Separation, energy requirement selection

Lipase-catalyzed glycerolysis of oils and fats using solvent-free system at atmospheric pressure and lower temperature have attracted interest in both academic and industrial fields. Because of the possibility of further separation of the reaction products by vacuum distillation, lower energy requirements, selectivity of the enzymes [13], and possibility of recoverability and recyclability of immobilized enzymes [14], it is believed to be a practical alternative method for MG and DG production. 

There are four principal factors that are paramount in selecting the best separation technique. They are the energy required for the separation, the capital required for the equipment used in the separation, the efficiency/effectiveness of the separation, and the vitality of the catalyst after the separation. General process considerations include ... 

A number of system approaches can be used to clean up the fuel feed. These include pressure swing adsorption, membrane separation, methanation, and selective oxidation. Although selective oxidation does not remove CO2, it is usually the preferred method for CO removal because of the parasitic system loads and energy required by the other methods. In selective... 

Step 9. The basic regulatory strategy has now been established (Fig. 10.2). We have some freedom to select several controller setpoints to optimize economics and plant performance. If reactor inlet temperature sets production rate, the setpoint of the total toluene flow controller can be selected to optimize reactor yield. However, there is an upper limit on this toluene flow to maintain at least a 5 1 hydrogen-to-aromatic ratio in the reactor feed since hydrogen recycle rate is maximized. The setpoint for the methane composition controller in the gas recycle loop must balance the trade-off between yield loss and reactor performance. Reflux flows to the stabilizer, product, and recycle columns must be determined on the basis of column energy requirements and potential yield losses of benzene (in the overhead of the stabilizer and recycle columns) and toluene (in the base of the recycle column). Since the separations are easy, in this system economics indicate that the reflux flows would probably be constant. 

The removal of both mineral matter and sulfur species to very low values would provide premium solid fuels and possibly new chemical feedstocks. Several techniques are being explored to achieve these goals. The mineral matter in a physically cleaned coal can be further reduced by the solubilization of the aluminosilicate minerals. This can technically be accomplished with the use of alkaline and then acid treatments. A variety of studies are under way to define the conditions required for effective removal of the mineral matter and establish the amount of sulfur reduction that can be accomplished. Others involve the use of fine grinding to liberate the coal from the mineral matter. Then an agglomerant is used to separate the coal matter from the aqueous phase containing suspended mineral matter. A new approach uses microwave energy to selectively decompose the clays into species that can be solubilized and removed. Still another technique involves treatment with carbon dioxide to reduce the particle size and permit the liberation of the mineral matter. Over the next few years these will be studied further and it is hoped that coal will become available in a form with less of these interesting, but not entirely desirable mineral species. 

We have considered the common non-solvent-based methods of separating postconsumer plastics. However, except for depolymerization, only selective dissolution is capable of purifying bonded, blended, and fill plastics effectively. Dissolution of the polymer releases the impurities which are then removed by filtration, adsorption, or flotation/sedimentation. This yields polymers of high purity for reuse in original applications. The major drawback of a solvent system is Ae increased expense due to the complexity of equipment and higher energy requirements. 

Other criteria for the selection of an extractor are the ease of separation of the two phases and the difficulty of extraction. For example, if the two phases have a large density difference, or at least one is quite viscous, the energy required to get a good enough dispersion for good extraction may lead to excessive backmixing of the continuous phase. 

Hall and Williams [96] doped thin films of lead azide with T1 and Bi. There was no marked effect on the photodecomposition efficiency at 330 nm as compared to undoped films. However, both the spectral dependence of the rate and the optical absorption were altered by thallium. The incorporation of T1 (10 mole fractions) removed the 375 nm peak from the optical absorption spectra while the incorporation of Bi left the peak unaltered. Partial decomposition of films (0.1%) also removed the 375 nm peak (dotted curve. Figure 32). The results are consistent with the fact that the Tl " impurities require anion vacancies for charge compensation. This is equivalent to partial decomposition. They concluded that the peaks in the optical absorption curve and spectral photodecomposition curves are probably a result of charge-transfer excitons. Furthermore, peak separations may arise because of differences in the interaction energies of inequivalent lead and azide ions in the unit cell. The selective removal with decomposition of the 375 nm peak may indicate selective decomposition of the azide site having the highest valence band energy. The selective decomposition would reduce the density of states and thus the extinction coefficient for electronic transitions from that particular azide band. 

To describe the influence of non-equilibrium plasma-treatment and cross-links on the permeability and selectivity of the gas-separating polymer membranes, let us first calculate the energy required for formation in an unbounded elastic medium of a hollow sphere with radius R corresponding to the radius of a penetrating molecule. Solving the Lame equation (9-90) in the absence of external forces (/ = 0) and for radial displacement Mr = R, the compression energy of the elastic medium can be found in this case as (Landau Lifshitz, 1986)... 

Other factors in selecting a suitable catalyst that we should consider include the cost and structure of the catalyst, the toxicity of the catalyst and solvent, the ease of separation of the catalyst from the products, the energy requirement for reaction, the stability of the catalyst in process conditions, and the ease of treatment of the waste streams, in order to lead to an efficient and economic PTC process. 

What makes a separation process green, or environmentally friendly. The first characteristics that come to mind are low energy requirements and minimal waste production. Imagine a separation process that relies on a force generated naturally from the materials involved in the separation itself and that is so selective for a particular target molecule that it requires only small amounts of adsorbent materials, which are relatively simple to recover and reuse. The potential to realize such green ideals is found in functionalized magnetic particles. 

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