Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/009—Preparation by separation, e.g. by filtration, decantation, screening
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2229/00—Aspects of molecular sieve catalysts not covered by B01J29/00
  • B01J2229/30—After treatment, characterised by the means used
  • B01J2229/37—Acid treatment
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J29/00—Catalysts comprising molecular sieves
  • B01J29/86—Borosilicates; Aluminoborosilicates
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/04—Mixing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/06—Washing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/08—Heat treatment
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B37/00—Compounds having molecular sieve properties but not having base-exchange properties
  • C01B37/007—Borosilicates

Definitions

• the present invention relates to a process for the preparation of catalysts based on boron-containing silicates of zeolitic structure and to catalysts obtainable by the process.
• Isobutene is a valuable raw material for the production of a variety of organic compounds in the chemical industry. It is used for the production of
• Polyisobutene a precursor for, among others, lubricant and fuel additives as well as for adhesives and sealants.
• isobutene is used as alkylating agent, in particular for the synthesis of tertiary butyl aromatics and as an intermediate for the production of peroxides.
• isobutene can be used as a precursor for methacrylic acid and its esters.
• methacrylic acid and its esters As an example, mention should be made here of methyl methacrylate, which is used to prepare Plexiglas®.
• Further products of isobutene are branched C 5 -aldehydes, -carboxylic acids, -alcohols and C 5 -olefins. Isobutene thus represents a high added value with increasing demand on the world market. The decisive factor for many applications is the chemical purity of isobutene; purities of up to 99.9% are required here.
• the raw material isobutene is obtained in the light benzene fraction, the C 4 fractions from the FCC units or from the steam crackers of the refineries and is therefore present in a mixture with other alkenes and saturated hydrocarbons with the same carbon atom number.
• the butadiene which constitutes about 50% of the C 4 fraction, is separated off by extractive rectification or converted by selective hydrogenation to form linear butenes.
• the remaining mixture, so-called raffinate 1 consists of up to 50% isobutene. Due to the almost identical physical properties of isobutene and 1-butene, economical separation of the isobutene by distillation or extraction processes is not possible.
• Derivatizing agent can be cleaved.
• Important processes here are the reactions with water to terf-butanol and with methanol to methyl-te / ⁇ -butyl ether (MTBE).
• MTBE methyl-te / ⁇ -butyl ether
• Ion exchangers such as sulfonated copolymers of styrene and divinylbenzene are used here as a heterogeneous catalyst.
• MTBE from the C 4 cut can easily be distilled off by distillation, owing to the large differences in the boiling temperatures, and then selectively split back into the products isobutene and methanol.
• the co-product methanol can be recycled in the MTBE synthesis.
• the existing plants for C 4 treatment and MTBE synthesis can thus be extended by the process step of MTBE fission.
• the cleavage of MTBE is an endothermic equilibrium reaction.
• Thermodynamic equilibrium thus shifts with increasing temperature in the direction of the cleavage products.
• An increase in pressure causes a shift in the chemical equilibrium in the direction of the educt MTBE.
• the MTBE cleavage can be carried out both homogeneously in the liquid phase and heterogeneously catalyzed in the gas phase. Due to the low stability of the homogeneous catalysts and the lower equilibrium conversions in the liquid phase, the
• Vapor pressures of the expected components in the reaction medium sought to save costs for the compression of the gases in downstream processing and at the same time be able to realize a condensation with cooling water.
• the MTBE cleavage takes place in the presence of an acidic catalyst.
• DME Derivative product dimethyl ether
• Catalyst system are other oligomerization reactions, such. the formation of trimers, not exclude.
• aluminosilicates When using aluminosilicates usually reaction temperatures of 150 to 300 ° C and pressures of 1 to 7 bar are driven. Many patents claim amorphous or even crystalline aluminosilicates, which have a proportion of 0.1 to 80% aluminum, and thus achieve this
• metal oxides of moderately strong electronegative elements such as magnesium, titanium, vanadium, chromium, iron, cobalt, manganese, nickel, zirconium and boron, are described for ether cleavage. Furthermore, a doping of the aluminosilicates with said metal oxides to influence the acidity of the catalyst can be made.
• Zeolites are hydrated crystalline aluminosilicates with a three-dimensional
• the zeolite framework usually forms a highly ordered
• Unit cell is given by the following general formula: Mx / n [(AIO2) x (SiO 2) y] wH 2 O ⁇ where n is the valence of the cation M and w denotes the number of water molecules per unit cell.
