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    公开号:ES2761840T9
    申请号:ES11838385T
    申请日:2011-08-02
    公开日:2022-01-19
    发明作者:James N Ziemer；Tracy M Davis；Stacey I Zones；Adeola Ojo
    申请人:Chevron USA Inc；
    IPC主号:
    专利说明:

    [0002] Procedure for the preparation of molecular sieves
    [0004] technical field
    [0006] The invention generally relates to processes for the synthesis of molecular sieves.
    [0008] Background
    [0010] Molecular sieves are an important class of materials used in the chemical industry for processes such as gas stream purification and hydrocarbon conversions. Molecular sieves are porous solids that have interconnected pores of different sizes. Molecular sieves typically have a one-, two-, or three-dimensional crystalline pore structure, which selectively adsorbs molecules that can enter the pores and excludes those molecules that are too large.
    [0012] Pore size, pore shape, interstitial spaces or channels, composition, crystal morphology, and structure are a few characteristics of molecular sieves, which determine their use in different hydrocarbon adsorption and conversion processes.
    [0014] During the synthesis the reactants are mixed to form a "gel" which can be aged at one temperature for a given period, before reacting for a period of time to provide a crystalline molecular sieve. Conventional procedures used in the synthesis of these materials may employ reactors or autoclaves for stepwise mixing, gel maturation, and final crystallization of the product. Molecular sieves can also be manufactured in a continuous process. Due to the costs associated with such crystallisers, it is advantageous to maximize the production of each unit, which can conventionally be achieved in two ways: minimizing crystallization time or maximizing yield.
    [0016] In order to minimize the crystallization time, it is customary to monitor the degree of crystallization, so that the reaction can be terminated as soon as the product achieves a required yield. Conventionally, the termination point is determined by removing a sample from the reaction mixture and measuring its crystallinity by powder X-ray diffraction (XRD) on a dry sample. This is relatively labor and time intensive, and is generally not suitable for monitoring crystallization progress, as it does not provide results quickly enough to allow satisfactory control of process variables.
    [0018] Typically, methodologies for determining the appropriate reaction period are directed more toward maximizing product yield than achieving other properties such as particular crystal size. In addition, the maximum yield of product is often reached long before the reaction period is over, thereby unnecessarily consuming time and resources, and sometimes giving undesired by-product phases. Process variations from batch to batch can also lead to inconsistent physical properties between batches. In the absence of a reliable procedure for determining the end point of the synthesis, the reaction mixture can be heated for an unnecessarily long period of time, with the concomitant production of undesirable large crystals. It would be desirable to have a crystallization progress monitoring method for continuous and batch molecular sieve synthesis procedures that could provide information on crystallization faster than conventional powder XRD analysis.
    [0019] It would also be desirable to monitor the progress of molecular sieve crystallization so that the end point of the synthesis reaction could be predicted in advance of the true end point. Early determination of the end point of the reaction would allow the synthesis process to be stopped at a time when molecular sieve crystals are most desirable, eg relative to crystal size.
    [0021] Thus, there is a need for methods for monitoring crystallization during molecular sieve synthesis that allow early detection of the reaction endpoint, thereby enabling the consistent and reliable production of molecular sieves having desirable characteristics, in particular. the minimum amount of time and with maximum energy efficiency.
    [0023] Document GB2005653 describes a process for the preparation of zeolites by hydrothermal crystallization of an alumino-silicate gel made by combining solutions of silica, alumina and alkali metal sources so as to produce a completely dispersed gel with a translucent creamy appearance and without visible gel particles.
    [0025] WO2005042144 describes a process for making SSZ-32X.
    [0027] Document US2003187312 describes the manufacture of a molecular sieve catalyst composition, by forming a liquid paste, combining a molecular sieve, a binder and a matrix material, wherein the liquid paste has a pH, above or below the isoelectric point of the molecular sieve.
    [0028] Follens et al. "Viscosity sensing in heated alkaline zeolite synthesis media" Physical Chemistry Chemical Physics, (20090101), vol. 11, no. 16, page 2854, describes in situ viscosity monitoring during zeolite crystal formation.
    [0029] Summary of the invention
    [0030] In one aspect, the invention is directed to a process for the synthesis of a molecular sieve comprising: providing a reaction mixture sufficient to synthesize the molecular sieve; maintaining the reaction mixture under crystallization conditions; monitoring at least one viscometric parameter of the reaction mixture, wherein the monitoring step comprises:
    [0031] a) periodic removal of a sample from the reaction mixture;
    [0032] b) cooling each sample to a pre-established temperature; Y
    [0033] c) measurement of at least one viscosity parameter of each sample; or
    [0034] a) periodic removal of a sample from the reaction mixture;
    [0035] b) subjecting each sample to a plurality of shear rates;
    [0036] c) recording a shear stress corresponding to each of the plurality of shear rates, to provide a plurality of shear stress values; Y
    [0037] d) determining a viscosity shear rate index for each sample; Y
    [0038] determination of an end point based on monitoring of at least one viscometric parameter, wherein the end point is the stage of the reaction or process when the target product has been formed and has obtained at least one attribute or characteristic of the desired product.
    [0039] Also described herein is a method for monitoring the crystallization of a molecular sieve from a reaction mixture, during a molecular sieve synthesis process, wherein the method comprises: monitoring at least one viscosity parameter of the reaction mixture; and determining an end point of the molecular sieve synthesis process.
    [0040] Brief description of the figures
    [0041] Figure 1 provides a comparison between the XRD patterns of standard SSZ-32 and small-crystal SSZ-32 (hereinafter referred to as SSZ-32X).
    [0042] Figure 2 shows changes in the apparent viscosity and pH of liquid paste samples, during a molecular sieve synthesis process.
