Even if the suitability of Finite Volume discretization methods for Pressure Swing Adsorption modelling is well-established, when simulating the peculiar process called Dual Reflux-Pressure Swing Adsorption, simulations relying only on Finite Difference discretization methods are available in literature. Therefore, a detailed single-bed model of the Dual Reflux-Pressure Swing Adsorption process, the solution of which is based on the Finite Volume discretization method, is proposed in this work and validated against experimental data. Details of the system representation, the numerical schemes and the implementation of the boundary conditions are given. Moreover, a comparison between the performances and limitations of the Finite Volume and Finite Difference discretization methods when simulating a Dual Reflux-Pressure Swing Adsorption process are discussed through two case studies, leading to conclude that Finite Volume Method is the most effective approach for simulating this specific separation process.

In the frame of dual-reflux pressure swing adsorption processes, design strategies applicable to the complete separation of binary gas mixtures are available only in the case of linear adsorption isotherms. Therefore, in this work we propose a simple and efficient design procedure which enables the selection of suitable operating conditions when sharp separation is required and Langmuir adsorption isotherms are involved. Starting from the available strategy for the linear adsorption case, we adapt it to the non-linear case tuning properly the pressure ratio. Then, the resulting design strategy is validated by application to selected study cases involving different values of key parameters such as different levels of non-linearity of the isotherms, but also different values of pressure ratio, feed composition and selectivity.

Among the adsorption-based separation processes for gaseous mixtures, those exploiting pressure variations, so-called Pressure Swing Adsorption (PSA) processes, are the most popular. In this work, we focus on the specific PSA configuration known as Dual Reflux-Pressure Swing Adsorption (DR-PSA) given its ability to achieve sharp separations. In the case of binary mixtures, an analytical approach based on Equilibrium Theory has been proposed to identify the operating conditions for complete separation under the assumption of linear isotherms. This same approach is not available when the separation is not complete. Accordingly, in this work we study the features of non-complete separations by solving numerically a general DR-PSA model with parameter values suitable to approach equilibrium conditions (no mass transport resistances, no axial mixing, isothermal conditions and no pressure drop), thus reproducing the analytical solution when complete separations are examined. Even for non-complete separations, triangularly shaped regions at constant purity can be identified on a plane whose axes correspond to suitable design parameters. Moreover, we found a general indication on how to select the lateral feed injection position to limit the loss in product purities when complete separation is not established, whatever is the composition of the feeding mixture. Finally, a sensitivity analysis with respect to pressure ratio, light reflux ratio and heavy product flowrate is proposed in order to assess how to recover product purities according to the specific degrees of freedom of a DR-PSA apparatus.

Dual reflux pressure swing adsorption is a peculiar application of pressure swing adsorption with relevant separation potential. In a proper range of operating parameters, high separation performances are achieved in many applications, including complete separation in the case of binary mixtures. In this work, a new representation of the design parameters suitable for complete separation based on the semi-analytical solution of the corresponding Equilibrium Theory model is proposed for the four basic process configurations. Namely, given feed position, feed composition, and adsorbent separation selectivity, the combinations of the remaining process parameters ensuring complete separation are identified in a 3D plot. Furthermore, the same model equations have been solved numerically to explore conditions of incomplete separation, where the semi-analytical solution is not available. In particular, the sensitivity of the separation performances of each configuration to the pressure ratio has been explored. More specifically, given the region of operating conditions suitable for complete separation, selected operating conditions outside this region have been explored aimed to recover/improve the separation quality. Even though the different configurations exhibit different behaviors, the general dependence of the product purity upon the pressure ratio is quite limited and only minor improvements can be obtained with a few exceptions.

Whenever the productivity of an indirectly cooled, isoperibolic semibatch reactor (SBR) must be enhanced keeping the reaction temperature nearly constant, an additional heat transfer surface with respect to that provided by the reactor jacket only must be installed. In these cases, internal coils are normally adopted, which additional surface is however intrinsically limited and not fully available since from the beginning of the supply period. However, a suitable fraction of the overall heat transfer surface can be installed on an external reactor recycle loop: this allows also for a simpler monitoring of the reaction system by comparing the measured temperature to a nearly constant target value. In this work a kinetic-free sizing criterion has been developed for isoperibolic SBRs (both homogeneous and heterogeneous), through which the required external heat transfer surface can be easily estimated.