P. K. NICCUM, Contributing Author, Houston, Texas (U.S.)
Part 1 of this article provided an account of the > 80-yr evolution of fluid catalytic cracking (FCC) regenerator flue gas emissions controls since the process’s inception in World War II (WW II) to minimize flue gas pollutants including carbon monoxide (CO), sulfur oxides (SOx) nitrogen oxides (NOx) and catalyst dust.
Part 2 of this article discusses initiatives to capture carbon dioxide (CO2) emissions from FCC unit (FCCU) operations as well as the impact of rising atmospheric CO2 concentrations on plant growth and food production and the impact on society from the widespread use of fossil fuels.
CAPTURE OF CO2 IN FCCU REGENERATOR FLUE GAS
Over the past 40 yrs, work has been completed to capture the CO2 in FCCU regenerator flue gas for industrial applications.
In 1985, Air Products and Chemical Co. patented a process to produce CO2 for enhanced oil recovery while also helping the environment by reducing SOx and NOx emissions.
As shown in FIG. 9, the FCCU flue gas combustion in a mixture of pure oxygen diluted with CO2 is processed to provide a CO2-rich recycle gas stream to be mixed with oxygen. A net-combustion product stream from which SOx and NOx are recovered to eliminate atmospheric emissions and a pure CO2 product are produced for export. An alternate embodiment also produces hydrogen (H2) or synthesis gas (syngas) for export.
The regenerator is supplied with oxygen captured from the air to burn the regenerator coke, while the largely CO2-containing flue gas is cooled and cleaned in a scrubber and recycled back to the regenerator to maintain the unit heat balance and fluidization quality. This controls the desired oxygen concentration in the regenerator for burning the coke, with the net CO2 being cleaned and exported for enhanced oil recovery and other industrial uses.
While technically sound, after many technical reviews extending into the 1990s, the process was not found to be economically viable.
A consortium that included Petrobras, bp, Chevron, Eni, Shell and Suncor built a large-scale FCCU pilot unit in 2011 at a Petrobras research facility in State of Paraná, Brazil. In 2012, the 33-bpd FCCU pilot plant (FIGS. 10 and 11) proved the technical viability of the oxygen-blown FCCU operation for capturing 95% of the CO2 produced by the FCCU.39
A technical evaluation was made of the oxygen-blown FCCU vs. a more traditional amine absorption CO2 capture system. While the amine absorption system was found to be less costly, the lower estimated operating cost for the oxygen-blown FCC system provided a lower overall CO2 capture cost.
In addition to the support of energy companies, the CO2 capture project is supported by government organizations, including the U.S. Department of Energy (DOE), the European Commission and more than 60 academic bodies and global research institutions.39
UOP authored an article based on process simulations (FIG. 12) that describes the utilization of an air separation plant to provide oxygen to the FCCU regenerator while recycling CO2 to control regenerator oxygen content and fluidization and producing CO2 at greater than 90 vol% purity for export.40
Processing bio-oils and wood in FCCUs. Biologically derived oils and carbohydrates such as sugar cane have been processed in FCCUs to produce some useful products while sometimes earning government renewable fuel credits. While not specifically related to FCC flue gas emissions, this information is presented as it also relates to environmentally driven aspects of FCC technology.
The fast pyrolysis of biomass has been demonstrated to produce a range of products in pilot plants and demonstration plants. The main component of biomass is cellulose depicted in FIG. 13 showing its carbon, H2 and oxygen structure.
Published data for the fast pyrolysis of biomass reveals a diverse range of products, including chemically reactive and corrosive oxygenated hydrocarbon molecules that polymerize over time.41,42
Adams states:41
“Fast pyrolysis is not an equilibrium process, hence the product, the bio-oil, is not in thermodynamic equilibrium at storage temperatures. Bio-oil contains a large number of oxygenated organic compounds with a wide range of molecular weights, typically in small percentages. During storage, the chemical composition of the bio-oil changes toward thermodynamic equilibrium, resulting in changes in viscosity, molecular weight and co-solubility of its many compounds. In addition, the simple phase bio-oil can separate into various tarry, sludgy, waxy, and thin aqueous phases during aging. Tarry sludges and waxes still in suspension cause rapid plugging of fuel filters.”
