Product removal

Potential problems associated with product removal are  

Since at least one species can permeate through the membrane, the reaction side gas mixture does not define a closed system. The proper comparison for equilibrium is a diluted PFR fed with the combined PBMR feed, or run at a lower pressure (if more favorable). If the proper comparison is made, equilibrium conversion is never exceeded in a cocurrent membrane reactor. Itoh has shown that exceeding reaction equilibrium in a countercurrent PBMR is possible. 

The PBMR may still have advantages over the PFR, however. The large gas volume and lowered partial pressures, and thus lowered reaction rates, of the diluted PFR would cause large catalyst volumes to be needed, as noted by Itoh and Tsotsis et a/.A recent approach by Reo et attempts to 

This range, of course, depended on the choices of membrane materials and reaction parameters. 

Their analysis was extended to the porous PBMR with a pressure difference between reaction and permeate sides in a subsequent publication, in which the authors claimed that the appropriate basis for comparison was a PFR network. This allowed one PFR to work at the reaction side pressure, and a second one to work at the permeate side pressure, so that for both PFR and PBMR, two product streams at different pressures were produced. Broadly similar conclusions to the first study were reached. 

---

Product removal during reaction. Sometimes the equilibrium conversion can be increased by removing the product (or one of the products) continuously from the reactor as the reaction progresses, e.g., by allowing it to vaporize from a liquid-phase reactor. Another way is to carry out the reaction in stages with intermediate separation of the products. As an example of intermediate separation, consider the production of sulfuric acid as illustrated in Fig. 2.4. Sulfur dioxide is oxidized to sulfur trioxide ... 

Mixed-suspension, mixed-product removal crystallizer... 

Production Product liability Product reliability Product removal... 

The retorts must be opened, the reaction products removed, and the retorts filled with raw materials and resealed. The typical cycle is 8—10 hours. Capacity is controlled by the number of retorts used and the number of furnaces available. The metal crowns are removed, remelted, and cast iato iagots, or alloyed and then cast. 

The American faciUties also differed fundamentally from the British faciUties in regard to maintenance philosophy. The American plants were designed to employ remote maintenance, ie, to remove and replace equipment using shielded cranes operating inside the shielded stmcture. The British developed a contact approach based on simplified designs for equipment downstream of the fission product removal step. The British approach has been used at all commercial faciUties. 

Low molecular weight ether hydroperoxides are similarly dangerous and therefore ethers should be tested for peroxides and any peroxidic products removed from them before ethers are distilled or evaporated to dryness. Many ethers autoxidize so readily that peroxidic compounds form at dangerous levels when stored in containers that are not airtight (133). Used ether containers should be handled cautiously and if they are found to contain hazardous soHd ether peroxides, bomb-squad assisted disposal may be required (134). ZeoHtes have been used for removal of peroxide impurities from ethers (135). 

Esterification. Extensive commercial use is made of primary amyl acetate, a mixture of 1-pentyl acetate [28-63-7] and 2-metliylbutyl acetate [53496-15-4]. Esterifications with acetic acid are generally conducted in the Hquid phase in the presence of a strong acid catalyst such as sulfuric acid (34). Increased reaction rates are reported when esterifications are carried out in the presence of heteropoly acids supported on macroreticular cation-exchange resins (35) and 2eohte (36) catalysts in a heterogeneous process. Judging from the many patents issued in recent years, there appears to be considerable effort underway to find an appropriate soHd catalyst for a reactive distillation esterification process to avoid the product removal difficulties of the conventional process. 

Sodium and Potassium Benzoate. These salts are available in grades meeting the specifications of the 25ationalVormulary (18) and the Vood Chemicals Codex (19) (Table 7). Sodium benzoate [532-32-1] is produced by the neutralization of benzoic acid with caustic soda and/or soda ash. The resulting solution is then treated to remove trace impurities as weU as color bodies and then dried in steam heated double dmm dryers. The product removed from the dryers is light and fluffy and in order to reduce shipping and storage space the sodium benzoate is normally compacted. It is then milled and classified into various product forms, the names of which often bear Httle relationship to the actual form of the product. 

The crystallizer model that led to the development of equations 44 and 45 is referred to as the mixed-suspension, mixed-product removal (MSMPR) crystallizer. 

Char-liquor advance is simply the removal of mother Hquor from the crystallizer without simultaneous removal of crystals. The primary objective of fines removal is preferential withdrawal from the crystallizer of crystals whose size is below some specified value. Such crystals may be redissolved and the resulting solution returned to the crystallizer. Classified-product removal is carried out to remove preferentially those crystals whose size is larger than some specified value. 

