Predictive maintenance approach

The AMI Hamiltonian with a 2 x 2 CAS-CI (two electrons in the space of the HOMO and LUMO) was used to describe the surfaces and coupling elements. The electron-transfer process studied takes place on the ground-state, with the upper state providing diabatic effects, that is, passage to this surface can delay, or even hinder, the transfer process. A surface hopping approach was used for the dynamics with a Landau-Zener hopping probability and using the Miller-George correction for the momentum after a hop. The charge distii-bution was used to describe the positions along the reaction coordinate with charge localization on the left and right corresponding to reactant and product, and the symmetric delocalized charge denoting the non-adiabatic region. The studies used trajectories taken from thermalized ensembles to provide detailed dynamic information for the transfer processes, and the relationship between energy gap, electronic coupling between states and rates of transfer.  [c.310]

As we have seen, a common route to calculating both the partition coefficient and molar refractivity is by combining in some way the contributions from the fragments or atoms in the molecule. The fragment contributions are often determined using multiple linear regression, which will be discussed below (Section 12.12.2). Such an approach can be applied to many other properties, of which we shall mention only one other here, solubility, Klopman and colleagues were able to derive a regression model for predicting aqueous solubility based upon the presence of groups, most of which corresponded to a single atom in a specific hybridisation state but also included acid, ester and amide groups [Klopman et al. 1992]. This gave a reasonably general model that was able to predict the solubility of a test set within about 1.3 log units. A more specific model which contained more groups performed better but was of less generic applicability.  [c.687]

Microorganisms that secrete proteins often secrete proteases. Many secreted enzymes are actually resistant to proteolytic degradation, at least in their natural host, but some are not. To maintain product stabiUty, it maybe necessary to remove or reduce the proteolytic activity of the host. This can be achieved by classical mutagenesis, particulady in those cases where the microorganism only produces one protease, or by replacing normal genes on the chromosome with genes that have been inactivated in the test tube. This precise modification normally does not affect other properties of the host, and proteases maybe inactivated one after another. This approach, however, requires that suitable genetic engineering techniques be appHed to the particular host strain, and that each of the proteases is cloned.  [c.286]

Mechanical thermocompression may employ reciprocating, rotary positive-displacement, centrifugal, or axial-flow compressors. Positive-displacement compressors are impractical for all but the smallest capacities, such as portable seawater evaporators. Axial-flow compressors can be built for capacities of more than 472 mVs (1 X 10 ftVmin). Centrifugal compressors are usually cheapest for the intermediate-capacity ranges that are normally encountered. In all cases, great care must be taken to keep entrainment at a minimum, since the vapor becomes superheated on compression and any liquid present will evaporate, leaving the dissolved solids behind. In some cases a vapor-scrubbing tower may be installed to protect the compressor. A mechanical recompression evaporator usually requires more heat than is available from the compressed vapor. Some of this extra heat can be obtained by preheating the feed with the condensate and, if possible, with the product. Rather extensive heat-exchange systems with close approach temperatures are usually justified, especially if the evaporator is operated at high temperature to reduce the volume of vapor to be compressed. When the product is a sohd, an elutriation leg such as that shown in Fig. 11-1225 is advantageous, since it cools the product almost to feed temperature. The remaining heat needed to maintain the evaporator in operation must be obtained from outside sources.  [c.1143]

A 500-nil three-necked flask is fitted with a mechanical stirrer, thermometer, and a dropping funnel, and all openings are protected by drying tubes. Ethylene chloride (120 ml) is placed in the flask and anhydrous aluminum chloride (50 g, 0.38 mole) is added in several portions with stirring. The flask is cooled to maintain the temperature at approx. 25°, and acetyl chloride (47 g, 0.6 mole) is gradually added over about 10 minutes. The stirred solution is now cooled to 5-10° and Decalin (technical grade, 36 g, 0.26 mole) is added slowly over 2 hours. The solution is maintained at 5-10° for 3 hours with continued stirring after the addition is completed. The mixture is now added gradually to a vigorously stirred slurry of crushed ice and water (600 g). The organic (lower) layer is separated, and the aqueous phase is extracted once with 100 ml of ethylene chloride. The combined ethylene chloride solutions are washed several times with cold water, and finally dried over potassium carbonate. The solvent is evaporated (rotary evaporator) and the residue is fractionally distilled. The forerun consists of unchanged Decalin, bp 65-70°/10 mm (185-190°/ atm). The product is collected at bp 105-111°/8 mm and the yield is about 11 g.  [c.148]

