Method for removing particulate matter from an aqueous stream

Abstract

A method for removing particulate matter from an aqueous stream containing concentrated acid, preferably concentrated sulfuric acid, comprising mechanical filtration of the aqueous stream by passing the aqueous stream through a filter unit, the filter unit comprising a metallic, ceramic or polymeric filter, or a filter containing a filter aid on a diaphragm, wherein the aqueous stream is the outlet stream of a sulfuric acid condenser, optionally the outlet stream of a sulfuric acid concentrator located downstream of the sulfuric acid condenser.

Description

[Technical Field]

[0001] For the removal of particulate matter from an aqueous stream containing concentrated acid, particularly concentrated sulfuric acid (H2SO4) containing at least 60% by weight, e.g., at least 85% by weight, H2SO4, the particulate matter having an average particle size ranging from 0.05 to 10 μm, e.g., 0.1 to 5 μm. The particulate matter is removed using mechanical filtration by passing the aqueous stream through a filter unit comprising a metallic, ceramic, or polymeric filter or a filter containing a filter aid on a diaphragm. The diaphragm is preferably made of a polymeric, ceramic, or steel material. An embodiment of the invention includes the metallic filter or the filter aid on a diaphragm having a filter media grade ranging from 0.1 to 14 μm, preferably 0.5 to 12 μm. The concentrated sulfuric acid stream is produced in a plant for the treatment of a process gas stream containing sulfur, particularly sulfur in the form of sulfur dioxide (SO2), and the particulate matter. The process gas stream is particularly an off-gas stream from a carbon black plant. [Background technology]

[0002] Currently, wet gas sulfuric acid (WSA) plants are used to treat the off-gas, or exhaust gas, emitted from carbon black plants. This off-gas contains sulfur in the form of SO2, NO x, and particulate matter in the form of soot, particularly carbon black particles. In a WSA plant, a process gas stream containing sulfur in the form of SO2 and particulate matter is passed through an SO2 converter containing one or more beds of an SO2 oxidation catalyst. The SO2 oxidation catalyst typically contains vanadium as V2O5, sulfur in the form of sulfate, pyrosulfate, tri- or tetrasulfate, SiO2, and an alkali metal promoter, such as Li, Na, K, Rb, and Cs, and combinations thereof, typically melted on a diatomaceous earth or SiO2 support. In the SO2 converter, the SO2 in the process gas is converted to SO3, which then reacts with water to produce concentrated sulfuric acid in a sulfuric acid condenser. This sulfuric acid is also condensed as a liquid in the sulfuric acid condenser. The WSA plant optionally also converts nitrogen oxides (NO3) to sulfuric acid. x A selective catalytic reduction (SCR) catalyst may also be provided for the removal of . See the applicant's WO 2016 / 169822, EP 0417200 and EP 0419539, which describe this process in detail.

[0003] While the vast majority of carbon black particles are oxidized on the SO2 oxidation catalyst, a small amount, i.e., 0.002 mg / Nm 3 to 100mg / Nm 3 , e.g., 0.003 mg / Nm 3 to 25mg / Nm 3 or 0.004 mg / Nm 3 to 10mg / Nm 3 Small amounts of carbon black particles, up to concentrations of 0.01g or less, can find their way into the catalyst bed and, consequently, into the sulfuric acid produced, turning it gray / black. In other words, the carbon black is washed away with the sulfuric acid produced, which is therefore contaminated and loses its commercial value.

[0004] It is known to use chemical treatments with strong oxidizing agents, such as hydrogen peroxide (H2O2), ozone (O3), and the like, to oxidize carbon particles to remove undesirable colors and thus also remove acid contamination by such particles. For example, the "Handbook of sulfuric acid manufacturing" (Non-Patent Document 1) devotes a section to this topic (Sulfuric Acid Decolouration, 1999). st In the paper "Bleaching of Acids and Acids," ed. 2008, the primary focus is on bleaching via the use of strong oxidizing agents (see especially pages 7-15 of said document). This undesirable color is stated to be the result of unburned organic matter carried over in the off-gas of sulfuric acid-producing plants. It is also known to use so-called dual drying tower technology to address the problem of colored (contaminated) acids, as well as the use of activated carbon. The use of activated carbon is said to work by adsorption, mechanical filtration, or ion exchange. Therefore, mechanical filtration is only disclosed with respect to the use of activated carbon and for the removal of undesirable color resulting from unburned organic matter carried over in sulfuric acid-producing plants.