The catalytic and non-catalytic pyrolysis of wood was made in a fast pyrolysis pilot plant. The stability of the products was improved by catalysts, with ZSM-5 catalysts being the most effective.43
FIG. 14 shows data from the fast pyrolysis of biomass in the presence of AL-MCM-41 (ZSM-5 containing) catalyst appended to Adam’s thesis provides some insight into the wood product composition with just wood vs. wood with four different catalysts. In all cases, water and CO2 are the primary reaction products, with water and CO2 being more pronounced in the catalyzed yield structures.44
In 2012, KiOR in Columbus, Mississippi (U.S.) processed ground wood chips in a commercial scale FCCU to produce gasoline and diesel products.45
Flue gas health considerations. Significant concentrations of CO, SOx, NOx and fine catalyst exit the flue gas stack and are considered unhealthy to breath, depending on their concentrations after being dispersed into the atmosphere.
CO can be a deadly poison, as it can interfere with the uptake of oxygen into the bloodstream.
SOx are corrosive gases that can irritate lungs.
NOx can be a respiratory irritant and is a component in smog formation by the reaction with ozone and sunlight.
Fine catalyst particles, particulate matter (PM) can build up in lungs and cause lung damage.
CO2,46 nitrogen (N2) and water vapor (H2O) are not unhealthy. However, oxygen-deficient gases without CO2 are very dangerous, as CO2 controls our breathing reflex.
The impact of atmospheric CO2 concentrations and fossil fuel use. CO2 is not poisonous and sustains life on earth through the process of photosynthesis, feeding plant life while generating oxygen for the atmosphere. It is well known that increasing CO2 concentrations in the atmosphere causes plant life to flourish and bolsters worldwide food production. At the same time, the use of fossil fuels has made our planet more livable.47
The impact of atmospheric CO2 concentrations on plant growth. Numerous scientific studies over the past 100 yrs have documented increasing plant growth rates from increasing the CO2 concentration in their atmosphere.48
Idso, et al., documented the increase in plant growth rates at the U.S. Water Conservation Laboratory with ambient air enriched with 150 ppm, 300 ppm and 450 ppm CO2, respectively (FIG. 15). As of 2021, CO2 levels were 420 ppm, while at some studies have shown that most plants die at 120 ppm–150 ppm.49
References to hundreds of other studies were also provided by Idso, et al., to further support the conclusion that CO2 enrichment has a significant impact on the growth of plants, trees, vegetables and grains (TABLES 3–5).
Changes in atmospheric CO concentration and ambient temperatures. CO2 concentrations of only several hundred ppm in our atmosphere for the past century are far lower that values seen (FIG. 16) in the longer-term history of the world, where life flourished for hundreds of millions of years at CO2 levels of 5,000 ppm–6,000 ppm.51
FIGS. 17 and 18 show shorter term changes in atmospheric CO2 and temperature.
As bad as naturally dangerously hot temperatures are, naturally occurring cold temperatures have long been and remain a far greater danger. A study over the past two decades found that deaths from cold have been many times higher than deaths from heat.54
For much of the world’s population, increasing ambient temperatures would be considered a good thing as low temperatures kill many times more people on this planet than high temperatures do.
Fossil fuels use. As shown in FIG. 19, beginning in the mid-1800s coal began to contribute an energy demand that had been based on burning wood and other biomass. In the early-1900s, coal, oil and gas began to rapidly add to the energy supply with fossil fuels dominating ever since.55
One assertion is that the increased use of fossil fuels has made our planet more livable for billions of people by mitigating the impact of extremes in weather such as droughts, wildfires, storms, floods, cold spells and heat waves. For example, in cases of famine or drought, food and water can be supplied to the local population from other parts of the world.56
FIG. 20 shows the rate of climate disaster deaths has decreased by 98% over the last century with rapidly increasing fossil fuels use, where the climate-related death rate had been ~2,400 deaths/1 MM people per yr in the 1920s, falling to < 50 climate-related deaths/1 MM people per yr in the 1990s and beyond.57
Climate-related disaster deaths have plummeted by 98% over the last century as CO2 levels have increased from 280 ppm to 420 ppm and temperatures increased by 1°C.58
It is noteworthy that CO2 levels today are less than one tenth of the planet’s historical high points, which were some of the most life-friendly times in the planet’s history.59,60
Historical note. Special attention should be paid to the development of large-scale natural gas-fed ammonia plants by the M.W Kellogg company in the 1960s that revolutionized fertilizer production by cutting fertilizer production costs in half, dramatically increasing crop production throughout the world. FIG. 21 shows the increased ammonia capacity. The process was credited by UNESCO (United Nations Educational, Scientific and Cultural Organization) as having “staved off a Malthusian revolution,” saving much of the world from starvation in the 1970s.61
Governments, non-governmental organizations (NGOs) and media. While cost/benefit analysis has been the bedrock of industrial development, claims of catastrophic results from rising CO2 concentrations in the atmosphere are amplified while restricting reference to the benefits of fossil fuels use and the benefits of increasing atmospheric CO2 concentrations on plant growth and food production.62 At the same time, communication of the staggering financial and human costs of proposed carbon reduction strategies are rarely discussed.
