In the present review article, the definitions and the most advanced findings within Process Intensification are collected and discussed. The intention is to give the readers the basic concepts, fixing the syllabus, as well as some relevant application examples of a discipline that is well-established and considered a hot topic in the chemical reaction engineering field at present.

Hydrodynamics, mass transfer and reaction rates were studied experimentally in a microreactor that had a square channel with a size of 1.0 × 1.0 mm × mm. The gas-limited hydrogenation of alpha-methylstyrene was chosen as the model reaction. The experiments covered superficial two-phase velocities in the range from 0.05 to 0.30 m/s and gas holdups at the channel inlet between 0.25 and 0.94. Overall hydrogen mass transfer elevated mainly with two-phase velocity and reached values between 0.1 and 1.2 1/s. Novel mass transfer equations were derived because the film theory which had often been applied was not applicable in this case. These equations are based on Reynolds, Schmidt and Sherwood numbers as well as the specific interfacial areas from the hydrodynamic observations.

A new approach for biomass liquefaction was developed and evaluated in a joint research project. Focus of the project, called FEBio@H₂O, lies on a two-step hydrothermal conversion. Within step 1, the input biomass is converted employing a hydrothermal degradation without added catalyst or by homogeneous catalysis. Within step 2, the hydrogen accepting products of step 1, e.g., levulinic acid (LA) are upgraded by a heterogeneously catalyzed hydrogenation with hydrogen donor substances, e.g., formic acid (FA). As a result, components with an even lower oxygen content in comparison to step 1 products are formed; as an example, γ-valerolactone (GVL) can be named. Therefore, the products are more stable and contained less oxygen as requested for a possible application as liquid fuel. As a hydrothermal process, FEBio@H₂O is especially suitable for highly water-containing feedstock. The evaluation involves hydrothermal conversion tests with model substances, degradation of real biomasses, transfer hydrogenation or hydrogenation with hydrogen donor of model substances and real products of step 1, catalyst selection and further development, investigation of the influence of reactor design, the experimental test of the whole process chain, and process assessment.