Extraction extractor column

In general, the sulfolane extraction unit consists of four basic parts extractor, extractive stripper, extract recovery column, and water—wash tower. The hydrocarbon feed is first contacted with sulfolane in the extractor, where the aromatics and some light nonaromatics dissolve in the sulfolane. The rich solvent then passes to the extractive stripper where the light nonaromatics are stripped. The bottom stream, which consists of sulfolane and aromatic components, and which at this point is essentiaHy free of nonaromatics, enters the recovery column where the aromatics are removed. The sulfolane is returned to the extractor. The non aromatic raffinate obtained initially from the extractor is contacted with water in the wash tower to remove dissolved sulfolane, which is subsequently recovered in the extract recovery column. Benzene and toluene recoveries in the process are routinely greater than 99%, and xylene recoveries exceed 95%. 

In the extraction process, the LPG from the prewash tower enters the bottom of an extractor column. The extractor is a liquid/liquid contactor in which the LPG is counter-currently contacted by a caustic solution. Another option is the use of a fiber film contacting device. The mercaptans dissolve in the caustic (Equation 1-14). The treated LPG leaves the top of the extractor and goes on to a settler, where entrained caustic is separated. 

The modelling approach to multistage countercurrent equilibrium extraction cascades, based on a mass transfer rate term as shown in Sec. 1.4, can therefore usefully be applied to such types of extractor column. The magnitude of the... 

The modelling approach to multistage countercurrent equilibrium extraction cascades, based on a mass transfer rate term as shown in Section 1.4, can therefore usefully be applied to such types of extractor column. The magnitude of the mass transfer capacity coefficient term, now used in the model equations, must however be a realistic value corresponding to the hydrodynamic conditions, actually existing within the column and, of course, will be substantially less than that leading to an equilibrium condition. 

In this process developed by Lurgi [17], the phenolic effluent is contacted with the solvent in a multistage mixer-settler countercurrent extractor (Fig. 10.8). The extract, containing phenol, is separated into phenol and solvent by distillation and solvent is recycled to the extractor. The aqueous raffinate phase is stripped from solvent with gas, and the solvent is recovered from the stripping gas by washing with crude phenol and passed to the extract distillation column. 

With liquid feed solutions, however, it is possible to work in a manner analogous to traditional solvent extraction. Pressurized columns can be of the packed-bed type or agitated by magnetic stirrers. Because of the efforts of pilot plant tests, much of the scale-up work has to be carried out in laboratory extractors. From solubility measurements, it is possible to determine parameters in thermodynamic models (e.g., equations of state), which can be used for the simulation of large-scale applications. 

Thus the extractor column raffinate outlet rate and the solvent inlet rate are approximately equal. This is indeed the minimum solvent rate allowed, since a lower rate will overload the solvent, referencing the plait point. This rate will also set the required minimum extractor column diameter. For some refinery-type extraction operations, such as lube oil extractors, where relatively much larger solvent-raffinate rates apply, this method for determining minimum solvent rate is very economical and desirable. 

A last note about the continuous phase is the fact that it must completely immerse the packing section where the mixing of the two phases takes place. The inner phase between the two liquid phases is therefore to be near the extractor column s dispersed-phase outlet. The extract stream, having gained the transferred solute, exits the column at the opposite end from where the raffinate stream exits. The raffinate stream is the inlet feed stream containing the extracted solute. 

Determination of theoretical stage number and stage efficiency, or more simply HETS, has been established for any extraction process. The next item of order is the packed extractor column flooding limit. Just as fractionation columns must be sized for vapor and liquid, liquid-liquid extraction columns must be sized for flood limits. 

Timothy C. Frank, Ph.D. Research Scientist and Sr. Technical Leader, The Dow Chemical Company Member, American Institute of Chemical Engineers (Section Editor, Introduction and Overview, Thermodynamic Basis for Liquid-Liquid Extraction, Solvent Screening Methods, Liquid-Liquid Diversion Fundamentals, Process Fundamentals and Basic Calculation Methods, Dual-Solvent Fractional Extraction, Extractor Selection, Packed Columns, Agitated Extraction Columns, Mixer-Settler Equipment, Centrifugal Extractors, Process Control Considerations, Liquid-Liquid Phase Separation Equipment, Emerging Developments)... 

POis separated from methanol by extractive distillation, using water (or in another embodiment, propene glycol) as the extractor. PO is distilled overhead from the extractive column as top stream, while the bottom stream contains methanol and water [17d, fj. The energy integration of the column is one important issue of the patents the vapors of the top stream are compressed, and the condensation heat is returned to the vaporizer employed in the extractive distillation column. 

Extractors with reflux at one or both ends of the column (or series of mixing vessels) may be used to enhance the purity of the products. An extractor column with both extract and raffinate reflux is shown in Figure 11.1. In this configuration, the feed is sent to an intermediate stage, and the extractor performs as a distillation column, separating two components in the feed. In the column section above the feed, the raffinate phase is stripped of the extract component (the solute), and in the lower section the extract phase is enriched in the extract component. 

Feed stream 2o> flowing at a rate of 1000 kg/h, contains 45 wt% acetone in solution with water. It is required to extract the acetone in an extractor column, using 1,1,2-trichloroethane as the solvent, at a rate of 350 kg/h. The raffinate, Qf, should contain 10 wt% acetone. 

