JPH0134281B2 - - Google Patents

Description

Claim 1: Maintaining in the interior space of the muffler an adsorbent material comprising a mixture of a crystalline zeolite aluminosilicate having a chabazite crystal structure and a zeolite aluminosilicate having a haujasite crystal structure; A method for suppressing corrosion of metal parts of an internal combustion engine and a muffler used in communication with an internal combustion engine that comes into contact with gas entering the muffler from the surrounding atmosphere.

2. The zeolite aluminosilicate having a chabazite crystal structure is the mineral chiabazite, and the zeolite aluminosilicate having a haujasite crystal structure is a type-Y zeolite having a _SiO2 / _Al2O3 molar ratio of about 4 to about ₂₀ . A method according to claim 1.

3 Apply zeolite adsorbent to the muffler interior space.
^3. The method of claim 2, wherein the method is used in an amount of about 2 to about 100 grams per 1000 in 3 (16387 cm ³ ).

4. The method of claim 2, wherein the zeolite aluminosilicate having a chabazite crystal structure is present in an amount from 1/3 to 3 times the amount of the zeolite aluminosilicate having a haujasite crystal structure on an anhydrous weight basis.

5. At least about 50% of the A10 ₄ -framed tetrahedra of the Type-Y zeolite are associated with sodium cations, and at least about 50% of the A10 ₄ -framed tetrahedra of the mineral chiabazite are associated with sodium cations or calcium cations or 3. A method according to claim 2, wherein the components are combined in a mixture.

6. Claim 4 wherein the zeolite aluminosilicate constitutes at least 70% of the total adsorbent material on a dry weight basis, with the remainder consisting essentially of an inorganic binder.
The method described in section.

7. a metal casing having an exhaust gas inlet and an outlet and adapted for the exhaust gas to flow therethrough;
an adsorbent material comprising a mixture of a crystalline aluminosilicate having a chabazite crystal structure and a zeolitic aluminosilicate having a haujasite crystal structure, the adsorbent material being in contact with gases entering the casing from an internal combustion engine and the ambient atmosphere. Exhaust muffler for internal combustion engines.

8. The zeolite aluminosilicate having a chabazite crystal structure is the mineral chiabazite, and the zeolite aluminosilicate having a haujasite crystal structure is a type-Y zeolite having a _SiO2 / _Al2O3 molar ratio of about 4 to about ₂₀ . A muffler device according to claim 7.

9 Zeolite adsorbent fills the muffler interior space
9. The muffler device of claim 8, wherein the muffler device is present in an amount of about 2 to about 50 grams per 1000 ^{in 3} (16387 cm ³ ).

10. The muffler device according to claim 8, wherein the zeolite aluminosilicate having a chabazite crystal structure is present in an amount of 1/3 to 3 times the amount of the zeolite aluminosilicate having a haujasite crystal structure on an anhydrous weight basis. .

11 At least about 50% of the A10 ₄ -framed tetrahedra of the Type-Y zeolite are associated with sodium cations, and at least about 50% of the A10 ₄ -framed tetrahedra of the mineral chiabazite are associated with sodium cations or calcium cations or 9. The muffler device of claim 8, wherein the muffler device is assembled in a mixture.

12. The muffler device of claim 10, wherein the zeolite aluminosilicate constitutes at least 70% of the total adsorbent on an anhydrous basis, with the remainder consisting essentially of an inorganic binder.

DETAILED DESCRIPTION The present invention relates generally to adsorbent compositions, and more particularly to mixtures of crystalline zeolite molecular sieves that exhibit synergistic effects in their ability to keep the interior space of an automobile muffler free of condensed water vapor. Regarding. The invention further relates to mufflers containing such adsorbent compositions and to the use of such materials to inhibit corrosion of interior exposed metal surfaces of mufflers used in conjunction with internal combustion engines.

Corrosion and resulting muffler failure is primarily due to two corrosion mechanisms. Stress corrosion is caused by vibration, applied stress, and chemical action without metal loss. Failure is typified by cracks initiated by pitting. Cracking can occur near non-stress relief welds, and corrosion fatigue can occur under dynamic or fluctuating stresses in a corrosive environment. Chemical or general corrosion is caused by fairly uniform thinning and metal loss without localized effects such as pitting or cracking. The corrosivity of the environment is determined by temperature, pressure,
The rate and/or composition can be reduced or changed to reduce. In conventional automobile systems, the degree of freedom to significantly change these parameters is not very large, since the optimal performance of the internal combustion engine involved is more important than the life of the muffler system.

