METHOD FOR SYNTHESIZING ZEOLITIC SOLIDS CONTAINING MESOPORES AND CONTROLLED-SIZE PARTICLES

Abstract

The present invention relates to a method of synthesis of zeolitic LTA adsorbents containing intercrystalline mesoporosity and controlled particle size, which can, for example, be used in natural gas dehydration processes, seeking to comply not only with the specifications on moisture content in the natural gas, but also improving the efficiency of the gas drying process in regard to the adsorption kinetics, not compromising the adsorption capacity, water selectivity, and the regeneration cycles of the adsorbent. Another possible application of these compounds is as the support for catalysts for oil refining processes. The method of obtaining the zeolitic adsorbent solids, the purpose of this invention, consists of including an aging step of the reaction mixture in conjunction with the addition of N,N-dimethyl-N-[3-(trimethoxysilane)propyl]octadecyl ammonium chloride (TPOAC) to the reaction mixture.

Claims

1-4. (canceled)

5. A method for synthesizing zeolitic solids that comprise mesoporous and controlled-size particles, the method comprising: preparing solution A by mixing a deionized water, sodium hydroxide, sodium metasilicate, and N,N-dimethyl-N-[3-(trimethoxysilane)-propyl]octadecyl ammonium chloride (TPOAC) and agitating the mixture at 100 rpm to 400 rpm for 15 minutes to 45 minutes or for a sufficient amount of time to dissolve the sodium metasilicate and the TPOAC; preparing solution B by mixing water, sodium hydroxide, and sodium aluminate and agitating the mixture at 100 rpm to 400 rpm for 15 minutes to 45 minutes or for a sufficient amount of time to dissolve the sodium aluminate; combining solution A and solution B and agitating the combination mechanically at 400 rpm to 600 rpm for 30 minutes to 190 minutes, until the combination is homogenized, white, and more viscous than solution A and solution B; dividing the combination into portions, placing the portions in containers, and aging the portions in the containers in one or more thermostatic baths between 25° C. and 35° C. for aging times ranging from 0 to 96 hours; placing the containers with the aged portions in one or more autoclaves for thermal treatment in an oven, with internal air circulation between 90° C. and 110° C. for 3 hours to 5 hours; and collecting, cooling, and filtering the thermal treated portions, washing the collected, cooled, and filtered portions with deionized water to a pH of 8.0, and drying the washed collection at 80° C. in an oven.

6. A zeolitic solid as prepared by the method of claim 5, comprising an LTA structure with intercrystalline mesoporosity and a particle size with micrometric or nanometric dimensions.

7. The zeolitic solid of claim 6, wherein the average particle diameter is equal to 632 nm.

8. A method comprising: using the zeolitic solid as prepared in claim 5 in a natural gas drying process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The present invention will be described in greater detail below, referencing the attached figures, which clearly and unrestrictedly of the inventive scope, provide examples of its realization. The designs show:

[0038] FIG. 1 illustrates X-ray diffractograms of the LTA zeolite obtained in this invention without TPOAC, with addition of TPOAC in the reaction mixture and with different aging times;

[0039] FIG. 2 illustrates a mass-loss thermogram of the LTA zeolite samples obtained in this invention without the addition of TPOAC and with the addition of the surfactant in the reaction mixture and with different aging times;

[0040] FIG. 3 illustrates a thermogram of the result of the loss of mass of the LTA zeolite samples obtained in this invention without the addition of TPOAC and with the addition of the surfactant in the reaction mixture and with different aging times;

[0041] FIG. 4 illustrates N.sub.2 physisorption isotherms from the LTA zeolite sample obtained in this invention without the addition of TPOAC and with the addition of the surfactant in the reaction mixture with variation in the aging time;

[0042] FIG. 5 shows a micrography obtained using sweep electron microscopy of the LTA zeolite sample obtained in this invention, without the addition of TPOAC, without aging of the reaction mixture, and with a 50KX increase;

[0043] FIG. 6 shows a micrography obtained using sweep electron microscopy of the LTA zeolite sample obtained in this invention, without the addition of TPOAC, without aging of the reaction mixture, and with a 100KX increase;

[0044] FIG. 7 shows a micrography obtained using sweep electron microscopy of the LTA zeolite sample obtained in this invention, with the addition of TPOAC, without aging of the reaction mixture, and with a 50KX increase;

[0045] FIG. 8 shows a micrography obtained using sweep electron microscopy of the LTA zeolite sample obtained in this invention, with the addition of TPOAC, without aging of the reaction mixture, and with a 100KX increase;

[0046] FIG. 9 shows a micrography obtained using sweep electron microscopy of the LTA zeolite sample obtained in this invention, with the addition of TPOAC, without aging of the reaction mixture for 48 h, and with a 50KX increase;

[0047] FIG. 10 shows a micrography obtained using sweep electron microscopy of the LTA zeolite sample obtained in this invention, with the addition of TPOAC, with aging of the reaction mixture for 48 h, and with a 150KX increase;

[0048] FIG. 11 shows a micrography obtained using sweep electron microscopy of the LTA zeolite sample obtained in this invention, with the addition of TPOAC, with aging of the reaction mixture for 96 h, and with a 50KX increase;

[0049] FIG. 12 shows a micrography obtained using sweep electron microscopy of the LTA zeolite sample obtained in this invention, with the addition of TPOAC, with aging of the reaction mixture for 96 h, and with a 150KX increase;

DETAILED DESCRIPTION OF THE INVENTION

[0050] The present invention consisted of developing a method of synthesis to obtain zeolitic adsorbents containing mesopores, one of whose objectives is application in the drying of natural gas. With the new method, the dimensions of the particles can be controlled, and the nanometric scale can be reached through the aging of the reaction mixture.

