Chlorohydrin reactor

Commercial chlorohydrin reactors are usually towers provided with a chlorine distributor plate at the bottom, an olefin distributor plate about half way up, a recirculation pipe to allow the chlorohydrin solution to be recycled from the top to the bottom of the tower, a water feed iato the recirculation pipe, an overflow pipe for the product solution, and an effluent gas takeoff (46). The propylene and chlorine feeds are controlled so that no free gaseous chlorine remains at the poiat where the propylene enters the tower. The gas lift effect of the feeds provides the energy for the recirculation of the reaction solution from the top of the tower. 

Fig. 2. Diagram of a typical chlorohydrin reactor for manufacture of propylene oxide. M.O.L. = milk of lime. To convert kPa to mm Hg, multiply by 7.5.

In the chlorohydrin reactor, gaseous propylene and chlorine (equimolar amount) are mixed with an excess of water. Propylene chlorohydrin is formed at 35-50 °C and 2-3 bar. The water plays an important role in this reaction step. The reaction products remain in aqueous solution and water, acting as diluent, minimizes the formation of by-products. Water is also a reactant [Eq. (6.12.8)] and direct cooling medium. In the separator the vent gas (mixture of propane, propylene, CI2, O2, N2, H2, and CO2) is removed from the propylene chlorohydrin solution and sent to the... 

Only industrial producers (e.g. Dow) with a highly integrated and cost competitive supply chain of chlorine-caustic soda (through production from caustic soda by NaCl electrolysis) to provide chlorine for the chlorohydrin reactor and sodium hydroxide for the dehydrochlorination step can operate chlorohydrin units for propylene oxide production competitively with indirect oxidation units. 

Two of the reactions calce place in the same reactor in this plant. The formation of the hypochlorous acid (HOCl) from chlorine and water, and the reaction with propylene all occur simultaneously on the left in Figure 11—2. Propylene reacts readily with chlorine to form that unwanted by-product, propylene dichloride. To limit that, the HOCl and HCl are kept very dilute. But as a consequence, the concentration of the propylene leaving the reactor is very low—only 3—5% Ac any higher concentration, a separate phase or second layer in the reactor would form. It would preferentially suck up (dissolve) the propylene and chlorine coming in, leading to runaway dichloride yields. The low concentration levels of the propylene chlorohydrin and the need to recycle so many pounds of material is the reason the process is so energy intensive. It just takes a lot of electricity to pump all that stuff around. 

The degree of polymerization in AM ROP is given by the ratio of the total amount of monomer supplied to the reactor to the amount of alcohol. AM polymerization has been successfully demonstrated for the synthesis of telechelic polymers of propylene oxide and epi-chlorohydrin with number-average molecular weights of 1000-4000. Higher molecular weights are difficult to achieve because a large amount of alcohol is needed to suppress conventional ROP. 

The reactor is placed in an ice bath, and its contents are stirred vigorously while the ethylene chlorohydrin is added dropwise at a rate of approximately 2 ml./min. (hood). The reaction mixture is maintained at 0° until the addition is completed. Stirring is continued for 45 minutes after all the ethylene chlorohydrin has been added, while the reaction mixture is allowed to warm slowly to room temperature. 

Synthesis is carried out in two separate steps (Scheme 6.1). In the first reactor, propene reacts with CI2 to produce propene chlorohydrin via intermediate formation of the propene chloronium complex, then quenched by water. In the epoxidation reactor, the dehydrochlorination of propene chlorohydrin occurs using a base (usually calcium hydroxide). 

The solvent-free biocatalytic processes are considered more environmentally friendly, because this technology has the additional advantage of using the volume of the reactor more efficiently. For example, this system has been applied for the produaion of biodiesel, allyl and chlorohydrin acrylates, isobutyl propionate, etc. 

The chlorohydrin process has largely been replaced by the direct oxidation of ethylene with silver as catalyst. By-products are CO2 and water, formed by total oxidation of ethylene or EO. The reactor design is dominated by the demand for an exact temperature and selectivity control. The conversion per pass is low (about 10%) to avoid the consecutive oxidation of EO, and the unconverted ethylene is recycled. A multi-tubular reactor guarantees efficient heat transfer. 

A pilot reactor is used to determine the economic feasibility of ethylene glycol production from two available process streams containing 1.79mol/dm sodium bicarbonate and 3.73 mol/dm ethylene chlorohydrine in water. 

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