SI9200263A - Process for catalytic oxidation of organic impurities in waste waters - Google Patents

Abstract

An effective process combines the adsorption of toxic organic pollutants of waste water on active coal, the desorption of the pollutants in boiling water and the oxidative decomposition of the desorbed pollutants in a dropping bed reactor.

Description

PROCEDURE FOR THE CLEANING OF INDUSTRIAL WASTE WATERS WITH LOW CONTENT OF TOXIC ORGANIC SUBSTANCES

Technical field of the invention

The present invention relates to chemical technology and environmental protection, specifically to a new process for the treatment of industrial wastewater with a low content of toxic organic matter, in particular highly toxic, biodegradable organic matter, using catalytic oxidation.

The problem solved by the invention

There was a need for a new, technologically advanced process for the treatment of low-toxic industrial wastewater, especially highly toxic organic matter.

The state of the art

The closest prior art to this patent application is patent application DE 39 38 835.2 Al and European patent application 90 111 927.7, which deals with the catalytic oxidation of toxic and biodegradable organic compounds in industrial wastewater. Both patent applications cite describe a process in which wastewater is contacted with oxygen (air) on a suitable catalyst, which is also subject to protection. Waste water which does not evaporate due to the elevated pressure in the reactor and oxygen (air) passes through the downstream catalyst bed where the dissolved toxic substances are oxidized to harmless carbon monoxide. The process is intended for the treatment of wastewater laden with a relatively high content of toxic substances, but below the limit of cost-effective recovery. The downside of the process is the partial solubility of the active components in the catalyst, which reduces the life of the catalyst, but at the same time these components in the wastewater can also burden the environment.

Adsorption on activated carbon - as an effective process for the removal of toxic and biodegradable organic matter - has been present in the purification technique for a long time (W.W. Eckenfelder Jr. et al., Chem. Engng., September 2, 1985, p. 60). With toxic compounds, saturated charcoal is regenerated by controlled oxidation (V.D. Mundale et al., Can. J. Chem. Eng., 69, 1991, p. 1149). The adsorbed compounds break down, and due to the oxidizing conditions, some activated charcoal burns with each regeneration. That is why the regeneration of activated carbon is the critical part of the process that most diminishes its economic efficiency.

Description of solution to the problem with implementation examples:

Now we have found that we can solve the above problems with a new method of the invention, which consists of:

a) adsorption phases, where the aqueous solution of toxic, biodegradable organic substances is saturated through a column filled with activated carbon at atmospheric or elevated pressure and at temperatures of 15 to 25 ° C,

b) desorption phases, where regeneration of activated carbon in the liquid phase is carried out at atmospheric or elevated pressure and temperatures from 80 to 150 ° C; and

c) reaction phases where, on a catalyst subject to DE 39 38 835.2 Al and consisting of 20 to 40 wt. % copper oxide, .15 to 25 wt. % zinc oxide, 2 to 4 wt. % chromium oxide and 20 to 40 wt. % of aluminum oxide, after desorption on carbon adsorbed organic compounds, is catalytically decomposed in the liquid phase at elevated pressure such that the partial pressure of oxygen is at least 3 bar and at temperatures between 120 and 200 ° C to carbon dioxide, the flow being liquid phases in the adsorber both in the adsorption and desorption-regeneration cycles can be directed downward or upward, the flow of the gaseous and liquid phases in the catalytic reactor may be co-directed downstream or counter-current so that the liquid phase current is directed downwards and gaseous upwards.

A preferred embodiment of the process according to the invention consists of:

a) adsorption phases, where an aqueous solution containing 1.0 g / l of phenol is led at a rate of 3.01 / h to saturation through a column filled with activated carbon, at atmospheric or elevated pressures up to 20 bar and temperatures of 15 to 25 ° C.

b) desorption phases, where regeneration of activated carbon in the liquid phase is carried out at atmospheric or elevated pressure up to 20 bar and temperatures from 80 to 150 ° C; and

c) reaction phases, wherein on the catalyst, which is subject to DE 39 38 835.2 Al and is present from 20 to 40 wt. % copper oxide, 15 to 25 wt. % zinc oxide, 2 to 4 wt. % chromium oxide and 20 to 40 wt. % of alumina, after desorption on carbon adsorbed organic compounds, is catalytically decomposed in the liquid phase at an elevated pressure of up to 20 bar, such that the partial pressure of oxygen is at least 3 bar and at temperatures between 120 and 200 ° C to carbon dioxide, the liquid phase flow in the adsorber, both in the adsorption and desorption regeneration cycle, can be directed downward or upward, the gas and liquid phase flow in the catalytic reactor may be downstream or counterflow so that the liquid phase flow is downward and gaseous upward.

