Paraffin separation processes

Each Molex process employs a unique set of process operating conditions, process configuration and desorbent. The specific process details for each of the three n-paraffin separation process are revealed in this chapter, but before we review these details, we first discuss the important adsorbent and desorbent performance characteristics that are common to all. 

The n-paraffin separation process utilizes the conventional Sorbex flow scheme shown in Figure 8.1. There are three main sections of a Sorbex unit depicted (i) adsorbent chambers, (ii) Sorbex rotary valve, (iii) product/desorbent fractionation columns. As indicated earlier, desorbent is typically recycled to the Sorbex adsorbent chambers via fractionation. Figure 8.1 depicts a post-Sorbex fractionation scheme using a light desorbent. This term refers to the boiling point of the... 

The use of n-paraffins recovered include octane value enhancement of gasoline, solvents and raw materials for biodegradable detergents, fire retardants, plasticizers, alcohol, fatty acids, synthetic proteins, lube oil additives, and a-olefins. A detailed discussion on n-paraffin separation processes is available (1). 

Optimizer For MOO of the olefin/paraffin separation process, the elitist non-dominated sorting algorithm (NSGA-II) implemented in MS Excel using binary coding was employed (Sharma et al, 2012). This optimization program is referred to as EMOO for Excel-based MOO. The optimizer in Excel generates trial solutions, each of which is sent to Aspen... 

In contrast to trace impurity removal, the use of adsorption for bulk separation in the liquid phase on a commercial scale is a relatively recent development. The first commercial operation occurred in 1964 with the advent of the UOP Molex process for recovery of high purity / -paraffins (6—8). Since that time, bulk adsorptive separation of liquids has been used to solve a broad range of problems, including individual isomer separations and class separations. The commercial availability of synthetic molecular sieves and ion-exchange resins and the development of novel process concepts have been the two significant factors in the success of these processes. This article is devoted mainly to the theory and operation of these Hquid-phase bulk adsorptive separation processes. 

FacilitatedTransport Process for Eow-Cost Olefin—Paraffin Separation, ATv2iacedTec m.o ogyPi.ogt.2im.E o. 70NANB4H1528 National Institute of Science and Technology, 1994. 

So, Sulfolane and Carom, ca 1997, are two current rival processes. Sulfolane has a slight advantage over Carom ia energy consumption, while Carom has 6—8% less capital for the same capacity Sulfolane unit. In 1995, Exxon (37) commercialized the most recent technology for aromatics recovery when it used copolymer hoUow-fiber membrane ia concentration-driven processes, pervaporation and perstraction, for aromatic—paraffin separation. Once the non aromatic paraffins and cycloparaffins are removed, fractionation to separate the C to C aromatics is relatively simple. 

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). 

Because of the wide availability of chlor-alkali technology, it was decided to tender for fixed-price contracts for engineering, procurement and construction of the two chlor-alkali plants. The other areas - namely Outside Battery Limits for both plants and the chlor-paraffin plant in Melbourne - were managed by Orica under separate contracts. The chlor-paraffin plant process design (batch chlorination of paraffin oil and wax) was carried out in-house by Orica. 

The coimnerdal liquid adsorptive separation process of Ciq-Ch -olefins from Cio-Ci4 n-paraffins is another unique example of how zeolite adsorption can be applied. As shown in Table 6.1, distillation is not an option to separate C10-C14 olefins from Ciq-Cu paraffins because of their close boiling points. In this case, the UOP Olex process using NaX adsorbent is used to separate Ciq-Cm olefins from Cio-Ci4 paraffins. 

Kulprathipanja, S. (2001) Monomethyl paraffin adsorptive separation process. U.S. Patent 5,222,088 Bl. 

