Char retention

Solutions of these fire retardant formulations are impregnated into wood under fliU cell pressure treatment to obtain dry chemical retentions of 65 to 95 kg/m this type of treatment greatly reduces flame-spread and afterglow. These effects are the result of changed thermal decomposition reactions that favor production of carbon dioxide and water (vapor) as opposed to more flammable components (55). Char oxidation (glowing or smoldering) is also inhibited. 

This is derived from the retention of carbon in char consequent upon prior dehydrogenation (Table VI) and is considered to be the maximum estimate of the sum of the aromatic and hydroaromatic carbon. Individual determinations of aromatic and hydroaromatic carbon also lead to a similar assessment (Table II). 

Experimental data were obtained on the carbonaceous residue (char), and sulfur distribution was calculated for the solid and gaseous products from the pyrolysis of model compounds. Sharp differences were observed in the quantity of char and the sulfur distribution for the different substances studied. The quantity of volatile matter varied from 21 to 43%. The sulfur retained by the char varied from 21 to 74% of the total present in the compound pyrolyzed (see Table I). The raw data show a possible relationship between the volatile matter and sulfur retention which indicates that as volatile matter decreases, sulfur retention generally increases (Table I). Neither structural features nor the molecular size of the various model compounds appear to have a significant relationship to sulfur distribution. 

Values of Pt calculated from Equation 2 also appear in Table I, and the relationship between Pt and experimental values of sulfur retained is presented graphically in Figure 3. The data indicate that sulfur retention by the char increases as the value of Pt decreases. 

Values of Pt were therefore calculated from Equation 1 wherein Ph,s = Pt for blended materials. The calculated values can be seen in Table II, and the graphical relationship between Pt and sulfur retained in the char can be seen in Figure 3. It is again apparent that sulfur retention increases as Pt decreases. The curve obtained from the data on the model compounds and blended materials can be used to predict the sulfur retention from the analytical data of the material pyrolyzed. 

Figure 2 shows the results of the pyrolysis experiments conducted with the Spanish lignite at 750-960°C at residence times of 0.52-0.72 sec. It is seen that under the pyrolysis conditions used, 60 - 70% of the sulfur in this coal appears in the gaseous products as H2S, COS, and CS2. As in the previous sulfur study (1), the principal sulfur gaseous product at all temperatures is H2S, with some CS2 formed at T >840°C. The CS2 is apparently formed at the expense of the H2S, by any of several reactions H2S may react with the carbon of the coal and/or the methane evolved in the pyrolysis of the coal to form CS2- A small amount of COS is detected at all temperatures trace amounts of SO2 are also detected. Moreover, the total sulfur yield appears to reach a maximum about 900°C. The decrease in sulfur volatilization as pyrolysis temperature is increased above 900°C is attributed to sulfur retention in the char due to the reaction of H2S with coke or char to form more stable thiophenic structures (2). GC/MS analysis of the tars (diluted to 10 ml) from the pyrolysis at 750 and 850°C did not reveal any sulfur-containing structures. Tars from the pyrolysis at 900 and 950°C, however, contain dibenzothiophene. 

The predominant mode of action of phosphorus-containing flame retardants (both additives and reactives), when present in thermoplastics or thermosets, is considered to be in the condensed phase. Generally, as with cellulose, flammable gas generation is reduced and char formation is promoted. In some cases, the char cohesiveness is also enhanced. The retention of phosphorus in the chars in... 

Figure 1. Retention of Acridine Char Nitrogen as a Function of Burnoff in Air at 773 K...

Acridine char nitrogen, retention as function of burnoff, 307/, 308/ Advection fluxes, calculation, 41-43 Aerosol particle size distribution, molecular clusters, 317 Aerosol scavenging pathway, acetic and formic acid formation, 223 Aerosol species, transformation over the western Atlantic, 52 Aerosol sulfate airborne determination, 298 See also Sulfate... 

It (1 ) deals with the derivation of relations giving the particle size distribution in the bed, overflow, and carryover streams and their respective weights. This theory will be extended to include the effects of particle growth or shrinkage (Z>1 or Z<1). For typical combustion of char containing sulfur followed by sulfur dioxide absorption by limestone, relations will be derived to determine the extent of sulfur retention. The reaction, carryover, and overflow rates will be evaluated with particular attention to their dependence on Z. 

Once the volatile products escaped from wood, the N2 flow swept them from the hot zone to the exit in less than 1 s. In this study, 80 s was the minimum total pyrolysis time at 450 to 500 C and 200 s at 500 C The combination of 80 or 200 s and 450 °C led to the desired result that is high retention of As in char along with a high oil yield At longer pyrolysis times such as 1800 and 3600 s the products in the hot-zone undergo... 

The interaction of phosphorus and nitrogen compounds produces a more effective catalyst for the dehydration because the combination leads to further increases in the char formation and greater phosphorus retention in the char 43, 71-73). This result may be caused by the cross-linking of the cellulose during pyrolysis through... 

Residence time for supercritical water oxidation systems may be as short as several minutes at temperatures of 600 to 650°C. More than 99.9 percent conversion of EPA priority pollutants such as chlorinated solvents has been achieved in a pilot-scale plant with retention time less than 5 minutes. The system is limited to treatment of liquid wastes or solids less than 200 microns in diameter. Char formation during reaction may impact the oxidation time of the organics, while separation of inorganic salts during the process may be a problem. Typical materials for the reactor are Hastelloy C-276 and Iconel 625 (high nickel alloys), which can withstand high temperatures and pressmes and the corrosive conditions. 

Many investigators place value on retentivity data. Retentivity cannot be defined exactly but it refers to the phenomenon that when a char has taken up a vapor to capacity from a relatively strong concentration, a certain proportion of this adsorbed vapor can be removed with ease in a current of air while the remainder is retained more firmly. Data retentivity, as given by different investigators, are comparable only if obtained under corresponding conditions of time, temperature, and velocity of air stream.20,21 Chaney13 describes an accelerated routine procedure. In this,... 

These data emphasize the considerable range of char conversion and effluent gas compositions that could be obtained simultaneously by varying hydrogen char ratios and retention times. Only a few minutes retention time was required to convert one-fourth to one-third of the char to methane under the conditions used. For equal retention times, more char was converted at 1500 p.s.i.g. and 900°C. than was converted at 3000 p.s.i.g. and 700°C. hence, temperature had a greater influence than pressure on char conversion. 

Retention time of acceptor particles was measured in the continuous unit by circulation through the char bed until steady state was reached. The bed was frozen by shutting off all flows and draining it above the acceptor-char interface. Retention times were obtained from bed analysis, reed rates, and bed height. 

Features Increases permanency, moisture retention, water resist. Regulatay EDA 21CFR 175.105 DOT nonregulated SARA 311/313 nonreportable Canada DSL, EU, Australia, Japan listed Properties Grease-like char, waxy odor negligible sol. in water dens. 0.85 g/cc vise. 35 cps (140 C) drop pt. 85 C acid no. 15 flash pt. (OC) > 255 C hardness 90.0 dmm (D1321) = 100% act. 

Chem. Descrip. Polyol resin In butyl acetate Uses Polyol for high performance urethane coatings Features High solids exc. pot-llfe and dry time chars. exc. QUV gloss retention... 

Features General purpose Neoprene, greater storage stability, better processing chars., and color retention during curing than the G types Prqrerhes Creamy wh. chips Mooney vise. 42-51 (ML1+4,212 F) Toxicology TSCA listed... 

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