CN1081083C - Quick catalytic dechlorination of poly-chloro-organocompound in water using zero-valence Fe and pd catalyst - Google Patents

Abstract

In the field of water treatment and water pollution prevention and control, zero-valent iron and palladium catalysts are used to rapidly dechlorinate polychlorinated organic compounds in water, including catalysts, reducing agents and carriers. It is characterized in that the catalyst is elemental palladium, the reducing agent is zero-valent iron, its dosage ratio (wt) is (1-10): 10000, the carrier is activated carbon, ceramics or zeolite, and the ratio of zero-valent iron-palladium catalyst and carrier is 1: (1 -10) Mix into filler. The process is to fill the fixed tower with evenly mixed packing, the thickness is (300-8000mm), and the sewage passes through the packing layer for 3-10 minutes. Advantages: (1) fast, efficient, small footprint, (2) simple process, (3) low energy consumption, low operating costs, iron consumption is 0.01-0.06 yuan/m ³ water.

Description

Rapid catalytic dechlorination of polychlorinated organic compounds in water using zero-valent iron and palladium catalysts

The invention relates to rapid catalytic dechlorination of polychlorinated organic compounds in water, and belongs to the field of water treatment and water pollution prevention and control.

Polychlorinated organic compounds (especially polychlorinated organic compounds with low carbon number) have been proved by the scientific community to have "carcinogenic, teratogenic, mutagenic" effects or suspicious "three-induced effects" at trace concentration levels. Therefore, the treatment of polychlorinated organic compounds has always been a subject of concern in the field of environmental protection. Because polychlorinated organic compounds are difficult to biodegrade, the methods of treating polychlorinated organic compounds with traditional microorganisms are limited.

At present, there are mainly the following methods for the treatment of polychlorinated organic compounds in water:

(1) Activated carbon adsorption method: This method uses activated carbon to remove polychlorinated organic compounds in water based on physical and chemical principles, (2) Air stripping method: This method utilizes polychlorinated organic compounds with low carbon number and high volatility Features: use gas stripping method to separate polychlorinated organic compounds from water phase, (3) microbial anaerobic treatment method: polychlorinated organic compounds are generally difficult to degrade with oxygen, and anaerobic method can achieve the purpose of reductive dechlorination.

The above-mentioned several methods have the following common problems: (1) the treatment period is long, the floor area is large, (2) the energy consumption and the operation cost are high, (3) the concentration of polychlorinated organic compounds in the treated water is still relatively high . Among the new treatment technologies developed in recent years are semiconductor photocatalytic oxidation. The method utilizes the characteristic that semiconductors such as TiO ₂ have a catalytic effect on oxidation, and finally oxidizes polychlorinated organic compounds into carbon dioxide and chloride ions, which has the characteristics of thorough oxidation. It is suitable for the treatment of low concentration organic matter in water. However, this method is currently in the development stage, and many problems (such as the stable absorption of light energy, the reasonable loading method of the catalyst, the reduction of energy consumption, etc.) have to be solved in order to adapt to practical applications. Another method is the catalytic transfer hydrogenation method, the most typical of which is Zhao Yi's "Research on Catalytic Transfer Hydrogenation and Dechlorination of Polychlorinated Biphenyls" published in the 1994 "Environmental Chemistry" Volume 13 No. 4, which reports In the presence of 10% palladium/carbon, using ammonium formate as the hydrogen donor to dechlorinate polychlorinated biphenyls (PCB _s ) by catalytic transfer hydrogenation, in neutral medium, low temperature (60 ℃) and atmospheric pressure, PCB _{The s} dechlorination efficiency reaches 98-100% (equivalent to the PCB _s concentration in the treated water being 0.1-170ppm). The reaction mechanism is: ammonium formate decomposes to release hydrogen under the action of palladium/carbon catalyst. In the heterogeneous catalytic system, the reactant molecular hydrogen and _PCBs can interact with the active center of the catalyst, be adsorbed and deformed by the catalyst, relax the chemical bond, and form The active adsorption complex reduces the activation energy of the reaction and enables the dechlorination reaction _{of PCBs} . This method obtained high dechlorination efficiency and has been used for dechlorination of _PCBs in capacitors. But it has the following disadvantages: (1) the amount of palladium added in the catalyst is relatively large (10%d/C), and the treatment cost is high; effect, (3) the method needs to add organic acid as a reducing agent, (4) the treatment time is longer (0.5～2h), (5) the method is more toxic to other aliphatic polychlorinated organic compounds with low carbon number The dechlorination efficiency has not been reported, and the dechlorination efficiency of the method for low concentration (0.05-200ppm) polychlorinated organic compounds in water has not been reported either.

