Separation of Linear Paraffins

A numerical simulation of the system has been developed in order to allow optimization of the initial design and continuous optimization of the process conditions during operation to take account of slow deactivation of the adsorbent. 

Conder, Production Scale Chromatography, in New Developments in Gas Chromatography, H. Purnell (ed.). Wiley, New York, 1973, pp. 137-185. 

Valentin, in Percolation Processes, A. E. Rodrigues and D. Tondeur (eds.), NATO ASI No. 33. Sijthoff and Noordhoff, Alphen den Rijn, Holland, 1981, p. 141. 

NATO ASI Zeolites, Esloril-Sinlra, Portugal, May, 1983 (Martinus Nijhoff, to be published). 

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The titanosilicate version of UTD-1 has been shown to be an effective catalyst for the oxidation of alkanes, alkenes, and alcohols (77-79) by using peroxides as the oxidant. The large pores of Ti-UTD-1 readily accommodate large molecules such as 2,6-di-ferf-butylphenol (2,6-DTBP). The bulky 2,6-DTBP substrate can be converted to the corresponding quinone with activity and selectivity comparable to the mesoporous catalysts Ti-MCM-41 and Ti-HMS (80), where HMS = hexagonal mesoporous silica. Both Ti-UTD-1 and UTD-1 have also been prepared as oriented thin films via a laser ablation technique (81-85). Continuous UTD-1 membranes with the channels oriented normal to the substrate surface have been employed in a catalytic oxidation-separation process (82). At room temperature, a cyclohexene-ferf-butylhydroperoxide was passed through the membrane and epoxidation products were trapped on the down stream side. The UTD-1 membranes supported on metal frits have also been evaluated for the separation of linear paraffins and aromatics (83). In a model separation of n-hexane and toluene, enhanced permeation of the linear alkane was observed. Oriented UTD-1 films have also been evenly coated on small 3D objects such as glass and metal beads (84, 85). 

Several different adsorption processes for the separation of linear paraffins have been developed including Ensorb (Exxon), IsoSiv (Union Carbide), T. S. F. (Texaco), the Shell process, and the Leuna Werke process. The latter has been called Parex (paraffin extraction) but the choice of name is unfortunate because of possible confusion with the UOP Parex process for separation of xylene isomers. All these processes use a 5A molecular sieve, generally in binderless form to minimize nonselective adsorption. The C,o-C,g linear paraffins are strongly adsorbed even at temperatures as high as 350°C. Thermal swing desorption is not feasible since the temperature required for desorption is so high that coking would occur. The alternatives are therefore vacuum desorption, which is used in some versions of the IsoSiv process, or displacement desorption which is used in most if not all of the other processes. 

Vacuum (special case of pressure swing) Rapid cycling gives efficient use of sorbent Desorbate recovered at low purity Separation of linear paraffins 5A mol sieve Shape selective sievii ... 

Commercial processes for the separation of linear paraffins from mixtures... 

There are several routes for the production of LAB. In most cases, a linear paraffin feedstock is used to produce olefins for alkylation. The paraffin feedstock is typically a mixture of linear paraffins in the range of C10-C14. The paraffins are derived from kerosene by means of adsorptive separation. 

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 separation of linear and branched alkanes is also of importance in the process known as dewaxing, in which the removal of normal alkanes makes the product hydrocarbon less viscous and reduces the so-called pour point temperature. Such processes can be combined with catalytic isomerisations to optimise the value of oil fractions (Chapter 8). Linear paraffins are also separated using a zeolite-based process from kerosene fractions to give reactants for the synthesis of linear alkylbenzene sulfonate anionic surfactants, which are both cost effective and biodegradable. 

Dbplacement Good for strongly held species. Avoids risk of cracking reactions during regeneration. Avoids thermal ageing of sorbent Product separation and recovery needed (choice of desorbent Quid is crucial) Separation of linear from branched and cyclic paraffins 5A mol sieve Shape selective sieving... 

