DD285241A7 - ADSORPTION AGENTS FOR SEPARATING FLUORESCANCES OF N-PARAFFING MIXTURES - Google Patents

Abstract

The adsorbent consists of silica gels which according to the invention have a specific surface area of greater than or equal to 750 m 2 / g, a specific pore volume of from 0.45 to 0.65 ml / g, a maximum pore radius of from 0.8 to 3.0 nm and a p H Value of the 50% aqueous extract from 2 to 3 have. When contacting with 1.3% paraffinic naphthalene solution in a mass ratio of silica gel: naphthalene equal to 1:20, an equilibrium loading of at least 0.05 g of naphthalene / g of silica gel is achieved within 20 minutes. {Dearomatization; n-paraffin mixtures; silica gels; adsorbents; Aromatenkapazitaet}

Description

Field of application of the invention

The invention relates to an adsorbent for the separation of Aromatenbeimengungen from n-paraffin mixtures, which consists of silica gels.

Characteristic of the known state of the art

The use of silica gels for the adsorptive separation of hydrocarbon mixtures has been known for some time.

According to DD-PS 12614 silica gels are used for the decomposition of synthetic or mineral hydrocarbon mixtures, which were prepared by delaying the gelatinization for at least 3 days.

According to German Pat. No. 717,651, a silica gelatin of pH 1.7 is dried unwashed and used for the adsorption of benzene.

Apart from the technological disadvantages associated with gelation in the more acidic range, these processes provide gels that have high specific surface areas but small pore volumes. Statements on aromatics capacity are not apparent.

It is with these gels the difficulty to achieve sufficient kinetics of mass transfer and displace the adsorbed adsorbent components so much that reuse is possible.

Accordingly, a process for the purification of hydrocarbons using silica gel, alumina and / or clay is described in which the desorption is the easier the larger the pore size of the silica gel used

In order to exclude steric hindrance in the sorption process, the use of adsorbents with frequent pore radii of equal to or greater than 2 nm and sufficient surfaces, such as silica gels, is recommended according to DD-PS 160059 for dearomatization of n-paraffin mixtures.

These and other methods in which silica gels or modified silica gels are used as adsorbents, for. B.

SU-PS 924027, however, provide insufficient aromatics capacities.

It must therefore be stated that the adsorbents specified in accordance with the prior art do not meet the specific requirements of this field of application, which are also to be met with regard to the industrial use of such separation methods.

Object of the invention

The aim of the invention is an adsorbent for the separation of Aromatenbeimengungen from n-paraffin mixtures, wherein the silica gels used allow a high space-time yield of the process.

Essence of the invention

The invention has for its object to develop an adsorbent for the separation of Aromatenbeimengungen from n-paraffin mixtures in which using gravel flocs with specially prepared structural parameters and particular aromatics binding properties both a high aromatics capacity and a sufficient rate of mass transfer is guaranteed.

This object is achieved by an adsorbent consisting of silica gels in that the silica gels according to the invention have a specific surface area of greater than 75 μgVg, a specific pore volume of 0.45 to 0.65 ml / g, a most frequent pore radius of 0.8 to 3, 0 nm and a pH of the 50% aqueous extract from 2 to 3 have. It is favorable if in the adsorbent additionally up to 15% of amorphous silicic acid hydrate having a specific surface area of from 50 to 850 m 2 / g, a specific pore volume of from 0.40 to 0.70 ml / g, a most frequent pore radius of from 0.8 to 2 , 0 nm and a mean particle size before 0.1 to 10μηι are included.

Boi Rührkontaktierung with 1.3%, paraffinic Naphthalenlösung in the mass ratio KieselgehNaphthalen equal to 1:20 an equilibrium loading of at least 0.05 g naphthalene / g silica gel within 20 minutes, advantageously of 0.06g naphthalene / g silica gel within 15 minutes.

Important for the suitability of the Keiselgele is not only the aromatics uptake capacity, but also the time in which sets the adsorption weight.

The silica gel according to the invention is of a high pore size on the specific surface, but it has a pore volume which is too high for narrow-pore gels, but is typical of wide-pore gels and has narrow pores, which is due to a modified pore radius distribution. The silica gel according to the invention is a special gel and as such has not yet been described. Essential for the invention is that the silica gel according to the invention has the claimed properties / parameters. The basis of the invention is the production, property and application relationship between the kieselgol and the n-paraffin to be dearomatized.

