Combined Reaction-Separation

So far, only a few microdevice-based separation operations have been reported [28-34]. Even less well known is the combination of separation with reaction. In one case, extraction (not reaction) was performed by the use of micromixers, followed by a classical phase separation in laboratory-made minisetders [35]. 

Enei source Form of application Intensified element 

High-gravity field Spinning disc reactor Heat transfer from liquid film Mass transfer in liquid film Reaction time Equipment size Impurities level 

Electric field - static Extraction systems Heat transfer from droplets Mass transfer Interfadal area (by emulsitication) 

Electric field - dynamic Gaseous non- Energy consumption 

---

In the first case, product purities are controlled indirectly by controlling front positions. In distillation columns the front positions are easily controlled with cheap, reliable and fast online temperature measurements on sensitive trays inside the column [27]. A similar procedure was recently proposed for moving-bed chromatographic processes with UV rather than temperature measurement [37]. However, the performance of such an approach is usually limited. Exact product specifications cannot be guaranteed because of this indirect approach. Furthermore, in combined reaction separation processes the relationship between the measured variable and the variable to be controlled is often non-unique, which may lead to severe operational problems as shown for reactive distillation processes [23], It was concluded that these problems could be overcome if in addition some direct or indirect measure of conversion is taken into account. 

Fici. l.S. Flow model for combined reaction-separation targeting. 

Finally, we consider a preliminary approach for the optimal synthesis of reactor-separation systems. Here, we formulate a combined reaction-separation model by postulating a species-dependent residence time distribution. The optimization of this distribution function leads to a separation profile as a function of time along the reactor. The costs for maintaining a separation profile are handled through a separation index, which models the intensity of separation,... 

Layered zeolites offer new possibilities for catalytic conversion processes, as well as for petrochemicals production. Finally, new possibilities for zeolites will be opened in separation processes and for combined reaction/separation. 

One of the first examples of combined reaction-separation processes at the microscale included three reaction steps and two separation steps (Figure 14.8) [35]. 

In addition, many ILs have imusual solubility and miscibility properties, attractive electric conductivity, quite interesting polarity nucleophilicity for catalysis, and remarkable tribologic properties [Werner et al., 2010]. The thermodynamics and reaction kinetics of processes carried out in ILs media are different from those carried out in conventional media. This creates new opportunities for catalytic reactions, sep>arations, electrochemistry, and combined reaction/ separation processes [Anonymous, 2004]. 

Catalytic Membrane Reactors Membrane reactors combine reaction and separation in a single vessel. By removing one of the... 

Chemical reaction whereby two or more molecules combine and separate out water or other substance. When polymers are formed, it is referred to as polycondensation. 

The reaction mixture is cooled and the crude amines which separate are collected on a suction funnel and washed twice with 400-cc. portions of water. The filtrate and washings should be saved for the recovery of iodine (Note 8). The precipitate on the funnel is transferred to a 2-1. beaker, dissolved in about 11. of benzene, filtered, and the benzene-insoluble part washed three times with 75-cc. portions of benzene. The benzene solution and washings are combined and separated mechanically from as much water as is possible. The water is then completely removed by distilling until the distillate comes over clear. If necessary, dry benzene is added to the solution in order to have a final volume of about 1200 cc. 

Dorko et al. [442] have used the Weibull distribution function for the consideration of reactions in which decomposition is accompanied by melting. Following a procedure described by Kao [446], they used a mixed Weibull function, written as a linear combination of separate functions, viz. 

Figure 10.9 Combining reactions and separation steps leads to a loss in process design degrees of freedom.

The synthetic procedures for isolation of the salt appear to be rather simple. First, one prepares a solution in which the carbocation and carbanion coexist free from any combination reactions. Then, the hydrocarbon cation-anion salt is isolated after separation of the concomitant inorganic salt and evaporation of the solvent. For the purification of the crude salt recrystallization or reprecipitation with proper solvents is used. 

