Ethene/ethane separation

Bux H, Chmehk C, Krishna R, Caro J. Ethene/ethane separation by the MOE membrane ZlE-8 Molecular correlation of permeation, adsorption, diffusion. J Membr Sci 2011 369(1-2) 284-289. 

Successful separation of alkanes and alkenes has been documented when microporous membranes have been used [79,138]. The physiochemical properties, size, and shape of the molecules will play an important role for the separation, hence critical temperatures and gas molecule configurations should be carefully evaluated for the gases in mixture. On the basis of gas properties and process conditions, the separation may be performed according to selective surface flow or molecular sieving (refer to Section 4.2 on transport). The transport may also be enhanced by having a Ag compound in the membrane. The Ag ion will form a reversible complex with the alkene, and facilitated transport results. Selectivities in the range of 200-300 have been reported for separation of ethene-ethane and propene-propane [138]. Successful separation of alkanes and alkenes will be important for the petrochemical industry. Today the surplus hydrocarbons in the purge gas are usually flared. Membranes which should be suitable for this application are the carbon molecular sieves (see Section 4.3.2) and nanostructured materials (Section 4.3.3). 

In the conditions used, all the catalysts were active for the combustion of ethane, producing conversions from 1-5 % at 573 K up to 40 % at 648 K. The only detected products were CO2, H2O and small amounts of ethene, that is consistent with a triangular reaction scheme involving parallel formation of CO2 and ethene and the consecutive combustion of ethene. In separate measurements of CO oxidation on these catalysts, made in a Fl lR cell [26], CO was transformed conipletely into CO2 at tenoperatures as low as 573 K This would e q)lain the absence of CO among the reaction products of ethane oxidation, carried out here at hi er tenq>eratures. Fig. 3 shows the variation of areal rates of ethane oxidation over the LKx and NKx catalysts with terrqrerature. In all cases, ethane conversion increased with increasing... 

The reaction of ethanol with the catalyst with and without hydrogen was investigated. On passing ethanol in a helium carrier over the catalyst at 413 K, four gas-phase products were detected ethanal, hydrogen, water and ethene/ethane (these were not separated on the GC column). When ethanol was passed over the catalyst at 413 K in a hydrogen carrier only water and ethene/ethane were detected. 

Synthesis ofp-Ethyltoluene. j )i7n7-Ethyltoluene, the feedstock for j )-methylstyrene, is difficult to separate from the products of toluene alkylation with ethane using conventional acidic catalysts. The unique configurational diffusion effect of ZSM-5 permits -dialkylbenzenes to be produced in one step. In the alkylation of toluene with ethene over a chemically modified ZSM-5, -ethyltoluene is obtained at 97% purity (58). 

Particularly the chlorinated compounds have enjoyed range of applications vinyl chloride (chloro-ethene) as monomer for the production of PVC, tetra- and trichloroethenes as solvents for degreasing, and the insecticides l,l,l-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and isomers of hexachlorocyclohexane (HCH) (benzene hexachloride). The biodegradation of fluorinated aliphatic compounds is generally different from the outlines that have emerged from investigations on their chlorinated, brominated, and even iodinated analogues. They are therefore treated separately in Part 4 of this chapter. 

Consideration of the degree of metal substitution at the carbons of the C2 fragment and the separations of the two carbon atoms, has led to the formulation of polymetallic species as permetallated ethyne (E), ethene (F), or ethane (G) (Chart 2).35 Addition of metal fragments to the unsaturated species E leads to sequential formation of F and G and progressive saturation of the C=C triple bond. These ideas are broadly consistent with the results of computational studies (Section IX.D). Compounds of type E are described below, while the more highly metallated species are discussed in Sections VII, VIII, and IX. 

Transition metal derivatives assume p-p1 rj1 bridging modes which are assigned electronic structures H, I or J (Chart 3) on the basis of the central C-C separation, which can be related to those in ethyne (1.21 A), ethene (1.34 A), or ethane (1.53 A), respectively. 

Carbon atoms are well known for their tendency to link together to form the millions of organic molecules that are known. We can work out the simpler hydrocarbon chains by looking at each central atom separately. Thus ethene consists of two plane-trigonal CH2 units joined together, whereas ethane is essentially two CH3 tetrahedra joined end-to-end. 

