Pharmaceutical processing adsorption

The basic approach regarding how adsorption at solid surfaces affects different aspects of pharmaceutical development, especially for solid dosage forms, is briefly reviewed. The three broad fields addressed are general pharmaceutical processing, dissolution rate enhancement for poorly water-soluble compounds, and some other applications using adsorption at solid surfaces. Case studies are introduced to aid in understanding the applications and/or principles involved. 

Because of the interactions existing between different materials as well as between like materials, the performance of excipients in a formulation could be different from the performance of the excipients themselves. The most frequently used procedures in pharmaceutical processing for solid dosage formulations are mixing, granulation, and compaction, as well as storage of finished dosage forms. The effects of adsorption on these procedures have been studied, observed, and utilized widely in the pharmaceutical industry. 

Overall, factors that might affect the adsorption of actives on the carrier surface include surface properties, moisture content, the type and particle size/shape of carriers and actives, as well as the mixing ratio of actives and carriers. Pharmaceutical processes (i.e., milling and granulation) could affect the adsorption process by altering carrier and active properties (i.e., surface properties, size, and shape), hence the characteristics of blending and the quality of the final dosage form. 

There are a variety of different depth filter and membrane filter materials used within the pharmaceutical processes. Depth filter are fibrous materials for example, polypropylene, borosilicate, or glassfibre fleeces (Fig. 3). Borosilicate and glassfibre materials are highly adsorptive and commonly used to remove colloidal substances, like iron oxide from water or colloidal haze from sugar solutions. 

The need for high purity in a separations process is common in many industries semiconductor manufacture, pharmaceuticals processing, and the foods industry, as weil as in many cases of more-conventional chemical processing. It is also very important in separation processes that are oriented to cleaning gas, liquid, and solid streams for environmental purposes. The low concentrations required of many environmentally significant compounds prior to discharge from a chemical plant have created a need for a new class of separation methods and have focused attention on many techniques that often have been ignored. Adsorption, ultraflitration, electrostatic precipitation, reverse osmosis, and electrodialysis are just a few examples of separation processes in which there has been an increased level of interest partly because of their potential in environmental applications. 

The value of many chemical products, from pesticides to pharmaceuticals to high performance polymers, is based on unique properties of a particular isomer from which the product is ultimately derived. Eor example, trisubstituted aromatics may have as many as 10 possible geometric isomers whose ratio ia the mixture is determined by equiHbrium. Often the purity requirement for the desired product iacludes an upper limit on the content of one or more of the other isomers. This separation problem is a compHcated one, but one ia which adsorptive separation processes offer the greatest chances for success. 

Pharmaceuticals. Pharmaceuticals account for 6% of the Hquid-phase activated carbon consumption (74). Many antibiotics, vitarnins, and steroids are isolated from fermentation broths by adsorption onto carbon foUowed by solvent extraction and distillation (82). Other uses in pharmaceutical production include process water purification and removal of impurities from intravenous solutions prior to packaging (83). 

Polar organic compounds such as amino acids normally do not polymerize in water because of dipole-dipole interactions. However, polymerization of amino acids to peptides may occur on clay surfaces. For example, Degens and Metheja51 found kaolinite to serve as a catalyst for the polymerization of amino acids to peptides. In natural systems, Cu2+ is not very likely to exist in significant concentrations. However, Fe3+ may be present in the deep-well environment in sufficient amounts to enhance the adsorption of phenol, benzene, and related aromatics. Wastes from resinmanufacturing facilities, food-processing plants, pharmaceutical plants, and other types of chemical plants occasionally contain resin-like materials that may polymerize to form solids at deep-well-injection pressures and temperatures. 

Monoglyceride (MG) is one of the most important emulsifiers in food and pharmaceutical industries [280], MG is industrially produced by trans-esterification of fats and oils at high temperature with alkaline catalyst. The synthesis of MG by hydrolysis or glycerolysis of triglyceride (TG) with immobilized lipase attracted attention recently, because it has mild reaction conditions and avoids formation of side products. Silica and celite are often used as immobilization carriers [281], But the immobilized lipase particles are difficult to reuse due to adsorption of glycerol on this carriers [282], PVA/chitosan composite membrane reactor can be used for enzymatic processing of fats and oils. The immobilized activity of lipase was 2.64 IU/cm2 with a recovery of 24%. The membrane reactor was used in a two-phase system reaction to synthesize monoglyceride (MG) by hydrolysis of palm oil, which was reused for at least nine batches with yield of 32-50%. 

A good example of using adsorptive separation in a non-refining/petrochemical application is the separation of fructose from an aqueous solution of mixed sugars. This process allows the production of high concentration fructose which has a much higher sweetness to calorie ratio than simple glucose or sucrose. As in fine chemical and pharmaceutical applications we can often use adsorption when distillation is not possible or feasible or when the material is thermally sensitive. 

Physicochemical treatment of pharmaceutical wastewater includes screening, equalization, neutralization/pH adjustment, coagulation/flocculation, sedimentation, adsorption, and ozone and hydrogen peroxide treatment. Detailed descriptions of the various physicochemical treatment processes are described in the following sections. 

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