Using a case study without company's permission
Honestly, I would not do this.
I am not familiar with US law so I cannot give you any legal advice. However, there are several other non-legal risks you have to bear.

According to your description, you intend to stick closely to the real case in your presentation. The students might be intelligent enough to draw the necessary conclusions or could even be involved with the company. I would not risk this.

As a result, the company could get the impression, that you have leaked confidential data to the students. Indepdent from the question whether this is illegal or legal, facing a lawsuit can easily have a disastrous effect on your career. Furthermore, this can also result in loss of trust, again impacting your career.

I only see two possible options here:


You ask your former client for a written(!) permission
You largely modify your example / problem


Both methods, when done correctly, will save you from a lot of risk.

I had a similar problem, when I wanted to write a paper about work I did for an industry partner. Usually, this is quite strict, since nobody wants to have their confidential solutions published. However, I was able to chance the problem and solution sufficiently. Despite the same ideas were used, the original problem and client remained hidden and I was able to publish my ideas. This was quite a lot of work to do, since I had to redo most of the code and experiments. Altogether, this was worth the effort since I do not have any fear of legal consequences and we still have a good relationship to our clients.