Preparation method for recycling inorganic salt in printing and dyeing wastewater

Abstract

The present application relates to a preparation method for recycling inorganic salt in printing and dyeing wastewater and comprises the following process steps: S1, performing impurity removal, softening, COD removal and decoloration on reverse osmosis (RO) membrane concentrated water to obtain pretreated wastewater; S2, performing two-stage electrodialysis on the wastewater obtained in step S1: returning fresh water obtained in a first-stage electrodialysis desalination chamber to a front end of the RO process, and taking saline water obtained in a concentration chamber as raw water of a second-stage electrodialysis desalination chamber and a second-stage electrodialysis concentration chamber; and returning the fresh water obtained by the second-stage electrodialysis desalination chamber to the first-stage electrodialysis concentration chamber; and S3, dealkalizing the concentrated saline water obtained in the step S2 and then adjusting the pH value to obtain concentrated saline water capable of being reused for cloth dyeing in a printing and dyeing mill.

Claims

1. A preparation method for recycling inorganic salts in printing and dyeing wastewater, comprising the following process steps: step S1, wastewater pretreatment, comprising: step a1, impurity removal: treating RO concentrated water of a dyeing mill by column ultrafiltration to obtain ultrafiltered wastewater, wherein an ultrafiltration membrane used in the column ultrafiltration is a PVDF organic membrane with a pore size of 0.01-0.1 μm; step b1, softening: using chelating resin to soften the ultrafiltered wastewater obtained in the step a1 to obtain softened wastewater; and step c1, COD and chromaticity removal: treating with a spiral-wound ultrafiltration membrane the softened wastewater obtained in the step b1 to remove COD and chromaticity from the softened wastewater to obtain concentrated wastewater and pretreated wastewater, and further treating the concentrated wastewater so that the concentrated wastewater reaches the discharge standard, wherein a volume ratio of the concentrated water to influent water is 8 to 20%, Molecular Weight Cut Off of the spiral-wound ultrafiltration membrane is 1000-6000 Daltons, and an operating pressure is 0.7-1.2 MPa; step S2, inorganic salt concentration: performing two-stage electrodialysis on the pretreated wastewater in the step S1: returning fresh water obtained in a first-stage electrodialysis desalination chamber to a front end of the RO process, and taking saline water obtained in an electrodialysis concentration chamber as raw water of a second-stage electrodialysis desalination chamber and a second-stage electrodialysis concentration chamber; and returning the fresh water obtained by the second-stage electrodialysis desalination chamber to the first-stage electrodialysis concentration chamber, wherein the saline water obtained by the concentration chamber is concentrated saline water; and step S3, concentrated saline water recycling, comprising: step a3, adding 98% sulfuric acid to the concentrated saline water in the second-stage electrodialysis concentration chamber of the step S2 to dealkalize the concentrated saline water until the pH of the concentrated saline water is 1.2-3.5; step b3, adding 30% liquid caustic soda to the concentrated saline water after acid adjustment of the step a3 until the pH of the concentrated saline water is 8-9; and step c3, according to a dyeing requirement, adding sodium carbonate to the concentrated saline water after alkali adjustment of the step b3 to obtain concentrated saline water that can be used for cloth dyeing in the printing and dyeing mill, wherein the inorganic salts mainly comprise Na.sub.2SO.sub.4 and NaCl.

2. The preparation method for recycling inorganic salts in printing and dyeing wastewater according to claim 1, wherein the step S2 comprises the following process steps: step a2, introducing in the first-stage electrodialysis desalination chamber the pretreated wastewater obtained in the step S1; first introducing tap water in the concentration chamber; when the conductivity of the saline water in the electrodialysis concentration chamber reaches 35000-60000 μS/cm, returning the fresh water from the electrodialysis desalination chamber to the front end of the RO process; and transferring the saline water from the electrodialysis concentration chamber into the desalination chamber and concentration chamber of the second-stage electrodialysis; and step b2, when the conductivity of the saline water in the second-stage electrodialysis concentration chamber reaches 90,000-120,000 μS/cm, obtaining high-salt concentrated saline water in the concentration chamber in this case, and then returning the fresh water from the second-stage electrodialysis desalination chamber to the first-stage electrodialysis concentration chamber.

