Vapor pressures and heats of vaporization of primary coal tars

Abstract

Executive SummaryThis project had as its main focus the determination of vapor pressures of coal pyrolysis tars. It involved performing measurements of these vapor pressures and from them, developing vapor pressure correlations suitable for use in advanced pyrolysis models (those models which explicitly account for mass transport limitations).This report is divided into five main chapters. Each chapter is a relatively "stand-alone" section. Chapter A reviews the general nature of coal tars and gives a summary of existing vapor pressure correlations for coal tars and model compounds. It is shown that the heterogeneous nature and the complexity of coal tars have made it unrealistic to apply detailed vapor pressure correlations which take into account the variation in the chemical structure of the tars. The significant product of this study is a much improved understanding of the volatility and thermal behavior of coal tars. The volatility was studied by vacuum sublimation and Knudsen effusion experiments. The volatility behavior is considerably more complicated than had been earlier believed.The tars evaporate in a "distillation-like" fashion. More volatile species are lost earlier in the process, leaving behind a progressively less volatile residue. The results suggest that there are three very different classes of compounds, and therefore, at least three different vapor pressure behaviors. The first corresponds to compounds of high molecular weight and significant alkyl character, the second to compounds with significant hydroxyl group content and medium molecular weight, and the third to medium molecular weight aromatic compounds without hydroxyl groups. Hydrogen bonding plays a major role in the determining the tar volatility. vi There has been concern in pyrolysis modeling about how closely Raoult's law is followed in coal tar. It appears from our results that the assumption of ideal mixture behavior could be acceptable for rough models of pyrolysis despite the possibility of strong specific interactions between certain functional groups.The results from the current work show that measuring the vapor pressures of complicated and thermally unstable mixtures is possible at low temperatures. There has also been some concern about condensation-type reactions influencing the results of vapor

Estimation of Fuel Properties for the Heavy Fraction of Biomass Pyrolysis Oil Consisting of Proposed Structures for Pyrolytic Lignin and Humins

“…Among all others, the heat of vaporization may be the most difficult to measure experimentally. Examples of high-quality experimental work to measure H VAP using Knudsen effusion cells can be found in Gourdin for squalane and Suuberg and Oja for primary coal tars [85,86]. However, the correlations given in Equations ( 7)-( 10) may provide reliable empirical estimates if there is a high degree of confidence in T B and some level of chemical intuition about the polarity/non-polarity of the molecule.…”

“…Additionally, preparative gel permeation chromatography can segregate samples by molecular weight ranges. This is the approach utilized by Suuberg and Oja in vapor pressure measurement of primary coal tars, with values given for specific apparent molecular weight fractions from the whole tar sample [86]. Further discussion of the nature of molecular weight metrics for bio-oils specifically can be found in a recent review from Harman-Ware and Ferrell [113].…”

Progress in understanding the four dominant intra-particle phenomena of lignocellulose pyrolysis: chemical reactions, heat transfer, mass transfer, and phase change

“…For example, the boiling points of pyrolytic cellulose sugars levoglucosan, cellobiosan, and cellotriosan at 1 atm are 385°C, 269 580°C, 269 and 790°C, 270 respectively. Oja and Suuberg have studied the vapor pressures of polycyclic aromatic hydrocarbons similar to lignin dimers and oligomers 271,272 as well as other sugar monomers, 273 as illustrated in Fig. 14. Recent studies have elucidated the effect of vaporization on the nature of products from pyrolysis of cellulose, lignin, and wood.…”

On the atomization and combustion of liquid biofuels in gas turbines : towards the application of biomass-derived pyrolysis oil

“…f Estimated using the Girolami method [9]. g Derived from vapor pressure data measured by Suuberg and Oja [140]. An advanced model was developed by Hallett and Clark [69] based on the principles of continuous thermodynamics.…”

“…The properties of the components included in the fuel model for pyrolysis oil have largely been found in the Fluent built-in database, in other property databases [38,64,65,93] or in the literature [36,41,66,92,140,148]. Property data that were not directly available have been estimated using the specified methods.…”