DE102007046003A1 - To remove organic silicon compounds from waste water it is oxidized using ozone and hydrogen peroxide - Google Patents

Abstract

To oxidize organic silicon compounds in a watery medium, ozone is used as the oxidizing agent together with hydrogen peroxide (H2O2) if required.

Description

The The invention relates to a process for the oxidation of organosilicon Compounds, in particular silanols, in an aqueous medium, like in sewage.

sewage, those with readily soluble organosilicon compounds, Significantly silanols, polluted and thus heavily biological are degradable, usually fall in the production of silicones even in the synthesis of the necessary monomers and intermediates at.

The invention relates to a process for the oxidation of silizumorganischer compounds in an aqueous medium, characterized in that are used as the oxidizing agent ozone and optionally H ₂ O ₂ .

at the aqueous medium in which the organosilicon compounds solved, it can be water as well as all kinds of Wastewater act.

Prefers runs the oxidation of the invention predominantly radically.

Prefers the inventive method in a pH of 6 to 9 performed.

Prefers is ozone in quantities of 1.5 to 3.5 kg per kg of COD (based on Organosilicon compounds in aqueous medium).

H ₂ O ₂ is preferably used in the process according to the invention, with particular preference being given to small amounts. In particular, H ₂ O _{2 is used} in amounts of from 20 to 60 ppm by weight, based on the weight of the wastewater to be treated, in the process according to the invention.

Prefers the process according to the invention becomes continuous carried out.

Wastewater can thus be aftertreated after pretreatment with a radical-oxidative process using ozone and - if necessary - traces of H ₂ O _{2 in} order to decisively lower the concentration of silanols and thereby cause a further COD reduction.

A chemical mechanical pre-cleaning of the waste water to separate particles and to raise the pH to a slightly basic range and a biological purification to reduce dissolved organic compounds allow a targeted use of the oxidizing agent for the radical oxidation of the silanols. This prevents a stoichiometrically above-average consumption of starting materials (O ₃ , H ₂ O ₂ ) and energy. A targeted regulation of the input materials and the energy to the calculated COD load to be eliminated further contributes to the optimized use of operating resources.

The invention is directed primarily to the possibility of oxidizing the substance group of the organosilicon compounds, preferably silanols, dissolved in water / wastewater predominantly radically (OH radicals) by means of ozone and H ₂ O ₂ and thus resulting from an organosilicon freight to reduce chemical oxygen demand (COD). The reaction mechanism of the oxidation of organosilicon compounds can essentially run from the components trimethylsilanol to dimethylsilanediol and by further oxidation of the methyl groups on methylsilane triol to CO ₂ and H ₂ O, while the Si components can be mineralized to SiO ₂ . This way is possible but not compulsory. Decisive for the treatment goal here is the reduction of the chemical oxygen demand (COD) of the oxidized or partially oxidized compounds. Due to the production process, wastewater from silicone production contains a proportion of organically difficult-to-degrade organosilicon compounds. These can already be obtained in the synthesis of the necessary monomers and intermediates. (In order, for example, to be able to reliably comply with existing COD limit values even if production capacities are increased, the process according to the invention makes it possible to carry out further COD removal.) The oxidation process can be used for the treatment of organosilicon compounds as aftertreatment of e.g. B. classic end of pipe sewage systems can be used. Oxidizing agent-consuming particulate and dissolved organic substances are then already largely deprived of the water phase, whereby the oxidation potential can be used exclusively for the attack of the organosilicon compounds (s. 1 ). For the effectiveness of the process according to the invention, it is beneficial to set a basic pH in the pretreatment in order to force the OH radical formation. However, this is usually by z. For example, regulatory requirements are limited so that often only neutral to slightly basic pH levels will be acceptable for the treatment. By metering small amounts of H ₂ O ₂ , these restrictions can be significantly compensated if necessary.

Although a further biological treatment of only weakly oxidatively treated organosilicon compounds (cracking) is conceivable in principle, it does not lead to any detectable advantage due to the very low biological availability of the resulting intermediates. In the case of the organosilicon compound of the semi-radical / oxidative mineralization as a post-treatment process. In this arrangement, the necessary degree of oxidation can be precisely set and regulated and thus a reliable compliance with the target values for z. As the COD and resource savings can be achieved. For this purpose, the necessary freight to be eliminated can be determined online or analytically by COD or indirectly TOC (total organic carbon, convertible into COD). The determination of the cargo can be carried out by commercially available analysis and flowmeters. The calculated cargo can be used to determine and preset the required amount of oxidizing agent beyond the stoichiometrically required ozone requirement for the oxidation of the corresponding COD load. However, a regulation can also be made directly on the basis of a target COD / TOC concentration to be determined. A combination of both controlled variables, z. B. in a cascade control is also possible.

advantage the method of the invention is the targeted Removal of organosilicon compounds from most process wastewater from a silicone manufacturing plant. The treatment process is thus also against changes in the production network or product shifts more future-proof as many production integrated procedures.

