Basic design of a polybenzimidazole (PBI) production plant

Abstract

Polybenzimidazoles (PBIs) are a large family of engineering plastics comprised in a bigger category of polymers with benzimidazole groups as part of the structural repeat unit. PBIs can be partly or fully aromatic, and are typically characterized by outstanding thermo-mechanical properties. This makes them particularly suitable for various demanding high-temperature applications in the form of fibers, coatings, or membranes.[3] The objective of this study is to perform the basic design of a polybenzimidazole (PBI) production plant, operating in discontinuous. A market study is performed to determine global production of the polymer, and the designed plant is set to represent a 1 % of that production. Therefore, an annual production of 1000 tonnes/year has been selected. The produced PBI has an average chain molecular weight of 30 000 Mw, a purity of 99 % and a particle size between 100 and 200 μm, and will be packed in big bags of 500 kg. A recipe has been designed, based on existing processes found by a patent research. This recipe is detailed in writing and illustrated in the form of a block diagram. Batch size is 5000 kg, for which a mass balance is carried out, to show the necessary raw materials consist of 3800 kg of 3,3’,4,4’-tetraminobiphenyl (TAB) and 5650 kg of diphenyl isophthalate (DPIP). The appropriate equipment has been carefully selected for each unit of the process. This consists of two reaction vessels where polymerization occurs (V-01, V-02), with a humid mill between them (M-01), followed by a bag filter (F-01), a vessel where evaporation of solvent and precipitation of product occur (V-03), and a dryer to remove all remaining humidity (DR-01). In addition, there is a ball mill (M-02) that corrects particle size, and, finally, a sieving and packaging unit (SP-01). With the forementioned information, a P&ID is created, to display the process in depth.A time study is conducted for every existing operation, determining thus the occupation time of each piece of equipment. The resulting batch time (BT) is 63 h, while cycle time (CT), conditioned by the bottleneck (vessel V-02), is 25 h. Considering work conditions of the plant; 3 shifts, 24 h/day, 7 day a week, amounting to 6900 h a year, it has been proved that the proposed yearly production of 1000 tonnes is achievable with a total of 200 batches, configurated in 20 campaigns of 10 batches. The following KPIs have been calculated; a maximum number of batches of 274, the maximum production capacity of 1370 tonnes/year, and a minimum production time of 5038 h/year. The production planning of the plant allows for an additional 7 weeks where the line is available for a different process. Necessary plant services include nitrogen for inertization, deionized water for cleaning, and thermal oil, heated in a boiler and cooled in a heat exchanger.