Petroleum is a limited resource and if we keep using it global warming will accelerate. Since this realization has filtered in the quest for alternatives has begun. Shale gas and natural gas are only pseudo solutions as those supplies are finite and fossil, too. The only way out are fossil-free resources. Industry and academia are developing processes for bio-based feedstocks fervently and with the prerequisite that the products must not be more expensive than conventional ones. However, in late 2014 the price for crude oil dropped below $70 per barrel and has not recovered as of early 2018. The prices for the chemical building blocks ethylene and propylene have roughly halved from 2014 to 2016. The dismal prospects have made big players such as Braskem and Dow Chemical shelve their bio-based propylene development. Thyssen Krupp Industrial Solutions has sent its multipurpose plant for organic acid fermentation in Leuna, Germany into hibernation in 2015 until better times, selling it subsequently to EW Biotech.

However, at the current price for crude oil, bio-based chemicals can rarely compete with their fossil counterparts pricewise and cannot even play a trump card in the matter of climate change: the amount of “C” that ends up as part of products is marginal. Nonetheless, support for bio-based products is firmly anchored in the policies of many governments and the targets they have set are ambitious.

Bio-based Policies in Europe and the US

There is consensus in Europe and the US that guidelines on how to switch over to a bio-based economy need to be stipulated; the approaches to implement the change are quite different regarding the strategies of the different governments and the legislative conditions.

The European Union has agreed upon

• a 40% greenhouse gas reduction by 2030 (compared to 1990 levels)
• at least a 27% share of renewable energy consumption
• at least 27% energy savings

More explicitly 20% of the chemicals and materials in the European Union will be bio-based by 2020, rising to a quarter in 2030. In the United States the Biomass R&D board envisions a billion ton bioeconomy. By 2030 1 billion t of biomass is projected to be sustainably produced. It is supposed to be the base for emerging bioproducts industries, but mainly to target “a potential 30% penetration of biomass carbon into US transportation market by 2030”. Plainly spoken this means biofuel in the forms of biodiesel or the addition of ethanol to gasoline.

Which is the Most Promising Bio-based Chemical?

When new processes and products enter the market it is human nature to ask who does best in the competition. For the uninvolved observer it may be simple curiosity, for investors it’s a matter of money – and lots of it – to decide whether to jump on the bio-based bandwagon and which car to take.

In 2004 the US National Renewable Energy Laboratory (NREL) has defined 12 top value added chemicals from biomass. These products seemed to be the most promising at that time but a lot has happened in the last decade. In the follow-up report of 2016 there is again a list of 12 promising chemicals. The overlap between the two lists is moderate and consists of glycerol, succinic acid and para-xylene.

The European Union, too, strives to identify the chemicals that are predestined to be made from biomass. RoadToBio is a EU-funded project set up in mid-2017 to deliver a roadmap by 2019 illustrating the ‘sweet spots’ for Europe’s chemical industry. In a first step, a long list with 120 chemicals at technology readiness level of 6 (TRL 6) or higher was compiled that show potential for the chemicals market. In parallel, the value chains of 500 petrochemicals were analyzed from a purely technical point of view. 85% of the value chains offer entry points where a petrochemical could be replaced by a bio-based one. The chemicals that were cited most often as replaceable are ethylene, propylene and methanol.

Interface between Bio-based and Petrochemical

The NREL report and RoadToBio project have in common that they both examine products with a TRL 6 or greater meaning that the production process has reached pilot scale. Furthermore the studies so far both work along the value chain of petrochemical products. A typical product tree starts from a low value feedstock like ethylene and branches into many higher value intermediates like polyethylene, ethylene oxide and vinyl acetate. The intermediates again have multiple uses.

Whenever a chemical can in theory be replaced by a bio-based one this is called an entry point in RoadToBio. Overall, of the 120 chemicals identified in the long list for further analysis, only 49 have entry points into existing petrochemical value chains, while the other 71 are dedicated chemicals. Dedicated chemicals are those which have no fossil-based counterpart and thus offer unique production routes. Lactic acid as base for the bioplastic polylactic acid is a prominent example for a dedicated chemical. In contrast, drop-in chemicals are bio-based versions of existing chemicals. A third group, smart drop-in chemicals, are also chemically identical to their fossil counterparts but provide an additional advantage compared to ordinary drop-ins. This can be a faster and simpler production pathway or less energy use.

Four chemicals that appear on both the top twelve NREL list and among the 49 RoadToBio chemicals with potential entry points are succinic acid, para-xylene, 1,2-propanediol and glycerol.