3. The preparation method for recycling inorganic salts in printing and dyeing wastewater according to claim 2, wherein in the step S2, a volume ratio of the pretreated wastewater introduced into the first-stage electrodialysis desalination chamber to the tap water or the second-stage electrodialysis fresh water introduced into the first-stage electrodialysis concentration chamber is (3-5):1; a volume ratio of the saline water introduced into the second-stage electrodialysis desalination chamber from the first-stage electrodialysis concentration chamber to the saline water introduced into the second-stage electrodialysis concentration chamber is (2.5-3.5):1.

4. The preparation method for recycling inorganic salts in printing and dyeing wastewater according to claim 1, wherein the RO concentrated water in the step a1 has main water quality indicators as follows: COD content does not exceed 500 mg/L, the chromaticity does not exceed 400 degrees, turbidity does not exceed 1 NTU, and conductivity is 8000-20000 μS/cm.

5. The preparation method for recycling inorganic salts in printing and dyeing wastewater according to claim 1, wherein the concentrated saline water obtained in the step S3 has COD content of not higher than 300 mg/L, the chromaticity of not higher than 100 degrees, the conductivity of not lower than 90000 μS/cm, and the alkalinity of not higher than 1500 mg/L.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGURE is a process flowchart of an embodiment of the present application.

DESCRIPTION OF THE EMBODIMENTS

(2) In order to enable those skilled in the art to understand the present application more clearly, the present application will be described in further detail below in conjunction with the examples, but it should be understood that the following examples are only preferred embodiments of the present application, and the scope of the present application is not limited thereto.

(3) Equipment and Material Sources

(4) Column ultrafiltration membrane, Tianjin Motech Co., Ltd.;

(5) Chelating resin, D851, Zhejiang Zhengguang Industrial Co., Ltd.;

(6) Spiral-wound ultrafiltration membrane: American GE (China) Company;

(7) Electrodialysis device: Hangzhou Lanran Environmental Technology Co., Ltd.;

(8) Sulfuric acid: purity 98%, Shaoxing Dingyao Chemical Materials Co., Ltd.;

(9) Liquid caustic soda: purity 30%, Zhejiang Zhongxing Chemical Reagent Co., Ltd.;

(10) Sodium carbonate: Hangzhou Longshan Chemical Co., Ltd.

(11) RO concentrated water: a printing and dyeing enterprise in Shaoxing City, its water quality parameters are shown in Table 1 below.

(12) TABLE-US-00001 TABLE 1 Main water quality parameters of RO concentrated water Hardness, based on Turbidity Conductivity COD CaCO.sub.3 Alkalinity Indicator (NTU) (μS/cm) Chromaticity (mg/L) (mg/L) (mg/L) Value 0.84 14650 315 480 232 1623

Example 1

(13) With reference to FIGURE, the present application specifically includes the following process steps: step S1, wastewater pretreatment: performing impurity removal, softening, COD removal and decoloration on reverse osmosis (RO) membrane concentrated water to obtain pretreated wastewater; step S2, inorganic salt concentration: performing two-stage electrodialysis on the wastewater pretreated in step S1: returning fresh water obtained in a first-stage electrodialysis desalination chamber to a front end of the RO process, and taking saline water obtained in a concentration chamber as raw water of a second-stage electrodialysis desalination chamber and a second-stage electrodialysis concentration chamber; and returning the fresh water obtained by the second-stage electrodialysis desalination chamber to the first-stage electrodialysis concentration chamber, wherein the saline water obtained by the concentration chamber is concentrated saline water; and step S3, concentrated saline water recycling: dealkalizing the concentrated saline water obtained in step S2 and then adjusting the pH to a proper value to obtain concentrated saline water capable of being reused for cloth dyeing in a printing and dyeing mill.

(14) Step S1 specifically includes the following process steps: step a1. impurity removal: treating RO concentrated water of the dyeing mill by column ultrafiltration to remove most of impurity particles and obtain ultrafiltered wastewater, wherein an ultrafiltration membrane used is a PVDF organic membrane with a pore size of 0.03 μm; step b1. softening: using chelating resin to soften the ultrafiltered wastewater obtained in step a1 to obtain softened wastewater; and step c1. COD and chromaticity removal: treating with a spiral-wound ultrafiltration membrane the softened wastewater obtained in step b1 to remove COD and chromaticity from the softened wastewater, and further treating the concentrated water treated with the spiral-wound ultrafiltration membrane so that the concentrated water reaches the discharge standard; and carrying out subsequent electrodialysis on water produced from the treatment with the spiral-wound ultrafiltration membrane, wherein a volume ratio of the concentrated water to influent water is 10%; the relative MWCO of the spiral-wound ultrafiltration membrane is 2000 Daltons; an operating pressure is 0.9 MPa.

