Separation light olefins from paraffins

Application Separation of pure C4 olefins from olefinic/paraffinic C4 mixtures via extractive distillation using a selective solvent. BUTENEX is the Uhde technology to separate light olefins from various C4 feedstocks, which include ethylene cracker and FCC sources. 

In the early 1970s, Union Oil developed and patented a chromatographic system based on the principle of a simulated moving bed (SMB) [6-8]. A schematic of a SMB unit is shown in Figure 1.4. Streams of the mobile phase (the desorbent ) and of the feed to separate are continuously injected into the column while streams of the less retained (the raffinate ) and the more retained components (the extract ) are continuously withdrawn, all at constant flow rates. The rotary valves switch periodically the positions in the columns where these streams enter or exit. The operation of SMB imits is discussed in detail in Chapter 17. Manufacturing facilities have been built and are operated for the fractionation of various petroleiun distillates, for example, the selective separation of p-xylene, o-xylene and ethylbenzene from the C7-C8 aromatic fraction of light petroleum reformates, the separation of olefins from paraffins in feed mixtures of hydrocarbons having 10 to 14... 

Carbon dioxide removal by reactive absorption in amine solutions is also applied on the commercial scale, for instance, in the treatment of flue gas (see later in this chapter). Another possible application field of the technique is gas desulfurization, in which H2S is removed and converted to sulfur by means of reactive absorption. Aqueous solutions of ferric chelates (160-162) as well as tetramethylene sulfone, pyridine, quinoline, and polyglycol ether solutions of S02 (163,164) have been proposed as solvents. Reactive absorption can also be used for NOx reduction and removal from flue or exhaust gases (165,166). The separation of light olefins and paraffins by means of a reversible chemical com-plexation of olefins with Ag(I) or Cu(I) compounds in aqueous and nonaqueous solutions is another very interesting example of reactive absorption, one that could possibly replace the conventional cryogenic distillation technology (167). 

Separation of light olefins and paraffins is one of the challenging problems in the field of membrane gas separation [24]. Apart from the studies... 

Mobil MTG and MTO Process. Methanol from any source can be converted to gasoline range hydrocarbons using the Mobil MTG process. This process takes advantage of the shape selective activity of ZSM-5 zeoHte catalyst to limit the size of hydrocarbons in the product. The pore size and cavity dimensions favor the production of C-5—C-10 hydrocarbons. The first step in the conversion is the acid-catalyzed dehydration of methanol to form dimethyl ether. The ether subsequendy is converted to light olefins, then heavier olefins, paraffins, and aromatics. In practice the ether formation and hydrocarbon formation reactions may be performed in separate stages to faciHtate heat removal. 

Dehydrogenation of isobutane to isobutylene is highly endothermic and the reactions are conducted at high temperatures (535—650°C) so the fuel consumption is sizeable. Eor the catalytic processes, the product separation section requires a compressor to facHitate the separation of hydrogen, methane, and other light hydrocarbons from-the paraffinic raw material and the olefinic product. An exceHent overview of butylenes is avaHable (81). 

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.)... 

From the aforementioned products, light olefins are potentially valuable feedstocks, especially the C3-C5 fractions [29], which may be used as raw chemicals while the paraffin components may be used as a fuel. In addition, they can be easily separated as the number of isomers in these low carbon number fractions is fairly low. In contrast. 

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. 

There are two fresh feedstreams. One is methanol. The other is a mixture of C5 components that contains reactive isoamylenes plus other C5 paraffins, naphthenes, and olefins. This C5 stream typically comes from a petroleum refinery light-ends unit that separates light hydrocarbon components generated in catalytic cracking into various streams. Because the boiling points of aU of the C5 components are quite similar, it is uneconomical to separate out the isoamylene reactants from the other C5s. The C5 fresh feedstream contains 24 mol% reactive isoamylenes. The remaining components are pentanes and pentene (largely isopentane), which are inert in the TAME reaction. 

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. 

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. 

Idea] solution thermodynamics is most frequently applied to mixtures of nonpolar compounds, particularly hydrocarbons such as paraffins and olefins. Figure 4.5 shows experimental K-value curves for a light hydrocarbon, ethane, in various binary mixtures with other less volatile hydrocarbons at 100 F (310.93°K) at pressures from 100 psia (689.5 kPa) to convergence pressures between 720 and 780 psia (4.964 MPa to 5.378 MPa). At the convergence pressure, X-values of all species in a mixture become equal to a value of one, making separation by operations involving vapor-liquid equilibrium impossible. The temperature of lOO F is close to the critical temperature of 550.0°R (305.56°K) for ethane. Figure 4.5 shows that ethane does not form ideal solutions with all the other components because the X-values depend on the other component. 

After cooling and condensate separation, the product is subsequently compressed, light-ends are separated and the olefin product is separated from unconverted paraffins in the fractionation section. 

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