MFI type molecular sieve / PDMS composite membrane as well as preparation method and application thereof

Abstract

The invention discloses an MFI type molecular sieve / PDMS composite membrane as well as a preparation method and application thereof, and relates to the technical field of pervaporation membranes. The method comprises the following steps: step 1, preparation of an MFI molecular sieve seed crystal layer: firstly, soaking a pretreated carrier in a poly (diallyldimethylammonium chloride) solution, heating, taking out, airing, coating the carrier with an MFI molecular sieve seed crystal, and drying to obtain a carrier with a flat and uniform seed crystal layer; by introducing the PDMS membrane prepared by the invention, the hydrophobicity of the surface of the whole composite membrane can be enhanced, and meanwhile, the possible defects of a molecular sieve membrane are made up, so that the separation selectivity of the membrane is improved to a certain extent; in the pervaporation process, the PDMS membrane part in the composite membrane can effectively reduce the contact between a raw material solution and the surface of the MFI molecular sieve membrane, so that the reaction between silicon hydroxyl and raw materials is reduced, and the stability of the membrane is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of pervaporation membranes, and in particular relates to an MFI type molecular sieve / PDMS composite membrane and a preparation method and application thereof. Background Art

[0002] As a green alternative to fossil fuels, bioethanol has the advantages of being clean, efficient and renewable. Its use can reduce greenhouse gas emissions and is free of nitrogen oxides and sulfur oxides, which is of great significance for reducing air pollution and inhibiting the "greenhouse effect". Currently, it is mainly prepared by fermenting grains, wood fiber biomass, etc. In this process, the increase in bioethanol concentration will inhibit the production process and reduce production efficiency. Therefore, distillation is generally used to separate low-concentration ethanol in the fermentation liquid, but its high energy consumption and low efficiency make it unable to meet the current requirements for sustainable development of chemical production. Pervaporation membrane separation is a rapidly developing method in recent years. Pervaporation is an emerging separation technology. Compared with traditional separation processes, it has significant advantages such as low energy consumption, environmental protection, and mild operating conditions. It has great potential in recovering ethanol from dilute aqueous solutions or fermentation broths and has been widely studied. The preparation of high-quality membranes is the development direction of pervaporation technology. Currently, polydimethylsiloxane (PDMS) is the most commonly used hydrophobic membrane material in the pervaporation process, especially in the separation of low-concentration ethanol and water. It has good hydrophobicity, low permeation resistance and good stability. However, the separation factor of pure PDMS membrane is low, which limits its further application and development in industrial production.

[0003] MFI zeolite molecular sieve has two intersecting pore systems with a pore size of 0.55nm; the all-silicon MFI molecular sieve alcohol-philic membrane is composed of silicon atoms and oxygen atoms, has good organic matter preferential adsorption and efficient separation selectivity, is suitable for ethanol concentration and recovery, and has broad application prospects in the field of pervaporation separation of low-concentration fuel ethanol; Sano et al. applied all-silicon MFI molecular sieve membrane to pervaporation separation of low-concentration ethanol / water in 1994, and achieved good separation effect, which has set off a wave of preparation of high-performance pervaporation membrane materials; Chen et al. used silica ceramic tubes as carriers and adopted solution filling method to prepare silicalite-1 molecular sieve membrane with high separation performance and repeatability. Although the separation selectivity of the membrane for ethanol and water is improved, the flux is low; Wang Jinqu et al. introduced ethyltriethoxysilane (ETES) during the preparation of the synthetic solution, and through the promotion of ETES on the crystal growth of the silica molecular sieve membrane, a dense and continuous silicalite-1 membrane with good pervaporation performance was obtained on the support of a large-pore alumina tube carrier; Gu Xuehong et al. used the secondary growth method and fluoride salt as a mineralizer to successfully prepare the MFI zeolite molecular sieve membrane under neutral synthesis conditions, which showed good stability in the pervaporation removal of ethanol; the current research on MFI molecular sieve membranes has made certain progress, but the weak hydrophobicity and the formation of surface defects make it difficult to further improve its separation performance. More importantly, in the process of ethanol-water separation, the flux and separation factor of the membrane will continue to decrease with the operating time and eventually lose its separation ability, and the stability is poor, which cannot meet the requirements of industrial applications.