On a related note, regulations have been instituted in many countries to restrict the use of nitrogen-based fertilizers and other enablers of food production, such as water and land use.63,64
Investments in decarbonization processes—including the FCC process—are being studied and implemented at some locations.38,39,40,45,39
In January 2025, executive orders were issued by U.S. President Donald Trump soon after his inauguration, withdrawing the U.S. from the Paris Climate Accords and any agreement made under the United Nations Framework Convention on Climate Change, as well as rescinding the U.S. International Climate Finance Plan, which over the years has earmarked billions in U.S. taxpayer commitments.65
Government policies continue to evolve at a rapid pace. The policies listed here are just six of many examples:
In March 2025, changes in U.S. government policy were announced that will rollback U.S. government investments targeting green policies, including carbon limits on power plants, tailpipe emissions standards and protections for waterways.66
In April, 2025, the administration dismissed all 400 of the researchers and scientists working on the National Climate Change Assessment Report with an e-mail simply stating “At this time, the scope of the Climate Change Assessment Report 6 is currently being reevaluated.”67
May 28th 2025, General Motors announced it is investing nearly one billion dollars to upgrade its Buffalo, New York Tonawanda engine factory to produce a new (Generation 6) small block V-8 engine with more horsepower than ever.68
September 2nd 2025, The Net Zero Banking Alliance (NZBA) experienced a mass departure of members including all six of the United States largest banks. The NZBA put their operation on hold and began polling its remaining members concerning their views on a net-zero climate related economy transition in line with the Paris Agreement.69
September 28th 2025, Net-zero pledges were seen to be unravelling with major airlines, energy companies and financial institutions abandoning their net-zero commitments over the past two years. In the same time frame, many major energy companies have recalibrated their strategies to invest more in development of oil and natural gas reserves.70
October 5th 2025, While the European Commission leaders reportedly are against changing their course concerning a low carbon fuel future, in spite of the scientific and economic realities of low carbon fuels, reality will ultimately prevail.71
Takeaways. People and industry have worked tirelessly to improve lives though economic and responsible use of natural resources. It was in this climate that technologies evolved for extracting petroleum from the earth and refining it into valuable products with safety and environmental considerations playing increasingly important roles.
The FCC process was developed and commercialized in WW II to produce aviation fuel. After the war, production shifted to civilian use that demanded even higher production rates of gasoline and petrochemical feedstocks and lower levels of atmospheric pollutants.
Consistent efforts have been made to reduce the use of fossil fuels and other enablers of people’s lives such as food, water and transportation in the name of saving the environment. But now the tide is shifting due to increasing skepticism of climate policies and messaging. HP
ACKNOWLEDGEMENT
The author is grateful for Alexander Epstein’s work contained in his books, Fossil Future—Why Global Human Flourishing Requires More Oil, Coal and Natural Gas, Not Less (2022) and The Moral Case for Fossil Fuels (2014), which provided rich content and lists of references that enabled the creation of this article.
Following graduation with a chemical engineering degree in 1980 from California State Polytechnic University (U.S.), Phillip Niccum worked for Texaco for 9 yrs. He performed process design calculations and technical services for Texaco-owned and licensed FCCUs worldwide for 4 yrs, and then coordinated and developed FCCU technology, catalyst selection and operations in six Texaco U.S. refineries for 5 yrs.
At M.W. Kellogg Co./KBR, beginning in 1989, he served for 26 yrs executing FCC projects, technology development and licensing, including 8 yrs as FCC Chief Technology Engineer and 4 yrs as Director of FCC Technology.
More recently, Niccum served as FCC Technology Adviser at McDermott/Lummus in support of FCC projects and technology development. Throughout his career, he has been granted 17 U.S. Patents and authored numerous papers and publications for major industry conferences and trade journals.