I don’t think this is available, but you could create a custom icon that is a vertical line, what ever color works for you. Create some empty folders, and name them, somewhere (one for each separator you need), and then change the icon for each folder to the line icon you created. Now, pin the folders where you want separators on your taskbar. 

You could also use a dot, star, whatever for the separator icon. 

Let me know what you want and I’ll create them for you and post a link to download. 

Here's one I made very quickly to show you.