Vessels extraction rates

SEE extraction pressures of 500 bar at 80 to lOO C combined with countercurrent cascading mode of extraction using four extraction vessels, the rate of oleoresin extraction doubles again rate of oleoresin extraction under these conditions is four times that of traditional batch extraction at 300 bar and 60°C... 

In discussing the first two problems listed above, what we are really interested in, of course, is determining how the variables involved influence the rate of extraction we can obtain in an agitated vessel. The rate of mass transfer of solute from the solution to be extracted into an immiscible extraction solvent is usually described by some such relation as... 

HSS method made it possible to measure both an interfacial concentration and an extraction rate for the first time by a simple principle. When a two-phase system is highly stirred or agitated in a vessel and the interfacial area is extremely extended, the interfacial amount of an adsorbed compound is increased... 

Extraction Rates. The design of large-scale solvent extraction vessels must accommodate the rate at which equilibrium is attained between the free miscella flowing past the solid particles and the miscella absorbed within the solids. Attainment of equilibrium may be quite slow, particularly as the oil content of the solid material drops to low levels. Investigations show that the rate at which equilibrium is approached (in effect, the extraction rate) is influenced by many factors, including the intrinsic capacity for diffusion of solvent and oil, which is determined primarily by the viscosities of the two the size, the shape, and the internal structure of the solid particles and, at low oil levels in the solids, the rate at which the solvent dissolves nontriglyceride substances that are soluble but dissolve less readily than the triglycerides. 

U-tube shown in the figure. The term no more is a relative one since the rate of extraction will slow down markedly, but not necessarily to zero, after the polymer fraction that is most soluble, or more precisely, after the fraction that exhibits the highest distribution coefficient in the gas, is dissolved and removed from the column. When the extraction rate drops markedly, indicating that the oligomers of extractable molecular weight have been removed at the specific pressure level, the pressure level is raised, the collection vessel changed, and a new polymer fraction is collected in the U-tube. The sequential pressure increase/collection sequence is continued until all the polymer is dissolved, or until some maximum pressure dictated by the system design is reached. 

A pragmatic approach to extraction kinetics is to measure extraction rates under mass transfer conditions that are similar to those expected in processing equipment and that are characterized well enough io allow estimation of interfacial concentrations. With such measurements ons can dalarmine whether the kinetics of a particular system are fast or slow computed to mass transfer, and if they are slow, the rate can be correlaled with interfacial conditions. Several methods are used to measure extraction kinetics ihass include measurements with (l) well-stirred vessels, (2) single drops or jets, and (3) the Lewis cell. 

Solvent temperature also greatly impacts extraction rate, so the solvent is heated close to the boiling point (bp of industrial hexane is 65—70 C). Avoid solvent boiling, however, because extraction vessels are not designed for pressurization, and solvent losses increase and safety is compromised. 

The porosity (ie, pore size and amount of pores) of microparticles is also an important characteristic to take into consideration when fabricating microparticles because it plays an essential role in controlling the release of payloads. The porosity and morphology of particles are usually determined by scanning electron microscopy (SEM). For the emulsification solvent extraction/evaporation method of fabrication, the rate of solvent extraction, which depends on the flow in the stirred vessel the droplet size the temperature and the dispersed phase hold-up in the 0/W emulsion have an effect on porosity [87]. The porosity usually increases with a decrease in solvent extraction rate. The porosity of microparticles results in initial burst release due to pore diffusion [78,88]. Mao et al. studied the influence of different W/O/W emulsification solvent extraction/evaporation process parameters on internal and external porosity of PLGA microparticles [78]. The surface morphology of the microparticles can be influenced by the type of polymer, internal aqueous phase voliune (Wi), volume of continuous phase (W2), polymer concentration, homogenization speed, and equipment used for the primary emulsion [78,79]. 

The air extraction rate per minute for dust removal from cement bins and similar vessels associated with bulk cement handling should be approximately three times... 