Traditionally, natural or synthetic alkali or alkaline earth metal aluminosilicates have been shown to be effective in sorbing unburned hydrocarbons, such as in U.S. Pat. No. 3,067,002 (Reid, Jr.). It has been proposed to use adsorbents such as crystalline zeolites in automobile exhaust systems. While warming up the engine, hydrocarbons are first adsorbed and then desorbed when the exhaust gas temperature and catalyst become hot enough to burn these hydrocarbons. In order for the adsorbent to be effective in adsorbing hydrocarbons, the presence of moisture must be avoided when using hydrophilic zeolites. Non-flammable hydrophobic (organophilic) adsorbents are preferred products in the laid process. Krebs et al. (U.S. patent
No. 3,618,314) defines a NaX molecular sieve that incorporates an adsorbent into a chamber or bathtub and is effective for filtering out carbonaceous particulate matter.

In addition, the adsorbent properties of crystalline zeolites and activated alumina can be utilized in an essentially non-catalytic manner to modify the chemical composition of the corrosive environment periodically contained within the muffler section of the exhaust system, thus reducing corrosion. It has also been proposed that the service life of the metal parts of the muffler that are in direct contact with substances can be greatly increased. Such a proposal is found in U.S. Pat. No. 4,402,714, which discloses that an adsorbent material (mass), preferably a crystalline zeolite molecular sieve, is placed in a sufficient amount within the interior space of the muffler. A process is described which consists in preventing water vapor from the engine exhaust gases from condensing on the walls of the muffler after the engine has been shut down. This procedure considerably inhibits corrosion of metal parts. The patent further describes suitable zeolite adsorbent materials having a pore size of at least 3.2 angstroms, a surface area of at least 350 m ² /gm, a SiO ₂ /Al ₂ O ₃ molar ratio of 4 to 20;
The water adsorption capacity at 100°C and a water vapor pressure of 80 mmHg is at least 4% based on the dry weight of the zeolite.
The weight percentage is stated. Details of zeolites within this class include naturally occurring and synthetic zeolites such as mordenite, chiabazite, erionite, clinoptilolite,
Zeolite Y, Zeolite Omega, ZSM-5,
ZSM-11, ZSM-12, zeolite beta,
Includes zeolite T and zeolite L. Activated alumina is also said to produce similar results.

Accordingly, it is a general object of the present invention to provide improved adsorbent compositions that inhibit corrosion of internal metal surfaces of mufflers, and to provide improved corrosion resistance using such improved adsorbent compositions. The purpose of this project is to improve the muffler device.

These and other objects and advantages will become more apparent from the following detailed description and drawings. In the drawings, FIG. 1 is a plan view of a typical muffler containing a zeolite adsorbent composition according to one embodiment of the present invention, with the outer jacket partially cut away; FIG. 2 is a top view of the muffler of FIG. 1; FIG. 2 is a side front view with the outer cover partially cut away and taken along line 2--2 in FIG. 1;

FIG. 3 is an enlarged partial plan view of one of the insert adsorbent storage tubes, and FIG. 4 is a side elevational view of one of the insert tubes of FIG. 3, with the jacket partially cut away.

With particular reference to FIG. 1 of the drawings, one embodiment of the muffler apparatus of the present invention is shown generally at 10. The muffler 10 includes an oval metal casing 12 having end walls 14 and 15 and internal baffles or bulkheads 16, 17.
18, 19 and 20, and the partition wall connects the muffler internal space to chambers 21, 22, 23, 24,
Divide into 25 and 26 parts. three perforated tubes 28,2
9, 30 are carried within the partitions 18 and 19. The inlet tube 32 is carried by the partition walls 16, 17 and the end wall 14 and opens into the perforated tube 28. The outlet pipe 34 is connected to the partition wall 20
and is carried by the end wall 15 and communicates with the perforated tube 29 and extends therefrom out of the casing. The septum 20 has an opening 36 in line with the perforated tube 28 to interconnect the chambers 21 and 22, and the septum 17 and 16 have openings 38 and 40, respectively, in line with the perforated tube 30. chamber 24
and 25 and 26 are made to communicate with each other. Inlet pipe 3
The engine exhaust gases entering 2 are passed through perforated pipe 28 and the gas flow is divided and subdivided by the perforated pipe and chamber system, so that different parts of the gas flow are routed at different distances within the muffler. After being moved, it exits through the outlet pipe 34. Each of the chambers 21, 22, 23, 24, 25 and 26 receives an adsorbent containing cup 42 attached to the casing wall, which cup 42 is shown in more detail in FIGS.

