Showing papers in "Industrial & Engineering Chemistry Process Design and Development in 1985"

Product compositions and kinetics in the rapid pyrolysis of sweet gum hardwood

Abstract: Yields, composition, and rates of evolution of major products from batch pyrolysis of predried sweet gum hardwood were measured for the temperature range 600-1400 K under 5 psig of helium, at heating rates and residence times at final temperature of 1000 K/s and 0 s, respectively. Approximately 100-mg layers of 45-88 ..mu.. m wood powder, thinly spread on a hot stage, were heated, so that volatiles residence times at elevated temperatures were minimized. Total weight loss increased strongly with temperature to an asymptote of 93% at 1100 K. Tar is the major pyrolysis product above 800 K. It exhibits a maximum yield of 55 weight % at 900 K and declines to an asymptote of 46 weight % at 1300 K. Secondary cracking of the tar is significant above 900 K and contributes substantially to the yields of CO, CH/sub 4/, C/sub 2/H/sub 4/, and other light gases. Carbon monoxide dominates the gas produced above 850 K and attains an asymptote of 17 weight % above 1300 K. A single-reaction first-order decomposition model describes well the global rates of evolution of most major products except tar. However, the data imply that most products are evolved by more complex kinetic pathways.

Phase equilibria for mixtures containing very many components. development and application of continuous thermodynamics for chemical process design

Abstract: For some multicomponent mixtures, where detailed chemical analysis is not feasible, the compositio of the mixture may be described by a continuous distribution function of some convenient macroscopic property suc as normal boiling point or molecular weight. To attain a quantitative description of phase equilibria for such mixtures, this work has developed thermodynamic procedures for continuous systems; that procedure is called continuous thermodynamics. To illustrate, continuous thermodynamics is used to calculate dew points for natural-gas mixtures, solvent loss in a high-pressure absorber, and liquid-liquid phase equilibria in a polymer fractionation process. Continuous thermodynamics provides a rational method for calculating phase equilibria for those mixtures where complete chemical analysis is not available but where composition can be given by some statistical description. While continuous thermodynamics is only the logical limit of the well-known pseudo-component method, it is more efficient than that method because it is less arbitrary and it often requires less computer time.

Product compositions and kinetics in the rapid pyrolysis of milled wood lignin

Abstract: Yields, compositions, and rates of evolution of major products from batch pyrolysis of predried milled wood lignin from sweet gum hardwood were measured for the temperature range 600-1400 K under 5 psig of helium at heating rates and residence times at final temperature of 1000 K/s and 0 s, respectively. Approximately 100-mg layers of 100 ..mu.. m or less thick lignin flakes, thinly spread on a hot stage, were heated so that volatiles residence times at elevated temperatures were minimized. Total weight loss increased strongly with temperature to an asymptote of 86% at 1050 K. Tar is the major pyrolysis product above 800 K. Its yield exhibits a maximum of 53 weight % at 900 K and declines to 47 weight % at 1150 K. The latter represents 57% of the energy of the dry lignin. Secondary cracking of the tar contributes to the yields of CO, CH/sub 4/, C/sub 2/H/sub 4/, and other light gases above 950 K. Carbon monoxide dominates the gas yield above 850 K and attains a yield of 19 weight % at 1440 K. A single reaction first-order decomposition model describes well the global rates of evolution of most major products, except tar. However, themore » data imply that most products are evolved by more complex reaction pathways.« less

Primary and secondary lignin pyrolysis reaction pathways

Abstract: The reaction pathways involved in the pyrolysis of kraft lignin, kraft lignin plus tetralin, a milled wood lignin, and pine wood were examined. The temporal variations of the quantitative yields of 33 different products, including 12 gases, water, methanol, and 19 phenolics allowed resolution of primary and secondary pathways, description of the influence of reactor design and lignin type on product yields, and formulation of a simple kinetic lumping scheme. Products within separate guaiacol and catechol lumps attained maximal proportions at 7.5 and 15 min, respectively, during kraft lignin pyrolysis at 400/sup 0/C. Within a lump, the secondary reactions of individual species were nearly synchronous. Further, the similarity of the observed rate of the secondary decomposition of guaiacols during kraft lignin pyrolysis with that previously reported for pyrolysis of pure guaiacol suggest that the reactions of lignin's thermally liberated single-ring products are insensitive to the presence of other molecular species or poymer residuum. All of the foregoing indicates that a simple reaction network based on phenol, guaiacol, and catechol lumps could be a useful model of phenolics product evolution.

