Waste sulfuric acid treatment method and device

Abstract

The invention discloses a waste sulfuric acid treatment method and device, the device comprises a sintered filter element filter, a fine filtration coalescer, an adsorption tank and a membrane separator which are connected in sequence, and the fine filtration coalescer adopts a ceramic membrane tube or a polytetrafluoroethylene membrane tube or a silicon carbide lining membrane tube as a filter material; an adsorption material in the adsorption tank is one or a combined adsorption material of more than two of activated carbon, a modified molecular sieve, a metal organic framework material and a nano adsorption material; and the membrane separation system adopts one or a combined membrane of more than two of an ultrafiltration membrane, a reverse osmosis membrane and an electrodialysis membrane. The alkylation waste acid regeneration process can be simplified, the occupied area of the device is saved, the engineering investment is reduced, and the operation cost is greatly reduced compared with that of an existing process technology; according to the method, a physical separation means is adopted, organic polymeric oil, dissolved organic matters, dissolved salts and other impurities in the alkylated waste sulfuric acid can be effectively removed without decomposing and reconstructing the waste sulfuric acid, and the concentrated sulfuric acid after concentration completely meets the production requirements of an alkylation device.

Description

Technical Field

[0001] This invention belongs to the field of industrial waste sulfuric acid treatment, and relates to the treatment of waste sulfuric acid discharged during the production process of sulfuric acid alkylation unit, specifically to a waste sulfuric acid treatment method and apparatus. Background Technology

[0002] Alkylated gasoline is characterized by high octane rating, good anti-knock properties, low vapor pressure, low sulfur content, and absence of olefins and aromatics, making it an ideal high-octane blending component for clean gasoline. Adding alkylated gasoline to automotive gasoline can effectively increase the overall octane rating of the gasoline, while also optimizing the blending of sulfur and olefin content in catalytic gasoline and aromatics content in reformed gasoline, resulting in significant market demand. The sulfuric acid alkylation process is the most widely used technology among various methods. This technology typically uses 98% or 99.2% (mass fraction) concentrated sulfuric acid as a catalyst. During the alkylation reaction, a small amount of side reactions occur with hydrocarbons, generating various forms of sulfuric acid and enriching water, leading to a gradual decrease in acid concentration. When the acid concentration falls below 90%, the catalyst activity decreases, causing the alkylation unit to malfunction, necessitating the discharge of some waste acid and the replenishment of fresh acid. The waste acid discharged from the alkylation unit is a black, viscous liquid with a pungent odor. It mainly contains 85%–90% sulfuric acid, 8%–14% organic polymeric oil, and water. The organic polymeric oil is composed of high-molecular-weight olefins, dienes, alkyl sulfonic acids, sulfate esters, sulfonates, and dissolved thiols and sulfates, with more than 300 different monomers. Typically, producing 1 ton of alkylated gasoline generates 60–100 kg of alkylation waste acid. To reduce operating costs, the waste sulfuric acid needs to be treated and returned to the alkylation reaction unit for recycling.

[0003] The main methods for treating waste sulfuric acid from alkylation units include high-temperature pyrolysis, freeze crystallization, neutralization, silica production, oxidation, and solvent extraction.

[0004] Currently, the most mature and widely used industrial method for treating alkylation waste acid is high-temperature pyrolysis, as illustrated by Chinese patents CN106744716A, CN106315520A, CN105502306A, and CN107311117A. These methods all involve high-temperature cracking to decompose waste sulfuric acid into SO2, which is then converted to SO3 via a catalyst. After cooling or absorption with concentrated acid, high-concentration sulfuric acid is obtained. However, this method has a long process flow and requires fuel gas to provide energy for the cracking process, resulting in high operating costs and significantly limiting the amount of waste acid that can be treated.

[0005] The neutralization method involves converting waste sulfuric acid into various sulfate products, such as manganese sulfate, magnesium sulfate, calcium sulfate, zinc sulfate, copper sulfate, and aluminum sulfate. Chinese patents CN106673067A, CN106976896A, CN106745160A, CN105540642B, CN105565363A, and CN105480998B all employ the introduction of metal elements to recycle waste sulfuric acid into sulfates. However, the quality of the sulfate products obtained using this method is difficult to guarantee, requiring subsequent purification, which is costly.

