Classical Chemical Technology Wins Role in Bioprocessing

Integrating a thermochemical conversion step often provides significant benefits

By Michael Schultz, PTI Global Solutions

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The global market for bioproducts is robust and growing, as noted by several recent studies, including a 2016 report from Zion Research that estimates a 2015 renewable chemicals market of $50 billion, with a five-year compound annual growth rate of 11% [1], and BP’s annual world energy review that pegs 2015 global biofuels production at 74.2 million metric tons oil equivalent [2]. The Biotechnology Innovation Organization released a 2016 report that summarizes these studies [3].

However, thermochemical conversion of fossil fuels still dominates. For instance, BP’s review put the total consumption of gas, oil and coal for transportation, power, industrial use, non-combusted (primarily as a feedstock for chemicals) and buildings at 11,306 million mt oil equivalent — or 150 times biofuels’ production. Thermochemistry benefits from about 150 years of technology development for efficiently converting these feedstocks to energy, fuel and chemical products.

Some early forms of industrial bio-based processing are starting to reach a certain level of maturity — particularly in the field of conversion of starches and sugars to ethanol, the production of biodiesel from plant- or animal-based lipids, and the making of organic acids such as citric acid and lactic acid by fermentation. This is leading to the building of larger plants, declining production costs, and manufacture of multiple products at a single facility.

This advancing maturity of bioprocessing is enabling a new paradigm: the integration of a conventional or modified thermochemical conversion step to upgrade a bio-based feedstock or a product from a bio-based process. This effectively leverages the centuries of knowledge in chemistry, engineering and catalysis encapsulated in thermochemical processing to advance the bio economy. The emergence of these integrated schemes has the potential to produce fuels and chemicals that can reduce carbon footprint and increase profitability. In addition, the product from these integrated streams often is more easily accepted by the market and existing infrastructure.

The Drivers

Such integration marries bioprocessing’s advantages with mature thermochemical processes.

Bioprocessing advantages. A bio-based feedstock in many cases is an advantaged carbon source. For instance, the growing concerns over sustainability and carbon footprint have prompted a variety of government incentive and regulatory programs that favor fuels and chemicals from plant-based carbon [4]. This is spilling over to the private sector with consumer and shareholder demands driving an increasing focus on sustainable products. However, faced with the reality that the market won’t pay a premium for “green” products, bio-based routes must offer a cost or performance advantage. In some cases, the carbon in these feedstock routes is cheaper than fossil carbon, although this greatly depends on market forces. Tipping fees or low cost hauling charges associated with municipal solid waste, waste oils and other forms of waste organic matter are spurring interest in technologies that can convert these feedstocks into fuel and chemical products. In a similar manner, waste carbon from industrial sources can be “reused,” playing an important role in growing interest in the circular economy.

Reference 5 explores in some detail the processing conditions of biological routes versus thermochemical ones. For instance, biological materials impose limitations on the operating temperatures and pressures of reactors. This restriction against elevated temperatures and pressures actually provides an advantage: the carbon can be delivered to the reactor with much lower energy costs than a conventional thermochemical route. In addition, biological processes have greater tolerance to many species like hydrogen sulfide and ammonia that poison conventional catalysts, thereby simplifying and decreasing the cost of feedstock decontamination. Finally, biological routes often can cope better with changes to feedstock composition and are more forgiving than conventional thermochemical processes.

Thermochemical processes. The lower temperatures and pressures in biological processes limit the reaction rate. In addition, the catalyst “density” in a biological process is much lower than in a thermochemical route. Therefore, a thermochemical process requires a much smaller reactor volume than that of a similar biological conversion step. For instance, a very good biological process may run with a productivity of 100 g (product)/L (reactor volume)/d. In contrast, a typical refinery hydrocracker provides a “productivity” exceeding 30,000 g/L/d (to use the nomenclature of the bioprocessing industry). In other words, the refining process can produce more than 300 times the amount of product per unit of reactor volume.

Moreover, as already mentioned, thermochemical processes have the advantage of maturity. The chemical engineering profession first was established at the University of Manchester in the U.K. in 1887, followed shortly thereafter by a program set up by Massachusetts Institute of Technology, building upon centuries of operational knowledge about chemicals’ production. The growth of chemical engineering, the concept of unit operations, and best practices for process design and operation largely grew in parallel with the petroleum-based economy. This scale-up experience has been encapsulated in a subset of chemical engineering related to process design, with robust approaches ranging from empirical models based on operating data, rigorous algorithms built up from first principles, and shortcut approaches derived from both empirical and first-principle design methodologies. As a result, while scale-up of new thermochemical technology innovations isn’t trivial, using these tools often enables successful scale-up by two to three orders of magnitude.

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  • Great article! Good summary of technologies. I would add one more that is gaining momentum; Hydrothermal Liquefaction (HTL). This processes wet feedstocks, but eliminates the need for front end drying. It can process waste feeds, such as biosolids from wastewater treatment. This revenue stream from accepting the feed greatly improves the economics.

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