DE1667430C3 - Process for hardening shaped silica gels - Google Patents

Description

The new advantages also affect others Process used gel particles from favorable, since increased hardness and abrasion resistance, which none Opposite disadvantages are advantageous in every fullness.

The progress that can be made is clear from an exemplary embodiment in which in particular pronounced way the grains are moved:

example 1

Esterification of terephthalic acid (TPS) with methanol in a rotary kiln in accordance with DT-PS 12 24 313

A horizontally lying tube made of alloyed steels, e.g. B. Clirom-Nickel-Molybdenum (-18-8-2-) steel of 700 mm length and 125 mm diameter. The tube is filled to around 40% by volume with pearl-shaped silica gel, grain size 3 to 5 mm. The furnace is heated up to around 300 to 320 ^° C. by means of an electrical heater. Mixing mechanisms rotate in the furnace which are designed in such a way that as far as possible no Koinzerquetschimg occurs. At the top of the furnace end opposite the feed point, the gaseous reaction products [dimethyl terephthalate (DMT), monomethyl terephthalate (MMT), water] including the excess methanol are drawn off. To avoid contact dust and

S also impurities from terephthalic acid can originate to · remove, the gas stream is then passed through a cyclone and from there through a solid contact bed filled with coarse-grained silica gel (3 to 8 mm) of about

ίο 101 content guided. In this post-reactor, which is electrically heated to 320 ° C, the esterification completed, d. H. small amounts of MMT (about 5 to 10%), which with high exposure to the Gas'sttom can escape from the rotary kiln, are here practically quantitatively converted into diesters. The vaporous discharge mixture is then passed through a suitable cooling system, whereby a suspension of methanol and DMT forms, which in the usual way by filtration, Drying and distillation can be worked up to the desired end product.

A pressureless esterification was carried out for 150 hours under the following conditions:

Input:

TPS:

CH ₃ OH:

Discharge:

DMT unwashed

Mother liquor:

270 kg, 98.2% = 265 kg TPS 100% ig = 1.76 kg / h 820 kg = 5.46 kg / h

282 kg, SZ = 1.14

833 kg with 2.86% solids = 23.8 kg

SZ in the solid = 92.2 = 29.6% MMT = 7.1 kg MMT

282.0 kg DMT, SZ = 1.14 = 0.35% MMT = 281.0 kg DMT + 1.0 kg MMT

23.8 kg DMT (mother liquor) SZ = 92.2 = 29.6% MMT = 16.7 kg DMT + 7.1 kg MMT

297.7 kg DMT + 8.1 kg MMT
97.3% 2.7%

96.0% of theory
98.5% of theory
250 g DMT / liter and hour

Yield (based on DMT):
Yield (based on DMT + MMT):
Space-time yield:

During this continuous esterification, 300 g of fine contact dust is deposited in the cyclone, which was created by mechanical abrasion in the rotary kiln. This corresponds to about 1 g loss of contact per kg DMT produced. In addition, a burst of Kieselgelgranulates (300 ⁰ C, water concentration in the gas stream to 10%) is observed in the fixed contact bed, where grain splinters to about 1 mm in size. As a result, the gas resistance in the fixed contact bed rises to 0.3 to 0.4 atmospheres after a long period of travel.

The experiment is repeated, but instead of the commercially available silica gel beads, those are used which, before the start of the actual esterification, ie before the TPS is introduced, at ^{temperatures slowly rising from 250 to 300 °} C. over a period of about 1 hour with methanol Steam, to which about 3% water is added, has been pretreated in the rotary kiln while turning.

In the esterification, the esters are obtained in practically identical yields, as shown above. On the other hand, the accumulation of fine contact dust in the cyclone after the running time of 150 hours is only 50 g. At the end of the esterification there is still rW gas resistance in the fixed contact bed, which with the same silica gel beads of the preliminary experiment was charged, unchanged at 0.1 atm. After opening of the fixed contact bed, no changes in the pearls can be perceived.

Example 2

The size of the coarse grain disintegration under the esterification conditions can be demonstrated with the following experimental set-up:

The reaction has a diameter of 50 mm and a length of 1000 mm and is electrical Jacket heating. The lower part of the reaction tube is with an intimate mixture of 100 g TPS and 500 ecm contact loaded. The upper part of the tube is filled with Raschig rings. Here will the methanol dropped in from above evaporates and overheats. In the lowest part of the reaction tube is a porcelain perforated plate installed as a conclusion. At the bottom the tube is on via a ground joint put on a 2-1 round bottom flask. This round bottom flask is equipped with an intensive reflux condenser, in which the overheated methanol condenses, so that methanol and DMT collect in the flask.