(15) Step S2 specifically includes the following process steps: step a2. introducing in the first-stage electrodialysis desalination chamber the wastewater pretreated in step S1; first introducing tap water in the concentration chamber and then introducing second-stage electrodialysis fresh water in the later stage, wherein the volume ratio of the pretreated wastewater introduced into the first-stage electrodialysis desalination chamber to the tap water (or second-stage electrodialysis fresh water) introduced into the first-stage electrodialysis concentration chamber is 3.5:1; starting an electrodialysis device; when the conductivity of the saline water in the concentration chamber reaches 40000 μS/cm, returning the fresh water from the electrodialysis desalination chamber to the front end of the RO process; and transferring the saline water from the concentration chamber into the second-stage electrodialysis desalination chamber and the second-stage electrodialysis concentration chamber; and step b2. introducing the saline water from the first-stage electrodialysis concentration chamber in step a2 into both the second-stage electrodialysis concentration chamber and the second-stage electrodialysis desalination chamber, wherein the volume ratio of the saline water (from the first-stage electrodialysis concentration chamber) introduced into the second-stage electrodialysis desalination chamber to the saline water introduced into the second-stage electrodialysis concentration chamber is 3:1; when the conductivity of the saline water in the second-stage electrodialysis concentration chamber reaches 100,000 μS/cm, obtaining high-salt concentrated saline water in the concentration chamber in this case, and then returning the fresh water from the electrodialysis desalination chamber to the first-stage electrodialysis concentration chamber.

(16) Step S3 specifically includes the following process steps: step a3. adding 98% sulfuric acid to the concentrated saline water in the second-stage electrodialysis concentration chamber of step S2 to dealkalize the concentrated saline water until the pH of the concentrated saline water is 1.5; step b3. adding 30% liquid caustic soda (NaOH) to the concentrated saline water after acid adjustment of step a3 until the pH of the concentrated saline water is 8.5; and step c3. according to a dyeing requirement, adding an appropriate amount of sodium carbonate (Na.sub.2CO.sub.3) to the concentrated saline water after alkali adjustment of step b3 to obtain the concentrated saline water that can be used for cloth dyeing in the printing and dyeing mill.

Examples 2-13

(17) Examples 2 to 13 are identical to Example 1 except the difference in various process parameters. The various process parameters are shown in Table 2.

(18) TABLE-US-00002 TABLE 2 Process parameters of Examples Volume ratio of concentrated Conductivity water to influent of saline water water in Operating at the end ultrafiltration Relative pressure of the point of first- Pore size of with spiral- MWCO of the spiral-wound stage column wound spiral-wound ultrafiltration electrodialysis Process ultrafiltration ultrafiltration ultrafiltration membrane concentration Parameter membrane (μm) membrane (%) membrane (D) (MPa) (μS/cm) Example 1 0.03 10 2000 0.9 40000 Example 2 0.03 8 2000 1.1 40000 Example 3 0.03 20 2000 0.7 40000 Example 4 0.03 10 1000 1.2 40000 Example 5 0.03 10 6000 0.7 40000 Example 6 0.03 10 2000 0.9 35000 Example 7 0.03 10 2000 0.9 40000 Example 8 0.03 10 2000 0.9 50000 Example 9 0.03 10 2000 0.9 60000 Example 10 0.03 10 2000 0.9 40000 Example 11 0.03 10 2000 0.9 40000 Example 12 0.01 10 2000 0.9 40000 Example 13 0.1 10 2000 0.9 40000 Volume ratio of Volume ratio of water in the water in the first-stage second-stage electrodialysis electrodialysis End point of desalination Conductivity of desalination pH of chamber to saline water at chamber to concentrated water in the the end point of water in the saline water in first-stage second-stage second-stage the case of electrodialysis electrodialysis electrodialysis dealkalization Process concentration concentration concentration by addition of Parameter chamber (μS/cm) chamber acid Example 1 3.5:1 100000 3:1 1.5 Example 2 3.5:1 100000 3:1 1.5 Example 3 3.5:1 100000 3:1 1.5 Example 4 3.5:1 100000 3:1 1.5 Example 5 3.5:1 100000 3:1 1.5 Example 6 .sup. 3:1 95000 3:1 1.5 Example 7 3.5:1 90000 2.5:1.sup.  1.5 Example 8 .sup. 4:1 120000 3.5:1.sup.  1.5 Example 9 .sup. 5:1 120000 2.5:1.sup.  1.5 Example 10 3.5:1 100000 3:1 1.2 Example 11 3.5:1 100000 3:1 3.5 Example 12 3.5:1 100000 3:1 1.5 Example 13 3.5:1 100000 3:1 1.5

