Piezoelectric probe for detection and measurement of gaseous pollutants

• US 4,111,036 A
• Filed: 07/29/1974
• Issued: 09/05/1978
• Est. Priority Date: 07/29/1974
• Status: Expired due to Term

• Current Assignee: The Board of Regents for Education for the State of Rhode Island
• Original Assignee: The Board of Regents for Education for the State of Rhode Island
• Inventors: Fasching, James L., Frechette, Michael W.
• Primary Examiner(s): Kreitman, Stephen A.
• Application Number:
  US05/492,737
• Time in Patent Office: 1,499 Days
• Field of Search: 73/23, 23/232 R, 23/232 E, 23/254 R, 23/254 E, 310/8, 310/8.1, 310/8.9
• US Class Current: 73/24.06
• CPC Class Codes: G01N 2291/0256 Adsorption, desorption, surface mass change, e.g. on biosensors
• CPC Class Codes: G01N 29/036 by measuring frequency or resonance of acoustic waves
• CPC Class Codes: G01N 33/0042 for SO2, SO3

Abstract

A new static system for the detection and measurement of gaseous air pollnts such as sulfur dioxide using a coated piezoelectric crystal is disclosed. The system is rugged, portable and inexpensive. It is readily adapted for automatic, periodic, multiple-component monitoring of an industrial exhaust stream. Also disclosed are materials especially suitable for coating the piezoelectric crystals of the present invention.

Claims

1. An apparatus for the static detection and measurement of a sulfur dioxide component of a mixed gas stream flowing in a conduit comprising in combination:

a. for each fluid component to be measured, a single vibrateable piezoelectric material mounted on a readily-transportable support base for contacting said piezoelectric material with said gas;

substrate means coated on said piezoelectric material capable of sorbing said fluid component of said gas stream to thereby change the weight of said coated piezoelectric material, said substrate means comprising a polyamine; and

, electronic oscillator means operatively connected to said coated piezoelectric material for oscillating said material;

b. means for withdrawing a portion of said gas stream from said conduit and for bringing said portion into a test chamber;

c. valve means for sealing said test chamber so as to bring said withdrawn portion of the gas stream into contact with said coated piezoelectric material under substantially static conditions; and

,

d. means for determining when the change in vibrational frequency of said coated piezoelectric material is substantially complete, said determining means comprising counter-timer means operatively connected to said coated piezoelectric material, and a digital converter and a recorder operatively connected to said counter-timer means.

2. A process for periodically monitoring a mixed gas stream flowing in a conduit to detect and measure a sulfur dioxide component thereof comprising the following steps:

a. coating a single vibrateable piezoelectric material with a substrate capable of sorbing said sulfur dioxide component of said gas stream, said substrate comprising a polyamine;

mounting said coated piezoelectric material on a readily-transportable support base;

operatively connecting said coated piezoelectric material to electronic oscillator means for oscillating said material;

b. withdrawing a portion of said gas stream from said conduit and passing it into a test chamber;

c. sealing said test chamber by valve means so as to bring said portion of said gas stream into contact with said coated piezoelectric material under substantially static conditions; and

,

d. recording the frequency response of said coated piezoelectric material until the change in vibrational frequency is substantially complete.

3. In an analyzer comprising in combination a detection device having a piezoelectric element bearing a substrate which interacts with one component of a fluid being analyzed, oscillating circuit means for oscillating said detection device, and measuring means for recording the frequency of oscillation of said detection device, the improvement which comprises employing a substrate selected from the group consisting of 1:

1 copolymers of styrene and N,N-dimethylaminopropyl maleimide having the general formula ##STR5## and copolymers of 2-vinyl and 2-methyl, 5-vinyl pyridines having the general formula ##STR6## wherein R₁ is a methyl or vinyl group and R₂ is hydrogen or a vinyl group.

4. In an analyzer comprising in combination a plurality of detection devices each having a piezoelectric element bearing a substrate which interacts with one component of a fluid being analyzed, oscillating circuit means for oscillating said detection devices, and measuring means for recording the frequency of oscillation of said detection devices, the improvement which comprises employing a substrate selected from the group consisting of 1:

1 copolymers of styrene and N,N-dimethylaminopropyl malemide having the general formula ##STR7## and copolymers of 2-vinyl and 2-methyl, 5-vinyl pyridines having the general formula ##STR8## wherein R₁ is a methyl or vinyl group and R₂ is hydrogen or a vinyl group.

5. An apparatus for the static detection and measurement of a sulfur dioxide component of a mixed gas stream comprising in combination:

a. a vibrateable piezoelectric material mounted on a readily-transportable support base for contacting said piezoelectric material with said gas;

b. substrate means coated on said piezoelectric material capable of sorbing at least one of said fluid components of said gas stream to thereby change the weight of said coated piezoelectric material, wherein said substrate is a polyamine selected from the group consisting of 1;

1 copolymers of stryene and N,N-dimethylaminopropyl maleimide having the general formula ##STR9## and copolymers of 2-vinyl and 2-methyl, 5-vinyl pyridines having the general formula ##STR10## wherein R₁ is a methyl or vinyl group and R₂ is hydrogen or a vinyl group; and

,

c. electronic oscillator means operatively connected to said coated piezoelectric material for oscillating said material.

6. A process for the static detection and measurement of a sulfur dioxide component of a mixed gas stream comprising the following steps:

a. coating a vibrateable piezoelectric material with a polyamine substrate selected from the group consisting of 1;

1 copolymers of styrene and N,N-dimethylaminopropyl maleimide having the general formula ##STR11## and copolymers of 2-vinyl and 2-methyl, 5-vinyl pyridines having the general formula ##STR12## wherein R₁ is a methyl or vinyl group and R₂ is hydrogen or a vinyl group;

b. mounting said coated piezoelectric material on a readily-transportable support base and operatively connecting said coated piezoelectric material to electronic oscillator means for oscillating said material;

c. withdrawing a portion of said gas stream from said conduit and passing it into a test chamber;

d. sealing said test chamber by valve means so as to bring said portion of said gas stream into contact with said coated piezoelectric material under substantially static conditions; and

,

e. recording the frequency response of said coated piezoelectric material until the change in vibrational frequency is substantially complete.

7. The process of claim 6 wherein the concentration of sulfur dioxide is said gas stream is on the order of 1000 ppm. or less and said polyamine comprises substantially all of said substrate.

8. The process of claim 6 wherein the concentration of sulfur dioxide in said gas stream is greater than about 1000 ppm. and said substrate comprises polyamine dispersed as a solid solution in an inert matrix.

9. The process of claim 8 wherein said polyamine is dispersed in Carbowax 6000 in an amount of about 1-50 wt.-%.