The Preparation of Nanosized Pd/ZSM-23 Bifunctional Catalysts for n-Hexadecane Hydroisomerization by Employing PHMB as the Growth Modifi er

The development of highly effective metal-zeolite bifunctional catalysts for the hydroisomerization of n-alkanes is a paramount strategy to produce second-generation biofuels with high quality.In this study,polyhexamethylene biguanide hydrochloride(PHMB)is precisely added to the initial gel to synthesize nanosized ZSM-23 zeolites(Z23-x PH).Due to orientation adsorption and steric hindrance effects of PHMB,each sample of Z23-x PH demonstrates enhanced mesoporosity in comparison with the conventional Z23-C zeolite.Furthermore,the Bronsted acid density of the Z23-x PH samples is also signifi cantly reduced due to a reduction in the distribution of framework Al at T2-T5 sites.The corresponding Pd/23-C and Pd/Z23-x PH bifunctional catalysts with 0.5 wt%Pd loading for n-hexadecane hydroisomerization are prepared by incorporating ZSM-23 zeolites as acid supports.According to the catalytic test results,the suitable addition of PHMB can effectively promote the iso-hexadecane yield.The Pd/Z23-2PH catalyst with an n_(PHMB)/n(_Si)molar ratio of 0.002 demonstrates the highest maximum iso-hexadecane yield of 74.1%at an n-hexadecane conversion of 88.3%.Therefore,the employment of PHMB has provided a simple route for the development of highly effective Pd/ZSM-23 catalysts for n-alkane hydroisomerization.

n-Hexadecane and pyrene biodegradation and metabolization by Rhodococcus sp. T1 isolated from oil contaminated soil

The high-molecular weight polycyclic aromatic hydrocarbons(PAHs) pyrene and typical long chain alkane nhexadecane are both difficult to degrade. In this study, n-hexadecane and pyrene degrading strain Rhodococcus sp. T1 was isolated from oil contaminated soil. Strain T1 could remove 90.81% n-hexadecane(2 vol%) and 42.79% pyrene(200 mg·L^(-1)) as a single carbon within 5 days, respectively. Comparatively, the degradation of pyrene increased to 60.63%, but the degradation of n-hexadecane decreased to 87.55% when these compounds were mixed. Additionally, identification and analysis of degradation metabolites of Rhodococcus sp. T1 in the above experiments showed that there were significant changes in alanine, methylamine, citric acid and heptadecanoic acid between sole and dual substrate degradation. The optimal conditions for degradation were then determined based on analysis of the pH, salinity, additional nutrient sources and liquid surface activity.Under the optimal conditions of pH 7.0, 35 °C, 0.5% NaCl, 5 mg·L^(-1) of yeast extract and 90 mg·L^(-1) of surfactant,the degradation increased in single or dual carbon sources. To our knowledge, this is the first study to discuss metabolite changes in Rhodococcus sp. T1 using sole substrate and dual substrate to enhance the long-chain alkanes and PAHs degradation potential.

SOLUBILITIES OF CARBON DIOXIDE IN MIXTURES OF n-DECANE-n-HEXADECANE AND n-HEPTANE-TOLUENE

Solubilities of CO2 in binary mixtures of n-decane-n-hexadecane and n-heptane-toluenewere measured in a glass apparatus by a synthetic method.Henry’s constants at several temperaturesand solvent compositions were reported.While the Henry’s constants of CO2 in mixtures of decaneand hexadecane can be satisfactorily predicted by a simple linear interpolation,prediction of Henry’sconstants for CO2 in mixtures of heptane and toluene requires excess Gibbs energy of the solvent mix-tures.The standard thermodynamic functions of solution（ΔH0,ΔG0,and ΔS0）were reported.

The synergic effects of highly selective bimetallic Pt-Pd/SAPO-41 catalysts for the n-hexadecane hydroisomerization

The hydroisomerization of n-hexadecane over Pt-Pd bimetallic catalysts is an effective way to produce clean fuel oil.This work reports a useful preparation method of bimetallic bifunctional catalysts by a co-impregnation or sequential impregnation process.Furthermore,monometallic catalysts with loading either Pt or Pd are also prepared for comparison.The effects of the metal species and impregnation order on the characteristics and catalytic performance of the catalysts are investigated.The catalytic test results indicate that the maximum iso-hexadecane yield over different catalysts increases as follows:Pt/silicoaluminophosphate SAPO-41<Pd/SAPO-41<Pt^(*)-Pd/SAPO-41(prepared by sequential impregnation)<Pt-Pd/SAPO-41(prepared by co-impregnation).Owing to the synergic effects between Pt and Pd,the Pt-Pd/SAPO-41 catalyst prepared by the co-impregnation method demonstrates the effective promotion of(de)hydrogenation activity.Therefore,this catalyst exhibits the highest iso-hexadecane yield of 89.4%when the n-hexadecane conversion is 96.3%.Additionally,the Pt-Pd/SAPO-41 catalyst also presents the highest catalytic activity and best stability even after 150 h long-term tests.

An experimental and modeling study of n-hexadecane autoignition under low-to-intermediate temperatures

N-hexadecane is a potential candidate of diesel surrogate fuels and is also the largest linear alkane(n-alkanes)with known chemical kinetic models.The objective of this study is to investigate the autoignition characteristics of n-hexadecane in the lowto-intermediate temperature region and to validate the existing kinetic models.In this study,the ignition delay times(IDTs)of nhexadecane were measured using a heated rapid compression machine(RCM)at two pressures of 7 and 10 bar,and over equivalence ratios ranging from 0.5 to 1.3.Two-stage ignition characteristic and the negative temperature coefficient(NTC)behavior of total ignition delay time were experimentally captured.This study paid special attention to the influence of pressure,equivalence ratio,and oxygen content on the IDTs of n-hexadecane.It is observed that both the total IDTs and the first-stage IDTs decrease with the rise of those parameters.It is worth noting that the first-stage IDT is found to show a greater dependence on temperature but a weaker dependence on other parameters compared to the total IDT.The observed IDT dependence in the lowtemperature region(LTR)were quantitatively described by ignition delay time correlations.The newly measured IDTs were then validated against two kinetic models(LLNL and CRECK).Simulation results show that both models underpredict the first-stage IDT but generally capture the temperature dependence.The CRECK model well predicts the total IDTs of n-hexadecane while the LLNL model significantly underpredicts the total IDTs at most investigated conditions.To the best of our knowledge,this study is the first investigation on n-hexadecane autoignition under low-to-intermediate temperatures,which deepens the understanding of large n-alkane oxidation and contributes to the improvement of the existing kinetic models.