Liquefaction, natural sources

Imperial Chemical Industries (ICI) operated a coal hydrogenation plant at a pressure of 20 MPa (2900 psi) and a temperature of 400—500°C to produce Hquid hydrocarbon fuel from 1935 to the outbreak of World War II. As many as 12 such plants operated in Germany during World War II to make the country less dependent on petroleum from natural sources but the process was discontinued when hostihties ceased (see Coal conversion PROCESSES,liquefaction). Currentiy the Fisher-Tropsch process is being used at the Sasol plants in South Africa to convert synthesis gas into largely ahphatic hydrocarbons at 10—20 MPa and about 400°C to supply 70% of the fuel needed for transportation. 

A third natural source of alkylated phenols is coal gasification with tar byproducts (SASOL), complemented by the future possibility of cresols in the gasoline and middle-oil cuts from coal liquefaction. 

Fundamental studies of coal liquefaction have shown that the structure of solvent molecules can determine the nature of liquid yields that result at any particular set of reaction conditions. One approach to understanding coal liquefaction chemistry is to use well-defined solvents or to study reactions of solvents with pure compounds which may represent bond-types that are likely present in coal [1,2]. It is postulated that one of the major routes in coal liquefaction is initiation by thermal activation to form free radicals which abstract hydrogen from any readily available source. The solvent may, therefore, function as a direct source of hydrogen (donor), indirect source of hydrogen (hydrogen-transfer agent), or may directly react with the coal (adduction). The actual role of solvent thus becomes a significant parameter. 

As with the sweetening application our most common need for CO2 removal is from natural gas prior to liquefaction. In this application we are often faced with amounts of oxygen in the feed that may range up to several hundred ppm by volume. The process is often limited to adsorption at a total pressure of about 3 5 bar. In this application however the feed gas is most often pipeline natural gas which gas will have been pre-dried to pipeline standards or about seven pounds (1 lb = 0.45 kg) of water per MMSCF of gas. In some cases the gas source may be other than pipeline and the water load needs to be estimated based on a given mole fraction. The liquefaction process, which runs at -260°F (127°C), demands very low levels of water in the product as well as trace levels of CO2 so that the heat exchangers in the downstream process remain clean. 

The development of new syngas-based processes is one of the objectives for the near future, despite the current low price of oil. Syngas can be produced from various carbonaceous sources, including coal, heavy residue, biomass and gas, the latter being the most economical and abundant feedstock. Chemical valorization of natural or associated gas is a priority objective, since liquefaction of remote gas via alcohol synthesis permits convenient shipping to markets not directly connected to the gas source by pipeline. 

Energy demand, the implementation of sulfur oxide pollution controls, and the future commercialization of coal gasification and liquefaction have increased the potential for the development of considerable supplies of sulfur and sulfuric acid as a result of abatement, desulfurization and conversion processes. Lesser potential sources include shale oil, domestic tar sands and heavy oil, and unconventional sources of natural gas. Current supply sources of saleable sulfur values include refineries, sour natural gas processing and smelting operations. To this, Frasch sulfur production must be added. 

Starch Liquefaction. Starch in its natural state is only degraded slowly by CC-amylases. To make the starch susceptible to enzymatic breakdown, it is necessary to gelatinize and liquefy a slurry with a 30—40% dry matter content. Gelatinization temperature depends on the type of starch (67) com is the most common source of industrial starches followed by wheat, tapioca, and potatoes. Liquefaction is achieved by adding a heat-stable a-amylase to the starch slurry. The equipment used for liquefaction may be stirred tank reactors, continuous stirred tank reactors (CSTR), or a jet cooker. Most starch processing plants liquefy the starch with a single enzyme dose in a process using a jet cooker (Fig. 9). 

Small amounts of helium are extracted from the atmosphere by fractionation methods, but not commercially because of the small amount of helium in the atmosphere. A number of natural gas wells contain helium, which can be recovered by a liquefaction and stripping process. Natural gas containing at least 0.2 percent helium has been found in the American Southwest, where the natural gas fields are the major U.S. source of helium. Those helium-rich fields are within 250 miles of Amarillo, Texas other helium-bearing fields have been found in Saskatchewan, Canada, and in areas near the Black Sea. Helium cannot be synthesized so conservation and cleanup recycle systems for spent gas are important means of preserving the earth s helium resources. 

An element that is also found in natural gas represents the world s best source for the element and that is helium which, in some U.S. and polishgas supplies, can reach 7% by weight. This valuable gas is collected by liquefaction of the natural gas, which leaves the remaining gas significantly enriched in helium. Helium originates from radioactive decay and, because it is a fugitive gas and can escape the earth s atmosphere, it is not practical to recover helium from the air. 

Petroleum chemicals fulfill two functions. They provide alternative and more economic routes to existing chemicals already made from other raw materials, and they lead to new industrial chemicals. The reactions of and outlets for chemicals more economically synthesized from petroleum have already been worked out, although perhaps not completely, in connection with the older routes. Those countries not favored with petroleum as an economic raw material have had to make use of alternative sources for these chemicals. In surveying the literature, it is, therefore, necessary to take account of the history of those petroleum chemicals which have been made from alternative sources. The reactions of methane are the same whether it is obtained from natural gas or as a by-product of the hydrogenation of coal or as a fraction in the liquefaction of coke oven gas depending on the source, the economics may be quite different. 

The present world rcscr es of natural gas that contains mainly methane are still underutilized due to high cost of transportation. Considerable interest is therefore presently shown in the conversion of methane to transportable liquids and feedstocks in addition to its previous sole use for heating purposes by combustion. One possible new route for the utilization of methane derived from natural gas or other sources for conversion to more valuable higher hydrocarbons is the methylation of aromatic hydrocarbons. This chapter provides a general overview of the work that has been done so far on the use of methane for catalytic methylation of model aromatic compounds and for direct liquefaction of coal for the production of liquid hydrocarbons. The review is especially focused on the use of both acidic and basic zeolites in acid-catalyzed and base-catalyzed methylation reactions, respectively. The base-catalyzed methylation reaction covered in this discussion is mainly the oxidative methylation of toluene to produce ethylbenzene and styrene. This reaction has been found to occur over basic sites incorporated into zeolites by chemical modification or by changing the electronegative charge of the zeolite framework. 

This paper provides a general overview of the recent work that has been done on the use of methane for catalytic methylation of aromatic compounds and for direct liquefaction of coal for the production of liquid hydrocarbons. Such methylation reactions constitute a new route for the utilization of methane derived from natural gas or other sources for conversion to more valuable hydrocarbons. The review focuses on the use of both acidic and basic zeolites in acid-catalyzed and base-catalyzed reactions, respectively. 

Methane and ethane have attracted special attention because of the potential importance of natural gas liquefaction. Conversion of methane to a transportahle liquid such as methanol would make many remote gas sources economically viable. Sen [124] has reported a number of unusual reactions of methane, such as the conversion of methane, CO and oxygen to acetic acid with RhCE as catalyst and of methane, trifluoroacetic anhydride and H2O2 to the methyl esters with Pd(II) as catalyst. 

Thus, it can be argued (often successfully to a point but not ad nauseam) that an understanding of the chemical nature of coal constituents is, just like an understanding of the chemical and thermal behavior of coal (Chapters 13 and 14), a valuable part of projecting the successful use of coal for conversion and/or utilization processes such as combustion (Chapters 14 and 15), carbonization an briquetting (Chapters 16 and 17), liquefaction (Chapters 18 and 19), gasification (Chapters 20 and 21), or as a source of chemicals (Chapter 24). 

---