    [0043] Figure 3 demonstrates the observed differences in measured viscosity versus shear rate, for liquid paste samples at two different stages of molecular sieve synthesis.
    [0044] Figure 4 gives the natural logarithm of shear stress versus the natural logarithm of shear rate, for liquid paste samples at different stages of a molecular sieve synthesis.
    [0045] Figure 5 shows the corresponding changes in viscosity and pH shear rate index of the molecular sieve synthesis process, depicted in Figure 2.
    [0046] Detailed description
    [0047] Throughout the specification the following terms will be used and have the following meanings, unless otherwise indicated.
    [0048] The term "measured viscosity" refers to a value of the viscosity of a fluid, such as a reaction mixture for molecular sieve synthesis, as recorded, determined or measured, for example, using an instrument such as a rheometer. The measured viscosity of a sample withdrawn from the reaction mixture at a given point in time may be different from the actual viscosity of the reaction mixture in situ at that time due, for example, to differences in the dynamics of aggregation and disaggregation. of crystallite in a reactor and in a sample withdrawn from the reactor. However, changes over time in the measured viscosity of our reaction mixtures have been found to have predictive value in determining the end point of sieve synthesis. molecular. The terms "measured viscosity" and "apparent viscosity" may be used herein, interchangeably and synonymously.
    [0050] The term "viscosity shear rate index" refers to a measure of the deviation from the Newtonian flow characteristics of a fluid, such as a reaction slurry for molecular sieve synthesis. The degree of deviation from Newtonian fluid behavior can be quantified by assuming a Herschel-Bulkley flow model, in which the relationship between shear stress (o) and shear rate (y) is given by:
    [0055] The Herschel-Bulkley exponent, or viscosity shear rate index (n), can be determined by fitting a straight line to a plot of the natural logarithm of the shear stress data (Pascals; y-axis) versus the data. natural logarithm of the shear rate (s-1; x-axis). The term viscosity shear rate index may be abbreviated herein as "shear rate."
    [0057] The term "end point" refers to the stage of the reaction or process when the target product has been formed and has achieved at least one desired product characteristic or attribute, for example, in terms of crystal size, physical properties, catalytic activity, yield and the like. For a given product and synthesis process, the end point may vary depending on the desired attribute(s) of the product, for example, in relation to the intended use(s) for the product. product.
    [0059] The term "reaction time" refers to the time elapsed from a point when the reaction mixture has achieved the target or designated reaction temperature; for example, for a reaction mixture that has an eight hour ramp from ambient to reaction temperature, the end of the eight hour ramp period represents zero reaction time. The terms "reaction time" and "flow time" may be used interchangeably and synonymously herein.
    [0061] Described herein is a method for the synthesis of a molecular sieve comprising: providing a reaction mixture sufficient to synthesize the molecular sieve; maintaining the reaction mixture under crystallization conditions; monitoring of at least one viscometric parameter of the reaction mixture; and determining an end point based on monitoring the at least one viscometric parameter.
    [0063] The process of the present invention can be used to make a multiplicity of molecular sieves. Non-limiting examples include zeolites and their zeotypes having the framework types described in Atlas of Zeolite Framework Types, Ch. Baerlocher, L.B. McCusker and D.H. Olson, 6th revised edition, Elsevier, Amsterdam (2007), including physical admixtures and structural intergrowths of them.
    [0065] In general, a molecular sieve can be prepared by contacting, under crystallization conditions, a reaction mixture comprising: (1) at least one source of at least one oxide of a tetravalent element (Y); (2) optionally, one or more sources of one or more oxides selected from the group consisting of oxides of trivalent elements, oxides of pentavalent elements, and mixtures (W) thereof; (3) hydroxide ions; and (4) an agent (SDA) that directs the structure.
    [0067] Typically, molecular sieves synthesized using the methods of the present invention contain one or more tetravalent framework elements (Y), and optionally a trivalent element, a pentavalent element, or a mixture (W) thereof, and are represented by the molar rate ratio (m):
    [0069] m = Y02/W2Oa
    [0071] in which: Y is selected from the group consisting of tetravalent elements from groups 4 to 14 of the Periodic Table, and mixtures thereof; W is selected from the group consisting of trivalent elements and pentavalent elements from groups 3 to 13 of the Periodic Table, and mixtures thereof; and the stoichiometric variable a is equal to the valence state of the compositional variable W (that is, when W is trivalent, a = 3; and when W is pentavalent, a = 5)
    [0073] The ratio of Y to W (eg silica to alumina for zeolites) may vary according to a particular intended end use application for the molecular sieve. In one embodiment, the molecular sieve may have a high concentration of tetravalent elements (for example, a high silica sieve) in which (m) has a high value, typically 20 to ~ In another embodiment, the molecular sieve may have a high concentration of trivalent and/or pentavalent elements (for example, a high alumina sieve) in which the molar (m) ratio is less than 4.
    [0075] The product obtained from the synthesis will naturally depend on the selected system of synthesis and can be, for for example, a small pore size molecular sieve, such as SSZ-13, SSZ-16, SSZ-36, SSZ-39, SSZ-50, SSZ-52, or SSZ-73; an intermediate pore size molecular sieve, such as SM-3, SM-6, SSZ-32, ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-38 , ZSM-48, or ZSM-57; or a large pore size molecular sieve such as Zeolite Y, SSZ-26, SSZ-33, SSZ-64, ZSM-4 or ZSM-20. The invention is not limited to any particular type of zeolites or molecular sieves.
