Mechanochemical Applications of Reactive Extrusion from Organic Synthesis to Catalytic and Active Materials

Abstract

In the past, the use of mechanochemical methods in organic synthesis was reported as somewhat of a curiosity. However, perceptions have changed over the last two decades, and this technology is now being appreciated as a greener and more efficient synthetic method. The qualified “offer” of ball mills that make use of different set-ups, materials, and dimensions has allowed this technology to mature. Nevertheless, the intrinsic batch nature of mechanochemical methods hinders industrial scale-ups. New studies have found, in reactive extrusion, a powerful technique with which to activate chemical reactions with mechanical forces in a continuous flow. This new environmentally friendly mechanochemical synthetic method may be able to miniaturize production plants with outstanding process intensifications by removing organic solvents and working in a flow mode. Compared to conventional processes, reactive extrusions display high simplicity, safety, and cleanliness, which can be exploited in a variety of applications. This paper presents perspective examples in the better-known areas of reactive extrusions, including oxidation reactions, polymer processing, and biomass conversion. This work should stimulate further developments, as it highlights the versatility of reactive extrusion and the huge potential of solid-phase flow chemistry.

Spiers Memorial Lecture: Mechanochemistry, tribochemistry, mechanical alloying – retrospect, achievements and challenges

“…A large variety of reactions have been documented, which are highly selective, which have yields approaching 100%, or that are ecologically friendly and economically acceptable. 19–24,27,29–43 To date, a few examples of inorganic and organic reactions have been scaled up to levels suitable for practical applications. 9,15,39,43,122,123,131–140…”

“…Mechanical treatment can result in decomposition, 7,9,11,17,19,50,111,112 or synthesis of inorganic or organic compounds. 12,17,20–24,27,29–42,78,113,116–119,141–143 Quite often these compounds can be obtained as metastable polymorphs, 144 mesophases, quasicrystals, 145 or in amorphous states. 94,96,97,146 Mechanochemical processes can be used, in order to prepare product particles not only with target composition and structure, but also with a desirable shape, e.g .…”

“…5–18 “Dry”, or liquid assisted mechanochemical organic synthesis by ball milling, grinding, extrusion, or resonant acoustic mixing (RAM) is becoming increasingly popular. 19–43 Based on what is observed today, it can be expected that more inorganic and organic syntheses will be soon conducted mechanochemically at the industrial level, alongside – and perhaps instead of – the long-standing “classical” solution thermal synthesis. However, scaling up practically relevant syntheses requires the community to achieve a better understanding of the processes that take place in a mechanoreactor during and after mechanical action.…”

The Mechanochemical Fries Rearrangement: Manipulating Isomer Ratios in the Synthesis of p‐Hydroxyacetophenone at Different Scales**

“…At the same time, the drawbacks of ball milling, namely poor temperature and reaction control as well as discontinuous operation prevent the widespread use of this technology in the industry. As a continuous alternative, mechanochemical extrusion has recently provided promising results [37,38] . Extruders have broad applications in a range of industries from food and polymers to pharmaceuticals.…”

“…As a continuous alternative, mechanochemical extrusion has recently provided promising results. [37,38] Extruders have broad applications in a range of industries from food and polymers to pharmaceuticals. The small diameter of extruder barrels compared to their length allows for precise temperature and reaction control along the length of the barrel.…”