Feedstock carbon-based

Gasification technologies offer the potential of clean and efficient energy. The technologies enable the production of synthetic gas from low or negative-value carbon-based feedstocks such as coal, petroleum coke, high sulfur fuel oil, materials that would otherwise be disposed as waste, and biomass. The gas can be used in place of natural gas to generate electricity, or as a basic raw material to produce chemicals and liquid fuels. 

The primary product is fuel-grade, coal-derived gas which is similar to natural gas. The basic gasification process can also be applied to other carbon-based feedstocks such as biomass or municipal waste. 

Improved gasifier designs would be more durable and capable of handling a variety of carbon-based feedstocks. Advanced gas cleaning technologies would capture virtually all of the ash particles, sulfur, nitrogen, alkali, chlorine and hazardous air pollutants. 

As we mentioned in Section 4.1.2 and in Chapter 1, the ready availability of syngas and the increasingly short supply, or difficulty of access, of other carbon-based feedstocks, implies that syngas based reactions will increase in significance in the chemical industry. Amongst the most important is the Fischer-Tropsch (F-T) process, and there has therefore been considerable interest in its mechanism. 

A more detailed description of the GTL process is (1) the prodnction of synthesis gas (syngas) from carbon-based feedstocks, (2) the FT reaction for conversion of syngas to higher liqnid hydrocarbons and long-chain waxy paraffins, and (3) the conversion of the solid long-chain waxy paraffins through hydrocracking and hydroisomerization back to liquid fuels. 

Carbon-based feedstocks include natural gas, light hydrocarbons, coal, and biomass. Basically, carbon-based hydrogen production technologies are thermal catalytic processes in which part of the feedstock is burned to provide the thermal energy needed for the hydrogen production. A brief review of these basic hydrogen production technologies follows. 

Carbon monoxide is one of the most common impurities in hydrogen fuel streams that can cause significant performance degradation of a hydrogen PEM fuel cell. When carbon-based feedstock is used for the production of hydrogen, the CO impurity in the hydrogen stream is unavoidable. To illustrate this fact. Table 9.8 lists the compositions of hydrogen feed streams produced from carbon-based feedstocks [42]. 

The market for tar-based road binders has declined considerably for a variety of reasons. Less cmde tar is available and the profits from the sales of electrode pitch and wood-preservation creosote or creosote as carbon-black feedstock are higher than those from road tar. In most industrial countries, road constmction in more recent years has been concentrated on high speed motorways. Concrete, petroleum bitumen, or lake asphalt are used in the constmction of these motorways. In the United Kingdom, for example, the use of tar products in road making and maintenance had fallen from 330,000 t in 1960 to 100,000 t in 1975 and is less than 100 t in 1994, mainly based on low temperature pitch which is not suitable for electrode or briquetting binders, but which is perfectly satisfactory as the basis for road binders. 

LAB is derived exclusively from petroleum- or natural gas-based feedstocks. Thus, it is referred to as a petrochemical (or synthetic) surfactant intermediate. Feedstocks for LAB production are generally paraffins (carbon chain length in the range of C8-C14) derived from kerosene and benzene. Internal olefins derived from ethylene are sometimes used in place of paraffins. 

The potential of combining a lower need for deoxygenation and a higher product value is illustrated in Fig. 2.15. It shows that the selective incorporation of oxygen into a hydrocarbon, as done in the petrochemical industry, is very expensive. In contrast, the bio-based alternative enjoys two advantages. Firstly, the feedstock is cheaper than crude oil, even on an energy and carbon base, as discussed above. Secondly, its selective deoxygenation has been proven to cheaper than the petrochemical route in a few cases, e.g., for ethanol and furfural. The same can be expected for other biomass derivates in the future. 

The chemical and enzymatic oxidative degradation of lignin (and coal) is used to obtain not only vanillin and benzoic acid, but also other aromatics (Baciocchi et al. 1999, references therein). In principle, lignin could be a major nonfossil and renewable source of aromatic compounds, a feedstock for synthesis of useful products. The problem deserves finding new ion-radical routes to cleave lignin. At present, there is some shortage in oil, gas, and even coal, which had usually been well-available natural sources of aromatics. In the near future, biomass may (and must) replace fossil-originated materials in the manufacture of commercial carbon-based products. 

Only about 5% of the fossil fuels consumed today are used as feedstocks for the production of synthetic carbon-based products. This includes the products of the chemical and drug industries with a major portion acting as the feedstocks for plastics, elastomers, coatings, fibers, etc. 

The gasification of hydrocarbons to produce hydrogen is a continuous, non-catalytic process (Figure 10-2) that involves partial oxidation of the hydrocarbon. Air or oxygen (with steam or carbon dioxide) is used as the oxidant at 1095— 1480°C (2000-2700°F). Any carbon produced (2-3 wt% of the feedstock) during the process is removed as a slurry in a carbon separator and pelleted for use either as a fuel or as raw material for carbon-based products. 

For organic chemicals, transmaterialisation must mean a shift from fossil (mainly petroleum) feedstocks (which have a cycle time of > 107 years) to plant-based feedstocks (with cycle times of < 103 years). This immediately raises several fundamentally important questions Can we produce and use enough plants to satisfy the carbon needs of chemical and related manufacturing, while not compromising other (essentially food and feed) needs Do we have the technologies necessary to carry out the conversions (biomass to chemicals) and in a way that does not completely compromise the environmental and transmaterialisation characteristics of the new process ... 

Typical results tor the cracking of the base feedstock, n-hexadecane, are presented in Fig. I, in terms of product distribution. Components are listed as carbon numbers up to Cl5, but also including the amount of coke formed. The product distribution attains a maximum at the C3t C4 and C5 region, following which there is a monotonic decrease in product concentration to 04. An increase then occurs for the C15 concentration and the coke. 

Small carbon-containing molecules such as atmospheric CO2 are considered to be important renewable feedstocks (144,145). In the context of mankind s increasing demand for carbon-based materials, food, and liquid fuels, the photocatalytic reduction of carbon dioxide under solar light irradiation is an attractive option. Such types of artificial photosynthetic processes could greatly enlarge the possibilities of abiotic CO2 recycling. 

It is clear that for a number of political and economic reasons the FT-synthesis, as the only large-volume carbon-based process having survived on the industrial scene, can only compete in countries where coal is both abundant and cheap and where the political situation favors or requires a domestic base of chemical feedstock. It seems that South Africa was the only place to meet these requirements. 

Carbon dioxide could at least be engaged in the synthesis of carboxylic compounds and certain heterocycles, quite apart from the consideration that it may eventually substitute for the more expensive carbon monoxide in specific applications. For reductive processes, however, a C02-based feedstock stituation could prove more expensive sinee an extra equivalent of a reductant is required (cf. Sections 3.2.11 and 3.3.4). 

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). 

Investigate C0/C02-free production of hydrogen and carbon products via efficient thermocatalytic decomposition of hydrocarbon feedstocks over carbon-based catalysts in an air/water-Ifee environment... 

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