With reference to FIG. 4, the adsorbent containing cup 42 comprises a cylindrical metal mesh side wall 44 sealed to a metal disk 45, the latter of which is attached to the casing wall by any conventional means such as spot welding, riveting, etc. It plays the role of attaching to. The adsorbent particles 46 are retained within the cup 42 by a coated metal mesh 47 which allows for easy contact of the adsorbent particles with the gas within the muffler.

The improved adsorbent composition provided in accordance with the present invention includes a combination of a crystalline zeolite having a chabazite crystal structure and a crystalline zeolite having a haujasite crystal structure. This zeolite combination exhibits an unexpected synergistic effect in reducing the amount of muffler corrosion when used in the muffler described above to practice the method of the present invention.

The mineral chiabazite (also traditionally called Acadialite, Haydenite, Phacolite and Glottalite) is a widely occurring zeolite found in Ireland, Nova Scotia, Colorado, United States, among others, and ₂
[It has a typical unit cell fraction of (AlO ₂ ) ₄ (SiO ₂ ) ₈ ·13H ₂ O. It is the chabazite type zeolite suitable for use in the present invention. Composites of chabazite type structure are also known, especially zeolite D, the synthesis and structure of which are described in detail in British Patent No. 868,846 (1961).

Phujasite type crystalline zeolites are mainly known synthetic zeolite X and zeolite Y.
represented by. Currently, no significant deposits of the mineral horsiasite are known to exist. Zeolite X has a maximum molar ratio of SiO ₂ /Al ₂ O ₃ of 3 and therefore does not have very high resistance to structural collapse due to acid attack. Zeolite Y and its countless modified forms are larger than 3 and up to several hundred.
It can have a molar ratio of SiO ₂ /Al ₂ O ₃ . In the present invention, preference is given to using zeolite Y with a _SiO2 / _Al2O3 molar ratio of 4 _to 20.

A synergistic effect of the combination of a zeolite of the chabazite type and a zeolite of the haujasite type has been demonstrated in all proportions in mixtures of the two, but one of the zeolite types is less active than the other on a dry weight basis. This is more noticeable when the amount is 1/3 to 3 times the amount of As used herein, the dry weight of a zeolite component is optionally defined as the weight after calcining the zeolite in vacuo at 300° C. for 3 hours. More preferably, the combined zeolites of the chabazite and haujasite types constitute at least about 70% by weight of the total adsorbent-containing material inserted into the inner cavity of the muffler. The remaining 30% by weight of the material can include any of several known zeolite binders such as clay, alumina or silica.
Granules, extrudates, beads or other monolithic forms of adsorbent material are preferred over powders because high local gas flow rates through the muffler can fluidize the particles and carry them out of the exhaust system.

Of the various cationic forms in which the present zeolitic materials may exist, in Hojiasite-type zeolites, at least about 50% of the AlO ₄ framework tetrahedra are associated with sodium cations, and in the AlO Preferably, at least about 50% of the ₄ -tetrahedrons are associated with sodium cations or calcium cations or a combination of these two cationic species. (for example,
Donald D'Avrille on April 21, 1964. US Pat. No. 3,130,007 issued to Bretzk et al.; published by John Willey and Sons, Donald D. "Zeolite Molecular Sieve" by Bretzk, 107~
(See page 109).

