WO2025032303A1

WO2025032303A1 - Recycling of solid ionomer components

Info

Publication number: WO2025032303A1
Application number: PCT/GB2024/051575
Authority: WO
Inventors: Gareth HART
Original assignee: Johnson Matthey Public Limited Company
Priority date: 2023-08-04
Filing date: 2024-06-20
Publication date: 2025-02-13
Also published as: GB2633441A; GB202311972D0; GB202408868D0

Abstract

A method of recycling a solid ionomer material contaminated with seal material used for mounting the solid ionomer material in use, the method comprising: heating the solid ionomer material in a solvent to disperse the solid ionomer material forming a dispersion of ionomer in the solvent, the dispersion also containing one or more breakdown products from the seal material; adding an acid to the dispersion to reduce the pH of the dispersion and precipitate the one or more breakdown products; and separating the precipitated breakdown products from the dispersion.

Description

RECYCLING OF SOLID IONOMER COMPONENTS

Field

This specification relates to recycling of solid ionomer components / materials such as ionomer membranes, catalyst coated ionomer membranes, and/or ionomer containing catalyst layers used in fuel cells and hydrogen producing water electrolysers.

Background

Fuel cell and hydrogen producing water electrolyser production is set for rapid growth as investment is placed into the global hydrogen economy. Catalyst coated membranes (CCMs) are a major functional component of both fuel cells and electrolysers. Such CCMs generally comprise a conductive polymer membrane coated on either side by a catalyst containing layer. The CCMs are configured to drive oxidation and reduction reactions and support proton and electron transport, these processes being required for the fuel cell and electrolyser technologies to function.

While variations in CCM component materials and configurations exist according to functional performance requirements in end use applications, they generally contain several components of value including one or more platinum group metal (PGM) catalysts and one or more proton conducting polymers.

Typically, the membrane is formed of one or more ionomers such as perfluorosulfonic-acid (PFSA) ionomers. Ionomer may also be provided in one or both of the catalyst layers. The ionomer in the catalyst layers may be the same or different to the ionomer in the main membrane component and/or in other catalyst layer(s). The membrane may also include a reinforcement layer for mechanical durability, such as polytetrafluoroethylene (PTFE).

A CCM may comprise two different catalysts, one for driving an oxidation reaction on one side of the CCM and one for driving a reduction reaction on the other side of the CCM. A CCM may also comprise a recombination catalyst which is provided to catalyse the recombination of hydrogen and oxygen to form water, reducing the quantity of hydrogen crossing the membrane and mixing with oxygen to form a potentially explosive mixture. A CCM may also include a multivalent cation delivered as a salt or oxide (supported or unsupported) as a peroxide scavenger, e.g., a metal oxide such as CeCh.

CCM catalysts can be based on platinum group metals such as platinum, ruthenium, iridium, palladium, or mixtures thereof. The platinum group metals may be provided in elemental (metallic) form, in compound form (e.g., an oxide, such as an iridium oxide catalyst), or as a PGM-base metal alloy (e.g., PtCo). Furthermore, the PGM catalyst materials may be supported on a substrate material, such as a carbonaceous substrate material (e.g., carbon, such as a platinum-on-carbon catalyst comprising particles of carbon on which platinum is disposed or PtCo-on-carbon, or an organic material, e.g., nanostructured thin film catalyst (NTFC) technology as described in US2020102659 and W02006089180). The CCM catalyst may contain an ionomer as part of its formulation.

Catalyst coated membranes (CCMs) can also be provided in combination with additional functional layers to form multi-layer membrane electrode assemblies (MEAs). Such MEAs may have 3, 5, or 7 layers for example. One or more seal materials are utilized to construct, bond, and/or seal such assemblies. With the increase in CCM manufacture for fuel cells and electrolysers, there is an associated increase in CCM waste materials, including a significant volume of scrap material created during CCM manufacture (e.g., due to failure at quality control) and also an increase in end-of-life (EoL) CCMs. Since CCMs contain several components which are rare and/or valuable, including platinum group metals (notably Pt, Pd, Ir and Ru) and ionomer (both in the membrane and catalyst layers), there is a growing demand for methods of recycling such components from waste CCM materials.