Due to the increasingly stringent restrictions on the use of polychlorinated organic compounds in countries around the world, relatively high concentrations of emission sources are becoming less and less. At present, the treatment of low-concentration polychlorinated organic compounds produced by chlorine gas disinfection in drinking water and low-concentration polychlorinated organic compounds in water systems polluted by polychlorinated organic compounds has gradually become the focus of polychlorinated organic compound treatment. Therefore, it is of great significance to develop a fast, efficient and low-consumption treatment technology for low-concentration polychlorinated organic compounds in water.

Purpose and task of the present invention are to overcome existing in polychlorinated organic compound treatment technology in water: (1) the content of palladium in the catalyzer is big, expensive, (2) can not handle the aliphatic polychlorinated organic compound of low carbon number, (3) Low concentration polychlorinated organic compound treatment efficiency, long time, (4) need to add organic acid in addition as the deficiency of reducing agent. It also provides a new fast, high-efficiency, and low-energy water treatment technology suitable for the treatment of low-concentration (0.05-200ppm) polychlorinated organic compounds in water. It is especially proposed to use zero-valent iron and palladium catalysts to quickly treat polychlorinated organic compounds in water. Technical solutions for catalytic dechlorination.

The basic concept of the present invention is based on the fact that polychlorinated organic compounds can be oxidized under specific conditions, and the final oxidation products are carbon dioxide and chloride ions, but this oxidation is relatively difficult, and the reduction of such substances is relatively easy. The cheap and easy-to-obtain substance is the reducing agent, instead of ammonium formate as the hydrogen source, H ₂ O is used as the hydrogen source, and then an appropriate catalyst is selected to reduce and dechlorinate polychlorinated organic compounds to form slightly toxic or non-toxic original parent organic compounds and chloride ions. The idea of this method is expressed as a reaction formula:

The reducing agent adopted in the formula is heavy metal catalysts such as cheap zero-valent iron (elemental iron) and common catalyst palladium.

The present invention proposes using zero-valent iron and palladium catalysts to quickly catalyze dechlorination of polychlorinated organic compounds in water. In the technical scheme, the formula of zero-valent iron-palladium catalyst mainly includes catalyst, reducing agent and carrier, and is characterized in that: reducing agent It is zero-valent iron (iron powder, iron grain or iron filings); the catalyst is elemental palladium; the amount ratio (wt, the same below) of the catalyst used and the reducing agent is (1-10): 10000; the zero-valent iron-palladium catalyst Obtaining is prepared by reacting palladium complex salt with iron to plate palladium on the surface of iron; the carrier used is activated carbon, pottery or zeolite; the prepared zero-valent iron-palladium catalyst and carrier are prepared in a ratio of 1: (1- 10) The ratio is evenly mixed into the filler.

The implementation process of the technology of the present invention is: uniformly mix the prepared zero-valent iron-palladium catalyst and the carrier (activated carbon, ceramic particles or zeolite) into a filler in a ratio of 1: (1-10), and then fill the filler evenly Into the fixed tower (tower diameter is generally Φ = 80 ~ 3000mm), the packing layer h can be 300 ~ 8000mm, the water containing polychlorinated organic compounds is passed through the fixed tower in the way of upflow or downflow, and the water is in the packing layer in the tower The residence time in the medium is 3 to 10 minutes.

