Foster A. Agblevor

The influence of aeration and hemicellulosic sugars on xylitol production by Candida tropicalis.

The influence of other hemicellulosic sugars (arabinose, galactose, mannose and glucose), oxygen limitation, and initial xylose concentration on the fermentation of xylose to xylitol was investigated using experimental design methodology. Oxygen limitation and initial xylose concentration had considerable influences on xylitol production by Canadida tropicalis ATCC 96745. Under semiaerobic conditions, the maximum xylitol yield was 0.62 g/g substrate, while under aerobic conditions, the maximum volumetric productivity was 0.90 g/l h. In the presence of glucose, xylose utilization was strongly repressed and sequential sugar utilization was observed. Ethanol produced from the glucose caused 50% reduction in xylitol yield when its concentration exceeded 30 g/l. When complex synthetic hemicellulosic sugars were fermented, glucose was initially consumed followed by a simultaneous uptake of the other sugars. The maximum xylitol yield (0.84 g/g) and volumetric productivity (0.49 g/l h) were obtained for substrates containing high arabinose and low glucose and mannose contents.

Pyrolysis as a technique for separating heavy metals from hyperaccumulators. Part II: Lab-scale pyrolysis of synthetic hyperaccumulator biomass

Abstract Synthetic hyperaccumulator biomass (SHB) impregnated with Ni, Zn, Cu, Co or Cr was used to conduct 11 experiments in a lab-scale fluidized bed reactor. Two runs with blank corn stover, with no metal added, were also conducted. The reactor was operated in an entrained mode in a oxygen-free (N 2 ) environment at 873 K and 1 atm . The apparent gas residence time through the lab-scale reactor was 0.6 s at 873 K . The material balance for the lab-scale experiments on N 2 -free basis varied between 81% and 98%. The presence of a heavy metal in the SHB decreased the char yield and increased the tar yield, compared to the blank. The char and gas yields appeared to depend on the form of the metal salt used to prepare the SHB. However, the metal distribution in the product streams did not seem to be influenced by the chemical form of the metal salt used to prepare the SHB. Greater than 98.5% of the metal in the product stream was concentrated in the char formed by pyrolyzing and gasifying the SHB in the reactor. The metal concentration in the char varied between 0.7 and 15.3% depending on the type of metal in the SHB. However, the metal concentration was increased 4 to 6 times in the char compared to the feed.

Biocrude oils from the fast pyrolysis of poultry litter and hardwood.

The safe and economical disposal of poultry litter is becoming a major problem for the USA poultry industry. Current disposal methods such as land application and feeding to cattle are now under pressure because of pollution of water resources due to leaching, runoffs and concern for mad cow disease contamination of the food chain. Incineration or combustion is potentially applicable to large scale operations, but for small scale growers and EPA non-attainment areas, this is not a suitable option because of the high cost of operation. Thus, there is a need for developing appropriate technologies to dispose poultry litter. Poultry litters from broiler chicken and turkey houses, as well as bedding material were converted into biocrude oil in a fast pyrolysis fluidized bed reactor. The biocrude oil yields were relatively low ranging from 36 wt% to 50 wt% depending on the age and bedding material content of the litter. The bedding material (which was mostly hardwood shavings) biocrude oil yield was 63 wt%. The higher heating value (HHV) of the poultry litter biocrude oils ranged from 26 MJ/kg to 29 MJ/kg while that of the bedding material was 24 MJ/kg. The oils had relatively high nitrogen content ranging from 4 wt% to 8 wt%, very low sulfur (<1 wt%) content and high viscosity. The viscosities of the oils appeared to be a function of both the source of litter and the pyrolysis temperature. The biochar yield ranged from 27 wt% to 40 wt% depending on the source, age and composition of the poultry litter. The biochar ash content ranged from 24 wt% to 54 wt% and was very rich in inorganic components such as potassium and phosphorous.

