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Methanizer is an appliance used in gas chromatography (GC), which allows the user to detect very low concentrations of carbon monoxide and carbon dioxide. It consists of a flame ionization detector, preceded by a hydrogenating reactor, which converts CO2 and CO into methane CH4. Methanizers contain a hydrogenation catalyst to achieve this conversion. Nickel is commonly used as the catalyst and there are alternatives available. [1]
On-line catalytic reduction of carbon monoxide to methane for detection by FID was described by Porter & Volman, [2] who suggested that both carbon dioxide and carbon monoxide could also be converted to methane with the same nickel catalyst. This was confirmed by Johns & Thompson, [3] who determined optimum operating parameters for each of the gases.
CO2 + 2H2 ↔ CH4 + O2
2CO + 4H2 ↔ 2CH4 + O2
The catalyst traditionally consists of a 2% coating of Ni in the form of nickel nitrate deposited on a chromatographic packing material (e.g. Chromosorb G).
A 1½" long bed is packed around the bend of an 8"×1/8" SS U-tube. The tube is clamped in a block so that the ends protrude down into the column oven for connection between column or TCD outlet and FID base. Heat is provided by a pair of cartridge heaters and controlled by a temperature controller.
Hydrogen for the reduction can be provided either by adding it via a tee at the inlet to the catalyst (preferred), or by using hydrogen as carrier gas.
If the raw catalyst is supplied in the form of nickel oxide, it is necessary to reduce it to metallic nickel before it will operate properly. Alternative catalysts do not necessarily need a reduction treatment. Methanizers should not be heated without hydrogen being supplied to them.
Conversion of both CO and CO2 to CH4 starts at a catalyst temperature below 300°C, but the conversion is incomplete and peak tailing is evident. At around 340°C, conversion is complete, as indicated by area measurements, but some tailing limits the peak height. At 360-380°C, tailing is eliminated and there is little change in peak height up to 400°C. Operating temperatures for various methanizers range from 350-400°C.
Although carbonization of CO has been reported at temperatures above 350°, [4] it is rather a rare phenomenon.
The conversion efficiency is essentially 100% from minimum detectable levels up to a flow of CO or CO2 at the detector of about 5×10−5g/s. These represent a detection limit of about 200 ppb and a maximum concentration of about 10% in a 0.5mL sample. Both values are dependent upon peak width.
Nickel catalyst methanizers have been known to undergo deactivation with certain elements and compounds:
In general, the catalyst works perfectly unless it is degraded by sample components, possible minute amounts of sulfur gases at otherwise undetectable levels. The effect is always the same — the CO and CO2 peaks start to tail. If only CO tails, it might well be a column effect, e.g., a Mol. Sieve 13X always causes slight tailing of CO. If the tailing is minimal, raising the catalyst temperature might provide enough improvement to permit further use.
With a newly packed nickel catalyst, tailing usually indicates that part of the catalyst bed is not hot enough. This can happen if the bed extends too far up the arms of the U-tube. Possibly a longer bed will improve the upper conversion limit, but if this is the aim, the packing must not extend beyond the confines of the heater block.
No catalyst preparation is required with a 3D printed jet.
For nickel catalyst methanizers:
Dissolve 1g of nickel nitrate Ni(NO3)2•6H2O in 4-5mL of methanol. Add 10g of Chromosorb G. A/W, 80-100 mesh. There should be just enough methanol to completely wet the support without excess. Mix the slurry, pour into a flat Pyrex pan and dry on a hot plate at about 80-90°C with occasional gentle shaking or mixing. When dry, heat in air at about 400°C to decompose the salt to NiO. Note that NO2 is emitted during baking — provide adequate ventilation. About an hour at 400°C, longer at lower temperatures, will be needed to complete the process. After baking, the material is dark gray, with no trace of the original green.
Pour the raw catalyst into both arms of an 8"×1/8" nickel U-tube, checking the depth in both with a wire. The final bed should extend 3/8" to 1/2" above the bottom of the U in both arms. Plug with glass wool and install in the injector block.