    [0077] Y can be selected from the group consisting of Ge, Si, Ti, and mixtures thereof. In one embodiment, Y may be selected from the group consisting of Ge, Si, and mixtures thereof. In another embodiment, Y is Yes. Element sources selected for composition variable Y include oxides, hydroxides, acetates, oxalates, ammonium salts, and sulfates of the element(s) selected for Y. In one embodiment, each of the sources of the( The element(s) selected for composition variable Y is an oxide. When Y is Si, useful sources for Si include fumed silica, precipitated silicates, silica hydrogel, silicic acid, colloidal silica, tetraalkyl orthosilicates (eg, tetraethyl orthosilicate), and silica hydroxides. In one embodiment, useful sources for Si include alumina-coated silica nanoparticle sols. Useful sources for Ge include germanium oxide and germanium ethoxide.
    [0079] W may be selected from the group consisting of elements from groups 3 to 13 of the Periodic Table. In one embodiment, W is selected from the group consisting of Ga, Al, Fe, B, In, and mixtures thereof. In another embodiment, W is selected from the group consisting of Al, B, Fe, Ga, and mixtures thereof. Element sources selected for the optional composition variable W include oxides, hydroxides, acetates, oxalates, ammonium salts, and sulfates of the element(s) selected for W. When W is Al, typical sources Examples of aluminum oxide include aluminates, alumina, and aluminum compounds such as AlCb, Ab(SO 4 ) 3 , Al(OH) 3 , kaolin clays, and other zeolites.
    [0081] Metal aluminophosphate molecular sieves can be synthesized using the process of this invention. In one embodiment, metal aluminophosphate molecular sieves can be represented by the empirical formula, on an anhydrous basis, mR:(M x Al y P z )O 2 , where R represents at least one structure-directing agent ; m is the number of moles of R per mole of (M x Al and P z )O 2 and m has a value from 0 to 1; and x, y, and z represent the mole fraction of Al, P and M, where M is a metal selected from groups 1 to 10 of the Periodic Table. In one embodiment, M is selected from the group consisting of Si, Ge, Co, Cr, Cu, Fe, Ga, Mg, Mn, Ni, Sn, Ti, Zn, Zr, and mixtures thereof. In one embodiment, m is greater than or equal to 0.2, and x, y, and z are greater than or equal to 0.01. In another embodiment, x is from 0.01 to 0.2, y is from 0.4 to 0.5, and z is from 0.3 to 0.5.
    [0083] Metal aluminophosphate molecular sieves include silicoaluminophosphate (SAPO) molecular sieves, aluminophosphate (AlPO) molecular sieves, and metal-substituted forms thereof. Non-limiting examples of SAPO and AlPO molecular sieves under the present invention include molecular sieves selected from the group consisting of SAPO-5, SAPO-8, SAPO-11, SAPO-16, SAPO-17, SAPO-18, SAPO- 20, SAPO-31, SAPO-34, SAPO-35, SAPO-36, SAPO-37, SAPO-40, SAPO-41, SAPO-42, SAPO-44, SAPO-47, SAPO-56, AlPO-5, AlPO-11, AlPO-18, AlPO-31, AlPO-34, AlPO-36, AlPO-37, AlPO-46, metal-containing molecular sieves thereof, and mixtures thereof. In one embodiment, the molecular sieve is selected from the group consisting of SAPO-18, SAPO-34, SAPO-35, SAPO-44, SAPO-56, AlPO-18, AlPO-34, metal-containing molecular sieves thereof, and mixtures of them.
    [0085] Depending on the particular target molecular sieve, a structure directing agent (SDA) may be employed, in order to promote crystallization of the target product. As is well known to those skilled in the art, the particular SDA used in the synthesis of a molecular sieve can be selected according to the particular target molecular sieve.
    [0087] A person skilled in the art will understand that the molecular sieves described herein may contain impurities, such as amorphous materials, unit cells that have infrastructure topologies that do not match the molecular sieve, and/or other impurities (for example, certain materials organic).
    [0089] The reaction mixture is maintained under crystallization conditions, for example, at an elevated temperature. Generally, the reaction conditions include a temperature in the range of 125°C to 220°C, typically 150°C to 200°C, and frequently 160°C to 180°C. The reaction can be carried out under hydrothermal conditions. In one embodiment, the reaction can be run in an autoclave such that the reaction mixture is subjected to autogenous pressure. The reaction mixture may be subjected to gentle agitation or shaking during the crystallization step, for example, generally at a speed in the range of 140 rpm to 160 rpm.
    [0091] It is desirable that the reaction mixture contain a minimum amount of solid reactants. In one embodiment, the reaction mixture contains at least 8% by weight of solid reactants. In another embodiment, the reaction mixture contains at least 10% by weight of solid reactants.
    [0092] During the hydrothermal crystallization step, molecular sieve crystals may be allowed to spontaneously nucleate from the reaction mixture. The use of molecular sieve crystals as seed material may be advantageous in reducing the time required for crystallization to occur and for the synthesis to be completed. Additionally, seeding can promote nucleation and/or molecular sieve formation on any unwanted phase, leading to an increase in the purity of the target product. When used as seeds, the seed crystals are typically added in an amount between 1% and 10% of the weight of the silicon source used in the reaction mixture.
    [0094] During hydrothermal synthesis, crystals exhibit several different stages of growth during which the reaction mixture can change from being a reasonably homogeneous medium composed of, for example, colloidal silica and alumina, to one that is more heterogeneous where distinct substances begin to appear. submicron molecular sieve crystals, which have limited solubility in the parent solution. Without being bound by any particular theory, as crystallites and their aggregates grow in size and number during the synthesis process, they displace increasingly larger volumes of fluid under critical conditions, thereby causing the overall viscosity of the crystallite to decrease. liquid paste increase. See, for example, W. J. Moore, Physical Chemistry, 4th edition, Prentice Hall, p. 946 (1972).
