PYROLYTIC LIQUEFACTION

Techniques for the chemical recycling of plastics into monomers and petrochemical feedstocks are described, including chemical and thermal depolymerisation, pyrolytic liquefaction, pyrolytic gasification and partial oxidation. BRITISH PETROLEUM CO.PLC... 

This paper discusses in depth advanced technologies for recycled materials from solid waste streams. Chemical depolymerisation, thermal depolymerisation, pyrolytic liquefaction, pyrolytic gasification, partial oxidation, and feedstock compatibility are all explained. The economic feasibility of the methods are considered. 

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. 

Pyrolytic liquefaction produces liquid precursor products or synthetic crade oil that are suitable as refinery feedstock for new monomers. Further products from this process are non-condensable gas, which is used to provide process heat, and solid residues in the form of char. 

Thermochemical Liquefaction. Most of the research done since 1970 on the direct thermochemical Hquefaction of biomass has been concentrated on the use of various pyrolytic techniques for the production of Hquid fuels and fuel components (96,112,125,166,167). Some of the techniques investigated are entrained-flow pyrolysis, vacuum pyrolysis, rapid and flash pyrolysis, ultrafast pyrolysis in vortex reactors, fluid-bed pyrolysis, low temperature pyrolysis at long reaction times, and updraft fixed-bed pyrolysis. Other research has been done to develop low cost, upgrading methods to convert the complex mixtures formed on pyrolysis of biomass to high quaHty transportation fuels, and to study Hquefaction at high pressures via solvolysis, steam—water treatment, catalytic hydrotreatment, and noncatalytic and catalytic treatment in aqueous systems. 

In liquefaction systems wood and wood wastes are the most common fuelstocks. They are reacted with steam or hydrogen and carbon monoxide to produce liquids and chemicals. The chemical reactions that take place are similar to gasification but lower temperatures and higher pressure are used. Liquefaction processes can be direct or indirect. The product from liquefaction is pyrolytic oil which has a high oxygen content. It can be converted to diesel fuel, gasoline or methanol. 

Confirmation that conversion of coal Into liquids depends on limited pyrolytic disruption of coal "molecules" and on prompt stabilization of the resultant fragments by hydrogen Is provided by liquefaction In a hydrogen-donor viUxcU allows such reactions as... 

Based on this method, suitability of various biomass for pyrolytic conversion is studied and is found that based on the conqiosition of biomass, different biomass are suited for different applications such as carbonisation, liquefaction, gasification and making of char adsorbent. 

Prior to a run, fresh catalyst was demoisturised at 450 C for a 3 h period by intermittently passing nitrogen over the catalyst bed. High demoisturisation was necessary in order to activate the catalyst. One hour of treatment was inadequate, and two hours was only barely adequate to activate the catalyst. Immediately before commencing liquefaction, a nitrogen environment was established in the pyrolytic system. 

Pyrolysis results are very important for coal characterization, as all conversion processes of coal such as combustion, liquefaction, and gasification start with a pyrolytic step. For this reason, pyrolysis was frequently used for the analysis of coals [17,18). Pyrolysis data were correlated with coal composition, coal characterization and ranking [18a], prediction of coal reactivity as well as of other properties related to coal utilization. Techniques such as Py-MS, Py-GC/MS with different ionization modes, Py-FTIR, or evolved gas analysis (EGA) [19] were described for coal analysis. Programmed temperature pyrolysis is another technique that has been proposed [17] for a complete evaluation of the two types of molecules present in coal. 

Pyrolytic oils are acidic and may contain carcinogens. By analogy with heavy petroleum-derived oil fractions, the fuel oils produced by catalytic liquefaction may contain carcinogens. This suggests the need for special handling and storage precautions for the liquid fuels. 

The product from liquefaction is pyrolytic oil which has a high oxygen content. It can be converted to diesel fuel, gasoline or methanol. 

The data in this paper are drawn from a number of studies performed at Pacific Northwest Laboratory (3,7-9). We have examined biomass pyrolysis tar samples from many types of pyrolytic gasification and liquefaction systems through the U.S. Department of Energy support of domestic biomass thermochemical conversion research and international cooperative efforts. Many of these can be compared directly as a function of temperature since they are all produced at short residence time, approximately one second. Others produced at longer residence time or pressure require discussion separately. 

Alternatively, flash pyrolysis processes were developed for biomass liquefaction as well [5]. On a water- and ash-free basis, from wood typically 75% liquids (including 25% of water), 10% of solid char, and 15% of gases, mainly CO2 and CO, are formed at 5 00 ° C with gas retention times of only a few seconds. Several reactor concepts such as stationary and fluidized fluidized beds, the mechanically agitated rotating cone and Auger reactors, a well as ablative and vacuum pyrolysis have been carried out and operated on a semi-technical and pilot scale. For fast pyrolytic treatment of... 

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