Many technologies and processes exist for converting feedstocks into liquid or gaseous products using heterogeneous catalyst systems. Such processes are typically categorized based upon whether the feedstock (reactant) and/or product are in a single phase (solid, gas or liquid) or a multi-phase involving two or more of the foregoing. The processes are also categorized based upon the flow pattern in which the feedstock and product flow through the catalyst; namely, either a concurrent configuration where both the feedstock and product flow in the same direction or a countercurrent configuration where the feedstock and product flow across each other in opposite directions. The processes are also typically classified as downflow when the feedstock and product flow down with gravity through the catalyst bed and upflow when the feedstock and product flow up against gravity through the catalyst bed.
The type of reactor system utilized for any given process depends on the nature of the feedstock and its resulting products. For example, concurrent downflow reactors are often used in reactions involving the catalytic conversion of gaseous reactants to gaseous products, or liquid reactants to liquid products, or in trickle bed reactors involving the concurrent flow of both a gas and liquid reactant that react together to produce the desirable product. Concurrent downflow reactors are generally not used for reactions involving the conversion of liquid feedstocks to gas products as the hydrodynamic flow patterns usually become irregular and unpredictable due to the variance between the density and buoyancy of the liquid reactant and the gas phase products. The flow pattern is critical as an irregular or unpredictable flow pattern can lead to vapor-lock and other hydrodynamic problems. In multi-tubular reactor systems, this is significant as vapor-lock and other hydrodynamic problems can lead to mal-distribution of the liquid feedstock or other negative effects (e.g., hot spots, selectivity issues, reactor performance, etc.). Expeditious removal of the gas products from the reactor system is also desirable in order to prevent subsequent, undesired reactions from taking place. As a result, concurrent upflow systems are used in reactions involving the catalytic conversion of a liquid reactant to gaseous products, a process termed flooded flow.
One process which differs from conventional systems is disclosed in European Patent Application No. 88202871.5 (Publication No. 0323663A2) to Terlouw et al. The disclosed process generally relates to controlling the exothermic nature of catalytic reactions between two or more reactants by causing the reactions to occur under substantially isothermic conditions. The reaction mixture includes at least one compound having a boiling point lower than the other compounds in the mixture, and that the one compound is present in an amount sufficient to consume, by vaporization thereof, the heat generated by the exothermic reaction of the mixture. To achieve an isothermic state, the reactor is operated at the boiling pressure of the one compound and in a manner as to provide a concurrent downflow of a liquid and gas phase, wherein the gas phase is the vaporized form of the one compound having the lowest boiling point. The process differs from conventional fixed-bed reactors in that the gas or vapor phase comprises a vaporized component from the liquid phase. The fact that the vapor phase is substantially a vaporized component of the liquid phase is critical to the functionality of the system. Here, vapor-lock and hydrodynamic concerns are limited due to the ability of any vapor trapped within the system to recondense into its liquid form for either continued use or removal from the system.