    [0096] It has been found that the extent of crystallization during synthesis can be assessed by monitoring changes in the rheological behavior of the reaction slurry under carefully controlled conditions. In the case of concentrated molecular sieve particles, growing in an autoclave paste, the viscometric behavior can be highly complex since the individual crystallites themselves tend to agglomerate into aggregates, thereby markedly increasing the bulk (i.e., the effective volume) of the molecular sieve material. Such increases in bulk due to crystallite agglomeration result in a much higher reaction mixture viscosity than would be expected based on the average size of the individual molecular sieve crystallites. See, for example, I.M. Krieger et al., Trans. Soc. Rheology, 3, 137-152 (1959), for a discussion of the relationship between particle bulk and solution viscosity.
    [0098] Furthermore, since the crystal aggregates are only loosely held together, their bulks at any given time are dependent on the degree to which the liquid paste is mixed or sheared, for example, during agitation in the reactor or during mixing. sample handling of the reaction mixture for viscosity measurements. The net result is that the measured viscosity of a sample of the reaction slurry at any given time depends not only on the average size and concentration of the crystallites, but also on various other factors including the tendency of the crystallites to form aggregates, the degree of mixing/shearing of the sample at the time of measurement, and the viscosity of the liquid phase of the reaction mixture (the latter of which is highly dependent on temperature). Despite these apparent complexities, and again without being bound by any particular theory, it has been discovered that measurement of at least one viscometric parameter of the reaction mixture under carefully controlled conditions can be used to assess the extent of crystallization of the crystal. molecular sieve in a liquid reaction paste.
    [0100] During the reaction, the extent of molecular sieve crystallization can be monitored by measuring, at various time points, at least one viscometric parameter of the reaction mixture. It has been found that during molecular sieve crystallization, certain bulk properties of the reaction mixture vary concurrently with the progress of the molecular sieve synthesis process, thereby allowing measurement of the bulk properties of the reaction mixture. reaction, to form a basis for determining the state of one or more properties of the molecular sieve. Such molecular sieve properties may include the state of crystallization of the reaction mixture (crystallite size, degree of crystallite agglomeration), as well as the quantitative yield of product, and characteristics related to the catalytic activity of the molecular sieve. Unlike prior art methods used to monitor crystallization during molecular sieve synthesis, the methods of the present invention allow the measurement of properties of the reaction mixture, and either instantaneously or within shorter periods of time than those of the prior art, the use of commercially available equipment. The properties of the reaction mixture can be measured in situ, or by removing a bulk sample of the reaction mixture for testing. Such measurements can be made continuously, or intermittently/periodically.
    [0102] In one embodiment, the at least one viscometric parameter of the reaction mixture is selected from the group consisting of viscosity shear rate index, measured viscosity, and combinations thereof.
    [0103] As a non-limiting example of reaction monitoring in accordance with the present invention, a sample of a reaction mixture to be monitored for a viscometric parameter is loaded into a rheometer at about room temperature, and the sample can be equilibrated in the rheometer at a preset temperature. Establishing equilibrium in the rheometer serves to homogeneously suspend molecular sieve crystallites, or aggregates of them, to provide a homogeneous sample for analysis. rheological. In one embodiment, the sample is brought to equilibrium in the rheometer by subjecting the sample to a preset shear rate, typically in the range of 500 s-1 to 1200 s-1, usually 800 s-1 to 1100 s-1, and frequently 1000 s-1, for a period in the typical range of 30 seconds to 60 seconds.
    [0105] The present invention is not limited to monitoring molecular sieve synthesis through a rheometer; rather, within the scope of the present invention are also different techniques, methods, protocols or secondary or complementary measurement tools, capable of detecting changes in the viscosity of the liquid paste and/or in the behavior of the Newtonian fluid, during growth. of the glass. Such secondary tools may include the use of inline/high pressure viscometers coupled with fluid circulation loops in the autoclave, and vibration analyzers coupled with the autoclave or external agitator shaft.
    [0107] In one embodiment, a viscosity shear rate index is determined for each of a plurality of samples of the reaction mixture, taken at a plurality of time points during the molecular sieve synthesis process. The viscosity shear rate index of each sample of the reaction mixture is quantified or determined, assuming a Herschel-Bulkley flow model, subjecting the sample to a plurality of shear rates at the preset temperature, and recording a value of shear stress corresponding to each of the plurality of shear rates, to provide a plurality of shear stress values. Typically each of the plurality of shear rates may be within the range of 100 s-1 to 1000 s-1. Thereafter, the viscosity shear rate index (Herschel-Bulkley exponent, n) for the sample is determined based on the plurality of shear rates and the corresponding plurality of shear stress values, where the relationship between shear rate ( y ) and shear stress (o) is given by: oa Yn. As an example, the viscosity shear rate index (n) can be determined by fitting a straight line to a plot of the natural logarithm of the shear stress values (ln(o), Pascal; y-axis) against the natural logarithm of the shear rate values (ln(Y), s-1; x-axis). Using this model, Newtonian fluids have n = 1, while fluids (liquid pastes of reaction mixture) with loosely agglomerated crystallites will typically exhibit pseudoplastic (or shear thinning) behavior, with n < 1. In general, when the smaller the viscosity shear rate index of a liquid paste, the higher the degree of pseudoplasticity.
    [0109] In one embodiment, the measured viscosity is determined for each of a plurality of samples of the reaction mixture, taken at a plurality of time points during the molecular sieve synthesis process. The measured viscosity of each sample can be determined with a rheometer, subjecting the sample to at least one shear rate at the preset temperature, and recording at least one shear stress corresponding to the at least one shear rate. Thereafter, the measured viscosity (|j) of the sample can be determined by dividing the shear stress (o) by the corresponding shear rate (y), ie j = o/y. Typically, the at least one shear rate to which the sample is subjected may be in the range of 100 s-1 to 1000 s-1.
