Process of Manufacturing Adsorbent for Removing Siloxane Compound

Abstract

A method of preparing an adsorbent for removing siloxane, in which the method includes mixing a silica particle and an OH compound to bond OH functional groups to the silica particle; measuring percentage by weight of OH bonded to the silica particle; calculating a bonding number and spacing of the OH functional groups by the percentage by weight of OH bonded to the silica particle; performing an evaluation of an adsorption rate and desorption rate of the silica particle to which the OH functional groups, of which the bonding number and spacing are calculated, are bonded; and adjusting the bonding number of the OH functional groups in the silica particle according to the evaluation.

Claims

1. A method of preparing an adsorbent for removing siloxane, the method comprising: mixing a silica particle and an OH compound to attach OH functional groups to the silica particle; measuring percentage by weight of OH bonded to the silica particle; calculating a bonding number and spacing of the OH functional groups by the percentage by weight of OH bonded to the silica particle; performing an evaluation of an adsorption rate and desorption rate of the silica particle to which the OH functional groups, of which the bonding number and spacing is calculated, are bonded; and adjusting the bonding number of the OH functional groups on the silica particle according to the evaluation.

2. The method of claim 1, wherein the percentage by weight of OH bonded to the silica particle is measured via thermogravimetric analysis (TGA).

3. The method of claim 1, wherein the bonding number and spacing of the OH functional groups are calculated by $\mathrm{OH}/{\mathrm{nm}}^2=a\frac{{\left(\mathrm{OH}/{\mathrm{nm}}^2\right)}_{T.Math..Math.2}S.Math..Math.S.Math..Math.A{\mathrm{wt}}_{T.Math..Math.2}+\left[\frac{\left({\mathrm{wt}}_{T.Math..Math.1}-{\mathrm{wt}}_{T.Math..Math.2}\right)}{\frac{M.Math..Math.W_{H.Math..Math.2.Math..Math.O}}{\mathrm{NA}}}2\right]}{S.Math..Math.S.Math..Math.A{\mathrm{wt}}_{T.Math..Math.1}},$ wherein nm is a unit of area, SSA is a specific surface area, wt.sub.T1 is the weight reduction from room temperature to 120 C. in Step 1 on thermogravimetric analysis (TGA), wt.sub.T2 is the weight reduction from 120 C. to 800 C. in Step 2 on TGA, NA is Avogadro's constant, MW.sub.H2O is a molecular weight of H.sub.2O, and a is a calibration constant derived from experiment or experience.

4. An adsorbent to remove siloxane, the adsorbent comprising: a silica particle; and 5 OH groups to 10 OH groups bonded to the silica particle, wherein an adsorption rate of the adsorbent is 99% or more at an adsorption temperature of 25 C. to 50 C., and a desorption rate of the adsorbent is 99% or more at a desorption temperature of 120 C. to 150 C. for a siloxane compound.

5. The adsorbent of claim 4, wherein the OH bonded to the silica particle has a spacing of 2 to 5 .

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The patent or application contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the U.S. Patent and Trademark Office upon request and payment of the necessary fee.

[0018] The above and other aspects, features and other advantages of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0019] FIG. 1 illustrates a process of producing an adsorbent according to the present disclosure;

[0020] FIG. 2 illustrates results of the thermogravimetric analysis (TGA) for an adsorbent according to the present disclosure;

[0021] FIG. 3 illustrates the siloxane removal effect according to the number of OH groups of an adsorbent according to the present disclosure; and

[0022] FIG. 4 illustrates the siloxane desorption effect according to the number of OH groups of an adsorbent according to the present disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0023] Hereinafter, the technical configuration of the method of preparing an adsorbent for removing siloxane according to the present disclosure will be described with reference to the accompanying drawings.

[0024] It will be understood that the terms such as include, have, or comprise in this specification, specify the presence of stated features, numbers, steps, components, parts, or combinations thereof, but do not preclude the possibility of presence or addition of one or more other features, numbers, steps, operations, elements, components, parts, or combinations thereof.

[0025] Further, unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meanings as those generally understood by those with ordinary knowledge in the field of the art to which the present disclosure belongs. Such terms as those defined in generally used dictionaries are to be interpreted as having meanings equivalent to the contextual meanings in the relevant field of art and are not to be interpreted as having ideal or excessively formal meanings unless clearly defined as having such meanings in the present application.