Traditional nickel catalyst methanizers are designed to only convert CO and CO2 to methane. Due to this limitation, deactivation commonly occurs when other compounds are present in the sample matrix, such as olefins and sulfur containing compounds. Thus, the use of methanizers often requires complex valve systems that may include backflush and heartcutting. Nickel catalyst replacement and conditioning steps are time consuming and require operator skill to perform properly.
An alternative methanizer design known as the Jetanizer, where the methanizer is fully contained in a 3D-printed FID jet with novel catalyst, is available from Activated Research Company. The Jetanizer utilizes the heater and hydrogen supply of the FID, reducing the need for additional fittings and temperature control. Similarly to the polyarc reactor, the Jetanizer is resilient to poisoning by compounds containing sulfur, halogens, nitrogen, oxygen, and others. A limitation includes its inability to convert compounds other than CO and CO2 to methane. Literature has been published in the American Chemical Society and the Journal of Separation Science explaining the industry changing benefits of the design which is approachable by any skill level of GC operator given its optimized and simplistic design. [5]
A post-column reactor that overcomes methanizer limitations is a two-step oxidation-reduction reactor that converts nearly all organic compounds to methane. [6] This technique enables the accurate quantification of any number of compounds that contain carbon beyond just CO and CO2, including those with low sensitivity in the FID such as carbon disulfide (CS2), carbonyl sulfide (COS), hydrogen cyanide (HCN), formamide (CH3NO), formaldehyde (CH2O) and formic acid (CH2O2). In addition to increasing the sensitivity of the FID to particular compounds, the response factors of all species become equivalent to that of methane, thereby minimizing or eliminating the need for calibration curves and the standards they rely on. The reactor is available exclusively from Activated Research Company [7] and is known as the Polyarc reactor.
The Haber process, also called the Haber–Bosch process, is the main industrial procedure for the production of ammonia. The German chemists Fritz Haber and Carl Bosch developed it in the first decade of the 20th century. The process converts atmospheric nitrogen (N2) to ammonia (NH3) by a reaction with hydrogen (H2) using an iron metal catalyst under high temperatures and pressures. This reaction is slightly exothermic (i.e. it releases energy), meaning that the reaction is favoured at lower temperatures and higher pressures. It decreases entropy, complicating the process. Hydrogen is produced via steam reforming, followed by an iterative closed cycle to react hydrogen with nitrogen to produce ammonia.
The pyrolysis process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere.
Industrial processes are procedures involving chemical, physical, electrical, or mechanical steps to aid in the manufacturing of an item or items, usually carried out on a very large scale. Industrial processes are the key components of heavy industry.
The Fischer–Tropsch process (FT) is a collection of chemical reactions that converts a mixture of carbon monoxide and hydrogen, known as syngas, into liquid hydrocarbons. These reactions occur in the presence of metal catalysts, typically at temperatures of 150–300 °C (302–572 °F) and pressures of one to several tens of atmospheres. The Fischer–Tropsch process is an important reaction in both coal liquefaction and gas to liquids technology for producing liquid hydrocarbons.
Steam reforming or steam methane reforming (SMR) is a method for producing syngas (hydrogen and carbon monoxide) by reaction of hydrocarbons with water. Commonly natural gas is the feedstock. The main purpose of this technology is hydrogen production. The reaction is represented by this equilibrium:
The Sabatier reaction or Sabatier process produces methane and water from a reaction of hydrogen with carbon dioxide at elevated temperatures and pressures in the presence of a nickel catalyst. It was discovered by the French chemists Paul Sabatier and Jean-Baptiste Senderens in 1897. Optionally, ruthenium on alumina makes a more efficient catalyst. It is described by the following exothermic reaction:
The water–gas shift reaction (WGSR) describes the reaction of carbon monoxide and water vapor to form carbon dioxide and hydrogen:
Catalytic reforming is a chemical process used to convert petroleum refinery naphthas distilled from crude oil into high-octane liquid products called reformates, which are premium blending stocks for high-octane gasoline. The process converts low-octane linear hydrocarbons (paraffins) into branched alkanes (isoparaffins) and cyclic naphthenes, which are then partially dehydrogenated to produce high-octane aromatic hydrocarbons. The dehydrogenation also produces significant amounts of byproduct hydrogen gas, which is fed into other refinery processes such as hydrocracking. A side reaction is hydrogenolysis, which produces light hydrocarbons of lower value, such as methane, ethane, propane and butanes.