    [0111] In one embodiment, the monitoring step comprises periodically removing a sample from the reaction mixture, cooling each sample to a preset temperature, and measuring the at least one viscosity parameter of each sample. The frequency with which the reaction mixture is sampled can be hourly, or more or less frequently. For example, the reactor may be sampled as often as once every 10 minutes to 120 minutes, and typically once every 15 minutes to 60 minutes. Cooling of each sample to a preset temperature may generally be in the range of 5°C to 50°C, typically 10°C to 30°C, and frequently 15°C to 25°C. Generally, the viscometric parameter (for example, viscosity shear rate index, or measured viscosity) of each sample is measured within ± 0.2°C of the preset temperature, typically within ± 0.1°C, and frequently within ± 0.05°C from the preset temperature. Thereafter, an end point of the molecular sieve synthesis process can be determined based on, for example, a change in the measured viscosity of the reaction mixture, viscosity shear rate index of the reaction mixture, and combinations from them.
    [0113] In one embodiment, the monitoring step comprises periodically removing a sample from the reaction mixture; subjecting each sample to a plurality of shear rates; recording a shear rate corresponding to each of the plurality of shear rates, to provide a plurality of shear stress values, and determining a viscosity shear rate index (n) for each sample. Accordingly, in one aspect of the present invention, the rheological properties of an autoclave reaction slurry may be related to different stages of molecular sieve crystal growth, for example relative to the end point of a synthesis process. of molecular sieve. As a non-limiting example, the degree of crystallization of a molecular sieve from a suitable reaction mixture during the course of a molecular sieve synthesis process can be monitored or evaluated by monitoring at least one viscosity-related or viscosity-related parameter. viscosity of the reaction mixture. Furthermore, an end point of the molecular sieve synthesis process can be determined, based on monitoring the at least one viscometric parameter of the reaction mixture.
    [0114] In one embodiment, the end point of the molecular sieve synthesis process may be determined at a time preceding the end point; that is, the end point can be predicted, such that the molecular sieve synthesis reaction can be quenched, and the process stopped at a time that matches optimal molecular sieve characteristics. As an example, for certain applications including different molecular sieve catalyzed processes, smaller crystals provide superior results over their larger crystal counterparts. After nucleation in the reactor or autoclave under crystallization conditions, the individual molecular sieve crystals grow over time and, in the absence of some mechanism to monitor the extent of crystal growth, may reach a supraoptimal size range. Each XRD analysis of a liquid reaction paste, as used in conventional molecular sieve crystallization monitoring, typically takes several hours, after which time the molecular sieve product may have substantially degraded, for example, by obtaining crystals. excessively large in size. By monitoring a viscometric parameter of the reaction mixture according to an embodiment of the present invention, the molecular sieve synthesis process can be terminated in a timely manner so that molecular sieve crystals having the most desirable attributes are obtained. (for example, small size crystal). In one embodiment, the monitoring of molecular sieve crystallization from the reaction mixture can be suspended after the reaction end point has been predicted and before the reaction end point has occurred.
    [0116] In one embodiment, the end point of a molecular sieve process is determined based on monitoring of at least one viscometric parameter. In one embodiment, the end point of the synthesis reaction is determined or predicted based on a particular qualitative or quantitative change in the at least one viscometric parameter of the reaction mixture. Reference herein to "a change" in a parameter of a reaction mixture, such as measured viscosity or viscosity shear rate index, includes one or more changes or a series of changes that may occur during the course of a reaction. reaction or process for the synthesis of a molecular sieve or molecular sieve. In one embodiment, the end point of the synthesis process is determined based on a change in the measured viscosity of the reaction mixture, a change in the viscosity shear rate index of the reaction mixture, and combinations thereof. . In one embodiment, the at least one viscometric parameter is the measured viscosity of the reaction mixture, and the end point of the synthesis reaction may be determined based on a change in the measured viscosity of the reaction mixture. In another embodiment, the at least one viscometric parameter is the viscosity shear rate index of the reaction mixture, and an end point of the synthesis reaction is determined based on a change in the monitored shear rate index. viscosity shear. In yet another embodiment, both the viscosity shear rate index and the measured viscosity of the reaction mixture can be monitored during the course of the synthesis process, and the end point of the synthesis reaction can be determined based on from a change in the combination of the viscosity shear rate index and the measured viscosity of the reaction mixture.
    [0118] In one embodiment, the at least one viscometric parameter can be monitored by withdrawing a sample from the reaction mixture, at each of a plurality of time points during the course of the molecular sieve synthesis process, and then measuring the (the) viscometric parameter(s) of the samples. In another embodiment, the at least one viscometric parameter of the reaction mixture, eg, viscosity shear rate index (q) or measured viscosity (p), is measured using a rheometer. In yet another embodiment, the viscometric parameter of the reaction mixture is measured using a rheometer having a cone and disk geometry. Flat disc and concentric cylinder rheometer geometries can also be used under the invention. Viscometric analyzes under the present invention are not limited by any particular rheometer geometry.
    [0120] In accordance with one aspect of the present invention, during the synthesis of the molecular sieve, at least one property of the sieve, for example, crystal size or yield, is estimated by comparing one or more values of a measured parameter of the molecular sieve mixture. reaction, with data from a predetermined relationship between the properties of the sieve and the measured property. The predetermined relationship between the sieve property and the measured property is derived from one or more previous synthesis processes, for example, using the same or substantially the same equipment, and the same or substantially the same reaction mixture and conditions, during the which at least one measured property and at least one of the sieve properties were correlated as a function of time. Thus, once the system has been calibrated by correlating measured properties of the reaction mixture with observed properties of the molecular sieve, the measured properties of the reaction mixture can serve as a basis for determining the progress of the reaction, relative to one or more properties of the molecular sieve, during subsequent syntheses.