[0005] US Pat. No. 4,702,836 (Patent Document 4) discloses a porous membrane that enables high-precision filtration purification, such as hot concentrated sulfuric acid filtration.

[0006] GB2394428A (Patent Document 5) discloses a metallic filter material containing a protective coating of ceramic, silica, or metallic material, which is used to remove or recover particles from gas and liquid streams and is coated with the protective material to reduce degradation during use.

[0007] US 4,405,548 discloses an improved method for filtering molten polymeric materials, in this case using a filter bed of permeable ceramic material, which comprises microcrystalline sintered bauxite particles.

[0008] EP1264916A1 (Patent Document 7) discloses a method for inhibiting corrosion of stainless steel or carbon steel exposed to an environment of sulfuric acid or a sulfuric acid-containing solution by contacting a portion of the stainless steel with a noble metal such as platinum, gold or silver.

[0009] US6287534 (Patent Document 8) describes a method for accelerating chemical reactions by high time-temperature change rates, more specifically SO2, CO, H2S, H2, NO x This paper discloses a method for using rapid temperature changes in one direction to accelerate the oxidation of polyatomic molecules such as N2, Cl2, Br2, non-hydrocarbon-based volatile organic compounds, hydrocarbon-based volatile organic compounds, and aryl and alkyl-acid halides. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] WO2016 / 169822 [Patent Document 2] EP0417200 [Patent Document 3] EP0419539 [Patent Document 4] US4702836 [Patent Document 5] GB2394428A [Patent Document 6] US4405548 [Patent Document 7] EP1264916A1 [Patent Document 8] US6287534 [Patent Document 9] WO2018 / 108739 [Non-patent literature]

[0011] [Non-Patent Document 1] “Handbook of sulfuric acid manufacturing”, “Sulfuric Acid Decolourization”, 1st ed.2008 Summary of the Invention [Problem to be solved by the invention]

[0012] The inventors have discovered that using certain forms of mechanical filtration, in which filter units containing metal, ceramic, or polymeric filters or filters containing filter aids on diaphragms are used, it is now possible to remove particulate matter, particularly carbon, from concentrated acids without the use of expensive materials such as activated carbon or oxidizing agents, thereby significantly improving operational safety because gases are not formed during filtration. In addition, the side reactions and attendant by-products that normally occur during the use of bleaching (oxidizing) agents are avoided. [Means for solving the problem]

[0013] The present invention therefore provides a method for removing particulate matter from an aqueous stream comprising concentrated acid, preferably concentrated sulfuric acid, comprising: The average particle size of the granules is in the range of 0.05 to 10 μm, and the concentration of the sulfuric acid in the aqueous stream is greater than 60% by weight; the method comprises mechanical filtration of the aqueous stream by passing it through a filter unit, wherein the filter unit comprises a metallic, ceramic or polymeric filter or a filter containing a filter aid on a diaphragm, the aqueous stream is the outlet stream of a sulfuric acid condenser of a process plant for producing sulfuric acid from a process gas stream, optionally the outlet stream of a sulfuric acid concentrator arranged downstream of the sulfuric acid condenser, the process gas stream comprises sulfur and the particulate matter; The process plant converting sulfur in the form of SO from the process gas stream to a SO-rich gas stream in an SO conversion unit, wherein the SO conversion unit includes a catalyst bed and passing the process gas through the catalyst bed; converting the SO3-rich gas stream to the outlet stream of the sulfuric acid condenser or to the outlet stream of the sulfuric acid concentrator; and Optionally, providing an acid cooling step to reduce the temperature of the outlet stream; The method includes:

[0014] Therefore, the process plant may include a sulfuric acid concentrator disposed downstream of the sulfuric acid condenser for increasing the concentration of sulfuric acid in the outlet stream from the sulfuric acid condenser. In one particular embodiment, the sulfuric acid concentrator may be integrated with or separate from the sulfuric acid condenser.

[0015] The term "integrated" means that the inlet of the sulfuric acid concentrator is in fluid communication with the outlet of the sulfuric acid condenser. Thus, the sulfuric acid condensed in the sulfuric acid condenser flows directly into the top of the sulfuric acid concentrator, for example.

[0016] The term "separate" means that the sulfuric acid concentrator is installed in a vessel external to the sulfuric acid condenser. For example, sulfuric acid condensed in the sulfuric acid concentrator is pumped into the sulfuric acid concentrator installed in the external vessel.

