Patent Application
20230191355
Broadly, the present invention pertains to the sector of chemical processes of synthesis of nanoparticles, in particular of systems for the production of nanoparticles of zeolites in continuous flow for application in catalysis of chemical reactions applied to the field of oil refining. More specifically, the invention relates to a Y zeolite nanoparticle synthesis system, which is formed by three modules, which are a microfluidics mixer system with two inlets and one outlet, an intermediate buffer system and a tubular hydrothermal system for crystallization by hydrothermy with controlled temperature and pressure, thus generating a complete system for synthesis in continuous flow. This system is adaptable to operating conditions, allowing adjustment to obtain zeolites with specific characteristics.
Currently, there is a demand for constant improvement of the performance of catalysts used in fluidized catalytic cracking (FCC), a process that within refining is primarily responsible for the conversion of heavy fractions from petroleum distillation. This demand is due to the need of increasing the scale of production of derivatives with commercial value, which can be translated into the need of increasing refining capacity.
The catalysts employed in this conversion process are based on a crystalline active component, matrices and functional ingredients.
With respect to the active component, zeolite is used and has an important influence on the performance of the catalyst. The intrinsic characteristics of these particles include the benefit of shape selectivity, an advantage that is associated with the steric restriction of certain molecules.
However, as a consequence, this steric restriction also influences the mass transfer rate of reactants and products, making it impossible for larger molecules of the reactants to access the active sites, thus enabling the occurrence of secondary reactions, since the products remain in contact with active sites for longer.
With this, an important search began for methods of zeolite synthesis that presented the same characteristics that sustain the benefit of shape selectivity, but that were also capable of reducing the negative effect of the diffusion rate.
And, since there is this demand for zeolites with greater accessibility to acidic sites, capable of increasing the conversion capacity into desired products and without loss of quality, the synthesis of zeolites on a nanometric scale (nanozeolites), with greater surface area, presents great potential for the intended application. This is due to the possibility that they have to reduce the effect of the low mass transfer rate, still maintaining the characteristic of shape selectivity.
In the literature, the nanozeolite synthesis strategy employing the method based on sol-gel and coprecipitation, followed by a hydrothermal process, has already been reported, but it has limitations related to the low synthesis yield, the long crystallization times, the difficulty in controlling the size and granulometric distribution of the particles, as well as the process of separating the particles.
Thus, the challenges encountered in the current synthesis routes of nanozeolites drive the need of searching for new approaches that are able to overcome such challenges. The flame spraying technique (Flame Spray) and the possibility of carrying out the synthesis in a confined environment, based on inverse emulsions of precursor solutions in the oily dispersed phase, are examples of strategies that have been studied in this context.
This scenario motivated the creation of a new technological approach for the hydrothermal synthesis of nanozeolites from clear homogeneous solutions (clear synthesis solutions), with the differential use of microfluidic processes of continuous flow to intensify the steps that constitute the process to obtain such particles.
Microfluidics is a technology based on the manipulation of fluids in small volumes, on the order of microliters, in microchannel systems, with great potential for scientific applications, going beyond laboratory investigations, given the possibility of miniaturization of industrial processes.
The need of improving analytical methods, making them capable of delivering reliable results quickly, gave rise to microfluidics, which since then has contributed significantly to technological innovations with miniaturized processes, precisely controlled and carried out in one operating time reduced when compared to other processes carried out in conventional ways.
Another advantage of microfluidics lies in the operating conditions, such as the flow rate used in a miniaturized process and the reduced size of the cross-section of the microchannels, which induce a laminar flow, given the low Reynolds number (Re<100), also allowing a more precise control of the reactions that occur inside the microchannels. The mass and heat transfer processes are also more efficient when compared to macrometric scales. These factors make microfluidic systems attractive for developing analytical techniques (Lab on a chip) and for exploring complex reactions.
The interest in using microfluidic technology for both scientific and industrial applications has resulted in different configurations of microfluidic systems, and the versatility in terms of micromanufacturing, types of geometries and microchannel structures is also an advantage that makes them interesting for innovation in analysis and continuous flow processes.
