Short-contact-time continued

In delayed coking, the reactor system consists of a short contact-time heater coupled to a large drum in which the preheated feed soaks on a hatch basis. Coke gradually forms in the drum. A delayed coking unit has at least a pair of drums. When the coke reaches a predetermined level in one drum, flow is diverted to the other so that the process is continuous. 

The aqueous solution flows from the jet nozzle to a receiving capillary with no overflow into the outer stream, resulting in short contact times of around 0.05 s. Analysis is implemented by flowing the outer organic phase continually through a closed loop and monitoring concentration changes spectrophotometrically. The apparatus used by Freeman and Tavlarides employed capillaries with internal diameters of 2 mm, and the... 

Continuous Bench-Scale Experimentation With encouraging results obtained from microautoclave tests, experimentation emphasis moved to the bench-scale unit Here the concept of adding Light SRC to the recycle solvent on a continuous basis was tested Earlier work (j>) performed on short contact time coal liquefaction showed Indiana V coal to be out-of-solvent balance Also the operability of the continuous bench-scale SRT unit was highly dependent upon the quality of the solvent ... 

Continuous refining process, on the other hand, offers the following major advantages over the batch-type operation (1) saponification of neutral oil is minimized due to a short contact time of 30-45 s between oil and sodium hydroxide (2) the time consumed for the separation of the aqueous soapstock and wash water from the oil is reduced considerably by passage through centrifugal separators. 

Meade (26), who made use of an alkali metal alkoxide as a catalyst at 100°C at atmospheric and shghtly above atmospheric pressure. Further refinement was made by Tesoro (27), who conducted the reaction at 55-75°C and a vacuum of 4—8 kPa. Schurman (28) patented a continuous process for making alkanolamide, which makes use of a thin film reactor. It is claimed the short contact time in the reactor produces a high-purity alkanolamide (29). 

Until recently only a few papers were available on moving beds in cross flow [11-18]. This type of reactor is sometimes a favorable process solution for a selective catalytic process with a moderate catalyst rcsidence time and with a short gas residence time, especially when the process is accompanied by a continuous catalyst regeneration. The use of conventional short-contact-time reactors like fluidized-bed reactors, risers, and fixed-bed reactors does not always yield satisfactory results. This may be explained by problems connected with gas back-mixing, channeling of gas, low catalyst holdup, attrition of the solid catalyst, or difficulties in temperature control. 

When long residence time is not needed for chemical reaction or other purposes, small highly powered tank mixers may be suitable, with energy inputs measured in HP/gal rather than HP/1000 gal. They bring together several streams continuously for a short contact time (at most a second or two) and may be used whenever the effluent remains naturally blended for a sufficiently long time, that is, when a true solution is formed or a stable emulsion-like mixture. When it is essential that the mixing be immediate each stream will... 

Advantages of entrained-flow reactors are the high mass-transfer rates, short contact times, and the possibility of continuous catalyst replacement. Dis-... 

There are few reports of successful one-step synthesis of primary diamines, and the examples are limited to amines with a special structure. Amination of 1,4-cy-clohexanediol in supercritical ammonia (135 bar) over a Co-Fe catalyst alforded 67 % 1,4-diaminocyclohexane [21]. Excess ammonia, as both supercritical solvent and reactant, and short contact time in the continuous fixed-bed reactor favored the desired reactions. In the best example the cumulative selectivity for the diamine and the intermediate amino alcohol was 97 % at 76 % conversion. Recycling of the unreacted diol and amino alcohol can provide an alternative to the eurrent process, the hydrogenation of pnra-phenylenediamine. The high seleetivity was because of the rigid structure and the relative positions of OH functionality in the substrate. For comparison, amination of 1,4-butanediol under similar conditions yielded pyiTolidine as the major product 1,4-diaminobutane was barely detectable. When 1,3-cyclohexanediol was aminated with the same catalyst in the continuous system, the yield of 1,3-diaminoeyclohexane dropped below 5%, mainly because elimination of water led to undesired monofunctional products via a,/9-unsaturated alcohol, ketone, and/or amine intermediates [22]. 

For practical use, it is commonly preferred a high degree of mixing, as in an ideal CSTR configuration, to properly control the I/O ratio within the whole reactor. In these configurations, catalyst pellets are commonly slurried in the liquid hydrocarbons. To account for a continuous catalyst removal and reactivation, the slurry-riser reactor has been chosen as a suited configuration. In the riser reactors, the feed and the catalyst pellets flow in cocurrent and the solid is Anally separated from the liquid, usually by decanting, after a short contact time. 

A very common preparation of OF2 is the alkaline hydrolysis of F2, see Fluor Erg.-Bd. 1, 1959, p. 223, and also [1]. Fluorine (2 to 6 L/h) is bubbled through a 3% aqueous NaOH solution (precooled in an ice bath). The base solution is continuously replaced at the rate of 1 to 2 L/h. Short contact time limits the formation of O2. Purification by repeated distillation yields almost 100% OF2 [3]. Variations of this method for large scale preparation of OF2 are given [4, 5]. 

In the experiments conducted with additives the amount of additive was kept around 10 % of the solid material. From the point of view of solid waste disposal and possible utilization of this product, the CaS03/CaS04 ratio plays an important role. In general, CaS03 is not desired in the product. The contact time in the spray drier was less than one second. On the other hand, residence time in a conventional spray drier is between 5 and 12 seconds. Results of this work showed that over 70% SO2 removal could be achieved in such a short contact time. This indicates that most of the sorption reaction takes place in a small region around the nozzle. Reaction between SO2 and droplets takes place with a simultaneous evaporation. After the drying is completed the reaction probably continues, but at a relatively slower rate in the presence of moisture. If the relative humidity is not sufficiently high, no ftirther sorption of SO2 can be expected after completion of the evaporation step. 

---