DD143631A1 - METHOD FOR RECOVERING MERCURY - Google Patents

Abstract

In the production of vinyl chloride from acetylene and. Hydrogen chloride contains the spent mercury (II) chloride-activated carbon catalysts still up to 4 wt .-% Mercury (II) chloride, The object of the invention is a improved and economical process for the recovery of Mercury from the consumed mercury (II) chloride-activated carbon catalysts at elevated temperatures with the aid of carrier gases develop. According to the invention as the carrier gas acetylene or a acetylene-containing exhaust gas at a reaction temperature between 200 and 350 ° C used. By applying this method will be get good yields of mercury and waste products, such as acetylene-containing exhaust gases and spent mercury (II) chloride catalysts, successfully exploited economically.

Description

- Λ ~

Field of application of the invention

The invention relates to a process for the recovery of mercury from spent mercury (II) chloride-activated carbon catalysts, which are obtained in the production of vinyl chloride from acetylene and hydrogen chloride and in the Eegel still up to 4 wt .-% mercury (II) chloride.

ta 9 4L <? 4 /% £

Characteristic of the known technical solutions

In the production of vinyl chloride from acetylene and hydrogen chloride, a mercury (H) chloride activated carbon catalyst having a mercury (II) chloride content of about 10% by weight is generally used. The reaction is highly exothermic, raising the temperature in the reaction zone of the catalyst to about 150 to 200 ° C. At these temperatures, sublimation of the mercury (II) chloride from the surface of the activated charcoal carrier occurs to some extent. The resulting reduction in the mercury (II) chloride content of the vinyl chloride synthesis catalyst is considered to be the main cause of its loss of activity during the technical synthesis process. If the activity of the catalyst has fallen below a certain value, it must be removed from the technical reactor and replaced by fresh catalyst.

The spent mercury (II) chloride activated carbon catalyst usually contains about 2 to 4 wt .-% mercury (II) chloride. The dumping of such a substance on heap is not safe because of the risk of contamination of the groundwater with mercury (II) chloride even with consideration of additional safety measures. In addition, the recovery of mercury contained in the spent mercury (II) chloride activated carbon catalyst is still of economic importance.

Therefore, various methods have been developed for the recovery of mercury or mercury compounds _e.

Thus, it is known that one can win the Mercury contained in spent mercury (II) chloride activated carbon catalysts in the form of its chloride by

-3 - 212 99

passing a carrier gas stream through the spent catalyst at temperatures between 27o and 6ooo G and then cooling the mixture of carrier and desorption gas in a scrubber. As a carrier gas nitrogen, hydrogen chloride, carbon dioxide, water vapor, hydrogen, chlorine and air are proposed (DE-AS I2o57o5). This process has the disadvantage that it requires relatively high temperatures and that, depending on the temperature used and the carrier gas used, different products, such as mercury (II) chloride, mercury (I) chloride, metallic mercury and mixtures thereof, are obtained.

In addition, it has been proposed in DE-AS 2o5> 41o2 to treat the spent mercury-containing catalyst at temperatures of 15 ° to 27 ° C. with chlorine (diluted with an inert gas). This alone gives mercury (II) chloride. However, the complete separation of the highly toxic mercury (II) chloride from the carrier and Desorptionsgasstrom requires a lot of equipment.

There are also known methods for working up a spent mercury (II) chloride activated carbon catalyst in which the activated carbon burned and the mixture contained in the combustion gases of mercury, mercury (II) chloride and mercury (I) chloride by cooling and laundry is deposited (DE-PS 1558415, DD-AP II5I08). In the combustion of the activated carbon is obtained but a very large volume of CO and CO ₀ , so that the partial pressure of the mercury and its compounds in aera Ee aktions gas stream is extremely low, whereby their complete separation is difficult.

\ €

Finally, it has been proposed to heat the spent catalyst of Vinylchloridsynthese with 5% nitric acid to boiling, with almost all of the mercury contained in metallic form at the bottom of the vessel to deposit (Th. Kraus, Austrian Chemist newspaper £ 2 (195I) -Io , 185-186). However, this method fails with spent technical mercury (II) chloride activated carbon catalysts.

Aim of the invention

The object of the invention is to mitigate the above-described deficiencies, the known methods with regard to the processing of spent mercury (II) chloride-activated carbon catalysts, by a method is given by the application succeeds that in the consumed spent catalysts in the form of its chloride mercury in an economically advantageous manner to win.

Presentation of the essence of the invention

- The technical task

The invention has for its object to develop an improved and economical process for the recovery of mercury from spent mercury (II) chloride activated carbon catalysts at elevated temperatures by means of a carrier gas *

- Mer kmale the invention.

The object of the invention was achieved by using acetylene or an acetylene-containing exhaust gas as the carrier gas,

  - 5 '-

The carrier gas of the invention is at a reaction temperature of 2oo to 35o ° C, preferably 2 ^ o to 3oo ° C, passed through the bed of spent mercury (II) chloride ^ activated carbon catalyst The metallic mercury is from the mixture of carrier and desorption gas by cooling and / or washing in a known manner.

The gas stream freed from mercury in this condensation zone is finally passed through a washing zone charged with an alkaline liquid before it is blown off into the open air. The separated mercury is purified in a known manner by distillation. The inventive method allows the recovery of metallic mercury by the use of a new carrier gas, wherein the reaction is carried out at lower temperatures than the reaction temperatures indicated in known methods and unexpectedly good yields of mercury are achieved. Another advantage of the invention is that two waste products, such as spent mercury (II) chloride activated carbon catalysts and acetylene-containing waste gases, are successfully utilized economically, so that the environment is not poisoned or molested by these waste products,

Outsource ₁ P ₁ S pecial le

The invention will be explained in more detail below with reference to two Ausführungsbeispieien;

example 1

In a reaction tube , which is surrounded by an electrically heated oven, 5o g of a consumed

~ 6

Added mercury (II) chloride activated carbon catalyst whose content of mercury (II) chloride is still 4.2 wt .-%. At a temperature of 26 ° C., a carrier gas stream of 15 l / hour consisting of acetylene is passed through the bed of spent catalyst

 Immediately connected to the reaction tube is cooled with ice water cooling zone. In it, the majority of the released metallic mercury separates out. The gas stream is then passed through a wash bottle filled with water, in which the remaining mercury separates, before it passes through another, filled with dilute sodium hydroxide wash bottle into the open air.

After a. Reaction time of 6o minutes, 1.5 g of metallic mercury have been deposited in the cooling zone and in the wash bottle. This is 97 % of the amount of mercury contained in the 5o g of used spent mercury (II) chloride activated carbon catalyst.

Example 2

5o g of spent mercury (II) chloride activated carbon catalyst containing 4.2% by weight of mercury (II) chloride at 26 ° C. with a carrier gas stream consisting of 10 l / hour of nitrogen are used as in Example 1 and 2 1 / hour of acetylene.

After a reaction time of 9o minutes, 1 ₉ 45 g of metallic mercury have been deposited in the cooling zone and in the washing bottle. "This is 93.5 % of the mercury amount used in the 5o g of spent mercury (II) chioride activated carbon catalyst used were included.

7 -

Claims (1)

Erfindurigsanspruch Process for the recovery of mercury from spent mercury (II) chloride-activated carbon catalysts, wherein a carrier gas is passed through a bed of these spent catalysts at elevated temperature and from the mixture of carrier and desorption gas metallic mercury is deposited by cooling and / or scrubbing , characterized in that as the carrier gas acetylene or an acetylene-containing offgas at an reaction temperature between 2oo and 35o ° C, preferably between 25o and 3oo C, is used »