Comparative Example 1

(19) Comparative Example 1 differs from Example 1 in that the volume ratio of the concentrated water to the influent water in ultrafiltration with a spiral-wound ultrafiltration membrane is 25%.

Comparative Example 2

(20) Comparative Example 2 differs from Example 1 in that the MWCO of the spiral-wound ultrafiltration membrane is 10000 D.

Comparative Example 3

(21) Comparative Example 3 differs from Example 1 in that the printing and dyeing wastewater softened by the chelating resin is directly treated by first-stage electrodialysis.

Comparative Example 4

(22) Comparative Example 4 differs from Example 1 in that the volume ratio of water in the first-stage electrodialysis desalination chamber to water in the first-stage electrodialysis concentration chamber is 2:1.

Comparative Example 5

(23) Comparative Example 5 differs from Example 1 in that the volume ratio of water in the second-stage electrodialysis desalination chamber to water in the second-stage electrodialysis concentration chamber is 2:1.

Comparative Example 6

(24) Comparative Example 6 differs from Example 1 in that the end point of pH of concentrated saline water in the case of dealkalization by addition of acid is 4.

Comparative Example 7

(25) Comparative Example 7 differs from Example 1 in that the concentrated saline water is directly used for dyeing without being dealkalized.

(26) The process parameters of Comparative Examples 1 to 7 are shown in Table 3.

(27) TABLE-US-00003 TABLE 3 Process parameters of Comparative Examples Volume ratio of concentrated water to influent water Conductivity of in Operating saline water at Pore size of ultrafiltration Relative pressure of the the end point of column with spiral- MWCO of the spiral-wound first-stage ultrafiltration wound spiral-wound ultrafiltration electrodialysis Process membrane ultrafiltration ultrafiltration membrane concentration Parameter (μm) membrane (%) membrane (D) (MPa) (μS/cm) Comparative 0.03 25 2000 0.7 40000 Example 1 Comparative 0.03 10 10000  0.6 40000 Example 2 Comparative 0.03 / / / 40000 Example 3 Comparative 0.03 10 2000 0.9 25000 Example 4 Comparative 0.03 10 2000 0.9 40000 Example 5 Comparative 0.03 10 2000 0.9 40000 Example 6 Comparative 0.03 10 2000 0.9 40000 Example 7 Volume ratio Volume ratio of water in the of water in the first-stage second-stage electrodialysis Conductivity electrodialysis End point of desalination of saline water desalination pH of chamber to at the end chamber to concentrated water in the point of water in the saline water in first-stage second-stage second-stage the case of electrodialysis electrodialysis electrodialysis dealkalization Process concentration concentration concentration by addition of Parameter chamber (μS/cm) chamber acid Comparative 3.5:1 100000 3:1 1.5 Example 1 Comparative 3.5:1 100000 3:1 1.5 Example 2 Comparative 3.5:1 100000 3:1 1.5 Example 3 Comparative .sup. 2:1 70000 3:1 1.5 Example 4 Comparative 3.5:1 75000 2:1 1.5 Example 5 Comparative 3.5:1 100000 3:1 4 Example 6 Comparative 3.5:1 100000 3:1 / Example 7

(28) Test Method:

(29) DDS-11A conductivity meter was used to test the conductivity of water. Chromaticity was tested in accordance with the regulations in GB11903-1989-Determination of Chromaticity in Water Quality. COD was tested in accordance with the regulations in HJ-T 399-2007 Determination of Chemical Oxygen Demand in Water Quality. Alkalinity was tested in accordance with the regulations in GB/T15451-2006 Determination of Total Alkali and Phenolphthalein Alkalinity in Industrial Circulating Cooling Water. Color difference was determined by Datacolor 60 colorimeter. TDS was determined in accordance with GB/T 5750.4-2006 Standard test method for drinking water-Sensory Characteristics and Physical Indicators.