These Targeted removal of organosilicon according to the invention Components from the sewage allows a fairly reliable Compliance with the prescribed wastewater limit values. An anticipatory High resource usage is due to a possible regulation of oxygen and energy use avoided, as these online analytical the target value can be regulated. This allows advantageously against oxygen and energy costs Method with fixed power setting or sole control by the amount of water / wastewater to be treated can be saved. alternative Prior art method, although integrated production are effective, carry in addition to higher investment costs and comparable to higher energy costs a significantly higher production risk into the monomer composite in siloxane production. Further are these procedures usually do not focus on future "new" Emmitent applicable, so that the scope of action in the removal Organosilicon components from the wastewater significantly restricted would.

example

Water from the effluent of a classical biological wastewater treatment is continuously fed to an oxidation plant and subsequently discharged into the discharge point. In the oxidation stage, the largely biologically treated wastewaters are aftertreated. In this case, in the case of ozone use of technical oxygen, ozone can be prepared as an oxygen / ozone gas mixture and introduced into the wastewater cycle via ozone introduction systems and H ₂ O _{2 can} be metered in as a radical promoter on the suction side of the entry system. The optionally doped with H ₂ O ₂ water / ozone mixture is then fed to the reaction and the downstream degassing. Here, the wet-chemical ozone / radical reaction with the wastewater in the reaction cycle and the subsequent separation of gas and water take place. A possible procedure is based essentially on the in EP 0 478 583 B2 or DE 199 42 184 A1 basically explained technical procedure. Notwithstanding, no UV irradiation but a dosage of H ₂ O _{2 is provided} for the radical promotion, which can be used before the ozone entry system. The use cases, substance groups and sources are fundamentally different.

1 shows an exemplary method arrangement for the mineralization in water / wastewater dissolved organosilicon compounds.

• 1. Abwasser mit einem Konzentrationsniveau von ~150 mg/L an gelösten siliziumorganischen Verbindungen wird mit einem pH-Wert von 6,5 bis 8,5 und mit einem minimalen Gehalt an Feststoffpartikeln und sonstiger organischer Fracht einer Ozonungsanlage zwecks Reduzierung des CSB kontinuierlich zugeführt (s. 1). Dabei wird Abwasser mit Ozon unter einem Druck von 2,0 bis 3,0 bar mit einer Ausbeute von 0,22 kg eliminierter silizumorganischer Verbindungen pro eingesetztem kg Ozon zur Reaktion gebracht. Die mittlere Verweilzeit des Abwassers im Kreislauf beträgt dabei minimal 35 Minuten. Die Effektivität der CSB-Elimination liegt aufgrund des naturgemäß stöchiometrisch größeren Sauerstoffbedarfs zur Oxidation der siliziumorganischen Komponenten entsprechend erheblich höher.
• 2. Wird das Abwasser unter den gleichen Randbedingungen wie bei 1. behandelt, zusätzlich aber noch mit etwa 0,12 kg H₂O₂ (35%) pro kg Ozon vor dem Ozoneintragssystem beaufschlagt, so erhält man neben einem sehr stabilen Betrieb mit einer spezifischen Ausbeute von 0,23 kg silizumorganischer Verbindungen pro eingesetztem kg Ozon. Aufgrund der vermutlich weitergehenden Reaktion erhöht sich aber die Effektivität der CSB-Elimination gegenüber 1. deutlich um ca. weitere 30%. Diese Ausbeuten lassen sich auch auf einem Konzentrationsniveau von ~100 mg/L siliziumorganischer Verbindungen realisieren. Ozongerüche lassen sich in dieser Verfahrenskombination zuverlässig vermeiden.

With this method arrangement, the following exemplary oxidation targets can be achieved:

• 1. Wastewater with a concentration level of ~ 150 mg / L of dissolved organosilicon compounds is continuously supplied to an ozonisation plant at a pH of 6.5 to 8.5 and with a minimum content of solid particles and other organic cargo in order to reduce the COD ( s. 1 ). In this case, wastewater is reacted with ozone under a pressure of 2.0 to 3.0 bar with a yield of 0.22 kg of eliminated silizumorganischer compounds per kg of ozone used reacted. The average residence time of the waste water in the circulation is minimal 35 minutes. The effectiveness of the COD elimination is due to the naturally stoichiometrically greater oxygen demand for the oxidation of the organosilicon components correspondingly higher.
• 2. If the wastewater under the same boundary conditions as in 1. Treated, but in addition still charged with about 0.12 kg H ₂ O ₂ (35%) per kg of ozone in front of the ozone input system, we obtain in addition to a very stable operation with a specific yield of 0.23 kg of organosilicon compounds per kg of ozone used. Due to the presumably further reaction, however, the effectiveness of the COD elimination increases significantly compared to 1. by about another 30%. These yields can also be realized at a concentration level of ~ 100 mg / L of organosilicon compounds. Ozone dishes can be combined in this process combination reliably avoid.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• EP 0478583 B2 [0016]
• - DE 19942184 A1 [0016]

Claims (4)

Process for the oxidation of organosilicon compounds in an aqueous medium, characterized in that ozone and optionally H ₂ O ₂ are used as the oxidizing agent. Method according to claim 1, characterized in that that ozone in quantities of 1.5 to 3.5 kg per kg of COD (based on Organosilicon compounds in aqueous medium) used becomes. A method according to claim 1 or 2, characterized in that H ₂ O _{2 is} used. Method according to one of claims 1 to 3, characterized in that it pre-cleaned for post-treatment Wastewater is used (end of pipe).