DE1160570B - Process for the preparation of fluorine-containing silica-magnesia catalysts for cracking hydrocarbons - Google Patents

Description

Process for the production of fluorine-containing silica-magnesium oxide catalysts for cracking hydrocarbons The invention relates to the production of fluorine-containing Silicic acid magnesium oxide catalysts for cracking carbon hydrides.

Silicic acid magnesium oxide catalysts are known to be produced by making a silica gel with a colloidal magnesium oxide-magnesium oxysalt complex is treated to cause swelling of the product obtained. A disadvantage this procedure consists in that magnesia with water and with certain aqueous salt solutions reacts to form cementitious substances. This is how for example from magnesium oxide and magnesium chloride Sorel cement or a similar one Product if a sulphate is used instead of the chloride.

To prevent solidification or lump formation of the reaction mixture must therefore in the manufacture of silica-magnesia catalysts on the Extremely careful working conditions are adhered to via the oxysalt, whereby, inter alia, additional water to the reaction mixture of magnesium oxide and magnesium oxysalt must be added. However, this addition of water is disadvantageous, because once the formation of the oxysalt is considerably delayed, which in turn is the combination of magnesium oxide with the silica gel adversely affects further processing, and since the additional water continues to place a greater burden on the devices and plants especially for filtering and drying the magnesium oxide-silica slurry represents.

It is also known, a silica-magnesium oxide complex via the oxysalt, filter it off and then remove it suspend the free magnesium ions in sulfuric acid solution. The received Slurry is then aged, the solids separated and reapplied with a Solution of a fluorine compound slurried to form the silica-magnesia complex impregnate with fluorine, whereupon the product obtained is washed and dried will. This procedure is true to some extent for the prevention of formation of Sorel cement successful; however, there remains a tendency towards the formation of small pockets or inclusions of Sorel cement exist, which give rise to particles that the nozzles clog when spray drying.

It is already a process for making a silica-magnesia catalyst known in which a silica-magnesia hydrosol, for example by mixing made from sodium silicate solutions, sulfuric acid and a magnesium oxide slurry will. The hydrosol is then gelled and forms a hydrogel, which is washed, dried and subjected to a heat treatment with water before it is again is dried and activated. However, such catalysts are insufficient Resistance to abrasion or attrition, as detailed later will be shown.

The purpose of the invention is now to provide a silica-magnesia catalyst for the cracking of hydrocarbons by way of the magnesium oxy salt, without taking special precautions to prevent lump formation Need to become.

Accordingly, the invention relates to a process for the production of silicic acid-magnesium oxide catalysts containing iluorine for cracking hydrocarbons, in which a silicic acid hydrogel produced by acidifying a dilute sodium silicate solution with mineral acid, such as sulfuric acid, is processed with magnesium oxide and then treated with fluorine, the process thereby is characterized in that the amount of sulfuric acid added is sufficient to neutralize over 800 % of the sodium oxide in the sodium silicate, whereupon the originally formed hydrogel is aged and a silica-magnesium oxide salt complex is formed in situ by adding a mineral acid such as sulfuric acid. and magnesium oxide are added together to the silica hydrogel.

Through the direct addition of calcined magnesium oxide to the silica hydrogel the advantage of the large volume of dispersing medium is used, which the Use any ratio of magnesia to the appropriate Salt is permitted and the use of extremely active magnesium oxide is safe a lump formation or solidification of the mass allowed. The simultaneous addition of acid, such as Schi vefelsäure, with the required amount of magnesium oxide produces the Desired cleavage and formation of magnesium sulfate and oxysulfate in situ.

When carrying out the process, the silica component can through Reaction of an aqueous alkali silicate solution, such as sodium silicate, with a mineral acid, such as sulfuric acid, hydrochloric acid or nitric acid can be obtained. For economic reasons, sulfuric acid is generally used. The sodium silicate starting solution can be made by diluting a commercially available water glass solution with a SiO2: Na.0 weight ratio from 1: 1 to 4.0: 1 are obtained; usually it will be one of the most accessible Water glass solution is used at a ratio of 3.25: 1 to 3.03: 1. In which The method according to the invention is the SiO.-Coil concentration of the dilute silicate solution between 4 and 120%, and preferably between 5 and 10%; generally will they are kept as high as possible in order to increase the activation properties of the catalyst obtained to improve and enable higher production speeds.

