Acid hydrolysis process

In the acid hydrolysis process (79—81), wood is treated with concentrated or dilute acid solution to produce a lignin-rich residue and a Hquor containing sugars, organic acids, furfural, and other chemicals. The process is adaptable to all species and all forms of wood waste. The Hquor can be concentrated to a molasses for animal feed (82), used as a substrate for fermentation to ethanol or yeast (82), or dehydrated to furfural and levulinic acid (83—86). Attempts have been made to obtain marketable products from the lignin residue (87) rather than using it as a fuel, but currently only carbohydrate-derived products appear practical. 

The present results suggest that the enzymatic hydrolysis process is at least competitive with the acid hydrolysis process. The main difficulty with it is the long time required for the hydrolysis, compared with the acid process. The present work suggested a mechanism for overcoming this problem, which is to remove the sugars as formed, perhaps by combining the enzymatic hydrolysis and the fermentation in one vessel at the same time. 

A two-stage acid hydrolysis process is employed in over 40 Soviet wood hydrolysis plants (15). These plants have an average annual output per plant of 10,000 t of wood sugar. Most of the output is converted to industrial alcohol and fodder yeast. 

The major soluble components of acid hydrolysates are sugars, such as xylose, glucose, and cellobiose furfurals, such as furfuraldehyde and hydroxymethyl furfural and organic acids, such as levulinic acid, formic acid, and acetic acid (13). When natural sources of cellulose are acid-hydrolized, numerous products can result, largely because of the hemicellulose materials. These make it difficult to produce a relatively pure sugar product and limit the utility of the acid hydrolysis process. 

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.,... 

We have therefore studied the kinetics of cellulose hydrolysis and glucose decomposition under extremely dilute H2S04 (0.05-0.2 wt%, pH 1.5-2.2) and high-temperature (200-230°C) conditions. Our ultimate goal is to better understand the kinetics of dilute-acid hydrolysis of biomass and develop promising acid hydrolysis processes that can give both high... 

This provides an explanation for the unaccounted glucose loss during the acid hydrolysis process. It also gives an explanation for the generally low yield for dilute acid hydrolysis processes and previously unclosed carbon mass balance. 

The U.S. Forest Products Laboratory (FPL) in cooperation with the Tennessee Valley Authority (TVA) has been studying a two-stage dilute acid hydrolysis process based in part on studies of Cederquist in Sweden during the 1950s. The first stage (pre-hydrolysis)... 

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... 

Wirght, J., Power, A., and Bergeron, P. Evaluation of Concentrated Halogen Acid Hydrolysis Processes for Alcohol Fuel Production-, SERI/ TR-232-2386 Solar Energy Research Institute Golden, CO, 1985. 

Wright, J. D. and D Agincourt, C. G., Evaluation of sulfuric acid hydrolysis processes for alcohol fuel production. Biotechnology and Bioengineering Symp. 1984, 14, 105-121. 

Soy Sauce. Soy sauce is a weU-known condiment made by fermentation or acid hydrolysis. In the fermentation process defatted soybean meal is cooked and then mixed with roasted, coarsely ground wheat and mixed with a culture oiy spergillus oyc e oi ispergillus sojae. After the mold grows for 2—3 d to form koji, brine is added, and the mixture is allowed to ferment for 6—8 m. The product is then filtered and pasteurized (94). Popularization of fermented soy sauce in the U.S. began in the late 1940s with imports from Japan, followed by constmetion of a plant in Wisconsin in 1973. Soy sauce is widely available in U.S. supermarkets and restaurants. In the acid hydrolysis process, defatted soybean flour is refluxed with hydrochloric acid to hydrolyze the proteins. The hydrolysate is then filtered, neutralized, and botded. 

Parker, S., Calnon, M., Feinberg, D., Power, A., and Weiss, L. (1983). The Value of Furfural/ Ethanol Coproduction from Acid Hydrolysis Processes, SERI/TR-231-2000. National Renewable Energy Laboratory, Golden CO. 

Introduce the cyanide alkaline chlorination, excess chlorination (superchlorination), and acid hydrolysis processes, which treat industrial effluents containing cyanide. 

An acid hydrolysis process using sulfuric, hydrochloric, nitric, or phosphoric acids cleaves the glycosidic bonds [6]. The a(l-3) and a(l-2) bonds being more labile, hydrolysis releases first L-arabinose residues. Then the bonds in the xylan chains and with other substituents are hydrolyzed. The reaction products are mainly monomeric sugars. Hydrolysis is performed between 80 and 150°C for reaction times between 300 min and 20 min, respectively, and with concentrations in wheat bran of up to 150 g/L. The amount of acid used is 0.1-0.5 mol/L. Yields of hydrolysis range from 70 to 95% in sugars released. 