[0026] The method of preparing an adsorbent for removing siloxane according to the present disclosure is essentially configured to include the steps of: 1) mixing a silica particle and an OH compound to attach OH functional groups to the silica particle; 2) measuring percentage by weight of OH groups bonded to the silica particle; 3) calculating the bonding number and spacing of the OH functional groups by the percentage by weight of OH groups bonded to the silica particle; 4) performing an evaluation of an adsorption rate and desorption rate of the silica particle to which the OH functional groups, of which the bonding number and spacing is calculated, are bonded; and 5) adjusting the bonding number of the OH functional groups in the silica particle according to the evaluation of step 4.

[0027] As described above, in the present disclosure, the silica adsorbent is used in order to remove the siloxane compound, and the adsorbent is configured in a form in which a hydroxyl group is introduced onto the surface of the silica particle. In this connection, the silica adsorbent may optimize the number of hydroxyl groups and spacing between the hydroxyl groups, introduced onto the surface of the silica particle so as to increase the adsorption efficiency of the siloxane compound and to easily control adsorption and desorption of the siloxane compound according to temperature changes.

[0028] In order to attach the OH functional groups to the silica particle in step 1 of the method of preparing the adsorbent for removing siloxane according to the present disclosure, it is easy to use a hydrothermal synthesis method using the silica particle and sodium hydroxide as reactants in terms of the number and spacing of the OH functional groups introduced onto the surface of the silica particle. The silica particle is generally used in the field of adsorbents and preferably has a particle diameter of 0.5 mm to 5 mm. When the particle diameter is less than 0.5 mm, the pressure loss may occur. When the particle diameter exceeds 5 mm, the problem of passing through the adsorption bed may occur. It is preferable to use 0.5 moles to 5 moles of sodium hydroxide per 1 mole of the silica particle.

[0029] FIG. 1 illustrates a process for preparing the adsorbent for removing siloxane by introducing the OH functional group onto the surface of the silica particle in step 1 (in the method of preparing the adsorbent for removing siloxane according to the present disclosure), in which the silica particle is dispersed in an aqueous NaOH solution, thereby preparing the OH functional group-introduced silica adsorbent through hydrothermal synthesis. With a specific description of the process, NaOH is dissolved in distilled water to prepare an aqueous solution. Then, the silica particle is immersed in the solution, stirred at 120 C. to 130 C. for 12 hours under a pressure of 3 atm, and dried at 100 C. for 4 hours, thereby preparing the OH functionalized silica adsorbent.

Example 1

[0030] After the SiO.sub.2 powder was immersed in 1 L of a 3M NaOH solution and stirred for 2 hours, the mixture was stirred at 120 C. to 130 C. under a pressure of 3 atm for 12 hours. Thereafter, the mixture was dried at 100 C. for 4 hours to prepare SiO.sub.2-OH particles.

[0031] For the performance of the silica adsorbent for removing siloxane prepared through the preparing process as illustrated in FIG. 1 as described above, the adsorption and desorption performance are affected depending on how much OH functional groups are attached to the silica adsorbent. Therefore, the step 2 of measuring the percentage by weight of the OH functional groups bonded to the silica particle and the step 3 of calculating the number and spacing of the OH functional groups through the percentage by weight of the OH groups bonded to the silica particle are important in the method of producing the adsorbent for removing siloxane according to the present invention. It is important to accurately measure the amount of OH functional groups bound to the adsorbent, as described above. When it is measured, the optimum OH functional groups may be adjusted to be available at the operating temperature of the system for removing siloxane. For this purpose, the silica adsorbent for removing siloxane, according to the present disclosure, prepared through the preparing process as illustrated in FIG. 1 may be analyzed through a thermogravimetric analysis (TGA) to measure the bonding number and spacing of OH functional groups introduced onto the silica particle and to calculate the optimal value at specific temperature. In the TGA used in the present disclosure, the weighing scale is combined with the heating furnace, and the sample is put in the furnace and is heated. While the sample is heated, the change in the weight of the sample per hour is measured. The TGA results are expressed in a normalized weight. In order to calculate the number of OH functional groups from the weight percentage per unit nm area, a calculation formula such as the formula 1 is required. In the formula 1, the number of OH groups is converted with respect to the amount of silanol groups. SSA refers to a specific surface area, wt.sub.T1 is the weight reduction from room temperature to 120 C. in Step 1 on the TGA analysis, wt.sub.T2 is the weight reduction from 120 C. to 800 C. in Step 2 on the TGA analysis, NA refers to Avogadro's constant, and MW.sub.H2O refers to the molecular weight of H.sub.2O, and a is a calibration factor derived from experiment or experience.

