Liquid-Solid Phase Reactions

The surface is the interface between gas-solid and liquid-solid phase reactions for both chemical and electrochemical applications. 

The concentrations of reactants are of little significance in the theoretical treatment of the kinetics of solid phase reactions, since this parameter does not usually vary in a manner which is readily related to changes in the quantity of undecomposed reactant remaining. The inhomogeneity inherent in solid state rate processes makes it necessary to consider always both numbers and local spatial distributions of the participants in a chemical change, rather than the total numbers present in the volume of reactant studied. This is in sharp contrast with methods used to analyse rate data for homogeneous reactions in the liquid or gas phases. 

In liquid-solid processes reaction takes place between a liquid reactant and an insoluble or sparingly soluble solid which must be finely divided to speed up the process. Another measure to accelerate the process is to use an aqueous solution of a phase-transfer agent (typically a quaternary ammonium salt). The solid can also be a catalyst for reactions between liquid components, e.g. in acylations, carried out both conventionally in the presence of metal chlorides (mostly AICI3) or catalysed by zeolites and Grignard reactions. 

We first present further examples of the types of reactions involved in two main classifications, and then a preliminary discussion of various types of reactors used. Following an examination of some factors affecting the choice of reactor, we develop design equations for some reactor types, and illustrate their use with examples. The chapter concludes with a brief introduction to trickle-bed reactors for three-phase gas-liquid-solid (catalyst) reactions. 

In addition, a novel fluorous support has been developed recently as an alternative to traditional polymer supports and applied successfully to oligosaccharide synthesis in combination with the trichloroacetimidate method [541]. Each intermediate in the fluorous oligosaccharide synthesis [542,543] could be obtained by simple fluorous-organic solvent extraction, and the reactions could be monitored by TLC, NMR and MS, in contrast to solid-phase reactions. Moreover, the new liquid-phase technique is anticipated to be easily applicable to the large-scale synthesis. 

The HTE characteristics that apply for gas-phase reactions (i.e., measurement under nondiffusion-limited conditions, equal distribution of gas flows and temperature, avoidance of crosscontamination, etc.) also apply for catalytic reactions in the liquid-phase. In addition, in liquid phase reactions mass-transport phenomena of the reactants are a vital point, especially if one of the reactants is a gas. It is worth spending some time to reflect on the topic of mass transfer related to liquid-gas-phase reactions. As we discussed before, for gas-phase catalysis, a crucial point is the measurement of catalysts under conditions where mass transport is not limiting the reaction and yields true microkinetic data. As an additional factor for mass transport in liquid-gas-phase reactions, the rate of reaction gas saturation of the liquid can also determine the kinetics of the reaction [81], In order to avoid mass-transport limitations with regard to gas/liquid mass transport, the transfer rate of the gas into the liquid (saturation of the liquid with gas) must be higher than the consumption of the reactant gas by the reaction. Otherwise, it is not possible to obtain true kinetic data of the catalytic reaction, which allow a comparison of the different catalyst candidates on a microkinetic basis, as only the gas uptake of the liquid will govern the result of the experiment (see Figure 11.32a). In three-phase reactions (gas-liquid-solid), the transport of the reactants to the surface of the solid (and the transport from the resulting products from this surface) will also... 

Crown ethers have been used successfully as phase-transfer catalysts for liquid-liquid and liquid-solid oxidation reactions. Sam and Simmons (1972) observed that potassium permanganate can be solubilized in benzene by dicyclohexyl-18-crown-6 to yield concentrations as high as 0.06 M. From... 

The problems encountered in the catalytic transfer of highly hydrophilic anions from aqueous solutions into the organic phase can be countered by the use of anhydrous solid salts the organic reactant is dissolved in the organic solvent or, if liquid, may be used neat. Solid liquid two-phase reactions using ammonium salts have widespread application (see, for example, the many examples cited in later chapters) frequently with shortened reaction times, lower reaction temperatures, and higher yields [e.g. 66, 67] and are generally superior to solidrliquid reactions catalysed by crown ethers [68]. The process is particularly useful in base-initiated reactions with fluorides, hydroxides or carbonates. 

FT-IR microspectroscopy is a new nondestructive, fast and rehable technique for solid-phase reaction monitoring. It is the most powerful of the currently available IR methods as it usually requires only a single bead for analysis, thus it is referred to as single bead FT-IR [166]. (See also Chapter 12 for further details). The high sensitivity of the FT-IR microscope is achieved thanks to the use of an expensive liquid nitrogen-cooled mercury cadmium telluride (MCT) detector. Despite the high cost of the instrument, this technique should become more widely used in the future as it represents the most convenient real-time reaction monitoring tool in SPOS [166, 167]. 

The gas phase enthalpies of reaction 6 for the variously unsaturated peroxides are also consistent, with one exception. The values are ieri-butyl cumyl peroxide, —288.5 kJmol [l,4-phenylenebis(l-methylethylidene)]bis[(l,l-dimethylethyl) peroxide" (normalized for two peroxy groups), —287.1 kJmol 1,1-dimethylethyl-l-methyl-l-[4-(l-methylethyl)phenyl]ethyl peroxide, —276.6 kJmol and 2-tert-butylperoxy-2-methylhex-5-en-3-yne, —305.8 kJmor. The last species named also has a disparate liquid phase enthalpy of reaction, —344.9 kJ mol . The only solid phase reaction enthalpy, for [l,4-phenylenebis(l-methylethylidene)]bis[(l,l-dimethylethyl) peroxide (normalized for two peroxy groups), is —357.2 kJmol . 

