Natural gas hydrate has been a critical risk to the safety of offshore oil and gas well test and subsea transportation. Herein, the effect of three quaternary ammonium salt (QAS) surfactants with monoethylene glycol (MEG) to methane hydrate agglomeration in water-oil system was experimentally studied by a rocking cell. Based on the hydrate volume fraction and the slider trajectory, a classification method of the gas hydrate anti-agglomerants was established. All the QASs in this work show the capability of reducing hydrate agglomeration, among which N 1 ,N 3 -didodecyl-N 1 ,N 1 ,N 3 ,N 3 -tetramethylpropane-1,3-diaminium chloride (AA-2) has the best anti-agglomerating performance, and the slider moved at a large trajectory of 61–174 mm. The three QASs were compounded with 5, 10, and 15 wt% (based on water) MEG, respectively. Experimental results showed that AA-2 compounded with MEG (10 wt%) can effectively prevent hydrate agglomeration. The slider moved in the cell at the full trajectory range, showing the compound of grade A performance. The compound of QAS and MEG shows a synergistic effect. The addition of QAS can significantly reduce the required MEG dosage for the hydrate blockage prevention than the MEG only situation. Considering the economic factors of the filed hydrate management, the combination application of QAS + MEG may provide a promising option.
Monoethylene glycol (1, 2-ethanediol; MEG) is an important monomer for producing polyester. It must be very pure, which is usually indicated by a high ultraviolet (UV) transmittance. Low UV transmittance, especially at wavelength of 220, 250 and 275 nm, usually indicates the presence of undesirable impurities that lower polyester quality. Without a practical analytical method, tracing these impurities is difficult, rather than improving the refining process. Therefore, a facile, fast and sensitive method based on ultra-high performance liquid chromatography (UHPLC) equipped with photodiode array (PDA) detector and coupled with quadrupole time-of-flight mass spectrometry (Q-TOF MS) was developed for qualification and quantification of UV impurities in this paper. The UV impurities were identified as 3-methyl-1, 2-cyclopentanedione, 3, 5-dimethyl-1, 2-cyclopentanedione, and 3-ethyl-1, 2-cyclopentanedione. For tracing these impurities, the samples were directly injected without pretreatment and the compounds were analyzed within 8 min. The limit of detection (LOD) of the proposed method was around 0.07 mg/L. This method has been used to trace these impurities in MEG plants for optimizing process parameters and developing purification techniques. A probable pathway of impurity formation by base (or acid)-catalyzed model was proposed. Hydroxypropanone and 1-hydroxy-2-butanone were identified after 2, 4-dinitrophenylhydrazine (DNPH) treatment and they were supposed to be the precursors of UV impurities.
Kinetic hydrate inhibitors (KHIs) combined with thermodynamic inhibitors (THIs) such as monoethylene glycol (MEG) have been good additives for the prevention of hydrate blockages in oil and gas industry operations. The regeneration and recycling of MEG are conventional process steps used to reduce costs. However, the recovery of THIs in the presence of KHIs or the recovery of the KHIs alone has rarely been investigated. In this paper, a series of experiments was designed to study the recovery of both a KHI based poly (N-vinylcaprolactam) and MEG. The results showed that the MEG recovery rate was closely related to the recovery temperature, but was not influenced by the KHI. The MEG recovery rate from solutions consisting of MEG and the KHI was as high as 94.52%, and the KHI was recovered along with the MEG. The polymer structure of the KHI was rarely changed when the recovery temperature was close to its polymerization temperature. The presence of the KHI had a negative impact on the thermodynamic inhibition efficiency of the MEG. The KHI performance of the recovered solution obtained at the KHI polymerization temperature could reach the level of the fresh combination inhibitor, but the recovered solutions obtained at temperatures far above the KHI polymerization temperature demonstrated worse inhibitory performance. The kinetic performance could be restored by adding 5.0 wt% fresh MEG. MEG enabled a subcooling temperature decrease into the range in which KHI which could play its role effectively, leading to the improved kinetic performance of the recovered solution.
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