[00002]$\mathrm{OH}/{\mathrm{nm}}^2=a\frac{{\left(\mathrm{OH}/{\mathrm{nm}}^2\right)}_{T.Math..Math.2}S.Math..Math.S.Math..Math.A{\mathrm{wt}}_{T.Math..Math.2}+\left[\frac{\left({\mathrm{wt}}_{T.Math..Math.1}-{\mathrm{wt}}_{T.Math..Math.2}\right)}{\frac{M.Math..Math.W_{H.Math..Math.2.Math..Math.O}}{\mathrm{NA}}}2\right]}{S.Math..Math.S.Math..Math.A{\mathrm{wt}}_{T.Math..Math.1}}$

Example 2

[0032] SiO.sub.2-OH particles were prepared using 0 moles to 5 moles of NaOH according to Example 1, and TGA was performed on the SiO.sub.2-OH particles. Here, TGA was carried out under a condition of a temperature range of from room temperature to 800 C. for a heating time of 0 minutes to 60 minutes. TGA was performed on SiO.sub.2 without OH bonding and OH-bound SiO.sub.2-OH. FIG. 2 illustrates TGA results for SiO.sub.2 without OH bonding and OH-bound SiO.sub.2-OH according to the present disclosure. SiO.sub.2 without OH bonding showed 98% by weight at a heating time of 55 minutes, while SiO.sub.2-OH showed 98, 94, 89, and 85% by weight, respectively, in the same heating time of 55 minutes depending on 0.5 moles, 1 mole, 2 moles, and 3 moles or more of NaOH. At the heating time of 55 minutes, 98, 94, 89, and 85% by weight, respectively refer to the number of OH functional groups, 02, 07, 12, and 16 according to the formula 1.

[0033] When the OH functional groups are bound to the silica particles as described above, the weights of the OH functional groups bound to the silica surface are measured by TGA, the bonding number and distance between the OH functional groups may be calculated according to the formula 1, and step 4 is required to evaluate the adsorption rate and the desorption rate of the silica particles to which the OH functional groups are bound, in which the bonding number and spacing of OH functional groups are calculated. Such process may optimize the number of functional group required for adsorption and desorption at the optimum operating temperature.

[0034] In this regard, it is generally advantageous for the silica adsorbent to adsorb siloxane compounds at 25 C. to 60 C., and to desorb the siloxane compounds at 100 C. to 150 C. If possible, it is important to configure the bonding number and distance of OH functional groups, which are capable of adsorption and desorption in a range of the normal temperature of the biogas production system. In the present disclosure, the number and percentage by weight of OH functional groups and the amount of siloxane adsorbed according to the number and distance were evaluated at an adsorption temperature of 25 C. in order to obtain the optimum values as described above.

Example 3

[0035] Adsorption capacities were evaluated at 25 C. for SiO.sub.2 and SiO.sub.2-OH, in which the number of OH groups is 10 to 16 at heating time of 55 minutes in TGA. The adsorption capacity was measured with a weight of 1 g of the adsorbent using a reaction tube with a flow rate of 100 ml/min for a siloxane compound, decamethylcyclopentasiloxane (D5).

[0036] FIG. 3 shows the effect of removing the siloxane depending on the number of OH groups of the adsorbent according to the present disclosure. As a result of evaluation of adsorption amount in Example 3, the adsorption amount at 25 C. to 60 C. was optimized at 10 OH/nm.sup.2 to 16 OH/nm or more of the number of OH groups. In order to evaluate the desorption performance at the adsorption performance as described above, desorption performance was evaluated at 6 to 12 of the number of OH groups at a temperature of 120 C. The desorption performance was evaluated by desorbing and regenerating the siloxane and by reabsorbing the siloxane immediately after desorption while blowing nitrogen gas at a temperature of 120 C. As a result of the evaluation, the regeneration (desorption) was shown to be excellent at a desorption temperature of 120 C. to 150 C. and the number of OH groups of 6 OH/nm.sup.2 to 11 OH/nm.sup.2 as illustrated in FIG. 4, in which the regeneration (desorption) according to the number of OH groups of the adsorbent according to the present disclosure is shown.

[0037] When it is required to adjust the bonding number of OH functional groups to the silica particles according to the evaluation of step 4, the bonding number of OH functional groups which are bonded to the silica particles can be adjusted by mixing the silica particles and the OH compound so that the OH functional groups are attached to the silica particles as the step 1.

[0038] Although, as described above, the present disclosure has been described with reference to embodiments, it will be understood that various changes and modifications may be made by those skilled in the art. These changes and modifications may belong in the scope of the present disclosure as long as those do not depart from the scope of the technical concept provided by the present disclosure. Accordingly, the scope of the present disclosure should be determined by the following claims.