Thermal liquefaction processes

Thermal Liquefaction Process. In the thermal liquefaction process (see Fig. 1), a starch slurry containing no enzyme or added calcium is heated for several minutes. The slurry is slightly acidic and sufficient acid liquefaction is achieved to reduce viscosity. The hydrolyzate (at essentially zero DE) is flash-cooled to 95—100°C, a-amylase is added, and the pH is adjusted. The reaction then goes to completion. 

Although SRC-II was basically a thermal liquefaction process, it was most successful using bituminous coals with a high native pyrite content. Iron sulfides are well known to have catalytic properties for coal liquefaction. Recycling part of the ash-minerals-containing bottoms had two beneficial effects (1) it increased the pyrite concentration in the reactor feed, and (2) it increased the residence time for heavy components, thus giving them more time to hydrocrack to distillate products. A block flow diagram of the SRC-II process is shown in Fig. 19.19. 

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. 

The significance of the above-described work is that in all of the presently developing coal liquefaction processes, the initial step in the conversion is thermal fragmentation of the coal structure to produce very fragile molecules which are highly functional, low in solubility, and extremely reactive toward dehydrogenation and char formation. A more detailed discussion of the chemical nature of these initial products has been presented elsewhere (4). ... 

The formation of these thermal fragments is necessary to catalytic liquefaction processes before the catalysts can become effective for hydrogen introduction, cracking and/or heteroatom removal (10). ... 

In catalytic coal liquefaction processes, reaction temperatures must be high in order to insure that thermal reactions disrupt the coal structure to the point that the catalyst can act on the products. 

The liquefaction process is initiated by the thermal generation of coal-derived free radicals which in turn react with solvent to form solvent radicals by hydrogen abstraction. These sol-... 

Pyrolysis and liquefaction processes take an intermediate position in the sense that they maintain some larger molecular characteristics. Pyrolysis is a process in which the biomass material is quickly heated. The thermal cracking process, de-polymerizes waste or dry biomass and produces a liquid of complex composition (Fig. 1.17). 

Direct liquefaction processes under development are typically carried out at temperatures from about 450 to 475°C and at high pressures from 10 to 20 MPa and up to 30 MPa. Despite the slow rate at which liquefaction proceeds, the process itself is thermally rather efficient, since it is only slightly exothermic. However, hydrogen must be supplied and its manufacture accounts for an important fraction of the process energy consumption and cost of producing the liquid fuel. The hydrogen itself may be produced, for example, by the gasification of coal, char, and residual oil. 

Obtained data show that, the mixtures of the different types of the natural and synthetic organic polymers can be successfully converted with a high yield to light distillate fraction by pyrolysis under inert atmosphere and catalytic hydtopyrolysis in the autoclave conditions. The optimum tenqreiature of biomass / plastic mixtures conveision which coiresponds to the maximum yield of liquids is 390 - 400 C. In the CO liquefaction processes the interaction between products of natural and synthetic polymers thermal deconqwsition takes place. 

Overview of Pyrolysis, Thermal Gasification, and Liquefaction Processes in Japan... 

A Perkin-Elmer Auto-system gas chromatograph (GC), which houses a 30-m, 0.53-mm (ID) fused silica capillary column (Carboxen 1010 Plot, Supelco), was used to analyze the gaseous samples from the liquefaction process. Temperature programmed step heating was performed as follows 40°C for 1.7 min, increase by 40°C/min imtil 220°C, and leave at 220°C for 1.8 min. Argon was the carrier gas at a flow rate of 20 ml/min. Two detectors were used for gas analysis a flame ionization detector (FID) for carbon-bearing species and a thermal conductivity detector (TCD) for H2. Uncertainties in reported concentrations are estimated to be within 5% [8]. 

The process of converting coal to liquid products involves at least two, often overlapping, steps viz. coal depolymerization and product upgrading, the latter involving hydrogen transfer and heteroatom removal. Both processes employ catalysts, although considerable depolymerization does occur even under thermal conditions as discussed above. The role of the catalysts is to facilitate reactions, prevent retrograde reactions, and improve product selectivity. Thomas has reviewed direct coal liquefaction processes and... 

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. 

The three major thermal depolymerisation processes are pyrolytic liquefaction, gasification and hydrogenation. If heat is applied to waste plastics in the absence of air the process is called pyrolysis if done with a controlled oxygen flow it is called gasification. Hydrogenation is a modification of the refining process for petroleum. 

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. 

Liquefaction is the process of thermal decomposition of biomass by mixing the biomass with water and basic catalysts like sodium carbonate, usually carried out at a lower temperature than p)U olysis (300-400 K), at high pressure (120-200 atm) and longer residence time. The liquefaction process is potentially more expensive than pyrolysis due to the high pressure requirements. However, the bio-oil produced from liquefaction has less oxygen content (12-14%) than that obtained from pyrolysis. No pre-drying of biomass is required for the liquefaction process. 

It should also be pointed out that gasifiers operated at steam to oxygen ratios as low as possible provide the thermally most efficient and lowest cost route to the production of medium BTU gas (1). The co-production of pipeline gas in the gasification step improves the overall thermal efficiency of various liquefaction processes (Flscher-Tropsch, Methanol, Mobils MTG route) by 13 to 18 % (2). 

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