Mixing Characteristics And Simulation Of A Novel C₄ Alkylation Reactor

It has become the focus of people to reduce vehicle exhaust pollution and the standard of environmental protection is increasingly stringent.In order to meet the need of the market and the requirement of the environment,clean gasoline should be produced.Alkylation gasoline is an ideal clean gasoline regulating component.The alkylation process using sulfuric acid and hydrofluoric acid as catalyst has been industrialized,but these two kinds of catalysts have a series of inevitable problems.The basic method to solve these problems is to develop new alkylation process and reactor.This paper presents a new method of C₄ alkylation using sulfuric acid as catalyst.And a series of related studies are carried out on the novel packed loop reactor.A novel C₄ alkylation process with sulfuric acid as catalyst was proposed,in which butene gas was led into reactor and mixed with isobutane liquid and concentrated sulfuric acid,and then the C₄ alkylation was conducted in the liquid phase.By controlling pressure in the reactor,a part of the liquid evaporated so the reaction temperature could be kept stable.After gas-liquid separation,acid hydrocarbon separation and product distillation,the butene gas,isobutane and sulfuric acid formed loops separately.The novel process was simulated by means of Aspen Plus software.The results showed that both the temperatures at the inlet and outlet of the reactor were kept at about 7.2?under the conditions of the inlet pressure 0.2 MPa and the pressure drop 4.5k Pa.When the mass ratio of alkanes to olefins in the liquid phase at the reactor inlet was 145?1,side-reactions could be reduced.And the power consumption of the novel process was reduced by30%compared with traditional alkylation process.Micromixing characteristics of a tubular packed bed reactor with different packings were investigated by adopting the competitive parallel reaction,namely,the Villermaux-Dushman reaction.Better micromixing efficiency was achieved with the tube packed with Winpak compared to that packed with Mini Ring or Mellapak or the empty tube.The segregation index?X_S?decreased as the volumetric flow rate increased,but increased with increasing volumetric flow ratio.Moreover,the micromixing time?t_m?was calculated using an incorporation model based on the experimental data.The minimum t_m value of the tube packed with Winpak?t_m=1.54 ms?was less than that of the tube packed with Mini Ring?t_m=2.73 ms?or Mellapak?t_m=2.14 ms?or the empty tube?t_m=3.79 ms?.Based on the airlift loop reactor?ALR?,a liquid-liquid loop reactor was presented.An experiment setup on pilot plant scale was established to verify the feasibility of liquid-liquid circulation.At the same time,the phase holdup at different operation conditions and the mixing efficiency of sulfuric acid and naphtha was investigated in the liquid-liquid loop reactor.The results showed that the liquid-liquid loop reactor could reach the mixing efficiency of the conventional C₄ alkylation reactor.Then the ALR was simulated by commercial software FLUENT.The gas-liquid flow numerical model was built based on the Euler-Euler two fluid approaches to study the average gas holdup of selected area under different superficial gas velocity.The simulation results were compared with the data from cold state simulation.The simulation process has the numerical stability and the grid-independence of result was investigated.All the numerical simulations can reproduce the experimental results qualitative.In the process of simulation,this study analysis the influence of different interphase force to the numerical simulations,the result showed that lift has a decisive influence on the distribution of gas on radial.The flow state of numerical simulation and experimental result is more coincident by including lift model.The addition of virtual mass fore has a great influence on the stability of numerical simulation.The effect of different turbulence models on numerical simulation was also investigated.The results show that the RNG k-?can illustrates the fluctuation of gas holdup at high Reynolds number.These data provide the basis for the three dimensional numerical simulation in the future.Finally,the average gas holdup of the down comer with different draft height was investigated,and the theoretical analysis was carried based on the information obtained from the numerical simulation of CFD,which can provide theoretical guidance for the design of new type of reactor.