Chastrette and Chastrette showed that the cyclocooligomerization of furan and acetone was improved by the presence of lithium salts. Liotta and co-workers reported the synthesis of 12-crown-4 by a double Williamson approach in the presence of LiC104. They mention in a footnote that A run performed as detailed but without UCIO4 gave no product . Other inferential evidence has accumulated as well.  [c.14]

N,N-Dimethylcyclohexylmethylamine A 500-ml three-necked flask fitted with a reflux condenser (drying tube), a pressure-equalizing dropping funnel, and a magnetic stirrer is charged with a mixture of 5 g of lithium aluminum hydride in 60 ml of anhydrous ether. A solution of 20 g of A, A-dimethylcyclohexanecarboxamide in 50 ml of anhydrous ether is added to the stirred mixture at a rate so as to maintain a gentle reflux (about 30 minutes). The mixture is then stirred and heated (mantle) at reflux for 15 hours. The flask is fitted with a mechanical stirrer and cooled in an ice bath. Water (12 ml) is added slowly with vigorous stirring, and the stirring is continued for an additional 30 minutes. A cold solution of 30 g of sodium hydroxide in 75 ml of water is added and the mixture is steam-distilled until the distillate is neutral (about 225 ml of distillate). The distillate is acidified by addition of concentrated hydrochloric acid (approx. 15 ml) with cooling. The layers are separated, and the ether layer is washed with 10 ml of 3 A hydrochloric acid. The combined acidic solutions are concentrated at 20 mm pressure until no more distillate comes over at steam-bath temperature. The residue is dissolved in water (approx. 30 ml), the solution is cooled, and sodium hydroxide pellets (17 g) are added slowly, with stirring and cooling in an ice-water bath. The layers are separated, and the aqueous phase is extracted with three 15-ml portions of ether. The combined organic layer and ether extracts are dried over potassium hydroxide pellets for 3 hours. The solvent is removed by fractional distillation at atmospheric pressure, and the product is collected by distillation under reduced pressure. The yield is about 16 g (88%) of A,A-dimethylcyclohexylmethylamine, bp 76729 mm, 1.4462-1.4463.  [c.20]

A 250-ml, three-necked, round-bottom flask is fitted with a mechanical stirrer, a condenser, a nitrogen inlet and outlet, and a pressure-equalizing addition funnel. The flask is charged with 20 ml of anhydrous ether and 3 g (0.12 g-atom) of magnesium turnings. A nitrogen atmosphere is established and maintained in the system. The addition funnel is charged with 19.5 g (0.14 mole) of methyl iodide, and a few drops are added to the stirred flask. After the spontaneous reaction begins, the remainder of the methyl iodide is added at a rate so as to maintain a gentle reflux. After the methyl iodide has been added and the magnesium is completely dissolved, cuprous bromide (0.2 g) is added and the flask is cooled with stirring in an ice-water bath to 5°. A solution of isophorone (11 g, 0.08 mole) in 15 ml of ether is added to the stirred cooled flask over a period of about 20 minutes. The flask is allowed to stir at room temperature for 1 hour, and finally, the mixture is refluxed for 15 minutes. To the cooled reaction mixture is added a mixture of 50 g of ice and 6 g of acetic acid. The ether layer is separated, and the aqueous layer is extracted with an additional 25-ml portion of ether. The combined ether extracts are washed twice with sodium carbonate solution and twice with water. After drying (anhydrous sodium sulfate) and filtration, the ether is removed (rotary evaporator). The residual oil is fractionally distilled yielding a small forerun (approx. 7%) of l,3,5,5-tetramethyl-l,3-cyclohexadiene, bp 24-2577 mm (151-1557760 mm). The desired product, 3,3,5,5-tetramethylcyclohexanone, is obtained in about 80% yield, bp 59-6175.5 mm (196-1977760 mm).  [c.145]

See pages that mention the term Predictive maintenance approach : [c.519]    [c.2145]   
Turboexpanders and Process Applications (0) -- [ c.444 ]