Examining the role of particle size on ammonia-based bioprocessing of maize stover.

The role of particle size in carbohydrate fractionation upon pretreatment and glucan yields upon enzymatic hydrolysis was investigated at two different temperatures, to examine the possibility of pretreating under milder conditions smaller particles, in order to satisfy pilot-scale operational constraints. Maize stover was knife-milled through 1-mm and 0.5-mm screens and pretreated by soaking in aqueous ammonia pretreatment at 60 or 110°C for 6 h. Pretreated solids were analyzed for composition and a material balance calculated for glucan, xylan, and lignin. At 60°C, milling resulted in greater delignification compared to unmilled biomass. Delignification was more uniform at 110°C. Pretreated solids were washed and cellulase hydrolysis carried out at 10% w/w solids loading, with low and high enzyme loadings. Liquid samples were drawn and concentration data developed through HPLC to calculate 48-h glucan and xylan hydrolytic yields. The differences in hydrolytic yield between milled and unmilled treatments were found to vary with pretreatment temperature and enzyme loading. The results show that while particle size impacts carbohydrate recovery and hydrolytic yield, it is less important in bioprocessing than pretreatment temperature and enzyme loading, possibly owing to the particles' morphology rather than the size.

Microbial lipid production from pretreated and hydrolyzed corn fiber.

With its high content of carbohydrates and low percentage of lignin, corn fiber represents a renewable feedstock that can be processed to produce biofuels. Through a combination of pretreatment by lime and enzymatic hydrolysis, total reducing sugars of 700 mg/g corn fiber were released. This amount is equivalent to 92.7% of theoretically available sugars in corn fiber. The resulting hydrolysate itself did not support any growth of Cryptococcus curvatus. But with addition of minerals, C. curvatus grew to a cell density of 6.6 g/L in 6 days. Using the adapted cells, rapid sugar consumption and cell growth were observed. This study demonstrated that it is feasible to produce microbial lipids from corn fiber through pretreatment, enzymatic hydrolysis, and fermentation. In addition, C. curvatus is an excellent candidate for this application since it can utilize all major sugars, glucose, xylose, and arabinose with yield of cells and lipids as 0.55 and 0.27 g/g sugars, respectively.

One-electron oxidation of ruthenocene: reactions of the ruthenocenium ion in gentle electrolyte media.

The electrochemical oxidation of ruthenocene, RuCp(2) (Cp = eta(5)-C(5)H(5)), 1, has been studied in dichloromethane using a supporting electrolyte containing either the [B(C(6)F(5))(4)](-) (TFAB) or the [B(C(6)H(3)(CF(3))(2))(4)](-) (BArF(24)) counteranion. A quasi-Nernstian process was observed in both cases, with E(1/2) values of 0.41 and 0.57 V vs FeCp(2) in the respective electrolyte media. The ruthenocenium ion 1(+) equilibrates with a metal-metal bonded dimer [Ru(2)Cp(4)](2+), 2(2+), that is increasingly preferred at low temperatures. Dimerization equilibrium constants determined by digital simulation of cyclic voltammetry (CV) curves were in the range of 10(2)-10(4) M(-1) at temperatures of 256 to 298 K. Near room temperature, and particularly when BArF(24) is the counteranion, the dinuclear species [Ru(2)Cp(2)(sigma:eta(5)-C(5)H(4))(2)] (2+), 3(2+), in which each metal is sigma-bonded to a cyclopentadienyl ring, was the preferred electrolytic oxidation product. Cathodic reduction of 3(2+) regenerated ruthenocene. The two dinuclear products, 2(2+) and 3(2+), were characterized by (1)H NMR spectroscopy on anodically electrolyzed solutions of 1 at low temperatures in CD(2)Cl(2)/[NBu(4)][BArF(24)]. The variable temperature NMR behavior of these solutions showed that 3(2+) and 2(2+) take part in a thermal equilibrium, the latter being dominant at the lowest temperatures. Ruthenocene hydride, [1-H](+), was also identified as being present in the electrolysis solutions. The oxidation of ruthenocene is shown to be an inherent one-electron process, giving a ruthenocenium ion which is highly susceptible to reactions that allow it to regain an 18-electron configuration. In a dry non-donor solvent, and in the absence of nucleophiles, this electronic configuration is attained by self-reactions involving formation of Ru-Ru or Ru-C bonds. The present data offer a mechanistic explanation for the previously described results on the chemical oxidation of osmocene (Droege, M.W.; Harman, W.D.; Taube, H. Inorg. Chem. 1987, 26, 1309) and are relevant to the manner in which sigma:eta(5)-C(5)H(4)-complexes of other second and third-row metals are formed.

Electrochemical preparation of the bis(ruthenocenium) dication.

The electrochemical oxidation of ruthenocene (1) in CH(2)Cl(2)/[NBu(4)]A, where A = [B(C(6)F(5))(4)](-) or [B(C(6)H(3)(CF(3))(2))(4)](-), gives the dimeric dication [(RuCp(2))(2)](2+), 2(2+), in equilibrium with the 17-electron ruthenocenium ion 1(+). At room temperature the rapid equilibrium accounts for the quasi-Nernstian cyclic voltammetry (CV) behavior (E(1/2) = 0.41 V vs FeCp(2), A = [B(C(6)F(5))(4)](-)). Direct electrochemical evidence for 2(2+) is seen by CV and by bulk electrolysis at 243 K. The bis(ruthenocenium) dication undergoes a highly irreversible two-electron cathodic reaction at E(pc) ca. 0 V. Anodic electrolysis of 1 at 243 K using [B(C(6)H(3)(CF(3))(2))(4)](-) as the supporting electrolyte, followed by cathodic electrolysis of 2(2+), regenerates half of the original 1. Precipitation of 2(2+) occurs when the supporting electrolyte is [B(C(6)F(5))(4)](-), allowing facile isolation of [(RuCp(2))(2)][B(C(6)F(5))(4)](2). A second, unidentified, anodic product also reduces to give back ruthenocene. Digital simulations of the CV curves of 1 at 243 K give a dimerization equilibrium constant of 9 x 10(4) M(-1) for K(eq) = [(RuCp(2))(2)(2+)]/2 [RuCp(2)](+) in CH(2)Cl(2)/0.1 M [NBu(4)][B(C(6)F(5))(4)].