TWI891249B - Production method of low-carbon hydrogen - Google Patents

Abstract

The present invention discloses a low-carbon hydrogen production method, which includes step (a): drying the waste silicon mud; step (b): crushing the dried waste silicon mud and screening the crushed dried waste silicon mud to obtain waste silicon mud powder containing 40wt% to 95wt% of silicon metal and silicon oxide, wherein the silicon metal accounts for 5wt% to 40wt% of the combined content of the silicon metal and silicon oxide; and step (c): mixing the silicon metal and silicon oxide with an aqueous alkali metal solution, and controlling the reaction temperature between 100°C and 150°C to obtain hydrogen.

Description

Preparation method of low-carbon hydrogen

The present invention relates to a preparation method, in particular to a preparation method for low-carbon hydrogen.

Semiconductors are crucial to the operation of modern electronics, with ever-increasing performance, increasingly complex and sophisticated designs, and a growing range of applications. Thanks to semiconductors, we can use laptops, mobile phones, and tablets. Semiconductors have also fueled the development of modern automotive electronics, avionics, and medical equipment, significantly improving the energy efficiency of large and small appliances and lighting. While they are a crucial foundation of modern technology, they also generate significant amounts of waste. Semiconductor waste contains a variety of heavy metals, such as lead and cadmium, which can cause neurological problems if introduced into the human body; hexavalent chromium and arsenic, which can cause cancer. Furthermore, strong acids and bases are often found in semiconductor waste, posing an immediate risk if accidentally contacted by the human body.

Waste silicon sludge generated in semiconductor manufacturing is produced during wafer polishing or thinning processes, where chemical etching or mechanical forces are used to planarize silicon wafers or other substrate materials. Currently, waste silicon sludge generated during cutting or grinding processes is typically treated with wastewater to separate the solid and liquid components. The solids are then concentrated and collected before being sent to a disposal facility for landfill disposal. However, landfilling waste silicon sludge can easily pollute the environment, and since waste silicon sludge contains large amounts of silicon oxide (SiOx, x=1,2) or metallic silicon, direct landfilling is a significant waste of resources.

Furthermore, with the current global availability of oil and rising environmental awareness, automobiles, power generation equipment, and other sectors are actively seeking environmentally friendly alternatives to oil. Fuel cells, which utilize hydrogen and oxygen to generate large amounts of electricity through a reaction, are a promising next-generation power source. Fuel cells are a type of power generation device, but unlike conventional non-rechargeable batteries, they are not discarded upon use, nor do they require recharging like rechargeable batteries. As their name suggests, fuel cells require continuous refueling to maintain their power. This fuel is hydrogen, which is why they are classified as a new energy source.

The operating principle of a fuel cell is that it contains two electrodes, a cathode and an anode, separated by a permeable membrane. This space is filled with an electrolyte. Hydrogen enters the anode, while oxygen (or air) enters the cathode. A catalyst breaks down the hydrogen atoms in the anode into two hydrogen protons and two electrons. The protons are attracted to the oxygen and flow to the other side of the membrane, while the electrons flow through an external circuit to form an electric current and reach the cathode. Under the action of the cathode catalyst, the hydrogen protons, oxygen, and electrons react to form water molecules. Therefore, water is arguably the only emission from fuel cells. Because fuel cells utilize a chemical reaction between hydrogen and oxygen to generate electricity and water, they are not only completely pollution-free but also avoid the time-consuming charging of traditional batteries. They are currently the most promising new energy source. If widely adopted in vehicles and other high-pollution power generation vehicles, they will significantly reduce air pollution and greenhouse gas emissions.

The current method for producing hydrogen that can be directly supplied to fuel cells involves first using a carbon dioxide laser to crack pure silicon powder with a size of 10 to 100 nanometers, then passing the cracked pure silicon powder through alkaline water to produce hydrogen. However, the equipment and process of using a carbon dioxide laser to crack silicon powder increases the complexity and cost of hydrogen production and requires additional energy (i.e., the carbon dioxide laser). Furthermore, the size of the silicon powder particles must be limited to between 10 and 100 nanometers.

Therefore, in an era dominated by circular economy and green energy, converting waste generated by semiconductor manufacturing processes into reusable hydrogen while simultaneously meeting energy conservation, carbon reduction, and environmental protection requirements has become a pressing issue in the relevant technology field.