Classified removal of course material also can be used, as shown in Figure 16. In a crystallizer equipped with idealized classified-product removal, crystals above some size ate removed at a rate Z times the removal rate expected for a perfecdy mixed crystallizer, and crystals smaller than are not removed at all. Larger crystals can be removed selectively through the use of an elutriation leg, hydrocyclones, or screens. Using the analysis of classified-fines removal systems as a guide, it can be shown that the crystal population density within the crystallizer magma is given by the equations... 

Fig. 17. Effect of classified-product removal on population densities within a crystallizer and in the crystallizer product.

Fig. 18. Population density functions of crystals within a crystallizer, having both classified-fines and classified-product removal and of crystals in the...

Although many commercial crystallizers operate with some form of selective crystal removal, such devices can be difficult to operate because of fouling of heat exchanger surfaces or blinding of screens. In addition, several investigations identify interactions between classified fines and course product removal as causes of cycling of a crystal size distribution (7). Often such behavior can be rninirnized or even eliminated by increasing the fines removal rate (63,64). 

Fig. 18. Product removal arrangements for cocurrent spray dryers (a) simple outlet (b) product separation ia an agglomeration chamber and (c) classifyiag...

Completion of Esterification. Because the esterification of an alcohol and an organic acid involves a reversible equiUbrium, these reactions usually do not go to completion. Conversions approaching 100% can often be achieved by removing one of the products formed, either the ester or the water, provided the esterification reaction is equiUbrium limited and not rate limited. A variety of distillation methods can be appHed to afford ester and water product removal from the esterification reaction (see Distillation). Other methods such as reactive extraction and reverse osmosis can be used to remove the esterification products to maximize the reaction conversion (38). In general, esterifications are divided into three broad classes, depending on the volatility of the esters ... 

Although batch distillation is covered in a subsequent separate section, it is appropriate to consider the application of RCM and DRD to batch distulation at this time. With a conventional batch-rectification column, a charge of starting material is heated and fractionated, with a vapor product removed continuously. The composition of the vapor prodiic t changes continuously and at times drastically as the lighter component(s) are exhausted from the stiU. Between points of drastic change in the vapor composition, a cut is often made. Successive cuts can be removed until the still is nearly diy. The sequence, number, and limiting composition of each cut is dependent on the form of... 

Mixed-Suspension, Mixed-Product-Removal Crystallizers. 18-44... 

Mixed-Suspension, Classified-Product-Removal Crystallizers. 18-48... 

Equation (18-31) contains no information about the ciystalhzer s influence on the nucleation rate. If the ciystaUizer is of a mixed-suspension, mixed-product-removal (MSMPR) type, satisfying the criteria for Eq. (18-31), and if the model of Clontz and McCabe is vahd, the contribution to the nucleation rate by the circulating pump can be calculated [Bennett, Fiedelman, and Randolph, Chem. E/ig, Prog., 69(7), 86(1973)] ... 

Product removal mechanisms from apparatuses that are explosion resistant can be protected with a. double-slide system. Here, the shdes must be at least as resistant as the apparatuses. By means of proper control, it must be assured that a shde is always closed. 

Figure 4.22 As in Fig. 4.21 hut with deposits and corrosion products removed to reveal numerous depressions. (Magnification 7.5x.)... 

Figure 7.10 Fines destruction and classified product removal during continuous mixed suspension crystallization...

Crystal size-dependent product removal crystallizers... 

The treacheries inherent in naive attempts at pattern recognition are illustrated by the finding that ester known cetiedil, is said to be a peripheral vasodilator. Clemmen-sen reduction of Grignard product removes the superfluous benzylic hydroxyl group and esterification of the sodium salt of the resulting acid ) with 2- l-cycloheptylamino)ethyl chloride produces cetiedil (28). ... 

D) Preparation of 2-(1-Hydroxyethyi)-3-Methyi-5-(2-Oxo-2,5-Dihydro-4-Furyi)Benzo[b] Furan (3574 CB) 13,2 grams of compound 3556 CB of which the preparation is described in (C) are treated successively with 66 ml of methylene chloride, 27 ml of methanol and, with stirring, 1.6 grams of sodium borohydride added in stages. The reaciton takes 1 hour. The mixture is poured into water acidified with a sufficient amount of acetic acid, the solvents are stripped under vacuum, the crystalline product removed, washed with water, and recrystallized from ethyl acetate. Yield 90%. MP <=158°C. 

Biocatalysts in nature tend to be optimized to perform best in aqueous environments, at neutral pH, temperatures below 40 °C, and at low osmotic pressure. These conditions are sometimes in conflict with the need of the chemist or process engineer to optimize a reaction with respect to space-time yield or high product concentration in order to facilitate downstream processing. Furthermore, enzymes and whole cells are often inhibited by products or substrates. This might be overcome by the use of continuously operated stirred tank reactors, fed-batch reactors, or reactors with in situ product removal [14, 15]. The addition of organic solvents to increase the solubility of substrates and/or products is a common practice [16]. 

---