    [0122] In the event that the temperature of the molecular sieve product/reaction mixture is not immediately lowered, the reaction vessel will withstand a period of cooling during at least the initial stages of which molecular sieve crystal growth may continue. , albeit at a lower rate. In this case, when the end point of the reaction has been signaled, for example, by the measured reaction mixture parameter(s), the start of reaction cutoff or quench can be adjusted to account for the cooling period.
    [0124] Other complementary (eg, non-viscosymmetric) analyzes of the reaction mixture, eg, by pH measurements, electron microscopy, XRD, scanning electron microscopy (SEM), ultrasound, electrical conductivity, and the like, can also be performed to supply data that can be used to supplement, support, or confirm a reaction endpoint, as derived from viscosity-related data.
    [0126] For calibration of a molecular sieve synthesis process in accordance with one aspect of the present invention, the degree of molecular sieve crystallization for a given slurry sample may be determined directly by XRD powder analysis and/or XRD analysis. SEM, concurrently with measurements of at least one viscometric parameter of the same sample. Thus, a given molecular sieve synthesis process can be calibrated by temporal correlation of the degree of crystallization, as determined directly by XRD analysis, with the measured viscometric parameter(s).
    [0128] Viscometric parameter values, or changes in them, signaling a reaction endpoint may vary depending on factors such as the target molecular sieve, its desired properties, the composition of the reaction mixture, crystallization conditions, and the like. However, under standardized conditions of synthesis, for a given molecular sieve product, the values of viscometric parameters recorded during the course of the synthesis process are reproducible from preparation to preparation. Thus, after a given synthesis process for a particular molecular sieve has been calibrated with respect to the time course of the reaction to its end point, the calibration data can be used to estimate the end point of future processes to make the same product by the same or substantially the same process. Of course, such processes can be run under highly standardized conditions, eg, with respect to reaction mixture components, reaction mixture mole ratios, crystallization conditions, reactor size, and the like.
    [0130] Once the molecular sieve has been formed in an appropriate quantity and quality, the solid product can be separated from the reaction mixture by standard mechanical separation techniques, such as filtration. The crystals can be washed with water and then dried to obtain molecular sieve crystals as synthesized. The drying step can be performed at atmospheric pressure or under vacuum.
    [0132] Also described herein is a method for monitoring the crystallization of a molecular sieve from a reaction mixture, during a molecular sieve synthesis process, wherein the method comprises monitoring at least one viscosity parameter of the reaction mixture; and determining an end point of the molecular sieve synthesis process. In one embodiment, the at least one viscometric parameter is selected from the group consisting of viscosity shear rate index, measured viscosity, and combinations thereof. In another embodiment, the end point of the molecular sieve synthesis process is determined based on a change in the measured viscosity of the reaction mixture, a change in the viscosity shear rate index of the reaction mixture, in change in pH of the reaction mixture, and combinations thereof.
    [0134] In one embodiment, the method for monitoring crystallization during the course of a molecular sieve synthesis process may include monitoring the pH of the reaction mixture, and the monitored pH of the reaction mixture may be used to determine or confirm an end point of the molecular sieve synthesis process. The pH of the reaction mixture may also be monitored during crystallization to provide supplemental data to determine or confirm the status of one or more properties of the molecular sieve. The use of pH measurements to monitor crystallization is known in the art, see eg, J. L. Casci et al., Zeolites, 3, 186-187 (1983); B.M. Lowe, Zeolites, 3, 300-305 (1983); YES. Zones, Zeolites, 9, 458-467 (1989); what if. Zones et al., Microporous Mesoporous Mater., 58, 263-277 (2003).
    [0136] In general, reaction mixture viscosity shear rate index data can be more reproducible from batch to batch, when compared to measured viscosity data. Determination of the viscosity shear rate index of the reaction mixture provides an additional set of data that can be used alone, or in combination with other data (eg, measured viscosity, pH), to pinpoint or predict the end point. of the reaction. In one embodiment, the monitoring step is suspended before the end point of the molecular sieve synthesis process. In one embodiment, the measured viscosity and viscosity shear rate index of the reaction mixture are measured using a rheometer.
    [0138] Examples:
    [0140] The following examples are given to illustrate the present invention. However, it should be understood that the invention is not limited to the specific details or conditions described in these examples.
    [0141] The examples discuss the synthesis of SSZ-32X which, compared to standard SSZ-32, possesses less well defined crystallinity, altered argon adsorption ratios, increased external surface area, and reduced cleavage activity over other intermediate sized molecular sieves. pore, used for a variety of catalytic processes.
    [0143] Example 1
    [0145] Synthesis of SSZ-32X without seed addition
    [0147] A reaction mixture for the synthesis of SSZ-32X was prepared by sequential addition to deionized water of the following: aqueous KOH 45.8% KOH (M), N,N'-diisopropylimidazolium hydroxide 0.47M (Q), and Nalco 1SJ612 alumina-coated silica sol (a version with 25 wt% solids, a SiO2/Al2O3 ratio of 35, and acetate as counterion). The molar ratios of the components of the reaction mixture were as follows:
    [0152] The reaction mixture was heated at 170°C over a period of 8 hours and stirred continuously at 150 rpm for 135 hours.
    [0154] Throughout the course of the reaction, the pH and apparent viscosity of the reaction mixture were monitored to determine the end point of the reaction. The end point of the reaction was noted at a reaction time (at temperature) of about 135 hours.
