Pradeep K. Agrawal

Acid‐Catalyzed Conversion of Sugars and Furfurals in an Ionic‐Liquid Phase

The reactivity of monosaccharides, furfural, and 5-hydroxymethyl-2-furfural (HMF) in the presence of a Brønsted acid (added as H(2)SO(4)) in the ionic liquid 1-butyl-3-methylimidazolium chloride (BMImCl) is investigated at 120 °C. Fructose is converted much faster than mannose, glucose, and xylose and yields HMF with high selectivity, even in the absence of acid. Conversion of mannose, glucose, and xylose involves more complex reaction networks. Only small amounts of furfural and HMF are converted in the absence of other reactants but both compounds are consumed when monosaccharides and their degradation products are present. Acid-catalyzed degradation reactions also lead to the formation of solid residues (humins).

Depolymerization and Hydrodeoxygenation of Switchgrass Lignin with Formic Acid

Organosolv switchgrass lignin is depolymerized and hydrodeoxygenated with a formic acid hydrogen source, 20 wt % Pt/C catalyst, and ethanol solvent. The combination of formic acid and Pt/C is found to promote production of higher fractions of lower molecular weight compounds in the liquid products. After 4 h of reaction, all of the switchgrass lignin is solubilized and 21 wt % of the biomass is shown to be converted into seven prominent molecular species that are identified and quantified. Reaction time is shown to be an important variable in affecting changes in product distributions and bulk liquid product properties. At 20 h of reaction, the lignin is significantly depolymerized to form liquid products with a 76 % reduction in the weighted average molecular weight. Elemental analysis also shows that the resultant liquid products have a 50 % reduction in O/C and 10 % increase in H/C molar ratios compared to the switchgrass lignin after 20 h.

Gallosilicate molecular sieves: The role of framework and nonframework gallium on catalytic cracking activity

The acid properties of a molecular sieve zeolite can be modified by changing the SiO/sub 2//Al/sub 2/O/sub 3/ ratio or through isomorphous substitution, e.g., replacement of aluminum in the tetrahedral framework sites. Numerous examples of gallosilicates (isomorphous substitution of gallium for aluminum) have been reported. However, little is known of the ability of these materials to act as acid catalysts in the catalytic cracking of hydrocarbons. In addition, gallium oxide itself may be catalytically active. It is therefore important to understand the role a secondary phase or impurity of gallium oxide would have on the apparent acid activity of a gallosilicate containing such an impurity or secondary phase. This paper presents the results of n-butane cracking studies with the gallosilicate analog of zeolite ZSM-5, i.e., (Ga) ZSM-5, and a hydrothermally modified gallosilicate ZSM-5 material containing nonframework gallium.

Catalytic gasification of coal using eutectic salts: identification of eutectics

Abstract Different eutectic salt mixture catalysts for the gasification of Illinois No. 6 coal were identified and various impregnation or catalyst addition methods to improve catalyst dispersion were evaluated in this study. In addition, the effects of major process variables such as temperature, pressure, and steam/carbon ratio were investigated in a thermogravimetric analyzer (TGA) and fixed-bed bench scale reactor systems. The TGA studies showed that the eutectic catalysts increased CO2 gasification rate significantly. The methods of catalyst preparation and addition had significant effect on the catalytic activity and coal gasification. Based on the TGA studies of several eutectic systems, the 43.5% Li2CO3–31.5% Na2CO3–25% K2CO3 and 39% Li2CO3–38.5% Na2CO3–22.5% Rb2CO3 ternary eutectics, the 29% Na2CO3–71% K2CO3 binary eutectic and the K2CO3 single salt catalysts were selected for the fixed-bed studies. The catalyst loading increased the gasification rate and almost complete conversion of carbon was observed when 10 wt.% of catalyst was added to the coal. Upon further increasing the catalyst amount to 20 wt.% and above, there was no significant rise in gasification rate.

1-D model for forced flow-thermal gradient chemical vapor infiltration process for carbon/carbon composites

A one-dimensional model was developed for the forced flow-thermal gradient chemical vapor infiltration of carbon/carbon composites. The infiltration time predicted by the model agreed very well with experiments, where propylene and propane were used as the hydrocarbon source. The model was also validated by interrupting the infiltration and comparing predicted with observed densities.

