Learn Turkish: Bir şahıs olarak değil, dernek adına söz almak istiyorum. - I want to take the floor not as an individual, but on behalf of the association.

Both are correct, but they have a subtle difference. Using the bare noun in dernek adına treats it like a general category or institution, meaning 'on behalf of the association.' Adding the genitive to make derneğin adına points to a specific, previously mentioned association. In formal speech, dropping the genitive is very common when representing an organization.

Could I use için instead of adına in this sentence?

You could say dernek için (for the association), but it changes the nuance. İçin simply means you are doing something for their benefit. Adına specifically means 'in the name of' or 'on behalf of,' which emphasizes formal representation.

What does the phrase söz almak mean literally, and how is it used?

Literally, it translates to 'to take word.' It is a fixed idiom used in meetings, panels, or assemblies meaning 'to take the floor' or 'to get permission to speak.'

How does the negation work with olarak değil?

Olarak means 'as' (in the capacity of). By placing değil immediately after it, you negate that specific role. The structure [X] olarak değil, [Y] adına... creates a strong contrast: 'Not as [X], but on behalf of [Y]...' You do not need a word for 'but' because the contrast is implied by the comma and the sentence flow.