3D-printing which has found applications in a wide variety of fields has also been recently used to manufacture catalysts with novel architectures. These morphologies offer improved transport properties at lower energy requirements. Catalysts can also be customised for specific and unique outcomes that are not possible with conventional catalysts.

Hideo Kodama is widely regarded as the inventor of 3D Printing in 1981. He came up with a layer-by-layer technique for rapid prototyping using a photosensitive resin that was polymerised by UV light. But the honour of developing the first commercial 3D Printer in 1984 goes to Chuck Hull, who copyrighted the term “Stereolithography” for his technique of curing liquid monomers layer by layer. 3D-printing has come a long way in the last four decades and today it is one of the nine pillars of Industry 4.0. ASTM has developed a taxonomy to classify various 3D-printing technologies under seven categories: Binder Jetting, Directed Energy Deposition (DED), Powder Bed Fusion (PBF), Sheet Lamination, Material Extrusion, Material Jetting and Vat Photo Polymerisation. 3D-printing, also known as Additive Manufacturing, have found applications in a wide variety of areas like automotive manufacturing, aerospace engineering, electronics, medicine, construction, art and jewellery. But use of 3D-printing in catalysis is a relatively recent development and is full of exciting possibilities.

Catalysts
Catalysts have traditionally been in the form of granules, pellets and extrudates. Millimetre-sized spherical granules are the most basic catalyst geometry used in fixed bed reactors. Elaborate protocols are adopted to fill such catalysts in reactors to achieve the desired void fraction and to prevent attrition. Pellets are formed by pressing catalyst powder in millimetre-sized moulds with a pressurised die to impart the desired mechanical strength. They have a far more uniform size distribution than spherical granules and offer lower pressure drop for the same mass transfer. Extruded forms, produced by passing a slurry of catalyst and additives through a screw extruder and die, are widely used in the industry, especially in refineries. Extrusion allows for more geometrical variations compared to granules and pellets but the process is limited by the rheological properties of the slurry. Extrudates offer greater flexibility to the designer to vary the surface to volume ratio, which ultimately influences the residence times and pressure drops in the reactor.

Monoliths
Monolithic structures are an interesting alternative to the traditional catalyst forms because of many benefits. They offer lower pressure drops, have higher mechanical and thermal stability and confer improved heat and mass transfer properties over conventional catalysts. Monoliths are essentially uniform blocks consisting of parallel channels. They can be manufactured in various shapes: cylindrical, cubic, hexagonal amongst others. The heat and mass transfer properties and hence the catalytic performance is influenced by the geometries of the channels. An important feature of the monolithic catalysts is the higher void fraction compared to pellets. The lower resistance to flow through the channels allows for high space velocities, which is an useful tool to tweak product selectivity and yield. Honeycomb-shaped monoliths are used within standalone reactors in automobile exhaust clean-up.

Monolithic structures are of two types – ceramic and metallic. They differ greatly in physical and chemical properties. Ceramic monoliths have higher porosity and better thermal stability. Metallic monoliths provide better mechanical stability and heat transfer properties. Monoliths are usually produced from an inert material and subsequently washcoated with catalyst. The washcoat is a secondary support that confers improved adherence and increased dispersion of the active species. Gamma-alumina is a typically used washcoat for monoliths. Washcoating involves repeated cycles of dipping and drying followed by a final calcination.

3D-Printing
Conventional methods of fabricating monoliths lead to either very densely packed beds or very open cellular structures. 3D-printing unlocks opportunities to structure the catalysts in a variety of ways. It could, for example, introduce local variations throughout the catalyst structure. The porosity of the catalyst structure could be locally tuned along both the axial and transverse directions. Multiple materials could be used within one printed structure to alter the catalyst performance in many different permutations and combinations. 3D-printing overcomes the limitations of conventional shaping methods and allows for customisation of structures to suit specific operating parameters. Computer Aided Design (CAD) coupled with 3D-printing makes it possible to develop unique monolithic structures which would otherwise be impossible using conventional techniques.

The active catalytic material can be integrated with the monolithic structure during the 3D-printing stage itself or separately deposited on the printed objects. Many catalysts require a finishing step, which usually consists of drying and sintering to remove the binders and decompose the precursors. Other finishing processes involve reduction of metal ions. 3D-printing has been used to produce monolithic structures from doped polymeric materials, carbon materials, metals, metal oxides and zeolites. The performance of such 3D-printed catalysts have been studied extensively in many processes and the results have been more than encouraging. One limitation for 3D-printing is in the use of ceramic materials and they are yet to be deployed on a commercial scale.

Robocasting
Robocasting, also known as robotic material extrusion, was the first technique for 3D-printing monolithic structures. Metal-organic frameworks (MOF) are among the best materials for catalysts and adsorbents, and a critical problem in their design is finding the best compromise between porosity and mechanical strength for a specific application. Robocasting has been used to produce MOF solids with controlled morphology and superior textural properties. The technique has been used to produce zeolite-based catalysts for application in methanol to olefins conversion. The 3D-printed structure with zigzag channels exhibited improved activity and higher stability than a conventionally fabricated monolith with parallel channels.

Digital Light Processing
Digital Light Processing (DLP), one of the most promising 3D-printing technologies, has been used for indirect synthesis of monolithic structures. DLP is a type of vat polymerisation using photopolymers that can be cured with a light source. DLP is used to print templates of polymeric materials, which are then filled with ceramic pastes containing active catalytic materials. The filled templates are then dried and calcined to remove the polymeric material and set the ceramic structure. The DLP technique allows to build customised templates for a very specific purpose and then replicate them into monolithic architectures with unmatched precision.