Commercially available silica gel, 3 to 8 mm, narrow-pored, is used to remove existing ones

Fine dust fractions sieved through a 2.5 mm mesh network to constant weight. 500 g of this sighted contact mixed with 100 g of TPS and bcgast in the heated reaction tube in one hour with 500 g of methanol at 300 ⁰ C. The cooled contact is then passed through a 2.5 mm sieve and the contact break is measured below 2.5 mm. It shows that about 150 g of the original granulate have burst into a grain of 0.8 to 1 mm, ie after 1 hour the grain disintegration ία is about 30%.

If this experiment is repeated, but after 500 g have been sifted before the start of the esterification Silica gel beads for 60 minutes at 250 to 300 ° C while turning the rotating mixer with 500 g If methanol had been fumigated under otherwise identical conditions, then after an hour of waiting time at all no pearl disintegration occurs.

Example 3

500 g of silica gel beads, d - 3 to 5 mm, which have not been pretreated with methanol, are mixed with 100 g of TPS and, as described in Example 2, gassed with methanol ^{at 300 ° C. in a reaction tube.}

After 1 hour, 42 g of DMT collect in the template. This "corresponds to a conversion of 36%.

The experiment is repeated with a silica gel contact, which was subjected to a pretreatment according to Example 1. Lie after 1 hour 63 g DMT in the template. This corresponds to a turnover of 54 "," ,.

The pretreatment of the contact results in an increase under otherwise identical test conditions of sales by 50 ", ', reached.

Example 4

The compressive strength of the silica beads is determined as follows:

The individual silica gel beads are placed between plane-parallel steel plates. The lower plate is fixed, while the upper, movable plate is part of a balance beam with movable weights.

By placing the weight on the balance beam until the grain bursts, it becomes immediately the pressure load is determined in kg.

product

Sample no.
1 2 3 7th Pressure-
load in
kg, by
cut 10 12th 17th 9.7 13th 19th 19.5 16.5 14th 19th 17.8

Silica gel beads 3 to 5 mm
untreated

Silica gel beads 3 to 5 mm
Pre-treatment with methanol

Silica gel beads 3 to 5 mm
Pretreatment with 97% methanol
and 3% acetic acid

Silica gel beads 3 to 5 mm
Pretreatment with 97% methanol
and 3% water

14th

19th

14th

15.6

The results of these short tests are representative of detailed tests with 50 individual measurements each.

These examples show that the inventive method even under conditions as severe as it uses the process of DT-PS 12 24 313 on the silica gels, very substantial improvements in the Gels yields. This is especially valuable because this esterification process is very special is to be regarded as progressive and now also the silica gel abrasion, which is the only smaller one Deficiency of this procedure could have been safely mastered. This applies to everyone in DT-PS 12 24 313 mentioned process variants. It is also advantageous that the method according to the invention can be applied to any Can apply gel grains. Thus, one is free to choose the size and can do this taking into account the determine other procedural optima. This leaves an important further advantage of the esterification process guaranteed, because on the one hand this is quantitatively far superior to the fixed bed process and on the other hand is not subject to the restrictions of the fluidized bed process, which is optimal only with the same Grain size of contact and terephthalic acid work.

Example 4 also shows that the very substantial increase in strength of the silica gel beads that one achieved according to the invention, the beads are also suitable for improved use in other processes power. That this improvement does not come at the expense of activity, but on the contrary of one The increase in activity is accompanied by example 3.

Naturally, the process according to the invention is not aimed at improving bead-shaped silica gels limited, but it can also be used for lumpy material with the same advantage. This is preferably used in a fixed arrangement, e.g. B. in drying towers, but is subject to angular structure on the rarer occasions when it is agitated, an increased one Abrasion. The new method is therefore of considerable advantage here too.

Another advantage over fresh, narrow-pored silica beads, which do not require any post-treatment have experienced, lies in the fact that according to the invention steamed pearls on contact with liquid water no longer burst.