[0051] The zeolitic adsorbent obtained in this invention combines two important characteristics for the adsorption processes. The first corresponds to water selectivity, and the second is related to the quite favorable adsorption kinetics, as there is generation of intercrystalline mesoporosity both in the zeolitic particles with micrometric dimensions, as well as in those with nanometric dimensions, allowing more rapid access to the zeolite micropores. This is possible due to rigorously following the steps present in the method of this invention.

[0052] The method developed for synthesis of optimized adsorbent materials in the present invention is quite simple; however, the details make it exclusive, mainly in relation to the order of the steps to be followed.

[0053] The method of this invention consists of inclusion of an aging step of the reaction mixture in conjunction with the addition of N,N-dimethyl-N-[3-(trimethoxysilane)propyl]octadecyl ammonium chloride (TPOAC) to the reaction mixture.

[0054] The synthesis of the adsorbents was based on two methods published previously, as described in Thompson, R. W.; Huber, M. J., “Analysis of the Growth of Molecular Sieve Zeolite NaA in a Batch Precipitation System,” J. Cryst. Gr., v.56, pp. 711-722, 1982; and in Cho, K., Cho, H. S., Menorval, L. C., Ryoo, R., “Generation of Mesoporosity in LTA Zeolites by Organosilane Surfactant for Rapid Molecular Transport in Catalytic Application,” Chem. Mater., v.21, pp. 5664-5673, November 2009.

[0055] The procedure consists of the following steps: [0056] Prepare two solutions: SOLUTION A, containing: deionized water, sodium hydroxide, sodium metasilicate, and TPOAC. The mixture should be agitated (100 to 400 rpm) for 15 to 45 minutes, or a sufficient amount of time to dissolve the silica source. It is necessary for the TPOAC surfactant to be added in this step; that is, prior to aging the reaction mixture, as its subsequent addition compromises formation of the mesoporous zeolite. [0057] SOLUTION B, containing: deionized water, sodium hydroxide and sodium aluminate. The mixture should be agitated (100 to 400 rpm) for 15 to 45 minutes, or enough time to dissolve the source of alumina. [0058] Next, solutions A and B are mixed (SOLUTION A under SOLUTION B) and left to agitate mechanically for 30 to 190 minutes (400 to 600 rpm) until total homogenization, which is characterized by a white-colored, more viscous reaction mixture than in the precursor solutions. [0059] The reaction mixture is then divided into smaller portions, placed in Teflon® cups, and left in a thermostatic bath (25 to 35° C.) for the aging step of the reaction mixture, with aging times varying from 0 to 96 hours. [0060] Once the aging time of the reaction mixture has passed, the containers are placed in stainless steel autoclaves for oven thermal treatment, with internal air circulation between 90 and 110° C. for 3 to 5 hours. [0061] Finally, the solid compound obtained is collected, cooled, filtered, washed with deionized water until it has a pH close to 8, and dried in an oven at 80° C.

[0062] The type of zeolite obtained from the method developed in the present invention may allow construction of smaller adsorption columns in natural gas dehydration processes, which is a crucial factor for optimizing and reducing costs, as it means taking up less space at an industrial plant.

EXAMPLES

[0063] Various embodiments were realized with the post-synthesis material in powder form, in order to verify the intended structure and the new properties acquired by the adsorbent with the application of the new method. The embodiments and the principal results acquired were:

a) X-Ray Diffractometry

[0064] This analysis was done to obtain the diffraction profiles of the samples, and to evaluate the intended structure or crystalline phase. A Miniflex 600 diffractometer from Rigaku was used, and radiation of CuKα (λ=0.1542 nm) with a sweep angle in the region of Bragg 2 θ=5-50°, under the conditions of 40 KV and 15 mA, a nickel filter and goniometer speed of 10° (2 θ)/min. The samples were evaluated in powder form, compacted on a glass slide. The diffractograms are shown in FIG. 1, where the profiles of the LTA zeolites obtained with the addition of TPOAC to the reaction mixture with different aging times can be seen.

[0065] Comparing the diffraction profiles obtained with the official collection of diffraction standards available on the site of the International Zeolite Association—IZA, zeolite formation with an LTA structure was found. The presence of the additive (surfactant) did not harm formation of the zeolite 4A.

b) Thermogravimetric Analysis

[0066] Mass-loss profiles were obtained with the temperature for the samples obtained. Thermograms were generated using a thermobalance (TA Instruments SDQ 600). The samples were subjected to an oxidizing atmosphere (synthetic air), using a heating rate of 10° C.min.sup.−1, until reaching a temperature of 850° C., and air discharge of 30 mL.min.sup.−1. The thermograms are illustrated in FIG. 2 for LTA zeolites obtained without the addition of TPOAC and with the addition of TPOAC in the reaction mixture with variation in the aging time.

