Addition rate

The 4-hydroxy-THISs react with electron-deficient alkynes to give cycloadducts (3) that spontaneously eliminate sulfur, producing 2-pyridones (3). Bulky 5-substituents lead to a decrease in the addition rate, and elimination of isocyanate with formation of thiophenes becomes favored (3, 12, 13). Benzyne yields an isolable adduct that exclusively extrudes isocyanate on thermolysis, but sulfur on irradiation (Scheme 7)... 

The following conditions are stipulated the catalyst decomposition rate constant must be one hour or greater the residence time of the continuous reactor must be sufficient to decompose the catalyst to at least 50% of the feed level the catalyst concentration must be greater than or equal to 0.002 x Q, where the residence time, is expressed in hours. An upper limit on the rate of radical formation was also noted that is, when the rate of radical formation is greater than the addition rate of the primary radicals to the monomers, initiation efficiency is reduced by the recombination of primary radicals. 

The extent of the initial hydrolysis depends on temperature and how the water is added. Hydrolysis is reduced at slower addition rates and lower temperatures. The hydrolysis subsequent to the initial fast reaction is slow, presumably because part of the acid is converted to fluorosulfate ions which hydrolyze slowly even at elevated temperatures. The hydrolysis in basic solution has also been studied (17). Under controlled conditions, hydrates of HSO F containing one, two, and four molecules of water have been observed (18,19). 

Initiators. The degree of polymerization is controlled by the addition rate of initiator(s). Initiators (qv) are chosen primarily on the basis of half-life, the time required for one-half of the initiator to decay at a specified temperature. In general, initiators of longer half-Hves are chosen as the desired reaction temperature increases they must be well dispersed in the reactor prior to the time any substantial reaction takes place. When choosing an initiator, several factors must be considered. For the autoclave reactor, these factors include the time permitted for completion of reaction in each zone, how well the reactor is stirred, the desired reaction temperature, initiator solubiUty in the carrier, and the cost of initiator in terms of active oxygen content. For the tubular reactors, an additional factor to take into account is the position of the peak temperature along the length of the tube (9). 

Shell Higher Olefins Process (SHOP). In the Shell ethylene oligomerization process (7), a nickel ligand catalyst is dissolved in a solvent such as 1,4-butanediol (Eig. 4). Ethylene is oligomerized on the catalyst to form a-olefins. Because a-olefins have low solubiUty in the solvent, they form a second Hquid phase. Once formed, olefins can have Htfle further reaction because most of them are no longer in contact with the catalyst. Three continuously stirred reactors operate at ca 120°C and ca 14 MPa (140 atm). Reactor conditions and catalyst addition rates allow Shell to vary the carbon distribution. 

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). 

Economics vary, depending onlocation and country. In Japan, for example, the quinone of choice is the disodium salt of l,4-dihydto-9,10-dihydtoxyanthtacene (DDA). Unlike AQ, DDA is direcdy soluble in white Hquor and thus readily penetrates the chip. AQ works well with both hardwoods and softwoods. Addition rates as low as 0.025% by weight give satisfactory increases (ca 1—2%) in pulping rate and yield, especially for hardwoods. In the United States in 1987, the FDA put a limitation to the amount of AQ that can be added to most pulp to 0.11%. This typically is the amount added to softwoods lesser amounts ate employed with hardwoods. 

Because PEA is such an important fragrance material this simple, essentially one-step process has been exhaustively studied to optimize reaction conditions and purification procedures. Because of the high reactivity of the iatermediates and the tendency toward polymer formation, critical factors such as throughput, temperature, molar ratios of reactants, addition rates, reactor materials and design, and agitation rate must be carefully balanced to provide an economical product with acceptable odor properties. 

The equivalent nickel content of the feed to the FCCU can vary from <0.05 ppm for a weU-hydrotreated VGO to >20 ppm for a feed containing a high resid content. The nickel and vanadium deposit essentially quantitatively on the cracking catalyst and, depending on catalyst addition rates to the FCCU, result in total metals concentrations on the equiUbrium catalyst from 100 to 10,000 ppm. 

These values assume chlorination in carbon tetrachloride solution under homogeneous conditions favoring random distribution of chlorine atoms along the chain. Viscous reaction conditions, faster chlorine addition rates, lower temperature conditions, etc, can lead to higher AH at equivalent chlorine levels because of more blocky chlorine distribution on the polymer chain. 

Tlocciilant addition rate can be regulated in proportion to the thickener oliirnetric feed rate or solids mass How in a feed-fonvard mode, or in a feed-back mode on either rake torque, iindertlow density, settling solids (sludge) bed le el, or solids settling rate. Of these, feed-fonvard on mass How or feed-back on bed le el are probably the most common. In some feed-fonvard schemes, the ratio multiplier is trimmed by one of the other parameters. 

Thus the requirement for the use of man-made drugs and dietary additives as veterinary medicines for the treatment of farmed animals is considerable and worth about 100 million pounds sterling annually in the UK ( 104 million in 1994j io jjjg investment in dietary additives such as vitamins, trace minerals, coccidiostats, pigmenters, enzymes and other probiotics to feed compounders in the UK is worth about 110 million, assuming an addition rate of 2.5 kg per tonne and a cost of approximately 3% of the total concentrate dietary cost (calculated from MAFF data, 1995). ° These data can be increased by a factor of about 10 when the compound feed produced within Europe is considered. 