In light of the above-mentioned issues, the present invention aims to provide a method for producing low-carbon hydrogen. This method can achieve energy conservation and carbon reduction while also meeting green and environmental protection requirements.

To achieve the above objectives, the present invention provides a method for preparing low-carbon hydrogen, comprising the steps of (a) drying waste silicon sludge; (b) crushing and screening the dried waste silicon sludge, wherein the weight percentage (wt%) of metallic silicon and silicon oxide (SiOx, x = 1, 2) in the screened waste silicon sludge powder is between 40 and 95, with metallic silicon accounting for between 5 and 40 wt% of the total metallic silicon and silicon oxide content; and (c) mixing the metallic silicon and silicon oxide from step (b) with an alkaline metal aqueous solution, controlling the reaction temperature between 100°C and 150°C, to produce hydrogen.

In one embodiment, in step (a), the waste silicon sludge is generated during the semiconductor manufacturing process.

In one embodiment, in step (a), the moisture content of the dried waste silicon sludge is less than 10 wt%.

In one embodiment, in step (c), the alkaline metal aqueous solution is a sodium hydroxide aqueous solution.

In one embodiment, the concentration of the aqueous sodium hydroxide solution is 45 wt%.

In one embodiment, in step (c), the reaction temperature of the metallic silicon and silicon oxide with the alkaline metal aqueous solution is controlled to be between 100°C and 150°C by controlling the metallic silicon content in the metallic silicon and silicon oxide.

In one embodiment, the higher the content of metallic silicon, the higher the reaction temperature tends to be 150°C.

In one embodiment, in step (c), the reaction time is greater than or equal to 2 hours.

As described above, the low-carbon hydrogen production method of the present invention utilizes waste silicon sludge and, through the exothermic reaction between metallic silicon and silicon oxide and an alkaline metal aqueous solution, generates hydrogen by utilizing the metallic silicon contained in the waste silicon sludge. This reaction temperature is then reached to produce the desired hydrogen. Compared to existing methods using carbon dioxide lasers to produce hydrogen, the present method requires no additional energy to produce hydrogen, thus achieving energy savings and carbon reduction. Furthermore, since the waste silicon sludge used is a process waste generated during semiconductor manufacturing, the present method also meets green and environmentally friendly requirements.

a,b,c: Steps

Figure 1 is a flow chart of a method for preparing low-carbon hydrogen according to an embodiment of the present invention.

The following describes the method for preparing low-carbon hydrogen according to the present invention with reference to the relevant figures, wherein the same elements are represented by the same reference symbols.

Figure 1 is a flow chart of a method for preparing low-carbon hydrogen according to an embodiment of the present invention. As shown in Figure 1 , the method for preparing low-carbon hydrogen according to the present invention includes steps (a) to (c). The details of each step are described below.

First, step (a) involves drying the waste silicon sludge. The waste silicon sludge can originate from semiconductor manufacturing processes, such as, but not limited to, scrapped wafers, wafer dicing processes, wafer grinding, or waste silicon sludge generated in packaging and testing plants. In step (a), the waste silicon sludge generated from the semiconductor process is placed in a drying furnace for drying. After removing the moisture, dried waste silicon sludge with a moisture content of less than 10 wt% (weight percentage) is obtained.

Next, step (b) is performed: the dried waste silicon sludge is crushed and screened to obtain a waste silicon sludge powder having a weight percentage (wt%) of metallic silicon and silicon oxide (SiOx, x=1,2) ranging from 40 to 95%, of which metallic silicon accounts for between 5wt% and 40wt% of the total content of metallic silicon and silicon oxide. Here, waste silicon sludge is separated based on its metallic silicon content, screening out those with metallic silicon and silicon oxide contents between 40wt% and 95wt%, with metallic silicon (Si) accounting for 5wt% to 40wt% of the total. This is done to control the reaction temperature in the subsequent mixing reaction in step (c). By controlling the metallic silicon content, the chemical reaction in step (c) reaches the required reaction temperature.

Finally, step (c) is performed: the metallic silicon and silicon oxide from step (b) are mixed and reacted with an alkaline metal aqueous solution at a temperature controlled between 100°C and 150°C to produce hydrogen. In step (c), as previously described, the reaction temperature is controlled by adjusting the metallic silicon content in the metallic silicon and silicon oxide to maintain a temperature between 100°C and 150°C, thereby producing an aqueous sodium silicate solution. The higher the metallic silicon content in the silicon oxide, the higher the reaction temperature, i.e., closer to 150°C. In addition, in step (c), the reaction time for the mixed reaction of metallic silicon and silicon oxide with the alkaline metal aqueous solution may be greater than or equal to 2 hours to allow the metallic silicon and silicon oxide to fully react with the alkaline metal aqueous solution.