Characterization and fermentation of steam exploded cotton gin waste

Abstract Cotton gin waste was collected from a cotton ginning plant in Virginia and characterized before and after steam explosion to evaluate its potential applications for higher value products such as ethanol. The raw cotton gin waste had high levels of ash ( 10.5 wt % ) and acid insoluble material ( 28.8 wt % ). The xylan and cellulose contents were, respectively, 9 and 37 wt % . The cotton gin waste was steam exploded in a batch gun at severities ranging from 2 to 4.9. Substantial solubilization/degradation of fiber material (9– 17 wt % ) occurred during steam explosion pretreatment especially at the high severities. Mannan, galactan, and arabinan were completely solubilized/degraded at severities greater than 3.56. Both glucan and xylan were solubilized/degraded at all severities, but xylan loss was considerably higher. The steam exploded material was essentially cellulose and acid insoluble material and small fractions of xylan at severities greater than 3.56. Steam explosion improved the enzyme hydrolysis of the material from 42% to 67% during 24 h incubation. E. coli KO11 was effective in converting the enzyme hydrolyzed substrate to ethanol. The highest ethanol yield (83% of theoretical yield) was achieved for material treated at a severity of 3.56. Both xylose and glucose were fermented to ethanol by the microorganism.

Effect of detoxification of dilute-acid corn fiber hydrolysate on xylitol production

Four different detoxification methods were evaluated for the production of xylitol from corn fiber dilute-acid hydrolysate using Candida tropicalis. Although C. tropicalis could ferment the dilute partially neutralized hydrolysate to xylitol in low yields (0.1 g/g), it could not ferment the concentrated hydrolysate. Overliming, calcium hydroxide neutralization, neutralization combined with activated charcoal, and overliming combined with activated charcoal methods were used to improve the fermentation of the concentrated hydrolysates. The partial neutralization combined with activated charcoal treatment was the most effective method with respect to xylitol yield and productivity. The highest xylitol yield (0.4 g of xylitol/g of xylose) was obtained for the highest concentration of hydrolysate (three times the original) that had been treated with calcium hydroxide and activated charcoal. The corresponding productivity was 0.23 g/(L.h). Overliming caused reduction in xylitol yield.

The influence of recycling non-condensable gases in the fractional catalytic pyrolysis of biomass

In this study, the effect of recycling the non-condensable gases (NCG) in the catalytic pyrolysis of hybrid poplar using FCC catalyst was investigated. A 50mm bench scale fluidized bed reactor at 475°C with a weight hourly space velocity (WHSV) of 2h(-1) and a gas recycling capability was used for the studies. Model fluidizing gas mixtures of CO/N(2), CO(2)/N(2), CO/CO(2)/N(2) and H(2)/N(2) were used to determine their independent effects. Recycling of the NCG in the process was found to potentially increase the liquid yield and decrease char/coke yield. The model fluidizing gases increased the liquid yield and the CO(2)/N(2) fluidizing gas had the lowest char/coke yield. The (13)C-NMR analysis showed that recycling of NCG increases the aromatic fractions and decreases the methoxy, carboxylic and sugar fractions. Recycling of NCG increased the higher heating value and the pH of the bio-oil as well as decreased the viscosity and density.

Scale-up of microbubble dispersion generator for aerobic fermentation

A laboratory-scale microbubble dispersion (MBD) generator was shown to improve oxygen transfer to aerobic microorganisms when coupled to the conventional air-sparger. However, the process was not demonstrated on a large scale to prove its practical application. We investigated the scale-up of a spinning-disk MBD generator for the aerobic fermentation of Saccharomyces cerevisiae (baker’s yeast). A 1-L spinning-disk MBD generator was used to supply air for 1- and 50-L working volume fermentation of baker’s yeast. For the two levels investigated, the MBD generator maintained an adequate supply of surfactant-stabilized air microbubbles to the microorganisms at a relatively low agitation rate (150 rpm). There was a significant improvement in oxygen transfer to the microorganism relative to the conventional sparger. The volumetric mass transfer coefficient, kLa, for the MBD system at 150 rpm was 765 h−1 compared to 937 h−1 for the conventional sparger at 500 rpm. It is plausible to surmise that fermentation using larger working volumes may further improve the kLa values and the dissolved oxygen (DO) levels because of longer hold-up times and, consequently, improve cell growth. There was no statistically significant difference between the cell mass yield on substrate (0.43 g/g) under the MBD regime at an agitation rate of 150 rpm and that achieved for the conventional air-sparged system (0.53 g/g) at an agitation rate of 500 rpm. The total power consumption per unit volume of broth in the 50-L conventional air-sparged system was threefold that for the MBD unit for a similar product yield. Practical application of the MBD technology can be expected to reduce power consumption and therefore operating costs for aerobic fermentation.

Storage stability of biocrude oils from fast pyrolysis of poultry litter.