The addition rate of the hydrogen peroxide must be adjusted so that the temperature of the reaction mixture does not rise above 10 C. The yield is reduced if the temperature is allowed to rise above that point. The end point of the reaction, when excess peroxide is present, can be determined with potassium iodide - starch test paper. The yield also is reduced if more than a slight excess of hydrogen peroxide is used. 

The addition rate is such that a gentle reflux is maintained... 

It is important that the formaldehyde addition rate be balanced with the alkali content of the system and the engineering control capability. At high alkali contents, the exotherm will be more vigorous and create more load on the heat exchangers. At low alkali contents, the reaction rate may be quite slow. While this temporarily reduces the difficulty in instantaneous heat load, it may permit potentially hazardous levels of unreacted formaldehyde to accumulate. Such accumulations could become dangerous as batch temperature rises. In both cases. 

Since the catalyst is so important to the cracking operation, its activity, selectivity, and other important properties should be measured. A variety of fixed or fluidized bed tests have been used, in which standard feedstocks are cracked over plant catalysts and the results compared with those for standard samples. Activity is expressed as conversion, yield of gasoline, or as relative activity. Selectivity is expressed in terms of carbon producing factor (CPF) and gas producing factor (GPF). These may be related to catalyst addition rates, surface area, and metals contamination from feedstocks. 

Limit the total possible charge to a batch reactor by using a precharge or feed tank of limited capacity. Alternatively, limit the addition rate by selecting a pump with a maximum capacity lower than the safe maximum addition rate for the process, or by using restriction orifices. 

Consecutive reactions involving one first-order reaction and one second-order reaction, or two second-order reactions, are very difficult problems. Chien has obtained closed-form integral solutions for many of the possible kinetic schemes, but the results are too complex for straightforward application of the equations. Chien recommends that the kineticist follow the concentration of the initial reactant A, and from this information rate constant k, can be estimated. Then families of curves plotted for the various kinetic schemes, making use of an abscissa scale that is a function of c kit, are compared with concentration-time data for an intermediate or product, seeking a match that will identify the kinetic scheme and possibly lead to additional rate constant estimates. 

This class of substrate is the only real problematic substrate for the AE reaction. The enantioseleetivity of the AE reaction with this class of substrate is often variable. In addition, rates of the catalytic reactions are often sluggish, thus requiring stoichiometric loadings of Ti/tartrate. Some representative product epoxides from AE reaction of 3Z-substituted allyl alcohols are shown below. 

Partial Load at Rated or Reduced Speed tenth Hand Valve. ° The hand valves are considered to give the turbine additional ratings (as percent of original rating), and these values may be used as rating points following the oudine given for rated and also for partial loads. 

A small amount of nickel in the FCC feed has a significant influence on the unit operation. In a clean gas oil operation, the hydrogen yield is about 40 standard cubic feet (scf) per barrel of feed (0.07 wi /r ). This is a manageable rate that most units can handle. If the nickel level increases to 1.5 ppm, the hydrogen yield increases up to 100 scf per barrel (0.17 wt%). Note that in a 50,000 barrel/day unit, this corresponds to a mere 16 pounds per day of nickel. Unless the catalyst addition rate is increased or the nickel in the feed is passivated (see Chapter 3), the feed rate or conversion may need to be reduced. The wet gas will become lean and may limit the pumping capacity of the wet gas compressor. 

A higher catalyst addition rate dilutes the concentration of metals and allows less time for the vanadium to get fully oxidized. 

These contaminates originate largely from the heavy (1,050-t- °F/ 566-t- °C), high-molecular weight fraction of the FCC feed. The quantity of these metals on the E-cat is determined by their levels in the feedstock and the catalyst addition rate. Essentially, all these metals in the feed are deposited on the catalyst. Most of the iron on the E-cat comes from metal scale from piping and from the fresh catalyst. 

B = Catalyst addition rate, pounds of catalyst per barrel of feed... 

Figure 3-14 is the graphical solution to the above equation and can be employed to estimate metals content of the E-cat, based on feed metals and catalyst addition rate. 

Figure 3-14. Catalyst metals content versus catalyst addition rate for 22°API Gravity Feed. (Source Katalystics Regional Technology Seminar, New Orleans, Louisiana, December 15, 1998.)...

The amount of fresh catalyst added is usually a balance between catalyst cost and desired activity. Most refiners monitor the MAT data from the catalyst vendor s equilibrium data sheet to adjust the fresh catalyst addition rate. It should be noted that MAT numbers are based on a fixed-bed reactor system and, therefore, do not truly reflect the dynamics of an FCC unit. A catalyst with a high MAT number may or may not produce the desired yields. An alternate method of measuring catalyst performance is dynamic activity. Dynamic activity is calculated as shown below ... 

A jj = Catalyst microactivity at anytime Aq = Catalyst inicroactivity at starting time t = Time after changing catalyst or makeup rate S = Daily fractional replacement rate = addition rate/inventory K = Deactivation constant = fn(A, - A )/-t... 

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