Sorbex configuration) utilizes a 5A zeolite adsorbent and light naphtha as desorbent for the separation of linear and branched chain paraffins. Olefins may be separated from saturated hydrocarbon isomers by the Olex process using CaX zeolite as adsorbent and heavy naphtha as desorbent. Separation of fructose from glucose is achieved in the Sarex process using CaY zeolite as adsorbent and water as desorbent. All of these processes are summarized in Table 5.1. 

Olefin—Paraffin Separation. The catalytic dehydrogenation of / -paraffins offers a route to the commercial production of linear olefins. Because of limitations imposed by equiUbrium and side reactions, conversion is incomplete. Therefore, to obtain a concentrated olefin product, the olefins must be separated from the reactor effluent (81—85), and the unreacted / -paraffins must be recycled to the catalytic reactor for further conversion. 

Vista, Huntsman, and other linear alkylben2ene (LAB) producers feed chlorinated paraffins to an alkylation reactor to produce detergent alkylate without prior separation of the unreacted paraffins. Large amounts of paraffins must be recycled in these processes. 

A few companies, eg, Enichem in Italy, Mitsubishi in Japan, and a plant under constmction at Eushun in China, separate the olefins from the paraffins to recover high purity (95—96%) linear internal olefins (LIO) for use in the production of oxo-alcohols and, in one case, in the production of polylinear internal olefins (PIO) for use in synthetic lubricants (syn lubes). In contrast, the UOP Olex process is used for the separation of olefins from paraffins in the Hquid phase over a wide carbon range. 

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.)... 

The size of the free space varies slightly as a result of the size and the shape of the molecule to be included. This fact is used in the separation of molecules. A relevant example in petroleum refinement is the separation of paraffins from other compounds with urea. In this case, a channel-like lattice is formed by urea. In the free space linear alkanes (n-octane) find space, whereas branched alkanes (i-octane) cannot be included. 

Ceresine is the white end-product of the purification of the fossil wax ozokerite, which is found in Miocene lignite deposits at considerable depths, by the separation of foreign and resinous matter and decolorisation by active agents. It is harder than paraffin wax, and has linear and cyclic hydrocarbons with high molecular weight [2]. It is used for waterproofing and oil absorption. 

A particularly valuable use lor chlorparaffins is in preparation of linear, primarily internal olefins as fcedslock Ihr long-chain synthetic oxoalcohols. Typically. ii-paraffins (C M -Cu 1 are chlorinated in a IIiodized bed at ahoul 300 C. Conversion is maintained low to limit multiple chlorination. Aher separation of the monoclilorinaicd alkanes hy distillation, dehydrochlo-rinalion over nickel acetate at 3(K)LC yields the desired internal olefins. Unreacied paraffins are recycled. 

Synthetic fatty alcohols fall into three broad categories and are manufactured from two basic raw materials—ethylene and n-paraffins. One group is secondary alcohols which are prepared by oxidation of n-paraffins in the presence of boric acid. A second group consists of oxo alcohols manufactured by hydroformylation of linear olefins which are derived from either n-paraffins or ethylene. Both of these alcohol types are discussed in separate chapters. The last group is Ziegler alcohols which are prepared from ethylene and are the primary subject of this chapter. 

Description Linear paraffins are fed to a Pacol reactor (1) to dehydrogenate the feed into corresponding linear olefins. Reactor effluent is separated into gas and liquid phases in a separator (2). Diolefins in the separator liquid are selectively converted to mono-olefins in a DeFine reactor (3). Light ends are removed in a stripper (4) and the resulting olefin-paraffin mixture is sent to a Detal reactor (5) where the olefins are alkylated with benzene. The reactor effluent is sent to a fractionation section (6, 7) for separation and recycle of unreacted benzene to the Detal reactor, and separation and recycle of unreacted paraffins to the Pacol reactor. A rerun column (8) separates the LAB product from the heavy alkylate bottoms stream. 

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