METHODS FOR TREATING ODORS

Abstract

There are provided methods for treating a gas having an undesirable odor. The methods comprise contacting the gas with an acidic aqueous oxidizing composition having a pH of about 2.0 to about 3.0 and comprising at least one cation of a metal; a sequestering agent; and H.sub.2O.sub.2 and submitting the gas and the composition to UV radiation when the gas and the composition are contacting each other, wherein the treatment permits to reduce by at least 60% intensity of the undesirable odor.

Claims

1-89. (canceled)

90. A method for treating a gas having an undesirable odor, said method comprising: contacting said gas with a basic aqueous oxidizing composition having a pH of about 9.0 to about 10.0, and comprising H.sub.2O.sub.2 at a concentration of about 20 mg/L to about 700 mg/L and a cation of a metal chosen from Fe, Cu, Ni, Mn, Ti, Cr, Ce, Zn, Pd, Mo, and mixtures thereof, wherein said contacting includes mixing said gas with said basic oxidizing composition so as to at least partially dissolve at least one compound contained in said gas into said basic oxidizing composition, said gas and said basic oxidizing composition being mixed together in a packed column, and wherein said gas is introduced at a bottom portion of said column and said basic aqueous composition is introduced at a top portion of said column, said gas and said basic aqueous composition being mixed together into said column over a predetermined amount of transfer units and submitting said gas and said composition to UV radiation when said gas and said composition are contacting each other, wherein said treatment permits to reduce by at least 70% intensity of said undesirable odor, as determined by dynamic olfactometry measurements carried out by a panel of individuals, in which the olfactometer was composed of six beakers in which three test specimens were found, each beaker corresponded to a different dilution level of the odorous gas and wherein in each beaker, a single test specimen diffused odorous air, each of the individuals that made up the panel had to identify, in each beaker, which of the test specimens was diffusing the odorous gas, the data from the panel were compiled and the results were calculated with the aid of a table by using the air dilution and odorous gas flow rates of each of the test specimens.

91. The method of claim 90, wherein said treatment permits to reduce by at least 80% intensity of said undesirable odor, as determined by dynamic olfactometry measurements been carried out by a panel of individuals.

92. The method of claim 90, wherein said treatment permits to reduce by at least 85% intensity of said undesirable odor, as determined by dynamic olfactometry measurements been carried out by a panel of individuals.

93. The method of claim 90, wherein said basic aqueous oxidizing composition has a pH of about 9.3 to about 9.7.

94. The method of claim 90, wherein said basic aqueous oxidizing composition has a pH of about 9.0 to about 9.5.

95. The method of claim 90, wherein said basic aqueous oxidizing composition has a pH of about 9.5 to about 10.0.

96. The method of claim 90, wherein the at least one cation is Fe.sup.2+, Cu.sup.2+, or a mixture thereof.

97. The method of claim 90, wherein the at least one cation is Fe.sup.2+.

99. The method of claim 90, wherein said basic aqueous oxidizing composition further comprises a sequestering agent.

100. The method of claim 99, wherein said sequestering agent is chosen from diethylenetriaminepentaacetic acid (DTPA), nitrolotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), sodium hexametaphosphate, sodium citrate, and mixtures thereof.

100. The method of claim 99, wherein said sequestering agent is NTA.

101. The method of claim 99, wherein said sequestering agent is DPTA.

102. The method of claim 1, wherein said method further comprises contacting said gas with an acidic aqueous oxidizing composition.

103. The method of claim 102, wherein the gas is treated with the basic aqueous oxidizing composition and then with the acidic aqueous oxidizing composition.

104. The method of claim 102, wherein the gas is treated with the acidic aqueous oxidizing composition and then with the basic aqueous oxidizing composition.

