCG extraction of low-rank coals with toluene or tetrahydrofuran at about 350°C appears to cause little thermolysis and can yield relatively large quantities of paraffinic hydrocarbons, representative of the original coals, and useful as geochemical markers.

ISSN:0149-6395    

DOI:10.1080/01496398208058145

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Samples of spruce wood and of dioxane-lignin prepared from spruce wood were subjected to supercritical dioxane extraction at 330 C. To compare the yield and the nature of the compounds present in distillate obtained upon pyrolysis to those of supercritical gas extract, the same samples were pyrolysed at 340°C.

ISSN:0149-6395    

DOI:10.1080/01496398208058146

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The solubility of fatty acids and their glycerides in dense supercritical gases increases with increasing pressure at constant temperature. The temperature influences the solution equilibria in a more complicated way than the pressure. Addition of an entrainer increases the solubility in the gas phase. Furthermore, the temperature dependence of the solvent power is increased so much that the regeneration of the circulating gas in a separation process becomes possible by a change of temperature only. By a suitable entrainer the separation factor can also be improved.

ISSN:0149-6395    

DOI:10.1080/01496398208058147

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The mean-field lattice-gas model in the present form has proven to be well able to describe nearly quantitatively fluid phase behaviour of non-polar and polar pure components and mixtures over a large temperature and pressure range. In our version of the model it is assumed that: all lattice sites have the same volume, independent of temperature and pressure, and that every kind of lattice site has a characteristic interacting surface area. The combinatory entropy of the system is corrected with an empirical parameter. For mixtures the same procedure cart be followed and a description of fluid phase behaviour, based upon the parameters of the pure components and two binary interaction parameters, appear to come out quite reasonably.

ISSN:0149-6395    

DOI:10.1080/01496398208058148

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

For the design of separation processes with supercritical dense gases, referred to as vapour phase extraction processes, high-pressure vapour-liquid equilibria have to be known. In the present investigation the Redlich-Kwong equation of state has been applied to a parametric study of high-pressure phase equilibria. The study has developed a generalized description of the phase behaviour of binary and multicomponent systems and provided general rules for the design of vapour phase extraction processes.

ISSN:0149-6395    

DOI:10.1080/01496398208058149

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Binary diffusion coefficients D12have been determined for benzene, phenol, naphthalene and caffeine in supercritical CO2at 40°C between 80 and 160 bar using the chrpmatographic peak-broadening method (CPB). The observed diffusion coefficients are of the order of 10−4cm2/s and decrease by about 50% for a pressure rise from 80 to 160 bar. For naphthalene in CO2the effect of temperature on D12was investigated between 35 and 60°C at a constant C02 density of 0.6 g/cm3; the energy of activation was found to be 4.7 kJ/mol, With increasing molecular size and polarity of the diffusing compound, adsorption effects are observed which can lead to serious errors.

ISSN:0149-6395    

DOI:10.1080/01496398208058150

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The versatility of dense gases or supercritical fluids as solvents is briefly reviewed., It is pointed out that gas density is the key parameter controlling solvent power and it is argued that density programming should replace pressure programming for chro-matographlc and extractive separations. Our previous theory of dense gas solubility and solubility thresholds is then used to explain why relatively high pressures are desirable for dense gas separations. The theory is also used to examine peak spacing for linear density programs to develop a speeial density program for uniform peak spacing.

ISSN:0149-6395    

DOI:10.1080/01496398208058151

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor