Liquefaction studies, thermal

Coal liquefaction studies with Illinois No. 6 coal in supercritical water/CO systems have demonstrated that a suitable model for liquefaction includes a branch point. Thus coal is partitioned between reducing (i.e. liquefying) steps, and steps where strictly thermal reactions consume convertible sites and yield unconvertible char. 

Traditionally thermal liquefaction studies on biomass have been carried out in the presence of one or both of the reducing gases, hydrogen and carbon monoxide (2, 3 4 J5, 6). Equation 1, in which cellulose has been used to approximate the elemental composition of wood, shows that theoretically a reducing gas is not required for wood liquefaction when internal carbon is used to remove the oxygen. 

A more complex reaction model was proposed from the results of a kinetic study of thermal liquefaction of subbituminous coal. Data were obtained over a temperature range of 673 to 743 K (752 to 878°F) at 13.8 MPa (2000 psia) by using two solvents, hydrogenated anthracene oil (HAO), and hydrogenated phenanthrene oil (HPO), at a coal-solvent ratio of 1 15. Results were correlated with the following model ... 

Polymers have inherently high hydrocarbon ratios, making liquefaction of waste plastics into liquid fuel feedstocks a potentially viable commercial process. The objective is to characterise the thermal degradation of polymers during hydrogenation. LDPE is studied due to its simple strueture. Isothermal and non-isothermal TGA were used to obtain degradation kinetics. Systems of homopolymer, polymer mixtures, and solvent-swollen polymer are studied. The significant variables for... 

Conversion of coal to benzene or hexane soluble form has been shown to consist of a series of very fast reactions followed by slower reactions (2 3). The fast initial reactions have been proposed to involve only the thermal disruption of the coal structure to produce free radical fragments. Solvents which are present interact with these fragments to stabilize them through hydrogen donation. In fact, Wiser showed that there exists a strong similarity between coal pyrolysis and liquefaction (5). Recent studies by Petrakis have shown that suspensions of coals in various solvents when heated to 450°C produce large quantities of free radicals (. 1 molar solutions ) even when subsequently measured at room temperature. The radical concentration was significantly lower in H-donor solvents (Tetralin) then in non-donor solvents (naphthalene) (6). 

We have studied the thermal decomposition of diaryl ether in detail, since the cleavage of ether linkage must be one of the most responsible reactions for coal liquefaction among the various types of decomposition reaction and we found that the C-0 bond of polynucleus aromatic ethers is cleaved considerably at coal liquefaction temperature. 

The Thermal Decomposition of Aromatic Ethers. According to the results of Table I, the bond scission of oxygen containing polynucleus aromatic structure of coal at liquefaction temperature of 450°C seems to occur mainly at methylene or ether structures. Therefore, it will be very important to study the... 

A number of basic studies in the area of donor solvent liquefaction have been reported (2 -9). Franz (10J reported on the interaction of a subbituminous coal with deuterium-labelled tetra-lin, Cronauer, et al. (11) examined the interaction of deuterium-labelled Tetralin with coal model compounds and Benjamin, et al. (12) examined the pyrolysis of Tetralin-l-13C and the formation of tetralin from naphthalene with and without vitrinite and hydrogen. Other related studies have been conducted on the thermal stability of Tetralin, 1,2-dihydronaphthalene, cis-oecalin and 2-methylin-dene (13,14). 

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. 

Many of the feedstocks for the chemical industry, especially aromatic hydrocarbons, were originally obtained as by-products from the carbonization of coal. (1,2) However, nowadays, most of these chemical feedstocks are derived from petroleum. Nevertheless, it is probable that, within the next few decades, the shortage of world reserves of petroleum will mean that BTX will once again have to be produced from coal, as will ethylene. It is, therefore, appropriate to examine ways in which these materials can be produced from coal the present investigation was designed to study the formation of BTX and ethylene by the thermal cracking of coal-derived materials from the NCB coal liquefaction/hydrogenation processes. (3)... 

