Chars In Air Research Articles

Catalytic influence of mineral compounds on the reactivity of cellulose-derived char in O2-, CO2-, and H2O-containing atmospheres

The catalytic effects of mineral compounds on the conversion of a biomass-derived char in air- and oxyfuel-related atmospheres were investigated by thermogravimetric analysis at atmospheric pressure. The applied char originated from the hydrothermal carbonization (HTC) of cellulose followed by pyrolysis at 1073 K and subsequent mixing with 20 wt% of minerals by grinding to achieve tight contact. The reactivities of the mineral-loaded HTC chars were evaluated based on isothermal experiments in O2-, CO2-, and H2O-containing atmospheres as a function of their composition applying a magnetic suspension balance. The reactivity sequence K2CO3 > Na2CO3 ≫ Fe2O3 > CaO > MgO ≥ mineral-free was derived consistently for char oxidation in O2/inert as well as for char gasification in diluted H2O and CO2 mixtures. In addition to this qualitative assessment, the kinetic experiments were first modelled based on a simple global nth-order power-law rate expression. Then, the more complex Carbon Burnout Kinetics (CBK/G) model and the PoliMi model were applied. All three modeling approaches enabled a systematic quantification of the catalytic effects and led to a comparable lowering in the apparent activation energy. In combination with the kinetic parameters determined for the mineral-free char, the lowered apparent activation energies specific for the applied mineral and atmosphere facilitate the implementation of catalytic effects on the conversion of biomass-derived char into combustion models.

Novel metal complexes as potential synergists with phosphorus based flame retardants in polyamide 6.6

Aluminium (AlW), tin (II) (SnW) and zinc (ZnW) tungstates were previously found to increase char formation in polyamide 6.6 (PA66), but have never before been studied for their potential as synergists when present with phosphorus-containing (PFRs) flame retardants. We investigate this gap in the scientific knowledge in this publication. Tungstate-PFR interactions of PA66 composites were investigated by thermal analysis, limiting oxygen index (LOI), UL94, cone calorimetry and evolved gas analysis (TGA-FTIR).Of the three tungstates, AlW in the presence of aluminium diethylphosphinate (AlPi) or a mixture of AlPi and melamine polyphosphate (MPP), promotes the highest level of flame retardancy in terms of a balance of high LOI, V-rating and TGA residual char in air at 500 °C and reduction in cone calorimetric peak heat release rate (RPHRR = 80%). This observation has been related to AlW having the highest Lewis acidic properties. While zinc tungstate displays the lowest levels of interaction with either PFR, it shows significant smoke suppressant properties.Elemental analysis of cone calorimetric chars suggests that while some loss of phosphorus occurred from SnW/AlPi/MPP-containing composites, most likely via volatile diethyl phosphinic acid formation, nearly 10% reduction also occurred in the Sn/W molar ratio indicating some volatilisation of tin. The TGA (in air)-FTIR results for carbon dioxide, ammonia and hydrocarbon fuel species evolution enabled discussions of the effect that each tungstate had on the flame retardant mechanisms operating.

In situ experimental and modeling study on coal char combustion for coarse particle with effect of gasification in air (O2/N2) and O2/CO2 atmospheres

This study applied the high temperature stage microscope to investigate coal char combustion in air (O2/N2) and O2/CO2 (volume, 21%/79%) atmospheres with the effect of gasification. A reaction front combustion model was also proposed, coupled with effect of char gasification, to predict the key parameters of char combustion in the O2/CO2 atmospheres. The combustion process and particle evolution of coarse chars were observed and measured to calculate the carbon conversion. Experimental results showed that the burnout time of the char particle in the O2/CO2 atmosphere in the was prolonged about 20–25%, compared to the burnout time of chars in air. The overall reaction rates of char particles in the O2/CO2 atmosphere were lower than the rates in the air for different particle sizes. In addition, reaction rates from model prediction showed good agreements with the experimental data for different particle sizes both in the air and O2/CO2 atmospheres, which proved the reaction front combustion model was applicable for the char combustion in this study. The reaction front combustion model also predicted that the reaction front decreased with burning time and mass consumption of char particle. For the char combustion in the O2/CO2 atmosphere, the gasification with CO2 absorbed part of the combustion heat or radiation heat and caused lower particle temperatures and heat fluxes for different particle sizes. The proposed combustion model also predicted that although the effect of the gasification reaction was dominant at the beginning of combustion and then reduced, the conversion of particles was hindered compared to the combustion of char in air.