[0017] When referring to the (aqueous) outlet stream, e.g., a SO3-rich gas stream that is converted to the (aqueous) outlet stream of the sulfuric acid condenser, it will be understood that a gaseous outlet stream containing non-condensable compounds such as nitrogen, oxygen, and carbon dioxide is also formed.

[0018] The acid cooling step may involve heat exchange between sulfuric acid and a cooling medium such as water or air, or an acid cooling circuit, for example by heat exchange with a cold acid feed, for example with a circulated cold acid feed. For details about the acid cooling circuit, see the applicant's patent application WO2018 / 108739 (Patent Document 9).

[0019] In one embodiment, the filter unit is provided downstream of the acid cooling step. This particular arrangement of the filter unit, i.e., outside the acid cooling step of the filtration apparatus, allows for the use of simpler and cheaper materials due to the relatively low temperature at this location, i.e., as low as about 40°C. For example, the filter unit is provided downstream of a cooling unit, such as a heat exchanger, to reduce the temperature of the sulfuric acid before it is pumped to the storage tank. The filter unit can have its own pump to reduce the pressure drop across the filter, or can use the existing pressure provided by a pump outside the filter unit.

[0020] In another embodiment, the filter unit is provided within the acid cooling step as part of or integrated within the acid cooling circuit, i.e., the acid cooling loop. The phrase "part of or integrated within" will be understood to mean "part of" and "integrated within" interchangeably. Although the temperature at this location is relatively high, i.e., approximately 70°C within the acid cooling loop, this has been found to reduce viscosity by 50% compared to 40°C outside the loop (downstream of the acid cooling step). Therefore, the pressure drop is only half that outside the loop, thereby allowing for more efficient filtering. Alternatively, for example, the filter unit may be provided in the outlet stream, e.g., before any cooling.

[0021] The term "acid cooling loop" refers to a recirculation loop in which the (aqueous) outlet stream from a sulfuric acid condenser or sulfuric acid concentrator (e.g., having a temperature in the range of 180-270°C) is first blended with a cooled recycle sulfuric acid stream (e.g., having a temperature of about 40°C). This blended sulfuric acid, now having a temperature of about 70°C, is pumped and cooled through an exchanger, thereby producing a cooled sulfuric acid stream having a temperature of about 40°C. A portion of this cooled sulfuric acid stream is split into the cooled recycle sulfuric acid stream and an export sulfuric acid stream, also having a temperature of about 40°C and removed from the loop. Thus, the filter unit is suitably applied to the blended sulfuric acid stream (having a sulfuric acid temperature of about 70°C, as detailed above), e.g., after the pumping, as part of or integrated within the acid cooling loop. The filter unit is also suitably applied to the export sulfuric acid stream (also having a sulfuric acid temperature of about 40°C, as described above), outside the loop.

[0022] The sulfuric acid concentrator may include a recycle loop, i.e., a sulfuric acid concentrator recycle loop, which refers to recycling a portion of the sulfuric acid concentrator outlet stream, for example, to the sulfuric acid concentrator inlet, and may include heating the portion of the outlet stream, for example, to about 180-280°C, before entering the sulfuric acid concentrator.

[0023] As used herein, the term "average particle size" refers to the average diameter of particles as measured by a laser diffraction particle size analyzer such as a Malvern Mastersizer 3000.

[0024] As used herein, the term "particulates" refers to particles that impart undesirable effects to concentrated acids. One specific example is carbon particles, particularly carbon black particles, which impart undesirable color to concentrated acids. As used herein, particulates include soot, which is a general term for impure carbon particles resulting from the incomplete combustion of hydrocarbons. As used herein, the term "carbon black" refers to a form of paracrystalline carbon that has a high surface area:volume ratio, though lower than activated carbon, and differs from ordinary soot in its significantly higher surface area:volume ratio, higher carbon concentration (e.g., >95 wt. %, such as 97 or 99.0 wt. %), and significantly lower polycyclic aromatic hydrocarbon (PAH) content.

[0025] As used herein, the term "filter aid" means one or more inert materials applied to a substrate to aid in filtration. Filter aids are typically inert materials that contribute to the formation of a porous filter cake and may include materials such as diatomaceous earth, perlite, silica, or alumina.

[0026] As used herein, the term "diatomaceous earth" refers to a material made from siliceous sedimentary rock having a composition by weight of 80-90% silica, 2-4% alumina, and 0.5-2% iron oxide (the composition of oven-dried diatomaceous earth).

