Synthesis gases

Synthesis gas generally refers to a mixture of carbon monoxide and hydrogen. The ratio of hydrogen to carbon monoxide varies according to the type of feed, the method of production, and the end use of the gas. 

There are different sources for obtaining synthesis gas. It can be produced by steam reforming or partial oxidation of any hydrocarbon ranging from natural gas (methane) to heavy petroleum residues. It can also 

Selected properties of carbon black from an oil furnace process 

A major route for producing synthesis gas is the steam reforming of natural gas over a promoted nickel catalyst at about 800°C  

This route is used when natural gas is abundant and inexpensive, as it is in Saudi Arabia and the USA. 

Synthesis gas is a mixture of carbon monoxide and hydrogen, which is used fur methanoi synthesis (3) (1, 2, 3] and to some extent, for hydrogen production (1) and the water-gas shift reaction (2). 

Hydrogen (and oxygen) production by the met Hanoi-water splitting cycle, 

Methane (SNG = Synthetic Natural Gas) can be prepared by a Fischer Tropsch reaction from coal via CO hydrogenation (niethanation). but this is not of much practical interest, except in particular cases(e.g.,in South Africa), because more valuable raw materials can be obtained by CO hydre enation. The direct production of methane by coat stfication in the presence of hydrogen has also received much attention in South Africa (5). 

The synthesis gas reaction (I) is limited to an equilibrium and is therefore run in the presence of an excess of water, which has another beneficial role that of reducing the carbon formation on the catalyst. As reaction (1) produces too much hydrogen fur the methanol synthesis ( ). the process may be operated in the presence of CO2. in order to adjust the gas composition (5)  

The catalyst is nickel oxide supported by a refractory material, for example. NiO on calcium aluininatc as Raschig rings, or on alumina. 

The term synthesis gas is given to mixtures of CO and H2 of different compositions according to the way in which they are made and also if they are destined for the manufacture of NH3, of CH3OH or fuels. 

The manufacturing processes of synthesis gases used to be based on the gasification of coke obtained from anthracite or lignite by the action of air and steam. After the Second World War, natural gas and petroleum fractions were mainly used as raw materials. Two very different methods can be used. 

The process can cope with very different feeds, which include natural gases and petroleum fractions and ranging from the light naphthas to the asphalts, as well as refinery gases. 

The fact that the reaction takes place in the gas phase and without a catalyst means that it is not necessary to eliminate sulphur from the feed. 

The reactants are preheated to different temperatures according to the nature of the feed. They are mixed with oxygen and steam in proportions which also depend on the type of feed used. 

Blaugas Coal Coal briquettes, hot Coal gas, 2.3 Coal gas, compressed, 2.1, 2.3 Coal tar, crude and solvent Coal tar distillates, flammable, 3, 3.2,3.3 Coal tar naphtha Coal tar oil Coke, hot Creosote Creosote (coal tar or wood tar) Creosote salts Cresols (o-, m-, p-), 6.1, 8 Cresols (ortho- meta- para-), liquid or solid, 6.1 Dead oil Fischer Tropsch gas Fischer-Tropsch gas compressed, 2.2 Iron oxide, spent (obtained fix)m coal gas purification), 4.2 Iron sponge, spent, 4.2 Iron sponge, spent (obtained from coal gas purification), 4.2 Prilled coal tar Synthesis gas Synthesis gas, compressed Water gas Water gas, compressed 

Coal is a black or brown, solid, combustible mineral formed by the alteration of prehistoric plant life by bacterial decomposition, with subsequent chemical changes caused by temperature and pressure. These processes result in a range of carbonaceous materials, the first of which is peat and the last of which is graphite (pure carbon). The coals lie between these two extremes  

The destructive distillation (heating in the absence of oxygen) of coal (mostly bituminous coal) at temperatures ranging from 500 to 1200°C, generates a number of derivatives  

Coal tar contains an estimated 10,000 compounds, many of which are important organic chemicals. The use of coal tar as a source of these compounds has been largely relegated to a position below numerous synthetic processes, primarily based on petroleum. Fractionation of coal tar yields the following (approximate temperatures and yields given)  

5% Light oil syn. coal tar distillates, coal tar solvents, or coal tar oil. a highly flammable mixture of toluene, xylene, cumenes, etc. 

