Fine structuration of low-temperature co-fired ceramic (LTCC) microreactors

Abstract

The development of microreactors that operate under harsh conditions is always of great interest for many applications. Here we present a microfabrication process based on low-temperature co-fired ceramic (LTCC) technology for producing microreactors which are able to perform chemical processes at elevated temperature (>400°C) and against concentrated harsh chemicals such as sodium hydroxide, sulfuric acid and hydrochloric acid. Various micro-scale cavities and/or fluidic channels were successfully fabricated in these microreactors using a set of combined and optimized LTCC manufacturing processes. Among them, it has been found that laser micromachining and multi-step low-pressure lamination are particularly critical to the fabrication and quality of these microreactors. Demonstration of LTCC microreactors with various embedded fluidic structures is illustrated with a number of examples, including micro-mixers for studies of exothermic reactions, multiple-injection microreactors for ionone production, and high-temperature microreactors for portable hydrogen generation. IntroductionChemical microreactors are a type of meso-scaled reaction systems that have fluidic channels with characteristic dimensions in the sub-millimeter range. By combining process intensification concepts with microfabrication techniques, these microreactors have been rapidly developed to perform liquid/gas phase chemical reactions, particularly the quasiinstantaneous endothermic or exothermic ones.1,2 Ceramic materials in general feature high chemical and thermal stability. Hence they are very preferable to be used as reactor construction materials, especially for reactors involved with high temperature and/or harsh chemical reactions. be used as the embedded fluidic structures (e.g. channels or cavities) get easily damaged in the stacked LTCC tapes by the high lamination temperature and/or pressure, causing sagging, tearing and cracking issues. Several approaches have been proposed so far in order to reduce these deformations and improve the quality of integrated LTCC fluidic structures. One method is using temporary inserts to introduce mechanical supports to the LTCC cavities to avoid deformation and/or sagging during lamination. These inserts, usually solid flexible objects, 23 are removed right after lamination. However, the removal of inserts from the laminate can cause permanent damage to these fluidic structures. Besides, this method is not applicable for fabricating fully embedded fluidic channels. Alternatively, a chemical-assisted lamination process has been proposed that enables low-pressure and/or lowtemperature bonding of LTCC green tapes. Roosen et al. 24used double-sided adhesive tape that contains acrylate adhesives and a polyethylene terephthalate (PET) film to ensure temporary binding of green tapes under a low lamination pressure at ambient temperature. Upon heating (40-60°C), these adhesives, together with the binders in the LTCC green tapes, soften and join the laminates through capillary forces. Aside from adhesives, ...

Meso-scale ceramic hotplates – A playground for high temperature microsystems

“…One example in the use of the LTCC meso-hotplate is a high temperature micro-reactor developed in our group for hydrogen production [47,59]. The LTCC hotplate provides mechanical attachment, electrical/fluidic connections and the necessary thermal energy for the hydrogen reforming reactions.…”

“…12f. Such an meso-scale ceramic reactor is able to carry out partial oxidation of propane with a high hydrogen yield (∼75%) at temperature of 650 • C [47,59]. These LTCC microreactors have shown promising potential for on-site hydrogen production in portable fuel cells, or as micro-combustors for the heat production [60].…”

A low-temperature co-fired ceramic micro-reactor system for high-efficiency on-site hydrogen production

“…7.4 MJ kg À1 for propane,~3.0 MJ kg À1 for methanol) are greatly larger than the ones of Li-ion batteries (~0.9 MJ kg À1 ) [1,2].…”

“…3). Details of this LTCC fine fluidic structure fabrication process can be found in the available literature [33].…”

“…The microreactor technology is widely considered as a robust solution for on-site hydrogen production from hydrocarbon fuels [2,4]. The dramatic reduction of characteristic lengths within micro-reactors greatly enhances mass and heat transport, minimizes catalyst materials, improves process stability against thermal runaway, and thus facilitates process control.…”