Rate of Solubility—The rath of solubility of small particles depends on a great number of variables. Eq (12-2) takes into account free surface energy (a) and particle surface (1 /d). These are purely surface considerations, and are scarcely complete in themselves. The shape of the surface and its physical state must also be specified, that is, its relative freedom from contamination which might influence the speed of reaction. The effect of packing density and the extent of agitation imparted to the particles are also important, particularly with regard to exposure of fresh surfaces and formation of possible gas pockets. The liquid and liquid-solid phases jointly are additional important considerations. The volume of the liquid, its temperature, and the amount of dissolved solid already in solution must enter into all calculations. Nor can we ignore the chemical nature of the substances involved in the... 

CjCqmHBFJ Pd(PPh3)4 Na2C03 110 °C. Solid-phase reaction coupling of 4-iodophenol immobilised on a polystyrene-Wang resin with arylboronic acids DMF as co-solvent acceleration in the presence of the ionic liquid catalyst recycling not practical. [102]... 

Liquid-phase and solid-phase reactions Antibody or antigen reactions can occur where both components are in the same liquid phase (in solution), or one component is in the solid phase and the other is in the liquid phase (solid-liquid interface). The former liquid phase assays were the first type used but have since largely been superseded by various forms of solid-phase immunoassay. Solid-phase assays... 

Ti allows three-phase gas-liquid-solid (reactant) reactions to operate in the presence of a solid catalyst without Drugging of the reactoij e.g.. the H-COAI. process for coal liquefaction. 

The gas-liquid and gas-solid reaction processes can be analyzed by several different physical models, namely film, penetration, surface renewal, Danckwerts, film-penetration, etc. These models are described by Danckwerts.39 Although each of these models gives a somewhat different physical picture of the reaction process, in many instances the final desired answer for the rate of absorption of gas in the presence of a liquid- or a solid-phase reaction is similar. Since film and penetration theories are most widely used, we review their applications here. 

Proper scaleup of a reactor is always a difficult but very important prohlem. What system parameter would you consider to be important in the proper scaleup of a trickle-bed reactor for a gas-liquid-solid catalytic reaction if the reaction is occurring in the liquid phase and is controlled by... 

In solid phase reaction s3mthesis, there are three types of chemical reactions oxidation or reduction of a solid, thermal decomposition of a solid, and solid state reaction between two t3 s of solid. With liquid phase ssmthesis of ceramic powders, there are five different methods drying of a liquid, precipitation, sol-gel sjmthesis, hydrothermal S5m-thesis, and reactions of a liquid metal melt with a gas to give a solid ceramic. There are basically three operational principles for precipitation temperature change, evaporation, and chemical reaction. Sol—gel... 

What we mean in this report by equilibrium and disequilibrium requires a brief discussion of definitions. Natural physicochemical systems contain gases, liquids and solids with interfaces forming the boundary between phases and with some solubility of the components from one phase in another depending on the chemical potential of each component. When equilibrium is reached by a heterogeneous system, the rate of transfer of any component between phases is equal in both directions across every interface. This definition demands that all solution reactions in the liquid phase be simultaneously in equilibrium with both gas and solid phases which make contact with that liquid. Homogeneous solution phase reactions, however, are commonly much faster than gas phase or solid phase reactions and faster than gas-liquid, gas-solid and... 

YBa2Cu307 has a relatively high of 92 K and is easy to synthesize. Therefore research on YBa2Cu307 is the most widely carried out for the development of practical applications at 77 K (the boiling point of liquid nitrogen). Usual sintered samples are synthesized by the standard high-temperature solid phase reaction method. A general procedure is as follows ... 

SAXSAVAXS/RAMAN is especially useful when dealing with chemically induced phase transitions. The example shown in Figure 2(e) is the polymerisation of solvent styrene into polystyrene in which polyethylene is in solution. Polyethylene is soluble in styrene but insoluble in polystyrene. RAMAN allows the determination of the reaction kinetics of polystyrene formation and monitors the crystallisation of the polyethylene. The SAXS monitors the liquid-liquid phase separation followed by the liquid-solid phase transition, whilst the WAXS also observes the liquid solid phase by monitoring the appearance of peaks due to the crystallisation of polyethylene. These are very valuable parameters when trying to define any new manufacturing process. ... 

One may wonder what makes clusters in general, and small van der Waals (vdW) complexes in particular, an interesting subject in the broad field of reaction dynamics. Aside from the novelty of the subject, which by itself contributes to the interest, there are several other reasons for the recent rise in the number of publications on this topic. Clusters and vdW molecules provide the ability to simulate liquid- or solid-phase reactions under controlled conditions, due to the capability to attach one or more solvent molecules to the reacting species. By varying the number of molecules or... 

Multiphase Reactors Reactions between gas-liquid, liquid-liquid, and gas-liquid-solid phases are often tested in CSTRs. Other laboratory types are suggested by the commercial units depicted in appropriate sketches in Sec. 19 and in Fig. 7-17 [Charpentier, Mass Transfer Rates in Gas-Liquid Absorbers and Reactors, in Drew et al. (eds.), Advances in Chemical Engineering, vol. 11, Academic Press, 1981]. Liquids can be reacted with gases of low solubilities in stirred vessels, with the liquid charged first and the gas fed continuously at the rate of reaction or dissolution. Some of these reactors are designed to have known interfacial areas. Most equipment for gas absorption without reaction is adaptable to absorption with reaction. The many types of equipment for liquid-liquid extraction also are adaptable to reactions of immiscible liquid phases. 

Fluorous affinity separation was originally used to remove catalysts from complex reaction mixtures [6], A perfluoroalkyl moiety (generally no shorter than -C6F13) is appended to a compound of interest. Tagged molecules are then rapidly separated from other components in the mixture by either liquid-liquid extraction or liquid-solid-phase extraction. Fluorous affinity-based separation has recently been used in biomolecule purification, proteomics, and microarray experiments [15-20],... 

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