One current method to recover PGMs from production scrap and end-of-life CCM material involves incineration. The incineration process yields a PGM rich (typically Pt and Ir) ash which is processed via conventional PGM refining routes. However, the incineration process releases harmful and toxic gases such as CO2 and HF from the polymers that are part of the membrane. Both these gases have negative impacts as they pollute the atmosphere, increase the greenhouse effect, and/or have harmful effects in the human body. As such, there is a need for a cleaner process which reduces or eliminates the emission of these gases.

In addition to the above, the incineration method destroys the ionomer component which also has significant value. As such, it would also be desirable to provide a process which is capable of recovering ionomer components as well as providing a process which is cleaner, safer, and more environmentally friendly.

Processes for recovering perfluorosulfonic acid ionomer from solid ionomer membranes are known. See, for example, WO2016/156815, US7255798, and WO2021250576. Such methods involve heating solid ionomer membranes in a solvent to disperse the ionomer. Solvents may include water, aqueous solutions (e.g., water and a base), organic solvents, or mixtures thereof such as mixtures of alcohols and water. The resultant ionomer dispersions can then be re-used to manufacture new membranes.

To enable fuel cells and electrolysers to become more sustainable technologies, there remains a need for commercially viable and environmentally friendly routes to recycle ionomer components from waste CCM materials including production scrap and end-of-life material. It is an aim of the present specification to address this problem.

Summary

It has been found that recycled ionomer materials, fabricated by dispersing waste solid ionomer components, contain certain organic contaminants such as organic acids and/or alcohols. These contaminants have been detected in ionomer recycling streams formed after heating waste solid ionomer components in a solvent to disperse the waste solid ionomer components. The contaminants have been identified as breakdown products from seal material utilized to construct, bond, and/or seal catalyst coated membrane assemblies, and which contaminate solid ionomer components from such assemblies after they are disassembled to be recycled. The seal material is at least partially broken down during the recycling process and, while solid components can be readily separated from the dispersed ionomer, the breakdown products remain in the ionomer dispersion and contaminate the resultant recycled ionomer product material. As such, there is a need for the ionomer recycling process to be modified to remove such contamination from seal material breakdown products and achieve a purer ionomer product at the end of the recycling process for re-use.

According to the present specification there is provided a method of recycling a solid ionomer material contaminated with seal material used for mounting the solid ionomer material in use, the method comprising: heating the solid ionomer material in a solvent to disperse the solid ionomer material forming a dispersion of ionomer in the solvent, the dispersion also containing one or more breakdown products from the seal material; adding an acid to reduce the pH of the dispersion and precipitate the one or more breakdown products; and separating the precipitated breakdown products from the dispersion (e.g., via filtration). The acid may be added before, during, or after the heating step in order to reduce the pH of the dispersion.

In accordance with this method, the contaminant seal breakdown product material is precipitated via the addition of an acid and then removed from the ionomer dispersion, e.g., via filtration, to achieve a higher purity ionomer product.

Advantageously, the acid added to precipitate the one or more seal material breakdown products is a H⁺ form of an ionomer, advantageously an acidic dispersion containing a H⁺ form of an ionomer. For example, the ionomer in the acidic dispersion can be the acid form of the ionomer in the solid ionomer material which is being recycled, with the ionomer in the solid ionomer material being in salt form as part of the recycling process. The use of an acidic form of ionomer as the acid used to precipitate the seal breakdown products is advantageous as it does not introduce unwanted contaminant anions from the addition of typical inorganic acids.

Brief Description of the Drawings

For a better understanding of the present invention and to show how the same may be carried into effect, certain embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

Figure 1 shows an example of an ionomer membrane recycling process in which seal breakdown products are precipitated by acid addition and then separated from the ionomer recycling stream;

Figure 2 shows another example in which the ionomer membrane is treated with an aqueous base solution to convert the ionomer membrane to salt form, the membrane is dispersed, and acid is added to precipitate seal breakdown products which are then separated from the ionomer recycling stream;

Figure 3 shows another example in which a catalyst coated membrane is subjected to one or more acid leaching steps to remove catalyst material, the ionomer membrane is treated with an aqueous base solution to convert the ionomer membrane to salt form, the membrane is dispersed, and acid is added to precipitate seal breakdown products which are then separated from the ionomer recycling stream;