[0027] As used herein, the term "membrane" means a substrate or substrate layer that is applied or coated with a filter aid, such as diatomaceous earth, and that is permeable to sulfuric acid.

[0028] In one embodiment, the metallic, ceramic, or polymeric filters or filters containing a filter aid on a diaphragm have a filter media grade of 0.1 to 14 μm, preferably 0.5 to 12 μm. In particular, it has been found that ceramic or polymeric filters or filters containing a filter aid on a diaphragm having a media grade of 15 μm or greater allow carbon black to pass with the aqueous stream, whereas tighter filters, such as those having filter media grades of 14 μm, 12 μm, 10 μm, or even much smaller filter media grades such as 1, 0.5, or 0.1 μm, particularly those having filter media grades in the range of 0.1 to 14 μm or 0.5 to 12 μm, efficiently remove particulate matter, albeit at the expense of a slightly increased pressure drop.

[0029] As used herein, the term "filter media grade" or "media grade" refers to the average pore size in a filter, determined dynamically by forcing air through a filter just submerged in water until air bubbles pass through. The pressure required correlates to the average pore size in the filter: pore size (microns) = 30 x surface tension (dynes / cm) / pressure (mmHG). Average pore size may alternatively be measured by electron microscopy.

[0030] Metallic, ceramic or polymeric filters or filters containing filter aid on a diaphragm can be provided in the form of discs, rectangular or square sheets, or as tubular or candle filters or pleated filters.

[0031] The diaphragm can also be in the form of a disk, a rectangular or square sheet, a tubular or candle or pleated.

[0032] In one embodiment, the metallic filter is sintered metal and the filter media grade is in the range of 3-7 μm, preferably 5 μm. For this particular filter in this particular range, it has been found that carbon black particles are efficiently removed without a substantial increase in pressure drop.

[0033] Preferably, the sintered metal filter has a thickness in the range of 0.2 to 10 mm, for example 1 to 2.5 mm.

[0034] Preferably, the metal is stainless steel, such as stainless steel 316L or C22. In one particular embodiment, the metal is coated with an acid-resistant material.

[0035] In one embodiment, the septum is a polymeric, ceramic, or steel material and the filter aid comprises diatomaceous earth. In one particular embodiment, the filter aid is diatomaceous earth.

[0036] In one embodiment, the ceramic of the ceramic filter or the membrane comprises one or more elements selected from the group consisting of aluminum, calcium, potassium, sodium, magnesium, tungsten, iron, and silicon, and in particular comprises glass fiber or sintered glass, such as fused silica; and the polymer material of the polymer filter or the membrane is polypropylene, a fluorinated polymer, such as tetrafluoroethylene, e.g., polytetrafluoroethylene (PTFE), polyvinyl chloride, polyphenylene sulfide, polyphenylene oxide, or a combination thereof.

[0037] The same ceramic materials may be used for ceramic filters and diaphragms, and the same polymer materials may be used for polymer filters and diaphragms.

[0038] The steel material of the diaphragm is also preferably stainless steel, for example stainless steel 316L or C22.

[0039] In one embodiment, the ceramic filter is glass fiber or sintered glass, e.g., fused silica, with a filter media grade in the range of 1-10 μm. For this particular filter in this particular range, carbon black particles were also efficiently removed without a substantial increase in pressure drop.

[0040] The filter unit may function by gravity (where gravity is used to move the fluid downward), by vacuum (where an appliance is used to create a pressure gradient across the filter), by forced filtration (where appliance or flow line pressure forces the liquid through the filter), or by centrifugal force imparted, for example, by a rotating drum.

[0041] The filter unit can also contain one or more filters in series to remove coarse particles first, minimizing the total pressure drop.

[0042] The filter unit may also contain one or more filters in parallel, allowing filters to work while other filters are being cleaned or replaced.

[0043] The present invention also encompasses the use of disposable cartridges or filters that can be cleaned manually or on-line, for example, by forcing the filtered liquid back through the filter to remove accumulated particulate matter. The cleaning process can also include removal of accumulated particulate matter and any filter aid.

[0044] In one embodiment, the polymeric material of the polymeric filter is PTFE. In one particular embodiment, the polymeric filter is a PTFE membrane, e.g., a PTFE membrane or ePTFE membrane, which is optionally pleated and optionally encased in a polypropylene housing to form a filter cartridge. The filter media grade, also referred to herein as "pore rating," is suitably in the range of 0.02 to 5 μm, e.g., 0.1, 0.2, 0.45, and 1.0 μm. The filter cartridge may be, for example, 40 inches (1016 mm) or 10 inches (254 mm) long and have an outer diameter of 70 mm.