The unstable nature of biocrude oils produced from conventional pyrolysis of biomass is one of the properties that limits its application. In the disposal of poultry litter via pyrolysis technology, the biocrude oil produced as a value-added product can be used for on farm applications. In this study, we investigated the influence of bedding material (wood shavings) on the storage stability of biocrude oils produced from the fast pyrolysis of poultry litter. The biocrude oils produced from manure, wood (pine and oak), and mixtures of manure and wood in proportions (75:25 50:50, and 25:75w/w%) were stored under ambient conditions in sealed glass vials for a period of 6 months and their stability were monitored by measuring the changes in viscosity over time. The manure oil had the lowest rate of viscosity change and thus was relatively the most stable and the oils from the 50:50w/w% litter mixtures were the least stable. The rate of viscosity change of the manure biocrude oil was 1.33cP/day and that of the 50/50 litter mixture was 7.6cP/day for pine and 4.17cP/day for oak. The spectrometric analyses of the biocrude oils showed that the presence of highly reactive oxygenated functionalities in the oil were responsible for the instability characteristic of the litter biocrude oils. The poor stability of the biocrude oil from the 50:50w/w% litter mixtures was attributed to reactions between nitrogenous compounds (amides) from protein degradation and oxygenated compounds from the decomposition of polysaccharides and lignin. The addition of 10% methanol and 10% ethanol to the oil from 50% manure and 50% pine reduced the initial viscosity of the oil and was also beneficial in slowing down the rate of viscosity change during storage.

Catalytic pyrolysis for the production of refinery-ready biocrude oils from six different biomass sources

This study focused on understanding the impact of catalytic pyrolysis and biomass feedstock on the physicochemical properties of upgraded bio-oils. Results from catalytic conversion of different types of biomass feedstocks (woody: pine, hybrid poplar and pinyon-juniper; herbaceous: switchgrass; agricultural residue: corn stover; and forest residue: pine bark) with HZSM-5 zeolite to biocrude oils are presented. The study showed that the source of biomass plays an important role in catalytic pyrolysis products. Significant differences were observed in product distribution, selectivity to aromatic hydrocarbons and physicochemical properties of the biocrude oils. The pyroprobe-GC/MS experiment showed that pine and pinyon-juniper produced the highest carbon yield of monoaromatic hydrocarbons. 13C NMR analysis revealed that aromatic hydrocarbon content of the oils followed this order: pinyon-juniper > corn stover > pine > poplar > switchgrass > pine bark. The chemical composition and the physicochemical properties indicated that it is critical to reduce carbonyls to achieve stable oils. Also, it was found that elimination of sugars (levoglucosan) and phenolics would improve oil specific gravity and viscosity. Furthermore, reducing the acidity of oils by catalytic pyrolysis appeared to be very challenging. Hence, phenols (weak acids) may have to be minimized in addition to other acids to increase the pH. The nitrogen contents correlated with pH values. Thus, feedstocks with high nitrogen content produced less acidic oils. Nonetheless, high content of nitrogenous compounds could make the biocrude oil highly unstable. The effects of the bio-oil chemical composition on the physicochemical properties are discussed as well as opportunities and challenges of utilizing biocrude oil as feed for standard refinery units.

Influence of pine wood shavings on the pyrolysis of poultry litter.

Poultry litter from broilers and turkeys are a mixture of manure, feathers, feed and wood shavings, thus pyrolysis oils produced from this material are influenced by the individual components. In order to determine the influence of wood shavings that are used as bedding material, we investigated the pyrolysis of pine wood shavings and poultry manure. Because manure from layer chickens are usually not contaminated with wood shavings, we made mixtures of layer manure and pine wood shavings in the following manure to wood ratios, 100:0, 75:25, 50:50, 25:75, and 0:100 w/w and pyrolyzed them in a fluidized bed reactor at 450 °C. The total liquid yield ranged from 43.3 to 62.7 wt.%. The layer manure oil had a HHV of 29.7 MJ/kg and pH of 5.89 compared to pine wood oil which had HHV of 25.6 MJ/kg and pH of 3.04. The addition of wood shavings to manure clearly influenced the physical properties of the oil, resulting in a decrease in pH and HHV and an increase in density. The oils had relatively high nitrogen content ranging from 1.36 to 5.88 wt.%. The ash (<0.07 wt.%) and sulfur (<0.28 wt.%) contents were very low. FTIR, (13)C NMR and (1)H NMR spectrometric analysis of the oils showed that manure oil was rich in hydrocarbons and nitrogenous compounds such as primary, secondary amides, aromatic amines and N-heterocyclic. The properties of the oils were strongly influenced by the amount of wood in the mixture.