Z. J. Pei

Organic solvent pretreatment of lignocellulosic biomass for biofuels and biochemicals: A review

Lignocellulosic biomass represents the largest potential volume and lowest cost for biofuel and biochemical production. Pretreatment is an essential component of biomass conversion process, affecting a majority of downstream processes, including enzymatic hydrolysis, fermentation, and final product separation. Organic solvent pretreatment is recognized as an emerging way ahead because of its inherent advantages, such as the ability to fractionate lignocellulosic biomass into cellulose, lignin, and hemicellulose components with high purity, as well as easy solvent recovery and solvent reuse. Objectives of this review were to update and extend previous works on pretreatment of lignocellulosic biomass for biofuels and biochemicals using organic solvents, especially on ethanol, methanol, ethylene glycol, glycerol, acetic acid, and formic acid. Perspectives and recommendations were given to fully describe implementation of proper organic solvent pretreatment for future research.

Biofuel Manufacturing from Woody Biomass: Effects of Sieve Size Used in Biomass Size Reduction

Size reduction is the first step for manufacturing biofuels from woody biomass. It is usually performed using milling machines and the particle size is controlled by the size of the sieve installed on a milling machine. There are reported studies about the effects of sieve size on energy consumption in milling of woody biomass. These studies show that energy consumption increased dramatically as sieve size became smaller. However, in these studies, the sugar yield (proportional to biofuel yield) in hydrolysis of the milled woody biomass was not measured. The lack of comprehensive studies about the effects of sieve size on energy consumption in biomass milling and sugar yield in hydrolysis process makes it difficult to decide which sieve size should be selected in order to minimize the energy consumption in size reduction and maximize the sugar yield in hydrolysis. The purpose of this paper is to fill this gap in the literature. In this paper, knife milling of poplar wood was conducted using sieves of three sizes (1, 2, and 4 mm). Results show that, as sieve size increased, energy consumption in knife milling decreased and sugar yield in hydrolysis increased in the tested range of particle sizes.

Grinding induced subsurface cracks in silicon wafers

Silicon wafers are used for production of most microchips. Various processes are needed to transfer a silicon crystal ingot into wafers. To ensure high surface quality, the damage layer generated by each of the machining processes (such as lapping and grinding) has to be removed by its subsequent processes. Therefore it is essential to assess the subsurface damage for each machining process. This paper presents the observation of subsurface cracks in silicon wafers machined by surface grinding process. Based on cross-sectional microscopy methods, several crack configurations are identified. Samples taken from different locations on the wafers are examined to investigate the effects of sample location on crack depth. The effects of grinding parameters such as feedrate and wheel rotational speed on the depth of subsurface crack have been studied by a set of factorial design experiments. Furthermore, the relation between the depth of subsurface crack and the wheel grit size is experimentally determined.

Modeling of ductile-mode material removal in rotary ultrasonic machining

In rotary ultrasonic machining of ceramic materials there exist two modes of material removal: brittle fracture mode and ductile mode. Two models were developed based on the assumption that the brittle fracture is the dominating mode of material removal, and were published previously. This paper presents the follow-up work on modeling of the ductile-mode material removal in rotary ultrasonic machining. After a brief review of the ductile phenomena in ceramic machining, an approach to modeling the ductile-mode removal in rotary ultrasonic machining is proposed. Then, magnesia stabilized zirconia is used to demonstrate the models capability of predicting the material removal rate from the process parameters and the material property of the workpiece. Finally, the results of the pilot experiments to verify the model are discussed.

Fine grinding of silicon wafers

Silicon wafers are used for the production of most microchips. Various processes are needed to transfer a silicon crystal ingot into wafers. As one of such processes, surface grinding of silicon wafers has attracted attention among various investigators and a limited number of articles can be found in the literature. However, no published articles are available regarding fine grinding of silicon wafers. In this paper, the uniqueness and the special requirements of the silicon wafer fine grinding process are introduced first. Then some experimental results on the fine grinding of silicon wafers are presented and discussed. Tests on different grinding wheels demonstrate the importance of choosing the correct wheel and an illustration of the proper selection of process parameters is included. Also discussed are the effects of the nozzle position and the flow rate of the grinding coolant.