Simple pyrolysis experiments for the preliminary assessment of biomass feedstocks and low-cost tar cracking catalysts for downdraft gasification applications

The pyrolysis behaviour of beech wood, two rice husk variants from Brazil (BRH) and Thailand (TRH) and a solid waste water treatment residue from textile manufacture (TIR) were investigated using a lab-scale, 2-stage fixed-bed reactor at 773 K. Char yields increased and volatile yields decreased with increasing ash content. The TRH released 40% less tar than the BRH which was attributed to the substantially higher potassium content of the Thai species. The combustion reactivity of the TRH char in air at 773 K was similar to the BW char and almost double the reactivity of the BRH and TIR chars. The BW and TRH chars had a greater volume of macropores indicating that char combustion occurs predominantly through the growth and extension of the macroporous pore network. A different trend was observed for the char gasification reactivity with CO2 at 1173 K. The Ca and Mg content of the chars were found to have a more important catalytic role in the char gasification reactions with CO2.The effect of exposing volatile products from beech wood pyrolysis to elevated temperatures (973–1173 K) and sand beds containing calcined limestone or dolomite in a simulated downdraft gasification environment was also investigated. Tar yields decreased after exposure to elevated temperature and calcined limestone or dolomite. Tar cracking favoured the production of CO. CO yields were between 22 and 23 wt% at 1173 K. Calcined dolomite was slightly more effective at cracking tar than calcined limestone, eliminating 98 wt% of the tar at 1173 K.

Degradation of p-Nitrophenol by Lignin and Cellulose Chars: H2O2-Mediated Reaction and Direct Reaction with the Char.

Chars and other black carbons are reactive toward certain compounds. Such reactivity has been attributed to reduction of O2 by persistent free radicals in the solid to H2O2, which then back-reacts with the solid to generate reactive oxygen species (ROS; especially HO•). We studied the decomposition of p-nitrophenol (PNP) by pure lignin and cellulose chars aged in moist air or a vacuum at room temperature for up to a month. In air, the chars chemisorbed oxygen, a portion of which was liberated as H2O2 when the char was submerged in water. The evolved H2O2 was simultaneously decomposed by the char. PNP reacted predominantly in the sorbed state and only reduction products (phenol, catechol) were identified. Aging the char in air sharply (within hours) reduced H2O2-producing capacity and free radical concentration, but more gradually reduced PNP decay rate over the month-long period. PNP decay was only modestly suppressed (12-30%) by H2O2 removal (catalase), and had little effect on the free radical signal (<6 radicals annihilated per 1000 PNP reacted). Contrasting with previous studies, the results show that direct reaction of PNP with char predominates over H2O2-dependent reactions, and the vast majority of direct-reacting sites are nonradical in character. Nonradical sites are also responsible in part for H2O2 decomposition; in fact, H2O2 pretreatment depleted PNP reactive sites. Lignin char was generally more reactive than cellulose char. The Fe impurity in lignin played no role. The results are relevant to the fate of pollutants in black carbon-rich environments and the use of carbons in remediation.

Durable flame retardant finishing of cotton fabrics with halogen-free organophosphonate by UV photoinitiated thiol-ene click chemistry

Cotton fabrics are treated with a synthetic non-halogenated organophosphorus flame retardant by UV photoinitiated thiol-ene click chemistry. Thiol reactive precursors on cotton surface were prepared by 3-Mercaptopropyltriethoxysilane. The flame retardant property has been tested with different concentrations of flame retardant treatment (i.e., wt 2%, 5%, and 8%) by limited oxygen index (LOI) and vertical burning tests and maintained after 30 washing cycles, which was improved with concentration increases. Thermogravimetric analysis showed that the treatment greatly enhanced the char forming ability of cellulose and the highest residue was left as much as 48.1% char in nitrogen and 19.8% char in air after heating to 600°C, which obviously more than those of untreated fabric. Scanning electronic microscopy (SEM) revealed that the weave structure and fiber shape in all treated fabrics were preserved. These results demonstrate that UV photoinitiated thiol-ene click chemistry is a facile method for imparting cotton fabric with durable flame-retardant properties.