105. The method of claim 102, wherein said gas is contacted with an acidic aqueous oxidizing composition having a pH of about 2.0 to about 3.0 and comprising at least one cation of a metal chosen from Fe, Cu, Ni, Mn, Ti, Cr, Ce, Zn, Pd, Mo, and mixtures thereof; sequestering agent chosen from ethylenediaminetetraacetic acid (EDTA), oxalic acid, citric acid, glycine, NTA, salicylic acid, sulfosalicylic acid, trithylenetetramine, and mixtures thereof; and H.sub.2O.sub.2 wherein said contacting includes mixing said gas with said acidic oxidizing composition so as to at least partially dissolve at least one compound contained in said gas into said acidic oxidizing composition, said gas and said acidic oxidizing composition being mixed together in a packed column, and wherein said gas is introduced at a bottom portion of said column and said acidic aqueous composition is introduced at a top portion of said column, said gas and said acidic aqueous composition being mixed together into said column over a predetermined amount of transfer units; and submitting said gas and said composition to UV radiation when said gas and said composition are contacting each other.

106. The method of claim 105, wherein the acidic aqueous oxidizing composition comprises Fe.sup.2+, Cu.sup.2+, or a mixture thereof.

107. The method of claim 105, wherein the acidic aqueous oxidizing composition comprises Fe.sup.2+.

108. The method of claim 105, wherein said acidic aqueous oxidizing composition has a pH of about 2.2 to about 2.6.

109. The method of claim 105, wherein said sequestering agent is oxalic acid.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0050] The following drawings represent in a non-limitative manner, various examples:

[0051] FIG. 1 shows a bloc diagram of an example of a method for treating a fluid;

[0052] FIG. 2 shows a bloc diagram of another example of a method for treating a fluid; and

[0053] FIG. 3 shows a bloc diagram of a further example of a method for treating a fluid.

DETAILED DESCRIPTION

[0054] Further features and advantages will become more readily apparent from the following non-limitative examples:

[0055] The following examples are non-limiting examples.

EXAMPLES

[0056] In order to determine the effectiveness of each of the treatments that are part of the examples, dynamic olfactometry measurements have been carried out. The olfactometer is composed of six beakers in which three test specimens are found. Each beaker corresponds to a different dilution level of the odorous gas. In each of these beakers, a single test specimen diffuses odorous air. Each of the individuals that make up the panel must identify, in each beaker, which of the test specimens diffuses the odorous gas. If the individual does not detect any odors, the person passes to the next beaker. The data from the panel are compiled and the results are calculated with the aid of a table by using the air dilution and odorous gas flow rates of each of the test specimens.

Example 1: Treatment by Oxidation and Absorption in Consecutive Basic and Acidic Media

[0057] The gas to be treated contains several organic compounds which, depending on their nature, are more soluble in a basic medium or in an acidic medium. In the present examples, compounds such as butyric acid, valeric acid, sulfides and disulfides were found to be compounds that are more soluble in a basic media and certain amines were found to be more soluble in an acidic media. FIG. 1 is a bloc diagram concerning the method carried out in Example 1.

[0058] The gas was treated by passing it through a packed column in which a basic aqueous oxidizing composition (comprising H.sub.2O.sub.2 and NaOH and having a pH of about 10.0) was flowing. The oxidizing composition contained about 510 mg/L of hydrogen peroxide, about 4 mg/L of Fe and NTA at a concentration of four times higher than the concentration of Fe on a molar basis. The temperature of the medium was about 22° C. The gas flow rate was about 3000 m.sup.3/h. Fe can be provided in various form such as FeSO.sub.4, FeCl.sub.2 or any suitable source of Fe.sup.2+. A reactor was disposed at the bottom of the column, and the oxidizing composition was recirculated from the reactor to a top portion of the column by means of a pump. The fluid was introduced at a bottom portion of the column in a counter-current manner.

[0059] Then, the gas is treated in a second packed column that also comprises an oxidizing composition comprising hydrogen peroxide. The composition flowing in the second column was an acidic aqueous oxidizing composition (H.sub.2SO.sub.4) having a pH of about 2.2. The oxidizing composition contained about 2360 mg/L of hydrogen peroxide, and about 50 mg/L of Fe. The temperature of the medium was about 23° C. The gas flow rate was about 3.6 m.sup.3/h.

[0060] These conditions were maintained for 19 days and five dynamic olfactometry analyses were carried out. The results were the following (average values): [0061] odor level at the inlet: 131; [0062] odor level after 1st treatment: 69; [0063] effectiveness after 1st treatment: 47%; [0064] odor level after 2nd treatment: 36; and [0065] effectiveness after 2nd treatment: 73%.

