Liquefaction short-contact-time

The second section of this volume describes several potentially new liquefaction processes which may have higher efficiencies than today s developing technologies. The theme of the Storch Award Symposium, featured throughout these six chapters, was new process potentials through the use of short-contact-time thermal processes followed by catalytic upgrading. 

A New Outlook on Coal Liquefaction Through Short-Contact-Time Thermal Reactions Factors Leading to High Reactivity... 

These observations suggest that new coal liquefaction technology may be possible based on short contact time reactions. The purpose of this and the related papers in this volume by R.H. Heck and W.C. Rovesti is to show some potential advantages for optimized or integrated short contact time liquefaction processes over conventional technology. 

This paper will concentrate on factors which lead to high conversion at short time. R.H. Heck, T.O. Mitchell, T.R. Stein and M.J. Dabkowski discuss the relative ease of conversion of short and long contact time SRCs to higher quality products. C.J. Kulik, W.C. Rovesti and H.E. Liebowitz discuss some new leads presently being explored at the Wilsonville PDU in which short contact time liquefaction is being coupled with rapid product isolation via the Kerr-McGee Critial Solvent Deashing Process. 

Advantages for Short Contact Time Coal Liquefaction... 

In order to understand the potential advantages for short contact time liquefaction processes, let us first consider some of the disadvantages for presently developing long contact time processes. These are enumerated below. 

The significance of these calculations is that lower rank coals will require 5% lower conversion than higher rank coals for a given end product. Also, the more severe a coal is to be upgraded, the lower its conversion has to be in the initial phases of liquefaction. One very pertinent question to be addressed is whether or not coals can be converted to the levels shown in Figure 5 in a short contact time process. This paper will deal with that question as well as what compositional features of the coal and the solvent influence short contact time conversions. 

The classic work of Storch and co-workers showed that essentially all coals below 89% C f can be converted in high yields to acetone soluble materials on extended reaction (12). We have investigated the behavior of coals of varying rank toward short contact time liquefaction. In one series of experiments, coals were admixed with about 5 volumes of a solvent of limited H-donor content (8.5% Tetralin) and heated to 425°C for either 3 or 90 minutes. The solvent also contained 18% p-cresol, 2% y-picolene, and 71.5% 2-methylnaphthalene and represented a synthetic SRC recycle solvent. The conversions of a variety of coals with this... 

To summarize, we have identified a number of features unique to short contact time coal liquefaction. The important factors... 

Continuous Bench-Scale Experimentation With encouraging results obtained from microautoclave tests, experimentation emphasis moved to the bench-scale unit Here the concept of adding Light SRC to the recycle solvent on a continuous basis was tested Earlier work (j>) performed on short contact time coal liquefaction showed Indiana V coal to be out-of-solvent balance Also the operability of the continuous bench-scale SRT unit was highly dependent upon the quality of the solvent ... 

Short-contact time liquefaction products from bituminous coal... 

Product characterization from liquefaction has not been extensive. Phi 1p and Russell (95) have examined products by Py-GCMS from metal halide catalyzed hydrogenation of a vitrinite, alginite, and inertinite, each from a different source. They were able to correlate Py-GCMS results with reaction temperature. King, et al. (96) examined the short contact time liquefaction of macerals separated by DGC from a single hvB bituminous coal. They found correlations between density and reactivity and composition of the products. 

The yields of the reaction of maceral concentrates with pyridine and iodine show some interesting trends and are given in Table V. Unlike the results from the thermal reactions such as vacuum pyrolysis (Table IV) or short contact time liquefaction (29), the vitrinites are more reactive than the spori-nites. The inertinites are less reactive but the magnitude of the difference in the comparison with the other maceral groups from the Indiana and Kentucky coals is much less than what has been found for the yields from the thermal reactions. 

MAF conversions to pyridine solubles from short contact time coal liquefaction are dependent on the coal type, solvent source, and reaction severity. As reaction severity increases conversions approach a maximum value with a hydrogen-enriched solvent but go through a maximum and decline with a hydrogen-depleted... 

Varghese, P., Derbyshire, F. J., and Whitdiurst, D. D. Control of Short Contact Time Coal Liquefaction EPRI Contractors Conference on Coal Liquefaction Palo Alto, California May 7-8, 1980. 

The purpose of this paper is to describe some of our findings which examine the liquefaction behavior of Western sub-bituminous coal to determine which components of the solvent are most critical in the short contact time dissolution stage. The work will be presented from two points of view ... 

Data Obtained from Solubilized Coal. We have found that the careful use of the structural information provided by short-contact-time coal thermal liquefaction products can give relevant information on coal structure. 

The elemental composition for the initial coal [for Monterey coal (2)] and its short-contact-time liquefaction products (defined as pyridine soluble) are shown in Table II. 

A corollary of this statement is the following If these polyaromatic or polycyclic saturated structures are present in the carbon skeleton of coal, they should be identified in the short-contact-time liquefaction products. The possibility of some isomerization reactions in the carbon skeleton cannot be excluded totally, but the most important fact is that no dramatic aromatization of hydroaromatic rings or saturation of aromatic rings takes place under these conditions. Many of the chemical functions also are stable under these conditions, especially the O, S, and N heterocyclic aromatic structures. Water formation by phenol dehydroxylation is minimal. In coal liquefaction under our conditions, even at long reaction times (up to 90 min) in the absence of an added catalyst, the -OH bonded to a monoaromatic ring is stable. Under the same conditions, dehydroxylation of polyaromatic phenols does occur (10). 

The data above show that the structure of short-contact-time products of coal liquefaction is indicative of the main characteristics of the carbon skeleton in coal itself, the distribution and abundance of the majority of heteroatomic functions, and the statistical distribution of the weak bonds in the parent coal. 

Short-Contact-Time Coal Liquefaction Products and the Initial Structure of Coal. Our own data and those from the literature indicate that no major changes take place in the different elements of coal structure under short-contact-time reaction conditions and at relatively low temperature. It is obvious, however, that fragmentation occurs by... 

In a study of short contact time coal liquefaction (109), in which major product fractions were examined with respect to their structure as well as their composition, the (nominal) high-molecular-weight product fractions of two similar subbituminous coals were found to possess radically different formal structures (cf. structure 6) one showed 73% and 60%, and the other showed 26% and H. 18%. Significantly, both fractions were deemed to closely resemble their respective precursor coals but to be slightly more aromatized than they. 

Coal liquefaction is normally carried out in the pressure range of 200-250 bar and temperature range of 400-450 C. Lower pressures and short contact times produce heavier liquids while higher temperatures and long contact times reduce liquid yield and increase the amount of gases produced [64], Iron oxide, iron oxide mixed with alumina, molybdenum and cobalt oxides supported on a highly porous alumina and oxides of other metals such as nickel... 

Data for the kinetics of coal liquefaction have been published in the literature (1-11). A review of the reported studies has recently been given by Oblad (12). The reported data were mostly obtained in bench-scale reactors. Guin et al. (7) studied the mechanism of coal particle dissolution, whereas Neavel (7), Kang et al. (8), and Gleim (10) examined the role of solvent on coal liquefaction. Tarrer et al. (9) examined the effects of coal minerals on reaction rates during coal liquefaction, whereas Whitehurst and Mitchell (11) studied the short contact time coal liquefaction process. It is believed that hydrogen donor solvent plays an important role in the coal liquefaction process. The reaction paths in a donor solvent coal liquefaction process have been reviewed by Squires (6). The reported studies examined both thermal and catalytic liquefaction processes. So far, however, very little effort has been made to present a detailed kinetic model for the intrinsic kinetics of coal liquefaction. 

---