Acid-Catalysed Hydrolysis of Cellulose

The first comprehensive and systematic work on the reasons for deterioration of paper was performed by WJ. Barrow in the 1960s who firmly established the link between the acidity of paper and its permanence. Although we talk about the acidity of a sheet of dry paper, the acidity of paper, expressed as pH is only measured in an aqueous extract, generally produced by macerating 1 g of paper in 50 mL of pure water. 

The pH is defined as pH = — log10 [H+] where [H+] is the hydrogen ion concentration. On this scale, pH 7 is neutral, pH 1 is extremely acid and pH 14 extremely alkaline. Each pH decrease of 1.0 represents a 10 times increase in hydrogen ion concentration. For example, there is 10 times more active acid at pH 4 than pH 5. 

Barrow measured the pH of many old pieces of paper and also measured their strength and found that alkaline papers were generally strong but acid 

Barrow s other approach to the problem was to obtain several pieces of paper and age them artificially and follow the decrease in strength. The results reinforced the relationship between initial acidity and loss of strength on ageing. There is more about artificial ageing later in this chapter. 

Alkaline degradation is possible but occurs much less readily than acid degradation. Degradation in alkaline conditions is of interest to the paper scientist mostly because of the degradation which may occur during analytical procedures rather than what may happen during the ageing of paper. 

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In addition to organic reactions, acid catalysed hydrolysis of cellulose has been performed in a rapid and controlled manner using a microwave reactor. Given this reaction, it is likely that aqueous phase microwave assisted reactions will play an important role in the rapid development of biorefinery based materials and chemicals. 

The acid catalysed hydrolysis of cellulose-containing biomass to levulinic acid (LA) has been known for a number of years but yields are low and tars are formed. However, by careful control of the temperature and pressure (i), Biofine Inc., has been able to develop a high yield process in a pilot plant. Commercial scaleup at several locations is in development (4). Although the literature contains numerous references to LA chemistry, the scope is limited. We now report a number of new reactions of levulinic acid. 

It is industrially produced by the acid-catalysed hydrolysis of carbohydrates such as cellulose or starch. The global production of levulinic aid is very small (<3,000 t/a), the acid is used as a solvent in the ethyl ester form and in small niche markets [16]. 

Enzymatic hydrolysis uses cellulose enzymes to perform hydrolysis of cellulose or hemicellulose under relative mild conditions (pH 4.8, 40-50 °C). The enzymatic methods avoid the use of corrosive acids. However, the hydrolysis reactions catalysed by enzymes are significantly slower than chemical hydrolysis, typically requiring days rather than minutes. 

Levulinic acid (4-oxopentanoic acid) obtained from cellulose and hemicellulose materials by acid-catalysed hydrolysis can be hydrogenated to y-valerolactone (5-methyldihydrofuran-2(3H)-one) which is a useful platform chemical precursor to liquid fuels, polymers and fine chemicals. Carbon-supported tin-ruthenium catalysts were active and selective in the hydrogenation of levulinic acid (Scheme 21.4). ... 

The conversion of ball-milled cellulose, glucose and fructose into micro-ciystalline lactic acid and 5-hydro g methylfurfural in water, catalysed by lead(ii) nitrate, has been reported (Scheme 22.5). The process involves a multistep cascade including the hydrolysis of cellulose to glucose, the isomerisation of glucose to fructose, retro-aldol fragmentation of fructose to trioses and their subsequent conversion to lactic acid lead(ii) catalyses both the conversion of glucose to fructose and the multistep cascade from fructose to lactic acid. The capacity of lead(ii) to be chelated by... 

Urea in kidney dialysate can be determined by immobilizing urease (via silylation or with glutaraldehyde as binder) on commercially available acid-base cellulose pads the process has to be modified slightly in order not to alter the dye contained in the pads [57]. The stopped-flow technique assures the required sensitivity for the enzymatic reaction, which takes 30-60 s. Synchronization of the peristaltic pumps PI and P2 in the valveless impulse-response flow injection manifold depicted in Fig. 5.19.B by means of a timer enables kinetic measurements [62]. Following a comprehensive study of the effect of hydrodynamic and (bio)chemical variables, the sensor was optimized for monitoring urea in real biological samples. A similar system was used for the determination of penicillin by penicillinase-catalysed hydrolysis. The enzyme was immobilized on acid-base cellulose strips via bovine serum albumin similarly as in enzyme electrodes [63], even though the above-described procedure would have been equally effective. 

Cellulose secondary acetate fibres are manufactured from cotton linters by steeping in glacial acetic acid and sulphuric acid-catalysed reaction with acetic anhydride. The reaction is exothermic and the final product in a maximum of 20 hours is cellulose triacetate, which is converted to secondary acetate by adding sufficient water. The hydrolysis is stopped when 1/6 of the acetate groups have been randomly changed to hydroxyl groups. The precipitated polymer flakes are dissoluted in acetone containing small amounts of water or alcohol. The chemical formula of cellulose triacetate and the diacetate fibre production chart are shown in Fig. 4.5. 

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