• Si / Al ratio y / x> 1.
• the isomorphous substitution of aluminum or silicon by other network-forming elements leads to variant-rich and diverse zeolite-analogous materials. Taking into account the substitution possibilities, the following formula results for zeolites and zeolite-analogous materials:
• Molecular diameters are due to the particular suitability of zeolites as selective adsorbents, for which the term "molecular sieves" has been established.
• IZA has included a nomenclature in the "Atlas of Zeolite Structure Types" based on the topology of the
• zeolites Host framework, proposed and approved by the IUPAC. Thus, most synthetic zeolites are named by the combination of a three-letter structure code. Examples include the structure types SOD (sodalite), LTA (zeolite A), MFI (Pentasil zeolite), FAU (zeolite X, zeolite Y, faujasite), BEA (zeolite beta) and MOR (mordenite) called.
• Structure-type zeolites MFI are so-called “medium-pore” zeolites, an advantage of this type of structure being the uniformity compared to the "narrow-pore” structural types (SOD, LTA) and “wide-pore” structural types (FAU, BEA, MOR) Channel Structure
• the MFI type of structure belongs to the series of crystalline, microporous aluminosilicates and is exceptionally shape-selective and temperature-stable, but also a highly acidic zeolite, but the use of strongly acidic zeolites as catalysts for the MTBE cleavage can, as already stated , lead to a collapse of isobutene selectivities.
• DE2953858C2 describes the use of "boralites” as catalysts in MTBE cleavage, which are double oxides of silicon and boron with a porous crystalline structure, which are boron-modified silicic acids and have a zeolitic structure to the structural type of this Boralite.
• the preparation takes place under hydrothermal conditions at a pH of 9 to 14.
• EP0284677A1 discloses a process for preparing a catalyst for cracking nitrogen-containing oil, such as shale oil, based on a boron-containing crystalline material of zeolitic structure.
• Possible zeolite structures are ZSM-5, ZSM-1 1, ZSM-12, beta and Nu-1. The production takes place in a basic environment. The suitability of these catalysts for MTBE cleavage is not described.
• Silicates are the salts and esters of orthosilicic acid Si (OH) and their
• a "boron-containing silicate” within the meaning of this invention is a silicate containing boron in oxidic form.
• zeolitic structure is to be understood as meaning a morphology corresponding to the zeolites, and the term “zeolite-analogue” is used synonymously.
• zeolites belong to the group of aluminosilicates, ie silicates containing aluminum in oxidic form.
• boron silicates described here correspond to the zeolites in terms of their morphology, they are also referred to below as “boron zeolites.” However, the use of the term “boron zeolite” does not mean that this material must necessarily contain aluminum. Preferred are
• boron zeolites according to the invention even impurities or trace constituents - even free of aluminum.
• the boron zeolites modified by the process according to the invention proved to be active and selective catalysts for the cleavage of MTBE in isobutene and methanol.
• the result is catalysts that generate up to 90% sales
• the present invention thus provides a process for the preparation of catalysts based on boron silicates, comprising the following steps: a) providing an aqueous suspension comprising at least one boron-containing silicate having a zeolitic structure,
• boron zeolites of the structural type MFI since they bring many advantages. It is known that the acidity of a zeolite can be influenced by incorporation of heteroatoms into the silicon skeleton as follows:
• a boron-containing zeolite is a much less acidic zeolite than a zeolite containing only aluminum and silicon. This is not expected as boron has a higher electronegativity than aluminum.
• the Si / B ratio can be varied over a wide range and thus offers many possibilities for adjusting the catalytic properties.
• zeolites of the structural type MFI have a uniform channel structure and are thus characterized as extremely form-selective and temperature-stable. Presumably due to the small dimensioning zeolites of this type of structure are particularly resistant to coke.
• the at least one zeolite in step a) advantageously has a molar ratio S1O2 / B2O3 of between 2 and 4, preferably between 2.3 and 3.7, more preferably of 3.
• the boron zeolite according to the invention is not a zeolite in the strict sense, since it contains no aluminum. It is preferably free of aluminum or has it at best in the form of impurity or as a trace constituent. A content of aluminum below 0.1 wt .-% is tolerable.
