Midterm #2 February 12, 2007
Name: ______
1. Please show all of the possible quinone methides that can be formed from each of these compounds in alkaline solution. (2 pts)I will show you during Wednesday’s lecture. /
2. Please label this bar chart (on the bars) with the appropriate labels. Possible label choices include lignin, cellulose, xylans, and glucomannans (2 pts).
Order from left to right:
Cellulose, glucomannans, xylans, lignin /
3. Which consumes the most base during kraft pulping? (1 pts) This question will be omitted, two answers very similar, it will not count.
a) Saponification of acetyl groups.
b) Neutralization of acid extractives
c) Lignin degradation reactions
d) Reactions with carbohydrate degradation products,
4. Please answer the following questions regarding the kraft pulping of this lignin fragment. This question is a little different. I want you to pulp this molecule until it is fragments. Therefore, you need to start at a reactive site and work your way through the molecule. Assume no condensation or retro aldo reactioins. (9 pts)
a) Which three rings end up as monomers? ______1,2,7______
b) There will be 2 dimers, which rings are involved? _____13-14, 5-6______
c) There is one trimer, which 3 rings are involved? _____3,4,12______
d) There is one tetramer, which rings are involved? ______8,9,10,11______
e) There are 2 stilbenes formed, which rings (total of 4) are involved? ______8-9, 13,14______
5. Please draw the mechanism (with arrows and intermediates) for the cleavage of this dimer with kraft liquor (3 pts)Similar reaction, Lecture 9, slide #4.
6. Please draw the reaction mechanism (with arrows and intermediates) for the formation of one product for the reaction of this model compound with NaOH. (3 pts).
Similar reaction, lecture 9, slide #3, the top reaction only because I want one product.
7. Please show the products of alkaline condensation of these molecules. For this question assume that the molecules cannot react with themselves; only the other molecule. (4 pts)
8. Please draw the complete mechanism of the conversion of galactose to galactoisosaccharinic acid. (4 pts)
9. True or false: Increasing EA increases the rate of lignin removal in the initial phase of a kraft cook. (1 pts)
a) True b) False
10. Please circle anthraquinone. Also, indicate which of these 2 react with lignin. (2 pts)
reacts with lignin / anthraquinone
11. Please explain the benefit of having polysulfides in a kraft cook (2 pts)
Polysulfides oxidize carbohydrate reducing end groups to carboxylic acid thus slowing peeling.
12. This figure shows the three phases of a kraft cook. To this figure, please do the following: (9pts)
a) Add the names for the three phases
b) Determine which phase the reactions shown before are most important (rate determining steps or are most prevalent). Write the letter corresponding to this reaction in the phase. It is possible that 2 phases fit the answer…..pick one of them.
A. Saponification of fats
B. Peeling of Glucomannans
C. Neutralization of acidic extractives
D. Alkaline hydrolysis of acetyl groups
E. Glycosidic cleavage of cellulose
F. Cleavage of non-phenolic β-O-4
13. Please answer the following questions using this information:
1000 kg wood charged to digester @ 60% moisture
650 liters of white liquor containing 100g/l NaOH and 25g/l Na2S
Black liquor charged to digester: 5g NaOH/l and 1 g/l Na2S
Liquor/wood ratio = 4liters/kg
a) What is the Effective Alkali of the white liquor? (3 pts)
EA=77.5(g/L)+0.5*(19.85 g/L)=87.43 (g/L) as Na2O or 56.84 kg Na2O
b) What is the sulfidity of the white liquor? (2pts)
={19.85 (g/L)/97.35 (g/L)}*100%=20.4%
c) What is the volume of black liquor charged to the digester? (2pts)
X=1600 (L) total-650 L (white)-600L (water)=350L (black)
d) What is the AA of the digester liquor? (2 pts)
AA= (77.5g/L+3.875g/L)+(19.87g/L+0.795g/L)=102 g/L
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