[0045] The term "ePTFE membrane" refers to expanded polytetrafluoroethylene, a membrane produced by expanding the linear polymer PTFE to form a microporous structure.

[0046] In one embodiment, the average particle size of the particulate material is in the range of 0.1 to 5 μm, for example, 0.1 to 2 μm.

[0047] In one embodiment, the particulate matter content in the aqueous stream is from 0.1 to 500 ppm by weight, preferably from 0.3 to 250 ppm by weight, for example 100 ppm by weight.

[0048] In one embodiment, the particulate matter is soot.

[0049] In one embodiment, the particulate is carbon black.

[0050] In one embodiment, the process gas stream comprises, together with the particulate matter, O and more than 200 ppm SO by volume, for example more than 500 ppm SO by volume (hence the sulfur in the process gas is predominantly in the form of SO), wherein the particulate matter is soot and / or carbon black, which is present in the process gas stream at a concentration of >2 mg / Nm 3Preferably, in the process gas, the soot has a composition comprising >20 wt% C (carbon), for example >50 wt% C, or >75 wt% C, or >90 wt% C, or >95 wt% C.

[0051] In one embodiment, the process gas stream is off-gas from a carbon black manufacturing plant. In certain embodiments, the WSA plant is preferably integrated into the carbon black manufacturing plant or serves as an extension of the carbon black manufacturing plant for the treatment of off-gas.

[0052] In one embodiment, the catalyst bed of the SO2 conversion unit comprises a catalyst comprising vanadium pentoxide, sulfur in the form of sulfate, pyrosulfate, tri- or tetrasulfate, and one or more alkali metals on a porous carrier, wherein the vanadium pentoxide content in the catalyst is 1 to 15 wt. %, the sulfur content in the catalyst is 1 to 25 wt. %, and the alkali metal content in the catalyst is 2 to 25 wt. %, and the porous carrier is diatomaceous earth or silica, i.e., silicon dioxide, optionally containing up to 10 wt. % alumina.

[0053] In one embodiment, the concentration of sulfuric acid in the aqueous stream is 85% by weight or greater (mass fraction of H2SO4), which is the concentration of acid obtained in a WSA plant. [Example]

[0054] Example 1: Metallic and ceramic filters Commercially available metallic and ceramic filter samples of various media grades were obtained.

[0055] Preliminary experiments showed that the behavior of carbon black particles in sulfuric acid and water was similar, as these are polar liquids that do not react with carbon black particles and therefore their interactions with carbon black particles would be identical. Therefore, carbon black and water-based suspensions were used in the filtration studies.

[0056] A 100 ppm by weight suspension in water was prepared by mixing carbon black powder with water in a dissolver.

[0057] Sintered metal filter discs of various filter grades were obtained from Mott. These discs had a 1-inch (25.4 mm) diameter and were made from stainless steel 316L. The ceramic discs tested were obtained from Sigma Aldrich and included sintered glass filters in the form of glass fiber and fused silica.

[0058] [Table 1]

[0059] All filter tests were performed by placing the filter sample in a custom-made funnel placed in a 1 L Buchner flask.

[0060] A 100 ppm by weight carbon black suspension was then poured onto the filter and drawn through the filter by a pump providing a trans-filter pressure of 0.6 bar. For filters 1-3 and 11-12, the applied trans-filter pressure was 0.8 bar. The liquid that passed through the filter was collected and subjected to determination of light obscuration using a Malvern Mastersize 3000. A standard curve for light obscuration was established by measuring the light obscuration of carbon black suspensions of known concentrations in water.

[0061] In particular, it was observed that ceramic or polymeric filters having a media grade of 15 μm or greater allowed carbon black to pass through with the aqueous stream, whereas denser filters such as those having filter media grades of 14 μm, 12 μm, or 10 μm, or even much smaller filter media grades such as 1, 0.5, or 0.1 μm, particularly those in the range of 0.1-14 μm or 0.5-12 μm, efficiently removed particulate matter, albeit at the expense of a slight increase in pressure drop.

[0062] High particle removal efficiencies were observed (as shown in the table) without a significant penalty in terms of pressure drop when metallic filters in the form of sintered metal with filter media grades in the 3-7 μm range, especially 5 μm, were used.

