Why does the proportion of lithium molecular sieve need to be ≥70%?

1. Core calculation basis: nitrogen adsorption capacity and oxygen purity requirements

Medical oxygen generators need to ensure that the oxygen purity is ≥90% (ideal target 94%), and the core is the adsorption capacity of lithium molecular sieve for nitrogen (N2).

Key formula:

Oxygen purity ≈1-residual nitrogen volume/intake nitrogen volume

Calculation steps:

Intake nitrogen volume: N2 accounts for 78% of the air, and at a flow rate of 5L/min, N2 flow rate = 3.9L/min.

Lithium molecular sieve adsorption capacity:

XINTAO lithium molecular sieve static N2 adsorption ≥22.5% (i.e., 22.5L N2 is adsorbed per 100g under standard conditions).

2. Interference effect of 13X-HP

Competitive adsorption: Although 13X-HP mainly adsorbs H₂O/CO₂, its N₂ adsorption capacity is ≥8ml/g, which will occupy the adsorption sites of lithium molecular sieve.

Selectivity difference:

Lithium molecular sieve N₂/O₂ selectivity is ≥6, 13X-HP is only ≥3 → After mixing, the overall selectivity decreases and the residual nitrogen volume increases.

3. Engineering verification of layered loading

Experimental data: Industrial cases show that when the proportion of lithium molecular sieve is ≥70%, the oxygen purity is stable at 93%-96%; when it is less than 60%, the purity fluctuates significantly (85%-90%).

Airflow dynamics:

High proportion of lithium molecular sieve ensures that the thickness of the main adsorption layer is sufficient to prevent nitrogen penetration (requires ≥30cm loading height, 5L model).

4. Conclusion: The necessity of the 70% ratio

Adsorption capacity: 70% is the minimum threshold to ensure that the total amount of nitrogen adsorption meets the purity of ≥94% at a flow rate of 5L/min.

Selectivity guarantee: Reduce the competitive adsorption of 13X-HP to avoid dilution of N₂/O₂ selectivity.

Stability requirements: Medical scenarios require long-term stable output, and high-proportion lithium molecular sieves can buffer intake fluctuations (such as humidity changes).

Formula summary: Lithium molecular sieve ratio ≥ target N₂ adsorption amount/total adsorption demand = 3.9×t×purity coefficient/

(0.225×loading amount×dynamic efficiency)

(where t is the adsorption cycle, and the purity coefficient is determined by selectivity)

5. Practical suggestions

Strict layered loading: upper layer 13X-HP (20%-30%), lower layer lithium molecular sieve (70%-80%).

Dynamic monitoring: Real-time detection of oxygen purity and adjustment of regeneration cycle (such as high-temperature regeneration of lithium molecular sieve every 30 minutes).

Inlet air pretreatment: dryer (dew point < -40°C) + CO₂ adsorber, reducing 13X-HP load.

If 94%+ purity is required, 70% lithium molecular sieve is the common conclusion of scientific and engineering experience.