(30) Calculation Method of Recycling Rate of Inorganic Salts:

(31) In conjunction with FIGURE, in the whole process of the present application, except the concentrated water from the ultrafiltration process with the spiral-wound ultrafiltration membrane being discharged to the outside, no water is discharged to the outside in other process sections. Therefore, the recycling rate of inorganic salts in printing and dyeing wastewater can be calculated as follows:

(32) $\mathrm{the}\mathrm{recycling}\mathrm{rate}\mathrm{of}\mathrm{inorganic}\mathrm{salts}\left(\%\right)=\frac{\begin{array}{c}\mathrm{Volume}\mathrm{of}\mathrm{water}\mathrm{produced}\mathrm{by}\mathrm{spiral}-\\ \mathrm{wound}\mathrm{ultrafiltration}\mathrm{membrane}\left(L\right)\times \\ \mathrm{TDS}\mathrm{of}\mathrm{produced}\mathrm{water}\left(\mathrm{mg}/L\right)\end{array}}{\begin{array}{c}\mathrm{volume}\mathrm{of}\mathrm{influent}\mathrm{water}\mathrm{for}\mathrm{spiral}-\\ \mathrm{wound}\mathrm{ultrafiltration}\mathrm{membrane}\left(L\right)\times \\ \mathrm{TDS}\mathrm{of}\mathrm{influent}\mathrm{water}\left(\mathrm{mg}/L\right)\end{array}}$

(33) Table 4 shows the TDS values of the produced water and influent water in the ultrafiltration with the spiral-wound ultrafiltration membrane in the examples and the comparative examples and the recycling rates of inorganic salts calculated as above.

(34) TABLE-US-00004 TABLE 4 Recycling rates of inorganic salts Volume ratio of TDS of TDS of influent produced water produced water water in to influent in ultrafiltration ultrafiltration water in with spiral- with spiral- ultrafiltration wound wound with spiral- ultrafiltration ultrafiltration wound Recycling rate membrane membrane ultrafiltration of inorganic Example (mg/L) (mg/L) membrane salt Example 1 10.31 10.70 0.9 86.72 Example 2 10.30 10.71 0.92 88.48 Example 3 10.31 10.70 0.8 77.08 Example 4  9.81 10.72 0.9 82.36 Example 5 10.62 10.69 0.9 89.41 Example 6 10.29 10.70 0.9 86.55 Example 7 10.30 10.72 0.9 86.47 Example 8 10.31 10.72 0.9 86.56 Example 9 10.28 10.69 0.9 86.55 Example 10 10.32 10.71 0.9 86.72 Example 11 10.31 10.71 0.9 86.64 Example 12 10.29 10.70 0.9 86.55 Example 13 10.32 10.70 0.9 86.80 Comparative 10.32 10.71 0.75 72.27 Example 1 Comparative 10.70 10.71 0.9 89.92 Example 2 Comparative / / / 100 Example 3 Comparative 10.32 10.72 0.9 86.64 Example 4 Comparative 10.31 10.71 0.9 86.64 Example 5 Comparative 10.30 10.71 0.9 86.55 Example 6 Comparative 10.32 10.70 0.9 86.80 Example 7

(35) Table 5 shows various water quality indicators and dyeing color difference of concentrated saline water finally obtained in various examples and comparative examples.