[0006] Oxidation methods use oxidants to remove organic matter from waste sulfuric acid, such as hydrogen peroxide, ozone, sodium hypochlorite, and potassium permanganate. For example, Chinese patent CN106744723A discloses a method for regenerating alkylation waste acid, which includes adding 30% hydrogen peroxide to waste sulfuric acid. The organic matter or tiny carbon particles in the waste sulfuric acid react with the hydrogen peroxide to form carbon dioxide, nitrogen, and water. After stripping to remove impurities, regenerated sulfuric acid is obtained. This method is carried out under conditions of 1.0–5.0 MPa pressure and 100–300℃ temperature. The reaction pressure is high and it cannot efficiently degrade and remove organic matter from the waste sulfuric acid, failing to achieve complete degradation. The regenerated sulfuric acid is reused, which is detrimental to the alkylation reaction. Furthermore, it generates a large amount of waste gas. Chinese patent CN107032308A discloses a method for resource recovery of alkylation waste acid, which includes adding activated carbon for decolorization, then adding potassium permanganate to generate carbon oxides or sulfur oxides such as CO2 and SO2 from the organic matter. After washing and filtration, regenerated sulfuric acid is obtained. This method involves relatively mild reaction temperatures and pressures, but the concentration of sulfuric acid after regeneration is less than 90%, and it introduces other metallic impurities, which does not meet the production requirements of the alkylation unit. It also generates a significant amount of waste gas emissions.

[0007] Chinese patent CN109095442A discloses a method for treating waste sulfuric acid emitted during the alkylation process. The method includes: first, reducing the water content of the waste sulfuric acid; then, using a freeze-crystallization method to separate the sulfuric acid from other impurities. The purified sulfuric acid is returned for alkylation reuse, while the enriched impurities are incinerated. Although this method has a short process flow, it cannot effectively remove organic matter and metal ions from the waste sulfuric acid, which is detrimental to the alkylation reaction.

[0008] Chinese patent CN111003865A discloses a method for treating high-concentration waste sulfuric acid. The method involves first diluting the high-concentration waste sulfuric acid, then subjecting it to two-stage nanofiltration to obtain a clarified sulfuric acid solution and pure water. The concentrated sulfuric acid is then evaporated and concentrated to obtain concentrated sulfuric acid. This method is mainly applied in the field of hydrometallurgical technology, treating waste sulfuric acid with a concentration typically around 50%, primarily for removing metal ions. Furthermore, it requires diluting the sulfuric acid to approximately 20% concentration, releasing a large amount of heat, followed by subsequent concentration and evaporation, resulting in energy mismatch and high requirements for material selection, thus limiting its application prospects.

[0009] Chinese patent CN112794292B provides a method and system for purifying and reusing waste sulfuric acid. It uses nanofiltration and electrodialysis to treat waste sulfuric acid in the non-ferrous metals industry. The main purpose is to remove impurities in order to recover non-ferrous metal resources, and only dilute sulfuric acid with a concentration of 18-23% is obtained.

[0010] Chinese patent CN212356544U discloses a waste sulfuric acid treatment system. This system treats waste sulfuric acid generated during chloromethane production by adding a large amount of hydrogen peroxide and a small amount of hydrolysis accelerator. The operation is intermittent, with a reaction time of approximately 8 hours. After the reaction, the system is filtered and subsequently concentrated to obtain concentrated sulfuric acid with a maximum purity of 80%. However, this method uses a large amount of hydrogen peroxide, and if hydrocarbons are present in the concentrated sulfuric acid, it may pose an explosion risk, making it unsuitable for treating alkylation waste acid.

[0011] Except for the high-temperature pyrolysis method, which can effectively remove dissolved sulfates or sulfurous acid from the waste sulfuric acid in the alkylation unit, the other methods cannot or are not suitable for removing sulfates or sulfurous acid from the waste sulfuric acid in the alkylation unit, which is not conducive to the alkylation reaction. However, the high-temperature pyrolysis method for treating waste sulfuric acid in the alkylation unit has a long process flow, complex control, large footprint, high investment, high operating cost, and large solid waste discharge, which limits the development of sulfuric acid alkylation technology. Summary of the Invention

[0012] To address the problems existing in the prior art, the present invention provides a waste sulfuric acid treatment method and apparatus, which has a simple process route, high recovery rate, and low production cost.

[0013] The specific technical solution of this invention is: a method for treating waste sulfuric acid, comprising the following steps:

[0014] 1) Raw material pretreatment: Alkylation waste sulfuric acid is passed through a primary filter to remove mechanical impurities and a small amount of insoluble esters;

[0015] 2) Fine filtration: The pretreated waste sulfuric acid enters the fine filter coalescer. The organic polymer oil in the waste sulfuric acid is separated from the sulfuric acid by the filter material. The filtered organic polymer oil is collected for further processing.

[0016] 3) Adsorption desalination: The waste sulfuric acid obtained after fine filtration is adsorbed by adsorption materials to remove dissolved sulfates or sulfites.