Fig. 29. H PFG Fourier transform NMR spectra of an ethane-ethene mixture in NaX (1.5 C2H6 plus 1 C2H4 per supercage, 293 K) for increasing values of the width (S) of the field gradient pulses. The pulse separation (t) and the field gradient intensity (g) are 4 ms and 2.8 T m. The chemical shifts Si refer to TMS (/2S).

Figure 6b Fluxes of mixtures of ethane (A) and ethene (9) through a silicalite-1 membrane as a function of mol fraction in the feed (P = 101.3 kPa, T = 297 K). Feed was composed of 100% hydrocarbon (mol fraction of ethene = 1 - mol fraction of ethane) sweep gas used was helium. The measured separation selectivity toward ethane is also given (+) together with the separation selectivity predicted from single-component fluxes for identical partial pressures ratios ( ).

Reactions of n-hexane (nH) were studied in a closed loop glass circulation reactor [5, 8]. The catalyst (50 mg) was heated in air at 773 K and reduced in situ at 723 K with 500 Torr H2 for 3 h (with a liquid nitrogen trap). After evacuation, reaction mixtures consisting of 10 or 40 Torr n-hexane and 120 Torr hydrogen were introduced and runs between 5 and 50 (in some cases 0.5 and 135) min were carried out between 603 and 693 K. The products were analyzed by a capillary GLC column (50 m by 0.32 mm fused silica, CP Sil 5 coating) on a Packard Twe 437 GC. The range of analysis embraced Cj-Cg hydrocarbons including Cg aromatics. The pairs ethane-ethene and propane-propene could not be separated properly. Selectivities were calculated on the basis of effluent composition. 

In 1864, ethylene was first expressed graphically in its modem form with a double bond connecting the two carbon atoms (CH2=CH2). This was adopted by Wanklyn to represent the constitutional formula of rosaniline (6), and made public in September of that year at the annual meeting of the British Association for the Advancement of Science, held in Bath. Wanklyn s ethylene-type formula showed two carbon atoms separated from the four hydrogen atoms by a bracket18. The ethylene type, unlike other type formulas, was used only to express the constitutions of coal-tar dyes. Wanklyn argued that the constitutions of the members of the rosaniline series could be expressed by his ethylene type by virtue of known reduction and replacement reactions. Thus he compared the conversion of 6 into colorless leucaniline (10) with the ready reduction of ethylene (ethene) (11) to ethane (12), both of which involved the addition of two hydrogen atoms (Scheme 4)19 21. 

Chain-growth polymerization involves the sequential step-wise addition of monomer to a growing chain. Usually, the monomer is unsaturated, almost always a derivative of ethene, and most commonly vinylic, that is, a monosubstituted ethane, 1 particularly where the growing chain is a free radical. For such monomers, the polymerization process is classified by the way in which polymerization is initiated and thus the nature of the propagating chain, namely anionic, cationic, or free radical polymerization by coordination catalyst is generally considered separately as the nature of the growing chain-end may be less clear and coordination may bring about a substantial level of control not possible with other methods. ... 

Supercritical or near-critical fluids can be used both for extraction and chromatography. Many chemicals, primarily organic species, can be separated and analyzed using this approach [6], which is particularly useful in the food industry. Substances that are useful as supercritical fluids include carbon dioxide, water, ethane, ethene, propane, xenon, ammonia, nitrous oxide, and a fluoroform. Carbon dioxide is most commonly used, typically at a pressure near 100 bar. The required operating pressure ranges from about 43 bar for propane to 221 bar for water. Sometimes a solvent modifier is added (also called an entrainer or cosolvent), particularly when carbon dioxide is used. 

Brunner, E. 1985. Fluid mixtures at high pressures II. Phase separation and critical phenomena of (ethane + n-alkanol) and of (ethene + methanol) and (propane + methanol). J. Chem. Thermodynamics 17 871-885. 

WGSR conditions were found useful for hydrodechlorination of 1,2-dichloroethane [369], The primaiy product of the reaction is ethene (Scheme 3.62) which is reduced further to ethane in a separate catalytic cycle. 

