Coal contacting, catalyst

Figure 10 shows the sequence of chemical and physical effects leading to coal solubilization under mild conditions. The first step in the conversion involves catalyst-coal contacting a slow rate of contacting may limit the effective reactivity of the catalytic medium. The nature of the... 

Our new catalytic route utilizes a mobile catalyst to contact the coal and perform the activation at still lower... 

The nature or intimacy of contact of reactants can greatly affect the rate of reaction. Thus, finely divided coal bums much faster than lump coal. The titration of an acid with a base occurs much faster if the acid and base are stirred together than if the base is simply allowed to dribble into the acid solution. For a heterogeneous, catalytic reaction, the effect may show up in a more subtle way as the dependence of rate on the size of catalyst particle used. 

Solids in contact with fluids may be catalysts or they may be reactants as in combustion or calcination or coal liquefaction or uranium chlorination, etc. 

Fresh and used catalysts (CoMo, NiMo, ZnMo and ZnW) were used in hydroliquefaction experiments with batches of Point of Ayr coal liquid. One series of experiments was carried out at 400 C for 2 h with all four of the catalysts using five repeat contacts. A second series used only CoMo over three repeat contacts considered variations in reaction time and... 

In a continuous reactor, particularly of the trickle bed type, intimate contact between the coal liquid and the catalyst will be maintained throughout the pass of the liquid feed. In an autoclave, particularly of the stirred design, the contact between the liquid and the catalyst will not be as intimate. The action of the stirrer will produce a centrifugal force which will tend to throw the liquid away from the catalyst surface. Consequently, it can be visualised that less strongly adsoibed molecules will spend a shorter time at the catalyst surface so that reaction rates and mechanisms could be very different from those observed in continuous reactor studies. In addition, steady state conditions can be readily investigated in a continuous reactor, whereas for a single contact in an autoclave, steady state conditions may not have been established and changes in catalyst activity will become more relevant. 

In this series of experiments, the catalysts were used over five repeat contacts with fresh coal liquid. Point of Ayr coal liquid was supplied by the British Coal Corporation, Coal Research Establishment (CF ) one batch of this coal liquid was used in experiments with CoMo and NiMo catalysts and a further batch was used in experiments with ZnMo and ZnW. The catalysts were prepared as extrudates by the technique of incipient wetness which requires stirring the dry alumina support with a set volume of a pre-determined concentration of an appropriate soluble salt of the metal such that the pore space is just taken up by the metals at the required concentration. The alumina support was supplied by Akzo Chemie, The Netherlands and the catalysts were made up to contain 15% WO3 or M0O3 and 3% NiO, CoO, or ZnO, expressed as a weight percentage of the weight of support... 

Table V summarises the data of the sulphur analysis of the hydrocracked liquids and the various bpt fractions for CoMo and NiMo catalysed experiments. The sulphur contents of neither the total hydrocracked liquids nor the individual bpt fractions showed any dependence on repeat contact or catalyst type. The values did show that the sulphur concentrated in the recycle solvent fraction (275-450°C), suggesting that, even under the relatively strong conditions used, certain sulphur-containing compounds will survive to be recycled in the solvent However, the sulphur content of the coal liquid feed was reduced by about 50% and the sulphur content of the likely upgradable product was low.

The results have shown that spinning/falling basket autoclaves can be used effectively for gathering data on coal hydroliquefaction, a single contact being representative of steady state conditions. As with other types of reactors for coal liquefaction, the catalysts were deactivated to a constant activity but the rate of deactivation was much more rapid in tiie autoclaves. 

The second, catalytic liquefaction process is similar to the first except that there is a catalyst in direct contact with the coal. ZnCl2 and other Friedel-Crafts catalysts, including AICI3, as well as BFj-phenol and other complexes catalyze the depolymerization-hydrogenation of coals, but usually forceful conditions (375 t25°C, 100-200 atm) are needed. Superacidic HF-BF3-induced liquefaction of coals8 involves depolymerization-ionic hydrogenation at relatively modest 150-170°C. 

In coal liquefaction, highly dispersed, disposable, catalysts are needed because maximal contact between coal and catalysts is essential. It is assumed that one of the roles of the coal liquefaction catalyst is to assist in the rehydrogenation of the donor solvent (e.g. tetralin) by facilitating the hydrogen transfer from the gas phase.36,37... 

This study describes the results of processing both conventional solvent refined coal extract (SRC-I) and short contact time coal extract. Both coal extracts have been run at several space velocities, temperatures, and total reactor pressures for comparative purposes. The effect of catalyst deactivation has also been considered. The short residence time coal extract was run in both a deashed and non-deashed mode of operation. 

HDN as applied to coal liquefaction can be performed either during the liquefaction process itself or by hydrotreatment of the released oil. In H-Coal and Synthoil processes4 19,68d the coal is directly in contact with CoMo or NiMo catalysts in the H-Coal process, a slurry of H2, coal, ex-coal oil, and... 

The high enrichment ratio observed for titanium in the deposit is difficult to explain if all the metal in the coal is present in the mineral state. The data can be interpreted as an indirect indication of the presence in the feed slurry of an unstable titanium species which, upon contact with the catalyst surface, codeposits with carbon, boron, and other metals. A plausible explanation for this observation would be that organotitanium compounds exist in the coal and that they thermally or catalytic ally decompose to yield a stable inorganic species. Some recent model compound studies by Treblow and coworkers have indicated that... 

In the 1800s, the most important method for producing H2S04 was by the lead chamber process. Today, sulfuric acid is produced by a method known as the contact process. In the contact process, sulfur is burned to give S02 or the required S02 is recovered from coal burning or ore roasting processes. The S02 is then oxidized in the presence of a catalyst to produce SO3 (see Section 15.7.2). Typical catalysts are spongy platinum or sodium vanadate. Next, the SO3 is dissolved in 98% sulfuric acid ... 

Acid catalyzed depolymerization of coal with phenol affords a means for dissolution of coal under relatively mild conditions (185°C, ambient pressure). Once dissolved, separation of ash constituents and unreacted char is accomplished by filtration or centrifugation (also under mild conditions). Depolymerized coal recovered as a low ash product from excess phenol could be dissolved in a coal derived solvent and hydrogenated to stable liquids. It might be anticipated that access to hydrogen and contact with the catalyst would be more efficient in the case of the solubilized coal substance than for coal particle slurries. Hydrogenation might proceed more efficiently and with less... 

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). 

---