A. Vuori

Pyrolysis studies of some simple coal related aromatic methyl ethers

Abstract Pyrolysis of the coal related model compounds o -, m -, and p -hydroxy and methoxyanisoles has been studied under inert atmosphere at reaction temperatures from 598 to 673 K , and for reaction times from 1 to 600 min. The thermal decomposition of all these anisoles takes place via two main primary pathways, namely by demethylation of the methoxyl groups, and by an intramolecular ipso substitution of the methoxyl groups via a spiranic oxiran intermediate. The demethoxylation under mild reaction conditions obviously takes place as a secondary reaction via the ipso substitution pathway. The demethylation of o -hydroxyanisole (guaiacol) is partly concerted on the basis of kinetics and of e.p.r. measurements of the residual spin concentration of the pyrolysis products. There is, however, no indication of a concerted mechanism for 0-methoxyanisole (veratrole). The apparent first order activation energy of all the anisoles studied is of the order 240 ± 20 kJ mol −1 corresponding to the average bond energy of the methyl CO bond in the aromatic methoxyl group.

Influence of sulphur level on hydrodeoxygenation

The effect of catalyst sulphidation on hydrodeoxygenation was studied under pseudo-steady-state conditions in a continuous trickle-bed reactor at 523 K. Sulphur was added to the feed in the form of carbon disulphide. The catalyst used was a commercial CoO-MoO3/γ-Al2O3 hydrotreating catalyst which was presulphided at 523 or 623 K. Experiments were made both with a high and a low oxygen content of the feed by using o-methoxyphenol (guaiacol) as a model compound at different concentrations, and also with addition of other oxygen-containing compounds. The conversion of guaiacol increased with increasing sulphur content of the feed. The selectivity of the hydrodeoxygenation had its highest value, however, when a presulphided catalyst was used without sulphur added to the feed. This indicates that oxygen and sulphur compete for the same hydrogenolytically active sites. The effect on the selectivity of the formation of specific products varied with the sulphur content. This is at least partly due to steric effects. The proportion of both the O- and ring alkylation decreased with increasing sulphur content. The selectivity of phenol formation increased significantly even at the lowest level of sulphur addition, whereas the selectivity of veratrole formation decreased only gradually. In the competing hydrodeoxygenation systems, diphenyl ether did not have any effect, whereas isopropanol decreased the conversion of quaiacol. The sulphur content of the catalyst, measured after reaction, did not increase with increasing sulphur content of the feed but remained at a relatively low level. This was about 2 wt.-% for high and 3 wt.-% for low oxygen-content feeds. Presulphidation tests showed that a significantly higher sulphur-content of the catalyst could easily be achieved. This gives additional proof of competition between oxygen and sulphur atoms for the same active sites on the catalyst.

Liquefaction of Kraft Lignin: 1. Primary Reactions under Mild Thermolysis Conditions

Primary reactions of kraft lignin liquefaction were studied under mild batch reaction conditions. Experiments using tetralin äs reaction solvent were made both neat and in the presence of a heterogeneous hydrotreating catalyst (CoMo). Thermolysis at 345°C gave only a relatively low yield of gaseous and liquid products. The maximum yield, 20.3 wt-% (dry basis), for ether soluble phenols and acids was attained when a tetralin/m-cresol mixture was used äs a solvent. The main reaction under mild thermolysis conditions is the demethylation of the methoxyl group leading to the formation of methane, and also char through condensation. The high yields of char indicate the inability of both the gas phase hydrogen and the hydrogen from the donor solvent to prevent condensation reactions. Experiments with the hydrotreating catalyst gave a higher yield of both gaseous products and char than neat thermolysis indicating an enhanced reaction of the kraft lignin. The yield of liquid products remained, however, on a low level.

Thermal reactions of the bonds in lignin. I: Thermolysis of 4-propylguaiacol

The thermal reactions of 2-methoxy-4-propylphenol (4-propylguaiacol), a model of the propylguaiacol structure prevalent in lignin, were studied at temperatures from 598 to 673 K. The experiments were carried out under inert atmosphere in l ml boron silicate glass ampoules heated in a fluidized sand bath. Two-oxygen atom products were formed in larger proportions than one-oxygen atom products. The main primar> thermolysis reaction was the cleavage of the methyl C—O bond to form 4-propylpyrocatechol äs a major product. In addition, the cleavage of the aromatic C—O and propyl side chain C—C bonds occurred parallel with or consecutively to this main reaction to form minor products. The apparent first order activation energy (228 ± 27 KJ/mol) calculated for the decomposition of 4-propylguaiacol lies in the ränge of magnitude expected for the cleavage of the methyl C—O bond. The reaction pathways and mechanisms are described.

Hydrogenolysis and Hydrocracking of the Carbon-Oxygen Bond. 4. Thermal and Catalytic Hydrogenolysis of 4-Propylguaiacol

Thermal and Catalytic hydrogcnolysis of 4-propylguaiacol and some other rclated lignin modcl compounds was studied in a baten rcactor at 518-618 K. Bcnzcne, naphthalenc, tctralin or tetralin/m-cresol mixture (molar ratio 2:1) were uscd s solvents, and the expcrimcnts were made under nitrogcn or hydrogcn pressure. The catalysts were γ-ΑΙ2Ο3, CoMo/y-AI2O3, and Μο/γ-Α12Ο3. The main rcaction in the thermal hydrogenolysis was the clcavage of the mcthyl C—O bond of 4-propylguaiacol. The cleavage of the aromatic ring C-O bond was of minor importance without catalyst. Molecular hydrogen did not participate in the thermal rcaction. When tctralin was not present, the source of hydrogen was 4-propylguaiacol itself. The selcctivity of the cleavage of the aromatic ring C-O bond was affected to some extcnt by the reaction tcmperature and the sulphur content of the catalyst in the expcriments with CoMo/Y-AI2O3-catalyst.

Thermal Reactions of the Bonds in Lignin. II. Thermolysis of Dihydrodehydrodiisoeugenol

Reaction entre 603 et 673°K conduisant principalement au phenylbenzofuranne et diphenylethane