Claims (15)

can contain up to 3Vol .-% acetic acid, fumigated Claim: ^ eSrmtieme silica gel, which can be found Processes for hardening shaped silica gels according to can be improved according to those which one according to by treatment with alcohol, thereby any desired shaping experience, as pure characterized that the molded silica sols.! after drainage and given Silica rule within 20 to 120 minutes if calcination is in solid, dry, active form at temperatures increasing from 100 to 350 ° C. As an additive of open, pure gels with the vapor of a lower alcohol, which comes up to binders such as silica itself, given to 10 vol% of water by volume or up to 3 ^0, ', acetic io appropriate, organic binder in hi age. may contain acid, fumigated and then cooled. Preference is given to subjecting cngpor.ge gels to the ^b Processes, especially those in the form of pearls. The procedure consists of a temporary gassing of the gel particles with lower alcohols. When 15 alcohol is suitable for methanol, ethanol, propanol, isopropanol, butanols and amyl alcohols, The invention relates to a method for hardening, preferably methyl alcohol. shaped silica gels. The alcohol can be in pure form Shaped silica gels, as they are, for example, in but also in vapor form up to U) vol. -, "msbe-U M mann, Encyclopadie der technischen Chemie, 20 special 1 to 3VoI .- ..; ,, preferably 3VoI .-,;, water Vol. 15, pp. 723 and 724 (1964) are included. Even the presence of small amounts mainly as a desiccant and as acid catalysts, such as. B. I to 3 vol. "Bssigsaure, can used; changing admixtures can be an advantage. hold, mainly alumina. The silicic acid gels are attenuated at shaped silica gels in pearl form or by temperatures between about 100 and 350 C before mechanical deformation in lump form. assigned between 250 and 300 ^J C. A particularly useful purpose of the material has been shown to be moderate, at about 200 to the greatest possible hardness of the particles. 320 ° C, preferably from 250 to 300 C, increasing It is known that the abrasion resistance temperatures of the water-containing alcohol vapor to pass through the gels by dispersing finely divided solid additives in 30. The temperature should the silicic acid used to prepare the gel, e.g. B. within 30 minutes, from z. B. Hydrosol can increase (DT-PS 10 96 336). Here, 240 to 300 ° C can be increased, because at too fast But if you have to have very specific particle sizes when heating, the grain can burst. Adhere to additives; it is also usually a time of about to substances that are chemically different from hydrosol 35 20 minutes to about 2 hours of treatment time, are and therefore in catalytic processes, often Although the necessary or expedient duration result in undesirable response characteristics. also something depends on the working conditions It is also already known to give the fresh hydrogel grains, which generally require a time of about 60 minutes, shrinkage in order to avoid a noticeable improvement in the gels by first reaching the water completely. This time can of course, if you replace it with alcohol, if you are satisfied with heating and lower effects, if the pressure is still below the liquid level and then evaporate. In general it is not necessary that leaves (DT-PS 8 96 189, p. 4). According to DT-PS 8 78 637, to extend the duration beyond about 60 minutes, p. 8, the gel particles can be calcined with air or steam, but the time can also safely be calcined to inert gases or mixtures thereof. About 45 2 hours are extended,
stood the DT-PS 8 85 397 is the prevention of the one can use the procedure in any suitable Grain disintegration of the narrow-pore silica gels that operate in devices and apparatus. So suitable The particles come into contact with water, through standing or lying, wholly or partially with prior treatment of the gels with moist gases tubes filled with the formed gels. In many cases it is at normal temperature. The DT-AS 11 72 245 finally 50 expedient, the treatment in the apparatus first one can see that one is increasing finely divided silica, in which the gels then work acid through superficial esterification. So you can do the attenuation, for example Alcohols at higher temperatures also render hydrophobic in a drying tower or in a lying one has; this covers the active surface of the silica rotary kiln in which the gels are esterified. 55 catalysts are to be used. Principle- However, all these processes do not allow the methanol treatment to be borrowed here both easy way to gel the surface of formed silica in a resting layer as well as in a moving bed to harden sustainably without the activity of being led. The fumigation in a rotary kiln, Gels are damaged or the composition may also be in the vortex, has the advantage Incorporation of undesired inorganic solids 60 that the heat transfer in the granules and also the will be changed. The methanol concentration in the mixture is completely the same. The invention aims to solve this problem in a moderate manner. (No formation of channels.)
underlying. After steaming, the gels are preferably cooled According to the invention, this object is achieved slowly and has a direct and immediate effect that the formed silica gels are internally activated material of particular strength,
semi of 20 to 120 minutes at from 100 to 35O ⁰ C This material is eminently suitable for such increasing temperatures with the steam a process in which the gel particles are moved lower alcohol, which is subject to up to 10 vol .-% water or and thus an Abii: b; self-evident