Pre-heating temperature induced flowability and wax deposition characteristics of crude oil adding wax inhibitors

This paper investigated the effects of pre-heating treatment temperatures(T_(pre))on the flowability and wax deposition characteristics of a typical waxy crude oil after adding wax inhibitors.It is found that there is little difference in wax precipitation exothermic characteristics of crude oils at different T_(pre),as well as the wax crystal solubility coefficient in the temperature range of 25-30℃.For the undoped crude oil,the flowability after wax precipitation gets much improved and the wax deposition is alleviated as T_(pre)increasing.At T_(pre)=50℃,the viscosity and wax deposition rate of crude oil adding wax inhibitors are higher than those of the undoped crude oil.When the T_(pre)increases to 60,70,and 80℃,the flowability of the doped crude oil are largely improved and the wax deposition is suppressed with the T_(pre)increase,but the wax content of wax deposit increases gradually.It is speculated that,on the one hand,the T_(pre)increase helps the dispersion of asphaltenes into smaller sizes,which facilitates the co-crystallization with paraffin waxes and generates more aggregated wax crystal flocs.This weakens the low-temperature gel structure and increases the solid concentration required for the crosslink to form the wax deposit.On the other hand,the decrease in viscosity increases the diffusion rate of wax molecules and accelerates the aging of wax deposits.The experimental results have important guiding significance for the pipeline transportation of doped crude oils.

Effect of existence state of asphaltenes on the asphaltenes-wax interaction in wax deposition

Asphaltenes are the most elusive substances in waxy crude oil,especially the complex structures,which leads to significant precipitation and aggregation characteristics of asphaltenes,and affects the asphaltenes-wax interaction.In this study,the concept of the existence state of asphaltenes was introduced to semi-quantitatively investigate the precipitation and aggregation characteristics of asphaltenes.On this basis,the influence of the existence state of asphaltenes on wax deposition was studied by coldfinger device and high-temperature gas chromatography,and the composition and properties of the deposits were analyzed.Four main findings were made:(1)As the asphaltene concentration increases,the existence state of asphaltenes gradually transitions from dispersed state to aggregated state,and the asphaltene concentration of 0.30 wt%in this study is the starting point of the transition.(2)The existence state of asphaltenes in crude oil does affect the process of wax deposition,as shown in the fact that the dispersed asphaltenes promote the occurrence of wax deposition,while the aggregated asphaltenes can inhibit wax deposition.(3)In the presence of the aggregated asphaltenes,that is,when the asphaltene concentration is higher than 0.30 wt%,the shedding phenomenon of deposit layer was observed,and with the increase of aggregated asphaltenes,the deposit layer fell off earlier.(4)With the increase of the dispersed asphaltenes,the wax appearance temperature(WAT)and wax content of the deposits all showed an increasing trend,while with the appearance of the aggregated asphaltenes,the above situation was reversed.The findings of this study can help for better understanding of the interaction between the asphaltenes and wax in wax deposition.

Single-doped charged gold cluster with highly selective catalytic activity for the reduction of SO2 by CO: First-principles study

It is important for environmental protection to search for catalysts with excellent performance and cost-effective to reduce SO2 by CO. In this work, using first-principles calculation, we have studied the catalytic performance of Au5M^n(M = Ni, Pd, Pt, Cu, Ag, Au;n = 1, 0,-1) clusters, and showed that, by giving a negative charge to the Au5M(M = Cu,Ag, Au, Pd) clusters, we could improve the selectivity of SO2 and avoid effectively catalyst CO poisoning simultaneously.At the same time, the catalytic reaction rate for the reduction of SO2 by CO with Au5M^-(M = Cu, Ag, Au, Pd) clusters is greatly improved when the Au5M clusters are charged. These advantages can be well explained by the charge transfer between the clusters and adsorbed molecules, which means that we can effectively control the performance of the catalyst.The equilibrium structures of Au5M^n(M = Ni, Pd, Pt, Cu, Ag, Au;n = 1, 0,-1) clusters without or with adsorbed SO2 or CO molecule are also discussed, and the most stable geometrical structures of Aun5 M^n-ML(ML = SO2, CO, SO, and COS)can be explained very well by the match of orbitals symmetry and density of electron cloud through their frontier molecular orbitals. Considering the catalyst cost(Cu is much cheaper than Ag and Au), selectivity of SO2, and effectively avoiding the catalyst CO poisoning, we propose that Au5Cu-is an ideal catalyst for getting rid of SO2 and CO simultaneously.

Single boron atom anchored on graphitic carbon nitride nanosheet(B/g-C_(2)N)as a photocatalyst for nitrogen fixation:A first-principles study

It is essential to explore high efficient catalysts for nitrogen reduction in ammonia production.Based on the first-principles calculation,we find that B/g-C_(2)N can serve as high performance photocatalyst in N_(2)fixation,where single boron atom is anchored on the g-C_(2)N to form B/g-C_(2)N.With the introduction of B atom to g-C_(2)N,the energy gap reduces from 2.45 eV to 1.21 eV and shows strong absorption in the visible light region.In addition,N_(2)can be efficiently reduced on B/g-C_(2)N through the enzymatic mechanism with low onset potential of 0.07 V and rate-determining barrier of 0.50 eV.The"acceptance-donation"interaction between B/g-C_(2)N and N_(2)plays a key role to active N_(2),and the BN_(2)moiety of B/g-C_(2)N acts as active and transportation center.The activity originates from the strong interaction between 1π1π*orbitals of N_(2)and molecular orbitals of B/g-C_(2)N,the ionization of 1πorbital and the filling of 1π*orbital can increase the N≡N bond length greatly,making the activation of N_(2).Overall,this work demonstrates that B/g-C_(2)N is a promising photocatalyst for N_(2)fixation.

Enhancing ferromagnetic coupling in CrXY(X=O,S,Se;Y=Cl,Br,I)monolayers by turning the covalent character of Cr-X bonds

On the basis of first-principles calculations,we investigate the electronic and magnetic properties of 1T phase chromium sulfide halide CrXY(X=O,S,Se;Y=Cl,Br,I)monolayers in CrCl_(2) structure with the P3m1 space group.Except for the CrOI monolayer,all CrXY monolayers are stable and ferromagnetic semiconductors.Our results show that the ferromagnetic coupling is dominated by the kinetic exchange between the empty e_(g)-orbital of Cr atoms and the p-orbital of anions under the three-fold rotational symmetry.In this context,the coupling strength allows for being greatly enhanced by turning the nature of Cr–X bonds,i.e.,increasing the covalent contribution of the bonds by minimizing the energy difference of the coupled orbitals.As we illustrate for the example of CrOY,the Curie temperature(T_(c))is nearly tripled by substituting O by S/Se ion,eventually reaching the highest Tc in CrSeI monolayer(334 K).The high stabilities and Curie temperature manifest these monolayer ferromagnetic materials feasible for synthesis and applicable to 2D spintronic devices.