During the acid addition, the mixture is vigorously stirred to obtain the Hydrogel particles disperse well because it creates a better chemical bond between the gel particles and the subsequently added magnesium oxide particles is made possible. The amount of acid added to the silicate solution largely determines The extent of the abrasion or attrition properties of the finished catalyst, the activation properties of the silica gel-magnesium oxysalt mixture and the easy washing out of the dried Product. In order to achieve good abrasion properties in the end product, acid is used added in sufficient quantity to be more than 80 "/, and preferably about 90" /, to neutralize the Na2.0 in the sodium silicate. If neutralized to well over 90 ° / Q the silica gel tends to peptize and detrimental to occur Solidification, even if only small amounts of magnesium oxide are subsequently added will.

The acid is preferably added in two stages. In the first stage, enough acid is added to the sodium silicate solution that a hydrogel is formed which carries the remaining non-neutralized sodium silicate. After a short time, more acid is added. to neutralize up to at least 800/10 and preferably about 900 /, of Na20. During the neutralization, the reaction mixture is constantly stirred so that the hydrogel obtained does not harden or can settle as a solid mass. The pH of the slurry after the second addition of acid is in the range 5 to 8 and is preferably 6 to 7.

During and after neutralization until the desired pH value is reached the temperature of the slurry in the range of about 26 to 76-C, preferably 43 to 55-C. held. Higher temperatures should be avoided because before a adequate dispersion of the silicic acid hydrogel to form the magnesium oxide tends of hard lumps. After adding the required amount of acid to the silicate solution the hydrogel slurry will be about 1; with stirring. up to 4th hours for the above Temperatures aged. Aging at elevated temperature leads to a noticeable Increase in the pore size of the gel.

Determine the transmitter temperature and aging time of the hydrogel slurry furthermore the time or the temperature, which later after the addition of magnesium oxide and the oxysalt-forming acid must be expended in order to achieve the exact combination from silica hydrogel particles with magnesium oxide. The higher the encoder temperature and the longer the aging time of the hydrogel slurry, the more time and / or the higher the temperature will cause the silica-magnesia slurry to age needed. The desired pore volume and, to a certain extent, the surface area of the final product are obtained by considering the storage time and temperature coordinates the hydrogel preparation with the storage time and temperature values, which are necessary for the silica-magnesium oxide suspension.

After the hydrogel slurry has aged, a certain amount of magnesium oxide is added together with sulfuric acid with constant stirring. to achieve the required MgO content in the finished catalyst. In fact, slightly more magnesium oxide is even added to the gel slurry than that corresponding to the desired amount in the final product, so as to balance the loss of water-soluble magnesium compounds which nesiumoxyd or by reacting Magnesiunioxyd, of formed magnesium sulfate from Mag disfigured by numerous intermediate reactions. which occur when sulfuric acid reacts with magnesium oxide. It is advantageous to adjust the amount of magnesium oxide added so that 20 to 30 "/, Mao are obtained in the catalyst, which can be calculated from the SiO. = Content of the sodium silicate solution.

A magnesium oxide suitable for the process according to the invention has, based on the total amount, the following typical composition: Magnesium as Mg0. . . . . . . . . . . . . . . 94.86 "/, Aluminum as A1.0 .; . . . . . . . . . . . . . . . 1.09 Sulphate as SO., ...................... 1.65% Sodium as Na.0. . . . . . . . . . . . . . . . . 0.073% Iron as Fe. . . . . . . . . . . . . . . . . . . . . . . 0.0870 /. Calcium as Ca0 .................. l, 0 ° /, Silicon as SiO., ................... 0.26 ° / a Loss on ignition at 955-C .............. 2.38 °,: o Density (compressed). . . . . . ... ... . . . . .416 kg,! M3 Surface area. . . . . . . . . . . . . . . . . 45 m = ig The silica-magnesium oxysulfate complex obtained is stirred until a uniform colloidal dispersion is obtained. The temperature of the slurry is then increased to about 79.5 to 85.0, and preferably to 82 ° C; here the pH is about 7.5 to 8.5 and preferably 8.0. By depositing the electrolyte (SO, -) on the magnesium oxide, a more reactive form is obtained for a more intimate combination with the silica. The acid concentration when the oxy salt is formed can be between 20 and 700 /, and preferably between 20 and 400 /, H, SO4.