[0004] In summary, in order to overcome the shortcomings of MFI molecular sieve membrane and give full play to the advantages of PDMS membrane, MFI molecular sieve / PDMS composite membrane can be developed; the introduction of PDMS membrane can enhance the hydrophobicity of the surface, compensate for the possible defects of the molecular sieve membrane, and effectively reduce the contact between alcohol-water solution and the membrane surface, thereby improving the stability of the membrane.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art, provide an MFI type molecular sieve / PDMS composite membrane and a preparation method and application thereof, and solve the problems raised in the above background technology.

[0007] In order to solve the above technical problems, the basic concept of the technical solution adopted by the present invention is:

[0008] A method for preparing an MFI type molecular sieve / PDMS composite membrane comprises the following steps:

[0009] Step 1: Preparation of MFI molecular sieve seed layer: first, immerse the pretreated carrier in a polydiallyldimethylammonium chloride solution, heat it, take it out and dry it, apply the MFI molecular sieve seed on the carrier, and dry it to obtain a carrier with a flat and uniform seed layer; wherein the concentration of the polydiallyldimethylammonium chloride solution is 0.1-1%, the heating temperature is 60°C, and the heating time is 1h; the particle size of the MFI molecular sieve seed particles is 100-600nm, the carrier shape is tubular, the material is alumina, the average pore size is about 1-3μm, the porosity is 30-40%, the outer diameter of the tube is 8-20mm, and the tube wall thickness is 1-3mm;

[0010] Step 2: Synthesis of MFI molecular sieve membrane: silicon source, template and deionized water are mixed, stirred to obtain a clarified sol, and then both ends of the coated crystal carrier are sealed and placed in a polytetrafluoroethylene liner, the clarified sol is poured in, and the membrane is placed in a hydrothermal reactor for crystallization. After the reaction is completed, the membrane is washed and dried, and then calcined to obtain an MFI molecular sieve membrane; wherein the crystallization temperature is 175°C, the crystallization time is 4-12h, the calcination temperature is 500°C, the calcination time is 12h, the heating and cooling rate is 0.5°C / min, and the molar ratio of the precursor solution is: ethyl orthosilicate / tetrapropylammonium hydroxide / water = 1 / 0.05-0.32 / 100-165;

[0011] Step 3: Preparation of PDMS casting solution: dissolving hydroxyl-terminated PDMS in n-heptane, stirring to fully disperse and mix, then sequentially adding a crosslinking agent and a catalyst, stirring evenly to obtain a PDMS casting solution; wherein, the amount of PDMS added is 1-10% of the mass of the solvent, the crosslinking agent is ethyl orthosilicate, the catalyst is dibutyltin dilaurate, and the amounts of the crosslinking agent and the catalyst added are 5-30% and 0.5-5% of the mass of PDMS, respectively; the viscosity of PDMS is between 32-1000 mPa·s;

[0012] Step 4: Preparation of MFI molecular sieve / PDMS composite membrane: After the MFI molecular sieve membrane is vertically immersed in the PDMS casting solution, it is taken out at a uniform speed, placed at room temperature to evaporate the solvent and initially solidify, and then completely cross-linked under vacuum drying to prepare the MFI molecular sieve / PDMS composite membrane; wherein, the vacuum drying temperature is 60-100°C, the time is 5-12h, the MFI molecular sieve membrane is vertically immersed in the PDMS casting solution for 60s, and the uniform withdrawal rate is 0.5-5cm / min.

[0013] An MFI type molecular sieve / PDMS composite membrane is prepared by any one of the above preparation methods.

[0014] An application of an MFI molecular sieve / PDMS composite membrane is used to improve membrane separation performance and separate actual fermentation broth.