Figure 4 shows an equation illustrating an example of breakdown of seal material;

Figure 5 shows an equation illustrating another example of breakdown of seal material;

Figure 6 shows an equation illustrating an example of precipitation of seal breakdown product by addition of an acid;

Figure 7 shows an equation illustrating an example in which the acidic form of an ionomer is added as the acid to precipitate seal breakdown product;

Figure 8 shows an equation illustrating another example in which the acidic form of an ionomer is added as the acid to precipitate seal breakdown product;

Figure 9 shows an ⁿH NMR spectrum which was obtained for a recycled ionomer dispersion containing seal material breakdown product; Figure 10 shows an ⁿH NMR spectrum which was obtained for the recycled ionomer dispersion of Figure 9 after treatment with an acid (HCI) to precipitate seal material breakdown product and removal of the precipitate by filtration;

Figures 11 shows an ⁿH NMR spectrum which was obtained for another recycled ionomer dispersion containing seal material breakdown product; and

Figure 12 shows an ⁿH NMR spectrum which was obtained for the recycled ionomer dispersion of Figure 11 after treatment with another dispersion containing ionomer in acid form to precipitate seal material breakdown product and removal of the precipitate by filtration.

Detailed Description

As described in the summary section and illustrated in Figure 1, the present specification provides a method of recycling a solid ionomer material contaminated with seal material used for mounting the solid ionomer material in use. The method comprises: heating the solid ionomer material in a solvent to disperse the solid ionomer material forming a dispersion of ionomer in the solvent, the dispersion also containing one or more breakdown products from the seal material; adding an acid to the dispersion to reduce the pH of the dispersion and precipitate the one or more breakdown products; and separating the precipitated breakdown products from the dispersion (e.g., via filtration).

Advantageously, the acid added to precipitate the one or more seal material breakdown products is a H⁺ form of an ionomer, advantageously an acidic dispersion containing a H⁺ form of an ionomer. For example, the ionomer in the acidic dispersion can be the protonated version of the ionomer in the solid ionomer material, the ionomer in the solid ionomer material having been converted to salt form as part of the recycling process. The use of an acid form of ionomer to precipitate seal breakdown products is advantageous as it does not introduce unwanted contaminant anions from the addition of typical inorganic acids.

Alternatively, the H⁺ form of the ionomer which is added is the H⁺ form of a different ionomer to that which is in the solid ionomer material which is being recycled, the ionomers differing in terms of their molecular weight, equivalent weight, or sulfonated side chains. In this case, the different ionomers form an ionomer blend after the solid ionomer material is dispersed. This approach can be advantageous to tune the recycled product to a particular blend composition with particular functional properties as part of the recycling process to yield a new target ionomer blend composition for use in manufacturing new CCM components.

Alternatively still, the acid may not be a H⁺ form of an ionomer. In this case, optionally the acid is selected from an inorganic acid, hydrochloric acid, sulfuric acid, an organic acid, and/or a sulfonic acid. If such non-ionomer acids are utilized, preferably residual anions from the acid (e.g., chloride or sulfate) are subsequently removed from the ionomer dispersion, optionally using membrane filtration or ion exchange. The acid may be in solution (e.g., hydrochloric acid or sulfuric acid) or in the form of a solid media (e.g., sulfonic acid).

The solid ionomer material can be an ionomer membrane, a catalyst-coated ionomer membrane, or a catalyst layer material containing ionomer. The solid ionomer material is typically scrap or used ionomer material from a fuel cell or electrolyser application. Such solid ionomer material is typically formed of a fluorinated polymer comprising a fluorinated polymer backbone chain and a plurality of groups represented by formula -SO3Z, wherein Z is hydrogen or a cation, optionally a metal cation or a quaternary ammonium cation. zi The seal material is typically a polymer, optionally selected from a polyethylene material, a polyethylene terephthalate, a polyethylene naphthalate, a poly(alkylene naphthalenedicarboxylate), or a poly ethylene-vinyl acetate. Such seal materials result in one or more breakdown products after being subjected to the ionomer dispersal step, typically organic acid or alcohol breakdown products, optionally selected from a naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, or a terephthalic acid.

