Wiebren de Jong

Chloride ions enhance furfural formation from D-xylose in dilute aqueous acidic solutions

Furfural production through traditional processes is accompanied by acidic waste stream production and high energy consumption. Modern furfural production process concepts will have to consider environmental concerns and energy requirements besides economics, moreover will have to be integrated within widened biorefinery concepts. In this paper, some particular aspects of the chemistry of D-xylose reaction to furfural are addressed, with the aim to clarify the reaction mechanism leading to furfural and to define new green catalytic pathways for its production. Specifically, reducing the use of mineral acids is addressed by the introduction of alternative catalysts. In this sense, chloride salts were tested in dilute acidic solutions at temperatures between 170 and 200 °C. Results indicate that the Cl− ions promote the formation of the 1,2-enediol from the acyclic form of xylose, and thus the subsequent acid catalyzed dehydration to furfural. For this reason the presence of Cl− ions led to significant improvements with respect to the H2SO4 case. The addition of NaCl to a 50 mM HCl aqueous solution gave 90% selectivity to furfural. Among the salts tested FeCl3 showed very interesting preliminary results, producing exceptionally high xylose reaction rates.

Mechanistic and kinetic aspects of pentose dehydration towards furfural in aqueous media employing homogeneous catalysis

In this paper both the mechanistic and kinetic aspects of furfural formation from pentoses in aqueous acidic media have been reviewed. Based on the reviewed literature, a comprehensive reaction mechanism has been proposed consisting of more than one route, all starting from acyclic xylose, and involving alternately 1,2-enolization, β-elimination or isomerization via 1,2-hydride shift as key steps. Those studies that employ combined acid–base catalysts, soluble halide salts and trivalent cations in aqueous solutions appear to be most promising. Next, a detailed overview is presented of the results of kinetic studies on furfural formation from pentoses and furfural disappearance in aqueous acidic media. Although these results span over a very wide range of both experimental conditions and different kinetic models employed, an attempt has been made to present the published kinetic data in such a manner that it allows a global comparison. Since even in those cases where the reaction conditions seemed to be comparable, the reported kinetic constants often agree merely in the order of magnitude, thus, the validity of most of the data presented here is restricted to the specific conditions as used by each author. Additionally, a very concise overview is included of research on direct furfural production from lignocellulosic materials. In conclusion, the intricate set of reactions accompanying furfural formation from pentoses, although appearing well established in some aspects, is yet to be fully unraveled, especially with regard to the complex set of side and loss reactions seemingly involving largely unknown reaction intermediates. Such uncertainties are reflected in the contradictory kinetic models exploited and kinetic data presented in the literature, which still prevent a common and coherent interpretation.

Coal/biomass co-gasification in a pressurised fluidised bed reactor

Biomass and coal co-gasification is performed using a 1.5 MWth pressurised bubbling fluidised bed gasifier in the framework of a 3 year multinational EU JOULE project concerning research on efficient, environmentally acceptable large scale power generation systems based on IGCC technology.

Selection and Use of Manganese Dioxide by Neanderthals.

Several Mousterian sites in France have yielded large numbers of small black blocs. The usual interpretation is that these ‘manganese oxides’ were collected for their colouring properties and used in body decoration, potentially for symbolic expression. Neanderthals habitually used fire and if they needed black material for decoration, soot and charcoal were readily available, whereas obtaining manganese oxides would have incurred considerably higher costs. Compositional analyses lead us to infer that late Neanderthals at Pech-de-l’Azé I were deliberately selecting manganese dioxide. Combustion experiments and thermo-gravimetric measurements demonstrate that manganese dioxide reduces wood’s auto-ignition temperature and substantially increases the rate of char combustion, leading us to conclude that the most beneficial use for manganese dioxide was in fire-making. With archaeological evidence for fire places and the conversion of the manganese dioxide to powder, we argue that Neanderthals at Pech-de-l’Azé I used manganese dioxide in fire-making and produced fire on demand.