A further feature of the present invention is that its formula and its implementation process produce a reaction with obvious fast and efficient dechlorination efficiency under the following conditions: in nature, the water temperature is a common range of 0 to 40 ° C, and the general optimum value The temperature is 15-25°C (normal temperature); the pressure is 0.8-1.2 atmospheres, usually 1 atmosphere (normal pressure); the pH of water is 2-10, and the best value is 5-7; the most suitable The concentration range of polychlorinated organic compounds in common sewage is 0.05-200ppm.

The consumption ratio of the selected catalyst of the present invention and reducing agent is lower when sewage concentration is lower, and its consumption ratio is smaller; The smaller the ratio is; when the water temperature is high, the residence time can be appropriately shortened, and when the pH<5 or pH<7, the residence time can be extended to achieve a higher dechlorination efficiency. In practice, the residence time (that is, the time of water in the packing layer) depends on the diameter of the tower, the height of the packing layer and the void ratio to adjust. At the same hydraulic retention time, different polychlorinated organic compounds have different dechlorination efficiencies. The more chlorine substituents, the higher the dechlorination efficiency, and the lower the concentration, the shorter the time required for the same dechlorination efficiency.

The main advantages of the present invention are:

(1) Fast and small footprint. If the dechlorination efficiency reaches 70-98% (equivalent to the concentration of polychlorinated organic compounds in the treated water is 0.001-4ppm), the residence time is less than 10 minutes, while the residence time of the catalytic transfer hydrogenation method is 0.5-2 hours, it can be seen that This method dechlorination is rapid. The main equipment is a fixed tower with a small footprint.

(2) The process is simple. The whole process only needs to add the specified packing layer in the fixed tower to pass water.

(3) Low energy consumption. The treatment process is carried out at normal temperature, and there is no other energy consumption except the power consumption of the pump.

(4) Low operating cost. A major part of operating costs is reflected in iron consumption. In the common organic chlorine concentration range (0.5-200ppm), the iron consumption is equivalent to RMB 0.01-0.06/m3 water.

The concrete implementation of the present invention is as follows:

Example 1:

A certain factory adopts the inventive method to process a sewage containing trichlorethylene under normal pressure, and its steps are:

The first step: water survey:

The properties of water are:

Trichlorethylene concentration: 46ppm

Sewage pH value: 6.7

Chloride ion concentration: <2ppm

Sewage temperature: 20°C

The second step: preparation of filler:

The complex salt of palladium is reacted with iron and palladium is plated on the surface of iron powder (palladium: iron=3: 10000), then the prepared zero-valent iron-palladium catalyst and active carbon (20 orders) are pressed 1: 2 Proportions mix into a homogeneous filling.

Step 3: Handle the implementation:

Put the prepared packing into the fixed tower (filling layer φ × h = 80 × 330mm, porosity ε = 0.6), ensure that when the water volume is controlled to Q=5L/h, the residence time of water in the packing layer is 4 Minutes; connect the sewage tank, metering water pump, fixed tower and treated water collection tank with pipelines; turn on the water pump, adjust the water volume (Q=5L/h), make the water stay in the packing layer of the fixed tower for 4 minutes to fully react and dechlorinate.

Step 4: The water quality inspection results after treatment are:

Trichlorethylene concentration: Trichlorethylene was not detected in the water

pH of water: 6.8

Chloride ion concentration: 34.8ppm (equivalent dechlorination efficiency > 93%)

Temperature of treated water: 20°C

meet drinking water standards.

Example 2:

A factory adopts the inventive method to process a sewage containing benzene hexachloride under normal pressure, and its steps are with embodiment 1:

The first step: water survey:

The properties of water are:

Benzene hexachloride concentration: 30ppm

Sewage pH value: 3.5

Chloride ion concentration: ＜2ppm

Sewage temperature: 23°C

The second step: preparation of filler:

React the complex salt of palladium with iron and palladium is plated on the surface of iron grain (palladium: iron=5: 10000), then prepare zero valent iron-palladium catalyst and ceramic grain (10 orders) by 1: 5 Proportions mix into a homogeneous filling.