In some embodiments, the alkaline metal aqueous solution may be, for example, but not limited to, an aqueous sodium hydroxide solution (NaOH _(aq) ), and the concentration of the aqueous sodium hydroxide solution may be, for example, 45 wt%. In some embodiments, the metallic silicon and silicon oxide obtained in step (b) and a 45 wt% aqueous sodium hydroxide solution may be added to a reaction vessel. By controlling the metallic silicon content in the metallic silicon and silicon oxide between 5 wt% and 40 wt%, and utilizing the exothermic reaction of the metallic silicon and silicon oxide with the sodium hydroxide, the reaction temperature is controlled between 100°C and 150°C, and hydrogen ( _H2 ) is produced after 2 hours of reaction.

Here, the reaction formula of step (c) can be: Si + 2H ₂ O → SiO ₂ + 2H ₂ + heat (339KJ/mole) ... reaction formula (1)

SiO ₂ + 2NaOH → Na ₂ SiO ₃ + H ₂ O + heat (85KJ/mole)... Reaction equation (2).

In some applications, hydrogen can be used in fuel cells, for example. Because fuel cells utilize a chemical reaction between hydrogen and oxygen to generate electricity and water, they are not only completely pollution-free (the product is water), but also avoid the time-consuming charging of traditional batteries. They are currently one of the most promising new energy sources. If widely used in vehicles and other high-pollution power generation vehicles, they will significantly reduce air pollution and greenhouse gas emissions.

It is worth mentioning that in some subsequent applications, silicon dioxide (SiO ₂ ) can be obtained by reacting the sodium silicate aqueous solution in step (c) with sulfuric acid (H ₂ SO ₄ ), followed by solid-liquid separation and drying. The reaction time can range from 30 minutes to 2 hours, and the resulting silicon dioxide can have a purity greater than 94 wt %. The reaction equation is: Na ₂ SiO ₃ + H ₂ SO ₄ → Na ₂ SO ₄ + SiO ₂ + H ₂ O

The concentration of the aforementioned sulfuric acid can range between 30wt% and 80wt%, and the source of the sulfuric acid can also come from waste sulfuric acid generated during semiconductor manufacturing. For example, wafer foundries use high-purity sulfuric acid to clean the surface of silicon wafers during wafer manufacturing, primarily for cleaning silicon wafers after photoresist removal. The sulfuric acid used is added with hydrogen _peroxide ( _H2O2 ), making it a strong oxidizing agent. This oxidizes organic matter in the wafers into _CO2 and _H2O , generating waste sulfuric acid. Applying this waste sulfuric acid for this purpose can also achieve the goals of circular economy and resource reuse.

The following six examples demonstrate that the preparation method of the present invention can indeed produce hydrogen (see Table 1 below).

Example 1:

Weigh 3g of dried waste silicon mud powder (metallic silicon and silicon oxide content: 50.52wt%, with metallic silicon accounting for 9.36wt% of the total). Add 3.9g of 45% liquid alkali (sodium hydroxide aqueous solution) and 20g of water to the mixture in a reactor and stir uniformly. The reaction temperature naturally rises to 103.8°C due to the exothermic reaction. After 2 hours of reaction, 0.492 liters (L) of hydrogen are produced.

Example 2:

Weigh 3g of dried waste silica powder (metallic silicon and silicon oxide content: 58.07wt%, with metallic silicon accounting for 12.74wt% of the total). Add 3.9g of 45% liquid alkali and 20g of water to the mixture in a reactor and stir evenly. The reaction temperature naturally rises to 119.6°C due to the exothermic reaction. After 2 hours of reaction, 0.670L of hydrogen is produced.

Example 3:

Weigh 3g of dried waste silicon mud powder (metallic silicon and silicon oxide content: 76.39wt%, with metallic silicon accounting for 14.49wt% of the total). Add 3.9g of 45% liquid alkali and 20g of water to the mixture in a reactor and stir evenly. The reaction temperature will naturally rise to 135°C due to the exothermic reaction. After 2 hours of reaction, 0.762L of hydrogen will be produced.

