Tubular reactor polymerization initiator injector device, tubular reactor for continuous polymerization of olefins, and a process for production of polymers and copolymers of ethylene

Abstract

The present invention refers, in its generality, to a tubular reactor for homo or copolymerization of olefins, with one of more initiator injection devices. The invention also refers to an initiator device in a process fluid stream in a reactor polymerization reactor, and to a process for the production of polymers and copolymers of ethylene, particularly low density polymers (LDPE), that use the said device.

Claims

1. An injector device of polymerization initiator in a tubular reactor comprising: a constriction to the flow of a process fluid, said constriction being provided with a throat at its median point, said constriction being provided with a tubular through-bayonet transversal to the whole of the throat, and said through-bayonet having at least one injection orifice along the throat of the constriction.

2. The device according to claim 1, wherein the at least one injection orifice along the throat is selected from among the following: one sole orifice at the median point or near the median point; two orifices distanced symmetrically or approximately symmetrically from the median point; two or more orifices at the proximities of the median point; any number of orifices, with symmetric or non-symmetric spreading, at the proximities of the median point.

3. The device according to claim 1, wherein the at least one injection orifice is oriented downwards relative to the flow of the process fluid.

4. The device according to claim 1, wherein the device is located between a portion of piping upstream thereof, which intercepts the constriction in an inlet of the process fluid, and a portion of piping downstream thereof, which intercepts the constriction in an outlet of the process fluid.

5. The device, according to claim 4, wherein the distance between the inlet and the bayonet is the same distance that exists between the bayonet and the outlet.

6. The device according to claim 4, wherein the dimensions of the constituent parts of the injector are selected from among one or more of the alternatives: linear extension of the constriction: 50 to 500 mm; external diameter of the bayonet: 6 to 20 mm; linear extension of the throat: 6 to 20 mm; internal diameter of the bayonet: 0.5 to 5 mm; diameter of the throat: 20 to 200 mm; diameter of the inlet and of the outlet: 30-200 mm; diameter of the tube of the reactor being equal upstream and downstream of the injection device; distance between the inlet and the throat: 25-200 mm; distance between the outlet and the throat being the same distance between the inlet and the throat.

7. The device according to claim 1, wherein the device follows an equation C.sub.vtotal+0.0165R.sub.total0.1, wherein C.sub.vtotal and R.sub.total represent an index of mixture and index of recirculation, respectively.

8. A tubular reactor for continuous polymerization of olefins comprising one or more injection devices according to claim 1.

9. A process of production of polymers and copolymers of ethylene, comprising one or more steps of injection of initiator to a tubular reactor via one or more injection device(s) according to claim 1.

Description

DESCRIPTION OF THE FIGURES

(1) FIG. 1.lateral schematic view, in partial cutout, of an injector device of the invention. Comparative example 2.

(2) FIG. 2.Schematic view, in perspective, of an injector device of the invention. Comparative example 2.

(3) FIG. 3.Lateral schematic view, in partial cutout, of the device of Example 1.

(4) FIG. 4.Schematic view, in perspective, of the device of Example 1.

(5) FIG. 5.Lateral schematic view, in partial cutout, of the device of Example 2.

(6) FIG. 6.Schematic view, in perspective, of the device of Example 2.

(7) FIG. 7.lateral schematic view, in partial cutout, of the device of comparative example 1.

(8) FIG. 8.Schematic view, in perspective, of the device of comparative example 1.

(9) FIG. 9.Representation of cross section for calculating the variation coefficient Cv, in which A.sub.t is the total area of the cross section, A.sub.i is the area of a cell, x.sub.i the mass fraction in a cell, x is the global average mass fraction and N is the total number of cells. See the representation below

SUMMARIZED DESCRIPTION OF THE INVENTION

(10) The present invention, which provides advantages in terms of performance to a continuous polymerization process of ethylene in a tubular reactor, relates in a first aspect to device 10 injector of reaction initiator in a stream of monomer characterized by comprising a constriction 20 to the flow of process fluid, the said constriction 20 provided with a throat 30 at its median point, the said constriction 20 provided of a tubular through bayonet 40 transversal to the entire diameter of the throat 30, such through bayonet 40 having at least one injection orifice 50 along the throat 30 of the constriction 20.

(11) The reference to at least one injection orifice 50 along the throat 30 . . . has the following preferential realizations, without excluding any other: one single orifice at the median point or at the proximities of the median point; two orifices distanced symmetrically or approximately symmetrical from the median point; two or more orifices at the proximities of the median point; any number of orifices, symmetrically or non-symmetrically spread, at the proximities of the median point,

(12) In constriction 20 are comprised a region of diminishing of traversal section, a region of throat of minimum diameter, and a region of expansion of the transversal section.

