Carbon Dioxide Gets a New Fizz

Technologies transform greenhouse gas into a feedstock for chemicals.

By Seán Ottewell, Editor at Large

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Capture and conversion of carbon dioxide from the plant would yield over $1 billion/yr of PHA or other products, Sefton notes. It also would increase the value of the cement produced there because builders could claim credits for achieving green building standards by using it, he adds. On a broader note, capturing and converting the 2 billion t/y of carbon dioxide emitted by the worldwide cement industry could supply the entire global plastics market, he says.

Oakbio’s n-butanol is the newer of the two products. “This is an important chemical feedstock as well as a drop-in biofuel with an octane rating similar to gasoline. This model is also capable of producing thousands of other compounds, many of which we have made in small amounts already such as diacids, ketones, esters, fatty acids and organic acids,” notes Sefton.

The company currently uses bioreactors that vary in volume from 250 ml to 20 L. Oakbio is raising funds to take this program to pilot scale of 1,000–5,000 L.

The process has a number of advantages, says Sefton. First, it requires no costly extra ingredients such as promotors or antibiotics. This means the process water is very clean and can be re-used easily. “In addition, the process can uptake organic acids, acetone, benzene, diesel fuel and many other chemical compounds which are considered waste, including even dioxin, and break these down into energy and feedstocks for our target compounds.”

Oakbio is working closely with Ohio State University, Columbus, Ohio, to leverage the school’s molecular biology and enzymology expertise to increase n-butanol production to commercial levels. Sefton expects to achieve this in two years.

The PHA process is cost competitive and projected to be profitable at scale, he notes, while the n-butanol business is projected to be profitable once production levels reach the company target. Several chemical companies and fuel producers are watching developments closely, Sefton adds.


Meanwhile, Liquid Light has developed technology based on low-energy catalytic electrochemistry to use carbon dioxide to produce chemicals. By adjusting the catalyst design and combining hydrogenation and purification operations, the technology can make a range of commercially important multi-carbon chemicals including glycols, alcohols, olefins and organic acids.

The company believes that by using other feedstocks alongside carbon dioxide, a future plant would be able to manufacture multiple products simultaneously. “We are working on other catalysts to expand the list of possible products too,” adds Kyle Teamey, Liquid Light’s CEO.

A major chemical company is partnering in the work. This partner already has a variety of heterogeneous, homogenous and hybrid catalysts for the electrochemical reduction of carbon dioxide and also has developed catalysts for downstream processes, he notes.

In March, Liquid Light unveiled its first process — for the manufacture of monoethylene glycol (MEG). In lab-scale test runs, the demonstration electrocatalytic reaction cell met targets for energy needed per unit of output, rate of production, yield and stability/longevity of cell components.

Its process requires $125 or less of carbon dioxide to make a ton of MEG versus an estimated $617 to $1,113 of feedstocks derived from oil, natural gas or corn needed by other processes, claims the firm. These differences are especially significant because MEG sells for between $700 and $1,400 per metric ton.

The company says that current estimates indicate that licensees would gain more than $250 in added project value by opting for its process instead of the best currently available technology for a 400,000-t/y MEG plant. A 625,000-t/y plant would have a 15-year net present value of over $850 million to a licensee, it adds.

An added bonus is that intermittently available renewable energy sources such as solar and wind can power the process. The result is that chemicals can be made directly from renewable energy sources and carbon dioxide, boasts the firm.

The plan now is to build a pilot plant in Canada to produce a ton of products per day and help to further validate the technical and economic feasibility of the technology.

SEEKING A SOLAR SOLUTION
In Europe, a joint research/industry project has demonstrated the production path for so-called “solar” kerosene. Known as Solar-Jet, the project uses concentrated sunlight to convert carbon dioxide and water into a syngas via a redox cycle with metal-oxide-based materials at high temperatures (Figure 3). The syngas, a mixture of hydrogen and carbon monoxide, then is converted into kerosene using commercial Fisher-Tropsch technology.

ETH Zurich, Zurich, Switzerland; Bauhaus Luftfahrt (a research institute funded by four aerospace companies), Munich, Germany; the German Center for Aerospace, Cologne, Germany; research and technology development consultancy ARTTIC, Paris, France; and Shell Global Solutions, Amsterdam, The Netherlands, are pioneering the development of the new pathway.

The Swiss university is working on the solar splitting of water and carbon dioxide to produce solar syngas, while Shell is addressing the syngas-to-solar-kerosene step.

The solar reactor consists of a cavity receiver with a 4-cm-diameter aperture through which concentrated solar radiation can pass; the aperture incorporates a compound parabolic concentrator to further boost the concentration. A 24-cm-diameter, 3-mm-thick clear fused-quartz disk window seals the reactor front. Sunlight comes from ETH’s high-flux solar simulator.


The solar cavity receiver contains a reticulated porous ceramic foam made of pure cerium oxide. (The oxides of cerium have emerged as attractive redox active materials because of their ability to conduct oxygen ions faster than either ferrite-based oxides or other non-volatile metal oxides.)

This two-step thermochemical reaction’s big advantage is its elimination of the gas separation steps needed after traditional thermolysis.

“Increasing environmental and supply security issues are leading the aviation sector to seek alternative fuels which can be used interchangeably with today’s jet fuel, so-called ‘drop-in’ solutions, states Andreas Sizmann, the project coordinator at Bauhaus Luftfahrt. “With this first-ever proof-of-concept for ‘solar’ kerosene, the Solar-Jet project has made a major step towards truly sustainable fuels with virtually unlimited feedstocks in the future.”

“The solar reactor technology features enhanced radiative heat transfer and fast reaction kinetics, which are crucial for maximizing the solar-to-fuel energy conversion efficiency,” adds Aldo Steinfeld, who leads fundamental research and development of the solar reactor at ETH Zurich.

Although the solar-driven redox cycle for syngas production still is at an early stage of development, a number of companies including Shell already are processing syngas to kerosene on a global scale. “This is potentially a very interesting, novel pathway to liquid hydrocarbon fuels using focused solar power,” says Hans Geerlings, principal research scientist at the Shell Technology Center in Amsterdam. “Although the individual steps of the process have previously been demonstrated at various scales, no attempt had been made previously to integrate the end-to-end system. We look forward to working with the project partners to drive forward research and development in the next phase of the project on such an ambitious emerging technology.”

Within four years 50-kW solar reactor technology will be available but the first commercial, MW-scale application won’t appear for 15 years, believes Steinfeld.

“Commercial scale-up will take place in a region of rich solar irradiation, where there is at least 2,000 kWh per square meter annually. The technical challenges involved in such a scale-up include efficient heat transfer and rapid reaction kinetics for maximum solar-to-fuel energy conversion efficiency,” he adds.


ottewell.jpgSeán Ottewell is Chemical Processing's Editor at Large. You can e-mail him at sottewell@putman.net.

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