Gas turbine combustor for biomass derived LCV gas, a first approach towards fuel-NOx modelling and experimental validation

The section Thermal Power Engineering of Delft University of Technology operates a 1.5 MW pressurised fluidised bed gasification rig, including a hot gas cleaning unit and a pressurised downscaled Alstom gas turbines combustor. Regarding the combustion of low calorific value (LCV) gas, experiments are done to validate models describing turbulent steady state combustion. In this paper biomass derived LCV gas combustion experiments are described. The heating value of the gas was in the range of 2.5?4 MJ/mn3 and the process pressure was 3?8 bar. In all experiments, good combustion efficiency was observed. NOx formed, resulted from NH3 fueltextitnitrogen conversion to NOx was in the range of 10?60

Study of the behaviour of a catalytic ceramic candle filter in a lab-scale unit at high temperatures

Solid particles and tars are among the non-desirable products of synthesis gas produced during biomass gasification. Removal of fly ashes is necessary in order to comply with emission limits as well as avoid their deposition in downstream units. Condensation of tars, on the other side, can cause clogging. A catalytic hot gas filter can remove both solids and tars, when operating at temperatures as high as 850°C. Catalytic hot gas filter elements are under development in order to solve this issue.A lab-scale filtration unit has been designed and constructed at Delft University of Technology. The unit contains one ceramic hot gas filter candle which is made of a SiC porous structure coated with a mullite membrane. The integration of a Nickel-based catalyst layer allows the dual function of particle filtration and tar cracking. The filter vessel is part of a set-up that is equipped with a tar evaporator and a pre-heater, both located upstream of the filter unit.This paper presents the results of the first set of experimental tests that have been performed with this unit. A dust-free model gas was used and consisted of a mixture of CO (14%), CO2 (14%), H2 (7%), CH4 (5%), and varying concentrations of N2 (30, 40, 50%) and H2O (30, 20, 10%). Naphthalene (varying concentrations up to 9 g/Nm3) was adopted as model compound in order to study the catalytic conversion of heavier hydrocarbon species to H2. A gas face velocity of 2.5 cm/s and 3 cm/s was selected for tests performed at atmospheric conditions and at operating temperatures varying between 700 °C and 850 °C. The pressure drop through the filter candle was continuously monitored during the process. The gas composition was measured upstream and downstream of the filter unit by means of an on-line micro-GC, while naphthalene concentration was attained with the SPA method.The following findings were obtained: higher naphthalene conversion with increasing temperatures and better conversion at any temperature with lower concentrations. Tests at 850°C and 30 vol% H2O produced a conversion of 99.4% with 2.5 g/Nm3 while 98.5% with 7.8 g/Nm3. Experiments with higher steam content showed higher conversion values. Methane concentration was also affected thus indicating that reforming reactions took place as well. Low toluene concentration was detected as a product of the reactions while no benzene was identified.

Experimental Investigation on a Newly Designed Combustor for LCV Gas

Air blown gasification of biomass is one of the most promising and efficient ways to use alternative energy sources like organic matters from waste and biomass for producing LCV (Low Calorific Value) gas. This fuel is best used in highly efficient gas turbines (or combined cycles). The section Thermal Power Engineering of Delft University of Technology operates a 1.5 MW pressurized fluidized bed gasification rig, including a hot gas cleaning unit with the ability to test pressurized combustors designed and optimized for LCV gas combustion. In this paper, the results of six combustion experiments with the 1 MW non-swirling TUD (Technical University Delft) combustor are presented and compared with the results of experiments performed with a 1.0 MW swirling combustor designed by ALSTOM Power UK. The primary and cooling airflow of the TUD combustor can be altered independently for optimization purposes. The experiments were performed at 3.5 and 5.0 bara and stable combustion was accomplished with gas of heating values (HHV) ranging from 2.7 to 3.8 MJ/m3 n . Combustion efficiencies of the TUD combustor were well above 99.9% and emissions of CO were within the EU standards, except for one experiment where Minphyl as catalyst was added to the gasifier fuel. A high percentage of primary air was used in this experiment. Emissions of NO were outside the EU standards (100 ppm) for four of the six experiments because of the high fuel bound nitrogen (FBN) concentrations in the fuel gas. The FBN conversion rate ranged from 98% to 39% for FBN concentrations ranging from 238 to 2238 ppm.© 2003 ASME