[0015] After adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art. Of course, any product implementing the present invention does not necessarily need to achieve all the advantages described below at the same time:

[0016] The introduction of the PDMS membrane prepared by the present invention can enhance the hydrophobicity of the entire composite membrane surface, and at the same time make up for the possible defects of the molecular sieve membrane, so that the separation selectivity of the membrane is improved to a certain extent; in the pervaporation process, the PDMS membrane part in the composite membrane can effectively reduce the contact between the raw material liquid and the surface of the MFI molecular sieve membrane, thereby reducing the reaction of the silanol group with the raw material and improving the stability of the membrane; the MFI molecular sieve / PDMS composite membrane prepared by the present invention has a good separation effect on 5-10% ethanol water, and the separation stability is effectively improved. The PDMS membrane layer also provides a certain anti-pollution performance for separating actual fermentation liquid. Therefore, the design of the composite membrane provides theoretical guidance for improving the membrane separation performance and separating the industrial application of actual fermentation liquid; the preparation method of the present invention is simple, the reaction conditions are mild, the raw materials are cheap and easy to obtain, and it is conducive to large-scale production.

[0017] The specific implementation modes of the present invention are further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings described below are only some embodiments. For those skilled in the art, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0019] Figure 1 Surface and cross-sectional SEM images of the MFI molecular sieve / PDMS composite membrane prepared in Example 1 of the present invention.

[0020] Figure 2 Surface and cross-sectional SEM images of the MFI molecular sieve membrane prepared in Comparative Example 1 of the present invention.

[0021] Figure 3 The surface contact angle test results of the MFI molecular sieve membrane and the composite membrane prepared in Comparative Example 1 and Example 1 are shown.

[0022] Figure 4 The pervaporation stability test results of the composite membrane and the MFI molecular sieve membrane prepared in Example 1 of the present invention and Comparative Example 1 are shown.

[0023] It should be noted that these drawings and textual descriptions are not intended to limit the conceptual scope of the present invention in any way, but are intended to illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0024] The present invention will now be described in further detail with reference to the accompanying drawings.

[0025] See also Figure 1-4 As shown, in this embodiment, a method for preparing an MFI type molecular sieve / PDMS composite membrane is provided, comprising the following steps:

[0026] Step 1: Preparation of MFI molecular sieve seed layer: first, immerse the pretreated carrier in a polydiallyldimethylammonium chloride solution, heat it, take it out and dry it, apply the MFI molecular sieve seed on the carrier, and dry it to obtain a carrier with a flat and uniform seed layer; wherein the concentration of the polydiallyldimethylammonium chloride solution is 0.1-1%, the heating temperature is 60°C, and the heating time is 1h; the particle size of the MFI molecular sieve seed particles is 100-600nm, the carrier shape is tubular, the material is alumina, the average pore size is about 1-3μm, the porosity is 30-40%, the outer diameter of the tube is 8-20mm, and the tube wall thickness is 1-3mm;

[0027] Step 2: Synthesis of MFI molecular sieve membrane: silicon source, template and deionized water are mixed, stirred to obtain a clarified sol, and then both ends of the coated crystal carrier are sealed and placed in a polytetrafluoroethylene liner, the clarified sol is poured in, and the membrane is placed in a hydrothermal reactor for crystallization. After the reaction is completed, the membrane is washed and dried, and then calcined to obtain an MFI molecular sieve membrane; wherein the crystallization temperature is 175°C, the crystallization time is 4-12h, the calcination temperature is 500°C, the calcination time is 12h, the heating and cooling rate is 0.5°C / min, and the molar ratio of the precursor solution is: ethyl orthosilicate / tetrapropylammonium hydroxide / water = 1 / 0.05-0.32 / 100-165;

[0028] Step 3: Preparation of PDMS casting solution: dissolving hydroxyl-terminated PDMS in n-heptane, stirring to fully disperse and mix, then sequentially adding a crosslinking agent and a catalyst, stirring evenly to obtain a PDMS casting solution; wherein, the amount of PDMS added is 1-10% of the mass of the solvent, the crosslinking agent is ethyl orthosilicate, the catalyst is dibutyltin dilaurate, and the amounts of the crosslinking agent and the catalyst added are 5-30% and 0.5-5% of the mass of PDMS, respectively; the viscosity of PDMS is between 32-1000 mPa·s;

[0029] Step 4: Preparation of MFI molecular sieve / PDMS composite membrane: After the MFI molecular sieve membrane is vertically immersed in the PDMS casting solution, it is taken out at a uniform speed, placed at room temperature to evaporate the solvent and initially solidify, and then completely cross-linked under vacuum drying to prepare the MFI molecular sieve / PDMS composite membrane; wherein, the vacuum drying temperature is 60-100°C, the time is 5-12h, the MFI molecular sieve membrane is vertically immersed in the PDMS casting solution for 60s, and the uniform withdrawal rate is 0.5-5cm / min.