[0067] FIG. 3 shows the derivatives of the losses of mass from the synthesized zeolitic adsorbents in the presence of a surfactant, whose reaction mixture was aged for 0 h, 48 h, and 96 h. The curves show two principal regions of mass loss: (I) temperature 30-200° C. and (II) temperature 200-500° C.

[0068] These regions for the material without surfactant (x=0.00) basically represent a loss of physisorbed water in the alpha cavity (region I) and loss of water in the sodalite cavity (region II), as described in the works of Tounsia, H., Mseddi, S., Djemel, S. “Preparation and characterization of Na-LTA zeolite from Tunisian sand and aluminum scrap,” Physics Procedia, v.2, pp.1065-1074, 2009 and Demontis, P.; Gulin-Gonzalez, J.; Jobic, H.; Masia, M.; Sale, R.; Suffritti, G. B. “Dynamical Properties of Confined Water Nanoclusters: Simulation Study of Hydrated Zeolite NaA: Structural and Vibrational Properties,” ACS Nano, v. 2, pp. 1603-1614, 2008.

[0069] The materials synthesized in the presence of a surfactant presented a profile in which there was an increase of the signal in region II when the surfactant was added, suggesting that it is the area where the TPOAC decomposes.

c) Physisorption of Nitrogen at 77K

[0070] This technique was used to determine the textural properties of the material, such as external area and volume of holes. An ASAP 2020 machine from Micromeritics was used for this. Initially, the samples were placed in a vacuum for one hour at a temperature of 200° C. for removal of the physisorbed water from the surface of the adsorbent. After treatment, volume measurements were taken of N.sub.2 adsorbed for each sample at low pressures, at the boiling point of liquid nitrogen (−196° C.).

[0071] The isotherms are illustrated in FIG. 4, which presents the isotherms from nitrogen physisorption at 77K of the zeolitic adsorbents prepared in the presence of the surfactant, whose reaction mixture was aged for Oh (without aging of the reaction mixture), 48 h, and 96 h. The results showed a significant change in the profile of the isotherm in relation to the synthesized material without surfactant (x=0.00). The adsorbents prepared in the presence of the surfactant presented nitrogen adsorption due to the appearance of intercrystalline mesoporosity.

d) Electronic Sweep Microscopy

[0072] The materials obtained were evaluated in relation to the crystalline habit and to the other characteristics in regard to the format of the particles, using the sweep electron microscopy technique.

[0073] The samples were prepared using approximately 50 mg of powder, dispersed in methyl alcohol under ultrasound for 30 minutes. The supernatant was dripped onto an aluminum sample slide until a fine layer was obtained. The images were collected using an FEI sweep microscope, model Magellan 400L.

[0074] The results are shown in FIGS. 5 to 12, which present the micrographs of the adsorbents synthesized in the presence of the TPOAC surfactant, whose reaction mixture was aged for Oh (without aging the reaction mixture), 48 h, and 96 h. The images show two aspects in relation to the format of the particles from the materials obtained. The first of them refers to the presence of roughness on the surfaces for all adsorbents synthesized with the TPOAC surfactant. The second refers to the diameter of the aged zeolitic particles. The adsorbent obtained without aging the reaction mixture presented an average particle diameter of around 2.3 μm, while the adsorbents obtained after aging the reaction mixture for 48 h and 96 h presented an average particle diameter equal to 632 nm. This was a reduction of approximately 72% in particle size.

[0075] From these characterizations, the importance of the addition of an additive to synthesis of the zeolite 4A became evident, with the objective of causing formation of mesoporosity, which is an important factor for diffusing of the reagents to the solid. In addition, aging the reaction mixture also caused a reduction in the size of the zeolite particles, however preserving the mesoporosity created by the TPOAC. These two characteristics in a single material promote better diffusion of the reagents to the adsorbent.

[0076] The invention may be used in natural gas drying processes, where the commercial zeolitic adsorbent is used, which does not have mesoporosity or nanometric particle dimensions.

[0077] The adsorbent solids obtained with the new method of synthesis developed in this invention have the potential to increase the efficiency of the natural gas drying process, minimizing area, weight, and energy demands.

[0078] Drying of the natural gas seeks to eliminate the water present in the vapor phase in the produced gas, which is essential for use of this gas in reinjection in oil reservoirs (to increase the oil recovery factor) or in drainage to land, for use in the country's energy grid, without the risk of formation of hydrates or corrosion.

[0079] The natural gas drying step is today a very important step for obtaining gas associated with oil in the production units. Taking the severe restrictions on gas-flaring at the production units into account, the natural gas drying process ultimately allows the production of oil, which is today the most profitable component of oil production.

[0080] It should be noted that although the present invention has been described in relation to the attached drawings, it may be modified and adapted by those versed in the matter, depending on the specific situation, but remaining within the inventive scope defined herein.