An innovative technology for fabrication of metallic membranes for agro-food industry wastewater treatment

Transcription

1 An innovative technology for fabrication of metallic membranes for agro-food industry wastewater treatment Federico Rossi 1, Mirko Filipponi 1, Andrea Nicolini 1, Beatrice Castellani 2, Naida Corsi 2 1 Università degli Studi di Perugia, CIRIAF, Via G. Duranti, Perugia (PG), 2 IPASS S.c.ar.l. Ingegneria Per l Ambiente e lo Sviluppo Sostenibile, Via G. Guerra Perugia (PG)

2 INTRODUCTION Agro-food industry looks for cost-effective reduction and recycling technologies for wastewaters processing. Among filtration options membrane systems represent a primary source of separation for the agro-food processing industry. Membrane systems advantages: - lower energy use; - smaller space requirements; - better control of microbes and organic matter in the process effluent; - improved product quality. Metallic membranes have been introduced during the last few years for application in microfiltration. These membranes are expected to have longer lifetimes than the traditional polymeric or ceramic membranes because of their : - resistivity to high temperatures and corrosive environments; - mechanical robustness; - simple maintenance (possibility of steam cleaning and sterilization without affecting the duration of the filter). However, metallic membranes can be expensive compared to polymeric or ceramic membranes.

3 PRODUCTION PROCESS In the present work an innovative low cost production process based on tape casting technology is proposed to realize porous Ni-Cr based membranes in the form of tubes or planar components for agro-food wastewater filtration. BASE MIXTURES PREPARATION TAPE CASTING DRYING GREEN COMPONENTS MOLDING PRE-SINTERING THERMAL AND MECHANICAL CONSOLIDATION TREATMENTS

4 BASE MIXTURE PREPARATION The process begins with the preparation of the base mixtures by "wet" mixing of the matrix metal powders, the dispersoids (oxide particles) and any other additional elements with an agglomerating mixture of tires and solvents (binder). Composition of the alloy %w/w Alloy C Cr Ti Y 2 O 3 Fe Mn Ni Si P S Ni-Cr alloy 20,00 1,00 0,60 78,40

5 TAPE CASTING The alloys mixtures are tape casted DRYING After a phase of drying, in the warehouse 0,5 mm thick rubbery sheets (green tapes) are obtained.

6 GREEN COMPONENTS MOLDING Multi-layer flat components are realized by stacking and rolling seven layers of green tape. The rolling is carried out to compact the components, improve the sintering process and prevent the separation of individual layers. Tubular components are realized by wrapping green flat components on tubular supports.

7 PRE-SINTERING The components are pre-sinterized in controlled atmosphere using an electric oven. At the end of pre-sinternig there is a reduction in the geometric dimensions and components become hard and porous.

8 THERMAL AND MECHANICAL CONSOLIDATION TREATMENTS The pre-sintered components undergo the following range of thermal and mechanical treatments: - Rolling (flat components)/forging (tubular components); - sintering-and rolling /forging alternate processes repeated for four times. The finished components are obtained.

9 MEMBRANE CHARACTERIZATION The components are characterized by porosimetry and microscopy image analysis RESULTS After thermal and mechanical treatments a coherent, structurally strong, filter body with open porosities in the range of about 30 to 60% are obtained. Mesoporous membranes are obtained (for pore diameter between 2 and 50 nm), these are more suited for nanofiltration and ultrafiltration.

10 CONCLUSIONS In the present work porous Ni-Cr based components have been produced in order to assess their applicability as membranes for wastewater filtration. An innovative low cost process based on tape casting technology has been adopted. The proposed process simplifies and reduces the costs of the manufacture process and allows production of different types of materials for high performance filters. Different flat and tubular membranes were produced and characterized by microstructural analysis. According to the obtained results, it seems interesting to continue research into the proposed process for the production of mesopourus metallic membranes. Future goals of the research are the optimization of porous metallic components for wastewater filtration and the realization of a prototype system for the tests.