Continuous short-residence-time

CCDC built a continuous short residence time coal liquefaction unit with throughput of about 4.5 kg/hr of coal. The SRC unit consisted of a short residence time reactor constructed from 53.3 m of high pressure tubing having an ID of 0.516 or... 

Continuous Short Residence Time Experimentation After determining the effect of Light SRC addition to a conventional SRC-I operation, experimentation moved to determining the effect of Light SRC addition on short residence time coal liquefaction performance ... 

However, in a countercurrent column contactor as sketched in Figure 8, the holdup of the dispersed phase is considerably less than this, because the dispersed drops travel quite fast through the continuous phase and therefore have a relatively short residence time in the equipment. The holdup is related to the superficial velocities U of each phase, defined as the flow rate per unit cross section of the contactor, and to a sHp velocity U (71,72) ... 

The continuous sintering is mainly a zone sintering process in which the electrolyte tube is passed rapidly through the hot zone at about 1700 °C. This hot zone is small (about 60 mm) in zone sintering, no encapsulation devices are employed. The sodium oxide vapor pressure in the furnace is apparently controlled by the tubes themselves. Due to the short residence time in the hot zone, the problem of soda loss on evaporation can be circumvented. A detailed description of / "-alumina sintering is given by Duncan et al. [22]. 

Evaporation can be performed directly from reactors or kettles provided that substances are thermally stable. Such evaporation is time consuming because of the low heat-transfer surface area per unit volume. In the case of temperature sensitive materials, the residence time in the evaporator must be short and the temperature should be as low as possible. Consequently, continuous vacuum evaporators with a short residence time should be used to treat such materials. Falling-film (thin-film) evaporators are suitable to perform such operations. A typical falling-film evaporators is shown in Fig. 7.2-14. Centrifugal evaporators are also commonly used. 

Other advantages of the tubular reactor relative to stirred tanks include suitability for use at higher pressures and temperatures, and the fact that severe energy transfer constraints may be readily surmounted using this configuration. The tubular reactor is usually employed for liquid phase reactions when relatively short residence times are needed to effect the desired chemical transformation. It is the reactor of choice for continuous gas phase operations. 

The special process feature for case 3 is a relatively high reaction enthalpy in combination with a low maximum permissible temperature Texo- An alternative safety solution would be to control both these two parameters. For example by adding a pump to the reactor and with solvent makeup the process can be made continuous (CSTR). This allows the adoption of a higher maximum permissible temperature Texo, because of the short residence time and the dilution effect, and a reduction of the adiabatic temperature increase ATadiab because of the dilution effect. Such a (drastic) process and facility change will always require an iterative safety-technical reaction PHA furthermore additional may become necessary. 

One of the major advantages of flow reaetors is the short residence time of reaetions in the reaetor. This allows seleetive reaetions to pass through the system and out again before any side reaetion ean take plaee. This is very well illustrated in the synthesis of dithioketal and -aeetals, where the seleetive reaetion resulted in superior conversion using eontinuous flow when eompared to bateh synthesis. A dramatic increase of yield was noted in the hydrogenation reaetion performed by Kobayashi et al. when a residence time of less than 1 min was used. The yield inereased from 1% to 97% using the continuous-flow reactor. 

The most common route of exposure for the general population is probably inhalation. However, cresols have a short residence time in both day- and night- time air despite continual releases of cresols to the atmosphere, levels are probably low. Very few atmospheric monitoring data are available in the literature therefore, an average daily intake via inhalation was not calculated. Cigarette smoke is also a source of atmospheric exposure. An individual who smokes two packs of cigarettes a day may inhale 3.0 pg/day (Wynder and Hoffman 1967). 

In many industrial applications, contaminated airsfreams may be produced on a continuous or near-continuous basis, and short residence time flow reactors are needed to treat these streams continuously as they are produced. 

Short residence time means that this desired product is continuously removed from the reactor before any over oxidation can occur. 

The mean residence time of carbon in the mixed layer of the sea before transfer into the deep sea is of considerable interest, for as has already been pointed out, the rate of this transfer will eventually govern the levels of excess 14C in the atmosphere. There have been several estimates of this residence time. Craig (29) concluded that it was most probably not more than 10 years, and in one of his calculations he deduced a value of 4 years. Broecker et al. (14) concluded it was 5 years in the Atlantic Ocean and 8 years in the Pacific Ocean. Nydal (45) found that for the North Atlantic it was around 3 years or less. The profiles of Figure 6, and a few others which are not shown, all show a significant penetration of excess 14C below the mixed surface layer, pointing to a short residence time, of the order of 2 years, in the mixed layer of the sea before transfer below the thermocline into the deep sea. Considering the size of the oceans these data are very meager, and no firm conclusions can be drawn from them. However, continued measurements of 14C in the sea should help to establish a firmer estimate of this quantity. 

The combination of Deloxan-supported precious-metal fixed-bed catalysts and the use of liquid, near-critical, or supercritical C02 and/or propane mixtures creates new possibilities for continuous fixed-bed hydrogenations with significantly improved space-time yields and catalyst lifetimes. Short residence times and well-balanced diffusion and desorption of products and reactants results in a decrease in undesirable by-products and therefore higher selectivity. The characteristics of high-pressure hydrogenations in near-critical or supercritical fluids can be summarized as follows ... 

The lithium intermediate is unstable, even at temperatures as low as 60 °C. Only a continuous process with a short residence time between the two reactions was allowed to avoid decomposition and have sufficient selectivity for an economical process [44]. Clogging is a major issue for the first process. Owing to heat release issues, high dilution is applied, and the recycling of the solvent was an important issue that needed to be considered. 

DuPont and Dow use solution polymerization technology to produce LLDPE resins. The process is based on continuous polymerization of ethylene with 1-octene in cyclohexane at about 250°C and 1200 psi. The catalyst is again Ziegler type. Residence time is of the order of several minutes. The catalyst is deactivated by treatment with an alcohol or complexing agent such as acetyl-acetone, and adsorbed on a silaceous adsorbent before stripping the solvent. The Stamicarbon (Dutch State mines) process is similar to the DuPont process, and it uses a short-residence-time solution process for HDPE production. 

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