A mechanistic approach to the prediction of material removal rates in rotary ultrasonic machining

An approach to modeling the material removal rate (MRR) during rotary ultrasonic machining (RUM) of ceramics is proposed and applied to predicting the MRR for the case of magnesia stabilized zirconia. The model, a first attempt at predicting the MRR in RUM, is based on the assumption that brittle fracture is the primary mechanism of material removal. To justify this assumption, a model parameter (which models the ratio of the fractured volume to the indented volume of a single diamond particle) is shown to be invariant for most machining conditions. The model is mechanistic in the sense that this parameter can be observed experimentally from a few experiments for a particular material and then used in prediction of MRR over a wide range of process parameters. This is demonstrated for magnesia stabilized zirconia, where very good predictions are obtained using an estimate of this single parameter. On the basis of this model, relations between the material removal rate and the controllable machining parameters are deduced. These relationships agree well with the trends observed by experimental observations made by other investigators

Rotary ultrasonic machining for face milling of ceramics

Abstract Among the various material removal processes applicable to ceramic materials, rotary ultrasonic machining has the potential for high material removal rate while maintaining low machining pressure and resulting in less surface damage. The limitation of rotary ultrasonic machining is that only circular holes or cavities can be machined due to the rotary motion of the tool. Attempts have been made by other researchers to extend rotary ultrasonic machining process to machining flat surfaces or milling slots. However, these extensions either changed the material removal mechanisms or had some severe drawbacks. One of the reasons for this might be an insufficient understanding of the material removal mechanisms involved. In this paper, a new approach to extend rotary ultrasonic machining to face milling of ceramics is proposed, which keeps all the material removal mechanisms of rotary ultrasonic machining. The development of the experimental apparatus and the design of the cutting tool are described. Preliminary experimental results are presented and discussed.

Modeling of material removal rate in rotary ultrasonic machining: designed experiments

Abstract Advanced ceramic materials have many potential engineering applications. However, their widespread applications have been hindered by the high machining cost. There is a critical need for cost-effective machining processes for advanced ceramics. Rotary ultrasonic machining (RUM) is a hybrid machining process that combines the material removal mechanisms of diamond grinding and ultrasonic machining (USM), resulting in higher material removal rates (MRR) than those obtained by either diamond grinding or USM. An approach to modeling the MRR during RUM of ceramics has been proposed and applied to predicting the MRR for the case of magnesia stabilized zirconia. Relationships between MRR and the controllable machining parameters have been deduced. These relationships agreed well with the trends observed by experimental observations made by other investigators. However, the relationships have been studied by changing one variable at a time. Therefore, the interactions between these variables have not been revealed. In this paper a five-factor two-level factorial design is used to study the relationships between MRR and the controllable machining parameters. This study will provide the main effects of these variables, and two-factor interactions and three-factor interactions among these variables. The results will shed more light on the material removal mechanism in RUM. The comparison with experimental results will also serve as further validation of the model.

An experimental investigation of rotary ultrasonic face milling

Reliable and cost-effective machining of advanced ceramics is crucially important for them to be widely used in a number of critical engineering applications. The potential of Rotary Ultrasonic Machining (RUM) process has been recognized as one of the reliable and cost-effective machining methods for advanced ceramics and commercial machinery is available for the process. One limitation of the commercial RUM machines is that only circular holes can be efficiently machined. An approach to extend the RUM process to face milling of ceramics was proposed and the development of the experimental apparatus as well as the preliminary experimental results were published earlier in this journal. As a follow-up, this paper will present the results of an experimental investigation of the newly-developed Rotary Ultrasonic Face Milling (RUFM) process. In this investigation, a five-variable two-level fractional factorial design is used to conduct the experiments. The purpose of these experiments is to reveal the main effects as well as the interaction effects of the process parameters on the process outputs such as Material Removal Rate (MRR), cutting force, material removal mode and surface roughness.

Plastic flow in rotary ultrasonic machining of ceramics

Abstract Since rotary ultrasonic machining (RUM) appeared some 30 years ago, many experimental studies have been conducted to explore the relations between control variables (such as ultrasonic vibration amplitude, applied static pressure, rotational speed, diamond type, grit size and bond type, etc.) and process outputs (such as material removal rate, tool wear, etc.). However, few investigations into material removal mechanisms of RUM have been published. The material removal in RUM process has been mainly attributed to brittle fracture. In this paper, experimental evidence is presented to show that plastic flow can also be one of the material removal modes in RUM in addition to brittle fracture. To explain the experimental evidence, related work is reviewed and some theoretical analysis is provided.