Performance of selected hydrocarbon solvents

Particle size which relates to the surface area available for extraction and is obviously one of the most important factors for extraction study. Coats and Wingard noticed that par- 

Wingard and Philhps developed a madiematical model to describe the effect of temperature on extraction rate using a percolation extractor as follows  

Flakes of oilseeds were most fi equently used for the solvent extraction studies. Sometimes, ground oilseed kernels through a specified sieve size was used. Residual oil content in the extracted flakes after a certain specified extraction condition or oil content in miscella (mixture of oil and solvent) was examined and the percentage of total oil extracted was calculated. The total extractable oil of flakes was determined by four hours Soxhlet extraction. Wan et al. used a precision densitometer to determine the miscella concentration (percent of oil in miscella by weight) after a given time of extraction from which the per- 

Arnold and Choudhury reported results derived from a lab scale extraction of soybean and cottonseed flakes in a tubular percolation extractor at 135-140T with pure, high purity and commercial hexane, and reagent grade benzene. They claimed that pure hexane extracted soybean slower than high purity and commercial hexane. During the first 60 minutes of extraction, benzene extracted more oil than the hexanes. However, at the end of 80 minutes, benzene extracted only slightly more than pure hexane but definitely less than the commercial hexanes. Similar results were obtained for the four solvents when cottonseed flakes were extracted. 

Quality-Efficiency Rating = QA(Oil Yield Facter) + 0.4 Refining Less Facter) 

Quality-Efficiency Rating=0.4 (Oil Yield Factor) + 0.4 (Refining Loss Factor) 

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Molybdenum hexacarbonyl [Mo(CO)6] has been vised in combination with TBHP for the epoxidation of terminal olefins [44]. Good yields and selectivity for the epoxide products were obtained when reactions were performed under anhydrous conditions in hydrocarbon solvents such as benzene. The inexpensive and considerably less toxic Mo02(acac)2 is a robust alternative to Mo(CO)6 [2]. A number of different substrates ranging from simple ot-olefms to more complex terpenes have been oxidized with very low catalytic loadings of this particular molybdenum complex (Scheme 6.2). The epoxidations were carried out with use of dry TBHP (-70%) in toluene. 

When the distannyl reagent 7 is employed, the fate of the reaction apparently depends on the reaction conditions. Indeed, Eisch observed that the reaction of 7 with boron trichloride at —40 °C in hydrocarbon solvent is not always selective and leads to the formation of both a monoborylated intermediate (10) that slowly converts into 6 (Scheme 5). The outcome of these reactions is apparently further complicated by a fast methyl group transfer from the tin to the boron centers yielding the undesired monoborylated derivative 11. Eisch also found that such reactions are not limited to the case of boron trialide but can be performed with dialkyl boron halide starting materials. For example, the reaction of the distannane... 

Selection of an appropriate solvent for Friedel-Crafts acylation is an important question since solvents are known to affect regioselectivities.8,9 In many cases acylation is carried out in an excess of the reacting aromatic compound. Aromatics, however, are poor solvents for most Lewis acids and therefore, they merely serve as diluent in biphase systems. Carbon disulfide is a reasonably good solvent just as dichloromethane and dichloroethane. Although AICI3 is insoluble in chlorinated hydrocarbons, they dissolve many of the complexes formed between acyl halides and AICI3. Nitrobenzene and nitromethane are also suitable solvents. Moreover, the 1 1 addition complexes they form with AICI3 allow acylations to be performed under mild conditions often without side reactions. 

Reductive cyclocondensation of alkane-1,2-dithiols or alkane-1-thio-l,2-diols with [Re(0)3(Tp )] and PPI13 has been investigated and [Re(0)(Tp )(SCH2CH2S)] has also been structurally characterized. The 1,2-diolato complexes are less thermally stable than the sulfur analogs, stable in hydrocarbon solvents for more than one week at 120°C. DFT calculations have been performed on selected derivatives.208... 

Because the surfactants described previously were selected for hydrocarbon-miscible flooding, the effect of hydrocarbon solvent on foam performance should be included in the surfactant screening process. Data on the characteristics of foams generated with light hydrocarbons as the gas phase are not readily available in the literature. Limited data comparing nitrogen foams with hydrocarbon solvent foams are shown in Table... 

Adsorption/desorption and pore-transport are key parameters influencing the activity, effectiveness factors, and product selectivity in porous catalysts. With conventional reaction media (either gas or liqnid phase), one of these parameters is generally favorable while the other is not. For instance, while desorption of heavy hydrocarbons from the catalyst is nsnally the rate-limiting step (and therefore detrimental to catalyst performance) in gas-phase reactions, transport of the reactants/products is the limiting step in liquid-phase reaction media. Furthermore, with conventional media, it is usually difficult to achieve the desired combination of flnid properties for optimum system performance. In contrast, density and transport properties can be continuously pressure-tuned in the near-critical region to obtain unique fluid properties (eg, gas-like transport properties yet liquid-like solvent power and heat capacities). 

When heated to 125 °C in a hydrocarbon solvent in the presence of a thiol as the catalyst and DBPB as initiator, the c/s-cyclic ketal 7 underwent selective epimerization at the C-H center a to oxygen to give the thermodynamically more stable trans-epimer 8. Silanethiols were found to be more effective protic-polarity reversal catalysts than alkanethiols (eq 4). Thus, in the presence of TBST and a small amount of collidine as the scavenger of adventitious acid formed under the reaction conditions, the epimerization of 7 proceeded smoothly to give 8 in 84% conversion after 1 h. Interestingly, when triphenylsilanethiol was used as the catalyst, the coadministration of collidine proved to be detrimental, resulting in a suppression of the isomerization. This is probably because this latter thiol is susceptible to nucleophilic attack by the base. The improved performance of TBST is therefore attributed to its stability toward nucleophilic substitution at the silicon center. 

Recently Milczak et al.[57] have reported the nitration of o-xylene using 100% nitric acid over silica supported metal oxide solid acid catalysts with high yields (up to 90 %) but low selectivity to 4-o-NX (40-57 %). Choudary et a/. 5X 591 performed the nitration of o-xylene and other aromatic hydrocarbons by azeotropic removal of water over modified clay catalysts achieving low yields of 4-o-NX and a selectivity of 52%. Better results were obtained when HBeta zeolite was used as catalyst, performing the reaction in dichloromethane at reflux temperature.[60] Conversions of 40 % and maximum selectivity 68 % of 4-o-NX were obtained. Similar conversions and higher selectivities for 4-o-NX (65-75 %) were reported by Rao et al M 1 using a nanocrystaUine HBeta sample and working at 90 °C in the absence of solvent. 

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