Although it is preferred to combine both types of zeolites used in the present invention into the same adsorbent material,
It will be obvious to even those of ordinary skill in the art that many different arrangements are possible that achieve the desired results and are within the true scope of the invention.
For example, crystals of both zeolite types can be housed more uniformly or less uniformly within the same combined particles, and a large number of such particles can be combined or coagulated into a total absorbent material. can. Alternatively, the crystals of each zeolite species may be separately formed into particles with or without added binder, and the particles are then blended and optionally agglomerated to form one or more larger entities. Make it.
Additionally, aggregates of crystals of one zeolite species can be mixed with microcrystals (powders) of other species to form one or more larger adsorbent materials. A number of isolated adsorbent materials can be placed at various locations within the muffler. When placed in an automobile muffler, the sorbent material is regenerated in-situ by changing conditions, thereby achieving a differential working capacity for water of the material. Regeneration (desorption) occurs as the engine is operated and the exhaust gas temperature rises rapidly, while the temperature rise of the metal exhaust system is slow due to thermal sink. Hence, the preferred location for the regeneration of the adsorbent material is near and not far from the hot exhaust gas where the adsorbent material behaves as a heat absorber. The water content of the exhaust gas is high (10% by volume)
However, the relative saturation of this gas at 600 DEG -800 DEG C. (316 DEG -427 DEG C.) is low and the adsorbent material has a low equilibrium water load; therefore desorption must occur. The desorbed water is carried away from the exhaust system by the subsequent exhaust gas. Adsorption occurs when the engine is shut down and the flow of exhaust gases ceases, and the entire exhaust system begins to cool down to ambient temperature. As the exhaust gas cools, the relative saturation of the gas for constant water content (dew point) increases and the adsorbent material has a higher equilibrium load. This poses unique requirements for the sorbent material, since the sorbent material can be considered an insulator compared to the metal wall of the muffler. The adsorbent material must adsorb water vapor before the metal cools to below the dew point of the exhaust gas. Therefore, the amount of adsorbent required is always that amount that prevents water from condensing within the muffler chamber.
This is 2 to ^1000in3 ( ^16387cm3 ) muffler volume.
Represents total zeolite requirement quantity of 13 grams. It goes without saying that additional adsorbent is required to compensate for aging and the resulting decline in the adsorption properties of the adsorbent. Thus, the zeolite adsorbent is used in ^an amount of, for example, from about 2 to about 100 grams, preferably from about 2 to about 50 grams per 1000 inches of muffler volume.

The manner in which the adsorbent is placed within the interior space of the muffler is not a critical factor to the invention. It is self-evident that it is important that all of the internal space is in good communication with the adsorbent and that the adsorbent remains within the muffler despite its tendency to be released by the force of the exhaust gas passing through the muffler. . A muffler usually consists of a single jacket housing several internal chambers with interconnecting pipes. The chamber is created by an internal metal bulkhead that positions and supports the internal piping network. Since the flow of exhaust gas throughout the entire chamber is not necessarily constant or even continuous, it cannot be assumed that the exhaust gas is well mixed within the muffler. Therefore, it is preferred to distribute the adsorbent between all internal chambers of the muffler.

Independent storage devices such as tubes, pillows, bags, buckets, etc. can be fabricated from thermally stable permeable materials, each device containing a small amount (1-50 grams) of adsorbent. These devices can then be placed into each chamber during the manufacturing process. These devices may be free to move or fixed in place by clips, spot welds, or explosive rivets without requiring significant changes to existing manufacturing procedures. Adsorbent improvements can also be made to the muffler assembly by inserting these devices into at least two chambers via the exhaust and tailpipe connections.

Integral storage devices may also be used, but may require changes to existing designs and manufacturing procedures. These devices may consist of means for fixing the adsorbent within a porous metal box between a screen and a partition or in an expanded metal component. Also, the adsorbent can be sandwiched between an inner shell and an outer shell, the shells forming an outer jacket and the inner shell having perforations to allow gas to contact the adsorbent.

Coating of the tubes, septa and/or internal surfaces with adsorbents may also be carried out. A simulated coating can be carried out by adsorbent-filled materials or heat-resistant tapes. The surface can also be applied using an actual slip coating made from a silica-rich slurry of adsorbent powder. Any surface can be dipped, sprayed, or otherwise coated with such a slurry. The coating is cured during manufacture or on the vehicle by heating a portion to approximately 200°C.