[0030] An MFI type molecular sieve / PDMS composite membrane is prepared by any one of the above preparation methods.

[0031] An application of an MFI molecular sieve / PDMS composite membrane is used to improve membrane separation performance and separate actual fermentation broth.

[0032] The tubular alumina carriers used in the embodiments of the present invention and the comparative examples are all pretreated as follows: first, they are polished with 800# coarse sandpaper, and then finely polished with 1500# sandpaper until the carrier surface is smooth, and then ultrasonically cleaned and soaked in 1% hydrochloric acid solution and 1% sodium hydroxide solution in turn, and then washed with deionized water until neutral, dried at 80°C and calcined at 600°C for 6h, and finally both ends of the carrier are sealed.

[0033] Embodiment 1:

[0034] (1) Preparation of MFI molecular sieve seed layer: First, the pretreated carrier was immersed in a polydiallyldimethylammonium chloride solution with a mass concentration of 0.7%, heated at 60°C for 1 hour, and then taken out to dry. 0.028g of MFI molecular sieve seed was coated on the carrier, and after drying, a carrier with a flat and uniform seed layer was obtained.

[0035] (2) Synthesis of MFI molecular sieve membrane: TEOS / TPAOH / H2O=1 / 0.13 / 165 in molar ratio were mixed, and a clear sol was obtained after stirring at room temperature for several hours. The coated crystal carrier prepared in step (1) was placed in a polytetrafluoroethylene liner, and the sol was poured in. The crystallization was carried out at 175°C in a hydrothermal reactor for 9 hours. After the reaction, the membrane was washed and dried. Then, the membrane was calcined at 500°C for 12 hours, and the heating and cooling rate was 0.5°C / min to obtain an MFI molecular sieve membrane.

[0036] (3) Preparation of PDMS casting solution: 2.5 g of hydroxyl-terminated PDMS with a viscosity of 1000 mPa·s was dissolved in 25 g of n-heptane and stirred to fully disperse and mix. Then, 0.2 g of tetraethyl orthosilicate and 0.1 g of dibutyltin dilaurate were added in sequence and stirred evenly to obtain a PDMS casting solution.

[0037] (4) Preparation of MFI molecular sieve / PDMS composite membrane: The MFI molecular sieve membrane synthesized in step (2) was vertically immersed in the PDMS membrane solution prepared in step (3) for 60 seconds, then taken out at a uniform speed of 5 cm / min, placed at room temperature to evaporate the solvent and initially solidify, and then vacuum dried at 90°C for 12 hours to completely cross-link it, thereby preparing an MFI molecular sieve / PDMS composite membrane.

[0038] The prepared composite membrane was used in a low-concentration ethanol / water pervaporation separation test with an operating temperature of 60°C, an ethanol concentration of 5wt.%, a separation factor of 50, and a flux of 0.47kg / m2·h.

[0039] Embodiment 2:

[0040] The operating steps adopted are the same as those in Example 1, except that the molar ratio of the components in the synthesis sol of the MFI molecular sieve membrane in step (2) is TEOS / TPAOH / DDI=1 / 0.05 / 165. The synthesis time of the MFI molecular sieve membrane in step (2) is 12 hours.

[0041] The prepared composite membrane was used in a low-concentration ethanol / water pervaporation separation test at an operating temperature of 60°C, an ethanol concentration of 5 wt.%, a separation factor of 43, and a flux of 0.26 kg / m2·h.

[0042] Embodiment 3:

[0043] The operating steps adopted are the same as those in Example 1, except that the molar ratio of the components in the synthesis sol of the MFI molecular sieve membrane in step (2) is TEOS / TPAOH / DDI=1 / 0.32 / 165. The synthesis time of the MFI molecular sieve membrane in step (2) is 4 hours.

[0044] The prepared composite membrane was used in a low-concentration ethanol / water pervaporation separation test at an operating temperature of 60°C, an ethanol concentration of 5 wt.%, a separation factor of 13, and a flux of 1.02 kg / m2·h.

