Biomass Pyrolysis in Sealed Vessels. Fixed-Carbon Yields from Avicel Cellulose That Realize the Theoretical Limit

Abstract

In agreement with prior experimental work, thermodynamics predicts differences in the outcome of biomass pyrolysis conducted in sealed, constant-volume systems as opposed to constant-pressure systems. In particular, much higher values of the fixed-carbon yield can be expected in constant-volume systems. Avicel cellulose is known to give very low char and fixed-carbon yields; thus, char and fixed-carbon yields from cellulose have been given primary attention in this work. Our tubing bomb results reveal (i) fixed-carbon yields that realize the theoretical "limiting" values when the vessel is pre-pressurized to a modest pressure with N 2 gas, and (ii) a gas product composed of steam (water) and CO 2 , with traces of CO and virtually no tars. Above a small range of modest temperatures and pressures, the char endures a molten phase and becomes a hard coke. The ash content of the char/coke reflects the composition of the glass wool and kao wool materials used to hold the Avicel powder in place.

Effect of Processing Conditions on the Constant-Volume Carbonization of Biomass

“…Figure 1 shows the contrasting appearances of some CVC charcoals. Signs of a molten phase were evident in chars derived from CVC of birch particles of size <2 mm at a pretest pressure of 0.1 MPa N 2 , a HTT of 400 °C and a heating rate of ~1°C/s, [9] and in chars from the CVC of cellulose grains in a size range from 0.050-0.18 mm, at a pretest pressure of 2.40 MPa N 2 , a HTT of 260 °C and a similar heating rate [8]. To our knowledge, this is the first time molten charcoals have been observed in pyrolysis processes operating at moderate conditions of temperature and slow heating rates.…”

“…Proximate analysis on the final charcoals produced from later CVC experiments on cellulose confirmed the lack of influence of an inert gas pressure on the product yields. [8] Nonetheless, the fixed-carbon contents showed a slight improvement with higher inert pressures. [8] For example, when the initial nitrogen pressure was increased from 0.1 to 4.79 MPa, the fixed-carbon content improved from 54 to 58%.…”

“…In this most recent work on CVC, product yields are determined together with charcoal proximate analysis and in some instances with higher heating values (HHV) and SEM analysis [6,8,9]. CVC experiments consistently approached theoretical fixed-carbon yields across a variety of processing conditions [6,8,9], see Supporting Information Figure S1.…”

“…As conditions became more severe in the CVC 4 reactor, the charcoal solid structure transformed from a particulate solid retaining the original biomass morphology to a coke-looking piece that had undergone a transient plastic phase (TPP) and had adopted the shape of the reaction vessel. [8,9] The ultimate goal of this research is to enable the manufacture of charcoals with physical and chemical properties tailored to a targeted end use with a focus on the manufacture of metallurgical-grade charcoals. The present study provides a deeper understanding of the CVC process by exploring the effect of various processing variables (pretest pressure, temperature, immersion time, mass loading, heating rate and particle size) on char yields and properties.…”

Elucidating transfer hydrogenation mechanisms in non-catalytic lignin depolymerization

“…[5][6][7][8] Understanding biomass and more specifically lignin reaction mechanisms is also vital for the optimization of bio-carbon production through methods such as hydrothermal carbonization, flash carbonization™ and constant volume pyrolysis. [9][10][11] All these areas of study rely on the control, and thereby understanding, of reaction conditions to tailor product properties while reducing costs.…”