Example 4:

Weigh 3g of dried waste silicon mud powder (metallic silicon and silicon oxide content: 75.80wt%, with metallic silicon accounting for 16.61wt% of the total). Add 3.9g of 45% liquid alkali and 20g of water to the mixture in a reactor and stir evenly. The reaction temperature naturally rises to 142°C due to the exothermic reaction. After 2 hours of reaction, 0.874L of hydrogen gas is produced.

Example 5:

Weigh 3g of dried waste silicon mud powder (metallic silicon and silicon oxide content: 76.92wt%, with metallic silicon accounting for 20.16wt% of the total). Add 3.9g of 45% liquid alkali and 20g of water to the mixture in a reactor and stir evenly. The reaction temperature will naturally rise to 145°C due to the exothermic reaction. After 2 hours of reaction, 1.060L of hydrogen will be produced.

Example 6:

Weigh 3g of dried waste silicon mud powder (metallic silicon and silicon oxide content: 82.16wt%, with metallic silicon accounting for 32.60wt% of the total). Add 3.9g of 45% liquid alkali and 20g of water to the mixture in a reactor and stir evenly. The reaction temperature naturally rises to 149.5°C due to the exothermic reaction. After 2 hours of reaction, 1.724L of hydrogen is produced.

The above six embodiments are summarized in Table 1 below.

As can be seen from the six aforementioned embodiments, the present invention does not generate hydrogen using the traditional equipment and process of carbon dioxide laser cracking of silicon powder. Instead, it utilizes waste silicon sludge and controls the metallic silicon content in metallic silicon and silicon oxide to produce an exothermic reaction with an aqueous alkaline metal (sodium hydroxide) solution to achieve the desired reaction temperature for hydrogen production. Since hydrogen is generated without requiring additional energy, it can achieve energy conservation and carbon reduction benefits. Furthermore, since the raw material used, waste silicon sludge, is a waste product generated during semiconductor manufacturing, the preparation method of the present invention can also meet green and environmentally friendly requirements.

In summary, the low-carbon hydrogen production method of the present invention utilizes waste silicon sludge and, through the exothermic reaction between metallic silicon and silicon oxide and an alkaline metal aqueous solution, generates hydrogen by utilizing the metallic silicon contained in the metal silicon and silicon oxide. This reaction temperature is then reached to produce the desired hydrogen. Compared to existing methods using carbon dioxide lasers to produce hydrogen, the present method requires no additional energy to produce hydrogen, thus achieving energy savings and carbon reduction. Furthermore, since the raw material used, waste silicon sludge, is a process waste generated during semiconductor manufacturing, the present method also meets green and environmentally friendly requirements.

The above description is for illustrative purposes only and is not intended to be limiting. Any equivalent modifications or variations that do not depart from the spirit and scope of this invention shall be included in the scope of the patent application attached hereto.

a,b,c: Steps

Claims (8)

A method for preparing low-carbon hydrogen comprises: Step (a): drying waste silicon sludge; Step (b): crushing and screening the dried waste silicon sludge, wherein the waste silicon sludge powder obtained after screening comprises between 40 wt% and 95 wt% of metallic silicon and silicon oxide (SiOx, x = 1, 2), wherein metallic silicon accounts for between 5 wt% and 40 wt% of the total metallic silicon and silicon oxide content; and Step (c): mixing and reacting the metallic silicon and silicon oxide obtained in step (b) with an alkaline metal aqueous solution, controlling the reaction temperature between 100°C and 150°C, to produce hydrogen. The preparation method of claim 1, wherein in step (a), the waste silicon sludge is generated in a semiconductor manufacturing process. The preparation method of claim 1, wherein in step (a), the water content of the dried waste silicon sludge is less than 10 wt%. The preparation method as described in claim 1, wherein in step (c), the alkaline metal aqueous solution is a sodium hydroxide aqueous solution. The preparation method as described in claim 4, wherein the concentration of the sodium hydroxide solution is 45 wt%. The preparation method of claim 1, wherein in step (c), the reaction temperature of the metallic silicon and silicon oxide with the alkaline metal aqueous solution is controlled to be maintained between 100°C and 150°C by controlling the metallic silicon content in the metallic silicon and silicon oxide. The preparation method of claim 6, wherein the higher the content of the metallic silicon, the closer the reaction temperature is to 150°C. The preparation method as described in claim 1, wherein, in step (c), the reaction time is greater than or equal to 2 hours.