JPS5829836B2 - Chinese adsorption method Oyobi / Mataha Chinese adsorption method for the use of riboso - Google Patents

Description

DETAILED DESCRIPTION OF THE PRESENT EMBODIMENT The present invention relates to a process for producing pure hydrocarbons during extraction and/or extractive distillation operations using N-substituted morpholines as selective solvents.

Apparatuses of this type are used today on a large industrial scale to obtain, inter alia, pure aromatic substances, in which the selective solvents are, inter alia, N-acyl derivatives of morpholine, especially N-
- Formylmorpholine is used.

As long as normal extraction (liquid-liquid extraction) is used in this case,
Solvents are often used with the addition of water, and so-called extractive distillations are generally operated with anhydrous solvents.

In this case, one known method (German Patent Specification No. 2
No. 040025 operates using a combination of liquid-liquid extraction and extractive distillation.

However, corrosion phenomena sometimes occurred during the operation of such equipment, for which no satisfactory explanation was available at the time.

In this case, this corrosion phenomenon was observed above all in those parts of the equipment which were subjected to strong vapor-liquid loads, such as, for example, the heating tubes at the end of the stripper or extractive distillation column.

Based on preconceived notions in the art (as set out, for example, in German Auslegeschrift 1 545 365, column 2, lines 35-43), one could have started from the assumption that the corrosion was caused by hydrolysis or decomposition products of the morpholine derivative used as solvent.

However, detailed studies have failed to provide any indication that such an assumption is valid.

The known method of preventing corrosion in gas scrubbing systems, which involves adding tartaric acid in combination with Group 4 and 5 compounds to the amine solutions used as scrubbing agents, has not produced satisfactory results in this case.

The object of the present invention was therefore to obtain a method which makes it possible to effectively inhibit the aforementioned corrosion phenomena, the causes of which were hitherto completely unclear.

In this case, the process according to the invention for producing pure hydrocarbons during the operation of an extraction plant and/or an extractive distillation plant using N-substituted morpholines as selective solvents is characterized in that phosphoric acid or phosphates and/or vanadium compounds or molybdenum compounds are added to the solvent in amounts of 0.005 to 0.02% by weight.

In this case, the corrosion phenomena observed are, inter alia,
It starts from the realization that this can be attributed to free acid ions which are carried into the extraction plant by the feed hydrocarbon mixture to be treated.

Firstly, there are free chloride and sulfate ions which result from the upstream treatment of the feed hydrocarbon mixture.

Thus, for example, it has been found that when so-called reformate is used, the catalyst is activated with propyl chloride in the reforming unit so that chloride ions are carried along into the extraction unit.

In this case free hydrochloric acid is formed.

Subsequently (due to stripping of the reformate, no analytically detectable amounts of base ions remain in the product, but they enter the extraction unit together with the product,
There it becomes trapped in the basic solvent and becomes concentrated in said solvent over time.

For example, if the reformate used as feedstock has a free chloride ion content of 0.5 ppm - which is no longer analytically detectable by the methods used in practical operation - then at a plant feed rate of 40 kg of feedstock per hour this means that over the course of 33 operating days there will be 15.84 kg of free chloride ions in the solvent circulating in the extraction plant.

Starting from the fact that the amount of solvent circulating in the extraction device is about 200 ml, the concentration of free chloride ions in the solvent is
om9c1/l is produced.

This value is entirely sufficient to cause long-term corrosion phenomena in the parts of the equipment in contact with the solvent.

A similar situation exists with free sulfate ions if the feed hydrocarbon mixture is treated in a sulfuric acid wash (acid purification) connected prior to the extraction unit.

Suitable additives for the solvent are, in addition to phosphoric acid, inter alia, ammonium, sodium, potassium and ammonium phosphates, and also alkali and ammonium vanadates or molybdates.

Based on the studies carried out, the compounds H3PO4, V2O5 and M.

03 has been found to be particularly suitable as a solvent additive.

In this case the amount added to the solvent is preferably from 0.006 to 0.
0.01% by weight.

Furthermore, it has proven advantageous in many cases to additionally monitor the content of free acid ions in the solvent and to subject this partial stream to purification by distillation as soon as the content of free acid ions in the solvent reaches a value of 0.005 to 0.01% by weight, the regeneration of the circulating solvent being continued until this value falls to 0.0005 to 0.001% by weight.

In the following comparative example, the situation which arises in an extraction plant which after-treats as raw material so-called reformate, the content of free chloride ions of which is analytically practically no longer detectable, is examined.

When no special additives were added to the N-formylmorpholine used as the solvent and the content of acid ions in the solvent was not monitored, clear corrosion phenomena were observed on the parts of the equipment in contact with the solvent after just three months.

In this case, the heater at one end of the stripper is particularly relevant.

In a comparative experiment, H3PO4 was added to the solvent in an amount of 0.007 wt.%.

At the same time, the chloride ion concentration in the circulating solvent was continuously monitored.

As soon as the concentration reached a value of 0.0075% by weight, a partial stream of the solvent coming from the S1J tube was regenerated by distillation before being returned to the extraction column.

This regeneration is carried out so that the chloride ion concentration in the circulating solvent is 0.0
The reaction was continued until it decreased to a value of 0.075 wt. %.

Furthermore, the apparatus was operated under exactly the same operating conditions as in the first experiment.

However, in this case, no corrosion phenomenon could be confirmed in the device even after three months had passed.

This corrosion phenomenon was still not observed even after an operating period of six months.

This fact clearly demonstrates the superiority of the method of the present invention.

Next, embodiments of the present invention will be listed.

(1) Preferably the compounds H3PO4 and/or V2O5 or M are used as additives.

03 is used in an amount of 0.006 to 0.01% by weight.

The method of claim.

(2) additionally monitoring the content of free acid ions in the solvent;
As soon as this content reaches a value of 0.005-(0.01)% by weight, the partial stream is purified by distillation before being returned to the extraction stage, the regeneration being carried out until this value reaches 0.005-(0.01)% by weight.
2. The method of claim 1, wherein the concentration of the cation exchange resin is reduced to between 0.05 and 0.001 weight percent.

Claims (1)

[Claims] 1. A method for producing pure hydrocarbons during the operation of an extraction plant and/or an extractive distillation plant using N-substituted morpholines as selective solvents, characterized in that phosphoric acid or a phosphate and/or a vanadium compound or a molybdenum compound are added to the solvent in an amount of 0.005 to 0.02% by weight.