In this dissertation, the possibility of additive manufacturing technologies for the purpose of 3D printing of microreactors and microseparators used for oil transesterification into biodiesel was experimentally investigated. 3D printing technology offers superb versatility in the design and fabrication of custom reactionware for flow chemistry. There is potential for creating complex geometries in microfluidic devices to influence the yield of chemical reactions. Rapid fabrication of models, and the ability to easily modify designs open up the possibility of fast progress in flow chemistry. The role of computer-aided design (CAD), 3D printing, microfluidics, and computational fluid dynamics (CFD) was explored to optimise the production process of microreactors and biodiesel synthesis. The specific aim of the work is to 3D print an optimised modular system for biodiesel synthesis and separation, while also optimising the conditions of 3D printing. The modules in the system are a microreactor and microseparator connected by PTFE tubes. Seven different models of microreactors with static mixers and six models of microseparators were 3D printed to assess the efficiency of biodiesel synthesis and separation. The optimization of 3D printing and material post-processing was conducted in order to analyze and select the optimal material for 3D printing of all models. Mechanical, thermal, and physicochemical characterisation of the materials was performed, revealing correlations between the mechanical, thermal, and certain physicochemical properties of the materials. Various models of microreactors were designed in which the fluid movement in a microchannel was simulated and then 3D printed and in which the biodiesel synthesis reaction was finally carried out. After 3D printing of the microreactors using fused filament fabrication and stereolithography, the quality of the model production, the transparency and the layer visibility were analysed. Based on these analyses, the appropriate technology for 3D printing microreactors and microseparators was selected. Sampling from the 3D-printed microreactors was conducted at four different residence times. The criterion for selecting the optimum microreactor was to achieve a conversion of at least 96% in the shortest possible residence time. The separation process was then carried out in each of the six designed microseparators in conjunction with the selected microreactor. The characterisation of the materials used in stereolithography and the analysis of the quality of the 3D-printed objects according to specified criteria led to the selection of High Temp material for the fabrication of microreactors and microseparators. High Temp material and stereolithography as a manufacturing technology met the requirements for dimensional accuracy and transparency, and their mechanical, thermal and physicochemical properties were suitable for carrying out the biodiesel synthesis reaction. The results of the flow simulation in the microreactors predict the highest flow velocity in the centre of the circular cross-section and a change in the velocity distribution as the fluid passes through the bends. Gas chromatography and nuclear magnetic resonance analysis showed the influence of different types and numbers of static mixers on the reaction efficiency. In the 3D-printed tubular microreactor with seven bends (C7K), with a residence time of 19.9 minutes, and in the tubular microreactor with ten bends (C10K), with a residence time of 19.2 minutes, the conversion reached 100%. The 3D-printed microreactor C10K, which achieved a conversion of 96% with a residence time of 9.6 minutes and consists of microchannels with a circular cross-section and 10 static mixers in the form of 90° bends, was selected for the further performance of the synthesis and separation reaction. When performing synthesis and separation in an integrated modular system with five microseparators, there was no flow separation, while when using the MSv5 microseparator, which has the smallest volume compared to the other five, flow separation was achieved with a separation efficiency of 55%. The results obtained lead to the conclusion that additive manufacturing technology is suitable for the production of microfluidic systems. The results of the numerical flow simulations provide a good starting point for modifying and adapting various microreactor designs. By changing the reaction conditions, high efficiency can be achieved in the biodiesel synthesis reaction. The bends in the microreactor channel act as static mixers. Increasing the number of static mixers in the microreactor increases the efficiency of the biodiesel synthesis reaction. The feasibility of 3D printed modular system for biodiesel synthesis and separation was confirmed.