Regarding micromanufacturing techniques, the most used materials are glass plate, silicon wafer, elastomeric polymers such as polydimethylsiloxane (PDMS) and polymethylmethacrylate (PMMA) and also ceramics. For industrial applications, microfluidic systems in ceramic materials, specifically produced using LTCC (Low Temperature Co-fired Ceramic) technology, have features that provide conditions for large-scale operation. The green ceramic in LTCC allows the manufacturing of three-dimensional (3D) microchannels, being able to withstand high temperatures, high flows and internal pressures, enabling the scaling of microfluidic processes for different applications.
Among the possible uses of microfluidic systems built in LTCC, applications in the fields of chemical processes stand out, such as chemical microreactors, heat exchangers and micromixers. Therefore, microfluidics points to a potential for applications in different areas that aim at both fluid mixing and chemical reactions applied in processes, such as food, pharmaceutical, chemical and even the oil and gas industry.
In the synthesis of nanoparticles, microfluidics can be used as a technology to improve mixing processes and chemical reactions. This is because the laminar flow condition found in continuous flow microfluidic devices allows the controlled formation of what is called a reaction-diffusion (RD) environment that favors the control and optimization of the chemical processes that take place inside the microchannels.
Methods of synthesis of zeolites in continuous flow have been proposed in order to overcome the limitations found in methods performed in batch. Such methods usually involve the addition of seeds as a strategy to control particle size, as well as to accelerate the aging process, also reducing the total synthesis time. The crystallization process, in turn, takes place continuously, in a tubular reactor. However, the use of microfluidic mixers is not yet addressed to in this strategy, despite the potential that these devices have for acting in the step of reaction mixing and feeding the reactor, also performing this continuously. Therefore, current routes for continuous synthesis of zeolites present critical points/technical problems/limitations, among which the following stand out: the mixing process is carried out continuously, but without the use of a micromixer, which, in addition to miniaturizing the process is capable of delivering an effective mixture, and the specific obtention of Y-type zeolites, at the nanometer scale.
Thus, microfluidics presents itself as a promising technology to improve the synthesis of Y nanozeolites by continuous flow process, which can be carried out by integrating the three main steps of synthesis by hydrothermal route: mixing/nucleation, aging and crystallization.
Some proposed methods for the synthesis of zeolites in continuous flow are presented in detail in the documents described below.
Document EP0149929 addresses to a process for the production of 4A-type zeolites, in which there is continuous and simultaneous feeding of aqueous solutions of sodium silicate and sodium aluminate, thus performing continuous mixing in a venturi-type mixer, in a tubular-type reactor.
Document EP3596010 addresses to a continuous method of synthesis of zeolites of any type, in a reduced time when compared to the batch method. The method consists of feeding a tubular type crystallization reactor equipped with internal restriction systems and a pulsating device, which is operated under particular conditions, with a reaction mixture carried out continuously in a shear mixer, of the rod rotor type, which contains seeds, with the aim of eliminating the aging phase at low temperatures, and to carry out crystallization in a faster and more continuous way, using temperatures above 120° C.
Document EP3596013 addresses to a method of synthesizing X zeolite of high purity, comprising at least one step of adding seeds to the reaction mixture (which can be heated) and at least one step of crystallization at a temperature above 120° C., with reduced synthesis time, and can be conducted continuously, with crystallization in a continuous system, or semi-continuously, with crystallization carried out in batches.
Document JP2005289745 addresses to a method of synthesizing A-type zeolites, mold X and mold Y of high functionality, in continuous flow, using a multi-stage rotary reactor, which performs the mixing, feeding and synthesis of zeolites in continuous flow.
The study of an ultra-fast synthesis of BEA zeolites, without the aging step, adjusting the synthesis time from the control of the reaction mixture, using directing agents of organic structures, as well as seeds, is reported by J. Zhu et al. in the paper “Ultrafast synthesis of *BEA zeolite without the aid of aging pretreatment”, Microporous and Mesoporous Materials 268 (2018) 1-8.