Quantitative solid state NMR analysis of residues from acid hydrolysis of loblolly pine wood

The composition of solid residues from hydrolysis reactions of loblolly pine wood with dilute mineral acids is analyzed by (13)C Cross Polarization Magic Angle Spinning (CP MAS) NMR spectroscopy. Using this method, the carbohydrate and lignin fractions are quantified in less than 3h as compared to over a day using wet chemical methods. In addition to the quantitative information, (13)C CP MAS NMR spectroscopy provides information on the formation of additional extractives and pseudo lignin from the carbohydrates. Being a non-destructive technique, NMR spectroscopy provides unambiguous evidence of the presence of side reactions and products, which is a clear advantage over the wet chemical analytical methods. Quantitative results from NMR spectroscopy and proximate analysis are compared for the residues from hydrolysis of loblolly pine wood under 13 different conditions; samples were treated either at 150 degrees C or 200 degrees C in the presence of various acids (HCl, H(2)SO(4), H(3)PO(4), HNO(3) and TFA) or water. The lignin content determined by both methods differed on averaged by 2.9 wt% resulting in a standard deviation of 3.5 wt%. It is shown that solid degradation products are formed from saccharide precursors under harsh reaction conditions. These degradation reactions limit the total possible yield of monosaccharides from any subsequent reaction.

Carbon/carbon processing by forced flow-thermal gradient chemical vapor infiltration using propylene

Abstract The fabrication of carbon/carbon disks using the forced flow-thermal gradient chemical vapor infiltration process was studied using a 23 factorial statistical design. Propylene, diluted with hydrogen, was used as the reagent. The independent variables were the temperature of the bottom of the fibrous preform, concentration of the reagent, and total flow rate. The response variables were infiltration time, final porosity, rate of weight gain, and uniformity of densification. It was found that the infiltration time and rate of weight gain were affected by each of the three independent variables. It was also observed that the densification of the composites could be monitored by the in situ measurement of the back pressure. The composites were cut into 12 slices 1 cm long, 4 mm wide and 2 mm deep to measure the uniformity of densification. It was found that the density of the slices varied very little with position within an individual composite disk. Also, coating thickness as a function of position was measured for different composites. In most of the runs the coating thickness increased exponentially from the cold side to the hot side of the disk. The coating thicknesses near the cold and hot sides were used to calculate the rate constant for the pyrolysis of propylene in the preform. The activation energy was found to be ~21.0 kcal mol−1 and the rate constant is given by ln ks = 1.5–21034/RT.

Carbon distribution in char residue from gasification of kraft black liquor

Abstract The char residue yields and the total carbon and carbonate content were measured for dry black liquor solids after pyrolysis or gasification in a laminar entrained-flow reactor. The experimental conditions were 700–1000°C in N 2 ,CO 2 /N 2 or water vapor/N 2 at 1 bar total pressure, for residence times from 0.3 to 1.7 s . Fixed carbon yields, when measured at the same particle residence time, decreased with increasing reactor temperature. CO 2 and water vapor diminished the char carbon significantly at temperatures above 800°C, compared with pyrolysis in N 2 . Water vapor oxidized the char carbon more rapidly than did CO 2 . At 1000°C, the reactions of carbon with sulfate and carbonate became faster, resulting in a smaller difference between carbon conversion rates in the different gas environments. By the end of devolatilization, the amount of carbonate in the char had changed very little at 700–800°C. After devolatilization, carbonate was formed more rapidly at higher temperatures. The presence of CO 2 or water vapor increased the formation of carbonate. In the presence of these gases, more carbonate was measured at all temperatures and residence times. The maximum carbonate measured in the char was 16% of the carbon in the black liquor solids, as compared to 4.4% in the original dry liquor solids. Under most conditions, the carbonate, as a fraction of carbon input, first increased to a constant, temperature-independent value and then decreased.

Forced flow-thermal gradient chemical vapor infiltration (FCVI) for fabrication of carbon/ carbon

Abstract Carbon/carbon composites with porosities as low as 7% were fabricated within 8–12 hours using the forced flow-thermal gradient chemical vapor infiltration (FCVI) process. Preforms consisting of 40 layers of T-300 plain weave carbon cloth were infiltrated with a feed containing a carbon source and a diluent. The carbon sources studied in the present work included propylene, propane, and methane and the diluent was hydrogen. Shorter processing times were obtained when propylene and propane were used as compared to methane. The highest deposition rate obtained in the present study was ~ 3 μm/h which is more than an order of magnitude faster than the typical value of 0.1–0.25 μm/h for the isothermal infiltration process. In the infiltrated composites it was observed that the tows in a cloth were appreciably infiltrated, independent of their position in the preform. Whereas, the coating thickness between the tows and cloth layers strongly depended on the temperature, i.e. position within the preform.

Chemical vapor deposition of boron-carbon films using organometallic reagents

The feasibility of using organoboranes as precursors for the deposition of boron-carbon thin films in a hot-wall CVD furnace was investigated. The reagents studied include trimethylborane, triethylborane, and tributylborane. Triethylborane was the most suitable reagent in that higher boron to carbon ratios were obtained.