Of the toxic, biodegradable organic substances, phenol is mentioned as an example, but the process of the invention can also be used for the year of equivalent toxic substances.

The combination of adsorption with the desorption - regeneration cycle, when the total oxidation of toxic compounds' is carried out separately, in a catalytic reactor and is the subject of the present patent application has not yet been described in the published patent literature.

The process is shown on the basis of the accompanying Figure 1. Waste water containing dissolved toxic organic compounds e.g. phenol, is fed through conduit 1 and valve 2 into a column (absorber) 3 filled with activated carbon granules. The flow through the column can be gravitational or forced with a pressure difference, it can be directed down or up (see sketch). After a layer of activated charcoal is saturated with organic compounds (breakthrough) at operating temperature (about 25 ° C), the wastewater flow through this column is interrupted and redirected through line 7 to fresh or regenerated charcoal column 9, valve 2 to close line 1 and valve 4 at outlet 5. Turn on the heater 13 of the adsorber and reactor, open the valves 6 on line 7 and 14 on line 15, and start the pump 12 so that the water in which the temperature rises flows through the reactor and adsorber. When the circulating water reaches the desired temperature (130 - 150 ° C) in the system, the introduction of oxygen (air) through the line 8 into the reactor 9 is started. (water). The reactor can be operated in the sump or counterflow of both phases, the pressure is the same in both columns - up to 20 bar. Due to the elevated temperature, the adsorbed compounds on the carbon at lower temperature are now desorbed in a separator (separator 10) into the circulating water stream. As this water passes through the catalyst bed, the desorbed organic compounds are degraded (oxidized) to carbon dioxide (gas phase 11). The process of desorption - regeneration with catalytic incineration in the liquid phase is completed when the concentration of organic compounds falls below the desired limit in the effluent of the adsorber or reactor. It should be added that organic compounds do not need to be completely desorbed from activated carbon or decomposed in a reactor. In this case, the adsorption capacity of the charcoal will be reduced accordingly. It should be borne in mind that at low concentrations the contact times on the catalyst are substantially longer (higher catalyst bed) for the same degradation rate than at high concentrations.

The process described, which in a sense is a combination of adsorption and catalytic oxidation, takes advantage of the essential benefits of each process. With resorption of activated carbon regeneration, we no longer have unwanted charcoal combustion, and the active components extracted from the catalytic converter do not enter the watercourse as they circulate in a closed circle. Since these components are also active as homogeneous catalysts, deactivation of the catalyst is much slower than in the case of direct passage of wastewater through the catalyst bed. Due to the pre-concentration of toxic compounds on activated carbon, the catalyst layers are also lower.

Example l:

An aqueous solution of phenol (500 mg / l concentration) at a rate of 250 ml / min was passed through an adsorption column (3.2 cm in diameter) filled with 130 grams of activated carbon (average grain diameter 1.6 mm, layer height 38 cm) until the charcoal mass was reached saturated with phenol - 4.5 g of phenol per 100 g of dry charcoal. The degree of saturation of the charcoal layer was monitored by continuous measurement of phenol concentration (HPLC) in the solution leaving the adsorber. When phenol appeared in the adsorber effluent (conc. Less than 0.2 mg / l), the carbon was considered to be saturated with phenol. The adsorption process was carried out at atmospheric pressure and room temperature (22 ° C). The water circulation rate was 18 ml / min. Oxygen was introduced into the reactor (3.2 cm diameter), which was filled with 800 grams (grain diameter 0.6 mm, layer height 90 cm) in the patent P 39 38 835.2 described after circulating water reached a temperature of 130 ° C. . Oxygen was introduced at a pressure of 7.7 bar at a speed of 1400 ml / min. The pressure in the adsorber also increased to 7.7 bar. Hot water (130 ° C) was pumped for 30 minutes. During this time, the concentration of phenol in the solution in the reactor outlet stream, followed by HPLC and TOC analyzer, fell below 10 mg / l and was practically from carbon desorbed all phenol (balance!). The thus regenerated layer was prepared to process a new batch of model solution. After five adsorption and desorption - regeneration cycles, with separate phenol oxidation, the adsorption properties of charcoal in the layer did not change. In the water leaving the adsorber after each desorption-regeneration cycle, we practically did not find any oxidizing intermediates or metals that eventually leached from the catalyst.

