N-Paraffin separation

The IsoSiv process is an isobaric, isothermal adsorption technique used to separate n-paraffins from gas oils. The operation conditions are approximately 370°C and 100 psi. Desorption is achieved using n-pentane or n-hexane. The solvent is easily distilled from the heavier n-paraffins and then recycled. 

The SMB process was invented by Broughton in 1961 and developed by Universal Oil Products under the general name Sorbex . Initially used for separating n-paraffins in bulk, it is now used for a variety of individual-isomer separations and class separations, and is currently attracting considerable interest for separating pharmaceutical enantiomers. The SMB process is described in Section 17.9.4 and in a growing literaturel-21 22>11 - 74),... 

A 5 43 21.5 n-C4H,OH. Iso compounds, 4 carbons rings and larger Separates n-paraffins from branched and cyclic hydrocarbons... 

The LAB production process (process 1) is mainly developed and licensed by UOP. The N-paraffins are partially converted to internal /z-olefins by a catalytic dehydrogenation. The resulting mixture of /z-paraffins and n-olefins is selectively hydrogenated to reduce diolefins and then fed into an alkylation reactor, together with an excess benzene and with concentrated hydrofluoric acid (HF) which acts as the catalyst in a Friedel-Crafts reaction. In successive sections of the plant the HF, benzene, and unconverted /z-paraffins are recovered and recycled to the previous reaction stages. In the final stage of distillation, the LAB is separated from the heavy alkylates. 

As a result of its highly polar character, silica gel is particularly useful in the separation of polarizable materials such as the aromatic hydrocarbons and polynuclear aromatics. It is also useful in the separation of weakly polar solute mixtures such as ethers, esters and in some cases, ketones. The mobile phases that are commonly employed with silica gel are the n-paraffins and mixtures of the n-paraffins with methylene dichloride or chloroform. It should be borne in mind that chloroform is opaque to UV light at 254 nm and thus, if a fixed wavelength UV detector is being used, methylene dichloride might be a better choice. Furthermore, chloroform is considered toxic and requires special methods of waste disposal. Silica gel is strongly deactivated with water and thus, to ensure stable retentive characteristics, the solvent used for the mobile phase should either be completely dry or have a controlled amount of water present. The level of water in the solvent that will have significant effect on solute retention is extremely small. The solubility of water in n-heptane is... 

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. 

In this chapter a two a selectivity model is proposed that is based on the premise that the total product distribution from an Fe-low-temperature Fischer-Tropsch (LIFT) process is a combination of two separate product spectrums that are produced on two different surfaces of the catalyst. A carbide surface is proposed for the production of hydrocarbons (including n- and iso-paraffins and internal olefins), and an oxide surface is proposed for the production of light hydrocarbons (including n-paraffins, 1-olefins, and oxygenates) and the water-gas shift (WGS) reaction. This model was tested against a number of Fe-catalyzed FT runs with full selectivity data available and with catalyst age up to 1,000 h. In all cases the experimental observations could be justified in terms of the model proposed. 

Non-aromatic hydrocarbons separation (e.g., olefin/paraffin, -paraffin/ non-n-paraffin) ... 

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. 

Examples of rate-selective adsorption are demonstrated using silicalite adsorbent for separation of Ciq-Cm n-paraffins from non- -paraffins [40, 41] and Ciq-Ch mono-methyl-paraffins from non-n-paraffins [42-45]. Silicalite is a ten-ringed zeolite with a pore opening of 5.4A x 5.7 A [22]. In the case of -paraffins/non-n-paraffins separation [40, 41], n-paraffins enter the pores of silicalite freely, but non-n-paraffins such as aromatics, naphthenes and iso-paraffins diffuse into the pores more slowly. However, the diffusion rates of both normal -paraffins and non-n-paraffins increase with temperature. So, one would expect to see minimal separation of n-paraffins from non-n-paraffins at high temperatures but high separation at lower temperature. 

For the rate-selective separation of Ciq-Ch mono-methyl-paraffins from non-n-paraffins [42-45], diffusion simulations were carried out using the Solids Diffusion module in the Accelrys Insight II molecular modeling package [44]. The modeling results from the diffusion simulations of four paraffins of varying carbon numbers in siUcalite are summarized in Table 6.9. 

Figure 6.2 illustrates the separation of n-Csis and non-n-Cs/is in CaA molecular sieves or 5A. The separation mechanism is obvious when the kinetic diameter of the molecules and molecular sieve pore size opening are compared. n-Csjc have kinetic diameters of less than 4.4 A which can diffuse freely into the 4.7 A pores of the CaA molecular sieve, while non-n-Cs/ have kinetic diameters of 6.2A. A commercial example of shape-selective adsorption is the UOP Molex process, which uses CaA molecular sieves to separate Cio-C n-paraffins from non- -parafHns (aromatics, branched, naphthenes). 

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 UOP MaxEne process for the separation of n-paraffins from branched and cyclic hydrocarbons found in full-range naphtha is based on the well established. 

In 1998, UOP announced the development of a new Sorbex process called the MMP Sorbex process [15-19] that was capable of simultaneously separating both Cio i6 mono-branched paraffins and Cio i6 normal paraffins from a corresponding kerosene stream or n-paraffin-depleted Molex raffinate stream. Previously, no commercial process existed to isolate significant quantities of mono-methyl paraffin derived from either kerosene or n-paraffin depleted kerosene. Mono-methyl paraffins are desirable because they are needed for a new type of anionic surfactant. 

The MMP Sorbex process has many similarities but also some differences when compared to the detergent Molex process. As with all of Sorbex processes, the MMP Sorbex process operates in the Uquid phase, employing suitable conditions (pressure, temperature) to overcome any diffusion constraints to achieve target performance. Table 8.4 highlights and contrasts the different characteristics of the detergent Molex and MMP Sorbex processes. The process was successfully demonstrated in a continuous countercurrent moving bed separation pilot plant using commercial n-paraffin-depleted kerosene (Molex raffinate) feedstock. A typical gas... 

Sweetening of light hydrocarbon streams n-paraffin separation improving jet fuel quality purification of aromatics... 

Except for those few hydrocarbons in the volatile range that have boiling points relatively far from their neighbors, and for certain other hydrocarbons present in relatively large amount (as n-paraffins in a Pennsylvania or a Michigan petroleum), regular distillation alone will not separate pure hydrocarbons from petroleum, and one or more of the other methods (including the variations of distillation) must also be used. 

A part of the wax portion, which contained a considerable amount of oil in addition to the true wax, was further processed by fractionation by adsorption and by treatment with urea to form adducts of the latter with the n-paraffins. The wax portion was found to contain about 8% of aromatic hydrocarbons, which had been imperfectly separated from the main bulk of the aromatic hydrocarbons occurring in the extract oil portion. Of the remaining 92% of the wax portion, about 39% was determined to be n-paraffins and 53% cycloparaffins, with possibly a relatively small amount of branched paraffins. 

The quantity of each of the final homogeneous fractions of both in water-white oil and extract oil portions was about 15 grams, representing V oooth part of the original crude petroleum from which it came, and consisted of compounds of substantially similar sizes and types. These fractions, although far from being pure compounds, appear to be nearer to pure compounds than any material (except n-paraffin hydrocarbons) hitherto separated from the lubricant fraction of any crude petroleum. 

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). 

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... 

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