[0063] High particle removal efficiencies have also been observed using ceramic filters in the form of sintered glass, particularly fused silica, with filter media grades in the 1-10 μm range, without a significant penalty in terms of pressure drop.

[0064] The term "particle removal efficiency" refers to the percentage of carbon black in suspension retained by the filter, calculated by converting the light obscuration to ppm by weight using a standard curve.

[0065] Example 2: Polymer filter Commercially available cartridge filters (filter cartridges) having three different filter media grades, also referred to herein as pore grades, were obtained and tested in the laboratory to determine their particle removal efficiency in removing carbon black from a test liquid.

[0066] The cartridge filters consisted of a pleated ePTFE membrane housed in a polypropylene housing. Three different filter media grades (pore sizes) were provided: 1.0, 0.45, and 0.2 μm. The filters were 254 mm (10 inches) long and had an outer diameter of 70 mm. After the filtration test, two different measurements were performed on the filtrate: particle size distribution determination and residual carbon black content determination. Both measurements were performed using a Malvern Mastersize 3000.

[0067] The particle size distribution was measured for the filtrate from the filter cartridges with pore sizes of 1.0 and 0.45 μm and the 0.2 μm. In both cases, the particle size distribution of the carbon black remaining in the filtrate was less than the pore size, confirming that these filter cartridges were capable of removing carbon black particles at least up to the pore size. The filtrate from the filter cartridge with pore size of 0.2 μm was sufficiently clear that the particle size distribution could not be measured.

[0068] The particle size distribution was measured for the filtrate from the filter cartridges with pore sizes of 1.0 and 0.45 μm. In both cases, the particle size distribution of the carbon black remaining in the filtrate was less than the pore size, confirming that these filter cartridges were capable of removing carbon black particles at least up to their pore size. The filtrate from the filter cartridge with a pore size of 0.2 μm was sufficiently clear that the particle size distribution could not be measured.

[0069] These tests show that the cartridge filters are effective in removing carbon black particles up to the pore rating of the individual filters, and confirm that nearly all of the carbon black must be removed in order for the liquid to become visually clear. While this application is directed to the invention set forth in the claims, the disclosure of this application also includes: 1. A process for removing particulate matter from an aqueous stream containing concentrated acid, preferably concentrated sulfuric acid, comprising: The average particle size of the granules is 0.05 to 10 μm, and the concentration of the sulfuric acid in the aqueous stream is greater than 60% by weight; the method comprises mechanical filtration of the aqueous stream by passing it through a filter unit; the filter unit comprises a metallic, ceramic or polymeric filter or a filter containing a filter aid on a diaphragm, the aqueous stream is the outlet stream of a sulfuric acid condenser of a process plant for producing sulfuric acid from a process gas stream, optionally the outlet stream of a sulfuric acid concentrator arranged downstream of the sulfuric acid condenser, the process gas stream comprises sulfur and the particulate matter; The process plant SO of the process gas stream 2 Sulfur in the form of SO 2 SO in the conversion unit 3 a SO rich gas stream, 2 the conversion unit includes a catalyst bed and passes the process gas through the catalyst bed; The said SO 3 converting a rich gas stream to the outlet stream of the sulfuric acid condenser, optionally to the outlet stream of the sulfuric acid concentrator; and Optionally, providing an acid cooling step to reduce the temperature of the outlet stream; The method comprising: 2. The method according to claim 1, wherein the filter unit is provided downstream of the acid cooling step or within the acid cooling step as part of or integrated within the acid cooling circuit. 3. The method according to 1 or 2 above, wherein the metal, ceramic or polymer filter or the filter containing a filter aid on a diaphragm has a filter media grade of 0.1 to 14 μm, preferably 0.5 to 12 μm. 4. The method according to any one of 1. to 3. above, wherein the metal filter is a sintered metal and the filter media grade is in the range of 3 to 7 μm, preferably 5 μm. 5. The method according to any one of 1. to 3., wherein the diaphragm is made of a polymeric, ceramic, or steel material, and the filter aid comprises diatomaceous earth. 6. The method of any one of 1., 3. and 5., wherein the ceramic of the ceramic filter or the diaphragm contains one or more elements selected from the group consisting of aluminum, calcium, potassium, sodium, magnesium, tungsten, iron and silicon; and the polymer material of the polymer filter or the diaphragm is polypropylene, a fluorinated polymer such as tetrafluoroethylene, e.g., polytetrafluoroethylene (PTFE), polyvinyl chloride, polyphenylene sulfide, polyphenylene oxide, or a combination thereof. 7. The method of claim 7, wherein the polymer material of the polymeric filter is PTFE, and the polymeric filter is a PTFE membrane, such as a PTFE membrane or an ePTFE membrane, which is optionally pleated and optionally housed in a polypropylene housing to form a filter cartridge. 8. The method according to any one of 1. to 7. above, wherein the average particle size of the particulate matter is in the range of 0.1 to 5 μm, for example, 0.1 to 2 μm. 9. The method according to any one of 1. to 8. above, wherein the content of particulate matter in the aqueous stream is 0.1 to 500 ppm by weight, preferably 0.3 to 250 ppm by weight, for example 100 ppm by weight. 10. The method according to any one of 1 to 9 above, wherein the particulate matter is soot. 11. The method according to any one of 1 to 9 above, wherein the particulate material is carbon black. 12. The process gas stream, together with the particulate matter, 2 and SO exceeding 200 ppm by volume 2 , e.g., SO above 500 ppm by volume 2 wherein the particulate matter is soot and / or carbon black, which is present in the process gas stream at a concentration of >2 mg / Nm 3 12. The method according to any one of 1. to 11. above, wherein the compound is present at a concentration of 13. The method according to any one of 1. to 12. above, wherein the process gas stream is off-gas from a carbon black manufacturing plant. 14. The above SO 2 14. The process of any one of 1. to 13., wherein the catalyst bed of the conversion unit comprises a catalyst comprising vanadium pentoxide, sulfur in the form of sulfate, pyrosulfate, tri- or tetrasulfate, and one or more alkali metals on a porous carrier, wherein the vanadium pentoxide content in the catalyst is 1 to 15 wt. %, the sulfur content in the catalyst is 1 to 25 wt. %, and the alkali metal content in the catalyst is 2 to 25 wt. %, and the porous carrier is diatomaceous earth or silica, i.e., silicon dioxide, optionally containing up to 10 wt. % alumina. 15. The method according to any one of 1. to 14. above, wherein the concentration of sulfuric acid in the aqueous stream is 85% by weight or more.