An Experimental Study of Temperature of Burning Coal Particle in Fluidized Bed

The purpose of this study was to investigate the temperature of coal particle during combustion in fluidized bed (FB). It is necessary to know the coal particle temperature in order to predict kinetics of chemical reactions within and at the surface of coal particle, accurate NOx and SO2 emission, fragmentation, attrition, the possibility of ash melting, etc. The experimental investigations were conducted in order to obtain the reliable data on the temperature of particle burning in the FB. A method using thermocouple was developed and applied for measurements. Thermocouple was inserted in the center of the particle shaped into spherical form with various diameters: 5, 7, 8, and 10 mm. Two characteristic types of low-rank Serbian coals were investigated. Experiments were done at the FB temperature in the range of 590−710 °C. Two types of experiments were performed: (i) combustion using air as fluidization gas and (ii) devolatilization with N2 followed by combustion of obtained char in air. The temperatu...

Thermal decomposition of chlorinated poly(vinyl chloride) (CPVC)

AbstractChlorinated poly(vinyl chloride) (CPVC) shows reductions in flammability and smoke production over PVC. The thermal decomposition of pure CPVC (without stabilizer or lubricant) was studied by dynamic thermogravimetric analysis (TGA) at heating rates from 5 to 100°C/min in atmospheres of nitrogen, air, and oxygen. In each case, a two‐step decomposition was observed similar to that for PVC where dehydrochlorination is followed by pyrolysis/oxidation of the carbonaceous residue. The rate of dehydrochlorination was dependent on atmosphere, occurring slightly slower in nitrogen than in air, and slightly more quickly in oxygen than in air. The decomposition of the residual char was clearly dependent on the conditions in which it was formed. Under dynamic conditions, chars formed at high heating rates appeared more resilient to oxidative degradation than those formed more slowly. However, when chars were formed by heating at different rates and then held at 500°C, the char formed at the slowest heating rate was the slowest to be oxidized. The uptake of oxygen by the char appears to be rate‐limiting. At low heating rates char oxidation is similar in both air and oxygen. As the heating rate is raised, the rate of mass loss of char in air becomes progressively closer to that in nitrogen until at 100°C/min they are almost identical. This work is important to the understanding of the decomposition and flammability of CPVC and flame‐retarded CPVC, where the char formation is one of the flame‐retardant mechanisms.

The effect of coal particle size on pyrolysis and steam gasification

For future power generation from coal, one preferred option in the UK is the air-blown gasification cycle (ABGC). In this system coal particles sized up to 3 mm, perhaps up to 6 mm in a commercial plant, are pyrolysed and then gasified in air/steam in a spouted bed reactor. As this range of coal particle sizes is large it is of interest to investigate the importance of particle size for those two processes. In particular the relation between the coal and the char particle size distribution was investigated to assess the error involved in assuming the coal size distribution at the on-set of gasification. Different coal size fractions underwent different changes on pyrolysis. Smaller coal particles were more likely to produce char particles larger than themselves, larger coal particles had a greater tendency to fragment. However, for the sizes investigated in this study ranging from 0.5 to 2.8 mm, the pyrolysis and gasification behaviour was found not to vary significantly with particle size. The coal size fractions showed similar char yields, irrespective of the different char size distributions resulting from pyrolysis. Testing the reactivity of the chars in air and CO 2 did not reveal significant differences between size fractions of the char, nor did partial gasification in steam in the spouted bed reactor. From the work undertaken, it can be concluded that pyrolysis and gasification within the range of particle sizes investigated are relatively insensitive to particle size.

Gasification of biomass chars in air — effect of heat treatment temperature

Gasification of biomass chars in air — effect of heat treatment temperature

Gasification of Biomass Chars in Air − Effect of Heat Treatment Temperature

Three biomass materialscoir dust (CD), wheat straw (WS), and potato pulp (PP)were pyrolyzed under nitrogen, and the resulting chars were gasified in air at 400 °C. In all cases, gasification rate of the chars showed the “normal” dependence on heat treatment temperature (HTT), i.e., a decrease with increasing HTT, only up to a certain value of HTT (500, 550, and 750 °C for CD, WS, and PP, respectively), above which the rate dramatically increased. This contrasts with the monotonic decrease in reactivity reported for coal chars. The unusual HTT effect is suggested to be due to a change in the chemical state of the indigenous potassium species at the HTT inflection temperature.

