Creating Value from Landfill Gas? Landfills contain a toxic stew of biomass materials from old tires to food wastes to animal manure. It is literally the bottom of the rubbish barrel. The US EPA estimates that 250 million tons of municipal solid wastes are sent to landfills each year. These materials have a wide range of chemicals in them, including aromatics, paraffins, oxygenates, and nitrogen- and sulfur-containing compounds. Moreover, they are mixed with a variety of other non-organic debris such as cement and metals. Finding value in this mess seems counterintuitive.
More uniform biomass resources such as trees or crops can be the basis for producing valuable materials such as chemical intermediates, nutrients, pharmaceuticals, and fuels. Raw biomass can be monetized by breaking down the physical and/or chemical structure in a series of sometimes difficult and costly steps. Wood can be converted thermo-chemically to cellulose fiber, paper, or olefins and aromatics. Algae can be crushed and extracted to isolate small quantities of nutritional supplements such as the omega-3 fatty acids EPA and DHA. And, of course, corn or sugarcane can be fermented by microorganisms to produce ethanol, butanols, and lactic acid.
Mixed biomass digested under the anaerobic conditions in a landfill slowly forms bio-gas. Biogas has an objectionable odor and can move through soil and collect in nearby buildings or escape to the atmosphere. Biogas may contain more than 500 different impurities, including sulfur compounds that are corrosive in the presence of water, halogenated compounds (e.g., carbon tetrachloride, chlorobenzene, chloroform) that produce corrosive combustion products, and organic silicon compounds (e.g., siloxanes) that form siliceous deposits in downstream applications — like internal combustion engines. Thus, an initial cleanup or pre-purification step is needed before biogas can be used in any application involving combustion.
For every million tons of municipal solid waste (MSW) about 450,000 cubic feet per day of biogas is produced. The gas may be burned to generate power (about 0.78 megawatts (MW) of electricity per million tons MSW), added to an existing gas network, or converted to syngas (CO, CO2, H2, CH4, H2O, and a few impurities) by reforming just like natural gas from fossil sources. The resulting bio-syngas can be converted to methanol, dimethyl ether (DME), or Fischer-Tropsch products via the same commercial processes practiced at massive scale in the monetization of coal or natural gas.
Processing gases has many advantages compared to processing solids or liquids. Gas mixtures are easier to handle than solids, and have fewer corrosion, stability, or fouling issues than complex liquid bio-oil mixtures. Gas purification methods are well established. Many gas upgrading processes are commercially available. And natural gas can be processed along with bio-gas to boost plant capacities and provide project flexibility. It is no wonder that Synthesis Energy Systems, Primus Green Energy, Sundrop Fuels, Maverick Synfuels, Siluria, INFRA, Oberon, GTI, Velocys, and others want to generate liquids from biomass via gas intermediates.
Bio-Gas Resources and Upgrading
There are about two thousand landfills in the US alone that are continuously producing bio-gas. Although the volumes of biogas are modest, the gas is essentially free and its production is relatively continuous for decades. Collecting landfill gas into large quantities is impractical because landfills are widely dispersed across the country; local solutions are required. Landfills are usually associated with population centers so that materials derived from these local resources have ready local markets.
The most widespread use of biogas is for combustion to generate electricity. Worldwide, there are more than 12,000 biogas plants with a capacity of about 7,000 MW. About 90% of these are in Europe where the resulting electricity is subsidized. In the US, there are some 648 landfill gas projects with a generating capacity of 2,500 MW, and another 400 landfills identified by the EPA as ‘candidates.’
Methane is 20 times more effective at trapping heat as a ‘greenhouse gas’ than is carbon dioxide, and its emissions are more readily controlled than are CO2 emissions. The net availability of methane from biogas in the US is about 6.2 million tonnes of which 2.4 million tonnes come from landfills. This landfill gas represents about 17% of the total methane emitted each year, and about 40% of the bio-derived methane, so it represents an excellent opportunity both for meaningful environmental improvement and for bio-based materials.
Niche Applications Favor Modular Solutions
Landfill gas can be upgraded to fuels or chemicals by a variety of thermal and catalytic processes. In many cases most of the CO2 must be removed from the methane before upgrading. Steam or oxidative reforming can be used to convert the biogas to syngas, from which hydrogen may be separated, if desired. Syngas conversion to methanol, diesel, gasoline, or DME can follow.