Claims

1. A method for removing particulate matter from an aqueous stream containing concentrated sulfuric acid, comprising: The average particle size of the granules is 0.05 to 10 μm, and the concentration of the sulfuric acid in the aqueous stream is greater than 60% by weight; the method comprises mechanical filtration by passing the aqueous stream through a filter unit; the filter unit comprises a metallic or polymeric filter or a filter comprising a filter aid on a diaphragm; the aqueous stream is the outlet stream of a sulfuric acid condenser of a process plant for producing sulfuric acid from a process gas stream or the outlet stream of a sulfuric acid concentrator arranged downstream of the sulfuric acid condenser, the process gas stream comprises sulfur and the particulate matter; The process plant comprises: SO in the process gas stream ２ Sulfur in the form of SO ２ In the conversion unit, SO ３ a SO rich gas stream, ２ The conversion unit includes a catalyst bed and passes the process gas through the catalyst bed; and ...The SO ３ converting a rich gas stream to the outlet stream of the sulfuric acid condenser or to the outlet stream of the sulfuric acid concentrator; or additionally further comprising providing an acid cooling step to reduce the temperature of the outlet stream.

2. 10. The method of claim 1, wherein the mechanical filtration is performed after the acid cooling step or is performed in the acid cooling step as part of or integrated within the acid cooling circuit.

3. 3. The method according to claim 1 or 2, wherein the metallic or polymeric filter or the filter comprising a filter aid on a diaphragm has a filter media grade of 0.1 to 14 μm.

4. The method described in claim 3, wherein the filter media grade is 0.5 to 12 μm.

5. The method according to any one of claims 1 to 4, wherein the metal filter is a sintered metal and the filter media grade is in the range of 3 to 7 μm.

6. The method described in claim 5, wherein the filter media grade is 5 μm.

7. 5. The method of claim 1, wherein the septum is a polymeric, ceramic or steel material and the filter aid comprises diatomaceous earth.

8. The method of any one of claims 1, 3, 4 and 7, wherein the ceramic of the diaphragm contains one or more elements selected from the group consisting of aluminum, calcium, potassium, sodium, magnesium, tungsten, iron and silicon; and the polymer material of the polymer filter or the diaphragm is polypropylene, a fluorinated polymer, polyvinyl chloride, polyphenylene sulfide, polyphenylene oxide, or a combination thereof.