    [0156] The standard SSZ-32 and SSZ-32X have the infrastructure typology designated "MTT" by the International Zeolite Association. Zeolite SSZ-32X synthesized according to the present invention can be characterized by its X-ray diffraction (XRD) pattern. SSZ-32 standard and SSZ-32X can be distinguished by XRD because the XRD pattern broadens as crystallites decrease in size. Figure 1 compares the peak occurrence and relative intensity of SSZ-32X with that of standard SSZ-32. The powder XRD lines in Table 1 are representative of standard calcined SSZ-32. The powder XRD lines in Table 2 are representative of calcined SSZ-32X.
    [0158] Table 1
    [0163] Minor variations in the diffraction pattern may be the result of variations in the molar ratios of the infrastructure species of the particular sample, due to changes in the lattice constants. Additionally, sufficiently small crystals will affect the shape and intensity of the peaks, leading to significant broadening of the peaks. Minor variations in the diffraction pattern may be the result also from variations in the model organic agent used in the preparation, and from variations in the SiO 2 /Al 2 O molar ratio of different preparations. Calcination can also cause minor shifts in the XRD pattern. Despite these minor disturbances, the basic lattice structure of the crystal remains unchanged.
    [0165] The powder X-ray diffraction patterns presented herein were collected by standard techniques. The radiation was CuK radiation. The peak heights and positions, as a function of 20 where 0 is the Bragg angle, were read from the relative peak intensities (with noise adjustment), and d, the corresponding interplanar spacing in Angstroms, can be calculated. to registered lines.
    [0167] The product was determined to be SSZ-32X by powder XRD analysis.
    [0169] Example 2
    [0171] Synthesis of SSZ-32X with seed inoculation
    [0173] A reaction mixture for the synthesis of SSZ-32X was prepared by adding the same components as in Example 1, except that SSZ-32X paste seeds (3.15% by weight of SSZ-32X, on the basis of the SiO 2 content). Seed crystals were obtained from the previous preparation of SSZ-32X in example 1. The molar ratios of the components of the reaction mixture were as follows:
    [0178] The reaction mixture was heated at 170°C over a period of 8 hours and stirred continuously at 150 rpm for approximately 65 hours.
    [0180] During the course of the synthesis reaction, the measured viscosity, viscosity shear rate index, and pH of the reaction mixture were monitored. The end point of the reaction was evidenced in a reaction time (at temperature) of approximately 65 hours.
    [0182] The zeolite sample was calcined at 595°C and ion exchanged to the ammonium form, as described in US 7,390,763. The sample was preheated to 450°C to remove ammonia before micropore volume was determined according to ASTM D4365. The product had a micropore volume of 0.035 cc/g. In contrast, standard SSZ-32 had a micropore volume of approximately 0.06 cc/g.
    [0184] The product was confirmed to be SSZ-32X by powder XRD analysis. Analysis showed that the product had a SiO2/AbO3 molar ratio of 29.
    [0186] Example 3
    [0188] SSZ-32X overcrystallized
    [0190] A reaction mixture for the synthesis of SSZ-32X was prepared by adding the same components as in Example 1, except that seeds of SSZ-32X (3.15% by weight based on SiO 2 content) were included in the reaction mixture. reaction. The molar ratios of the components of the reaction mixture were as follows:
    [0193] The reaction mixture was heated at 170°C for a period of 8 hours and stirred continuously at 150 rpm for approximately 90 hours at 170°C.
    [0195] The pH and apparent viscosity of the reaction mixture were monitored throughout the course of the reaction to determine the end point of the reaction. The end point of the reaction was evident at a reaction time (at temperature) of about 65 hours, but the reaction was allowed to continue for an additional 25 hours after the end point determined to provide overcrystallized SSZ-32X.
    [0197] The product was determined to be SSZ-32X by powder XRD analysis.
    [0199] Concerning that the products of the invention could be a mixture of small crystals and considerable amorphous material, the product of Example 3 was analyzed by Transmission Electron Microscopy (TEM). A.W. Burton et al. in Microporous Mesoporous Mater. 117, 75-90, 2009 disclose TEM measurement methods. Microscopy work showed the product to be fairly uniform small crystals of SSZ-32 (product was SSZ-32X) with very little evidence of amorphous material. The product, as determined by TEM measurements, showed elongated crystals with an average length of at least 43 nanometers and an average width of at least 23 nanometers.
    [0201] Particularly desirable SSZ-32X crystals typically have a crystallite size of no greater than 40 nanometers. In contrast, standard SSZ-32 crystals are elongated with an average length of about 170 nanometers.
    [0203] Determination of measured viscosity of reaction mixtures
    [0205] The measured viscosity was determined using standard techniques at atmospheric pressure, using a controlled stress rheometer equipped with a cone and disk geometry. Samples of the hot liquid paste were taken from the autoclave every hour during the zeolite synthesis procedure and carefully cooled through a heat exchanger to sub-boiling temperatures before being transferred to a closed container to minimize changes in composition. due to steam loss. The sample in the closed container was actively cooled to approximately 25°C. The same sample can also be used to measure viscosity shear rate index and pH.
    [0207] Each cooled liquid paste sample was mixed or agitated before loading it to the rheometer disc to ensure sample homogeneity, and after loading the sample homogeneity was maintained by subjecting it to a preliminary shear rate of 1000 s. -1 for at least 30 seconds, in order to equilibrate the mixture at 25.0°C. After that, each sample was subjected to shear rates of 100 s-1, 200 s-1, 500 s-1, and 1000 s-1 at 25.0°C, and the corresponding values of shear stress necessary for maintain those shear rates. The "measured viscosity" of each sample was then determined by dividing the measured shear stress by its corresponding shear rate. Figure 2 shows the results of the measurement of the viscosity of the reaction mixture, during the course of the synthesis of SSZ-32X in example 2.