(13) The understanding of the constriction 20 includes the particular alternative in which both the reduction of the cross section and the expansion of the cross section are substantially nonexistent. That is, the mention to constriction 20 also encompasses the alternative in which there is no variation of cross section, as illustrated in FIGS. 7 and 8.

(14) Particularly, the cited at least one injection orifice 50 is oriented towards the downstream side of the process fluid flow.

(15) The injector device 10 of the invention is located between a portion of the piping 60 upstream thereof, which intercepts the constriction 20 at an inlet 65 of the process fluid, and a portion of piping 70 downstream thereof, which intercepts the constriction 20 at an outlet 75 of the process fluid.

(16) The process fluid displaces itself axially inside the piping of the tubular reactor, which crosses the injection device of the invention in the following order:

(17) a region of beginning of the constriction 20 (reduction of the cross section) starting from the inlet 65, a throat 30 where is located the transversal bayonet 40, a portion of expansion (increase of the cross section) of the constriction 20 until the outlet 75.

(18) That is, the process fluid displaces itself from the inlet 65 to the outlet 75 of the injector device, with the throat 30 and the pass-through bayonet 40 positioned between the inlet and the outlet. Particularly the distance between the inlet 65 and the bayonet 40 is identical to the distance between the bayonet 40 and the outlet 75.

(19) As important aspect of the performance of the injector 10 of the invention, containing the pass-through bayonet, that transverses the entire cross section of the fluid flow in the throat 30, is that it presents an advantageous balance between the reduction of recirculation and good mixing downstream thereof, aspects that allow an enhanced control of the polymerization process.

(20) Particularly the dimensions of the constituent parts of the injector 10 of the invention, without excluding any others, are: linear extension of the constriction 20: 50 to 500 mm, preferably 70 to 250 mm; external diameter of the bayonet 40: 6 to 20 mm, preferably 8 mm; linear extension of the throat 30: 6 to 20 mm, preferably 8 mm; internal diameter of the bayonet 40: 0.5 to 5 mm, preferably 0.8 to 3.2 mm; diameter of the throat 30: 20 to 200 mm, preferably 30 to 75 mm; diameter of the inlet 65 and of the outlet 75: 30 to 200 mm (corresponding to the diameter of the tube of the reactor, preferably the same diameter upstream and downstream of the injection device 10); distance between the inlet 65 and the throat 30: 25-250 mm, being preferably the same distance between the throat 30 and the outlet 75.

(21) Particularly, the injector device of the invention follows the equation C.sub.vtotal+0.0165R.sub.total0.1, which represents an advantageous compromise between the good homogenization and low recirculation of the process fluid after the injection of the initiator, where C.sub.vtotal is the index of mixture and R.sub.total is the index of recirculation.

(22) Index of Mixture

(23) The index of mixture is a parameter known in the art, for example such as defined by Olujic et al. in Effect of the initial gas distribution on the pressure drop of structure packings, published in Chemical Engineering and processing 43 (2004) 465-476.

(24) The variation coefficient Cv is used to quantify the degree of mixing upstream from the device 10 of the invention. It is a measure that characterizes the distribution of the mass fraction of the initiator in planes transversal to the outflow. For a cross section, it is defined as:

(25) $C_V={\left[\frac{1}{A_t}\underset{i=1}{\overset{N}{.Math.}}{A_i\left(\frac{x_i-\stackrel{\_}{x}}{\stackrel{\_}{x}}\right)}^2\right]}^2$
wherein

(26) $\stackrel{\_}{x}=\frac{1}{A_t}\underset{i=1}{\overset{N}{.Math.}}{A}_i{x}_i$
in which A.sub.t is the total area of the cross section, A.sub.i is the area of a cell, x.sub.i the mass fraction in a cell, x is the global average mass fraction and N is the total number of cells. See FIG. 9.

(27) Thus, there was evaluated the variation of C.sub.v across the integral of C.sub.v along the planes after the injector device measured until the distance where the mixture is already substantially homogenized (C.sub.vtotal, or index of mixture).

(28) The closest is the proximity of the index of mixture C.sub.vtotal to zero. the greater will be the uniformity of the mixture. Or, in the opposite sense, the higher is the value of C.sub.vtotal, the worse will be the homogeneity of the mixture.

(29) Recirculation Index

(30) The recirculation is defined as the ratio between the flow in the opposite sense to the main flow and the flow rate in the main flow (Vitor Dal B Abella, Estudo de aspectos geomtricos de injetor de iniciador na produo de PE PD em CD F [Study of geometric aspects of injector of initiator in the production of PE PD in CFD (Computational Fluid Dynamics)], Universidade Federal do Rio Grande do Sul, Escola de Engenharia [Federal University of Rio Grande do Sul, Engineering School], Departamento de Engenharia Qumica [Chemical Engineering Department], Trabalho de Diplomao em Engenharia Qumica [Graduation Paper in Chemical Engineering], ENG07053, Dec. 9, 2014, page 16.