At the start of the calculations the liquid flow rates in the column, Q and E in Equation 12.45, may be assumed equal to the inlet feed and solvent rates. The initial values for the activity coefficients may also be based on the inlet compositions and thermal conditions of the streams. The temperature and pressure variations in the extractor column are usually small, but the compositions will vary, and this may require recalculating the activity coefficients. The column calculations may be repeated with updated values of Q and E, taken as respective averages of each phase inlet and outlet stream flow rates calculated in the first trial. The activity coefficients can also be refined by recalculating them at the column top and bottom compositions for each phase. Averages of the top and bottom coefficients for each phase can be used in Equation 12.47 to calculate the new E-values. The extraction factors are then recalculated with the new values of Q, L, and E by Equation 12.45. The product component flow rates E v and Q i are Anally calculated by Equations 12.43 and 12.44. If large variations appear between the first and second trials, more trials may be considered. 

The DCCLC system was also designed to circumvent problems due to adsorption. After preparation and filtration, saturated solutions are transferred and extracted by a process that minimizes PAH contact with surfaces. The volume between the generator column and the extractor column is approximately 6 fxL. The time required for transfer of the saturated solutions at a flow rate of 5 mL/min is less than 75 msec. Furthermore, the walls of the transfer lines are presaturated with the compound being studied during the column-conditioning process. This further reduces the possibility of adsorptive losses of the PAHs during the brief time that the saturated solutions remain in these lines. 

A-l. Extractor Column Extraction Efficiency. Extraction of the PAHs from the generated solutions was accomplished by pumping volumes varying between 5.0-25.0 mL through the extractor column. Over this range, extraction efficiencies are quantitative for 11 of the 12 compounds studied in this investigation. Benzene was not extracted efficiently by the extractor column. The solubility of benzene, therefore, was determined by direct injection of 23.2 /xL of the generated solutions via a sample loop. 

A-2. Measurement of Sample Volume (see Figure 1). The volume of saturated solution extracted was determined and by placing the sample valve in the extract position, a designated volume of the effluent from the extractor column was collected in a class A 5-, 10-, or 25-mL volumetric flask. After the volumetric flask had been filled, the sample valve was manually switched to the analyze position, thus diverting the saturated solution to waste. 

The over-all performance of /3-methoxypropionitrile solvent in the pilot plant tests qualify it as a superior replacement solvent for furfural in butadiene extractive distillation plants. It offers distinct economic and operational advantages. Operation at lower solvent-to-C4 feed ratios greatly increases existing extractor capacity. In addition, the improved separation of trans-2-butene and butadiene in the extractive distillation column reduces the load on the final butadiene purification column. Operation at lower solvent-to-C4 feed ratio and lower reboiler temperature provides substantial utility savings. The lower reboiler temperature also reduces the rate of butadiene dimer formation. 

The contact area between the phases can be enlarged in film extraction and column extraction. The discussion of column extraction techniques will be postponed to the section on TREF. In film extraction, a thin pol5mier film is deposited onto a support material with a large surface area. This technique can also be performed inside Sohxlet extractors, but it is also prone to several experimental difficulties (11). 

An extractor column with both extract and raffinate reflux is shown in Figure 11.1. In this configuration the feed is sent to an intermediate stage in the column. 

The most convenient way of separating phenols from the bulk of the material excreted in urine is steam distillation. Comparatively few compounds, however, are volatile in steam and a more general method which can be applied to almost all simple phenols is to extract the hydrolywd urine with ether in a continuous extractor for several hours. By adjusting the pH of the urine, it may be possible to separate phenols from phenolic acids a pH of 7.8 usually serves to prevent extraction of the acids while it permits extraction of other phenols. The phenolic acids can be subsequently extracted if the residual urine is adjusted to pH 1 (cf. Schmidt (80)). Tests may then be applied to the residue left after evaporation of the ether. If the phenols are liable to oxidation by atmospheric oxygen, e. g., aminophe-nols, the ether should be removed in vacuo or in a stream of nitrogen. The ether extract can be fractionated by conventional methods. Chromatographic separation of an ether extract on columns of powdered cellulose often provides a convenient method for the separation of mixtures of phenolic compounds (Section 11,4). 

Note. In the older types of Soxhiet extractor, an external tube ran from B up to the top of C for conveying the ascending column of hot vapour. This type had the disadvantage not only of being more easily broken, but also that the condensed liquid in C received very little heat, and therefore the extraction, being carried out by the lukewarm solvent, was usually very slow. 

The earliest large-scale continuous industrial extraction equipment consisted of mixer—settlers and open-spray columns. The vertical stacking of a series of mixer—settlers was a feature of a patented column in 1935 (96) in which countercurrent flow occurred because of density difference between the phases, avoiding the necessity for interstage pumping. This was a precursor of the agitated column contactors which have been developed and commercialized since the late 1940s. There are several texts (1,2,6,97—98) and reviews (99—100) available that describe the various types of extractors. 

Extraction. Traditionally tea leaf is extracted with hot water either in columns or ketdes (88,89), although continuous Hquid soHd-type extractors have also been employed. To maintain a relatively low water-to-leaf ratio and achieve full extraction (35—45%), a countercurrent system is commonly used. The volatile aroma components are vacuum-stripped from the extract (90) or steam-distilled from the leaf before extraction (91). The diluted aroma (volatile constituents) is typically concentrated by distillation and retained for davoring products. Technology has been developed to employ enzymatic treatments prior to extraction to increase the yield of soHds (92) and induce cold water solubiUty (93,94). 

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