FR2485086A1 - PROCESS FOR REMOVING LEAD FROM EXHAUST GASES OF CONTROLLED IGNITION ENGINES AND FILTERS FOR ITS IMPLEMENTATION - Google Patents

Abstract

THE PRESENT INVENTION CONCERNS A PROCESS FOR REMOVING LEAD FROM THE EXHAUST GASES OF CONTROLLED IGNITION ENGINES, AND FILTERS FOR ITS IMPLEMENTATION. THE PROCESS ACCORDING TO THE PRESENT INVENTION IS CHARACTERIZED IN THAT VERY HOT EXHAUST GAS IS CONDUCTED THROUGH A MACROPOREOUS CERAMIC FILTER WITH A PORE SIZE OF 2 TO 800 MICROMETERS AND A WALL SIZE OF 0.15 TO 0.64MM .

Description

Legal requirements to limit exhaust emissions

  motor vehicles can often only be observed by a subsequent treatment of the exhaust gas. This subsequent treatment generally consists of a catalytic treatment with

  harmful products such as hydrocarbons

  burned, nitrous oxides and carbon monoxide are

  transformed into harmless compounds.

  When using leaded gasoline, the catalysts are relatively quickly poisoned by the lead in the exhaust, so that the life of the catalysts is extremely low.

  limited. There was no shortage of attempts to eliminate

  lead the exhaust gas before contact with the catalyst. It is already known to filter out lead by means of an electrostatic filter (German patent application No. 21 39 775), by separation by means of centrifugal force (cyclone effect, German Provisional Patent No. 24 09 952 ), by passing through a fiberglass paper filter (German Patent Application No. 22 52 121) or

  through steel wool or asbestos wool. Linen-

  The disadvantage of this process, however, is that either because of the small size required for the vehicles the degree of separation is not sufficient, that the service life of the filter materials, for example asbestos wool, is not sufficient. , or that filters can only be used at exhaust gas temperatures

  so low that this temperature of the exhaust gases

  is too weak for a quick

catalytic post-treatment.

  The object of the invention was therefore to find a method with which it is possible to achieve as complete a removal as possible of the lead, even from very hot exhaust gases, as well as a filter intended

to its implementation.

  This problem is solved according to the invention by a method characterized in that the exhaust gas is

  very hot through a macro ceramic filter

  porous with a pore size of 2 to 800 micrometers

  and a wall size of 0.15 to 0.64 mm.

  It turned out that when using a filter

  porous ceramic there is virtually no

  catalysts intercalated afterwards by lead or lead compounds, or by other poisons catalysts such as compounds

  sulfur or phosphorus over a long period.

  After a continuous run for 100 hours on the test bench, a catalyst on which a lead filter according to the invention has been mounted still has a degree of conversion of 80 to 90% for the pollutants, whereas with a catalyst without lead filter previously

  inserted, it only has a conversion rate of 40 to 50%.

  As materials for the filter, mention should be made of ceramic materials such as sillimanite, cordierite, silica, corundum, forsterite, zirconium arsenate, magnesia, titanium dioxide, etc., of which cordierite is preferred , which can also be used as supports for

  catalysts because of their high temperature resistance

  temperature. The thickness of the wall of the filter should not be less than 0.15 mm, since below this wall thickness the mechanical strength is too low, so that slots may appear in the filter at the same time. following changes in temperature and pressure. When a wall thickness of 0.64 mm is exceeded, there is no longer any essential improvement in the efficiency of the filter, it merely increases the pressure drop produced by the filter. Wall thicknesses of 0.30 to 0.45 mm are preferred since they provide good filtering efficiency at a

low pressure drop.

  The pore size of the filter must be

  between 2 and 800 micrometers. When the pore size is less than 2 microns, the pressure drop is too large, and when exceeding a pore size of 800 micrometers, the degree of separation of the lead is too low. A pore size of from 5 to 600 micrometers is preferred because a particularly favorable compromise is achieved between size, degree of separation, stability, mechanical strength and pressure drop. With a gas flow rate of 10 m3 / min.

  pressure drop should not exceed 0.2 bar.

  When the thickness of the wall of the filter is small it may be necessary to support the filter backwards by a support structure, for example metallic. It is however more interesting to build the filter with a structure having the necessary stability,

  for example a honeycomb structure (honeycomb).

  To prevent a lot of pressure buildup before the filter it is convenient to keep the filter surface as large as possible. The introduction of a large filter area on a small volume is carried out according to the known methods as folds of the filter surface, the presentation of the filter under

  form of set of filter discs or cellular structure

  different cavities of the cellular structure, etc.

  are alternately blocked on one side and the other

  be. The filters are manufactured according to the processes well known for ceramics. Pleated filters or honeycomb filters can be made from, for example,

  that can be manufactured for example according to the patent

  German visor n0 22 01 477 (fiber veil)

ceramic).

  With the process according to the invention

  achieve a very high degree of efficiency in eliminating

  lead and it is also possible to filter even very hot exhaust gases at temperatures (depending on the filter material) up to 1400 ° C. It thus becomes possible to dispose the filter immediately behind the engine and, given the high temperature of the gas, to operate the catalyst disposed subsequently in an optimum temperature range. Given the very good separation of the lead, it is also possible to provide the filter directly on the gas outlet side of a catalytically active coating, so that the lead filter and the catalyst are combined into

one body.

Claims (7)

  A method for removing lead from the exhaust gases of spark ignition engines by means of filtration, characterized in that the very hot exhaust gas is passed through a macroporous ceramic filter with a size of pores from 2 to 800 micrometers and one size wall thickness from 0.15 to 0.64 mm.   2. Method according to claim 1, characterized   in that the ceramic is cordierite.   3. Method according to claims 1 or 2,   characterized in that the ceramic has a pore size of 5 to 600 micrometers and a wall thickness of 0.30 mm to 0.45 mm.   4. Process according to one or more of the claims   cations 1 to 3, characterized in that the filter is pleated to increase its surface.   5. Filter intended for the implementation of   Method according to one of Claims 1 to 4, characterized   in that the filter is made of macroporous ceramic having a pore size of 2 to 800 μm, preferably 5 to 600 μm, and a wall size of 0.15 to 0.64 μm, preferably from 0.30 to 0.45.   6. Filter according to claim 5, characterized   in that said ceramic is cordierite.   7. Filter according to one of claims 5 and   6, characterized in that it is pleated to increase its surface.