The branch of engineering involved in the research, design, improvement, operation, and commercialization of plants, processes, and products for the chemical industry and related fields, such as biotechnology, energy, and materials. The work of chemical engineers has evolved continuously with the changing needs of society. Chemical engineering arose from attempts at inventing ways to make products such as gunpowder and wine. Early on (in the nineteenth century), the large-scale and efficient manufacturing of inorganic chemicals, such as salt, soda ash, sulfuric acid, and nitrogen fixation, were the main occupation of American chemical engineers. However, for the small-scale dyestuff and drug industries in Europe, chemical engineers were less involved. In the twentieth century, large-scale petroleum refining, petrochemicals, and polymers were the dominant industrial problems. In the twenty-first century, the focus has shifted to smaller-scale processes across many disciplines of science and technology, such as molecular biology, genetics, information technology, and nanotechnology.