• the boron content of the catalyst according to the invention is less than 1% by weight. Too much boron could promote byproduct formation. Preferably, the boron content is even below 0.5 wt .-%, most preferably at 0.3 wt .-%. If the boron-containing silicate provided in the suspension has too large boron content, it can be reduced by the acid treatment. Compared to AI, B can be washed out quite well with acid. Thus, it has been possible by acid treatment to reduce the boron content of an untreated silicate from 1% by weight to about 0.1% by weight. Thus, the silicate contained in the suspension should at least after addition of the acid have a boron content in said range.
• the boron silicate in step a) has a BET surface area between 300 m 2 / g and 500 m 2 / g, preferably between 330 and 470 m 2 / g, more preferably between 370 and 430 m 2 / g.
• hydrothermal synthesis provides a particularly suitable synthesis of
• the educts which are essential for zeolite synthesis, can be divided into the following four categories: source of T atoms (boron, or
• Silicon source Silicon source
• template Silicon source
• mineralizer mineralizer
• Silicon sources that are commonly used in zeolite synthesis are
• Alkalimetasilicate Common boron sources are boric acid or alkali borates.
• the template compounds have structure-directing properties and stabilize the resulting zeolite structure during the synthesis. Templates are usually mono- or polyvalent inorganic or organic cations. In addition to water, bases (NaOH), salts (NaCl) or acids (HF) are used as inorganic cations or
• Organic compounds which are suitable for zeolite syntheses are, in particular, alkyl or arylammonium hydroxides.
• the mineralizer catalyzes the formation of the transition states needed for nucleation and crystal formation. This is done by solution, precipitation or
• the mineralizer increases the solubility and thus the concentration of the components in the solution.
• a mineralizer can be any mineralizer.
• Hydroxide ions are used, whereby the ideal pH for the zeolite synthesis can be adjusted. With the increase in OH concentration occurs
• the reactive T-atom sources, the mineralizer, the template and the water are mixed to form a suspension.
• the molar composition of the synthesis gel is the most important factor for influencing the reaction products:
• M and N are alkali metal or alkaline earth metal ions and R is an organic template.
• the suspension is transferred to an autoclave and is exposed to alkaline conditions, autogenous pressure and temperatures of 100 to 250 ° C for a few hours to several weeks. Under hydrothermal conditions, there is a supersaturation of the synthesis solution, which initiates the nucleation and the subsequent crystal growth. In addition to the nucleation are in the
• crystallization time depends inter alia on the zeolite structure. In the case of zeolites of the structural type MFI, crystallization is concluded after 36 hours.
• the template is removed by calcination in the air stream at 400 to 600 ° C.
• the organics are burned to carbon dioxide, water and nitrogen oxides.
• step b In order to modify the boron silicate, an acid treatment is carried out in step b), resulting in a reduction of the boron content. This leads to an increase in the activity of the zeolites or to the selective production of desired active centers.
• step b) the adjustment of the pH in step b) therefore takes place by adding hydrochloric acid or phosphoric acid.
• the stirring of the suspension in step c) advantageously takes place at a maximum of 80 ° C.
• Preferred developments of the present invention therefore provide that the stirring of the suspension according to step c) takes place at a maximum of 80 ° C.
• the maximum stirring temperature depends on the acid used. While HCl requires a temperature of 80 ° C, good results were obtained with H 3 PO 4 even at 25 ° C. When using phosphoric acid, the maximum stirring temperature should therefore be 25 ° C.
• a minimum stirring temperature of 0 ° C should be kept as low as possible, since freezing water makes stirring difficult.
• the duration of the stirring is at least 6 hours, preferably from
• stirring times can be up to about 36 hours.
• the isolation of the solid in step d) can be carried out by any method. Depending on the particle size, the vacuum or overpressure filtration is suitable.
• the solid may optionally be repeatedly washed with water in a further step. It is possible that the generated defects in the framework are annealed at high calcination temperatures by silanol condensation to form a cristobalite.
• the calcination of the solid in step f) is preferably carried out at a temperature of at most 500 ° C, more preferably of at most 400 ° C, particularly preferably of at most 350 ° C.
• the calcination of the solid can be carried out in principle in the air stream.
• step f) consists in that the calcination of the solid in step f) takes place in the air stream.
• step f) the calcination of the solid in step f) takes place in pure nitrogen flow.