Pyrolysis of a wood-derived material. Effects of moisture and ash content

Abstract: The influence of moisture on the thermal degradation of wood waste was investigated by pyrolyzing ground samples in a batch fluid-bed reactor at between 320 and 470 °C in helium at 101-104 kPa. The wood samples were heated at about 300 °C/min, so that drying and pyrolysis were simultaneous. The presence of moisture increased the yield of char by as much as 5 yield % , relative to dry samples. Moisture suppressed tar formation from demineralized samples at 470 °C but enhanced the formation of tar above and below 390 °C from samples containing ash. Ash and added calcium catalyzed the conversion of tar into aqueous product, while moisture interacted with tar formation or trapping reactions to increase the yield of char. Moisture also modulated the activity of the ash components for the Conversion of tar Into aqueous product. The native mineral components in the wood waste gave effects equivalent to ion-exchanged calcium.

Hydrogen-donor solvents in biomass liquefaction

Abstract: The liquefaction of pure number61-cellulose with hydrogen-donor solvents such as tetralin and 2-propano was studied in a batch autoclave system under both inert and hydrogen atmospheres. Reaction conditions involved temperatures between 270 and 400/sup 0/ C, residence times between 0 and 60 min, and hydrogen pressures between 0 and 500 psi. The use of homogeneous and heterogeneous hydrogenolysis catalysts was also investigated. Unde these conditions, up to 100% of the initial cellulose feed was converted, resulting in oil yields greate than 50%. The oxygen content of the product oil was significantly lower than that of the cellulose feed (less than 25 wt % in most cases), and it generally decreased with increasing reaction temperature. Low and intermediate temperatures less than or equal to360 /sup 0/C) favored oil production, while higher temperatures induced severe hydrocracking of the product oil to gases.

Ethanol to gasoline process: effect of variables, mechanism, and kinetics

Abstract: The conversion of ethanol to hydrocarbons by use of a ZSM-5 zeolite catalyst was studied. The effects of zeolite Si/Al ratio, ethanol dilution, and process variables (temperature, space velocity, pressure, and recycle rate of gaseous products) were established. Results were justified in accordance with a carbenium ion mechanism previously suggested in the literature. This process could be described by a second-order reaction with simultaneous formation of paraffinic and aromatic hydrocarbons. The experimental data agreed with the model wit a mean deviation of less than 10%. The thermochemistry of the ethanol to hydrocarbon process is considered.

Effectiveness of magnetic water treatment in suppressing calcium carbonate scale deposition

Abstract: La principale variable etudiee est le niveau de supersaturation des ions formant CaCO 3 . Mesure de la vitesse de croissance du depot, de la duree de la periode d'induction, nature adhesive des incrustations

Solvent screening study and conceptual extractive distillation process to produce anhydrous ethanol from fermentation broth

Abstract: This solvent screening study indicates that glycols are very selective solvents for producing anhydrous ethanol from fermentation broth by extractive distillation. The promising solvents are glycerin, ethylene glycol, tetraethylene glycol, and triethylene glycol. An improved extractive distillation process for producing anhydrous ethanol was conceptually developed which was based on the analysis of the experimental solvent screening data. The basic idea of this process is to add an extractive solvent only to the ethanol-rich portion of the fractionator to eliminate the ethanol-water azeotrope and to change the undesirable shape of the vapor-liquid equilibrium curve to one more favorable for distillation. With a suitable solvent, such as ethylene glycol, anhydrous ethanol could be produced from the fermentation broth in a column with only 18 theoretical trays. A low reflux ratio of 1.5 and a low solvent-to-feed ratio of 0.27 (based on fermentation broth) would be needed for the separation.