Hybrid columns

The elution behavior of various polymers near their critical adsorption point with silica gel packings and various eluents has been studied (12). It was of interest to apply hybrid column systems composed of active ( critical ) packings (silica gels) in combination with nonactive (nonadsorptive) PS/DVB and DVB-based gels. Some PS/DVB and DVB gels exhibited rather strong... 

The ELSD is not plagued with the problem of baseline shift and is significantly more sensitive however it presents other disadvantages, such as the strong non-linearity of the detector response and the possibility of interference from non-volatile compounds in the sample matrix [87]. The HPLC method using traditionally reversed-phase solvents and a hybrid column/pre-column has demonstrated the separation of ethoxylated homologues of broadly distributed linear AEOs... 

Chapter 4 provides a discussion of zirconia and hybrid columns. We will only lightly cover here the hybrid columns and expand on the zirconia discussion. Hybrid columns were developed to reduce the amount of silanol activity as well as to impart better hydrolytic stability, especially at high pH. By incorporating different functional groups into the matrix. 

Aiouache F and Goto S. Reactive distillation-pervaporation hybrid column for tert-amyl alcohol etherification with ethanol. Chem Eng Sci 2003 58(12) 2465-2477. 

Figure 3 shows the internal profile in the composition tetrahedron after simulation of the hybrid column in Hysys. A loss of about 0.18 % w/w of ethanol in methanol-rich distillate occurs. The side streams are located near the maximum in ethanol (ethanol-rich stream, 88.98 % w/w) and fusel (fusel-rich stream, 18.5 % w/w), respectively. The column has 35 equilibrium stages, a column diameter of 1.372 m, a section pressure drop of 11.8 kPa and a steam flow rate of 1800 kg/h. The vapour ethanol-rich stream is diverted to the first effect of the evaporation sector to provide heating while minimizing the steam demand of the plant. The condensed ethanol-rich stream is then fed to the pervaporation sector to remove the excess water. 

The fusel-rich stream leaving the decanter is fed to the fusel sector where the stream is washed with water to recover about 96 % of the incoming ethanol. The resulting water-rich stream is recycled to the hybrid column. To do this, an overall amount of 363 kg/h wash-water and seven separation steps are necessary. The conceptual design of a cross-flow operation is performed using DISTIL, while process simulation is done in Hysys. 

A cost effective design for a bio-ethanol separation plant using conceptual design followed by rigorous simulation is found. The minimum in the operation costs corresponds to a minimum in the steam flow rate of the hybrid column (1600 kg/h). The minimum in steam flow rate can be only explained by the presence of the fusel component, which influences both the energy demand and feasible products of the process. Therefore, designs based on the binary system ethanol-water do not represent the system behaviour in an accurate way. 

Figure 3.11. A partial list of popular silica-based columns including some recent new offerings. Columns based on high-purity silica are underlined. Columns packed with hybrid particles are in bold. Note that the ACQUITY (Waters) and Gemini (Phenomenex) are new second-generation hybrid columns.

B.3.2 Generating Profiles for Hybrid Column For demonstration purposes, it will initially be assumed that operation will occur at 4 = 0.8. In order to display the profiles obtainable for this design, and npvalues were arbitrarily chosen. Furthermore, for the design to be feasible, it is required that the profiles of each section, including the membrane, intersect in the same order and direction as that of liquid flow in the system. Figure 9.14 shows the column and membrane profiles for operation at tai =40 with ni =5. 

Knowledge of the equilibrium is a fundamental prerequisite for the design of non-reactive as well as reactive distillation processes. However, the equilibrium in reactive distillation systems is more complex since the chemical equilibrium is superimposed on the vapor-liquid equilibrium. Surprisingly, the combination of reaction and distillation might lead to the formation of reactive azeotropes. This phenomenon has been described theoretically [2] and experimentally [3] and adds new considerations to feasibility analysis in RD [4]. Such reactive azeotropes cause the same difficulties and limitations in reactive distillation as azeotropes do in conventional distillation. On the basis of thermodynamic methods it is well known that feasibility should be assessed at the limit of established physical and chemical equilibrium. Unfortunately, we mostly deal with systems in the kinetic regime caused by finite reaction rates, mass transfer limitations and/or slow side-reactions. This might lead to different column structures depending on the severity of the kinetic limitations [5], However, feasibility studies should identify new column sequences, for example fully reactive columns, non-reactive columns, and/or hybrid columns, that deserve more detailed evaluation. 

As has been outlined in the first sections of this chapter, RD processes can efficiently replace reactor-separator flow-sheets by internalization of external recycling loops. This is demonstrated for a simple isomerization reaction in an ideal binary mixture. It is clearly shown that hybrid columns combining non-reactive and reactive sections overcome the restrictions of fully RD columns. The most simple and effective solution for isomerization reactions is a reactive total reboUer with a non-reactive column on top. 

Going one level up in aggregation we consider the structures of complete columns. Conventionally, RD columns are classified in hybrid and non-hybrid units, depending on the distribution of reactive trays inside the column. Thus, hybrid columns are distillation columns with a reactive core and nonreactive sections (rectifying and/or stripping sections). Non-hybrid RD columns denote columns where all trays including condenser and reboiler are reactive (Giittinger, 1998). Hybrid columns are commonly... 

Many papers point out the economic advantages of pervaporation over conventional processes. A quantitative economic comparison between azeotropic distillation and hybrid column-pervaporation is presented by Guerreri," whose results show higher capital cost but much lower energy cost for the ethanol-water separation. A review of industrial applications of pervaporation, coupled with either distillation columns or chemical reactors, is... 

Sandhya, S., Swaminathan, K., 2006. Kinetic analysis of treatment of textile wastewater in hybrid column upflow anaerobic fixed bed reactor. Chemical Engineering Journal 122 (1-2), 87-92. 

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