High-resolution analysis of the entire suite of C2-C12 NMHCs by conventional one-dimensional gas chromatography is typically performed with various siloxane-coated fused-silica capillaries or PLOT columns. Designing a single GC analysis which will adequately separate the entire complex mixture is very difficult to achieve, because ethene, acetylene, and ethane are difficult to separate, even with a 100 m siloxane-coated column. Furthermore, separations with a column of this length take approximately 70 min. The PLOT columns can completely resolve the C2-C3 NMHCs, but resolution of the Cg-Ci2 NMHCs is poor. If the sample is analyzed separately in a 60 m siloxane column, mounted in one GC and a PLOT column mounted in another, the analyses can be completed in approximately 45 min. The preconcentrated sample is transferred to a 60 m X 0.32 mm i.d. fused-silica capillary column coated with a 1 /rm-thick film of poly-dimethylsiloxane (PDMS) and a 30 m X 0.53 mm i.d., PLOT column coated with alumina to resolve the C4-C12 and C2-C3 NMHCs, respectively. The oven temperature for the PDMS column is held at — 50°C for 2 min, then increased to 210°C at 8°Cmin and thereafter to 250°C at... 

The separation of olefin and paraffins, particularly the C2 (ethane/ethene) and C3 (propane/propene) pairs is an extremely important and demanding separation in die petrochemical industry (56). It is currently performed via cryogenic distillation and is thus energy (and capital) intensive. Thus, the use of zeolites to perform this separation has been studied intensely. While many zeolites have been investigated to selectively adsorb the olefin, PSA-type approaches are not currently used for this separation. More recently, small-pore zeolites have been reported wherein a clear kinetic separation is observed in that the diffusion of propylene is dramatically faster than that of propane (57, 58). This potentially represents a significant breakthrough in the field. 

CH3) as alternatives to symmetrically-bonded species, either in the predominant route to ethene" and ethane, or just in conditions of low selectivity " (ii) the probable operation of two or three separate types of site during ethyne hydrogenation with excess ethene (Table 9.6) (iii) the likely importance of carbonaceous deposits in determining selectivity or in creating sites at which selective reaction can occur " and (iv) face sensitivity. Other imponderables already noted include the possible formation of carbide and hydride phases in palladium. To add to the misery, we have seen that even the sense of the particle size effect on TOF and selectivity cannot be agreed (Table 9.6), and supports appear to exert an important but poorly understood influence. 

The compositional modulation technique has been applied to the Fischer-Tropsch synthesis (FTS) reaction [2-5], It was found that the cyclic feeding of CO/H2 had an influence on the selectivity of the FTS products. Among the conclusions was that for an iron catalyst the selectivity for methane increased under periodic operation compared to the steady state operation [5], In the study [5] it was found that the propane/propene ratio increased under periodic operation and the largest changes were with periods between one and ten minutes. Due to the limitations of the anal5dical technique utilized, they could not separate ethane and ethene so that the selectivity basis was for the C3 hydrocarbons. In this study the analytical procedure permitted analysis of products only to the Cg-compoimds. 

ABSTRACT. An isosteric sorption system has been used to study the sorption of methane, ethane, ethene, propane, N2 and CO2 and some of their binary mixtures in silicalite-1. Isotherms of some of these sorbates have been determined at equilibrium pressures up to 20 atmospheres. Isosteric heats of sorption have been obtained from the slopes of the isosteres. Separation factors calculated from the Henry s Law constants determined from the initial slopes of the single conq>onent isotherms are found to be in good agreement with experim tal separation factors. The Langmuir-Freundlich equation has be used to lit the single component data and the Ideal Adsorbed Solution theory has be used to predict a binary sorption isotherm from the respective single component data. Comparison of the sorption behaviour of the hydrocarbons in silicalite-1 and NaY zeolites has been made. 

The aromatization of propane on supported (Si02/Al203)Ga, Zn or Pt catalysts is limited due to hydrocracking, dealkylation and hydrogen transfer reactions which lead to the formation of methane and ethane as the major products, and ethene and propene. However, the use of a Pd membrane reactor increases the yield of aromatics (e.g. benzene, toluene, Cg-Ci2 aromatics) dramatically by effective separation of the produced hydrogen gas from the reaction mixture by utilizing the H2 permeability of Pd thin films. 

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