Liquid product yields

Temperature and Product Yields. Most oil shale retorting processes are carried out at ca 480°C to maximize liquid product yield. The effect of increasing retort temperature on product type from 480 to 870°C has been studied using an entrained bed retort (17). The oil yield decreased and the retort gas increased with increased retorting temperature the oil became more aromatic as temperature increased, and maximum yields of olefinic gases occurred at about 760°C. Effects of retorting temperatures on a distillate fraction (to 300°C) are given in Table 6. 

Compared to amorphous silica-alumina catalysts, the zeolite catalysts are more active and more selective. The higher activity and selectivity translate to more profitable liquid product yields and additional cracking capacity. To take full advantage of the zeolite catalyst, refiners have revamped older units to crack more of the heavier, lower-value feedstocks. 

Fig. 2. Cumulative liquid product yield from thermal degradation of LDPE and HDPE at different temperature...

Indeed, this evidence suggests that the mineral matter can be beneficial in increasing both the conversion and liquid product yields. From a processing viewpoint, high mineral matter can create other problems, and a trade off between possible catalytic benefits and engineering process difficulties is necessary. 

Figure 12 clearly shows the effect of iron sulfide content of the coal on total conversion and liquid product yield during hydrogenation. The conversion increased from about 52 per cent to 70 per cent using the hot-rod reactor with no added catalyst. The yield of toluene soluble product (oil plus asphaltene) increased from about 30 to 44 per cent with total sulfur increase from 1 to 6.5 per cent. Thus it would appear that iron sulfide can act catalytically in the dry hydrogenation reaction as well as in slurried reactions (15). 

Standard cut points from ASTMD 2887 simulated distillation were used for liquid product yield calculation gasoline was defined as the C5-221°C fraction, light cycle oil (LCO) as the 221°C-343°C fraction and slurry oil as the 343°C fraction. Gasoline quality was determined by gas chromatography using PONA column and a variation of the methodology described by Anderson [1]. 

As can be seen from Table 3.2 there are some differences between the resnlts of the two pilot nnits. The gas yields are close to each other, bnt the liquid product yields and the coke yields showed differences. Bnt as was explained above, some differences between the resnlts from the two nnits were expected. The observed differences were defined as acceptable, and we were satisfied with the resnlts from cracking of atmospheric residne in the ARCO pilot nnit for this time. Later... 

Characteristics of feedstock quality, recycle ratio, and drum pressure affect the coke yield. Highly aromatic feedstock contains more carbon per feed volume and typically produces a high coke yield. Heavy coker gas oil can be recycled back into the coker feedstock to help improve the coke yield. Also, increasing the coking drum pressure tends to increase the coke yield. Typically, a higher coke yield results in a reduced liquid product yield. 

Pyrolysis is the degradation of macromolecular materials with heat alone in the absence of oxygen [45]. The development of pyrolysis processes for the production of liquids has gained much attention in the last decade because they offer a convenient way to convert low-value woody residues into liquid fuels and value-added products. Biomass pyrolysis is of growing interest as the liquid product can be stored and easily transported [46]. Pyrolysis processes yield a mixture of gas, liquid, and solid products. If pyrolysis is practiced alone, that is, without a subsequent gasification step (see Section 16.4.3), the process conditions are usually chosen to maximize liquid product yields. 

As crudes become heavier with higher levels of sulfur and metals, it becomes more difficult to produce acceptable marketable coke quality while maximizing desirable liquid product yield. This mandates that refiners and designers scrutinize physical properties, upstream processing and downstream requirements when selecting a feedstock. 

Because of the increased sulfur and impurity levels in crudes currently being processed, refiners in recent years have been considering residue desulfurization units upstream of the delayed coker. In addition to the reduction in sulfur content, residue desulfurization units also lower the metals and carbon residue contents. Due to the reduction in the carbon residue, the liquid product yield is increased and the coke yield reduced. In addition, the coke produced from a desulfurized residue may be suitable for use as anode grade coke. Table I shows the yields and product properties after coking Medium Arabian vacuum residue, with and without upstream residue desulfurization. 

Lee et al. (1996) applied step-wise crystallization fractionation to SME and reported similar results (Table 1.5). The liquid fraction had a total saturated FAME content = 5.5 wt% and crystallization onset temperature = -7.1 °C (determined by differential scanning calorimetry (DSC), compared to values of 15.6% and 3.7 °C before fractionation. Liquid product yield was also relatively low (25.5%). 

Lee et al. (1996) also investigated crystallization fractionation of SME from several solvents. Fractionation from hexane in three sequential steps with a final bath temperature of -28.4 °C resulted in a liquid product yield of 77% and total saturated FAME content of 6.0wt%. Crystallization onset temperature by DSC of the liquid fraction was -5.8 °C. Fractionation of SME from methanol solvent separated into two liquid layers as cooling temperatures approached -1.6°C. Acetone did not reduce crystallization onset temperature of the liquid fraction, and chloroform failed to form crystals at temperatures below -25 °C. Hanna et al. (1996) studied fractionation of TME... 

Indirect hydrogenation using tetralin at a reaction temperature of 410 C, a pressure of 400 bar and an overall reaction time of 2 h produced carbon conversion rates from 50 to 79 (%wt) and liquid product yields from 43 to 69 ( wt). Of the multitude of correlations established between the results of the hydrogenation tests and the micropetrographical composition of the coal types only a few examples are given. 

In another experiment conducted by Sakata [49], the degradation of PE produced liquid products which consisted of C5-C25 hydrocarbons with a yield of 70 wt%. In contrast, the degradation of PVC produced only 4.7 wt% liquid products which consisted of C5-C20 hydrocarbons while the degradation of PET surprisingly produced no liquid products. The addition of either PVC or PET to PE decreased the overall liquid product yield, however, it promoted the degradation of PE into low-molecular liquid hydrocarbon products. 

Operating the reactor at about 500°C increases the liquid product yield by about 10 weight percent, but changes the product composition, making it less suitable for use in an adhesive (see Table 3). Most of the compounds produced are 2,4 substituted phenols that only have one position available for polymerization. 

The maximums of liquid product yields (80 and 52.5 mass% in modes 1 and 2, respectively) were observed at the same dose values of about 6 kGy. However, gasoline fractions produced in the two modes considerably differed in their hydrocarbon contents. At the temperature of 375°C, isoalkane yields were comparable with those observed in the catalytic process at the temperatures above 600°C. The unusually high yields of isoparaffins in the RTC modes characterized by relatively low values of temperature and dose rate were attributed to the effects of energy transfer from paraffin to aromatic components of the hydrocarbon mixture. 

Some effort has recently been made to study copyrolysis of wood biomass and polyolefins.The effects of reaction temperature, wood-polymers mixture composition, and catalysts on the mixture s conversion into liquids and gases were established and discussed. The optimum temperature of wood—plastic mixture conversion, which corresponded to the maximum total liquid products yield, was close to 400°C. In the cohydropyrolysis processes the non-additive increase of the wood—plastic mixture conversion degree and of the distillable fractions yields took place as a result of the chemical interaction between radical fragments of wood and the thermal decomposition of polyethylene. 

---