What caused the unexpected curve in my cellulose to sugar conversion process?

[Hootenanny]

My coursework was to basically develop a process to turn cellulose into sugar. I decided to use a strong acid to hydrolyse the acetal linkages in cellulose to form D-glucose. I wanted to find the optimum conditions for the process starting with concentration. So I plotted a graph of concentration (x-axis) against percentage yield(y-axis). As I was varying concentration I expected a curve that would level off at some point. However, I found that the curve resembled that of a homogenous catalyst, with an increasing yield to a maxium point then a decrease. I can only think that the strong acid was reacting in someway with the sugars. I used Benedict's solution to test for the sugars. Any ideas would be helpful.

 

[Bystander]

Far as using Benedict's, the reaction is pH dependent. Give you any ideas?

 

[Hootenanny]

I neutralised the solution using sodium hydroxide before I carried out the benedict's reaction

 

[Bystander]

What have you got for a "run" protocol? _ wt. cellulose in _ vol. water plus acid made up to what? And on, and on. The question being, "Were you running the same volumes, weights of reagents and Benedict's every time?

 

[Hootenanny]

The initial mass of cellulose differed, but is accounted for in calculation as is the difference in volume due to neutalisation.

 

[Bystander]

What range of acid concentrations did you cover?

 

[Hootenanny]

from 0.1 mol to 2 mol, it was only on the 2 mol conc that it dipped, but five 'runs' were in agreement within acceptable limits.

 

[Bystander]

I'm beginning to remember some of the things I never liked about sugar chemistry. Acid plus cellulose at "low" concentrations results in ~95% hydrolysis; at "medium" concentrations (say in acid pulp mills), it's great for hydrolyzing ligno-cellulose linkage without breaking down excessive amounts of cellulose; at high concentrations, acid solutions are very good solvents for cellulose. The only paper chemist I ever talked with (actually, ex-paper chemist) couldn't get near the actual processes in the plant --- three or four generations of hereditary jobs, actual family legacies for eldest sons, plus deep south suspicion of a "Damyankee," plus a "union shop" fighting any and all threats to progress, automation, and other "newfangled" ideas kinda left the particulars of the process (T, m, t) hazy. Same game in the explosives industry (acid solvent), rayon --- you get the picture? I've never run into a decent explanation for this really rather weird concentration dependence. Never had occasion to look for one, and never took courses from faculty who were veterans of years work on sugars or cellulose --- there weren't any clear through my post-doc.

Do a little browsing on paper pulp, rayon, nitrocellulose mfr., and you might trip over something a little more specific.

2 M, or 2 m, has to be crowding the paper process range.

 

[Hootenanny]

Thanks for your help.