The slurry containing the silica-magnesium oxysulphate complex is aged for about 1 to 3 hours at about 82 ° C with stirring. Here the pH of the slurry drops to about 7.0 to 8.0, and generally up to 7.0 to 7.5 from. Following aging, the slurry becomes primarily filtered to remove the soluble sulfates. After filtering, the filter cake becomes slurried again in water, to which a magnesium salt solution, such as magnesium sulfate, can be added to deliver free magnesium ions.

The reslurried product then becomes so much fluorine-containing Solution added at a concentration sufficient to be present in the finished catalyst 0.5 to 5.0 percent by weight remain. Any soluble fluoride can be used which preferably forms an insoluble salt with magnesium ions and so it is held in the mass after washing. The use of soluble Fluoride enables maximum dispersion of the fluoride ion within the silica-magnesia mass, before the chemical bond occurs. Suitable fluoride-yielding compounds are HF, H2SiFs, (NH4) 2SiFg, NH, F and NH, HF2, being hydrogen fluoride because of its low levels Cost and easy accessibility is primarily preferred. In general is hydrogen fluoride with as much water, generally up to 50% Solution diluted to prevent smoking. Excess water should be avoided to prevent decomposition of the complex. After adding the fluoride compound the pH of the resulting slurry drops to about 6.5.

The addition of fluoride at this point in the process results in a better dispersion throughout the mass. In addition, tests have shown that with the addition of soluble fluorides before removal of the free sodium ions in the Catalyst insoluble sodium fluoride is formed. The detrimental effect of Sodium ions on the life of a catalyst is well known.

Following the addition of fluorine to the mass, the slurry can be passed into a spray dryer to achieve microspherical particles. These are then absorbed and washed with the remaining sodium and sulfate ions free. Care must be taken here to avoid any magnesium ions to remove. The washing process can be carried out well with a dilute aqueous magnesium sulfate solution or ammonium sulfate solution and subsequent rinsing with water several times will. The washed product is then filtered and dried again at about 149 ° C.

With the method according to the invention, no longer are unnecessary as before Amounts of water added to avoid the formation of hard lumps of Sorel cement. Rather, this is now achieved by the complex compound in situ forms by adding magnesium oxide and acid together to form the silica hydrogel slurry are given. The dragging of large amounts of water, which is an economical one Load on the work processes is thus completely eliminated, without affecting the quality of the finished catalyst in any way. About that In addition, the catalysts obtained by the process according to the invention, as already mentioned, an increased resistance to abrasion in comparison with catalysts such as are obtained by the known process.

The invention is explained in more detail below with the aid of examples Example 1 1021 sodium silicate of 49 ° C and with a content of 27.6 g each Liters of Na 2 O and 91 g per liter of SiO 2 were put in a mixing container with 3950 ml of 39% Sulfuric acid implemented. The reactants became vigorous with a stirrer mixed and constantly circulated with a centrifugal pump. Gelation took place within 7 minutes at 52 ° C and at a pH of 10.7. It got more Mixed for 10 minutes at 52 ° C., after which 4530 ml of 39% sulfuric acid were added. The pH dropped to 6.5 and the resulting silica hydrogel slurry was aged for 1.5 hours at 52 ° C. To the aged hydrogel slurry then simultaneously with stirring 3.9 kg of calcined magnesia and 2370 ml of 39% Sulfuric acid added. During the joint addition of acid and magnesium oxide the pH was between 9.0 and 9.4. The temperature of the obtained silica-magnesium oxysulfate complex mass was increased to 82 ° C in 20 minutes, the pH of the slurry increasing 8.05 fell off.

The mass of silica-magnesium oxysulphate complex produced by this process was divided into two portions A and B, with part B being further subdivided into a third portion B 1. The individual portions were treated as follows: Portion A The silica-magnesium oxysulphate complex was aged for 1 hour at 82 ° C., after which the pH dropped to 7.4. The mass was then filtered off, and the 6.8 kg of the filter cake obtained was slurried again with 720 ml of water which contained 210 g of magnesium sulfate, M9S04-7H20. 81 g of 48% hydrogen fluoride solution were then added and the fluorinated slurry was spray-dried. The dried product had a pH of 7.0 and a total volatile content of 12.63% 0. 400 g of the dried product were then washed with 21 2% strength ammonium sulfate solution which had been adjusted to a pH of 9.0 with ammonia. The temperature was maintained at 41 ° C and the particles were washed three times in this way. The product was then washed three times with 21% distilled water each time, which had been adjusted to a pH of 9.0 with ammonia. The product so purified was dried in an oven at 136 ° C to a total volatility of about 15.001.