[0017] 4) Sulfuric acid concentration: The waste sulfuric acid obtained in step 3) is further concentrated by membrane separation to obtain concentrated sulfuric acid with a concentration of over 98%.

[0018] Furthermore, after pretreatment in step 1), the content of insoluble oils in the waste sulfuric acid is ≤0.1%wt;

[0019] Furthermore, in step 2), the concentration of waste sulfuric acid after filtration by the fine filter coalescer is 90-96%.

[0020] Furthermore, in step 4), the operating temperature is 30–50°C and the operating pressure is 100–500 kPa (absolute pressure).

[0021] Furthermore, the adsorbent material employs aluminosilicate-based modified molecular sieves, and rare earth elements, including lanthanum (La), are introduced through ion exchange. 3+ , Cerium 3+ / Ce 4+ Neodymium (Nd) 3+ ,Pr 3+ , to regulate its acidity and catalytic activity.

[0022] Furthermore, the adsorption material uses a silicate-aluminate framework modified molecular sieve, introducing heteroatoms, including titanium (Ti) and gallium (Ga), and changing the pore properties through isomorphic substitution to obtain better adsorption effect.

[0023] To achieve the process flow of this invention, this invention also provides a waste sulfuric acid treatment device, comprising a sintered filter cartridge, a fine filter coalescer, an adsorption tank, and a membrane separator connected in sequence. The filter media of the fine filter coalescer is a ceramic membrane tube, a polytetrafluoroethylene membrane tube, or a silicon carbide-lined membrane tube. The adsorption material in the adsorption tank is one or more of the following adsorption materials: activated carbon, modified molecular sieve, metal-organic framework material, and nano-adsorption material. The membrane separation system uses one or more of the following membranes: ultrafiltration membrane, reverse osmosis membrane, and electrodialysis membrane.

[0024] Furthermore, sintered filter cartridges are made of Hastelloy alloy and fluoroplastic lined filter cartridges.

[0025] Furthermore, the sintered filter cartridge has a filtration accuracy of 30–50 μm, while the fine filter coalescer has a filtration accuracy of 5–10 μm.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1) It can greatly simplify the alkylation waste acid regeneration process, save equipment space, reduce engineering investment, and significantly reduce operating costs compared with existing process technologies;

[0028] 2) By using physical separation methods, it is not necessary to decompose or reconstruct the waste sulfuric acid. It can effectively remove impurities such as organic polymer oil, dissolved organic matter and dissolved salts from the alkylation waste sulfuric acid. The concentrated sulfuric acid after concentration fully meets the production requirements of the alkylation unit.

[0029] 3) Solid waste, wastewater, and exhaust gas emissions are minimal or nonexistent;

[0030] 4) The process is simple, easy to operate and maintain, and highly adaptable;

[0031] 5) The automatic control program is simple and does not involve complex control processes;

[0032] 6) The amount of hazardous materials involved in the equipment is significantly reduced compared to existing processes and technologies, making it easier for enterprises to manage. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the process of this invention;

[0034] In the picture:

[0035] 1. Sintered filter cartridge; 2. Fine filter coalescer; 3. Adsorption tank; 4. Adsorption material; 5. Coalescer filter cartridge; 6. Membrane separator;

[0036] 21. Waste sulfuric acid; 22. Organic waste; 23. Acidic wastewater; 24. Concentrated sulfuric acid. Detailed Implementation

[0037] The present invention will be further described below with reference to specific embodiments. These specific embodiments should not be considered as limiting the scope of protection of the present invention.

[0038] The composition of the waste sulfuric acid from the alkylation unit is as follows:

[0039] Components wt% Waste sulfuric acid 90.0 water 6.0 Hydrocarbons and organic polymer oils 4.0 total 100.0

[0040] The temperature of the alkylation waste sulfuric acid is 40℃, the pressure of the waste sulfuric acid is 1.0MPa (gauge pressure, the same below), and the flow rate of the waste sulfuric acid is 2917kg / h.

[0041] like Figure 1 As shown, the process of this embodiment is as follows:

[0042] 1) Waste sulfuric acid 21 passes through sintered filter element filter 1 with a filter accuracy of 50μm, initially filtering out mechanical impurities and a small amount of organic matter. Two sintered filter element filters 1 are set up, one in operation and one on standby. When the pressure difference exceeds 0.1MPa, the standby filter is switched.