The solvent can be water, an aqueous basic solution, an organic solvent, an alcohol, or a mixture thereof such as a mixture of alcohol and water. The heating step to disperse the solid ionomer material in the solvent may be at a temperature of: at least 150°C, 180°C, 200°C, 220°C, 230°C, or 240°C; no more than 400°C, 300°C, 275°C, or 250°C; or within a range defined by any combination of the aforementioned lower and upper limits. The heating may be for a time of: at least 15 minutes, 30 minutes, 1 hour, 2 hours, or 3 hours; no more than 72 hours, 48 hours, 24 hours, 10 hours, 6 hours, or 4 hours; or within a range defined by any combination of the aforementioned lower and upper limits.

The solid ionomer material can be in salt form or converted to salt form prior to or during heating to disperse the solid ionomer material. For example, as illustrated in the method of Figure 2, the solid ionomer material can be converted to salt form by treatment with an aqueous basic solution (e.g., a metal hydroxide solution). This treatment can be performed at low temperature (e.g., < 100°C) to convert the solid ionomer material to salt form without dispersing the material. In this case, the base can then be removed, and the solid ionomer material placed into another solvent and heated to disperse the solid ionomer material. Alternatively, the solid ionomer material can be heated in a basic solution to both convert the solid ionomer material to salt form and also disperse the material. In the case that the solid ionomer material is in salt form when it is dispersed, after precipitating and separating the breakdown products, the salt form of ionomer can be converted back to protonated acid form by ion exchange.

As illustrated in the method of Figure 3, the solid ionomer material may be a catalyst coated membrane. In this case, the catalyst coated membrane can be subjected to one or more acid leach treatments to leach the catalyst material from the ionomer membrane. For example, an oxidative acid leach can be utilized for leaching platinum catalyst material and/or a reductive acid leach can be utilized to leach iridium containing catalyst material. After removal of the catalyst material in this way, the remaining ionomer membrane material can be processed as previously described in relation to Figures 1 or 2.

It will thus be appreciated that recycling streams for ionomer materials contain breakdown products of seal materials. Typical seal materials break down to form soluble organic compounds such as organic acids and/or alcohols which contaminate the ionomer dispersion formed during recycling of solid ionomer components. This breakdown of seal material may occur, for example, as a result of basic hydrolysis due to the use of a base in the step of converting the ionomer to salt form. Alternatively, or additionally, this breakdown of seal material may occur, for example, as a result of acidic hydrolysis due to the use of acid in the leaching of catalyst material from the waste catalyst coated membrane material. Regardless of the source of the seal breakdown products, according to this specification, in order to remove the seal material breakdown products from the ionomer dispersion formed during recycling of the ionomer, acid is added to precipitate the breakdown products in the dispersed ionomer material. Optionally, the acid which is added is the acidic form of the perfluorinated sulfonic acid (PFSA) ionomer which is the intended product of the recycling process. This is advantageous as it does not introduce unwanted contaminant anions (such as chloride) from the addition of typical inorganic acids. Once the breakdown products are precipitated, they may be filtered from the ionomer dispersion. Removal of seal contaminants from the recycle process yields a purer recycled ionomer product.

Applicant is unaware of any prior disclosure of the problem of seal material breakdown products causing contamination of ionomer recycling streams or the present methodology for removing such contamination when recycling ionomers. W09900351A1 discloses a process for the recovery of naphthalenedicarboxylic acid from poly(alkylene naphthalenedicarboxylate). However, addition of acid, such as H⁺-form PFSA ionomer, has not been used previously in a process step to provide a change in pH within an ionomer recycling process to precipitate seal breakdown contaminants and separate them from an ionomer recycling stream.

According to an example of the present methodology, a dispersion containing H⁺-form PFSA ionomer is added to a dispersion (in water) containing PFSA ionomer (dispersed from membranes, catalyst- coated membranes, or catalyst layers), seal material breakdown product (e.g., 2,6- naphthalenedicarboxylic acid) and other contaminants. On addition of the acidic dispersion, the 2,6- naphthalenedicarboxylic acid precipitates and is separated by a solid-liquid separation (e.g., filtration, centrifugation).