Step 3: Handle the implementation:

Put the prepared packing into the fixed tower (filling layer φ × h = 280 × 700mm, porosity ε = 0.63), to ensure that when the water quantity is controlled to be Q=51L/h, the residence time of water in the packing layer is 10 Minutes; connect the sewage tank, metering water pump, fixed tower and treated water collection tank with pipelines; turn on the water pump, adjust the water volume (Q=51L/h), make the water stay in the packing layer of the fixed tower for 10 minutes to fully react and dechlorinate.

Step 4: The water quality inspection results after treatment are:

Concentration of benzene hexachloride: no detection of benzene hexachloride in water

Water pH: 4.2

Chloride ion concentration: 21.5ppm (equivalent dechlorination efficiency > 90%)

Temperature after treatment: 24°C

meet drinking water standards.

Example 3:

A certain factory adopts the inventive method to process a sewage containing carbon tetrachloride under normal pressure, and its step is with embodiment 1:

The first step: water survey:

The properties of water are:

Carbon tetrachloride concentration: 28ppm

Sewage pH value: 8

Chloride ion concentration: ＜2ppm

Sewage temperature: 25°C

The second step: preparation of filler:

React the complex salt of palladium with iron to plate palladium on the surface of iron filings (palladium: iron=10:10000), then prepare zero-valent iron-palladium catalyst and zeolite (8 mesh) in the ratio of 1:10 Blend into a homogeneous filling.

Step 3: Handle the implementation:

Put the prepared packing into the fixed tower (filling layer φ×h=210×500mm, porosity ε=0.68), ensure that when the water quantity is controlled to be Q=38L/h, the residence time of water in the packing layer is 6 Minutes; connect the sewage tank, metering water pump, fixed tower and treated water collection tank with pipelines; turn on the water pump, adjust the water volume (Q=38L/h), make the water stay in the packing layer of the fixed tower for 6 minutes to fully react and dechlorinate.

Step 4: The water quality inspection results after treatment are:

Carbon tetrachloride concentration: Carbon tetrachloride was not detected in the water

pH of water: 7.3

Chloride ion concentration: 25.8ppm (equivalent dechlorination efficiency > 95%)

Temperature of treated water: 25°C

meet drinking water standards.

Claims (3)

1. a kind of method with zero-valent iron-palladium catalyst to the fast catalytic dechlorination of polychlorinated organic compounds in water, the formula of zero-valent iron-palladium catalyst mainly comprises catalyst, reducing agent and carrier, it is characterized in that: a) The reducing agent is: zero-valent iron, b) the catalyst is: elemental palladium, c) The consumption ratio (wt, hereinafter the same) of catalyst and reducing agent is (1-10): 10000, and the acquisition of zero-valent iron-palladium catalyst is to use the complex salt of palladium to react with iron and palladium is plated on the surface of iron method preparation, d) The carrier is: activated carbon, ceramics or zeolite, e) uniformly mixing the prepared zero-valent iron-palladium catalyst and the carrier at a ratio of 1: (1-10) to form a filler. 2. according to claim 1, use zero-valent iron-palladium catalyst to the method for fast catalytic dechlorination of polychlorinated organic compounds in water, it is characterized in that: implementation process is: the prepared zero-valent iron-palladium catalyst and carrier are proportioned After being evenly mixed into a filler, fill the filler into the fixed tower, and pass the water containing polychlorinated organic compounds through the fixed tower in an upflow or downflow manner. The residence time of the water in the filler layer in the tower is 3 to 10 minutes. Finally, the water that passes through the packing layer of the fixed tower is introduced into the treated water collection tank to complete the purification process. 3. according to claim 1 and 2 described with zero valent iron-palladium catalyst to the method for polychlorinated organic compound fast catalytic dechlorination in water, it is characterized in that, reaction is to carry out under the following conditions: a) common temperature in nature is 0～40℃, b) The atmospheric pressure is 0.8 to 1.2 atmospheres, c) The pH value of the water is 2-10, d) The concentration range most suitable for common chlorine-containing organic compounds in sewage is 0.05-200ppm.