Portion B The treatment of this sample was different from the portion A only in the aging period of the silica-magnesium oxysulphate complex, which now 2 hours at 82'C. The pH dropped to 7.3, and the mass was then filtered and treated just like portion A.

Portion B 1 This portion was aged for 2 hours at 82 ° C., the pH dropping to 7.3. The portion was then filtered and reslurried with only 750 ml of water. There was no magnesium sulfate or Table 1 Portion A Portion B Portion B 1 Chemical composition in%, dry basis Mg0. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29.0 27.99 27.86 Na20 ....................................... 0.025 0.021 0.017 S04. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.52 0.080 0.11 Fe .......................................... 0.042 0.044 0.080 F ........................................... 2.62 2.49 no Physical Properties after 3 hours of thermal pretreatment 6770C Surface area, m2 / g. . . . . . . . . . . . . . . . . . 525 526 484 Pore volume (H20) cm3 / g. . . . . . . . . . . . . . . . 0.68 0.59 0.46 Pore volume (N2), cm3 / g ... . . . . . . . . ... . . . 0.56 0.52 0.43 after 3 hours of thermal pretreatment 843 ° C Attrition index ........................... 35.8 18.4 - Surface area, m2 / g. . . . . . . . . . . . . . . . . . 194 176 43 Pore volume (H20), cm3 / g. . . . . . . . . . . . . . . . 0.44 0.36 0.06 Pore volume (N2), cm3 / g. . . . . . . . . . . . . . . . . 0.35 0.29 0.06 The attrition index or the index of attrition is measured by treating the catalyst with a very rapid air jet according to a standard test procedure, the so-called roller test. The weight of the particles less than 20 microns in diameter formed in this experiment is considered to be a criterion for the resistance of the catalyst to interparticle abrasion. The attrition index is calculated using the following formula: in which A = content in grams of 0 to 20 micron particles of calcined catalyst after attrition, B = content in grams of 0 to 20 micron particles of calcined catalyst before attrition and C = content in grams of particles larger than 20 micron des calcined catalyst is before attrition.

The portion B catalyst was found to be satisfactory Attrition index showed what was not the case with the catalyst of portion A; at this last-mentioned portion the value was about twice as large, which is probably added to the hydrogen fluoride solution. The slurry then had a pH of 7.4 and was spray dried to a total liquid content of 12.91 "/, whereupon the thus dried product like portion A was washed.

The chemical composition and physical properties the catalysts prepared according to this example are shown in the table below 1 reproduced. incomplete aging of the silica-magnesium oxysulphate complex is due.

To determine the cracking activity and stability of the invention An accelerated test was used, which corresponds to the working conditions that prevail during the initial period of catalyst use and show the decrease in catalyst stability most clearly. This test will a sample of the fresh catalyst formed into spheres and divided into two portions; one serving is used for thermal deactivation and the other for steam deactivation used. The thermal deactivation of the catalyst prepared according to the example was first carried out for 3 hours at 677C, followed by the catalyst in two portions was divided. One serving was another 3 hours at 732'C and the second Portion exposed to heat treatment for 3 hours at 843 ° C. The deactivation by steam was first by a heat treatment of 3 hours at 677'C and then by a 24-hour steam treatment in a steam atmosphere of 4.2 kg / cm = and 566'C carried out.

When carrying out these activity tests, 200 ml of the deactivated catalyst were placed in a reaction vessel and stored at a temperature of 454.degree. A total of 238.2 ml of light oil (crude product from East Texas) were passed through the hot catalyst for 2 hours. The cracked products were isolated and separated. The fraction distilling below 204 ° C and the gaseous fraction and the losses were measured and designated as distillate plus loss or more simply as ND -1- L «. The results of these tests are shown in Table 2. Table 2 Portion A Portion B Portion B 1 Steam activity D -i- L,%. . . . . . . . 41.9 44.7 43.0 Gas generation factor 0.97 0.85 0.86 carbon generation factor .. 0.93 0.84 0.80 Thermal activity 3 hours at 732 ° C D -f- L, ° / a. . . . . . . 56.3 55.3 57.2 Gas generation factor 0.92 0.87 0.91 carbon generation factor .. 0.91 0.87 0.82 3 hours at 843'C D -i- L, ° / o. . . . . . . 31.1 27.4 5.4 Gas generation factor 0.87 0.83 2.03 carbon generation factor .. 0.84 0.81 2.50 The stated values of the gas generation factor and the carbon generation factor are proportional to the amount of gas and carbon which are generated with a standard catalyst and are assumed in both cases to be 1.00 and represent a measure of the selectivity of the catalyst. It was found that the fluoride-containing catalysts produced by the process according to the invention give carbon and gas values which are far below those of the standard catalyst. In addition, the excellent thermal stability of the catalysts thermally treated at 843 ° C. can be clearly seen.

