The Catalyst Review December 2019 - 10

SPECIAL FEATURE
Stability is a prerequisite in reaction conditions, otherwise performances would degrade as catalyst structure collapse. On the other
hand, we can also recognize that if defects would not exist in zeolites, they would possibly not be so active in acid catalysis. Indeed,
the steaming of Y zeolites leads to Ultra Stable Y zeolite (USY) or Dealimunated Y zeolites (DAY) which are active sites of FCC catalysts
partly due to the creation of Lewis sites as extra framework Aluminum species. As a conclusion, we have seen here many examples
of post-treatments, including washing and heating that can "activate" MOFs through the creation of defects. Clearly, post-processing
treatments which are relatively cheap and easy to implement, may play a major role in the future to turn "perfect" MOF structures
into practical catalysts.
Scale-up Studies and Pilot Lines of MOF Production

Most of the synthesis recipes found in the literature cannot be up-scaled due to safety reasons. Indeed, MOFs are typically
synthesized in mixture of metallic nitrate salt in organic solvent that can potentially explode. Another reason is the use of highly
concentrated HCl or acetic acid solution which are very corrosive agents. Because of their mixed composition of organic and
inorganic moieties, the synthesis of MOFs has often used polar organic solvents such as Dimethyl Formamide (DMF), a very toxic
chemical. Finally, MOF powder prepared in concentrated solution are generally in the form of submicrometer crystals which can
be hardly filtrated in a shift time when dealing with batches of hundreds of kg! So far, these technical and safety constraints have
prevented the scale up of MOF at industrial level. In contrast to academic consensus, scale-up is not just a matter of scale, meaning
larger vessels and faster stirring. Synthesis mechanisms and processes must be entirely revisited for enabling large production
of MOF with high purity grade. The program ProDIA has developed cutting edge manufacturing processes especially continuous
synthesis processes using water as solvent or without solvent, whilst maintaining high yields, purity and production rates which
allowed upscaling without compromising the nanoporous structure.
Mechanochemistry, also called "in reactive extrusion," represents a paradigm shift in chemical manufacture: instead of the
energy required to initiate a chemical reaction coming from a hot solvent, it is provided by mechanical energy. The MOF material
is continuously produced in a powder form without further treatment, or to be formed into shaped material. It is a cost-efficient
process with almost no environmental impact since the precursors are not dissolved in organic solvent. As a matter of fact, filtration
can be skipped which is a strong asset regarding daily throughput. In contrast to other manufacture process, mechanochemical
synthesis is fully scalable ensuring consistent high-quality of production.
MOF technologies utilizes mecanochemical Figure 3. Mecanochemical synthesis of 50kg of
Figure 4. Mecanochemical synthesis of 25kg of Alfumarate via extrusion at MOF Technologies.
synthesis to manufacture a series of MOFs HKUST-1 via extrusion at MOF Technologies.
using a patented mechanochemical process.
HKUST-1 and Al-Fumarate which is a
variation of MIL-53(Al) made with fumaric
acid as linker have been manufactured at
MOF Technology's pilot facility in Belfast.
This is a 50m2 ATEX classified process
development suite is located within
the School of Chemistry and Chemical
Engineering at Queen's University Belfast.
The facility boasts an array of advanced
Source: MOF Technologies.
Source: MOF Technologies.
extrusion equipment required for the
development and production of mechano-synthesised MOFs. The MOFs are produced via a twin-screw extruder (see Figures 3 & 4)
with a desired shape factor. The mecanosynthesis pilot facility can produce up to 10 kg/day of HKUST-1 and 5 kg/day of Al-fumarate
with a yield exceeding 99%. MOF technologies has demonstrated the production of up to 50kg of HKUST-1 and 25kg of Al-fumarate
with BET surface area consistently greater than 1500 m2g-1 and 950 m2g-1, respectively.
Spray-drying. The synthesis of MOFs by spray-drying has been discovered and patented by Prof. Daniel Maspoch and Inhar Imaz at
the Catalan Institute of Nanoscience and Nanotechnology (ICN2) in Spain which is licenced to the company MOFapps (Carne-Sanchez
et al. 2015). A liquid feedstock containing the right amount of precurors is dispersed into droplets by means of nozzles operating
under pressure. A hot process gas (air or nitrogen) is brought into contact with the atomized feed, initiating evaporation of the liquid.
As the liquid rapidly evaporates, a solid particle forms and falls to the bottom of the drying chamber. The dry powder can be easily
recovered and can be further processed without washing. The synthesis by spray-drying offer key advantages of the manufacture of
MOFs. It is a continuous process with a very high productivity. The powder is obtained dried and can be easily manipulated as they
are generally formed of large "flowing" aggregates of several 100┬Ám of diameter. Spray-driers are standard equipment which are
10

The Catalyst Review											

December 2019



The Catalyst Review December 2019

Table of Contents for the Digital Edition of The Catalyst Review December 2019

The Catalyst Review December 2019 - cover
The Catalyst Review December 2019 - contents
The Catalyst Review December 2019 - 1
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