The work in the early 1950,s aroused considerable interest in the possibility of producing dextrose from starch by means of glucoamylase, since the conventional acid hydrolysis process gives relatively poor yields of recoverable dextrose and an almost unusable hydrol residue containing high concentrations of salts and unpleasant tasting unfermentable reversion sugars. 

Reaction (5) describes the acidic hydrolysis process (the anation reaction) and does not lead to rupture of the M-M bond, its final product being Tc405 nHzO [80]. Reaction (6) is the complex formation reaction. The initially formed [Tc2X9]4 ion is extremely unstable it disproportionates with the rupture of M-M bonds according to reaction (7). The rate of the equilibrium complex formation reaction (6) limits the rate of the total disproportionation reaction of [Tc2X8]3 with the rupture of the Tc-Tc bond and increases down the sequence HC1, HBr, HI, and in proportion to the concentration of these acids [80,87]. In the absence of oxidants a total mobile equilibrium is attained and in their presence (e.g. oxygen of the air) the reduction to [TcC16]2 takes place [80,87]. 

Figure 2.2 shows a TEM micrograph of cellulose whiskers prepared from cotton. Geometrical characteristics of cellulose whiskers depend on the origin of cellulose microfibrils and on the conditions of the acid hydrolysis process such as time, temperature, and purity of materials. Samir et al. [75] have reported the dimensions of cotton and tunicin whiskers. The length (L) and lateral dimension (D) of cotton whiskers were around 200 and 5 nm, respectively (ratio L/D = 40). The length and lateral dimension of tunicin whiskers were reported to be around 1,000 and 15 nm, respectively (ratio L/D = 67). De Souza [76] studied cotton and tunicate whiskers in aqueous suspensions as well. The average size whisker dimensions reported were L = 255 nm and D = 15 nm for cotton whiskers (ratio L/D — 17) while the values were L — 1,160 nm and D = 6 nm (ratio L/D = 72.5) for tunicate whiskers. 

The main drawback of the acid hydrolysis processes is the formation of undesirable by-products. This not only lowers the yield of sugars, but several of the by-products severely inhibit the formation of ethanol in the fermentation process. Potential inhibitors are furfural, 5-hydro ethylfiirfural (HMF), levulinic acid, acetic acid, formic acid, uronic acid, 4-hydroxybenzoic acid, vanillic acid, vanillin, phenol, cinnamaldehyde, formaldehyde, etc. (I, 36). Some inhibitors, such as terpene compounds, are initially present in the wood, but apparently most of the inhibitors are formed in the hydrolysis process. 

This process can provide some advantages fi>r ethanol production, compared with acid hydrolysis process because of the extremely it >id reaction, ratha small and simple plant may be designed without use of add catalyst hi addition, lignin-derived products are not contaminated as in sulfuric acid lignin in the add hydrolysis process, so that th can be appropriate to be convated into the value-added aromatic products. Thus, the ovaall process would lead to the effidait utilization of the whole lignocellulosics. 

Sweeteners used throughout the world are usually derived from starch. Frequently, these are produced by an acid hydrolysis process into simpler carbohydrates. Nowadays, acid hydrolysis has been replaced by enzymes. In the enzymatic process, the treatment of starch results in various syrups that are used in the food, beverage, and pharmaceutical industries. 

In 1951, a process to degrade cellulosic fibers with H SO was introduced by Ranby for the first time [111]. Since then a series of attempts have been taken to prepare CNC from various cellulosic fibers such as curaua fibers [117], coconut husk [118], cotton and tunicates [119], sugarcane bagasse [120], and wood [ 121 ]. In the acid hydrolysis process a suspension with specific acid concentration for a particular time and temperature based on various sources of fibers is mechanically stirred. Then the reaction is quenched with cold water. Subsequently, the washing process is conducted... 

In this chapter, we will describe the production of cellulose nanocrystals (CNCs) by acid hydrolysis process from different cellulosic resources. Also, the drying process and extensive characterization of CNCs to better understand the inherent and processing properties of this nanomaterial with functionalization is discussed as potential nanoreinforcement. New developments in potential industrial and biomedical areas are also discussed. 

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