Cooling Deactivation, catalysts

The subsequent step, the epoxidation of propylene by EBHP, is carried out in the liquid phase over a proprietary heterogeneous catalyst, to produce crude PO and MPC. The feed to the reactors consists of make-up and recycle propylene and EBHP in EB. The reaction train consists of a number of adiabatic fixed bed reactors with interstage cooling. Deactivated catalyst is replaced, incinerated to remove residual hydrocarbons, and dispersed in a landfill. 

A major goal in wall cooling is to spread out the hot zone and prevent very high peak temperatures. High peak temperatures cause poor reaction selectivity, cause carbon formation, deactivate catalysts, and cause corrosion problems in the reactor walls. CocuJTent flows spread out the hot zone and cause lower peak temperatures, but many additional design features must be considered in designing jacketed reactors. 

Provide thermal sink In adiabatic reactors and in reactors where cooling is difficult and exothermic heat effects are large, it is often necessary to feed excess material to the reactor (an excess of one reactant or a product) so that the reactor temperature increase will not be too large. High temperature can potentially create several unpleasant events it can lead to thermal runaways, it can deactivate catalysts, it can cause undesirable side reactions, it can cause mechanical failure of equipment, etc. So the heat of reaction is absorbed by the sensible heat required to raise the temperature of the excess material in the stream flowing through the reactor. 

In order to gain a deeper understanding of the mechanism of the deposit growth, and of its active intermediates in particular, the catalytic experiments were undertaken in which the deactivated catalyst was used. After the reaction at 350 C the catalyst was cooled down to room temperature and the deposit was carefully removed from its surface, then the catalyst was heated up to the same temperature and another catalytic test was initiated by switching on the flow of the reactants. 

Hydrogenation of the oxides of carbon to methane according to the above reactions is sometimes referred to as the Sabatier reactions. Because of the high exothermicity of the methanization reactions, adequate and precise cooling is necessary in order to avoid catalyst deactivation, sintering, and carbon deposition by thermal cracking. 

The means by which a quench system works depends on the nature of the reactive material e.g., for water-reactive materials, a quench system will destroy the material in a last-resort situation and generally form less-hazardous products, and will at the same time absorb some of the heat of reaction. Most quench systems are designed to both cool down and dilute a material that may be reacting uncontrollably the quenching medium may also actually interfere with the chemical reaction or deactivate a catalyst. 

Propane was selected as solvent for the isobutene for experiments down to -145° the aluminium chloride was dissolved in ethyl chloride, for the work at lower temperatures a mixture of ethyl chloride and vinyl chloride was used. Although these catalyst solutions were made up at -78° they were yellow, and as stated above, they probably contained some hydrogen chloride and other catalytically active decomposition products. The polymerisations were carried out by running the cooled catalyst solution into the monomer solution. Polymer was formed, and came out of solution, almost immediately, and the reaction was very fast even at the lowest temperature (-185°) and lowest monomer concentration (0.6 mole/1). After the reaction was over, propanol at the reaction temperature was added to the reaction mixture to deactivate the catalyst. 

The optimization study discussed above suggests the use of a high temperature and a short-reaction time. Because of the heat-up and cool-down time limitations of the autoclaves used, this study was limited to reaction temperatures < 435°C. Verification studies at higher temperatures (>435°C) are required. The present study should be supported by complementary catalyst aging studies to determine the maximum temperature limit below which severe deactivation and aging does not occur. 

Reaction quench or chemical short stop systems to stop or slow the reaction by removing heat sources, cooling the reactants, deactivating any catalyst, or interfering with reaction chemistry ... 

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