(36) TABLE-US-00005 TABLE 5 Water quality indicators and dyeing color difference of concentrated saline water Dyeing Conductivity COD Alkalinity color Indicator (μS/cm) Chromaticity (mg/L) (mg/L) difference Remarks Raw water 14650 315 480 1623 / Example 1 112000 55 160 900 0.34 Dying is normal. Example 2 114000 70 210 950 0.62 Dying is normal. Example 3 111000 50 145 920 0.31 Dying is normal. Example 4 113000 45 120 980 0.28 Dying is normal. Example 5 110000 85 260 1050 0.78 Dying is normal. Example 6 106000 52 155 920 0.34 Dying is normal. Example 7 102000 53 158 880 0.32 Dying is normal. Example 8 131500 90 290 1200 0.81 Dying is normal. Example 9 131800 91 286 1180 0.80 Dying is normal. Example 10 116000 56 165 720 0.26 Dying is normal. Example 11 110000 55 162 1450 0.86 Dying is normal. Example 12 111000 54 162 910 0.34 Dying is normal. Example 13 113000 56 165 940 0.35 Dying is normal. Comparative 109000 50 155 860 0.32 Dying is normal. Example 1 Comparative 118000 115 350 1750 1.13 The color Example 2 difference is obvious. Comparative 121000 190 730 1900 2.45 The color Example 3 difference is obvious and the ion exchange membrane is fouled seriously. Comparative 79000 46 135 890 0.24 The salt content Example 4 of the concentrated saline water is low and additional salt needs to be added. Comparative 86000 48 140 930 0.29 The salt content Example 5 of the concentrated saline water is low and additional salt needs to be added. Comparative 113000 55 160 3600 1.89 The color Example 6 difference is obvious. Comparative 113000 55 160 22800 / Concentrated Example 7 saline water forms a buffered solution and cannot be used for dyeing.

(37) The present application provides a preparation method for recycling inorganic salts in printing and dyeing wastewater. The following aspects are mainly considered in evaluation of the implementation effect. First, dyeing color difference is considered and the dyeing effect should conform to the requirements of dyeing color difference ≤1 in GB/T 21898-2008 Textile Color Representation Method. Second, the recycling rate of inorganic salts should be as high as possible. Third, the main pollutant indicators in the printing and dyeing wastewater should be kept as low as possible to ensure the stable operation of each process section. Fourth, the concentrated saline water should have a certain salt content, and when the water is reused for cloth dyeing, the problem that additional solid salt is required due to the low concentration of saline water can be prevented. Fifth, the operating cost should be considered, and the energy consumption of the system should be as low as possible.

(38) Considering the above factors comprehensively, referring to Table 4 and Table 5, the dyeing color differences of Examples 1 to 13 all meet the requirements, and the recycling rates of inorganic salts are all above 77%, achieving the expected effect. From the perspective of inorganic salt recycling rate, Example 2 and Example 5 have higher recycling rate, but in Example 2, in order to reach the condition that the volume ratio of concentrated water to influent water in ultrafiltration with the spiral-wound ultrafiltration membrane is 8%, it is required to improve the operating pressure of the pump, the operating energy consumption is relatively increased, and the fouling of the spiral-wound ultrafiltration membrane is aggravated at the same time. in Example 5, due to the use of the spiral-wound ultrafiltration membrane with a relatively high MWCO, the concentration of the main pollutants in the produced water is increased to some degree, increasing the working pressure of the back-end electrodialysis. To sum up, the process parameters of Example 1 are preferred.

(39) For Comparative Example 1, although the dyeing color difference meets the requirements, its recycling rate of inorganic salts is relatively low, only 72.27%. Comparative Examples 2 and 3 have obvious dyeing color difference and do not meet the dyeing requirements. In particular, in Comparative Example 3, since the link of ultrafiltration with a spiral-wound ultrafiltration membrane is omitted, the back-end ion exchange membrane is rapidly fouled, and needs to be cleaned frequently, and the process cannot run stably. For Comparative Examples 4 and 5, although the dyeing effect meets the requirements, the content of inorganic salts in the concentrated saline water is relatively low, and additional solid inorganic salts need to be added, which increases the operation steps and costs. In Comparative Example 6, the end point of pH of concentrated saline water in the case of dealkalization by addition of acid is 4, the concentrated saline water is not sufficiently dealkalized, and the dyeing effect does not meet the requirements. In Comparative Example 7, the step of dealkalization is omitted, the alkalinity is as high as 22800 mg/L, and the concentrated saline water forms a buffer solution. In pH adjustment by addition of sodium carbonate, the saline water could not meet the requirements of the dyeing mill and could not be used for dyeing.

(40) The specific embodiments are merely an explanation of the present application and are not intended to limit the present application. Those skilled in the art may, after reading the description, make modifications without any creative contribution to the embodiments as needed. Any of the modifications within the scope of claims of the present application shall be protected by the Patent Law.