Shi-dong Zhou,Zhen-hao Ren,Yi-song Yu,Yang Liu,Xiao-fang Lv,Hui Du
During the operation of deep-sea pipelines, the accumulation and deposition of hydrates are important reasons for pipeline blockage. The current main measure to solve the hydrate plugging problem is the addition of low-dose inhibitors (LDHIs), but it is not yet known whether the precipitation of wax crystals will affect their effectiveness. Therefore, in this study, the hydrate cohesive force within the wax-free/wax-containing system was directly measured by using a micromechanical force device (MMF) and the reasons for the change in cohesive force were analyzed from a morphological point of view. The results showed that glycine was effective in reducing the cohesion between hydrate particles in both wax-free/wax-containing systems and still exerted the effect of antiagglomeration agent (AA) at very low concentrations (as low as 0.10 wt %). Moreover, the optimum concentration of glycine was 0.50 wt %. At this concentration, the cohesive force decreased from 8.54 to 7.07 mN/m in the wax-free system, a decrease of about 17.2%, while the cohesive force decreased from 5.94 to 2.15 mN/m in the wax-containing system, a decrease of about 63.8%. By observation of the morphology of the hydrate particles, the presence of glycine was found to reduce the volume of the liquid bridge by changing the surface roughness and wettability of the particles, thereby reducing the cohesive force. And when wax was contained in the system, the wax further reduced the wettability by adsorbing on the surface of the hydrate particles. However, under certain AA conditions, the increase in wax concentration (from 0.1 to 0.3 wt %) resulted in the free water inside the hydrate being more likely to form liquid bridges with the surrounding particles, thus weakening the effect of AA. This work analyzes the effect on cohesive force in the simultaneous presence of LDHIs and wax from a morphological point of view, which is beneficial in providing more insights into securing safe hydrate flow management.
Wax precipitation causes numerous challenges in the transportation and refining of crude oil. Wax deposition can be decreased and the flowability of waxy crude oil in cold temperatures can be increased by addition of polymer additives in the crude oil. Sequentially well-structured polymers synthesized by reversibly additive fragment chain transfer (RAFT) polymerization enhance the capability to inhibit the growing of wax crystals. In this paper, star chain-transfer agents (star-CTA) was synthesized by esterifying polyol with a tri-thiocarbonate RAFT reagent. Then, poly octadecyl acrylate-maleic anhydride (POM) copolymers with linear and star structure (3, 4, 6 arms) were synthesized via RAFT polymerization. The chemical structures were then characterized using FT-IR, 1 H NMR and GPC approaches. The effects of star copolymers on wax crystallization and cold flowability were analyzed by DSC, XRD, polarized light microscopy and rheology. The transformation from lamellar to fibrous crystals and a decrease in fractal dimensions of crystal growth upon adding all polymers were observed through kinetics of isothermal crystallization and non-isothermal crystallization (NIC) using DSC. Upon further calculations, the crystallization activation energy of NIC increased from 34.40 kJ/mol to 63.22 kJ/mol with the increase of arms. Revealed by XRD, both of the relative crystallinity index and the grain size of crystals are reduced by polymers. Further, the growth along the x and z axes is suppressed, resulting in fibrous growth. The viscosity initially decreases and then increases as the number of arms of polymer increases, with 4-arms POM (4X-POM) reducing the viscosity by 64.63 %. The present work reveals the mechanism of inhibiting wax crystal growth by star polymers, providing valuable theoretical guidance for the practical application.
The content, morphology, and structure of precipitated wax crystals are major factors affecting crude oil rheology. In this paper, model oils obtained by dissolving a realistic mixture of long-chain n-octacosane in diesel fuels were studied using terahertz time-domain spectroscopy (THz-TDS) and microscopy to gain insight into clusters composed of asphaltene and wax with increasing wax content. The fractal dimension was used for quantitative characterization of the morphology and structure of clusters in the model oils. From the measured absorption and extinction coefficients in the THz region, dynamic processes of the clusters in the model oils were analyzed and identified. The extinction coefficient in the THz region strongly depended on the dispersed and aggregated states of the asphaltene and wax crystals. These observations suggest that the aggregation state of the particles in model oils can be monitored with THz-TDS. In the future, THz-TDS technology may be used to effectively analyze particle dispersion or the aggregation state in crude oil and may thus be useful for rapid assessment of the effect of pour-point depressant on wax crystal aggregates.
危险品化学品经营许可证（带存储）