Low Fuel-NOx Combustion of Synthetic LCV Gas

Fuel NOx is one of the main issues related to the combustion of biomass derived Low Calorific Value (LCV) Gas. The high NOx emissions accompanying the combustion of that fuel in gas turbines or gas engines are compromising the CO2 neutral character of biomass and are a barrier towards the introduction of this green energy source in the market. The reduction of NOx emissions has been one of the main preoccupations of researchers in the LCV gas combustion field. Although, much has been achieved for thermal NOx which is caused mainly by the conversion of the nitrogen of the air in high temperature regions, less work has been devoted to the reduction of fuel NOx , which has as a main source the fuel bound nitrogen FBN, namely ammonia in case of biomass. Reducing the conversion of the FBN to NOx has been the main issue in recent research work. However, fuel NOx could be reduced significantly applying methods; like washing the gas in a scrubber prior its entrance to the combustor, and SNCR or SCR methods applied at the exhaust. But those solutions stay very expensive in terms of polluted waste water and catalyst cost. In this paper, the approach is to reduce the conversion of FBN to NOx inside a newly designed combustor. The idea is to optimize the combustion process ending up with the lowest possible conversion of FBN to NOx . The LCV gas used in the experiments described in this paper is made by mixing CO, CO2 , H2 , natural gas and N2 with proportions comparable to those of the real LCV gas. This gas is then doped with NH3 to simulate the FBN. In this paper the conversion ratio of FBN to NOx versus the FBN concentration is presented. Furthermore, the system is investigated in terms of the effect of CH4 concentration on the conversion of FBN to NOx . And measurements along the combustor axis were performed with a traversing probe where temperature and important emissions along the axis were measured. In all the experiments described in the paper, The LCV gas has an HHV (High Calorific Value) ranging from 4 to 7Mj/nm3 . The newly designed combustor contains an embedded inner cylinder. In these experiments presented are without that embedded cylinder. The purpose of the current experiments is to be compared to the later experiments with the insert in order to define clearly the effect of the inner cylinder. Furthermore, this arrangement, i.e. without the insert, gave us the opportunity to traverse the combustor by a probe and to measure temperature and species profiles, which is of a great importance in defining the key parameter controlling the conversion of NH3 to NOx .Copyright

Measurements Inside a Bluff-Body Stabilized Gas Turbine Combustor for Application of Pressurized Biomass Derived Low Calorific Value Fuel Gas and Comparison of the Results

In our previous paper [Van der Wel (2005)] the main results about combustion efficiency and emissions have been presented of experiments with a medium size (TUD) combustor of 1.5 MWth operated on low calorific value (LCV) fuel gas with heating values (HHV) ranging from 1.88 to 4.64 MJ/m3 n (50 to 120 Btu/scf). In the current paper the experiments are presented where the amount of primary and secondary air are varied in order to examine the effects of stoichiometry on the combustors performance and these results are compared with a previously tested downscaled typhoon combustor from ALSTOM. Also, results are presented with respect to traversing measurements behind the primary zone of the TUD combustor. It was found that the NH3 to NO conversion decreases at increasing pressure and that higher concentrations of methane in the fuel result in higher ammonia to NO conversions. Also it was observed that the swirling typhoon combustor seemed to have less problems achieving lower ammonia conversions than the bluff body stabilized TUD combustor.Copyright