Hydrolysis acid pretreatment

As the name implies, the acid hydrolysis pretreatment is intended to partially hydrolyze the lignocellulosic feedstock as well as remove alkali from it. This process converts hemicellulose to pentose sugar as well as removes alkali. Biomass was added to a 5 wt % solution of sulfuric acid in the proportion of about 150 g biomass for every liter of solution and boiled for 2 how s. The mixture was transferred to the glass column and excess liquid drained from the bottom. At this point 2 L of distilled water was pumped through die column at a superficial velocity of 0.08 mm/s to rinse acid from the biomass. The pretreated biomass was then dried at 105°C for subsequent pyrolysis. 

This result does not necessarily make hydrolysis more attractive than demineralization effective measures for recovering pentose sugar from the hydrolysis waste stream are required. Our analysis suggests that there is no clear advantage in the acid hydrolysis pretreatment, which is more complicated and expensive than the demineralization pretreatment. Furthermore, the hydrolyzed biomass is sticky and hard to feed into the pyrolysis reactor. 

GC requires low molecular weight molecules, and the macromolecular nature of proteinaceous materials (made up of 21 amino acids covalently condensed) means that they are typically too large to be readily identifiable and time consuming pretreatments of the sample are required. In order to free the amino acids, hydrolysis is required. Subsequent steps of purification to eliminate pigment interferences are also often necessary. Consequently sample pretreatments must be carefully carried out to reduce the risk of loss and/or contamination of the sample. 

Wood pretreated by autohydrolysis and extraction is necessary for successful enzymatic hydrolysis, and advantageous for acid hydrolysis. 

In general, the high specificity of enzymes limits the application of this method, because for the treatment of each wastewater sample it is necessary to use a special consortium of various types of enzymes. Therefore, for practical reasons the acid hydrolysis of wastewater is the preferred laboratory method for the pretreatment of polymers. By the use of acid hydrolysis for one hour at 148°C with 6 mol/1 HCl ( acid hydrolyse kit from Dr. Lange GmbH Berlin 1996 [48]), the polymers are decomposed to their monomers such as monosaccharides, glycerol, fatty acids, or amino acids, respectively. The hydrolysis of wastewater caused in most cases an increase of the BOD measured (Table 6), resulting in an improved concurrence of sensorBOD and BOD5 [53,68]. 

The extraction and measurement of lipids may require several steps, these include (1) Pretreatment, including drying, size reduction, and possibly acid hydrolysis to release lipids. (2) Homogenization of the tissue in the presence of a sol vent/solvent system. (3) Separation of liquids from solids. (4) Removal of nonlipid contaminants. (5) Removal of solvent and drying. (6) Calculating the content of lipids by weight difference. 

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

Acid hydrolysis of these samples led to the results to be expected, i.e., a lowering of LODP and residue value by NH3 pretreatment and mercerization as well as by mechanical disintegration prior to the hydrolytic treatment (Table XII). With regard to residue value, an NH3 pretreatment again proved to be more efficient in enhancing accessibility than a mercerization, while the rate constant of chain-length degradation was increased somewhat more by mercerization. 

The sugars in the liquid after pretreatment are partly obtained in oligomer form. To convert the residual oligosaccharides to mono- and disaccharides, the samples were hydrolyzed with 4% H2S04 at 121°C for 10 min. To determine the potential sugar degradation during the acid hydrolysis, the experiments were carried out in triplicate, and known amounts of monosaccharides were added to one of the hydrolysate samples. 

Figure 1 shows the experimental procedure used to evaluate the hydrolysis methods of SFF. First, the SFF material was subjected to saccharification with amyloglucosidase to determine the amount of starch available in the material. Second, the material was subjected to pretreatment in either a steam pretreatment unit or a microwave oven, followed by enzymatic hydrolysis. Pretreatment in a microwave oven was performed both with and without the addition of acid. Direct enzymatic hydrolysis was also performed. 

A microwave oven, MLS-1200 Mega Microwave workstation, from Milestone (Sorisole, Italy), described in a previous study (4), was used to pretreat a 5% DM SFF slurry. Heat treatment was performed at 170°C for 40 min and at 180°C for 30 min. Acid hydrolysis was performed with 1% H2S04 at 130°C for 40 min and with 0.2% H2S04at 160°C for 20 min. These pretreatment experiments were performed to allow analysis of the material, as well as to compare the SFF material with that used in a previous investigation (4). 

Sugar Yields After Pretreatment and Acid Hydrolysis Performed in Microwave Oven Followed by Enzymatic Hydrolysis... 

Table 3 shows the sugar yields obtained after pretreatment and enzymatic hydrolysis of the SFF material used in the present study and the SFF material utilized in a previous study (boldface in Table 3) (4). The sugar yields obtained with acid hydrolysis in a microwave oven followed by enzymatic hydrolysis are also given. Unless otherwise stated, the yields following pretreatment and enzymatic hydrolysis are expressed as g/100 g of dry SFF. Galactose was present at very low amounts in both materials.

Besides two different hydrolysis methods (i.e., acid hydrolysis and pretreatment without the addition of acid), two different pieces of pretreatment equipment were used to perform the experiments (Fig. 4). Acid hydrolysis was conducted in a microwave oven, while pretreatment was performed in a steam pretreatment unit. The microwave oven provides a closed system where the amount of water added is fixed and there is no loss of material during the process (17-18). On the other hand, the sampleshave to be rather diluted for the microwave oven to be efficient. Another disadvantage is that the microwaves penetrate the material only a few center-meters, and therefore this method is not feasible on a large scale. The microwave oven may, however, still be of interest in the laboratory as a screening method to analyze the composition of feedstock as well as to determine a range of optimal conditions for steam pretreatment. 

Acid hydrolysis with 0.2% H2S04 at 160°C for 20 min followed by enzymatic hydrolysis resulted in 88% of the theoretical yield. Because some acid is already used in the process to adjust the pH before fermentation, the addition of small amounts of acid in a pretreatment step could be a possibility. 

Acid hydrolysis was used to determine the amount of xylose present in the lignocellulosic materials without pretreatment, after thermal pretreatment, and after both alkali and thermal pretreatments. 

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