(31) In order to estimate the degree of recirculation, there was used a parameter r, measured along the planes transversal to the outflow, defined as:

(32) $R=\frac{\frac{v_x}{.Math.v_x.Math.}-1}{-2}$
where v.sub.x is the velocity component in the main flow direction.

(33) Therefore, where there is a flow in the direction opposite to the main flow direction, the value of R will be equal to 1. If there is not, the value of R will be equal to 0. Thus, there was evaluated the area occupied by the recirculation in each plane by means of the integration of R (R.sub.total, or index of recirculation) in the area of the plane. The greater is the index of recirculation R.sub.total, the greater will be the extension of the reactor occupied with recirculations.

(34) As a technician skilled in the art is aware, the values of Cv and R are magnitudes able to be used in CFD (Computational Fluid Dynamics), which application to chemical processes provides adequate tools for a better understanding of the turbulence and flow phenomena.

(35) In another aspect, the invention refers to a tubular reactor for continuous polymerization of olefins, partiality directed at low density polyethylene, characterized by comprising one of more initiator initiation devices such as de described hereinbefore.

(36) Within another aspect, the present invention refers to a process for the production of LDPE that uses the said device, a polymerization by free radicals, wherein initiator is injected at one or more points of a tubular reactor wherein flows a process fluid, totally or partially comprised of ethylene, that is converted into polymer by means of a highly exothermic reaction Rtotal in typical conditions of pressure between 1000 and 4000 bar and temperature between 100 and 400 C., in turbulent flow conditions and characterized by comprising one or more steps of injection of initiator to a tubular reactor using initiator injection device(s) such as described hereinbefore.

EXAMPLES

(37) There are provided in the following examples of realization of the invention, for the mere sake of illustration, without imposing any limitations to the scope of the invention beyond those contained in the claims presented further along. Operating conditions and hypothesis having been adopted

(38) To simulate the flow, it was assumed that the continuous phase is comprised only by ethene and that the solution of initiator is comprised only by its solvent isododecane. The flow was considered isothermal and uncompressible, that is, the specific mass and the viscosity of each fluid were constant throughout the entire simulation. There are no changes of phase nor chemical reactions.

(39) In the examples that follow, the CFD simulations were conducted using the software ANSYS Fluent version 14.5. The computing grid was generated using a mesher ANSYS Meshing. Initially there was discretized the geometry to be simulated in a finite number of elements through the generation of the grid by using predominantly hexahedral grids. The grid was refined in the wall regions and in the region of injector of initiator.

(40) C.sub.vtotal, or index of mixture that corresponds to the variation C.sub.v across the integral of C.sub.v along the planes after the injector device was measured until the distance of 100 the diameter of the piping.

(41) The software used to generate the geometry was the ANSYS DesignModeler.

(42) For the numeric solving of the transport equations there was used the simulation software ANSYS Fluent, version 14.5, which solves the transport equations (conservation of mass, amount of movement, species, etc.) by the method of finite volumes.

(43) Schemes of second order upwind spatial discretization were selected for the convective terms of the equations of momentum, turbulent kinetic energy and turbulent dissipation of energy, according to good practices of simulations of CFD (MALISKA, Clovis R. Transfrencia de calor e mecanica dos fluidos computacional [Computational heat transfer and fluid mechanics] 2.sup.nd ed. Rio de janeiro: LTC, 2004).

(44) The flow was considered uncompressible, and there was not considered the occurrence of change of phase or chemical reactions.

(45) For modeling of turbulence, there was used the approach named RANS (Reynolds-Averaged Navier-Stokes equations), in which the variables are decomposed using the Reynolds average.

(46) The multicomponent approach was used for modeling the distribution of the initiators in the reactor.

(47) In the multicomponent approach, the species initiator and ethene are mixed at the molecular level and conservation equations are solved for each of the species. In this approach, the specific mass and the viscosity of the mixture are calculated locally as a function of the composition.

(48) The output variables analyzed for each example were the recirculation, related with the formation of vortices and counter-flows in the flow, and the mixture between ethene and initiator. The recirculation was evaluated by means of the profile of velocities and the indexes of recirculation. The mixture was evaluated by means of profile of concentrations of initiator along the reactor and the index of mixture by plane and integral. The results of the simulation were treated statistically, in order to be able to observe and measure the degree of dispersion of the initiator along the reactor. There were used traditional criteria of analysis of dispersion relatively to an average. For this treatment, there was used the software ModeFrontier, of the company ESTECO, which allowed the obtainment of information on the influence of each of the input parameters on the efficiency of the mixture process and on the existence of recirculations.

