New trends

Microencapsulated drag reducing agent (mdra) is prepared by encapsulating high concentration of drag reducing polymer particles in the shell composed of some inert substances. The successful development of microcapsule drag reducer is a new trend in the development of drag reducer.

There are many ways to produce microcapsule drag reducing agent, including static extrusion, centrifugal extrusion, vibrating nozzle method, rotating disk method, interfacial polymerization, multi-component condensation, suspension polymerization, etc. To produce microcapsule drag reducer, polymerization monomer, catalyst and shell material are added from the central hole and outer ring sleeve respectively, and extruded from the lower end of the device at a certain speed to form microcapsule drag reducing agent particles. The extrusion speed is very important. When the extrusion speed is slow, the appearance of microcapsules is regular and the size is uniform; on the contrary, if the extrusion speed is fast, the microcapsule particles will adhere, resulting in abnormal shape and different sizes of microcapsules. It is beneficial to control the particle size of microcapsules by keeping a certain frequency of vibration in the production process.    

Because the monomer is polymerized in the closed microcapsules, the reaction scale is very small for a single microcapsule, so the reaction conditions can be well controlled, especially the reaction heat can be released in time. If the monomer is σ - olefin, Ziegler Natta catalyst is usually used and added before the formation of microcapsules. Because the catalyst of Ziegler Natta system will lose efficacy quickly when encountering oxygen, there is no oxygen in the reaction system. Some monomers can be polymerized using ultraviolet rays, but the ultraviolet rays must be able to penetrate the microcapsule shell.

The shell of microcapsule is an important part of drag reducing agent, and the reactants in the inner core of microcapsules can not react with each other or mix with each other. If the inner core of the microcapsules is a σ - olefin polymerization system, in order to avoid catalyst failure, there is no oxygen in the microcapsule shell, but a small amount of hydroxyl and carboxyl groups have little effect on the polymerization. The suitable shell materials are polybutylene, polymethacrylate, polyethylene glycol, wax, stearic acid, etc. However, the polymer microcapsules can not be formed in the process of polymer coating polymerization. In addition, the performance of microcapsule shell is required to be stable during transportation and storage, and its broken or dissolved residue has no effect on the physical and chemical properties of crude oil or petroleum products and the oil processing process. The microcapsule shell can be removed by dissolving in the injection medium or pipeline fluid, mechanical crushing, melting, photochemical crushing, biodegradation and chemical combination. As the microcapsule drag reducer is stored and transported in the form of solid particles, the cost of transporting solvent, slurry or other carriers is saved. If solvent or other carrier (i.e. injection medium) is needed for injection into oil pipeline, it can be purchased at low price locally and mixed on site instead of complex post-treatment process.