Acid hydrolysis of cellulose

DSC can be applied to study the acid hydrolysis reaction of cellulose [36,37], In order to eliminate the effect of vaporization of water during heating on the DSC curve, it is necessary that acid-proof, high-pressure stainless-steel or high-pressure gold-plated containers should be employed. The experiment can be made according to the 

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Acid hydrolysis of cellulosic materials that include some hemicellulose, produces D-xylose, D-glucose, and cellobiose, as well as 11, 2-furalde-hyde (5), levulinic acid, formic acid, and acetic acid. In order to lessen the contamination due to hemicellulose, acid hydrolysis is generally performed in two steps dilute sulfuric acid (1%) at 80-120° followed by 5-20% sulfuric acid at 180°. The initial stage removes most of the pentogly-cans (pentosans). 

Acid hydrolysis of cellulosic materials has been studied for many years (13,33). Although it is a relatively straightforward process, it has the problems of requiring acid-resistant equipment and yielding a poor grade of sugar (because the product contains many reaction product impurities). However, in terms of practical application, acid hydrolysis of cellulosic material is by far the most commonly used hydrolysis system. 

A considerable amount of experimentation has been done on the kinetics of acid hydrolysis of pure cellulose substrates. Little experimentation has been done on natural cellulosic materials. Typical examples of kinetic studies of acid hydrolysis of cellulose can be found in the papers of Saeman (33) and Grethlein (13). These researchers depict the acid hydrolysis process as a pseudo-first-order sequential process, with the rate constants as a function of the acid concentration raised to a power, i.e.,... 

The effect of ball milling on the dilute acid hydrolysis of cellulose is similar in many ways to the effect electron irradiation has on enhancing saccharification (18). In the case of cotton linters, for example, maximum irradiation lO d) resulted in a half life of hydrolysis of about 7 min... 

In this context, some experimental results relevant to these open questions of enzymatic degradation will be presented and will be discussed from the viewpoint of cellulose chemistry, together with a summary of our recent work on thermohydrolysis and acid hydrolysis of cellulose, performed in connection with research on cellulose powder manufacture (7). After a short survey of the experimental techniques applied, this contribution will be centered on three problems (1) the interaction of chain degradation and cross-linking in thermal and thermo-hydrolytic treatments of cellulose, (2) the influence of mechanical strain... 

Table IX. Acid Hydrolysis of Cellulose Powders after Different Pretreatment (5% HCl, 2 hr, 100°C)...

Acid hydrolysis of cellulose is considered to be a specific catalysis and the reaction rate depends on the concentration of proton. The addition of the proton to the oxygen atom of glucoside likage is preequilibrium state of the reaction (14). Some polymers containing sulfonic acid groups as catalytic sites have been prepared in the present investigation. 

A new model for the dilute acid hydrolysis of cellulose was developed at FPL in connection with studies of the two-stage dilute sulfuric acid hydrolysis process (Fig. 28.18).37 The model incorporates the effect of the neutralizing capacity of the substrate, the presence of readily hydrolyzable cellulose, and the reversion reactions of glucose in acid solution. Although general in nature, the model was developed specifically for application to... 

Fig. 28.18. Model for dilute acid hydrolysis of cellulosics. (From A. H. Conner eta ., in Cellulose Structure, Modification and Hydrolysis, ft A. Young and ft M. Rowell (Eds.), Copyright 1986, John Wiley Sons, New York with permission of John Wiley Sons Publisher.)...

However, further cellulose deconstruction is considerably more difficult after acid hydrolysis. Commercial processes for acid hydrolysis of cellulose were known in the early part of the twentieth century.434 The use of either low- or high-acid concentrations has disadvantages. 

Wright, J. High-Temperature Acid Hydrolysis of Cellulose for Alcohol Fuel Production SERI/TR-231-1714 Solat Energy Research Institute Golden, CO, 1983. 

Farone, W. A. and Cuzens, J. E., Methods of Producing Sugars Using Strong Acid Hydrolysis of Cellulosic and Hemicellulosic Materials. U S. Patent No. 5,562,777, October 8, 1996. 

Direct conversion of cellulose in an unpurifled state has been shown in the case of levulinic acid production. Production of levulinic acid as a high-yield direct product of controlled acid hydrolysis of cellulose is an exception to the complex product slate typically produced from biomass feedstocks. While the levulinic acid is only derived from the cellulose portion of the biomass and other components end up as byproducts, technology has now been demonstrated for recovery of the levulinic acid product at yields and purity sufiident to generate market interest". Based on related research developments, levulinic acid may prove to be an important building block for... 

The anhydride method of acetylation gives an acid by-product that results in an acidic condition in the wood and a loss of 50% of the reaction chemical. These by-products must be removed to prevent degradation. Acetic acid, the by-product of acetylation with acetic anhydride, is virtually impossible to remove completely from wood. This results in a product that smells of acetic acid, acid conditions that catalyze the removal of more acetyl groups, acid hydrolysis of cellulose fibers which results in strength losses over a long term, and acid corrosion of metal fasteners used in the wood product. 

A brief overview of the reaction kinetics concerning the acid hydrolysis of cellulose and hemicellulose is presented here for subsequent discussion on reactor design and operation. 

The reaction pattern of acid hydrolysis of cellulose by dilute acid is represented by the sequential first-order reaction ... 

The most unusual development in reactor design in dilute acid hydrolysis of cellulose hydrolysis is that of a counter-current reactor. It is defined as a mov-... 

A continuous counter-current reactor system has shown great promise as a process reactor in the dilute acid hydrolysis of cellulose. However, the findings on this unique reactor system have been limited to the theoretical aspects and the proof-of-concept laboratory experiments. It has to be developed into an upscale process reactor before it is adopted into the biomass conversion process. To this end, a pilot-scale process study is being conducted at NREL. This is only the first step. To be noted here is that reactors of similar design are being used in industry it took years of developmental work, however, before they were put into commercial service. It would probably take about the same degree of investment in this case. In addition to the reactor issue, there are other important issues that need to be addressed in the dilute acid process. 

Economically feasible processes for biomass conversion to ethanol requires the fermentation of the sugars generated in the pretreatment and hydrolysis steps. In agricultural residues and hardwoods, xylose constitutes about 45% of the total sugars, and therefore xylose conversion to ethanol is important for high yields. Dilute acid hydrolysis of cellulosic biomass generates inhibitory compounds such as furfural, hydroxymethyl furfural, and acetic acid [1], These inhibitors affect the ability of yeasts to ferment the hydrolyzates, and therefore a detoxification step is usually included in fermenting acid... 

The high yield and hence higher purity of sugar obtained by strong acid hydrolysis of cellulose makes it an attractive process, but the lack of a recovery system for strong acid complicates the outlook. The improvement of membrane technology will probably proceed because of potential applications to many problems. Application to cellulose hydrolysis adds justification for intensified work in the field. 

Rinaldi R, Schiith F (2009) Acid hydrolysis of cellulose as the entry point into biOTcfinery schemes. ChemSusChem 2(12) 1096-1107... 

Cellulose whiskers without surface modification display strong interactions and have been reported as difficult to disperse in water. Sulfate-functionalized tunicate whiskers were prepared by sulfuric acid hydrolysis of cellulose pulp derived from tunicates (StyelacldVa). These high aspect ratio nanoparticles formed colloidal suspensions in water (Figure 14.4). A stable suspension of tunicin whiskers was obtained in an organic solvent (Af,Af-dimethylformamide) without surfactant addition or chemical surface modification. Both the high value of the dielectric constant of DMF and the medium wettability of tunicin whiskers were supposed to control the stability of the suspension (Figure 14.5). 

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