It must be noted that an addition of 0.5 to 5.0 percent by weight Fluorine to the catalyst stabilizes the structure when operating at high temperatures. This is made clear, for example, by the catalyst according to portion B 1, which does not contain fluorine. With a thermal treatment of this catalyst at 843 ° C "D -I- L" values of only 5.40 /, are obtained. This lack of resilience against high temperatures shows essentially complete breakdown the catalyst structure.

Example 2 To demonstrate the improved abrasion properties of the inventive Catalysts compared to the catalysts prepared according to US Pat. No. 2,680,100 a catalyst was prepared in the following manner and the attrition index according to determined by the measuring method described in this USA patent.

A total of 1021 sodium silicate solution containing 27 g per liter of Na20 and 89 g per liter of Si02 were in a mixing tank with 3950 ml 39 % Sulfuric acid converted. . The reactants were, with the help of a Rotary mixer stirred and circulated continuously with a centrifugal pump. Gelation took place in less than 10 minutes at 57 ° C. Here was the pH 10.7. Mixing was continued at 57 ° C and 4530 ml of 39% sulfuric acid added, the pH of the slurry falling to 6.8. The resulting silica hydrogel slurry was aged for 11/2 hours at 57 ° C. To the aged hydrogel slurry at the same time 4 kg of lightly annealed magnesium oxide were added. After the distribution of the magnesium oxide by stirring for 15 minutes, 2370 ml of 39% sulfuric acid were obtained admitted. The temperature of the resulting mixture was raised to 82 ° C for 20 minutes increased with the pH of the slurry being 8.0. The silica-magnesium oxysulphate complex was aged 21/2 hours at 82 ° C, after which the pH dropped to 7.0. The slurry was filtered and a portion of 6.8 kg of the filter cake was mixed with 750 ml of water, which contained 210 g of magnesium sulfate (MgS04-7H2O), slurried again. Afterward 81 g of a 48% strength hydrogen fluoride solution were added. The pH was too this time 6.4.

The attrition indices were determined by the "Jersey method" in order to obtain a measured value on the same basis as in US Pat. No. 2,680,100. The following result was obtained: 1. Chemical analysis, ° / o Mg0 ......................... 25.56 Na20 ........................ 0.041 S04 .......................... 0.45 Fe ........................... 0.073 Fluorine ...................... 1.99 2. Attrition index after 3 hours at 677 ° C »Jersey Index«. . . . . . . . . . . . . 0.8 The attrition index was thus achieved after 3 hours at 677'C, which is difficult conditions compared to the 3 hours at 538'C according to the USA patent. The index showed a significant improvement over the product described in the USA patent.

Claims (3)

Claims: 1. Process for the production of fluorine-containing silica - Magnesium oxide - catalysts for cracking hydrocarbons, in which a prepared by acidifying a dilute sodium silicate solution with mineral acid Silicic acid hydrogel processed with magnesium oxide and then treated with fluorine is, d a d u r c h characterized that the amount of sulfuric acid added sufficient to neutralize more than 80% of the sodium oxide in the sodium silicate, whereupon the originally formed hydrogel aged and a silica-magnesium oxide salt complex Is formed in situ by adding a mineral acid and magnesium oxide together to the silica hydrogel can be added. 2. The method according to claim 1, characterized in that the the amount of magnesium added to the silica hydrogel together with the mineral acid corresponds to a magnesium oxide content in the finished catalyst of 20 to 30 ° / a. 3. The method according to claim 1 or 2, characterized in that after addition of magnesium oxide and acid, the silica-magnesiumoxy salt complex formed is filtered off and slurried again in water, the slurry a magnesium salt and a fluorine solution is added, whereupon the complex obtained washed and dried. Documents considered: German Auslegeschrift No. 1074 791; British Patent No. 820,986; USA. Pat. No. 2,901,440.