Epilogue
Currently, 3D-printing of catalysts is more expensive and labour-intensive than conventional processes for the shaping of these materials. The additional investment has to be economically offset by lower operating costs due to reduced pressure drop. Savings can also result from customising performance which will reduce the catalyst requirement and reactor volume for the same conversion and yield.

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The Stage-Gate process has evolved into a rigorous and robust tool for product development across industries. The Agile Manifesto borrowed from the software industry has burnished it with flexibility and adaptability. Together with digital technologies of Industry 4.0 it can accelerate product development even more.

The Stage-Gate system is a roadmap for product development. It breaks down the development process into discrete stages. Each stage is designed to gather information and carry out tasks required to move the project to the next stage. Before the project can move to the next stage it has to pass through a gate, where it is scrutinised by senior management. The management evaluates the project to determine whether the criteria necessary to move forward have been met. If the necessary prerequisites are not met, management may ask for more information or stop the project from going ahead. The Stage-Gate system has evolved into a powerful tool for managing the product innovation cycle in many industries.

The Stages

The number of stages typically range between 4 and 6. Stages are cross-functional and consist of a set of tasks that are carried out concurrently. A stage may be populated by personnel with expertise in R&D, engineering, operations, safety and marketing. Collectively, they seek information to reduce the project’s unknowns and uncertainties. As the project progresses through the sequential stages, its risks keep getting diminished. The Stage-Gate process is a risk mitigating model. A typical Stage-Gate process for new product development in the chemical industry will consist of 5 stages. The first stage called “Scoping” involves desk research to make a preliminary technical assessment and market potential. The second stage called “Build the Business Case” is usually the make or break stage. The technical feasibility of the project is examined in considerable detail and the outcome is a comprehensive report with financial and sensitivity analysis. The actual “development” of the product takes place in the third stage and consumes the most time. “Testing and Validation” is the fourth stage, where the product quality and product performance are examined under controlled conditions in the laboratory. The final stage is “Launch”, when the product is fully commercialised and introduced into the market.

The Gates

The different stages of the product development project are separated by “Gates”, where the outcomes of the preceding stage are intensely scrutinised by the senior management before committing more resources and allowing it to move forward to the subsequent stage. The outcome of a stage is a set of “Gate Deliverables”, which has been previously agreed upon. The “Gate Criteria” against which the project will be judged at each gate are also predefined. The “Gatekeepers” are usually drawn from the leadership team of the enterprise. They determine if the project meets the laid down criteria to move forward to the next stage. Three types of decision are possible by the Gatekeepers. A “Go” decision is a green signal to move the project forward and commits additional resources. “Recycle” is asking for more information to take a decision. If the stage deliverables fail to meet the gate criteria, the Gatekeepers may decide to shelve the project by a “Kill/Hold” decision. Criteria for assessing the progress of the project at each Gate must be unambiguous and sharp, yet also reasonable and practical.

The Benefits

The Stage-Gate process offers several advantages. Due diligence is in-built into the system. It is constructed around an empowered multidisciplinary and cross-functional team that work at great speed. Each stage has technical, marketing and financial expertise to work concurrently in parallel and this significantly speeds up the development process. The Gatekeepers are also drawn from different functions and they own the resources that are required to be committed for the next stage. The Stage-Gate process brings intense focus at the gates. Poor projects get weeded out early and allows the enterprise to prioritise scarce resources. The biggest advantage of the Stage-Gate process is its emphasis on front loading, where the market segment and the value proposition to customers are sharply delineated.Introducing market orientation and customer focus into the development process at a very early stage is extremely crucial to the success of the project.

The Modifications

The Stage-Gate process is the brainchild of Dr Robert G Cooper, who published and trademarked the concept way back in 1983. Early adopters of the technique were Exxon and DuPont. Since then, the floodgates have opened and a recent report says that nearly 75% of all new product development in USA uses the Stage-Gate process. This includes consumer products, industrial products and service providers like banks, insurance and telecom companies. Some companies have tweaked the Stage-Gate process to suit different types of applications. The tool has been successfully deployed for new process developments and for a wide variety of investment decisions. The biggest import into the Stage-Gate process has come from the software industry.

Agile Manifesto

In February 2001, a bunch of 17 people met at a ski resort in Utah and crafted the Agile Manifesto for software development. Put in a nutshell, the manifesto focuses on continuous incremental improvements through small and frequent releases of the software. Over the last two decades, many of the best practices of the Agile Manifesto have been co-opted into the Stage-Gate process to create hybrid models. These hybrid models combine the structure of the classic Stage-Gate process with the short cycle iterations of the Agile methodology. The longer “Development” stage, for example, is broken down into short cycles called “Sprints”, where the clear focus is to create a workable product in order to obtain valuable feedback from customers. Among the benefits of the Agile Stage-Gate are improved design flexibility, ability to respond to real-time changes and increased productivity through better communication and coordination across the project team. The bottom line is a 30% reduction in time-to-market.

Digitalisation

R&D scientists have woken up to the potential of harnessing digital technologies to accelerate product and process development. Artificial Intelligence and Machine Learning can harvest information from published literature at speed and shorten the screening process for new entities by one or two orders of magnitude. Robotic systems can be set up to perform experiments round the clock and eliminate the tedium. Digital Twins can be constructed to monitor the outcomes of incremental improvements. 3D-Printing can be used to develop prototypes for rapid testing and validating. In some situations, prototypes can be done away with by using Augmented Reality for virtual testing. The possibilities are limited only by our imagination.

Last Word

The world urgently needs new chemical entities for sustainable resolution of pressing problems in healthcare, energy, agriculture, transportation, construction and waste management. The full suite of Industry 4.0 digital technologies supervised by an appropriately defined Agile Stage-Gate methodology will bring the necessary rigour and speed for developing new products and processes.

Readers’ responses may be sent to:
k.sahasranaman@gmail.com or
chemindigest@gmail.com