As an introduction to the main part of the paper, it is pertinent to mention this year as the anniversary of a few significant events in thermal physics. Let us note the centenary of the first helium liquefaction by Heike Kamerlingh Onnes at Leiden. In his plenary report at the 18 European conference on thermophysical properties Dr. Amo Laesecke called this event a breakthrough in research on thermophysical properties of substances and, among other problems, he related the studies into metastable states of substances to uncharted territories in thermophysics. In this connection our workshop seems to be well-timed. 

In a further work,2 the authors studied the processing of plastic wastes in mixtures of tetralin and used automotive oil. Figure 6.2 shows the results obtained with different waste oil/tetralin ratios. ZSM-5 was again more active than the ferrihydrite-based catalyst, while the latter led to oil yields very close to those of the thermal degradation. In both thermal and catalytic experiments, the activity was strongly enhanced by an increase in the waste oil/tetralin ratio, which shows the latter is not the best solvent for the liquefaction of aliphatic plastics. 

In the early 1970 s, in response to the world oil crisis, studies on the direct thermal liquefaction of biomass were initiated. These studies could be classified into those on water-based processes and those on non-water-based processes. The focus in this chapter is on the water-based processes and, in particular, on a process which uses no catalysts or reducing gases. It should be noted that actual biomass used for commercial liquefaction would certainly contain significant moisture, and water is expected as a product of the liquefaction. Despite this, the water-based and non-water-based processes are significantly different. 

In the recent studies of thermal and thermochemical processes of wood liquefaction, considerable progress has been reported in the analysis of gaseous and liquid products. Some attention has been given to the composition of the solid products by wet chemistry analysis... 

Both liquefaction residues were studied by DSC in both inert (dynamic N2) and oxidizing (dynamic air) atmospheres. A computerized DSC system (Perkin-Elmer DSC-2C/TADS) was used in these studies, A flow-thru cover was used with the DSC sample holder asjsembly in all of these studies. Standard gold sample pans were employed for the oxidative profiles obtained in dynamic air atmosphere. For the lower temperature studies conducted in dynamic N2 atmosphere, experiments showed that the results obtained were the same regardless of whether standard aluminum or standard gold DSC pans were employed. All figures given here are hard copy printouts from the Perkin-Elmer Thermal Analysis Data Station. 

Since the residue from the catalyzed liquefaction process was observed to volatilize at temperatures above llO C, the compression study on this specimen was carried out from lO C to 90°G. As is shown in the thermal curves given in Figure 11, the Process 2 residue is observed to undergo softening over a broad temperature range with a maximum rate of compression observed at 34 C in the DTMA curve. 

The use of thermal methods of analysis for the characterization of coal liquefaction residues can provide much information regarding the physical nature and composition of such coal conversion byproducts. Their thermal and oxidative stabilities are readily assigned from both TG and DSC methods. Heat history effects may be observed from both DSC and WA techniques. Volatile matter content, fixed carbon values, and ash content are readily obtained from thermogravimetry, Calorific values are accurately determined by dynamic DSC studies in flowing air atmospheres. Furthermore, volatilization profiles by TG and combustion profiles by both DSC and DTG may be used as tools for fingerprinting such residues. The use of computerized DSC offers the additional concept of normalized comparisons and subtraction of these profiles versus temperature. A combination of the information obtained from thermal methods of analysis, elemental analysis, microscopic and spectroscopic techniques, and solubility studies may lead to the total characterization of coal conversion by-products. 

Thus, the solvent extraction of coal, far from being a theoretical study, is, in fact, very pertinent to the behavior of coal in a variety of utilization operations. For example, the liquefaction of coal (Chapters 18 and 19) often relies upon the use of solvent and, in addition, the thermal decomposition of coal can also be considered to be an aspect of the solvent extraction of coal. The generation of liquid products during thermal decomposition can be considered to result in the exposure of coal to (albeit coal-derived) solvents with the result that the solvent materials being able to influence the outcome of the process. And there are many more such examples. 

The preheater is essentially a plug flow reactor (L/D > 100) where the coal-solvent slurry and hydrogen gas are preheated to the liquefaction temperature. Extensive studies have been carried out to understand the exact nature of the processes, taking place in the preheater (2,11,13-16). Considerable work has also oeen performed to evaluate the dissolution process and its effect on thermal hydraulics of large-scale preheaters (13-16). 

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