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An example of such recychng in a parallel reaction system is in the Oxo process for the production of C4 alcohols. Propylene and synthesis gas (a mixture of carbon monoxide and hydrogen) are first reacted to ra- and isobutyraldehydes using a cobalt-based catalyst. Two parallel reactions occur ... 

As an example of the application of a fixed-bed tubular reactor, consider the production of methanol. Synthesis gas (a mixture of hydrogen, carbon monoxide, and carbon dioxide) is reacted over a copper-based cat dyst. The main reactions are... 

Carbon dioxide, COj. Sublimes — 78 5 C. A colourless gas at room temperature, occurs naturally and plays an important part in animal and plant respiration. Produced by the complete combustion of carbon-containing materials (industrially from flue gases and from synthesis gas used in ammonia production) and by heating metal carbonates or by... 

Fischer-Tropsch reaction The catalytic reaction of hydrogen and carbon monoxide (synthesis gas ) to produce high-molecular weight hydrocarbons. 

Volume 1. Synthesis-Gas Derivatives and Major Hydrocarbons. Volume 2. Major Oxygenated, Chlorinated and Nitrated Derivatives. 

The Fischer-Tropsch reaction is essentially that of Eq. XVIII-54 and is of great importance partly by itself and also as part of a coupled set of processes whereby steam or oxygen plus coal or coke is transformed into methane, olefins, alcohols, and gasolines. The first step is to produce a mixture of CO and H2 (called water-gas or synthesis gas ) by the high-temperature treatment of coal or coke with steam. The water-gas shift reaction CO + H2O = CO2 + H2 is then used to adjust the CO/H2 ratio for the feed to the Fischer-Tropsch or synthesis reactor. This last process was disclosed in 1913 and was extensively developed around 1925 by Fischer and Tropsch [268]. 

Oxygen enrichment of steel blast furnaces accounts for the greatest use of the gas. Large quantities are also used in making synthesis gas for ammonia and methanol, ethylene oxide, and for oxy-acetylene welding. 

Synthetic oil is feasible and can be produced from coal or natural gas via synthesis gas (a mixture of carbon monoxide and hydrogen obtained from incomplete combustion of coal or natural gas). However, these are themselves nonrenewable resources. Coal conversion was used in Germany during World War II by hydrogenation or. 

A mixture of the two reactants carbon monoxide and hydrogen is called synthesis gas and IS prepared by several processes The most widely used route to synthesis gas employs methane (from natural gas) and gives a 3 1 hydrogen to carbon monoxide ratio... 

COPPERALLOYS-WROUGHT COPPERAND WROUGHT COPPERALLOYS] (Vol 7) -catalysts for synthesis gas [NITROGEN FIXATION] (Vol 17)... 

Since 1960, the Hquid-phase oxidation of ethylene has been the process of choice for the manufacture of acetaldehyde. There is, however, stiU some commercial production by the partial oxidation of ethyl alcohol and hydration of acetylene. The economics of the various processes are strongly dependent on the prices of the feedstocks. Acetaldehyde is also formed as a coproduct in the high temperature oxidation of butane. A more recently developed rhodium catalyzed process produces acetaldehyde from synthesis gas as a coproduct with ethyl alcohol and acetic acid (83—94). 

From Synthesis Gas. A rhodium-catalyzed process capable of converting synthesis gas directly into acetaldehyde in a single step has been reported (83,84). 

This process comprises passing synthesis gas over 5% rhodium on Si02 at 300°C and 2.0 MPa (20 atm). Principal coproducts are acetaldehyde, 24% acetic acid, 20% and ethanol, 16%. Although interest in new routes to acetaldehyde has fallen as a result of the reduced demand for this chemical, one possible new route to both acetaldehyde and ethanol is the reductive carbonylation of methanol (85). 

The price of acetaldehyde duriag the period 1950 to 1973 ranged from 0.20 to 0.22/kg. Increased prices for hydrocarbon cracking feedstocks beginning in late 1973 resulted in higher costs for ethylene and concurrent higher costs for acetaldehyde. The posted prices for acetaldehyde were 0.26/kg in 1974, 0.78/kg in 1985, and 0.92/kg in 1988. The future of acetaldehyde growth appears to depend on the development of a lower cost production process based on synthesis gas and an increase in demand for processes based on acetaldehyde activation techniques and peracetic acid. 