The present invention differs from the mentioned documents in some respects. One of them consists of using a microfluidic micromixer, applied in the phase of obtaining the reaction mixture, which allows the miniaturization of this process and the obtaining of an efficient mixture in continuous flow. Another difference refers to the particle size, which is on a nanometric scale in the present invention. The aging step, present in some routes, is eliminated in this case; therefore, the mixing and feeding of the crystallization reactor occur continuously. And the crystallization reactor has no oscillatory devices inside the pipe.
The invention describes a process for synthesizing zeolite nanoparticles in a continuous flow system consisting of modules for each stage of the process (
More specifically, the invention refers to a system consisting of three modules: (i) a microfluidics mixer system (
The module i, called “microfluidics mixer system” (
The module ii, called the “buffer system” (
The module iii (
To obtain a visualization of the object of this invention, the figures are presented which, in a schematic way and not limiting the scope of the model, represent an example of its embodiment:
The invention describes a synthesis system for zeolite nanoparticles (
The module i, called a microfluidics mixer system (
The 3D crossing channels type microfluidic micromixer (
The microfluidic micromixer is formed by two segments (C) joined by an external connection. Through this connection, optionally, a new fluid can be included, for example, alumina or silica, aiming at controlling the Si/Al molar ratio of the mixture. In this case, a new pump and its proper piping and connections are included.
The microfluidic micromixer has the differential of performing an efficient mixing of reagent solutions, in continuous flow, in the production process of Y-type nanozeolites. It is applicable for fluids with Reynolds number that characterize the flow of fluids in the laminar regime. The mixing efficiency is favored by the induction of chaotic advection by changing the direction of the fluid and by the multiple lamination process, due to the splitting and recombination (SAR—Split and Recombine) of the fluidic streams in the microchannels.
The module ii, called the buffer module (
Specifically, the buffer module is formed by: a pump B3, for fluid displacement, preferably with a double piston; a container that receives the two fluids, made of non-corrosive and inert material, preferably PTFE; a stirrer system for the fluid in the container, magnetic or mechanical, preferably mechanical; connections and piping.
The module iii, called tubular hydrothermal system (
The tubular hydrothermal system comprises: a high-pressure pump B4, preferably with a double piston; a pipe (T), stainless steel or polytetrafluoroethylene (PTFE), inner diameter between 1/16 in. (1.5875 mm) and 1 inch (25.4 mm), preferably inch (12.7 mm), a heating system, through a thermal bath or heating tape, with temperature monitoring; a pressure control system, through a valve coupled to the fluid outlet end, preferably of the back pressure type; piping connections. Its function is to crystallize the zeolite nanoparticles.
The system is pressurized with a back pressure type valve to avoid evaporation, clogging and increased times for crystallization or the formation of zeolite structures different from Faujasite due to the absence of pressure in the system.
Thus, the present invention has the differential of presenting a complete system for the synthesis of zeolite nanoparticles in continuous flow, with all synthesis steps integrated, with a total time of up to 2 hours.
The present invention is not limited to the application in the synthesis of Y-type Faujasite nanozeolites, since the synthesis method and the temperature range practiced are applicable to obtaining other types of nanozeolites, provided that the chemical composition is changed according to the type of zeolite intended, and further, if necessary, the system allows the adjustment of configurations and operating conditions.
