DE10320067B4 - Suppression of aromatics and polycycles formation in high-temperature processes by means of CO2 - Google Patents

Abstract

method for suppression of unwanted Aromatic and Polyzyklenbildungen in combustion or pyrolysis processes above a temperature of 500 ° C and with the participation of organic matter, with a metered introduction of carbon dioxide in the gas phase takes place, leaving carbon dioxide above the temperature of 500 ° C at the origin of the aromatics and polycycles in sufficient quantity is available.

Description

The The invention relates to a method for suppressing unwanted Aromatic and Polyzyklenbildungen in combustion and pyrolysis processes above a temperature of 500 ° C and with the participation of organic substances.

at high temperatures or by transmission of energy by other mechanisms on atomic nuclei, chemical Elements or chemical compounds break due to high vibration amplitudes chemical bonds between atoms. This produces fragments (intermediates), which are either stable in themselves or are inclined to stabilize. If this happens in the gas phase, it is called the totality these processes and the macroscopic state as plasma. Is hydrogen and carbon - in which Form always - in Contact with such a plasma (both components must be in Contact with a plasma, but without necessarily even part of the plasma), one spontaneously observes the formation of hydrocarbons, primarily of methane, ethene and ethyne, but at the same time also of species with higher C number such as benzene, toluene and polycyclic aromatic hydrocarbons and soot, provided that the reaction products have the ability to stabilize, for example, in colder Enter zones.

• – Radikalbildung
• – Kettenpropagation durch Addition von Radikalen an ungesättigte Verbindungen jeder Art (auch CO, CO₂, flüchtige Oxide, Nitride u. s. w.)
• – Kombination zweier Radikale sowie
• – Zerfall oder Abbau größerer Moleküle (auch von Polymeren wie Kohlenstoff oder Russ)

eine Rolle spielen.The emergence of higher C-containing species occurs after complex radical chain mechanisms, which include elementary reaction steps such as

• - Radical formation
• - Chain propagation by addition of radicals to unsaturated compounds of all kinds (including CO, CO ₂ , volatile oxides, nitrides, etc.)
• - Combination of two radicals as well
• Disintegration or degradation of larger molecules (including polymers such as carbon or soot)

play a role.

in the The framework of these "high-temperature syntheses" arises - in different Yields and highly dependent from the conditions - one Variety of organic compounds, including aromatics (Benzene, benzene derivatives, Polycycles, fulvenes, azulene, naphthalene etc. and unsaturated aliphatics and cycloaliphatic).

The DE 41 04 252 C2 describes a process for burning carbonaceous waste in a metallurgical shaft furnace, particularly in a blast furnace. The flue gases formed during combustion contain, inter alia, the above-described polycyclic hydrocarbons, which, however, are degraded again at the temperatures prevailing in the combustion zone of 2000 ° C.

Of the DE 41 24 277 A1 a thermal procedure for decontamination of contaminated soil shall be taken. The excavated soil is heated to a maximum of 650 ° C under oxygen exclusion. The discharge of pollutants, such as polycyclic aromatic hydrocarbons, with the aid of a desorbent. As the desorbent, an inert carrier gas such as carbon dioxide can be used.

Of the Invention is now based on the problem that in combustion and pyrolysis the Benzene and Polyzyklenbildung represents an undesirable "side reaction", because it leads to polluting products. At foundries for example, this can cause that the emission limit value for benzene is not complied with by molding plants.

The The object of the invention is to provide a method which effectively suppresses aromatics formation and thus resulting problems be mitigated or eliminated.

The The object is achieved by the method mentioned in claim 1.

In Investigations on such reaction systems have been found that in a temperature window above 800 ° C - the optimal reaction window hangs again from the conditions and reaction components, by carbon dioxide one effective suppression the aromatics takes place. This is in terms of the synthesis guide at chemical transformations, but also in terms of prevention harmful Emissions of great interest in thermal processes (engines, burns, metallurgical reduction and sintering processes, heating of organic Compounds in fires, when casting by hot Metals in polymer-bound forms, in welding processes involving: organic material, grinding wheel emissions, etc.).

The essence of the invention is to bring to the place of origin of undesirable aromatic compounds, primarily benzene and polycyclic aromatic hydrocarbons, including heterocycles, targeted CO ₂ to suppress the above-described high-temperature synthesis of these substances.

• – durch thermische Zersetzung CO₂-abspaltender Substanzen
• – als Gas
• – durch Ausgasen von gelöstem, komplexiertem oder adsorbiertem/absorbiertem CO₂ aus Absorbentien oder Adsorbentien (wie Graphit, Silikate, Lösungen)
• – durch chemische Umwandlung von Stoffen, die zur CO₂-Bildung führen, beispielsweise durch das Verschieben des Boudouard-Gleichgewichtes in Richtung CO₂ durch Abfangen des Kohlenstoffs: (2 CO ↔ CO₂ + C).

