The present invention relates to a process for producing succinic anhydride by maleic anhydride hydrogenation, comprising (1) feeding a maleic anhydride solution and a hydrogen raw material respectively to a first-stage hydrogenation reactor from an upper liquid-phase feed port and a top gas-phase feed port of the first-stage hydrogenation reactor for a first-stage hydrogenation reaction to obtain a first-stage hydrogenation product; (2) feeding the first-stage hydrogenation product to a second-stage hydrogenation reactor for a second-stage hydrogenation reaction to obtain a second-stage hydrogenation product, optionally, before entering the second-stage hydrogenation reactor, subjecting the first-stage hydrogenation product to a first-stage gas-liquid separation to obtain a first-stage gas phase and a first-stage liquid phase, and then feeding the first-stage gas phase and the first-stage liquid phase respectively from a top gas-phase feed port and an upper liquid-phase feed port of the second-stage hydrogenation reactor; and (3) subjecting the second-stage hydrogenation product to a second-stage gas-liquid separation to obtain a second-stage gas phase and a second-stage liquid phase, returning a part of the second-stage liquid phase to step (1) to be mixed with the maleic anhydride solution for the first-stage hydrogenation reaction, and optionally, using part or all of the second-stage gas phase as a circulating hydrogen. The present invention also relates to a process for producing succinic acid comprising such process, a liquid-phase hydrogenation reaction system, and a system for producing succinic acid comprising such system.

In a process for carrying out a chemical reaction gaseous reactants are supplied to a first reaction zone including a first catalyst having a first particle equivalent diameter. The first reaction zone is operated such that when the reactants are contacted with the first catalyst a portion of the reactants is converted to the desired product. An intermediate stream of unreacted reactants and the desired product is removed and passed to a second reaction zone including a tubular reactor. Tubes of the reactor are catalyst carriers containing a second catalyst having a second particle equivalent diameter smaller than the first particle equivalent diameter. The second reaction zone is operated such that when the unreacted reactants are contacted with the second catalyst, at least some of the unreacted reactants are converted to the desired product. A product stream is then recovered. Apparatus for carrying out the process is also described.

A reactor for a catalytic process comprising one or more catalyst beds has catalyst bed supports constructed as a grid comprising a plurality of cassettes (01), which are covered with easily removable screens (02). The down-time and service costs for the reactor are thereby lowered.

Disclosed is a combined reformer including two or more catalyst tubes reacting at different temperatures, having different reforming reactions continuously performed as a combustion gas sequentially supplies heat to two or more catalyst tubes, and capable of easily replacing a catalyst, and a catalyst replacement method thereof.