To examine the potential use of synthesis gas as a carbon and energy source in fermentation processes, Rhodospirillum rubrum was cultured on synthesis gas generated from discarded seed corn. The growth rates, growth and poly-beta-hydroxyalkanoates (PHA) yields, and CO oxidation/H(2) evolution rates were evaluated in comparison to the rates observed with an artificial synthesis gas mixture. Depending on the gas conditioning system used, synthesis gas either stimulated or inhibited CO-oxidation rates compared to the observations with the artificial synthesis gas mixture. Inhibitory and stimulatory compounds in synthesis gas could be removed by the addition of activated charcoal, char-tar, or char-ash filters (char, tar, and ash are gasification residues). In batch fermentations, approximately 1.4 mol CO was oxidized per day per g cell protein with the production of 0.75 mol H(2) and 340 mg PHA per day per g cell protein. The PHA produced from R. rubrum grown on synthesis gas was composed of 86% beta-hydroxybutyrate and 14% beta-hydroxyvalerate. Mass transfer of CO into the liquid phase was determined as the rate-limiting step in the fermentation.

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A pilot-scale 25 kg/h fluidized bed, oxygen/steam blown gasifier and syngas cleaning system was developed to convert switchgrass into clean syngas. The system is rated for operation at gage pressures up to 1 bar. The reactor vessel incorporated a novel guard heating system to simulate near-adiabatic operation of large commercial-scale gasifiers, and was effective for gasification temperatures up to 900°C. After removing particulate from the gas stream via cyclones, a warm-gas cleaning operation based on oil scrubbing was used to remove tars. Sulfur compounds were removed via solid-phase adsorption. Ammonia was removed by water scrubbing. Baseline gasification tests with steam and oxygen were conducted at equivalence ratios (ER) between 0.21 and 0.38 using switchgrass as fuel. Measurements on the raw and cleaned syngas included permanent gas composition, C 2 hydrocarbons, water, heavy and light tars, gasification residues (char and ash), hydrogen sulfide (H 2 S), carbonyl sulfide (COS), carbon disulfide (CS 2 ), ammonia (NH 3 ), and the first reported measurements of hydrogen cyanide (HCN) for oxygen/steam blown gasification. Heavy tars were removed with high efficiency by the method employed, although more difficult to remove light tars reduced overall tar removal efficiency to less than 80%. The sulfur scrubbing system demonstrated 99.9% removal efficiency, resulting in less than 200 ppb of H 2 S in the cleaned gas. The NH 3 scrubbing system also accomplished greater than 99.9% removal efficiency, resulting in final NH 3 concentrations of less than 1 ppm.

A new method was developed for collecting, identifying and quantifying contaminants in hot process gas streams using time-weighted average (TWA) passive sampling with retracted solid-phase microextraction (SPME) and gas chromatography. The previous lab scale proof-of-concept with benzene was expanded to include the remaining major tar compounds of interest in syngas: toluene, styrene, indene, and naphthalene. The new method was tested on high T (⩾100 °C) process gas from a pilot-scale fluidized bed gasifier feeding switchgrass and compared side-by-side with conventional impingers-based method. Fourteen additional compounds were identified, representing 40-60% improvement over the conventional method's detection capacity. Differences between the two methods were 1-20% and as much as 40-100% depending on the sampling location. Compared to the inconsistent conventional method, the SPME-TWA offered a simplified, solvent-free approach capable of drastically reducing sampling and sample preparation time and improving analytical reliability. The improved sensitivity of the new method enabled identification and quantification of VOCs beyond the capability of the conventional approaches, reaching concentrations in the ppb range (low mg/m3). RSDs associated with the TWA-SPME were <10%, with most lab-based trials yielding <2%. Calibrations were performed down to the lowest expected values of tar concentrations in ppb ranges (low mg/N m3, with successful measurement of tar concentrations at times >4000 ppm (up to 10 g/N m3). The new method can be a valid alternative to the conventional method for light tar quantification under certain conditions. The opportunity also exists to exploit TWA-SPME for process gas streams analysis e.g., pyrolysis vapors and combustion exhaust.

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Gasification of biomass can produce process heat, electricity, liquid fuels, and chemicals without use of fossil fuels. Utilization of biomass and waste products for energy and fuels enables use of energy sources that are renewable, secure, and enable global climate change mitigation. Most feedstocks suitable for gasification contain small amounts of fuel-bound nitrogen (FBN), which converts during gasification to five major products: hydrogen cyanide (HCN), ammonia (NH3), char-bound nitrogen (char N), tar-bound nitrogen (tar N), and diatomic nitrogen (N2). Of these products, NH3 and HCN are of the greatest concern because they primarily convert into NO x species if the syngas is burned for heat or power applications. They are also potent catalyst poisons during chemical synthesis. Yields of NH3 and HCN from FBN vary broadly as a result of differences in feedstock properties and gasification conditions. To better understand nitrogen chemistry during gasification, switchgrass was gasified in a bubbling fluidized bed gasifier at 750 °C, while the equivalence ratio (ER) was varied from 0 to 0.4. The results demonstrated that major portions of the FBN can remain bound in the char and tar. This nitrogen can be released to the gas phase as the ER increases, leading to increased yields of NH3 and HCN.