Olefins liquid separation

Highly pure / -hexane can be produced by adsorption on molecular sieves (qv) (see Adsorption, liquid separation) (43). The pores admit normal paraffins but exclude isoparaffins, cycloparaffins, and aromatics. The normal paraffins are recovered by changing the temperature and/or pressure of the system or by elution with a Hquid that can be easily separated from / -hexane by distillation. Other than ben2ene, commercial hexanes also may contain small concentrations of olefins (qv) and compounds of sulfur, oxygen, and chlorine. These compounds caimot be tolerated in some chemical and solvent appHcations. In such cases, the commercial hexanes must be purified by hydrogenation. 

FIG. 11 Production of linear olefins from linear paraffins. AC, adsorbent chamber EC, extract column GLS, gas-liquid separator H, heater Rx, reactor RC raffinate column ST, stripper column LE, light end. (From Ref. 10.)... 

Because the thermal separation of products has been substituted by a liquid-liquid separation, the two phase technology should be best suited for hydroformylation of longer chain olefins. But with rising chain length of the olefins the solubility in the aqueous catalyst phase drops dramatically and as a consequence the reaction rate. Only the hydroformylation of 1-butene proceeds with bearable space-time yield. This is applied on a small scale for production of valeraldehyde starting from raffinate II. Because the sulfonated triphenylphosphane/rhodium catalyst exhibits only slow isomerization and virtually no hydroformylation of internal double bonds, only 1-butene is converted. The remaining raffinate III, with some unconverted 1-butene and the unconverted 2-butene, is used in a subsequent hydroformy-lation/hydrogenation for production of technical amylalcohol, a mixture of linear and branched C5-alcohols. 

The reactor effluent is cooled and fed to the ethylene separator for recovery of unreacted gaseous ethylene. The liquid phase is filtered to remove small amounts of polymer and then treated with aqueous caustic to remove the catalyst. The dissolved light ends (C2 and C4 olefins) are separated by suitable fractionating towers in series. A portion of the ethylene is purged to remove methane and ethane, and the remaining ethylene is recycled to the compressor. The butene-1 is removed to storage. 

D.T. Tsou, M.W. Blachman and J.G. Davis, Silver-facilitated Olefin/Paraffin Separation in a Liquid Membrane Contactor System, Ind. Eng. Chem. Res. 33, 3209 (1994). 

Unreacted ethylene from the separator (5) is recycled via a compressor (6) and a heat exchanger (7) together with ethylene makeup to the reactor. A liquid stream is withdrawn from the reactor (1) containing liquid a-olefins and catalyst, which is removed by the catalyst removal unit (8). The liquid stream from the catalyst removal unit (8) is combined with the liquid stream from the primary separation (5). These combined liquid streams are routed to a separation section in which, via a series of columns (9), the a-olefins are separated into the individual components. 

Bessarabov DG, Theron JP, and Sanderson RD. Novel application of membrane contactors Solubility measurements of 1-hexene in solvents containing silver ions for liquid olefin/paraffin separations. Desalination, 1998 115(3) 279-284. 

Nymeijer K. Gas-liquid membrane contactors for olefin/paraffin separation. PhD Thesis, University of Twente, The Netherlands, ISBN 90-365-1878, 2003. 

Normal Paraffin-Based Olefins, Detergent range -paraffins are currently isolated from refinery streams by molecular sieve processes (see ADSORPTION, LIQUID separation) and converted to olefins by two methods. In the process developed by Universal Oil Products and practiced by Enichem and Mitsubishi Petrochemical, a -paraffin of the desired chain length is dehydrogenated using the Pacol process in a catalytic fixed-bed reactor in the presence of excess hydrogen at low pressure and moderately high temperature. The product after adsorptive separation is a linear, random, primarily internal olefin. Shell formedy produced olefins by chlorination—dehydrochlorination. Typically, C —C14 -paraffins are chlorinated in a fluidized bed at 300°C with low conversion (10—15%) to limit dichloroalkane and trichloroalkane formation. Unreacted paraffin is recycled after distillation and the predominant monochloroalkane is dehydrochlorinated at 300°C over a catalyst such as nickel acetate [373-02-4]. The product is a linear, random, primarily internal olefin. 