(49) Table I below summarizes the data of the examples below, to wit, example 1, comparative example 1, example 2 and comparative example 2. The numbering used in FIGS. 1 and 2, repeated in any of the remaining figures, expresses an equivalent indication.

(50) TABLE-US-00001 TABLE I Comparative Comparative SIMULATION Example 1 example 1 Example 2 example 2 Diameter of the 50 mm 50 mm 50 mm 50 mm tube (60) Diameter of the 90 mm 90 mm 90 mm 90 mm constriction (20) Flow of ethene 40 ton/h 40 ton/h 40 ton/h 40 ton/h Flow of 40 l/h 40 l/h 40 l/h 40 l/h initiators Pressure 2451 bar 2451 bar 2451 bar 2451 bar Temperature 150 C. 150 C. 150.sup.a C. 150.sup.a C. Diameter of the 50 mm 50 mm 20 mm 30 mm throat (30) Depth of the 0 50 mm 0 30 mm bayonet External 7 mm 7 mm 7 mm 7 mm diameter of the bayonet 40 C.sub.vtotal 0.184916 0.88593 0.003747 0.015512 R.sub.total 0.000389 0.72071 10.287774 4.508572 C.sub.vtotal + 0.1849224 0.897823 0.1734951 0.0899033 0, .065 R.sub.total

Example 1Geometry of the Interior According to the Prior Art

(51) For the realization of this example there were adopted the parameters of column 1 of Table I, illustrated in FIGS. 3 and 4, wherein 100 indicates the initiator injection piping and 500 indicates the point of injection of initiator. The results obtained for Cv total and Rtotal were 0.184916 and 0.000389, respectively. The geometry of Example 1 does not present an adequate balance between mixture and recirculation. By the proposed Example 1 presented;

(52) C.sub.vtotal+0.165R.sub.total0.1849224. The geometry of Example 1 presents a poor mixture of the components and a low recirculation.

Comparative Example 1: Example 1 Versus Geometry of an Injector of the Invention

(53) For comparative Example 1 there were used the parameters of the 2.sup.nd column of Table I, FIGS. 7 and 8.

(54) In this example there was used as comparison the geometry that is the object of the invention (FIGS. 7 and 8), which constriction 20 is provide with a tubular through-bayonet 40 transversal to the entire diameter of the throat 30, and such through-bayonet 40 having an injection orifice 50 at the median point of the diameter of the throat 30 of the constriction 20, turned downstream.

(55) The values of Cv total and Rtotal were 0.088593 and 0.072071, respectively. The geometry of the comparative example presents an improved mixture of the components when compared with the geometry of Example 1.

(56) By the proposed equation with comparative Example 1 there is obtained: Cvtotal+0.0165Rtotal=0.0897823.

(57) On substituting the geometry of Example 1 by the geometry of comparative example 1, which is the object of the invention, we have an increase in ratio between mixture and recirculation, avoiding localized zones of high concentration of initiator within the flow of fluid of the process, the generation of incrustation and gels, thereby obtaining a production process without loss of control of reaction.

Example 2Geometry of Injector According to the Prior Art

(58) For the realization of this example there were adopted the parameters of the 3rd column of Table I, according to FIGS. 5 and 6, wherein 100 indicates the initiator injection piping and 500 indicates the point of injection of initiator.

(59) The results of Cvtotal and Rtotal were 0.00347 and 10.2877774, respectively. By the proposed equation Example 2 presents a C.sub.vtotal+0.165R.sub.total=0.1734951.

(60) The geometry of example 2 does no present an adequate balance between mixture and recirculation. This geometry presents a good mixture of the components and a poor recirculation.

Comparative Example 2: Example 2 Versus Geometry of an Injector of the Invention, with Parameters of the 4.SUP.th .Column of Table, FIGS. 1 and 2

(61) In this example there was used the geometry that constitutes the object of the invention which constriction 20 provided with a tubular through-bayonet 40 transversal to the whole diameter of the throat 30, and such through-bayonet 40 having at least one injection orifice 50 at the median point of the throat 30 of the constriction 20.

(62) The results of Cv total and Rtotal were 0.015512 and 4.508572, respectively. The geometry of the comparative example 2 presents an improved mixture of the components when compared with the geometry of Example 2.

(63) By the proposed equation comparative Example 2 has a CVtotal+0.0165Rtotal=0.0899033. On replacing the geometry of example 2 by the geometry of comparative example 2, which is the object of the invention, we have an increase in the balance between mixture and recirculations avoiding localized zones of high concentration of initiator within the flow of process fluid, the generation of incrustations and gels, obtaining thereby a process of production without losses of control of the reaction.

(64) An individual skilled in the art will be readily aware to evaluate the advantages of the invention, by means of the teachings contained in the text and in the examples having been presented, being able to propose equivalent variations and alternatives of realization not explicitly described without deviating from the scope of the invention, as defined in the attached claims.