The fifth and final adsorbent characteristic is zeolite type. The adsorbent used in the Molex process is a proprietary and is a particularly effective adsorbent for normal paraffin separation [4, 5] and has achieved purity and recovery targets for the Molex processes. A sampUng of various molecules (and their corresponding dimensions) that Molex can easily separate is listed in Table 8.1. As discussed in Chapter 6, a zeoUtes s pore structure is dependent on its silica aluminum ratio and the proprietary Molex adsorbent possess a uniform repeating three-dimensional porous structure with pores running perpendicular to each other in the x. 

The gasoline Molex process is the first of three processes since it separates the lowest molecular weight feed of the three Molex normal paraffin separahon processes. Gasoline Molex was developed to optimize a Refiner s octane pool by extracting low octane value normal paraffins (specifically C5, 5) from naphtha. In a typical refinery flow scheme, a gasoline Molex unit is integrated with a catalyhc isomeriza-hon unit (Penex unit) which converts the Molex unit s extracted normal paraffins into desired iso-paraffins. These iso-paraffins are desirable because they possess higher octane value than their linear counterpart. 

There are three liquid-phase adsorption Sorbex technology-based separation processes for the production of olefins. The first two are the UOP C4 Olex and UOP Sorbutene processes and the third is the detergent Olex process(Cio i,5) [25, 26]. The three olefin separation processes share many similarities. The first similarity between the three olefin separation processes is that each one utilizes a proprietary adsorbent whose empirical formula is represented by Cation,([(A102)),(Si02)2] [27]. The cation type imparts the desired selectivity for the particular separation. This zeolite has a three-dimensional pore structure with pores running perpendicular to each other in the x, y and z planes [28]. The second similarity between the three olefin separation processes is the use of a mixed olefin/paraffin desorbent. The specifics of each desorbent composition are discussed in their corresponding sections. The third similarity is the fact that all three utilize the standard Sorbex bed allotment that enables them to achieve product purities in excess of 98%. The following sechons review each process in detail. 

Major commercial processes in n-paraffin separation are U.O.P. s Molex process (2-5), B.P. s process (6-8), Exxon s Ensorb process (9, 10), Union Carbide s IsoSiv process (11-13), Texaco s T.S.F. process (14, 15), Shell s process (16), and VEB Leuna Werke s Parex process (17). Except... 

Olefin Separation. U.O.P. s Olex Process. U.O.P. s other hydrocarbon separation process developed recently—i.e., the Olex process—is used to separate olefins from a feedstock containing olefins and paraffins. The zeolite adsorbent used, according to patent literature 29, 30), is a synthetic faujasite with 1-40 wt % of at least one cation selected from groups I A, IIA, IB, and IIB. The Olex process is also believed to use the same simulated moving-bed operation in liquid phase as U.O.P. s other hydrocarbon separation processes—i.e., the Molex and Parex processes. 

Union Carbide s OlefinSiv Process. Union Carbide s OlefinSiv process is used mainly to separate n-butylenes from isobutylene 31). The basic hardware is the same as for the IsoSiv process for n-paraffin separation, and the process uses a rapid cycle, fixed-bed adsorption. Since this process separates straight-chain olefins from branched-chain olefins, it is reasonable to assume that a 5A molecular sieve is used as the adsorbent. Product purities are claimed to be above 99% for both n-butylene and isobutylene streams. 

Reactive absorption is probably the most widely applied type of a reactive separation process. It is used for production purposes in a number of classical bulk-chemical technologies, such as nitric or sulfuric acid. It is also often employed in gas purification processes, e.g., to remove carbon dioxide or hydrogen sulfide. Other interesting areas of application include olefin/paraffin separations, where reactive absorption with reversible chemical complexation appears to be a promising alternative to the cryogenic distillation (62). 

Zeolites are used in separation processes for extracting p-xylene and m-xylene at high purity and recovery. There are zeolitic processes for converting C3-C7 paraffins into aromatics. In addition, zeolitic processes can co-produce aromatics and chemical-grade light olefins, or co-produce superior feedstocks for catalytic reformers and naphtha crackers. 

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