[0045] Embodiment 4:

[0046] The operating steps adopted are the same as those in Example 1, except that in step (3), the PDMS casting solution is prepared: 0.75 g of hydroxyl-terminated PDMS with a viscosity of 1000 mPa·s is dissolved in 25 g of n-heptane, stirred to fully disperse and mix, and then 0.2 g of tetraethyl orthosilicate and 0.1 g of dibutyltin dilaurate are added in sequence, and stirred evenly to obtain a PDMS film solution.

[0047] The prepared composite membrane was used in a low-concentration ethanol / water pervaporation separation test with an operating temperature of 60°C, an ethanol concentration of 5 wt.%, a separation factor of 47, and a flux of 0.47 kg / m2·h.

[0048] Embodiment 5:

[0049] The operating steps adopted are the same as those in Example 1, except that in step (3), the PDMS casting solution is prepared: 2.5 g of hydroxyl-terminated PDMS with a viscosity of 32 mPa·s is dissolved in 25 g of n-heptane, stirred to fully disperse and mix, and then 0.2 g of tetraethyl orthosilicate and 0.1 g of dibutyltin dilaurate are added in sequence, and stirred evenly to obtain a PDMS film solution.

[0050] The prepared composite membrane was used in a low-concentration ethanol / water pervaporation separation test at an operating temperature of 60°C, an ethanol concentration of 5 wt.%, a separation factor of 47, and a flux of 0.5 kg / m2·h.

[0051] Embodiment 6:

[0052] The operating steps adopted are the same as those in Example 1, except that in step (3), the PDMS casting solution is prepared: 0.75 g of hydroxyl-terminated PDMS with a viscosity of 32 mPa·s is dissolved in 25 g of n-heptane, stirred to fully disperse and mix, and then 0.2 g of tetraethyl orthosilicate and 0.1 g of dibutyltin dilaurate are added in sequence, and stirred evenly to obtain a PDMS film solution.

[0053] The prepared composite membrane was used in a low-concentration ethanol / water pervaporation separation test at an operating temperature of 60°C, an ethanol concentration of 5 wt.%, a separation factor of 47, and a flux of 0.55 kg / m2·h.

[0054] Comparative Example 1:

[0055] 0.028g of MFI type molecular sieve seed was coated on the pretreated carrier, and a carrier with a flat and uniform seed layer was obtained after drying. TEOS, tetrapropylammonium hydroxide and deionized water were mixed in a molar ratio of TEOS / TPAOH / H2O=1 / 0.13 / 165, and a clear sol was obtained after stirring at room temperature for several hours. The prepared coated crystal carrier was placed in a polytetrafluoroethylene liner, and the above sol was poured in. Crystallization was carried out at 175°C in a hydrothermal reactor for 9h. After the reaction, the membrane was washed and dried. Then it was calcined at 500°C for 12h, and the heating and cooling rate was 0.5°C / min to obtain an MFI molecular sieve membrane.

[0056] The prepared MFI molecular sieve membrane was used in a low-concentration ethanol / water pervaporation separation test with an operating temperature of 60°C, an ethanol concentration of 5 wt.%, a separation factor of 45, and a flux of 1.67 kg / m2·h.

[0057] The introduction of the PDMS membrane prepared by the present invention can enhance the hydrophobicity of the entire composite membrane surface, and at the same time make up for the possible defects of the molecular sieve membrane, so that the separation selectivity of the membrane is improved to a certain extent; in the pervaporation process, the PDMS membrane part in the composite membrane can effectively reduce the contact between the raw material liquid and the surface of the MFI molecular sieve membrane, thereby reducing the reaction of the silanol group with the raw material and improving the stability of the membrane; the MFI molecular sieve / PDMS composite membrane prepared by the present invention has a good separation effect on 5-10% ethanol water, and the separation stability is effectively improved. The PDMS membrane layer also provides a certain anti-pollution performance for separating actual fermentation liquid. Therefore, the design of the composite membrane provides theoretical guidance for improving the membrane separation performance and separating the industrial application of actual fermentation liquid; the preparation method of the present invention is simple, the reaction conditions are mild, the raw materials are cheap and easy to obtain, and it is conducive to large-scale production.

