Tokyo
Settling down, specialization, population growth … you know the story. Densely populated areas created new challenges. Already in medieval ages, strolling through the city center was not exclusively romantic. Even back then, serious doubts were raised as to whether there is really no waste in nature when being hit by the contents of a chamber pot, emptied through the window above.

Sewage systems were the logical next step, and the benefits of living in a city continued to greatly outweigh the drawbacks for many of us. Today, Tokyo-Yokohama is the largest megacity in the world, and emptying the chamber pots—with much progress having been made on those—of 38 million people is a Herculean task. Which reminds us that discharging fryer grease via the kitchen sink could reopen the stables of Augeas.

Graz
But let us look back two decades to a much smaller city in Austria. In 1994, Graz became one of the first cities to establish collection of used cooking oil (UCO) from households and restaurants. It was explained to people why UCO is a precious resource. The nearby Südsteirische Energie und Eiweisserzeugung Genossenschaft biodiesel plant, built by BDI-BioEnergy International, was the first plant in the world to process UCO on an industrial scale. From then on, thousands of tons of fat waste were transformed into biodiesel every year. To close the recycling management, the public transportation bus fleet switched to UCO-based biodiesel, and if you were cycling behind a bus, you might have perceived a fine aroma of french fries.

This success was possible because recycling has a long tradition in Austria, going back to the lack of resources after World War II. Waste paper, plastics, metal, glass, etc., had been collected separately for decades. Collecting UCO made sense for everybody as it helped avoid sewage clogging, saved 10,000 euros per year on public transportation fuel and reduced emissions. And so it was done. Moreover, not to forget about biodiesel technology, which had been developed by BDI in close cooperation with researchers from universities. All it took was a wide viewing angle.

Hong Kong
Back in 1999, it was the wide viewing angle of a restaurant visitor who noticed how fryer grease was being discharged in Hong Kong. Home to 6.5 million people, fried culinary delights have an especially large fan base there. The road was long, but what previously ended up being worthless grease-trap waste finally found its dedication in 2014, as feedstock for ASB Biodiesel Hong Kong. From the outset, the BDI design of this plant had waste-based materials in mind and newly developed technologies were implemented for esterifying high levels of free fatty acids (FFA) and distilling methyl esters to reduce sulfur. Therefore, 100,000 tons (30 MMgy) of waste-based biodiesel from ASB provide an important contribution to greenhouse gas (GHG) reduction and fewer particulate emissions every year.

London
As to clean air, if you followed recent media coverage, a more pleasant scent might also be what sewage workers desired in London when they discovered multiple “fatbergs”—one bigger, more sumptuous and bizarre than the next.

While these fatbergs could have been prevented by establishing a UCO collection system, at least they now serve a purpose. Passengers of the red double-decker bus driving on the streets above for sure were not aware that these monsters help to keep them moving. A recently commissioned 75,000 tons (23 MMgy) biodiesel plant near Manchester, England, owned by Argent Energy, uses BDI equipment and is capable of converting even challenging resources into biodiesel meeting EN standards.

And Next: Los Angeles
Data published in 2002 by the National Renewable Energy Laboratory already showed a potential of 495 MMgy (1.65 million tons) of biodiesel per year that could be produced from urban waste grease in the U.S. Maybe not all of these waste greases are available today, but there is certainly enough to start the business. Crimson Renewable Energy LP is now realizing the potential of waste fats collected in the metropolitan areas of California and, in particular, from Los Angeles. Again, BDI is providing the technology to process this material, the latest of which is called RepCat.

Curiosity Built the RepCat
“Can we do even better?” was the initial question when RepCat, which stands for repeatable catalyst, was developed. Commissioning and process engineers at BDI went for a beer after work one day and discussed what a next-generation biodiesel plant should look like. On top of the wish list was an approach that avoids using   corrosive catalysts such as sulphuric acid and caustic potash, which, process-wise, would work fine but require a certain choice of materials and additional safety features. Second was unlimited FFA in feedstock, relieving operators from the permanent attention required when doing traditional acid esterification. Then sales added that the new process must be super stable and robust, because trap grease is the new UCO and this feedstock will be different every minute.

The scientific curiosity of the BDI R&D team was awakened by such pie in the sky—and they accepted the challenge. Finally, after many highs and lows (not only in FFA level), an elegant concept was developed. RepCat is based on recycling a harmless catalyst while being able to use feedstock beyond traditional boundaries, with up to 100 percent FFA.

In the RepCat reactors, esterification and transesterification with methanol take place simultaneously. It is a continuous process where feedstock and methanol react at a pressure above 50 barg (725 psig) and a temperature above 200 degrees Celsius (392 F) with help of the recyclable catalyst. Based on these conditions, a stable and robust process is given to handle fluctuating feedstock quality, even without time-consuming settling processes or expensive separators. The number of stages is defined by the FFA content in the feedstock, with a limit of 15 percent for a single-stage system and up to 100 percent for two stages.

The reuse of the catalyst, which is synthesized on-site, is one of the main characteristics of the RepCat process, and it is only possible because this special catalyst is not sensitive to feedstock impurities or other usual troubles like catalyst poisoning.

Downstream of the reactors, methyl esters and glycerin are distilled simultaneously in the BDI high-end distillation system, followed by a phase separation. The fine vacuum used during distillation considerably lowers the required temperature and avoids product degeneration and unwanted back reactions. In addition to the main rectification column, a short-path evaporator is installed as a squeezing stage to maximize product yield.

Monoglyceride levels below 0.1 percent and a sulfur reduction from 100 parts per million (ppm) down to below 10 ppm are guaranteed for the methyl esters, leading to the highest biodiesel quality, surpassing ASTM D6751 or EN14214 requirements.

As the glycerin is distilled simultaneously over top, a salt-free quality with a concentration above 95 percent is achieved, surpassing traditional concepts. No salts are generated in the whole RepCat process, and the byproduct treatment is reduced to a simple methanol recycling column.

In a nutshell, RepCat achieves higher profitability in the production of biodiesel from waste materials because catalyst and acid costs are cut by 90 percent, income from glycerin is raised by up to 70 percent (due to better quality) and fewer staff is needed due to smooth operation of the continuous process.

Again, it was the desire to do things better that was finally rewarded—with a compact process, unique in feedstock flexibility and a benchmark in production costs.

Resources are Plenty
“Nature is our great teacher—and we the miserable students,” poet Klaus Ender wrote. Let us not be too harsh. There are many examples of how evolving technologies made it possible to redefine waste as a resource, e.g., trap grease that was previously considered useless.

The benefits of waste-based biodiesel range from unique GHG reduction over permanent savings on sewage maintenance to a reliable withdrawal of problematic organic material from the food chain. The economic and environmental advantages of waste-based biodiesel are evident and BDI’s technology is fit for the purpose. All it takes now is a wide viewing angle.

Authors: Hermann Stockinger, Stefan Divjak
Vice President Global Sales, Technical Sales Manager
BDI-BioEnergy International AG
hermann.stockinger@bdi-bioenergy.com
stefan.divjak@bdi-bioenergy.com