• nitrogen-containing atmosphere is to be understood as a gas or gas mixture containing nitrogen in molecular form, and calcination may therefore be carried out in the presence of molecular nitrogen gas (N 2 ) or in the presence of a gas containing other types of nitrogen besides nitrogen contains, such as hydrogen (H 2 ).
• the solid obtained may, after cooling to room temperature, be washed several times with distilled water. Finally, the calcination is repeated in a stream of nitrogen or air.
• a preferred development of the invention is therefore also the method described above, wherein the solid obtained in step f) is washed with water and then step f) is repeated. After completion of the calcination, it is advisable with the obtained solid with
• the solid is immersed in standing methanol or overflowed by flowing methanol.
• the methanol can be liquid, gaseous or mixed liquid / gaseous in both cases.
• the treatment of the solid with methanol causes a reduction in the initial activity of the catalyst, which has proven to be advantageous in industrial use.
• the methanol treatment of the boron-silicate-based catalyst is analogous to the methanol treatment of aluminosilicate-based catalysts, which is described in the German patent application DE102012215956 still unpublished at the time of application. The content of this application is expressly incorporated herein by reference.
• the solid may also be treated with another preferably monohydric alcohol, such as ethanol.
• the aluminum-free boron silicate in step a), apart from impurities or trace constituents, has a molar ratio S1O2 / B2O3 of about 3, a boron content of less than 0.5% by weight and a surface measured After BET of about 405 m 2 / g, the adjustment of the pH in step b) by addition of phosphoric acid or hydrochloric acid, the stirring of the suspension in step c) between 20 and 80 ° C for a period of at least 24 hours and the isolation of the solid in step d)
• step e Vacuum filtration or overpressure filtration, the solid is washed with water in step e), and the calcination of the solid in step f) is carried out at a temperature of at most 350 ° C in a stream of nitrogen or in the air stream.
• the boron zeolites modified by the process according to the invention have low selectivities with respect to DME and Cs as catalysts in the cleavage of MTBE 90% of sales and thus represent a great potential for industrial application in the MTBE splitting.
• the present invention thus also provides a catalyst comprising a boron-containing silicate with zeolitic structure of the MFI type, obtainable by a
• zeolitic structure which have as catalysts for the cleavage of MTBE negligible DME and Cs selectivities at the same time high activities.
• the remaining filter cake is washed repeatedly with distilled water and then calcined.
• the calcination of the solid takes place in a muffle furnace in a stream of nitrogen (200 ml / min).
• the heating rate is 1 ° C / min, the final temperature of 500 ° C is held for five hours.
• TPABr tetrapropylammonium bromide
• 4 g of H 3 BO 3 and 524 g of distilled water are processed to form a suspension in a beaker. It turns a pH of 12.57.
• the synthesis solution is transferred to a stirred reactor and stirred for 24 hours at 165 ° C under autogenous pressure. After hydrothermal synthesis, the solid is recovered in the suspension via positive pressure filtration. The remaining filter cake is washed repeatedly with distilled water and then calcined.
• the calcination of the solid takes place in a muffle furnace in a stream of air (200 ml / min). The heating rate is 1 ° C / min, the final temperature of 450 ° C is held for eight hours.
• For ion exchange 5 g of the fine powder are treated in three passes at room temperature for two hours with a solution consisting of 0.1 molar NH 4 Cl and 1 molar NH 4 OH. With constant stirring turns a pH between 10 and 1 1 a. After completion of the ion exchange, the solid is separated again via an overpressure filtration of the suspension.
• the filter cake with 1 molar NH OH is subjected to a diffusion wash.
• the recovered solid is calcined in a muffle furnace in a stream of air (200 ml / min) (heating rate: 1 ° C / min, final temperature: 450 ° C, duration: 8 hours).
• Heat transfer oil ethylene glycol
• the suspension is cooled to ambient temperature and filtered depending on particle size via vacuum or overpressure filtration.
• the solid obtained from this is repeatedly washed with distilled water and calcined in a final step in a muffle furnace in nitrogen or air stream (200 ml / min) at 350 ° C (heating rate: 7 ° C / min) for 5 hours.
• the reaction components are from separate templates quantity or
• reaction products operated under pressure control via an evaporator on the catalyst beds.
• the analysis of the reaction products is carried out by means of online gas chromatography.
• the boron zeolite according to Example 2 shows a high activity with respect to MTBE cleavage and low selectivities with respect to DME (0.4%) and C 8 (0.015%) at 90% conversion.

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