EXAMPLE 2

Regeneration with the phenol of a saturated layer of charcoal in an adsorber (according to Primer

1) was carried out with demineralized water at elevated temperature and pressure. Water was passed through a saturated layer at a temperature of 150 ° C and a pressure of 10 bar and the HPLC concentration of the adsorber fluid outflow was measured. After the initial rise (Fig

2) the concentration then steadily decreased to 1.5 g / l, where the process of desorption or regeneration of the charcoal was interrupted. By appropriately evaluating the area under the curve (Figure 2) and the product thereof by volume flow of water, it was found that 26.7 g of phenol was desorbed or 5.6 g of phenol remained on activated carbon after desorption on charcoal. In other words, by raising the temperature, we regenerated 90% of the adsorption capacity of the charcoal used.

EXAMPLE 3

Regeneration with the phenol of the saturated carbon layer in the adsorber (according to Example 1) was carried out by liquid phase catalytic oxidation. For this purpose, a 34 mm internal diameter drip reactor filled with 730 g (average grain diameter 0.56 mm, layer height 81 cm) of the catalyst described in DE-patent P39 38 835.2 was used. We switched on the heating and turned on the pump. The water speed was 21 / h. Oxygen was introduced at a total pressure of 11 bar at a rate of 2 l / min. The pressure in the adsorber also increased to 11 bar. Hot water (150 ° C) was pumped for 10 hours. The concentration of phenol in circulating water, followed by high-performance liquid chromatography (HPLC), during this time was reduced to 0.8 g / l, corresponding to 90% regeneration of the activated carbon layer in the adsorber. The regenerated activated carbon layer in the adsorber was then prepared to process a new batch of model solution. After five adsorption and desorption - regeneration cycles, with separate catalytic oxidation of phenol, the adsorption properties of charcoal in the layer did not change. Concentrations of leached copper and zinc ions in water circulating in the regeneration - oxidation cycle were 20 and 32 mg / l after the first cycle, but did not exceed 25 and 40 mg / l after the fifth cycle.

Claims (2)

1. A process for the purification of industrial wastewater with a low content of toxic organic matter, characterized in that it consists of: a) adsorption phases, where the aqueous solution of toxic biodegradable organic matter is saturated through a column filled with activated carbon at atmospheric or elevated pressure and temperatures of 15 to 25 ° C, b) desorption phases, where regeneration of activated carbon in the liquid phase is carried out at atmospheric or elevated pressure and temperatures from 80 to 150 ° C; and c) reaction phases where on the catalyst which 15 exists from 20 to 40 wt. % copper oxide, 15 to 25 wt. % zinc oxide, 2 to 4 wt. % chromium oxide and 20 to 40 wt. % of alumina, after desorption on carbon adsorbed organic compounds, is catalytically decomposed in the liquid phase at elevated pressure such that the partial pressure of oxygen is at least 3 bar, and 20 at temperatures between 120 and 200 ° C, up to carbon dioxide, the liquid phase in the adsorber being in the adsorption as well as the desorption regeneration cycle can be directed downwards or upwards, the gas and liquid phase flows in the catalytic reactor may be downstream or countercurrent, so that the flow of the liquid phase is directed downward and gaseous upward. A method according to claim 1, characterized in that it consists of a) adsorption phases, where an aqueous solution containing 1.0 g / l of phenol is led at a rate of 3.01 / h to saturation through a column filled with activated carbon, at atmospheric or elevated pressure of up to 20 bar and temperatures of 15 to 25 ° C, b) desorption phases, where regeneration of activated carbon in the liquid phase is carried out at atmospheric or elevated pressure up to 20 bar and temperatures from 80 to 150 ° C; and c) reaction phases, wherein on a catalyst consisting of from 20 to 40 wt. % copper oxide, 15 to 25 wt. % zinc oxide, 2 to 4 wt /% chromium oxide and 20 to 40 wt. % of alumina, after desorption on carbon adsorbed organic compounds, is catalytically decomposed in the liquid phase at an elevated pressure of up to 20 bar, such that the partial pressure of oxygen is at least 3 bar and at temperatures between 120 and 200 ° C to carbon dioxide, the liquid phase flow in the adsorber, both in the adsorption and desorption regeneration cycle, can be directed downward or upward, the gas and liquid phase flow in the catalytic reactor may be downstream or counterflow so that the liquid phase flow is downward and gaseous upward.