WA 98195 and from the U.S. Forest Products Laboratory, Madison, WI 53705 Keywords Kraft lignin Lignin model compounds Hydrocracking Phenols Tetralin Schlüsselwörter (Sachgebiete) Kraftlignin Lignin-Modellverbindungen Hydro-Verkrackung Phenole Tetralin Thermal Degradation of Kraft Lignin in Tetralin SummaryHydrocracking of kraft lignin (Indulin-AT) and of model compounds p-ethylguaiacol and dehydrodihydrodiisoeugenol (DDDI) was studied with tetralin äs hydrogen donor in the temperature ränge 375 to 400° C. It was found that aliphatic oxygen functions reacted most rapidly. The aromatic methoxyl groups underwent either methyl-oxygen or ring-oxygen cleavage forming catechol and phenol groups, respectively. The former process is more prevalent at higher temperatures. Side-chain cleavages resulted in the general lowering of molecular weight and formation of monomeric phenols. Careful analysis of the latter products suggested that these cleavages occurred mostly between the a-and ß-carbon atoms but cleavages between the aromatic ring and the -carbon also occurred. Upon prolonged hydrocracking, guaiacols and catechols disappeared while a mixture of phenol, cresols and ethyl phenols was relatively resistant towards further conversions. Thermischer Abbau von Kraftlignin in TetralinZusammenfassung Die Hydro-Verkrackung von Kraftlignin (Indulin AT) und von Modellverbindungen wie p-Äthyl-guajakol und Dehydrodihydro-Diisoeugenol (DDDI) wurde mit Tetralin als Wasserstoff-Donator im Temperaturbereich von 375 bis 400° C untersucht. Dabei wurde festgestellt, daß die Sauerstofftragenden Seitenketten sehr schnell reagieren. Die aromatischen Methoxylgruppen unterliegen entweder Methyl-Sauerstoff-oder Ring-Sauerstoff-Spaltung, wobei Catechol-bzw. PhenolGruppen gebildet werden. Der erstgenannte Prozeß läuft vorzugsweise bei höheren Temperaturen ab. Infolge der Seitenketten-Spaltung erniedrigt sich allgemein das Molekulargewicht, und es entstehen monomere Phenole. Genaue Analysen der letztgenannten Produkte weisen darauf hin, daß diese Spaltungen meistens zwischen dem a-und /3-Kohlenstoffatom vorkommen, aber auch zwischen dem aromatischen Ring und dem «-Kohlenstoff. Bei längerer Verkrackung verschwinden die Guajakol-und Catechol-Verbindungen, während eine Mischung von Phenol, Kresol und Äthylpheriolen relativ resistent gegen weitere Umwandlungen war.

Some characteristics of gas pockets rising through beds of fluidized solids have been measured directly with a light probe technique. The vertical thickness, numerical frequency, and rate of rise of the bubbles were obtained from oscillographs of dual probe signals. Room-temperature air at 1-atm. pressure was used in 4-and 6-in. columns, Glass beads, a crushed rock, commercial cracking catalysts, coal, and hollow resin spheres were studied in particle sizes from 12-p fluid cracking catalyst to 450-p coal.Vertical bubble thickness was found to increase with particle size, distance above the bed support, and gas velocity. Size growth upon rising was mainly the result of coalescence of bubbles. The rise velocity ranged from 1 to 2 ft./sec., relatively unaffected by operating conditions. Bubble frequency decreased with height above the bed support owing to coalescence. Total bed-depth variation from 1.0 to 2.5 ft. did not significantly influence the results, which should be of interest in studying gas by-passing in fluidized beds and predicting the slugging behavior and fluidization uniformity.

This work is an experimental assessment of the Langmuir-Hinshelwood model of heterogeneous catalysis. The vopor-phase dehydration of ethanol to diethyl ether, as catalyzed by cation exchange resin in the acid form, was the reaction chosen for study.Initial reaction rate data, determined from the integral kinetic data obtained experimentally, allowed selection of the most suitable rate equation from among several plausible equations derived in accordance with the above model. The Langmuir equilibrium adsorption constants in the rate equation were compared with the corresponding constants determined directly from pure component studies in a static adsorption system. The adsorption constants determined for the three reacting components by these independent methods showed definite order-of-magnitude agreement. The adsorption studies also provided significant information about the nature of the catalytic site.The extent of agreement in the constants determined by these two independent approaches is considered to be evidence of the theoreticol validity of this model. Additional interpretation of the adsorption and kinetic data via this model suggests that the ethanol dehydration reaction proceeds through the reaction of adjacently adsorbed ethanol molecules.The Langmuir-Hinshelwood model of heterogeneous catalysis has been widely used by chemical engineers in the correlation of experimental reaction rate data. The model stems directly from the Langmuir theory of activated adsorption (14) and the application by Hinshelwood (8) of that theory to a large number of reactions. Hougen and Watson (10) extended and popularized this theory for chemical engineering use. Rate equations, derived for many situations, were systematized and put into a generalized form by Yang and Hougen ( 2 3 ) . Although the model has been used quite successfully in the correlation of kinetic data, its theoretical significance has been questioned. This argument has been put into focus in back-to-back articles by Weller ( 2 2 ) and Boudart (1).Weller suggests that the LangmuirHinshelwood approach does not have the theoretical validity commonly attributed to it and that, lacking theoretical validity, it is unnecessarily complex for use as an empirical equation when compared for simplicity to the common power function type of equation. Boudart has supported the rational use of the Langmuir-Hinshelwood approach with his discussion of the limitations and strengths of that theory. Because this model of heterogeneous catalysis has not been adequately tested the direct experimental evaluation presented in this paper has been carried out.The general approach utilized in this work was to correlate reaction rate data with an equation of the Langmuir-Hinshelwood model, obtaining values of the Langmuir equilibrium Robert L. Kabel is with the United States Air

No abstract

Rates of the dehydration of methanol to dimethyl ether catalyzed by cation exchange resin (polystyrenesulfonic acid) were measured with a differential flow reactor and gas chromatographic analysis. Reaction temperature was 119°C., pressure was 1 atm., and feeds were methanol and mixtures of methanol with argon, dimethyl ether, and water.Rata data for the methanol reaction as well as the previously investigated ethanol dehydration reaction are well represented by Langmuir‐Hinshelwood kinetics with adsorption parameters in the rate equations approximately equal to corresponding values of Langmuir adsorption equilibrium constants estimated from or available in the literature. The reaction model is consistent with previous conclusions regarding mechanism. Its pertinence suggests that at reaction conditions the ion exchange resin offers a nearly homogeneous array of catalytic sites.