[0058] The present invention is not limited to the above-mentioned embodiments. Anyone should be aware that any structural changes made under the enlightenment of the present invention, and any technical solutions that are the same or similar to the present invention, fall within the protection scope of the present invention. The technology, shape, and structural parts not described in detail in the present invention are all well-known technologies.

Claims

1. A method for preparing an MFI type molecular sieve / PDMS composite membrane, characterized in that: The following steps are involved: Step 1: Preparation of MFI molecular sieve seed layer: First, immerse the pretreated carrier in a polydiallyldimethylammonium chloride solution, heat it, take it out and dry it, coat the MFI molecular sieve seed on the carrier, and after drying, obtain a carrier with a flat and uniform seed layer; Step 2: Synthesis of MFI molecular sieve membrane: silicon source, template agent and deionized water are mixed and stirred to obtain a clear sol, and then both ends of the coated crystal carrier are sealed and placed in a polytetrafluoroethylene liner, and the clear sol is poured into the carrier and placed in a hydrothermal reactor for crystallization. After the reaction is completed, the membrane is washed, dried, and then calcined to obtain an MFI molecular sieve membrane; Step 3: Preparation of PDMS casting solution: dissolving hydroxyl-terminated PDMS in n-heptane, stirring to fully disperse and mix, then sequentially adding a crosslinking agent and a catalyst, stirring evenly to obtain a PDMS casting solution; Step 4: Preparation of MFI molecular sieve / PDMS composite membrane: After the MFI molecular sieve membrane is vertically immersed in the PDMS casting solution, it is taken out at a uniform speed, placed at room temperature to evaporate the solvent and initially solidify, and then completely cross-linked under vacuum drying to prepare the MFI molecular sieve / PDMS composite membrane.

2. The method for preparing a MFI type molecular sieve / PDMS composite membrane according to claim 1, characterized in that: In step 1, the concentration of the polydiallyldimethylammonium chloride solution is 0.1-1%, the heating temperature is 60° C., and the heating time is 1 hour.

3. The method for preparing a MFI type molecular sieve / PDMS composite membrane according to claim 1, characterized in that: In step 1, the particle size of the MFI molecular sieve seed particles is 100-600nm, the carrier shape is tubular, the material is alumina, the average pore size is about 1-3μm, the porosity is 30-40%, the outer diameter of the tube is 8-20mm, and the tube wall thickness is 1-3mm.

4. The method for preparing a MFI type molecular sieve / PDMS composite membrane according to claim 1, characterized in that: In step 2, the crystallization temperature is 175°C, the crystallization time is 4-12h, the calcination temperature is 500°C, the calcination time is 12h, and the heating and cooling rate is 0.5°C / min; the molar ratio of the precursor solution is: ethyl orthosilicate / tetrapropylammonium hydroxide / water = 1 / 0.05-0.32 / 100-165.

5. The method for preparing a MFI type molecular sieve / PDMS composite membrane according to claim 1, characterized in that: In step 2 and step 3, the amount of PDMS added is 1-10% of the mass of the solvent; the viscosity of PDMS is between 32-1000 mPa·s.

6. The method for preparing a MFI type molecular sieve / PDMS composite membrane according to claim 1, characterized in that: In step three, the crosslinking agent is ethyl orthosilicate, the catalyst is dibutyltin dilaurate, and the added amounts of the crosslinking agent and the catalyst are 5-30% and 0.5-5% of the mass of PDMS, respectively.

7. The method for preparing a MFI type molecular sieve / PDMS composite membrane according to claim 1, characterized in that: In step 4, the vacuum drying temperature is 60-100°C and the time is 5-12h.

8. The method for preparing a MFI type molecular sieve / PDMS composite membrane according to claim 1, characterized in that: In step 4, the MFI molecular sieve membrane is vertically immersed in the PDMS casting solution for 60 seconds, and the uniform withdrawal rate is 0.5-5 cm / min.

9. An MFI type molecular sieve / PDMS composite membrane, characterized in that: The method is prepared by the method according to any one of claims 1 to 8.

10. An application of an MFI type molecular sieve / PDMS composite membrane, characterized in that: It is used to improve membrane separation performance and separate actual fermentation liquid.

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