Product Slate Research Articles

Direct mass-spectrometric studies of the pyrolysis of carbonaceous fuels: III. Primary pyrolysis of lignin

The primary pyrolysis of lignins derived from different types of biomass and by the major separation methods has been investigated by molecular-beam sampling mass spectrometry. The lignins separated by the steam-explosion and kraft processes have altered pyrolysis characteristics while ball-milled lignins yield nearly the same product slate as observed in native biomass samples. The predominant and first-formed products, as determined by mass spectrometry, appear to be the precursor monomers, coniferyl and sinapyl alcohol. There is a distinct lack of higher-molecular-weight oligomers as is commonly observed in the pyrolysis of other types of natural and synthetic polymers. A group of peaks, with the most predominant being m/z 272, appear at masses greater than the monomer masses, but are significantly below the dimer mass range. A third group of predominant peaks are present at masses lighter than the monomers and consist of methoxyphenols that have double bonds and carbonyl groups in the alkyl side chains that are in conjugation with the aromatic ring, enhancing thermal stability. The results indicate that the thermolysis of the alkyl-aryl ether linkage, which is the major bonding unit in lignin, and the limited availability of transferable hydrogen, are the major factors that lead to the predominance of these products. The observed product distributions are indicative of specific, sterically favored rearrangement reactions, which allow devolatilization from the hydrogen deficient, solid matrix and favor double bond formation in the alkyl side chain of the products. A discussion of possible mechanisms of formation is given based on these results and the results of other workers in lignin pyrolysis.

An industry model of commodity chemicals from renewable resources

A systems model based on linear programming has been constructed for a commodity chemicals industry using renewable resources and coal, as well as gas and petroleum-derived resources. The results suggest that coal should precede biomass as a feedstock in the event of a significant reduction in the use of gas and petroleum-based feedstocks. However, a reasonable approximation to the current product slate for the petrochemical industry could be manufactured using only renewable resources for feedstocks. Use of the chemicals industry model to evaluate process technologies is demonstrated. Conceptual hypothetical technologies and improvements to existing technologies are considered in the context of input to program planning for research and development.

Catalytic aspects of industrial Fischer-Tropsch synthesis

A brief description of the commercial Sasol process is given. Two types of reactors using two different iron-based catalysts are used, the one producing predominantly gasoline and the other waxes. The hydrocarbon product spectrum can be varied over wide ranges ( e.g. CH 4 from ca. 1 to ca. 80%). The probability of chain-growth is influenced by the temperature, the catalyst type and its promoter level and the gas composition. It is not influenced by the type of reactor. By subjecting the products to additional processes, e.g. oligomerisation of olefins or selective hydrocracking of the waxes, the final product slate can be further altered. Thus a 75% overall yield of either gasoline or diesel fuel can be achieved. A major advantage of the Fischer-Tropsch process over other processes which produce fuel from coal is that a very high quality diesel fuel is produced. The exact nature of the chain-growth mechanism on the catalyst surface is still a disputed subject. It is probable that both ‘oxygen-containing’ and ‘oxygen-free’ hydrocarbon fragments participate in the surface reactions. Because of the likelihood that the bonds between the complexes and the catalyst are highly labile and consequently ill-defined, it is no simple task to assign ‘clear-cut’ structures to the intermediate complexes. The proposed reaction scheme accounts for the many different products obtained from CO + H 2 mixtures over various types of catalysts.

A process concept for the production of benzene-ethylene-SNG from coal using flash hydropyrolysis technology

Flash hydropyrolysis (FHP) of coal is an emerging technology for the direct production of methane, ethane and BTX in a single-stage, high throughput reactor. The FHP technique involves the short residence time (1–2 seconds), rapid heatup of coal in a dilute-phase, transport reactor. When integrated into an overall, grass-roots conversion complex, the FHP technique can be utilized to generate a product slate consisting of SNG, ethylene/propylene, benzene and Fischer-Tropsch-based alcohols. This paper summarizes the process engineering and economics of a conceptualized facility based on an FHP reactor operation with a lignitic coal. The plant is hypothetically sited near the extensive lignite fields located in the Texas region of the United States. Utilizing utility-financing methods for the costing of SNG, and selling the chemicals co-generated at petrochemical market prices, the 20-year average SNG cost has been computed to vary between $3–4/MM Btu, depending upon the coal costs, interest rates, debt/equity ratio, coproduct chemicals prices, etc.