    [0209] Determination of Viscosity Shear Rate Index of Reaction Mixtures
    [0211] The viscosity shear rate index (or rate index, n) of an autoclaved reaction mixture (slurry) was monitored during the course of the synthesis of zeolite SSZ-32X in Example 2 by periodic determination of the liquid paste sample rate index, at atmospheric pressure using a rheometer controlled tension equipped with a geometry of cone and disc. Samples of hot liquid paste from the autoclave were taken every hour during the zeolite crystallization process and carefully cooled to approximately 25.0°C.
    [0213] Each liquid paste sample was shaken or mixed, before loading to the rheometer disk, to ensure sample homogeneity, and sample homogeneity was maintained after loading by subjecting the sample to a preliminary shear rate of 1000 s. -1 for at least 30 seconds, in order to equilibrate the mixture at 22.0°C. Thereafter, each mixture was subjected to a series of increasing shear rates, ranging from 100 s-1 to 1000 s-1 at 25.0°C, and the corresponding shear stress required to maintain each shear rate was recorded. .
    [0215] At different time points during the course of the reaction, the rheological properties of the liquid paste samples ranged from Newtonian flow to shear thinning or pseudoplastic flow, depending on the size and number of the zeolite particles and their propensity for agglomeration ( see for example figure 3). It can be seen from Figure 3 that the sample of the reaction mixture taken at 65 hours exhibits a marked shift from Newtonian flow, towards shear thinning behaviour. The degree of deviation from the Newtonian fluid behavior of the liquid paste samples was quantified, assuming a Herschel-Bulkley flow model in which the relationship between shear stress (o) and shear rate (y) is given by or Yn. The Herschel-Bulkley exponent, or viscosity shear rate index (n), was determined by fitting a straight line to a plot of ln(o) (Pascals; y-axis) versus ln(Y) (s-1; x-axis) (see, for example, Figure 4). Figure 5 shows the results of monitoring the viscosity shear rate index of the reaction mixture during zeolite synthesis. After approximately 40 hours, the rate index began to fall and continued to fall through the reaction time of approximately 65 hours, with the most rapid decrease in rate index occurring between 62 and 65 hours. It can be seen from Figure 5 that this dramatic decrease in the rate index coincided with a sharp increase in the measured pH.
    [0217] Although the invention has been described primarily with respect to autoclave synthesis, aspects of the present invention may also be applicable to continuous processes for zeolite synthesis. Furthermore, while certain aspects of the invention have been described primarily with respect to SSZ-32X, the invention is not limited to SSZ-32X zeolite or molecular sieves having the MTT infrastructure. The procedures, techniques, and principles described herein may be generally applied to monitoring the synthesis of other zeolites and molecular sieves, from suitable reagents and under appropriate crystallization conditions. Such reagents and conditions will be generally known to those of ordinary skill.
    [0219] This written description uses examples to disclose the invention, including best mode, and also enables any person skilled in the art to make and use the invention. The patentable scope is defined by the claims.
    权利要求:
    Claims (5)
    [1]
    Claim 1. A process for the synthesis of a molecular sieve, comprising:
    a) supplying a reaction mixture sufficient to synthesize the molecular sieve;
    b) keeping the reaction mixture under crystallization conditions;
    c) monitoring of at least one viscometric parameter of the reaction mixture, wherein the monitoring step comprises:
    a) Periodic withdrawal of a sample of the reaction mixture;
    b) cooling each sample to a pre-established temperature; Y
    c) measurement of at least one viscosity parameter of each sample;
    or
    a) periodic removal of a sample from the reaction mixture;
    b) subjecting each sample to a plurality of shear rates;
    c) recording a shear stress corresponding to each of the plurality of shear rates, to provide a plurality of shear stress values; Y
    d) determining a viscosity shear rate index for each sample; Y
    d) determination of an end point based on the monitoring of the at least one viscometric parameter;
    wherein the end point is the stage of the reaction or process when the target product has been formed and has achieved at least one desired product characteristic or attribute.
    [2]
    2. The method of claim 1, wherein the reaction mixture contains at least 8% by weight of solid reactants.
    [3]
    3. The process of claim 1, wherein the reaction mixture contains at least 10% by weight of solid reactants.
    [4]
    4. The method of claim 1, wherein the at least one viscometric parameter is selected from the group consisting of viscosity shear rate index, measured viscosity, and combinations thereof.
    [5]
    5. The method of claim 1, wherein the end point is determined based on a change in the measured viscosity of the reaction mixture, a change in the viscosity shear rate index of the reaction mixture, or combinations of them.
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    同族专利:
    公开号 | 公开日
    CA2814745A1|2012-05-10|
    US8734758B2|2014-05-27|
    EP2635526B1|2019-09-25|
    BR112013006452B1|2019-12-24|
    BR112013006452A2|2016-07-26|
    DK2635526T3|2019-12-09|
    WO2012060911A1|2012-05-10|
    KR20140009236A|2014-01-22|
    ES2761840T3|2020-05-21|
    CN103189314A|2013-07-03|
    EP2635526A4|2015-09-16|
    CN103189314B|2015-08-19|
    EP2635526B9|2021-12-15|
    KR101891633B1|2018-08-27|
    US20120114552A1|2012-05-10|
    SG190768A1|2013-08-30|
    JP5780683B2|2015-09-16|
    CA2814745C|2018-09-11|
    JP2014500215A|2014-01-09|
    EP2635526A1|2013-09-11|
    MY156717A|2016-03-15|
    ZA201302125B|2014-05-28|
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    优先权:
    申请号 | 申请日 | 专利标题
    US12/940,785|US8734758B2|2010-11-05|2010-11-05|Method for preparing molecular sieves|
    PCT/US2011/046211|WO2012060911A1|2010-11-05|2011-08-02|Method for preparing molecular sieves|
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