cloisonner

Literally, to partition a space with walls or dividers (cloisonner un bureau en open space). Just as common figuratively, for compartmentalizing knowledge, departments, or social groups so they don't communicate — cloisonner les services d'une entreprise.

• Ils ont cloisonné le grand bureau en plusieurs espaces. — They partitioned the large office into several spaces.
• Cette organisation cloisonne trop les différents services. — This organization compartmentalizes its departments too much.
• Le système scolaire cloisonne parfois les filières trop tôt. — The school system sometimes separates tracks too rigidly, too early.

Cloisonner implies a rigid, often-criticized separation that prevents communication or flexibility — it's a more loaded word than the neutral séparer (to separate).