As to the equipment and materials used:
The method for synthesizing zeolite nanoparticles in continuous flow with a microfluidic micromixer, using the integrated system, comprises the following steps:
(a) Feeding solution S1 (of Al) through pump B1; and the solution S2 (of Si) through the pump B2 to the microfluidic micromixer (DNZ) immersed in an ice bath, continuously, wherein the flow rates of the solution S1 (of Al) and of the solution S2 (of Si) are of 0.1 to 50 mL·min−1 each;
(b) Transferring the mixture obtained in step (a) (S3) to a flask with magnetic stirring, into which a seed suspension of zeolite crystals (S4) is fed through pump B3, wherein the seed flow rate is from 0 to 20% of the microfluidic micromixer (DNZ) flow rate;
(c) Homogenizing the mixture from step (b) (S5);
(d) Transferring the solution resulting from step (c), by means of pump B4, to a pipe for carrying out a hydrothermal process, in which the hydrothermal process operates under operating conditions of: flow rate from 0.2 to 120.0 mL·min−1, pipe surface temperature from 50° C. to 170° C., pressure (vapor pressure and pressure drop associated with the process) from 15 to 220 psi (1 to 15 bar (0.1 to 1.5 MPa));
(e) Washing and drying the product, where the washing to remove residues from the synthesis is carried out by centrifuging at a range of 12,000 to 20,000 rpm in a conical pipe, discarding the supernatant, adding deionized water at room temperature and manual stirring to redisperse the material; repeating the process 5 to 10 times, until the supernatant reaches a pH of 7; at the end, the supernatant is discarded and the sample is frozen for later drying by lyophilization;
(f) After drying, subjecting the material to physicochemical characterizations.
The effluent fluid mixture of module i has the molar proportions of the chemical species in the range of 8-25 Na2O: 1 Al2O3: 9-36 SiO2: 180-750 H2O, for application in the synthesis of Faujasite-type nanozeolite.
There follows below a detailed description of one of the embodiments of the present invention, by way of example and in no way limiting. Nevertheless, it will be clear to a technician skilled on the subject, from reading this description, possible additional embodiments of the present invention still comprised by the essential and optional features below.
The module of the microfluidics mixer system was assembled with two double-piston pumps to feed the Al and Si solutions; a 3D crossing channels microfluidic micromixer/microreactor (
The microfluidic micromixer for mixing the reagents was developed through computer simulations, applying the Computational Fluid Dynamics (CFD) technique, to define the type of micromixer, its dimensions and the number of sections necessary to increase the mixing efficiency, as shown in
The buffer module was assembled with: a syringe pump, a 50 mL syringe (for the zeolite seed fluid), PTFE (polytetrafluoroethylene) pipe with an inner diameter of 1/16 in. (1.5875 mm), a polypropylene beaker of 250 mL with a magnetic bar and a magnetic stirrer. Pump flow rate can vary, preferably being 10% of the total micromixer flow rate, resulting in a 10% v/v seed ratio.
The hydrothermal system was assembled with: a double piston pump; a 40-cm stainless steel pipe, ½-in. (12.7 mm) outer diameter and 1.24 mm wall; a heating tape (with power regulator) wound over the pipe; a thermocouple coupled to a multimeter to check the temperature on the surface of the pipe; a manometer connected to the pipe outlet; a back pressure type valve connected in sequence to the manometer; a PTFE pipe and a polypropylene flask for collecting the material.
Application tests of the synthesis system were carried out, and, initially, the performance capacity of the modules was tested separately. For each test, the necessary reagent solutions for the synthesis of Y-type faujasite zeolite nanoparticles were prepared.
For all application tests, the preparation of reagent solutions followed the overall molar ratio of 8 Na2O: 0.7 Al2O3: 10 SiO2: 400 H2O. The reagents are divided into two solutions, Al and Si, respectively, both solubilized in NaOH and H2O. The reagents used were: aluminum powder (325 mesh, 99.5%) and colloidal silica (Ludox-HS 30, 30% SiO2 by weight, pH=9.8); sodium hydroxide (NaOH) F.A.; and hydrochloric acid (HCl). The masses used for the Al solution were 26.76 g of NaOH, 60.37 g of deionized water and 2.83 g of Al, and for the Si solution, 21.41 g of NaOH, 51.31 g of deionized water and 151.07 g of colloidal silica. The Si solution was heated at 90° C. in an oven for 15 min to solubilize the silica. The ratio between the final volumes of solutions A and B was 1:3.
