Co-hydropyrolysis

Utilization of wood-biomass residues as well as waste polymers is the important direction of recent research activities. It is known that direct catalytic liquefaction of plant biomass can be used to produce liquid fuels and chemicals [1,2]. Co-pyrolysis and co-hydropyrolysis processes have the potential for the environmentally friendly transformation of lignocellulosic and plastic waste to valuable chemicals. 

In co-hydropyrolysis experiments without catalysts the degree of pine wood/ polyethylene mixture (1 1 weight ratio) conversion was 80% wt. and yield of the light liquid fraction - 23% wt. The addition of iron ore catalyst activated by mechanochemical treatment increased the degree of mixture conversion by 5-13%. This increase was mainly due to light liquid fraction formation. The variation of catalyst nature (pyrite, pyrrhotite, haematite) influences on the product composition. Pyirhotite catalyst yields the highest amount of the light fraction (about 40% wt.). 

Brown coal, pine wood with the content of lignin 29.4% wt., pine wood after extraction with dimethyl sulfoxide (with the content of lignin 17.2 % wt.), as well as industrial cellulose were tested in co-hydropyrolysis with polyethylene at the same process conditions. 

GC-MC data show that the light liquid fractions of plastic / biomass co -hydropyrolysis contain mainly normal paraffins CrCij. Their content was 75% for pine wood / i-PP mixtures. Alkyl derivatives of benzene were also detected in the light liquid fractions. The content of unidentified substances was 15%, alkylbenzenes and alkytfriranes compounds - approximately 10% relative. 

It is probable that a combination of a lower temperatures (450 C) and higher pressures to those employed in this initial study will represent the optimum conditions for maintaining catalyst surface area. In order to prevent possible reduction of the promoter to the corresponding metal (Ni/Co), hydropyrolysis should be carried out in the presence of a small amount of hydrogen sulphide to help maintain the catalyst to remain in a reasonably fiilly sulfided form. Hydropyrolysis for the virtual complete carbon removal would need to be carried out off-line since the combination of temperature, pressure and flow rate required cannot be achieved in hydrotreating units. In terms of potential applications, carbon-supported catalysts may represent the major area since these cannot be regenerated oxidatively. 

The soft (chloroform-extractable) and hard coke fractions fi om a suite of deactivated Co/Mo hydrodesulfurisation (HDS) catalysts with carbon contents ranging from 5 to 18% have been characterised. The hard coke accounted for between 50 and 70% of the total carbon, but was responsible for much less of a reduction in BET surface area as the carbon content increased. Indeed, significant variations in hard coke structure were revealed by solid state C NMR with the aromaticity ranging from 0.6 to over 0.9 with increasing carbon content and time on stream. The relatively high aliphatic contents and atomic H/C ratios for the hard cokes obtained at low levels of carbon deposition (5-7%) suggested that much of the carbon should be removed under reductive conditions. Indeed, hydropyrolysis, in which the deactivated catalysts were heated from ambient to 500°C under a hydrogen pressure of 15 MPa, removed over 90% of the carbon and recovered 70% of the BET surface that had been lost. 

I) Pyrolysis and Hydropyrolysis Processes (Lurgi-Ruhrgas COEd/ Occidental etc.)... 

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