The targeted introduction of carbon dioxide in the reaction zone can be done in different ways:

• - By thermal decomposition of CO ₂ -dissing substances
• - as gas
• By outgassing of dissolved, complexed or adsorbed / absorbed CO ₂ from absorbents or adsorbents (such as graphite, silicates, solutions)
• - by chemical conversion of substances that cause CO ₂ formation, for example by shifting the Boudouard equilibrium towards CO ₂ by trapping the carbon: (2 CO ↔ CO ₂ + C).

The Method represents a universal method in that the Involvement of carbon dioxide in chain propagation (eg with hydrogen, Hydroxyl or hydrocarbon radicals) apparently unstable Intermediates leads or hinders the cyclization of polyolefins.

The invention is illustrated by the following exemplary embodiments in the form of experimental arrangements:
The figures show in detail:

1 a laboratory arrangement to demonstrate the reduction effect of gas reactions in flowing gases.

2 a laboratory arrangement to demonstrate the reduction effect in solid pyrolysis.

In a thermal reactor ( 1 ) according to 1 a temperature gradient of about 1070 ° C is generated up to room temperature. This is done in this example by inductive heating of the iron rod ( 3 ). Due to the cooling effect of the passing gas, the wall remains relatively cold. The temperature can be much higher, but not arbitrarily low. In this particular arrangement, at 1070 ° C, the maximum rate of formation of benzene is found.

Whether the reactor is a flow reactor or a batch reactor ( 2 ) according to 2 is driven, plays only a minor role optional, a gas supply is possible; Also, it is not crucial how the energy is brought into the reaction medium - here was an induction furnace ( 4 ). In the center of the induction coil is an iron rod ( 3 ) or an iron bead, which can be easily heated by the induction current to temperatures of 1300 ° C. Surrounding the metal rod of the reaction mixture, which can be introduced in any state of aggregation in the reactor vessel. As a reactor vessel, a quartz tube has proven itself.

The reactions can be observed homogeneously and heterogeneously; however, benzene formation always occurs at high temperatures and therefore in the gas phase. By heterogeneous is meant that a starting substance (s) in different states of aggregation can be introduced into the reactor, as coal which splits off gases (gas coal), as a carbonate which releases CO ₂ etc. In these cases, a two-stage reaction takes place. in the first of the essential reaction components are formed by thermal decomposition of the solids and then further react in the gas phase, but the decomposition temperatures and spatial arrangements of the solids are tuned so that the reaction components can react in the plasma.

• 1. Methan wird durch den heißen Reaktor geleitet und die Reaktionsprodukte bestimmt. In einem zweiten Versuch wird CO₂ zugemischt, was die Aromatenbildung unterdrückt.
• 2. Kohle wird als körniges Pulver, in dem der Eisenstab eingebettet liegt, in die Induktionszone des Batchreaktors (2) eingebracht und erhitzt. In einem zweiten Versuch wird der Kohle Soda zugemischt, um die Aromatenbildung zu unterdrücken.

In all embodiments described below, the reaction system is free of air, but this is not a mandatory condition, since even in flames with air benzene formation is observed, which can be suppressed by CO ₂ addition.

• 1. Methane is passed through the hot reactor and the reaction products determined. In a second experiment CO _{2 is added} , which suppresses the aromatics.
• 2. Coal is introduced as a granular powder in which the iron rod is embedded in the induction zone of the batch reactor ( 2 ) and heated. In a second experiment, the carbon is added to soda to suppress the formation of aromatics.

A mass-selective quadrupole mass spectrometer ( 6 ) detects the concentrations of the reaction components and the temporal change of the concentrations. The suppressed benzene formation can be observed with and without inert carrier gas. The best way to compare the rates of formation of benzene and other hydrocarbons in a light carrier gas stream, of which a part is replaced by carbon dioxide in the comparative experiment.

This arrangement is also a suitable device for determining the sufficient amount of CO ₂ needed to optimally suppress aromatics and polycycles formation. For this purpose, the CO ₂ feed is varied in its quantitative ratio to the rate of formation of the aromatics and polycycles and via the analyzer ( 6 ).

1

thermal reactor

2

batch reactor

3

iron rod

4

induction furnace

5

Temperature sensor, color pyrometer

6

analyzer mass spectrometry

7

pipe connectors

8th

loose Coke / lime filling o. a.

Claims (1)

Method of suppression of unwanted Aromatic and Polyzyklenbildungen in combustion or pyrolysis processes above a temperature of 500 ° C and with the participation of organic Substances, with a metered introduction of carbon dioxide in the Gas phase takes place so that carbon dioxide above the temperature of 500 ° C at the point of origin the aromatics and polycycles is present in sufficient quantity.