9. The method of claim 8, wherein the fluorinated polymer is polytetrafluoroethylene (PTFE).

10. 10. The method of claim 8 or 9, wherein the polymer material of the polymer filter is polytetrafluoroethylene (PTFE), and the polymer filter is a PTFE membrane, which may or may not be pleated and which may or may not be housed in a propylene housing to form a filter cartridge.

11. The method of claim 10, wherein the polymeric filter is an ePTFE membrane.

12. The method according to any one of claims 1 to 11, wherein the average particle size of the granules is in the range of 0.1 to 5 µm.

13. The method of claim 12, wherein the average particle size of the particulate material is in the range of 0.1 to 2 μm.

14. A method according to any one of the preceding claims, wherein the particulate matter content of the aqueous stream is from 0.1 to 500 ppm by weight.

15. The method of claim 14, wherein the particulate matter content in the aqueous stream is 0.3 to 250 ppm by weight.

16. The method of claim 14, wherein the particulate matter content in the aqueous stream is 100 ppm by weight.

17. The method of any one of claims 1 to 16, wherein the particulate matter is soot.

18. The method of any one of claims 1 to 16, wherein the particulate material is carbon black.

19. The process gas stream, together with the particulates, ２ and greater than 200 ppm by volume SO2, wherein the particulate matter is soot and / or carbon black, which is present in the process gas stream at a concentration of >2 mg / Nm3. ３ The method of any one of claims 1 to 18, wherein the compound is present in a concentration of 20. The method of claim 19, wherein the process gas stream, together with the particulate matter, comprises O 2 and greater than 500 ppm by volume of SO 2 .

21. 21. The method of any one of claims 1 to 20, wherein the process gas stream is off-gas from a carbon black manufacturing plant.

22. The SO ２ 22. The method of any one of claims 1 to 21, wherein the catalyst bed of the conversion unit comprises a catalyst comprising vanadium pentoxide, sulfur in the form of sulfate, pyrosulfate, tri- or tetrasulfate, and one or more alkali metals on a porous carrier, wherein the vanadium pentoxide content in the catalyst is 1 to 15 wt. %, the sulfur content in the catalyst is 1 to 25 wt. %, and the alkali metal content in the catalyst is 2 to 25 wt. %, and the porous carrier is diatomaceous earth or silica, i.e., silicon dioxide, and the porous carrier is either alumina-free or contains up to 10 wt. % alumina.

23. A method according to any one of the preceding claims, wherein the concentration of sulfuric acid in the aqueous stream is at least 85% by weight.

24. A method for removing particulate matter from an aqueous stream containing concentrated sulfuric acid, comprising: The average particle size of the granules is 0.05 to 10 μm, and the concentration of the sulfuric acid in the aqueous stream is greater than 60% by weight; the method comprises mechanical filtration by passing the aqueous stream through a filter unit; the filter unit comprises a metallic, ceramic or polymeric filter or a filter comprising a filter aid on a diaphragm; the aqueous stream is the outlet stream of a sulfuric acid condenser of a process plant for producing sulfuric acid from a process gas stream or the outlet stream of a sulfuric acid concentrator arranged downstream of the sulfuric acid condenser, the process gas stream comprises sulfur and the particulate matter; The process plant comprises: converting sulfur in the form of SO 2 of the process gas stream to an SO 3 -rich gas stream in an SO 2 conversion unit, wherein the SO 2 conversion unit includes a catalyst bed and the process gas is passed through the catalyst bed; and converting the SO 3 -rich gas stream to the outlet stream of the sulfuric acid condenser or to the outlet stream of the sulfuric acid concentrator; or additionally further comprising providing an acid cooling step to reduce the temperature of the outlet stream; and The catalyst bed of the SO 2 conversion unit comprises a catalyst comprising vanadium pentoxide, sulfur in the form of sulfate, pyrosulfate, tri- or tetrasulfate, and one or more alkali metals on a porous carrier, wherein the vanadium pentoxide content in the catalyst is 1 to 15 wt %, the sulfur content in the catalyst is 1 to 25 wt %, and the alkali metal content in the catalyst is 2 to 25 wt %, and the porous carrier is diatomaceous earth or silica, i.e., silicon dioxide, and the porous carrier contains no alumina or up to 10 wt % alumina. The method.

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