The invention and the improvements it provides are illustrated by the following examples: Example 1 Fifty-four passenger cars were fitted with new mufflers.
A trapdoor was installed at the bottom of each muffler to allow access to the internal chamber. Each muffler, except the control, contained 50 grams of sorbent in a fine wire mesh bag. In addition, all mufflers are made from the same stock of metal used to manufacture the same muffler.
It contained six corrosion test coupons fabricated from. Three coupons were installed in the central core area near the multi-way gas pipe. The corrosion rate measured here will hereinafter be referred to as the "B" position corrosion rate. remaining 3
Coupons were attached to the inner wall of the lower envelope where all condensate was expected to collect. The corrosion rate measured here is hereinafter referred to as the "A" position corrosion rate. Corrosion coupons were removed from each location at three intervals during the entire test period, which lasted slightly less than one year. The collected coupons were cleaned, pretreated and weighed by a systematic procedure. Weight loss due to metal thinning caused by corrosion was determined by subtracting the weight of the coupon from its original weight, which was recorded before the metal was placed in the corrosive environment of the muffler. The corrosion rate is calculated by dividing the weight loss by the number of days the coupon was in the muffler, and then calculating this rate by dividing the weight loss by the number of days the coupon was in the muffler.
It is expressed in terms of the decrease in thickness per year.
Not all sorbent materials were tested in the same number of vehicles and some coupons were lost during testing. In addition, using a variety of manufacturers and formats,
Each had its own unique driving history. All cars were originally equipped with contact converters whose activity and/or performance was variable and unknown. All engines in the test vehicles had either 4 or 6 cylinders and were primarily short range (<50 miles/min).
It was used as a passenger for suburban commuters (80km/day). Vehicles in the latter category appeared to produce the highest corrosion rates. Conventional statistical analysis was applied to the raw data, taking into account that the composition of the exhaust gases passing through the muffler may vary uncontrollably due to the different engines and catalytic converters of the test vehicles, as mentioned above. . In practice, each structural variable of the composition of the exhaust gas passing through the muffler is uncontrollable. On the other hand, the age of the engine, the number of cylinders, the type of intake and exhaust valves that are part of each cylinder, the shape of the catalytic converter, and the age and type of catalyst in each converter are all variables that can be controlled. It is. All of the corrosion rate data was analyzed both by adsorbent material treatment type and as a combined collection of data. An ensemble regression analysis was performed on the uncontrolled variables mentioned above. This is due to either treatment type having a lower or higher corrosion rate depending on the type of vehicle, age of the vehicle, total vehicle miles, drive test miles, cylinder, muffler internal volume. This was done to determine whether there was any inadvertent bias.
A small but significant correlation was found for the age of the vehicle and for the total number of miles on the vehicle, which is a somewhat redundant variable. Thus, each corrosion data point has a defined regression fit to the data.
The vehicle age (a variable that is taken into account along with other variables such as number of engine cylinders and average mileage) was adjusted using a regcession fit. Therefore, only adjusted and unbiased data are shown in the table below: [Table] Corrosion rates in the above table are expressed as relative averages. Namely, treatment type 1, zeolite type NaY
The average corrosion rate observed for 39 measurements in the control case was 60% of the average corrosion rate observed for 78 measurements in the control case. The confidence level associated with the relative reduction in corrosion rate relative to the control (type n vs. 4) is referred to as the "t-statistic" and the associated probability that the hypothesis is incorrect. For processing type 1,
There is only a 6.6% chance that measurements for NaY and treatment type 4 will come from the same population. In other words, the confidence level associated with the resulting relative average corrosion rate is 93.4%. If we consider only directional improvements, then the one-sided or one-sided probability is 96.7%
The confidence level will be (1-0.5×P>|t|). In the table of corrosion rates, data processing types 1 and 2 were combined in a mixture of about 50% by weight of each zeolite type and the appropriate amount of binder. Treatment types 1, 2, and 3 all showed significant corrosion rate reductions relative to the control, but treatment type 3 gave the lowest overall corrosion rate. It is not obvious or expected after analyzing the final results that combining processing types 1 and 2 would lead to any improvement. In fact, one would expect the combination to reduce the effectiveness (directionally toward Type 2) of good processing (Type 1). Since all tests were conducted in parallel, there was no way to anticipate this unexpected interaction. The confidence of the difference between the relative average corrosion rates between the individual treatments, Type 1 and Type 2 vs. 3 (Type n vs. 3) is also listed in the table. Because the means are closer to each other, it reduces confidence in the conclusion. From this, only 40% and 63.5% believe that processing types 1 and 2 are different from type 3, respectively.
%. If we consider Type 3 to be simply an improvement, then we would be 70% and 82.5% sure that it is an improvement (on one side). Even though treatment types 1 and 3 are essentially the same, treatment type 2 is worse and therefore
There is reasonable confidence that no directional improvements are expected.

An additional advantage is that bonded chiabazite has excellent physical integrity and is therefore resistant to the thermal and physical abuse experienced within the muffler under normal vehicle driving conditions. . Blends of cheaper mineral species with more expensive synthetic species (Y-type zeolites) are also economically attractive.