Carbon dioxide feedstocks

Since about 1950, most urea producing units have been based on ammonia-carbon dioxide feedstocks passed through high-pressure equipment, hence the close association with ammonia plants [63]. Over the last 20 years in North America urea production volumes have grown faster than ammonium nitrate for the supply of fertilizer nitrogen (Table 11.10). 

Synthesis gas, a mixture of CO and o known as syngas, is produced for the oxo process by partial oxidation (eq. 2) or steam reforming (eq. 3) of a carbonaceous feedstock, typically methane or naphtha. The ratio of CO to may be adjusted by cofeeding carbon dioxide (qv), CO2, as illustrated in equation 4, the water gas shift reaction. 

Steam-Reforming Natural Gas. Natural gas is the single most common raw material for the manufacture of ammonia. A typical flow sheet for a high capacity single-train ammonia plant is iadicated ia Figure 12. The important process steps are feedstock purification, primary and secondary reforming, shift conversion, carbon dioxide removal, synthesis gas purification, ammonia synthesis, and recovery. 

The equihbrium composition of the product gas can be altered by choice of suitable temperature, pressure, and steam to feedstock ratio to produce a gas mixture consisting largely of methane or largely of hydrogen having varying proportions of carbon monoxide (qv). In each case, some carbon dioxide (qv)... 

A more abundantiy produced substance is ethanol for use in alcohoHc beverages, and as a fuel, solvent, and feedstock for organic syntheses. Ethanol (qv) production from sucrose is carried out in Europe (eg, France and the Netherlands), India, Pakistan, China, and on a very large scale in Brazil, where it is used as a motor fuel. A valuable by-product of ethanol fermentation is industrial CO2 (see Carbon dioxide). 

Precipitated Calcium Carbonate. Precipitated calcium carbonate can be produced by several methods but only the carbonation process is commercially used in the United States. Limestone is calcined in a kiln to obtain carbon dioxide and quicklime. The quicklime is mixed with water to produce a milk-of-lime. Dry hydrated lime can also be used as a feedstock. Carbon dioxide gas is bubbled through the milk-of-lime in a reactor known as a carbonator. Gassing continues until the calcium hydroxide has been converted to the carbonate. The end point can be monitored chemically or by pH measurements. Reaction conditions determine the type of crystal, the size of particles, and the size distribution produced. 

The feedstocks to the styrene process are ethylbenzene and superheated steam, and a typical unit produces hydrogen, small amounts of light hydrocarbons and carbon dioxide as gaseous products, and a Hquid product stream containing 95% + styrene and minor amounts of toluene, benzene, and other aromatics. In an integrated plant, the benzene can be recycled to the ethylbenzene unit, while the other by-products usually are consumed as fuel for the highly endothermic process. 

Ammonia production from natural gas includes the following processes desulfurization of the feedstock primary and secondary reforming carbon monoxide shift conversion and removal of carbon dioxide, which can be used for urea manufacture methanation and ammonia synthesis. Catalysts used in the process may include cobalt, molybdenum, nickel, iron oxide/chromium oxide, copper oxide/zinc oxide, and iron. 

Direct conversion of methane to ethane and ethylene (C2 hydrocarbons) has a large implication towards the utilization of natural gas in the gas-based petrochemical and liquid fuels industries [ 1 ]. CO2 OCM process provides an alternative route to produce useful chemicals and materials where the process utilizes CO2 as the feedstock in an environmentally-benefiting chemical process. Carbon dioxide rather than oxygen seems to be an alternative oxidant as methyl radicals are induced in the presence of oxygen. Basicity, reducibility, and ability of catalyst to form oxygen vacancies are some of the physico-chemical criteria that are essential in designing a suitable catalyst for the CO2 OCM process [2]. The synergism between catalyst reducibility and basicity was reported to play an important role in the activation of the carbon dioxide and methane reaction [2]. 

If methane is used as a feedstock, it is apparent that, in this case, the possibility exists that carbon dioxide can be used as feedstock and that water can be produced as by-product. Since methane is rich in hydrogen (whereas coal is not),... 

When coal or biomass is heated, many reactions including dehydration, cracking, isomerization, dehydrogenation, aromatization, and condensations take place. Products are water, carbon dioxide, hydrogen, other gases, oils, tars, and char. The product yields vary, depending on the particular feedstock composition, particle size, heating rate, solids and gas residence times, and the reactor temperature. 

Like natural gas, the producer gas from coal is a clean fuel. Additionally, it is a rich source of chemicals. Coal-derived gas can also be recombined into liquid fuels, including high-grade transportation fuels, and a range of petrochemicals that serve as feedstock workhorses in the chemicals and refining industries. In contrast to conventional combustion, carbon dioxide exits a coal gasifier in a concentrated stream rather than diluted in a high volume of flue gas. This allows the carbon dioxide to be captured more effectively and then used... 

Methane, also referred to as marsh gas, is a gas composed of carbon and hydrogen with a chemical formula of CH4. It is the first member of the paraffin or alkane series of hydrocarbons. It is lighter than air, colorless, odorless, tasteless and is flammable. It occurs in natural gas and as a by-product of petroleum refining. In atmospheric burning no smoke production normally occurs. In air methane bums with a pale, faintly luminous flame. With excess air carbon dioxide and water vapor is formed during combustion, with an air deficiency carbon monoxide and water is formed. It forms an explosive mixture with air over a moderate range. Its primary uses are as a fuel and raw feedstock for petrochemical products. 

Considering the full production cycle, methanol from biomass emits less carbon dioxide than ethanol from biomass. This is because short rotation forestry, the feedstocks of methanol, requires the use of less fertilizer... 

When fuels are derived from biomass, the net increase in carbon dioxide emitted into the atmosphere is usually considered to be neutral or even negative since the plants used to produce the alcohol fuel have reabsorbed the same or more carbon than is emitted from burning the fuel. The net effect may not be as favorable when the carbon dioxide emitted by equipment for the harvesting of the biomass feedstocks is considered in the balance. Much of this depends on the differences in equipment, farming techniques and other regional factors. 

Fermenting grains with yeast produces a grain alcohol. The process also works with other biomass feedstocks. In fermentation, the yeast decomposes carbohydrates which are starches in grains, or sugar from sugar cane juice into ethyl alcohol (ethanol) and carbon dioxide. The process breaks down complex substances into simpler ones. 

Carbon dioxide can itself be used as a feedstock as well as a solvent for the synthesis of aliphatic polycarbonates by precipitation polymerization. Propylene oxide [39] and 1,2-cyclohexene oxide [40] can both be polymerized with CO2 using a heterogeneous zinc catalyst (Scheme 10.21). 

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