A hst of polyol producers is shown in Table 6. Each producer has a varied line of PPO and EOPO copolymers for polyurethane use. Polyols are usually produced in a semibatch mode in stainless steel autoclaves using basic catalysis. Autoclaves in use range from one gallon (3.785 L) size in research faciUties to 20,000 gallon (75.7 m ) commercial vessels. In semibatch operation, starter and catalyst are charged to the reactor and the water formed is removed under vacuum. Sometimes an intermediate is made and stored because a 30—100 dilution of starter with PO would require an extraordinary reactor to provide adequate stirring. PO and/or EO are added continuously until the desired OH No. is reached the reaction is stopped and the catalyst is removed. A uniform addition rate and temperature profile is required to keep unsaturation the same from batch to batch. The KOH catalyst can be removed by absorbent treatment (140), extraction into water (141), neutralization and/or crystallization of the salt (142—147), and ion exchange (148—150). 

The sulfur-bearing cap rock, being an enclosed formation, is essentially the equivalent of a pressure vessel. Hot water, pumped into the formation to melt sulfur, must be withdrawn after cooling at approximately the same rate as it is put in, otherwise the pressure in the formation would increase to the point where further water injection would be impossible. Bleedwater weUs, used to extract water from the formations, usually are located on the flanks of the dome away from the mining area where the water temperature is lowest. The water is treated to remove soluble sulfides and other impurities before being discharged to disposal ditches or canals. 

A solution of 12.5 g (0.088 mole) of l,4-dioxaspiro[4.5]decane (Chapter 7, Section IX) in 200 ml of anhydrous ether is added to the stirred mixture at a rate so as to maintain a gentle reflux. (Cooling in an ice bath is advisable.) The reaction mixture is then refluxed for 3 hours on a steam bath. Excess hydride is carefully destroyed by the dropwise addition of water (1-2 ml) to the ice-cooled vessel until hydrogen is no longer evolved. Sulfuric acid (100 ml of 10% solution) is now added followed by 40 ml of water, resulting in the formation of two clear layers. The ether layer is separated and the aqueous layer extracted with three 20-ml portions of ether. The combined ethereal extracts are washed with saturated sodium bicarbonate solution followed by saturated sodium chloride solution. The ethereal solution is dried over anhydrous potassium carbonate (20-24 hours), filtered, and concentrated by distillation at atmospheric pressure. The residue is distilled under reduced pressure affording 2-cyclohexyloxy-ethanol as a colorless liquid, bp 96-98°/ 3 mm, 1.4600-1.4610, in about 85% yield. 

The Penumbra stroke system (Penumbra Inc., San Leandro, CA) includes two different revascularization options (1) thrombus debulking and aspiration may be achieved by a reperfusion catheter that aspirates the clot while a separator device fragments it, and (2) direct thrombus extraction may be performed by a ring retriever while a balloon guide catheter is used to temporarily arrest flow. This system has been tested in a pilot trial in Europe. Twenty patients (mean NIHSS 21) with a total of 21 vessel occlusions (7 ICA, 5 MCA, and 9 Basilar) were treated up to 8 hours after symptom onset. Recanalization prior to lA lysis was achieved in all cases (48% TIMI 2 52% TIMI 3). Seven patients were also treated with lA UK or rt-PA. Good outcome at 30 days (defined as mRS < 2 or NIHSS 4-point improvement) was demonstrated in 42%. The mortality rate was 45%, but there were no device-related deaths. There was one asymptomatic SAH and three symptomatic ICHs. A prospective, single-arm, multicenter trial is being conducted in the United States and Europe currently. 

Volumes Vl and Vq of the two immiscible liquid phases, are added to the extraction vessel and a single solute distributes itself between the phases as concentrations X and Y, respectively, at a rate, Q, as shown in Fig. 3.30. 

A significant advance was made in this field by Watarai and Freiser [58], who developed a high-speed automatic system for solvent extraction kinetic studies. The extraction vessel was a 200 mL Morton flask fitted with a high speed stirrer (0-20,000 rpm) and a teflon phase separator. The mass transport rates generated with this approach were considered to be sufficiently high to effectively outrun the kinetics of the chemical processes of interest. With the aid of the separator, the bulk organic phase was cleanly separated from a fine dispersion of the two phases in the flask, circulated through a spectrophotometric flow cell, and returned to the reaction vessel. 

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