Mathematical modeling of fluidized bed combustion 3. Simultaneous combustion of char and combustible gases

The difficulties involved in developing system models for fluidized bed combustion which include details of the release of volatiles from coal and the subsequent simultaneous combustion of volatiles and residual char are well recognized. In previous papers, the heterogeneous combustion of char in air–fluidized beds, and the homogeneous combustion of combustible gases injected or pre–mixed with the fluidizing air were considered individually as parts of the more complex problem. The simultaneous combustion of char and propane (premixed with air used to fluidize the bed) is considered in this paper. The hydrodynamic description of the bubbling fluidized bed, as in our previous work, is based on the three–phase model. The non–isothermality of the bed resulting from the gas–phase combustion reactions is taken into account through inclusion of an energy balance for the bubble phase. The effect of the variation in superficial gas velocity — on bubble properties and cross–flow — is included through an overall mass balance. Calculations are compared with experimental data on the combustion of: (a) char; (b) propane; and (c) simultaneous combustion of char and propane. The agreement, in all cases, is very good. Particularly encouraging is the agreement with data on the variation of CO, CO 2 and O 2 concentrations in the freeboard with time resulting from the batch combustion of char in sand fluidized by air/2.5 vol.% propane. This agreement suggests that the model provides a good representation of the dynamics of the combustion of char as well as combustible gases. The model is then used to investigate the interaction of heterogeneous and homogeneous combustion reactions within the bed.

Heat treatment of rockrose char in air. Effect on surface chemistry and porous texture

The surface chemistry and the porous texture of activated carbons prepared from a charred product (C jex-600), which was obtained from rockrose ( Cistus ladaniferus, L.) extracted previously into petroleum ether, were studied. Activated carbons were prepared by heating C jex-600 between 350 and 850 °C in air to 40% burnoff. Methods of chemical analysis and FTIR spectroscopy as well as techniques of gas adsorption (N 2, 77 K; CO 2, 298 K), mercury porosimetry, and density measurements were applied. In the FTIR study of the samples, the presence of surface olefinic CC double bonds, aromatic rings, and oxygen functional groups was detected. Carbonyl groups were only found to a significant extent in C jex-600 and in the activated carbon prepared at 350 °C. The microporosity developed with increasing temperature between 350 and 750 °C. At higher temperatures, pore narrowings occurred. The gasifying action of air was strongly dependent on the removal of nonorganized matter from C jex-600 and on the pore size. The reaction time needed at 850 °C in air to reach burnoff 40% was less than a half of that at 350 °C, and was comparable to the times required in CO 2 and steam under the same experimental conditions.

Reactivity and ignition behaviour of residual chars from coal extraction

The reactivity, ignition behaviour and porous structure of the residual chars obtained from extraction of a bituminous coal were investigated. The porous structure of the samples was evaluated by CO 2 adsorption. The ignition temperature of the original coal and residual chars in air were determined, and the relationship between these temperatures and the surface area was discussed. The samples were also gasified by CO 2, and temperatures corresponding to a certain value of the reaction rate constant were compared with the ignition temperatures.

Synthesis, characterization, and platinum-catalyzed cross-linking of 1,4-bis(1-methyl-1-silacyclobutyl) benzene, co-oligo(1-silacyclobut-1-ylidene-1,4-phenylene), and co-oligo(1-silacyclobut-1-ylidene-4,4?-diphenylene)

