Reactions continuous

6 Continuous Reactions As a reaction vessel for a unimolecular reaction such as an ester pyrolysis, one thinks first of a pyrolysis tube, which is the simplest sort of continuous reactor. There are certain advantages to running bimolecular laboratory reactions in a similar manner Reaction times can be shorter, yields are higher (especially when heat-sensitive substances are involved), and less solvent is required. For large scale operations such as the first reactions in a long multistep synthesis, continuous reactors are worth considering. Two reactions are used to illustrate the technique. In the first, reactants are added from the top the volatile product distills out, and the nonvolatile product collects at the bottom. In the second, the nonvolatile reactant is added from the top and the volatile reactant from the side the products collect as before. 

The first example involves the reaction of ethyl benzoylacetate with aniline to give benzoylacetanilide and ethanol.f 

A mixture of the reactants is added via a dropping funnel [Fig. l-20(a)] to the heated (135°) column at the rate of 400 g per hr. Ethanol collects in flask B and ethyl benzoylacetate in flask A. 

The second example deals with the preparation of an acid chloride. This is usually accomplished by heating the carboxylic acid in refluxing thionyl chloride until the evolution of sulfur dioxide and hydrogen chloride ceases and then purifying the product by distillation or crystallization. This approach is unsatisfactory if the acid chloride—like oleoyl chloride—cannot tolerate prolonged heating. An excellent yield of oleoyl chloride, however, was obtained using the continuous reactor depicted in Fig. 1-20(b).  

Thionyl chloride is placed in the three-necked flask and heated to reflux. It distills through the U-tube and column, both of which are heated by electrical tape, is condensed by the Friedrichs condenser, and returns to the original flask. After the rate of distillation of thionyl chloride has reached a steady state, the acid is added dropwise to the column, which serves as a reaction chamber. As the acid chloride forms, it falls into the flask at the bottom of the column, while the gaseous by-products pass from the outlet provided into a gas absorption trap. This technique, based upon a counter-current reaction principle, produces the acid chloride in yields of 97-99% and can be run on a continuous basis if desired. It is suitable for the 

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The normal boiling points of the materials are given in Table 4.6. Synthesize a continuous reaction, separation, and recycle system for the process, bearing in mind that the process will later become batch. 

As the reaction beings to subside, run in from the dropping-funnel without delay a mixture of 25 ml. of acetone and 20 ml. of benzene, in order to maintain a brisk and continuous reaction. When the reaction finally subsides, heat the mixture on a boiling water-bath for 45 minutes with occasional shaking. If the shaking does not break up the spongy mass of magnesium pinacolate,... 

Synthetically Useful Transformations Involving Aryl Diazonium Ions (Continued) Reaction and comments General equation and specific example... 

Staged reactions, where only part of the initial reactants are added, either to consecutive reactors or with a time lag to the same reactor, maybe used to reduce dipentaerythritol content. This technique increases the effective formaldehyde-to-acetaldehyde mole ratio, maintaining the original stoichiometric one. It also permits easier thermal control of the reaction (66,67). Both batch and continuous reaction systems are used. The former have greater flexibiHty whereas the product of the latter has improved consistency (55,68). 

Manufacture and Uses. Acetoacetic esters are generally made from diketene and the corresponding alcohol as a solvent ia the presence of a catalyst. In the case of Hquid alcohols, manufacturiag is carried out by continuous reaction ia a tubular reactor with carefully adjusted feeds of diketene, alcohol, and catalyst, or alcohol—catalyst blend followed by continuous purification (Fig. 3). For soHd alcohols, an iaert solvent is used. Catalysts used iaclude strong acids, tertiary amines, salts such as sodium acetate [127-09-3], organophosphoms compounds, and organometaHic compounds (5). 

At present, thionyl chloride is produced commercially by the continuous reaction of sulfur dioxide (or sulfur trioxide) with sulfur monochloride (or sulfur dichloride) mixed with excess chlorine. The reaction is conducted in the gaseous phase at elevated temperature over activated carbon (178). Unreacted sulfur dioxide is mixed with the stoichiometric amount of chlorine and allowed to react at low temperature over activated carbon to form sulfuryl chloride, which is fed back to the main thionyl chloride reactor. 

At high ratios of fluidiziug velocity to minimum fluidizing velocity, tremendous solids circulation from top to bottom of the bed assures rapid mixing of the solids. For aU practical purposes, beds with L/D ratios of from 4 to 0.1 can be considered to be completely mixed continuous-reaction vessels insofar as the sohds are concerned. 

In a continuous reaction process, the true residence time of the reaction partners in the reactor plays a major role. It is governed by the residence time distribution characteristic of the reactor, which gives information on backmixing (macromixing) of the throughput. The principal objectives of studies into the macrokinetics of a process are to estimate the coefficients of a mathematical model of the process and to validate the model for adequacy. For this purpose, a pilot plant should provide the following ... 

The control of the reaction was based on the assumption that stopping the flow of chlorine would stop all reaction this was true on the pilot unit but not on the full-scale plant. On the pilot unit, there was no stirrer, as the incoming chlorine gave sufficient mixing. When chlorine addition stopped, mixing also stopped and so did the reaction. On the full-scale plant, a stiirer was necessary, and this continued in operation after chlorine addition stopped. In addition, on the pilot unit the cooling was sufficient to hide any continuing reaction that did occur. 

As in stoichiometric organic reactions, the application of nonvolatile ionic liquids can contribute to the reduction of atmospheric pollution. This is of special relevance for non-continuous reactions, in which complete recovery of a volatile organic solvent is usually difficult to integrate into the process. 

Continuous Reactions in an Ionic Liquid/Compressed CO2 System... 

During the continuous reaction, alkene, CO, H2, and CO2 were separately fed into the reactor containing the ionic liquid catalyst solution. The products and uncon-... 

In the continuous hydrovinylation experiments, the ionic catalyst solution was placed in the reactor R, where it was in intimate contact with the continuous reaction phase entering from the bottom (no stirring was used in these experiments). The reaction phase was made up in the mixer from a pulsed flow of ethylene and a continuous flow of styrene and compressed CO2. 

Continuous reactions can be obtained by the passage of the reactants through beds of ion-exchange catalysts. 

If glycerol is reacted with phthalic anhydride three ester links can be made from each glycerol unit. Continued reaction will eventually cause the molecules to link up in a three-dimensional network in which, theoretically at least, the whole polymer mass becomes one giant molecule. 

In bubble-column slurry reactors, momentum is transferred to the liquid phase by the movement of gas bubbles. The liquid medium is stationary in most cases. Finely divided solids with particle diameters of the order of 0.01 mm are used. The operation is usually carried out in columns with high height-to-diameter ratios. The operation may be employed for batchwise conversion of a liquid reactant, or for continuous reaction between gaseous reactants. 

The nucleation process involves conversion of a small volume of reactant into a stable particle of product and continued reaction (growth)... 

Continuous reaction of organic 290-420 ppm S03/inert gas passed in at 26-54°C. Reaction 170... 

These compounds contain the discrete linear Hg3 and Hg4 cations, respectively. The red-black needles of Hg4(AsF5>2 cannot be prepared in the absence of Hgj35AsF and Hg3(AsF5)2, but the latter can be prepared by continued reaction of AsF with... 

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