According to another example, solid PFSA ionomer is treated with an aqueous solution of LiOH to convert the PFSA ionomer to lithium salt form without dispersing the solid ionomer material. The remaining LiOH solution is then removed and replaced with another solvent such as water or a mixture of water and an alcohol. The solid ionomer material in that solvent is then subjected to a high temperature treatment to disperse the solid ionomer material. The dispersion is then mixed with a dispersion containing H⁺-form PFSA ionomer. On addition of the acidic dispersion, seal breakdown products such as 2,6-naphthalenedicarboxylic acid precipitate and are separated by a solid-liquid separation (e.g., filtration, centrifugation).

According to another example, the solid ionomer material is mixed with a dispersion containing H⁺- form PFSA ionomer prior to dispersion of the solid ionomer material. The solid ionomer material is then subjected to a high temperature treatment to disperse the solid ionomer material. The acidic dispersion causes seal breakdown products such as 2,6-naphthalenedicarboxylic acid to precipitate and these can be separated by a solid-liquid separation (e.g., filtration, centrifugation).

According to yet another example, solid catalyst coated PFSA ionomer is subjected to one or more acid leach steps to remove catalyst material. The remaining solid PFSA ionomer material is then treated with an aqueous solution of LiOH to convert the PFSA ionomer to lithium salt form without dispersing the solid ionomer material. The remaining LiOH solution is then removed and replaced with another solvent such as water or a mixture of water and an alcohol. The solid ionomer material in that solvent is then subjected to a high temperature treatment to disperse the solid ionomer material. The dispersion is then mixed with a dispersion containing H⁺-form PFSA ionomer. On addition of the acidic dispersion, seal breakdown products such as 2,6-naphthalenedicarboxylic acid precipitate and are separated by a solid-liquid separation (e.g., filtration, centrifugation).

Figure 4 shows an equation illustrating an example of breakdown of seal material. In this example, polyethylene naphthalate is broken down to 2,6-naphthalenedicarboxylate salt and ethylene glycol due to the presence of base (e.g., LiOH) which is used to convert ionomer to salt form as part of the recycling process.

Figure 5 shows an equation illustrating another example of breakdown of seal material. In this example, polyethylene terephthalate is broken down to terephthalate salt and ethylene glycol due to the presence of base (e.g., LiOH) which is used to convert ionomer to salt form as part of the recycling process.

Figure 6 shows an equation illustrating an example of precipitation of seal breakdown product by addition of an acid. In this example, 2,6-naphthalenedicarboxylate salt is converted to 2,6- naphthalenedicarboxylic acid. In the equation, "A" represents a counter ion for charge neutrality.

Figure 7 shows an equation illustrating another example in which the acidic form of an ionomer is added as the acid to precipitate seal breakdown product. In this example, as in Figure 6, 2,6- naphthalenedicarboxylate salt is converted to 2,6-naphthalenedicarboxylic acid by addition of an acidic ionomer RSO3H, where R represents the remainder of the perfluorinated ionomer.

Figure 8 shows an equation illustrating another example in which the acidic form of an ionomer is added as the acid to precipitate seal breakdown product. In this example, terephthalate salt is converted to terephthalic acid by addition of an acidic ionomer RSO3H, where R represents the remainder of the perfluorinated ionomer.

Figure 9 shows an ’H NMR spectrum which was obtained for a recycled ionomer dispersion containing seal material breakdown product. The spectrum contains peaks associated with seal breakdown product and thus illustrates the presence of seal breakdown product material in the recycled ionomer dispersion. To this dispersion (10 mL) was added 37% HCI dropwise. Precipitation was observed within 12 drops. The dispersion was filtered through a 0.45 pm PVDF syringe filter to remove the precipitate and a ’H NMR spectrum was taken of the remaining ionomer dispersion as shown in Figure 10. The spectrum illustrates that peaks associated with seal breakdown product have disappeared and thus illustrates the removal of seal breakdown product material from the recycled ionomer dispersion by the addition of the acid and filtration of the precipitate.

Figures 11 shows an ’H NMR spectrum which was obtained for another recycled ionomer dispersion containing seal material breakdown product. The spectrum contains peaks associated with seal breakdown product and thus illustrates the presence of seal breakdown product material in the recycled ionomer dispersion. To this dispersion (10 mL) was added another dispersion containing ionomer in acid form. Precipitation was observed within 40 drops. The dispersion was filtered through a 0.45 pm PVDF syringe filter and a ’H NMR spectrum was taken of the remaining ionomer dispersion as shown in Figure 12. The spectrum illustrates that peaks associated with seal breakdown product have disappeared and thus illustrates the removal of seal breakdown product material from the recycled ionomer dispersion by the addition of the acid form of an ionomer and filtration of the precipitate.

