In thermal cracking, use is made of severity factors to characterize the process conditions and to relate these in a concise way to the product slate. A fundamental, generalized severity factor, kV,IF,, based upon the equivalent reactor volume concept is derived from the model equations representing the cracking coil operation.It relates a modified exit conversion in a unique way to operating conditions (temperature and pressure profile, steam dilution ratio), no matter what the feedstock may be. In commercial units temperature and pressure profiles are in general insufficiently defined, so that only easily accessible exk yields can be used as a severity factor. From an inspection of a large data set on naphtha, kerosene, and gas oil cracking, it follows that the C3to propylene yield ratio is the best measure of the severity of operation.Evaporation and Wling heat-transfer coefficients are presented for thin water HLms flowing over the outsii of horizontal, electrically heated brass tubes. Tests were conducted with a 5.08-cm-dlameter smooth tube, a 5.08-cmdlameter clrcumferentially grooved tube, and a 5.08-cm-diameter axially grooved tube. Both local and average heat-transfer data were obtelned for nonboillng and bolilng conditions correspondi to feed-water temfrom 1.16 to 3.79 cm3/s per centimeter length of tube. Correlations of the average heat-transfer coefficients for nonboiling and boiling conditions were developed and compared. The results indicate that both enhanced tubes provlded hlgher heat-transfer coefficients than the smooth tube.peratures ranglng from 49 to 127 O C end heat-flux values ranging from 30 000 to 80 000 W/m 9 . Flow rates ranged
The product distribution and the kinetics of the thermal cracking of kerosene were investigated in a pilot plant under conditions of residence time, temperature, total pressure, and dilution close to those used in industrial operation. The influence of feed composition, total pressure, and inlet partial pressure on the product distribution were determined. Kinetics of the cracking of individual components in the kerosene mixture were calculated.
An Escherichia coli catalyst with tyrosine ammonia lyase activity (TAL) has been stabilized for repeated use in batch conversions of high tyrosine solids to p-hydroxycinnamic acid (pHCA). The TAL biocatalyst was stabilized by controlling the reaction pH to 9.8 +/- 0.1 and immobilizing the cells within a calcium alginate matrix that was cross-linked with glutaraldehyde and polyethyleneimine (GA/PEI). We found a GA range where the bead-encapsulated TAL was not inactivated, and the resulting cross-linking provided the beads with the mechanical stability necessary for repeated use in consecutive batch reactions with catalyst recycle. The GA/PEI calcium alginate TAL catalyst was used in 41 1-L batch reactions where 50 g L(-1) tyrosine was converted to 39 +/- 4 g L(-1) pHCA in each batch. The practical usefulness and ease of this process was demonstrated by scaling up the TAL bead immobilization and using the immobilized TAL catalyst in four 125-L bioconversion reactions to produce over 12 kg of purified pHCA.
Caustics are used in petroleum refining to remove hydrogen sulfide from various hydrocarbon streams. Spent sulfidic caustics from two Conoco refineries have been successfully biotreated on a bench scale, resulting in neutralization and removal of active sulfides. Sulfides were completely oxidized to sulfate by Thiobacillus denitrificans. Microbial oxidation of sulfide produced acid, which at least partially neutralized the caustic.
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