Membrane reactors are known on the macro scale for combining reaction and separation, with additional profits for the whole process as compared with the same separate functions. Microstructured reactors with permeable membranes are used in the same way, e.g. to increase conversion above the equilibrium limit of sole reaction [8, 10, 11, 83]. One way to achieve this is by preparing thin membranes over the pores of a mesh, e.g. by thin-fihn deposition techniques, separating reactant and product streams [11]. 

It is useful to combine reaction and separation for equilibrium-limited reactions and also for consecutive reactions, particularly when the desired intermediate products undergo faster undesirable reactions. The concept of extractive reactions for equilibrium-limited and consecutive reactions has been covered in Section 4.2.1. Distillation column reactors provide yet another strategy. 

Nickel sulfate can be produced from either pure or impure sources. The pure source involves the reaction of pure nickel or nickel oxide powder (combined or separately) with sulfuric acid to produce nickel sulfate that is filtered and crystallized to produce a solid product. The impure raw material may be spent industrial liquor that contains a high percentage of nickel sulfate. The impurities in the liquor are precipitated by sequential treatment with oxidizers lime and sulfides can later be filtered out. The treated liquor, which is a pure solution of nickel sulfate, can be packaged in a drum or further crystallized and dried to produce solid nickel sulfate. Nickel sulfate is used mainly in the metal plating industries. Other uses include dyeing and printing of fabrics and production of patina, an alloy of zinc and brass. 

In the ion-electron method of balancing redox equations, an equation for the oxidation half-reaction and one for the reduction half-reaction are written and balanced separately. Only when each of these is complete and balanced are the two combined into one complete equation for the reaction as a whole. It is worthwhile to balance the half-reactions separately since the two half-reactions can be carried out in separate vessels if they are suitably connected electrically. (See Chap. 14.) In general, net ionic equations are used in this process certainly some ions are required in each half-reaction. In the equations for the two half-reactions, electrons appear explicitly in the equation for the complete reaction—the combination of the two half-reactions—no electrons are included. 

In analytical chemistry there is an ever-increasing demand for rapid, sensitive, low-cost, and selective detection methods. When POCL has been employed as a detection method in combination with separation techniques, it has been shown to meet many of these requirements. Since 1977, when the first application dealing with detection of fluorophores was published [60], numerous articles have appeared in the literature [6-8], However, significant problems are still encountered with derivatization reactions, as outlined earlier. Consequently, improvements in the efficiency of labeling reactions will ultimately lead to significant improvements in the detection of these analytes by the POCL reaction. A promising trend is to apply this sensitive chemistry in other techniques, e.g., in supercritical fluid chromatography [186] and capillary electrophoresis [56-59], An alter-... 

Catalysis plays a relevant role in several of these areas of development but, generally, an innovative effort to find new catalytic materials and their integration into advanced reactor technologies is required, e.g., to combine reaction and separation to reduce the overall costs of the process. More specific needs include ... 

Development of robust processes based on new catalytic reactor engineering solutions to improve energy and process efficiency and economics, and which combine reaction and separation. Special attention needs to be paid to cope with the natural variability in the quality of raw materials. 

Selective combination of the secondary geminate radical pairs occurs in the micelle, compared to nonselective free-radical combination reactions in solution. This results from the micelle host effectively constraining the separation of the geminate radical pair. 

In this chapter the three main modes of large-scale chromatographic operation, and combined reaction and separation. Many useful but small-scale chromatographic methods have been omitted, as well as allied separation techniques which combine aspects of chromatographic principles or practice with aspects of adsorption, extraction, sedimentation or electrophoresis. Such is the pace of invention that novel processes related to chromatography are still being developed and described in the literature. 

Additionally, the concept of catalytic SILP materials may be easily combined with several advanced process options providing new opportimities for accomplishing reactions. One attractive approach involves the conductance of consecutive, homogeneous reactions in sequences using several fixed-bed reactors in-series. Another approach involves implementation of integrated reaction-separation techniques using, e.g., SILP-membranes or the use of SILP materials in catalytic distillation processes. 

---