1,4-bis(1-Methyl-1-silacyclobutyl)benzene (I) has been prepared by the reaction of 1-chloro-1-methyl-1-silacyclobutane with the di-Grignard reagent prepared fromp-dibromobenzene. In a similar manner, co-oligo(1-silacyclobut-1-ylidene-1,4-phenylene) (II) and co-oligo(1-silacyclobut-1-ylidene-4,4′-biphenylene) (III) have been prepared by condensation oligomerization between 1,1-dichloro-1-silacyclobutane and the di-Grignard reagents prepared fromp-dibromobenzene and 4,4′-dibromobiphenyl, respectively. These have been characterized by1H,13C, and29Si NMR as well as FT-IR and UV spectroscopy. The molecular weight distributions of these co-oligomers have been determined by GPC. Their thermal stabilities have been evaluated by TGA. Thermal degradation of these co-oligomers in nitrogen gives high (60%) char yields. The stability of these chars in air has been determined. TheTg's of these co-oligomers have been measured by DSC. Platinum-catalyzed ring opening of the silacyclobutane rings ofI,II, andIII cross-links these to thermoset materials. The bending moduli (logE′), tan δ, andTg's of these materials have been determined by DMTA. The dielectric constant and dissipation factor of cross-linkedII are reported.

A general method for determining chemical kinetic parameters during ignition of coal char particles

A new viewpoint is presented that the activation energy, E, is independent of coal type and only varies with the temperature of particle, but the frequency factor of coal char, k 0, ch, varies with coal type. We have determined that E = 152 kJ/mol (36.3 kcal/mol), which is a constant in oxidation of any kind of coal char in air during ignition. The relationship between k 0, ch and coal type, which is also applicable to any kind of coal, is presented. These are different from the previous references in which E and k 0, ch all vary with coal type, but no general rules have been found. A new dimensionless number, Fz, which is used to indicate the ignition characteristics of coal char, is also presented. Fz depends only on the proximate analysis of coal and reflects the ignition property in a combined way, so that Fz is called the ignition index of coal. It is a very useful parameter for engineers and operators to use in predicting the ignition characteristics of different types of coals.

Behaviour of Ag, Cu and Ag-Cu catalysts in the gasification reaction of a lignite char in air. Effect of SO 2 on these catalysts

The effect of several Ag, Cu and bimetallic Ag-Cu catalysts have been studied on the gasification reaction of a lignite char in dry air. In the bimetallic catalysts, the existence of alloy particles have been detected by SEM. The reactivity of the char with the bimetallic catalysts is higher than the addition of those obtained for the pure metals with the same metal amounts. The effect of SO 2 is to reduce the reactivity of the char in the catalysed reactions. An explanation for this phenomenon is given. The presence of Cu in Ag increases the resistance of some bimetallic catalysts to poisoning with SO 2.

153. Formation of stable oxygen complexes during the gasification of char in air at 648k

153. Formation of stable oxygen complexes during the gasification of char in air at 648k

Reactivity of heat-treated coals in steam

Reactivities of seventeen 40 × 100 mesh (U.S.) coals charred to 1000 °C have been measured at 910 °C in 0.1 MPa of a N 2H 2O mixture containing water vapour at a partial pressure of 2.27 kPa. Char reactivity decreases, in general, with increasing rank of the parent coal. The chars show a 250-fold difference in their reactivities. Results suggest that gasification of chars in air, CO 2 and steam involves essentially the same mechanism and that relative gasification rates are controlled by the same intermediate oxygen-transfer step. Removal of inorganic matter from raw coals prior to their charring or from chars produced from raw coals decreases the reactivities of lower-rank chars, whereas reactivities of higher-rank chars increase. Addition of H 2 to steam has a marked retarding effect on char reactivity in most cases. However, in a few cases H 2 acts as an accelerator for gasification. The effect of particle size, reaction temperature and water-vapour pressure on char reactivity is considered.

Ignition characteristics of chars made in the G R & D coal-gasification and coal-to-liquids processes

Chars are obtained as by-products in the coal-gasification and coal-to-liquids processes currently in the pilot-plant stage at Garrett Research & Development Company, Inc. Ignition tests have been carried out on these chars using an ignitability test, i.e. dispersing the chars in oxygen and igniting the mixture in a hot tube. DTA—TGA determinations have also been used to study the static reactions of the chars in air. Both types of char, under roughly simulated pulverized-fuel-firing conditions probably with a significantly lower heating rate, ignited readily at temperatures equal to or lower than those required to ignite the parent coals. Partial oxidation of the char raised the ignition temperature. The heats of combustion of the chars are slightly higher than those of the parent coals and approach that of petroleum coke; the sulphur content per unit of heating value is slightly lower. They are porous materials with a particle-size distribution suitable for use as pulverized fuel. Enough volatile matter remains to give a bright flame after ignition.