Example 2: Treatment by Oxidation and Absorption in a Basic Medium and Adsorption onto Activated Carbon

[0066] In the present example, a gas similar to the one treated in example 1 was treated by using a similar set-up. FIG. 2 is a bloc diagram concerning the method carried out in Example 2.

[0067] The gas was treated by passing it through a packed column in which a basic aqueous oxidizing composition (comprising H.sub.2O.sub.2 and NaOH and having a pH of about 9.8) was flowing. The oxidizing composition contained about 75 mg/L of hydrogen peroxide, about 2 mg/L of Fe and NTA at a concentration of four times higher than the concentration of Fe on a molar basis. The temperature of the medium was about 21° C. The gas flow rate was about 2040 m.sup.3/h.

[0068] Subsequently, the gas was treated by passing it through a bed of activated carbon. The temperature of the gas was about 24° C. at a gas flow rate of about 3 m.sup.3/h. The height of the activated carbon was about 180 mm.

[0069] These operating conditions were maintained for 5 days and 8 olfactometry measurements were taken. The results are the following: [0070] odor level at the inlet: 155; [0071] odor level after 1st treatment: 70; [0072] effectiveness after 1st treatment: 55%; [0073] odor level after 2nd treatment: 5; and [0074] effectiveness after 2nd treatment: 97%.

Example 3: Treatment by Oxidation and Absorption in a Basic Media and then, in an Acidic Media in which Oxidation is Enhanced by UV Radiation

[0075] In the present example, a gas similar to the one in example 1 was treated by using a similar set-up. FIG. 3 is a bloc diagram concerning the method carried out in example 3.

[0076] The gas was treated by passing it through a packed column in which a basic aqueous oxidizing composition (comprising H.sub.2O.sub.2 and NaOH and having a pH of about 9.8) was flowing. The oxidizing composition contained about 300 mg/L of hydrogen peroxide, about 2 mg/L of Fe and NTA at a concentration of four times higher than the concentration of Fe on a molar basis. The temperature of the medium was about 22° C. The gas was at a temperature of about 50° C. and a flow of 80 L/min.

[0077] Then, the gas was treated in a second packed column that also contained an oxidizing composition comprising hydrogen peroxide. The composition flowing in the second column was an acidic aqueous oxidizing composition (HNO.sub.3) having a pH of about 2.4. The oxidizing composition contained about 350 mg/L of hydrogen peroxide, about 30 mg/L of Fe and oxalic acid at was concentration of four times higher than the concentration of Fe on a molar basis. The temperature of the medium was about 22° C. The gas flow was about 80 L/min.

[0078] As explained in example 1, the mixture of the gas and the composition was flowing down from the packed column to a reactor. In Example 3, the mixture of the fluid and the composition in the reactor were submitted to UV radiation in order to enhance the oxidation rate of the organic compounds that cause the unpleasant and/or undesirable odor. The UV radiation was produced by a 254 nm lamp at a power of 9 Watts. After a predetermined residence time in the reactor, the mixture is recirculated to the top of the packed column to complete the loop.

[0079] These operating conditions were repeated over more than 30 tests. Each test was carried out over a period of time of about 8 to about 12 hours. The same amount of olfactometry measurements were taken. The results were the following: [0080] odor level at the inlet: 386 [0081] odor level after 1.sup.st treatment: 127 [0082] effectiveness after 1.sup.st treatment: 66% [0083] odor level after 2.sup.nd treatment: 50 [0084] effectiveness after 2.sup.nd treatment: 86%

[0085] It can thus be seen that the results presented in examples 1 to 3 clearly show that these three different methods permit to considerably reduce the intensity (or odor level) of the undesirable odor. It can thus be the that such methods permit to efficiently at least partially reduce the intensity or an undesirable or unpleasant odor.

[0086] The methods have been described with regard to specific examples. The description as much as the drawings were intended to help the understanding of the document, rather than to limit its scope. It will be apparent to one skilled in the art that various modifications may be made to the methods previously defined without departing from the scope of the document as described herein, and such modifications are intended to be covered by the present document.