It works much better the other way around.
Requirements are, when you boil them down, just statements that are objectively true of the final system. No intrinsic sequence unless you happen to build it in. (This shall happen after that).
A process is a directed graph of activities. Generally you can get the requirements by asking 'what do you do', what doesn't work well, and gathering requirements around the new process. A crucial aspect of processes is that you have inputs, outputs, and invariants. These may or may not have been captured in your requirement set.
Use cases, with the scenarios defined, are also sets of activities. To keep it textual all the paths through are flattened and listed separately. No reason not to represent it as an activity diagram though. The key difference is that it is one actor that walks through the activities (card in the slot, card out of slot, enter pin, select transaction, ...).
It's a little baffeling how you have requirements (unless they are just a list of complaints) without something rather like either a process or a use case.
There should absolutely be tracability from a requirement to it's origin in a process, use case scenario, or other business entitiy and to the classs, packages, or subsystems that satisfy it.