The aforementioned examples represent a non-exhaustive set of options. It will be appreciated that while this invention has been particularly shown and described with reference to certain examples, it will be understood to those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as defined by the appended claims.

Claims

1. A method of recycling a solid ionomer material contaminated with seal material used for mounting the solid ionomer material in use, the method comprising: heating the solid ionomer material in a solvent to disperse the solid ionomer material forming a dispersion of ionomer in the solvent, the dispersion also containing one or more breakdown products from the seal material; adding an acid to reduce the pH of the dispersion and precipitate the one or more breakdown products; and separating the precipitated breakdown products from the dispersion.

2. A method according to claim 1, wherein the solid ionomer material is an ionomer membrane, a catalyst-coated ionomer membrane, or a catalyst layer material containing ionomer.

3. A method according to claim 1 or 2, wherein the solid ionomer material is scrap or used ionomer material from a fuel cell or electrolyser application.

4. A method according to any preceding claim, wherein the solid ionomer material is formed of a fluorinated polymer comprising a fluorinated polymer backbone chain and a plurality of groups represented by formula -SO3Z, wherein Z is hydrogen or a cation, optionally a metal cation or a quaternary ammonium cation.

5. A method according to any preceding claim, wherein the seal material is a polymer, optionally selected from a polyethylene material, a polyethylene terephthalate, a polyethylene naphthalate, a poly(alkylene naphthalenedicarboxylate), or a poly ethylene-vinyl acetate.

6. A method according to any preceding claim, wherein the one or more breakdown products from the seal material are acid or alcohol breakdown products from polymer seal material, optionally selected from a naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, or a terephthalic acid.

7. A method according to any preceding claims, wherein the solvent is water, an aqueous basic solution, an organic solvent, an alcohol, or a mixture thereof.

R

8. A method according to any preceding claims, wherein the acid added to precipitate the one or more breakdown products is a H⁺ form of an ionomer, optionally a dispersion containing a H⁺ form of an ionomer.

9. A method according to claim 8, wherein the H⁺ form of the ionomer which is added is the H⁺ form of the same ionomer which is in the solid ionomer material which is being recycled.

10. A method according to claim 8, wherein the H⁺ form of the ionomer which is added is the H⁺ form of a different ionomer to that which is in the solid ionomer material which is being recycled, the ionomers differing in terms of their molecular weight, equivalent weight, or sulfonated side chains, the different ionomers forming an ionomer blend after the solid ionomer material is dispersed.

11. A method according to any one of claims 1 to 7, wherein the acid is not a H⁺ form of an ionomer, optionally the acid being selected from an inorganic acid, hydrochloric acid, sulfuric acid, an organic acid, and/or a sulfonic acid.

12. A method according to claim 11, wherein residual anions from the acid are subsequently removed from the ionomer dispersion, optionally using membrane filtration or ion exchange.

13. A method according to any preceding claims, wherein the precipitated breakdown products are separated from the dispersion via filtration or centrifugation.

14. A method according to any preceding claims, wherein the solid ionomer material is heated to a temperature of: at least 150°C, 180°C, 200°C, 220°C, 230°C, or 240°C; no more than 400°C, 300°C, 275°C, or 250°C; or within a range defined by any combination of the aforementioned lower and upper limits.

15. A method according to any preceding claims,

Q wherein the solid ionomer material is heated for: at least 15 minutes, 30 minutes, 1 hour, 2 hours, or 3 hours; no more than 72 hours, 48 hours, 24 hours, 10 hours, 6 hours, or 4 hours; or within a range defined by any combination of the aforementioned lower and upper limits.

16. A method according to any preceding claims, wherein the solid ionomer material is converted to salt form prior to or during heating to disperse the solid ionomer material.

17. A method according to claim 16, wherein the solid ionomer material is converted to salt form by treatment with an aqueous basic solution.

18. A method according to claim 16 or 17, wherein after precipitating and separating the breakdown products, the salt form of ionomer is converted back to protonated acid form by ion exchange. m