Succinic Acid

The current world market for the dicarboxylic acid is around 50,000 mt/y and intended as raw material for specialty chemicals. However, the projected market is large and that this projection is a very real thing is reflected in the production plants that are set up worldwide. Between the four of them and in various joint ventures Succinity, BioAmber, Myriant and Reverdia are building production capacities of more than 400,000 mt/y of succinic acid. Microorganisms used for the fermentation are B. succiniproducens, E. coli and S. cerevisiae. The companies count on succinic acid becoming a platform chemical, opening up a much broader product range. Hydrogenation of succinic acid to 1,4-butanediol and tetrahydrofuran could access another market of combined 2.4 million mt/y. If this becomes a reality your spandex clothing and polyurethane mattress can be bio-based, too, in the future.

Para-xylene

Para-xylene is used to produce both terephthalic acid and dimethyl terephthalate, the two constituents of polyethylene terephthalate (PET).

It is nearly exclusively used to manufacture polyesters with the majority destined for fibers and films. The 27% going into PET bottle resin, however, are the ones that got the most attention from bioeconomy media in the last few years. Major consumers of PET – the Coca-Cola Company, Ford, Heinz, Nike and Procter & Gamble – have funded research for the production of renewable PET. Virent has developed a hybrid biochemical and thermochemical process that converts biomass into a mixture of hydrocarbons. This can be treated just like petroleum-derived hydrocarbons. A 100% plant-based bottle was showcased at Expo Milan in 2015 (Lane 2015), made with para-xylene from a demonstration plant but commercial production is expected not before 2021. Micromidas and Annellotech base their chemo-catalytic processes on cellulosic feedstocks, too, while Biochemtex counts on lignin. The only company using fermentation is Gevo: sugars from biomass are converted by a yeast into isobutanol which is then chemically transformed into para-xylene.

For the time being none of the companies has the capacity to make a dent in the 65 million mt/y market.

1,2-Propanediol

1,2-propanediol has a myriad of uses ranging from pet food to polyester resins, resulting in a global market of around 2.5 million mt/y.

It is also known as propylene glycol and is currently produced from propylene as a coproduct of petroleum cracking, therefore its price is closely connected to the petroleum price. Bio-based 1,2-propanediol is usually produced by hydrogenolysis of glycerin with mixed-metal catalysts with the catalyst formulation and reaction conditions being the variables. ADM has 100,000 t/y production capacity in the US and Oleon 20,000 mt/y in Belgium. Global Bio-Chem operates a 200,000 mt/y plant in China using sorbitol from corn as feedstock. The sorbitol is hydrocracked into 1,2-propanediol, ethylene glycol and butanediol.

Glycerol

The sugar alcohol can be used in bodylotion as well as in marzipan, to keep both your skin and the almond paste soft and tender. Apart from that glycerol has more than 1,500 other uses. The petrochemical production route for glycerol starts from propene but plays only a minor role. The market is dominated by bio-based glycerol as a byproduct of biodiesel production. For this vegetable oil is transesterified with an alcohol; for every 10 t of biodiesel 1 t of glycerol is produced. With a yearly production of about 2 million t of glycerol worldwide the market is saturated, resulting in stable and historically low prices. Industry is therefore looking for ways to add value to glycerol. Use as a substrate for fermentation processes such as succinic acid, citric acid, 1,3-propanediol or biogas are in part commercially proven as is application as animal feed.

And the winner is…?

If predicting the success of a bio-based product were easy governments worldwide would not employ legions of scientists and commission studies to do so. Only time will tell which of the cited bio-based chemicals will become a blockbuster and whether RoadToBio will come to the same conclusions as the NREL study. The petroleum price and governmental interventions are only two of the more unpredictable factors in the multi-parameter matrix which determines the economic success of a bio-based product. One of the communalities of the four chemicals discussed above is that they are drop-in chemicals. They are chemically identical to their fossil counterparts and for further processing it doesn’t play a role whether they are made from petroleum or from biomass.

On closer inspection the production processes of promising drop-in chemicals are an eclectic mix of chemical and biotechnological. Fermentation steps are followed by chemical transformations; whether a metal catalyst or an enzyme is used is just a matter of what works best. Anything goes as long it is technically feasible. A process is no longer either chemical or biotechnological, cooperation is the new normal. Winners in the quest for the holy grail of bio-based chemicals are definitely the scientists from all the different disciplines involved. They have learned to look past the rim of the teacup of their own sector and gained a whole new perspective in their neighbor’s teacup.