The wide dispersion of biogas makes it a poor fit for the world scale processes such as Sasol’s Oryx or Shell’s Pearl gas-to-liquid (GTL) plants in Qatar that produce 30,000 and 120,000 barrels of liquids per day, respectively. A typical biogas conversion plant at a landfill will be scaled to produce a few hundred to a few thousand barrels per day of liquids. There are over 325 landfills in the US that could provide feed for GTL plants of at least 500 barrels per day. The American Biogas Council has identified more than 10,000 additional sites, including dairy farms and waste water treatment plants, that could produce biogas. A market with this many potential customers has attracted the attention of companies advancing small scale GTL processes.
Primus Green Energy is developing a syngas-to-gasoline (“STG+”) technology that is a variation on the Exxon-Mobil MTG process. Primus uses a “proprietary catalytic thermochemical process to minimize complexity, improve product quality and increase yield.” The Primus STG+ technology directly converts more than 35% of the syngas by mass to liquid fuels (> 70% of methane). STG+ consists of four fixed bed reaction steps and one gas/liquid separation step in one continuous process loop to produce high-octane synthetic gasoline. The modular process is suitable for deployment with landfill gas feed. Primus has been operating a 6.5 barrel per day (bpd) demonstration plant in New Jersey for a few years and has signed a takeoff agreement to supply Tauber Oil with 160 tons per day (tpd) of methanol made from Marcellus shale gas beginning in 4Q17.
Other companies that hope to enter the small scale GTL market producing methanol (either as product or intermediate) in their plans include Maverick Synfuels and Oberon. Maverick advertises a 200 bpd modular methanol plant. Oberon is targeting 3,000-10,000 gallons of DME per day.
Velocys has steel on the ground. The company has put aside its own Marcellus shale gas play in Ashtabula, OH, to concentrate its resources on ENVIA, a commercial reference plant to convert landfill gas to hydrocarbons. ENVIA Energy is a joint venture among Waste Management, NRG Energy, Ventech, and Velocys for the Oklahoma City based project. The plant includes a steam reformer to produce syngas and Velocys Fischer-Tropsch units to convert the syngas to a mix of naphtha, diesel, and waxes. The catalyst is claimed to be highly selective for C5+ (90%) with little methane (5%), which make it roughly comparable to the Shell and Sasol results.
INFRA technology is building a 100 bpd plant in Wharton TX based on its “4th generation” Fischer Tropsch technology. The INFRA technology achieves only 65% selectivity to the valuable C5+ products and modest conversion.
Siluria is taking a radically different approach, converting a mixture of methane and oxygen directly to ethylene using oxidative coupling. Ethylene is an intermediate to a host of products and is the basis of the modern chemical industry. The process has been intensely studied since the early 1980’s, but commercially viable yields have not yet been demonstrated.
Advances are occurring on the development of biogas generation and collection systems as well.
Holistic design of landfills to accelerate production and optimize collection of landfill gas is underway at Waste Management. Their ‘Bioreactor Landfill’ may one day revolutionize landfills from secure waste repositories to waste treatment systems, to significantly reduce or even eliminate long-term risk to the environment while simultaneously extracting value. String, a startup from India, is likewise developing a process to produce chemicals that uses anaerobic digestion followed by methane fermentation.
Landfill gases are available throughout the world, but the individual sites are relatively small and dispersed compared to natural gas deposits. So the solutions need to be tailored to the scale of the resources. At least a dozen companies are developing solutions that can produce chemicals or fuels. Very soon we expect one of these companies to break out from the pack and spark a landfill gas to products revolution.
About the Author
Dr. Terry Mazanec has been involved in the renewable fuels and chemicals area for much of his 35 years in R&D. Terry worked 21 years at BP in alternate energy R&D, and then as Chief Scientist at Velocys for 9 years where he led the team developing microchannel processes for natural gas upgrading and chemicals production, including catalyst development, corrosion resistance, and metals coating. He has been an independent consultant for the past 5 years serving clients in the USA, Europe, and Asia. He has authored 20 refereed publications and has been granted more than 60 US Patents as well as numerous international patents. He has experience in catalysis, biomass upgrading, chemicals process development, natural gas conversion, solid oxide fuel cells, algae production, risk analysis, technical due diligence, expert witness services, and intellectual property protection.
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