The Claus process is the most significant gas desulfurizing process, recovering elemental sulfur from gaseous hydrogen sulfide. First patented in 1883 by the chemist Carl Friedrich Claus, the Claus process has become the industry standard.
Gas to liquids (GTL) is a refinery process to convert natural gas or other gaseous hydrocarbons into longer-chain hydrocarbons, such as gasoline or diesel fuel. Methane-rich gases are converted into liquid synthetic fuels. Two general strategies exist: (i) direct partial combustion of methane to methanol and (ii) Fischer–Tropsch-like processes that convert carbon monoxide and hydrogen into hydrocarbons. Strategy ii is followed by diverse methods to convert the hydrogen-carbon monoxide mixtures to liquids. Direct partial combustion has been demonstrated in nature but not replicated commercially. Technologies reliant on partial combustion have been commercialized mainly in regions where natural gas is inexpensive.
A flame ionization detector (FID) is a scientific instrument that measures analytes in a gas stream. It is frequently used as a detector in gas chromatography. The measurement of ions per unit time makes this a mass sensitive instrument. Standalone FIDs can also be used in applications such as landfill gas monitoring, fugitive emissions monitoring and internal combustion engine emissions measurement in stationary or portable instruments.
Hydrogen gas is produced by several industrial methods. Nearly all of the world's current supply of hydrogen is created from fossil fuels. Most hydrogen is gray hydrogen made through steam methane reforming. In this process, hydrogen is produced from a chemical reaction between steam and methane, the main component of natural gas. Producing one tonne of hydrogen through this process emits 6.6–9.3 tonnes of carbon dioxide. When carbon capture and storage is used to remove a large fraction of these emissions, the product is known as blue hydrogen.
Landfill gas monitoring is the process by which gases that are collected or released from landfills are electronically monitored. Landfill gas may be measured as it escapes the landfill or may be measured as it is collected and redirected to a power plant or flare.
A methane reformer is a device based on steam reforming, autothermal reforming or partial oxidation and is a type of chemical synthesis which can produce pure hydrogen gas from methane using a catalyst. There are multiple types of reformers in development but the most common in industry are autothermal reforming (ATR) and steam methane reforming (SMR). Most methods work by exposing methane to a catalyst at high temperature and pressure.
Methanation is the conversion of carbon monoxide and carbon dioxide (COx) to methane (CH4) through hydrogenation. The methanation reactions of COx were first discovered by Sabatier and Senderens in 1902.
PROX is an acronym for PReferential OXidation, that refers to the preferential oxidation of carbon monoxide in a gas mixture by a catalyst. It is intended to remove trace amounts of CO from H2/CO/CO2 mixtures produced by steam reforming and water-gas shift. An ideal PROX catalyst preferentially oxidizes carbon monoxide (CO) using a heterogeneous catalyst placed upon a ceramic support. Catalysts include metals such as platinum, platinum/iron, platinum/ruthenium, gold nanoparticles as well as novel copper oxide/ceramic conglomerate catalysts.
Hydromethanation, [hahy-droh- meth-uh-ney-shuhn] is the process by which methane is produced through the combination of steam, carbonaceous solids and a catalyst in a fluidized bed reactor. The process, developed over the past 60 years by multiple research groups, enables the highly efficient conversion of coal, petroleum coke and biomass into clean, pipeline quality methane.
The electrochemical reduction of carbon dioxide, also known as CO2RR, is the conversion of carbon dioxide to more reduced chemical species using electrical energy. It represents one potential step in the broad scheme of carbon capture and utilization.
Carbon dioxide reforming is a method of producing synthesis gas from the reaction of carbon dioxide with hydrocarbons such as methane with the aid of noble metal catalysts. Synthesis gas is conventionally produced via the steam reforming reaction or coal gasification. In recent years, increased concerns on the contribution of greenhouse gases to global warming have increased interest in the replacement of steam as reactant with carbon dioxide.
A post column oxidation-reduction reactor is a chemical reactor that performs derivatization to improve the measurement of organic molecules. It is used in gas chromatography (GC), after the column, and before a flame ionization detector (FID), to make the detector response uniform for all organic molecules.