Recycling and waste management strategies for spent liquid organic hydrogen carriers (LOHCs) and catalysts are critical for ensuring the sustainability and economic viability of hydrogen storage systems. LOHCs are organic compounds that can reversibly absorb and release hydrogen through hydrogenation and dehydrogenation cycles. Over time, these carriers and their associated catalysts degrade, necessitating efficient recycling and disposal methods to minimize waste and recover valuable materials.

**Purification of Spent LOHCs**
Spent LOHCs often contain impurities such as dehydrogenation byproducts, catalyst residues, and degradation compounds. Purification is essential to restore the carrier’s hydrogenation capacity. Distillation is a common method for separating LOHCs from contaminants due to differences in boiling points. Fractional distillation can isolate high-purity LOHCs for reuse, while heavier byproducts are removed as waste.

Chemical washing is another purification technique, where solvents selectively dissolve impurities without affecting the LOHC. For example, polar solvents can extract polar degradation products from non-polar LOHCs like dibenzyltoluene. Filtration and adsorption processes using activated carbon or molecular sieves further remove fine particulates and dissolved impurities.

**Regeneration of LOHCs**
Some degraded LOHCs can be regenerated through re-hydrogenation or chemical treatment. If the carrier has undergone irreversible side reactions, catalytic hydrogenation may restore its original structure. For instance, partially hydrogenated LOHCs can be fully re-hydrogenated under high-pressure conditions with fresh catalysts.

Thermal cracking breaks down heavily degraded LOHCs into smaller, reusable fragments. Pyrolysis at controlled temperatures decomposes long-chain byproducts into lighter hydrocarbons, which can be reprocessed into fresh LOHCs or other useful chemicals. However, this method requires significant energy input and precise temperature control to avoid excessive carbonization.

**Catalyst Recovery and Recycling**
Catalysts used in LOHC systems, typically based on platinum, palladium, or ruthenium, degrade due to sintering, poisoning, or leaching. Recovery of precious metals is economically advantageous. Hydrometallurgical processes dissolve spent catalysts in acids or alkalis to extract metals. For example, aqua regia dissolves platinum-group metals, which are then precipitated and refined.

Pyrometallurgical methods involve high-temperature treatment to separate metals from support materials. Smelting oxidizes organic residues, leaving behind a metal-rich slag that undergoes further refining. Electrochemical recovery is another approach, where metals are selectively deposited from solution onto electrodes.

Support materials like alumina or carbon can also be recycled. Acid washing removes metal residues, allowing the supports to be reused in fresh catalyst formulations. Mechanical methods such as milling and sieving restore the structural integrity of porous supports.

**Disposal of Non-Recyclable Waste**
Some spent LOHCs and catalysts cannot be economically recycled and must be disposed of safely. Incineration with energy recovery is an option for organic waste, provided emissions are controlled to prevent harmful byproducts. Hazardous waste, including metal-contaminated residues, requires stabilization before landfill disposal. Encapsulation in cement or glass reduces leaching risks.

Chemical neutralization renders acidic or alkaline waste streams non-hazardous. For example, spent acid catalysts can be neutralized with bases to form stable salts. Solidification techniques mix liquid waste with binders to create inert solids suitable for landfill.

**Waste Minimization Strategies**
Optimizing LOHC and catalyst lifetimes reduces waste generation. Using robust catalysts with higher resistance to poisoning extends operational cycles. Continuous monitoring of LOHC quality allows timely purification before severe degradation occurs. Closed-loop systems integrate recycling steps directly into the hydrogen storage process, minimizing external waste streams.

**Industrial-Scale Recycling Practices**
Large-scale LOHC users often partner with specialized recycling firms. Centralized facilities handle bulk purification and metal recovery, achieving economies of scale. Automated sorting and processing improve efficiency in separating LOHCs, catalysts, and byproducts. Standardized protocols ensure consistent quality in recycled materials.

**Future Developments**
Research focuses on improving catalyst durability and developing LOHCs with easier recyclability. Self-cleaning catalysts that resist fouling could reduce replacement frequency. Novel separation technologies, such as membrane filtration or supercritical fluid extraction, may enhance purification efficiency. Advances in catalytic degradation could enable complete breakdown of spent LOHCs into feedstock for new production.

In summary, effective recycling and waste management of spent LOHCs and catalysts involve a combination of purification, regeneration, and disposal methods. These strategies ensure resource efficiency and support the scalability of hydrogen storage systems. Continuous innovation in material science and process engineering will further optimize these practices in the future.