Commercial production of acetic acid has been revolutionized in the decade 1978—1988. Butane—naphtha Hquid-phase catalytic oxidation has declined precipitously as methanol [67-56-1] or methyl acetate [79-20-9] carbonylation has become the technology of choice in the world market. By-product acetic acid recovery in other hydrocarbon oxidations, eg, in xylene oxidation to terephthaUc acid and propylene conversion to acryflc acid, has also grown. Production from synthesis gas is increasing and the development of alternative raw materials is under serious consideration following widespread dislocations in the cost of raw material (see Chemurgy). 

Currently, almost all acetic acid produced commercially comes from acetaldehyde oxidation, methanol or methyl acetate carbonylation, or light hydrocarbon Hquid-phase oxidation. Comparatively small amounts are generated by butane Hquid-phase oxidation, direct ethanol oxidation, and synthesis gas. Large amounts of acetic acid are recycled industrially in the production of cellulose acetate, poly(vinyl alcohol), and aspirin and in a broad array of other... 

Synthesis gas is obtained either from methane reforming or from coal gasification (see Coal conversion processes). Telescoping the methanol carbonylation into an esterification scheme furnishes methyl acetate directly. Thermal decomposition of methyl acetate yields carbon and acetic anhydride,... 

Gas purifications H2O/olefin-containing cracked gas, natural gas, air, synthesis gas, etc sHica, alumina, zeoHte... 

Hydroformylation of an olefin usiag synthesis gas, the 0x0 process (qv), was first commercialized ia Germany ia 1938 to produce propionaldehyde from ethylene and butyraldehydes from propylene (12). 

Fischer-Tropsch Process. The Hterature on the hydrogenation of carbon monoxide dates back to 1902 when the synthesis of methane from synthesis gas over a nickel catalyst was reported (17). In 1923, F. Fischer and H. Tropsch reported the formation of a mixture of organic compounds they called synthol by reaction of synthesis gas over alkalized iron turnings at 10—15 MPa (99—150 atm) and 400—450°C (18). This mixture contained mostly oxygenated compounds, but also contained a small amount of alkanes and alkenes. Further study of the reaction at 0.7 MPa (6.9 atm) revealed that low pressure favored olefinic and paraffinic hydrocarbons and minimized oxygenates, but at this pressure the reaction rate was very low. Because of their pioneering work on catalytic hydrocarbon synthesis, this class of reactions became known as the Fischer-Tropsch (FT) synthesis. 

Sasol produces synthetic fuels and chemicals from coal-derived synthesis gas. Two significant variations of this technology have been commercialized, and new process variations are continually under development. Sasol One used both the fixed-bed (Arge) process, operated at about 240°C, as weU as a circulating fluidized-bed (Synthol) system operating at 340°C. Each ET reactor type has a characteristic product distribution that includes coproducts isolated for use in the chemical industry. Paraffin wax is one of the principal coproducts of the low temperature Arge process. Alcohols, ketones, and lower paraffins are among the valuable coproducts obtained from the Synthol process. 

Dimethyl Ether. Synthesis gas conversion to methanol is limited by equiUbrium. One way to increase conversion of synthesis gas is to remove product methanol from the equiUbrium as it is formed. Air Products and others have developed a process that accomplishes this objective by dehydration of methanol to dimethyl ether [115-10-6]. Testing by Air Products at the pilot faciUty in LaPorte has demonstrated a 40% improvement in conversion. The reaction is similar to the Hquid-phase methanol process except that a soHd acid dehydration catalyst is added to the copper-based methanol catalyst slurried in an inert hydrocarbon Hquid (26). 

By selection of appropriate operating conditions, the proportion of coproduced methanol and dimethyl ether can be varied over a wide range. The process is attractive as a method to enhance production of Hquid fuel from CO-rich synthesis gas. Dimethyl ether potentially can be used as a starting material for oxygenated hydrocarbons such as methyl acetate and higher ethers suitable for use in reformulated gasoline. Also, dimethyl ether is an intermediate in the Mobil MTG process for production of gasoline from methanol. 

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