After the synthesis process of the material, described by the synthesis protocols below, the washing to remove the synthesis residues was performed through the following procedure: centrifugation at 15,000 rpm, in a 50 mL conical pipe, discarding the supernatant, addition of about 35 mL of deionized water at room temperature (about 22° C.) and manual stirring to redisperse the material. The procedure was repeated 6 to 8 times, until the supernatant reached a pH of 7. At the end, the supernatant was discarded and the sample was frozen at −80° C. for later drying by lyophilization. After drying, the material was subjected to physicochemical characterizations.
As an experiment for comparative purposes, synthesis of faujasite zeolite was carried out using the traditional batch method. The Al and Si solutions, prepared as described in Example 2, were mixed by dropping the Al solution to the Si solution, at a rate of approximately 1.2 mL·min−1, in a polypropylene beaker inserted in an ice bath, under gentle mechanical stirring, with a PTFE rod. At the end of the addition of Al, stirring was stopped and the resulting solution was allowed to stand at a temperature of 22° C. for 24 h. Then, the solution was transferred to a PTFE reactor, to carry out a hydrothermal process. The reactor was closed with a lid, enclosed in a stainless-steel support and placed in an oven at 120° C. for 70 min. At the end, the product was washed and dried, as described in Example 3.
The sample obtained was characterized by X-ray diffraction (XRD), as shown in
An application test was carried out only for the microfluidics mixer system module, with the rest of the synthesis carried out in a traditional way, called batch. After mixing, the solution was subjected to aging by being allowed to stand for 20 h at an ambient temperature of 22° C., and to a hydrothermal process in a closed PTFE reactor, enclosed in a stainless-steel support, in an oven at 120° C. for 70 min.
The pumps were positioned side by side, facing the flasks of solutions S1 and S2, both of which were connected to pumps B1 and B2 through PTFE pipes; the device was also connected to the pumps through a PTFE pipe, connected to the two inlets (A1 and A2); the device was inserted into an ice bath; and the mixture collection flask was also connected to the device through a PTFE pipe. The assembly is shown in
The test was carried out at a total flow rate of 1.0 mL·min−1 in the device, with the Al solution flow rate being 0.25 mL·min−1 and that of the Si solution being 0.75 mL·min−1.
The X-ray diffraction analysis of the sample, shown in
An application test of the mixer system module by microfluidics was carried out, with a period of 20 h of aging of the solution allowed to stand and application of the hydrothermal system module.
The mixing protocol in the microfluidics mixer system module was the same as described above, in Example 5.
After the resulting solution is allowed to stand for 20 h, the hydrothermal process was carried out using the tubular hydrothermal module, as shown in
According to analysis through X-ray diffraction measurement, shown in
A process of synthesis of zeolite nanoparticles was carried out to evaluate the integrated system in continuous flow.
The assembly scheme is shown in
The total flow rate in the device was 1.2 mL·min−1, with 0.3 mL·min−1 of the Al solution and 0.9 mL·min−1 of the Si solution; the seed flow rate was 10% of the microfluidic micromixer flow rate, therefore 0.12 mL·min−1. About 1 h after the beginning of mixing (time for the formation of sufficient volume for the pump B4 to operate), the hydrothermal process was started, with a flow rate of 2 mL·min−1 and a target temperature of 130° C.
The visual analyses of the samples produced by the synthesis system showed the generation of visually homogeneous, opaque, whitish mixtures. In the X-ray diffraction analysis (
The SEM images are registered in
The DLS result is recorded in
Using the integrated system with the three modules, in a process that takes less than 2 hours to obtain the products, nanoparticles of faujasite zeolite were formed, proving the feasibility of applying the system in the synthesis of Y zeolite in continuous flow.
In short, the present invention allows each of the steps that make up the synthesis of production of zeolite nanoparticles (nanozeolites) in continuous flow, to have their parameters adjusted according to the type of zeolite to be produced.
The development of the mixing step applying microfluidic technology and the addition of seeds ensure the reduction of aging time without affecting the quality of the nanozeolite produced through continuous flow synthesis.
The decrease in the aging time, in the synthesis of nanozeolites in continuous flow, allows the increase of the production of nanozeolites.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2021 025707 5 | Dec 2021 | BR | national |