During the early 1960s, linear aliphatic olefins, such as a olefins produced via ethylene oligomerization or linear internal olefins produced via catalytic dehydrogenation of linear paraffins, replaced the use of propylene tetramers ia iadustrialized countries, and production of more biodegradable linear alkylbenzene sulfonates (LABS) began (see ADSORPTION, LIQUID SEPARATION) (70). Except ia a few parts of the world, the use of DDES was phased out by 1980. 

The aromatic content of hydrocarbon mixture is estimated from the determination of aniline point.Aromatic hydrocarbons have the lowest and paraffins the highest aniline points. Cycloparaffins and olefins are between the two. Aniline point increases as the molecular weight increases. A mixture of specific aniline and solvent is heated at a controlled rate until it forms one phase. The mixture is then cooled and the temperature at which the miscible liquid separates into two phases is determined. Four methods are discussed in the standard suitable for transparent, non-transparent, easily vaporizing, and measured in small quantities. 

Olefin / Paraffin separation using Task-Specific Materials based on Ionic Liquids. 

To further investigate the liquid-liquid extraction capacity, the selectivity and distribution coefficient, which are two useful indices for evaluating the performance of olefin/parafihi separation, were determined as follows [10-12]... 

After the oligomerization reactor and the liquid-liquid separator, the organic product has to undergo an intensive product wash to make sure that no catalyst enters the distillation columns. In the following series of distillations, the technically desired 1-alkene cut Ce-Cig is separated and the too light C4 and the too heavy C18+ cuts are combined and isomerized to internal linear olefins in the isomerization reactor. These internal alkenes are then converted in the metathesis reactor to form internal alkenes. The desired C -Cig fraction is isolated, whereas the lights and the heavies are again recycled into the isomerization reaction. 

Similar copolyimide was prepared using 3,7-diamino-2,8(6)-dimethyldibenzothiopheneS,5-dioxide (DDBT) instead of m-SED and its performance for olefin/paraffm separation was investigated [74]. Block copolymers of liquid crystalline polyamide and amorphous PI were prepared from a two-pot polycondensation reaetions [75]. Hydrocarbon (C-2 and C-3) separations in copolyimide dense membranes derived from 6FDA, DDA and 1,5-naphthalene diamine (NDA) was studied [76]. Gas transport properties of 6FDA, DDA and 3, 3 -diaminodiphenyl sulfone (DIDS) was reported [77]. 

Vijitjunya, P. (2001). Dispersed liquid/pol3fmer mixed matrix membrane for olefin/paraffin separation. M.S. Thesis, The Petroleum and Petrochemical College, Chulalongkom University, Bangkok, Thailand. 

K. Nymeijer, T. Visser, R. Assen, M. Wessling, Super selective membranes in gas-liquid membrane contactors for olefin/paraffin separation, J. Memb. Sci. 232 (2004) 107-114. 

Another example of unique selectivities is the separation of olefins from paraffins in feed mixtures containing about five successive molecular sizes, eg, C Q to Liquid—Hquid extraction might be considered for this separation. However, polar solvents give solubiHty patterns of the type shown in Figure... 

Displacement-purge forms the basis for most simulated continuous countercurrent systems (see hereafter) such as the UOP Sorbex processes. UOP has licensed close to one hundred Sorbex units for its family of processes Parex to separate p-xylene from C3 aromatics, Molex tor /i-paraffin from branched and cyclic hydrocarbons, Olex for olefins from paraffin, Sarex for fruc tose from dextrose plus polysaccharides, Cymex forp- or m-cymene from cymene isomers, and Cresex for p- or m-cresol from cresol isomers. Toray Industries Aromax process is another for the production of p-xylene [Otani, Chem. Eng., 80(9), 106-107, (1973)]. Illinois Water Treatment [Making Wave.s in Liquid Processing, Illinois Water Treatment Company, IWT Adsep System, Rockford, IL, 6(1), (1984)] and Mitsubishi [Ishikawa, Tanabe, and Usui, U.S. Patent 4,182,633 (1980)] have also commercialized displacement-purge processes for the separation of fructose from dextrose. 

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