It is found that silica gels, which were produced from the same raw material system and according to the same process principle but differ in their properties / parameters from the range according to the invention, do not have the required aromatics capacities. It is important that all properties / parameters are met, whereby on the basis of a specific surface of> 750m ² / g, the pore volume of the gel is likely to be of particular importance, since even with the other texture data at pore volumes <0.40 ml / g no good suitability is demonstrable.

Surprisingly, it has been found that the addition of lepidoid silicic acid hydrate in the gelation process further improves the dearomatization properties thereof. Silica hydrate is prepared by freezing unstable silica sol. It is expedient here to use an ice mill, since smaller particle sizes are obtained than during static freezing. The particle size obtained can be further comminuted by milling. A silica gel was prepared in each case with and without addition of the hydrated silica and under otherwise identical conditions in a parallel experiment. With practically identical texture data of both gels, the aromatics capacity of the gel prepared with the additive is markedly increased. Since the texture oats of the lepidoid silica hydrate are also comparable to those of the gel, it is to be assumed that the improvement in the dearomatization properties was achieved by a mixing effect in conjunction with the other preparation conditions of the gel.

embodiments

example 1

15% sodium silicate solution (5 ⁰ C) and 13% sulfuric acid (5 ⁰ C) were reacted with intensive mixing to the unstable sol of pH 6.4. The sol gelled after 7s. The resulting hydrogel was crushed and treated after a holding time of 10 minutes with sulfuric acid water of pH 1.7 for two hours, then washed with sulfuric acid water of pH 2.5 and dried.

The xerogel obtained had a specific surface area of 868m ^J / g, a specific pore volume of 0,53ml / g, a mode pore radius of 1.2 nm with a narrow distribution. The pH of the aqueous extract at the ratio XerogehWasser = 1: 1 was 2.5.

The xerogel was dried at 150 ° C. for 2 h and its naphthalene capacity was determined by the following method:

1 g of the silica gel of grain size 0.2-0.63 mm was stirred with 20 g of 1.3%, paraffinic naphthalene solution at room temperature, so that the gel bodies were whirled up.

After a stirring time of 5 minutes, the naphthalene concentration of the solution was measured by UV spectroscopy. The equilibrium capacity had set after 15 minutes and was 0.074 g naphthalene / g silica gel (mean of 3 capacity determinations).

Example 2 (comparison)

The silica gel was prepared according to Example 1, but the acid treatment of the hydrogel was carried out with formic acid. The resulting Xergel had a specific surface area of 762 mVg, a specific pore volume of 0.36 ml / g, a common pore radius of 1.2 with narrow distribution. The pH of the aqueous extract was 3.6, the aromatics capacity 0.041 g Naphchalen / g silica gel after 30 minutes.

Example 3

The silica gel was prepared according to Example 1, but the sol preparation was carried out once with the addition of amorphous silicic acid hydrate in a proportion of 7.0% SiO _{2 of} the total SiO ₂ content of the mixture and secondly without this. The silica hydrate was prepared by freezing unstable, by the ion exchange method produced silica sol of Si0 ₂ concentration of 7.8% and the pH of 2.2. When dried, the silica hydrate had a specific surface area of 726 mg, a specific pore volume of 0.38 ml / g, a most frequent pore radius of 1.0 nm with a very narrow distribution and, after wet milling, a mean particle size of 3.2 nm obtained xerogels had the following properties:

parameter MVG without addition with addition specific surface ml / g 773 762 specific pore volume 0.48 0.48 most common pore radius nm with a narrow distribution 1.0 1.0 pH value of the aqueous extract gN./gK. 2.7 2.6 Aromatenkapazität min 0,071 0.079 Response time 15 15

Example 4 (comparison)

The unstable sol was prepared according to Example 1. The resulting hydrogel was crushed, washed neutral and dried. The resulting xerogel had a specific surface area of 380 mVg, a specific pore volume of 0.86 ml / g, a most common pore radius of 4.0 with a much broader distribution. The pH of the aqueous extract was 7.2 and the aromatics capacity was 0.033 g naphthalene / g silica gel after 15 minutes.

Claims (2)

1. adsorbent for the separation of aromatic admixtures of n-paraffin mixtures, which consists of silica gels, characterized in that the silica gels have a specific surface area greater than 750m ² / g, a specific pore volume of 0.45 to 0.65ml / g, a most common pore radius from 0.8 to 3.0 nm and a pH of the 50% aqueous extract from 2 to 3. 2. Adsorbent according to claim 1, characterized in that in addition to 15% amorphous Kieseisäurehydrat with a specific surface area of 650-850m ² / g, a specific pore volume of 0.40 to 0.70ml / g, a most common pore radius of 0.8 to 2.0 nm and an average particle size of 0.1 to 10 μm.