Protein absorption in one sitting

If we assume the final goal is health, you can consume a fair amount per sitting as the gut will tend to slow down absorption and feast happily on the amino acids. No study has looked at the 'maximal' amount that can be consumed though, as 'health' is hard to define accurately.

The same notion applies to building muscle and losing fat, which want amino acids floating around in the blood (systemic circulation) rather than hopping between the intestines and liver (portal circulation). The body will tend to slow down absorption in response to how much you eat, as the presence of amino acids can self-regulate their own digestion.

The body likes to adapt in response to stresses, and is pretty good at it. There isn't a single number which is the answer here, as the body tends to try and preserve all amino acids. How effective it is at this is individual.

In a study done on women, consumption of more than 54g of protein in a single meal versus across four meals resulted in no differences.[25] As these women had on average 90 lb of lean mass, it is highly plausible that more protein could be efficiently processed. The same researchers found that a single high protein meal was actually more effective in a population of elderly women.[26]

Research done on Intermittent Fasting supports the theory that your body can cope with far more protein than most people think, with two studies showing that the consumption of an average of 80-100g of protein in 4 hours yielded no differences in lean mass[27][28]

That being said, since fecal losses of protein and short-chain peptides tend to smell incredibly bad one can use a 'sniff-test' after bowel movements to assess if protein is being lost in the feces and thus not taken up by either the intestines or the muscle.