The Process Research Of Separating Normal Paraffin In Oil-field Light Hydrocarbon By Molecular Sieves Adsorption

There is a variety of applications and greatly increasing demands for many kinds of n-paraffins. However about30%n-paraffins in oilfield light hydrocarbon are not made full useof. Therefore, it is significant to explore a reasonable adsorption and separation technology toseparate the n-paraffins from light oils.The experiment mainly researched on Dagang oilfield light hydrocarbon and investigatedadsorption properties of the three absorbents by model compounds. It was indicated that5Amolecular sieves produced by SINOPEC Catalyst Plant of Nanjing and Universal OilProducts Company had preferable effects on n-paraffins’ adsorption and separation.The adsorption behaviours of different n-paraffins were studied on5A sieves packedcolumn by gas chromatographic method，which showed that in the temperature range from260℃to380℃, desorption of n-paraffins became easier with the increase of adsorptiontemperature or decrease of carbon number. Products with high n-paraffin yield could begained when the proportion of the corresponding normal alkanes in feed was increased orcarbon number of the corresponding normal alkanes was shortened. The results also indicatedthat components in raw material such as isooctane，cyclohexane and toluene had differenteffects on yield of the corresponding normal paraffin. This paper provided an method todetermine the dynamic saturation absorbing capacity of normal paraffins on5A molecularsieves. The method based on the principle that the chromatographic peak moved forwardcontinually with the increasing sample amount of n-paraffin. While when sample amountreached a certain level, the position of chromatographic peak wouldn’t change, then thesample amout at the moment was called dynamic saturation absorbing capacity. The dynamicsaturation absorbing capacitis of n-hexane, n-heptane and octane which measured in360℃,0.14MPa were0.13mL/g、0.15mL/g、0.16mL/g. Then the curves of the normal paraffin’s concentration were investigated by fixed bed. Atthe same time, influences of virous factors on adsorption of model compound weredetermined. The optimal operating conditions was320℃~380℃, ordinary pressure and flowvelocity in0.025m/s~0.110m/s. When the temperature and flow velocity of N2increased, thedesorption time of n-paraffins became shorter. The dynamic saturation absorptive capacitiesof n-hexane, n-heptane and octane on5A molecular sieves which measured in360℃, ordinarypressure and flow velocity in0.025m/s were0.19mL/g、0.23mL/g、0.26mL/g.It also could be concluded from the experiments that the desorptive time of n-paraffinson absorbent decreased with the increase of adsorption temperature and flow velocity ofnitrogen. Within a certain range, increasing pressure of system helped improve the dynamicsaturation absorptive capacity， utilization of5A sieves bed and the adsorption rate.After determining the adsorption/desorption technological conditions for modelcompound, it could be seen that if oil-field light hydrocarbon was separated to lightcomponents and heavy components adsorbed respectively by octane as the dividinig point，itwould be more appropriate for adsorption separation process.For the light oil-field lighthydrocarbon model compound, the optimum conditions were obtained, which were360℃,constant pressure, and lower velocity of stripping gas，then the n-paraffin products contentwas about82%. While the optimum conditions for the heavy ones were360℃, constantpressure, higher velocity of stripping gas, and using n-pentane as desorption agent. The n-paraffin content corresponding to the heavy oil-field light hydrocarbon model compound was92%.