[0043] 2) The waste sulfuric acid after preliminary filtration enters the fine filter coalescer 2. The coalescer filter element 5 uses silicon carbide-lined membrane tubes. Two fine filter coalescer 2 units are set up, one in operation and one on standby. Each fine filter coalescer 2 is equipped with 15 silicon carbide-lined membrane tubes, with a single membrane tube flux of 195 kg / h. When the pressure difference exceeds 0.20 MPa, the standby coalescer is switched on. After coalescence filtration, concentrated sulfuric acid with a concentration of 95.7% is obtained, with an organic matter content ≤100 ppmw. The coalesced organic waste 22 can be collected and recycled or incinerated as fuel.

[0044] 3) The concentrated sulfuric acid after coalescence filtration enters adsorption tank 3. The adsorbent material 4 in adsorption tank 3 is a modified molecular sieve. The concentrated sulfuric acid contains small amounts of FeSO4 and [Fe(HSO4)4]. - Fe2(SO4)3 or other metal sulfates and sulfites are adsorbed by the adsorbent. The concentration of metal ions in the concentrated sulfuric acid after adsorption is ≤10ppmw, which meets the requirements of the alkylation unit. After removing the metal salts, the concentrated sulfuric acid is sent to the concentration section for further processing.

[0045] 4) The concentrated sulfuric acid after coalescence filtration enters the permeate membrane in membrane separator 6 to further separate the water in the concentrated sulfuric acid, obtaining concentrated sulfuric acid 24 with a concentration of over 98%, which is returned to the alkylation unit for recycling. The separated acidic wastewater 23 is neutralized and then discharged to the wastewater treatment plant. In this embodiment, no waste gas is discharged.

[0046] The above description is merely a typical example of the present invention and does not impose any limitation on the present invention. Any changes or modifications made by those skilled in the art using the above technical content without departing from the scope of the present invention should be considered equivalent examples of equivalent variations. Any equivalent changes made to the above embodiments based on the technical essence of the present invention without departing from the content of the present invention are within the scope of the present invention.

Claims

1. A method for treating waste sulfuric acid, characterized in that, Includes the following steps: 1) Raw material pretreatment: Alkylation waste sulfuric acid is passed through a primary filter to remove mechanical impurities and a small amount of insoluble esters; 2) Fine filtration: The pretreated waste sulfuric acid enters the fine filter coalescer. The organic polymer oil in the waste sulfuric acid is separated from the sulfuric acid by the filter material. The filtered organic polymer oil is collected for further processing. 3) Adsorption desalination: The waste sulfuric acid obtained after fine filtration is adsorbed by adsorption materials to remove dissolved sulfates or sulfites. 4) Sulfuric acid concentration: The waste sulfuric acid obtained in step 3) is further concentrated by membrane separation to obtain concentrated sulfuric acid with a concentration of over 98%.

2. The waste sulfuric acid treatment method according to claim 1, characterized in that: Step 1) After pretreatment, the content of insoluble oils in waste sulfuric acid is ≤0.1%wt.

3. The waste sulfuric acid treatment method according to claim 1, characterized in that: Step 2) The concentration of waste sulfuric acid after filtration by the fine filter coalescer is 90-96%.

4. The waste sulfuric acid treatment method according to claim 1, characterized in that: Step 4) Operating temperature 30-50℃, operating pressure 100-500kPa (absolute pressure).

5. The waste sulfuric acid treatment method according to claim 1, characterized in that: The adsorbent material is a silicate-aluminate framework modified molecular sieve, with rare earth elements, including lanthanum (La), introduced through ion exchange. 3+ , Cerium 3+ / Ce 4+ Neodymium (Nd) 3+ ,Pr 3+ , to regulate its acidity and catalytic activity.

6. The waste sulfuric acid treatment method according to claim 1, characterized in that: The adsorbent material is a silicate-aluminate framework modified molecular sieve, which introduces heteroatoms, including titanium (Ti) and gallium (Ga), and changes the pore properties through isomorphic substitution.

7. A waste sulfuric acid treatment device, characterized in that: The system includes a sintered filter cartridge, a fine filter coalescer, an adsorption tank, and a membrane separator connected in sequence. The fine filter coalescer uses ceramic membrane tubes, polytetrafluoroethylene membrane tubes, or silicon carbide-lined membrane tubes as filter media. The adsorption material in the adsorption tank is one or more of the following: activated carbon, modified molecular sieves, metal-organic framework materials, and nano-adsorption materials. The membrane separation system uses one or more of the following: ultrafiltration membranes, reverse osmosis membranes, and electrodialysis membranes.

8. The waste sulfuric acid treatment device according to claim 7, characterized in that: The sintered filter element is made of Hastelloy alloy and fluoroplastic lining.

9. The waste sulfuric acid treatment device according to claim 7, characterized in that: The sintered filter element has a filtration accuracy of 30–50 μm, and the fine filter coalescer has a filtration accuracy of 5–10 μm.

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