Industrial Chemical Processes and Environmental Technologies

Posted on Mar 30, 2025 in Chemistry

Industrial Processes and Sustainable Technologies

Pesticide Active Ingredient Screening Evolution

Before the 1980s, screening for active ingredients in the pesticide industry involved expensive and time-consuming greenhouse tests requiring large product amounts. However, with the advent of molecular biology in the 1980s and 1990s, these methods declined, replaced by receptor-inhibitor models and pre-designed compounds. Since 1990, ‘sophisticated screening’ methods have become prevalent. These techniques offer several advantages:

  • Eliminate the need for emissions.
  • Provide endless testing possibilities.
  • Can be performed in test tubes using small sample amounts.
  • Yield a vast number of results, particularly with combinatorial chemistry.

Consequently, the number of identified active ingredients has increased dramatically, from approximately 1,300 to over 50,000 today.

Recovered Paper Pulping and Refining Process

The process of creating pulp from recovered paper begins with cleaning and sorting the paper into grades to ensure homogeneity. Fibers are then separated by removing additives through the pulping technique, which involves the following steps:

  1. Mixing paper with hot water and agitation to create a smooth paste.
  2. Adding reagents specific to the paper type (commonly sodium silicate, surfactants, or NaOH).
  3. Adding H2O2 (hydrogen peroxide) and detergents to form flocs (clumps).

Subsequent refining and de-inking steps include:

  1. Centrifugation to separate heavy particles and screening for small particles.
  2. Flotation de-inking to remove ink particles.
  3. Fine screening and further centrifugation (often using slotted sieves).

Environmentally Friendlier Fertilizer Options

Several alternatives to traditional fertilizers aim for cleaner application:

  • Liquid Fertilizers: These are often easier to use as they mix readily with water. However, they can be more expensive and may cause clogged pipes. An example is anhydrous ammonia, which is not suitable for rain-fed agriculture.
  • Slow-Release Dry Fertilizers: These provide gradual nutrient release over time. They include coated fertilizers or fertilizers formulated with low solubility.
  • Fertilizers with Nitrification Inhibitors: These contain substances (like pyrene derivatives) that are toxic to nitrifying bacteria, thus reducing nitrogen loss from the soil. They are commonly used for crops like cereals, maize, and cotton.
  • Organic Fertilizers: Often sourced from compost, these are rich in Nitrogen (N) and Phosphorus (P). Careful consideration of application rates and methods is necessary.

Mechanical Plastic Recycling Separation Techniques

Mechanical recycling aims to separate different types of plastics without destroying their chemical structure, thus maintaining their physical properties. Separation is a crucial prior step, primarily necessary for thermoplastics. The goal is to obtain homogeneous, uncontaminated plastic streams. Common separation techniques include:

  • Density-based methods: Such as hydraulic separation, flotation, and centrifugation.
  • Conductivity-based methods: Including electrostatic separation.
  • Softening Temperature-based methods: Utilizing equipment like hot rollers.
  • Solubility-based methods: Employing specific solvents, like cyclohexanone, particularly effective for separating PVC.
  • Composition/Structure-based methods: Techniques like X-ray fluorescence (XRF).

After separation, the plastics are typically dried, compacted, and processed further.

Storing Solar Photovoltaic Energy

While solar photovoltaic (PV) energy can be used immediately (requiring an inverter to convert DC to AC power), storage is often necessary for continuous supply. Various alternatives exist for storing PV-generated electricity:

  • Producing hydrogen (H2) via electrolysis (particularly suitable for large-scale storage).
  • Using fuel cells to convert stored chemical energy (like hydrogen) back into electricity continuously.
  • Storing electrical energy directly in batteries.
  • Utilizing mechanical storage methods like compressed air energy storage (CAES) or pumped hydro storage (pumping water to a higher elevation).
  • Exploring advanced technologies like superconducting magnetic energy storage (SMES).

Solar Thermal Power Plant Components

Solar thermal power plants concentrate sunlight to generate heat, which is then used to produce electricity. A typical plant includes:

  • Solar Collector System: Concentrates sunlight onto a receiver. Examples include parabolic troughs or central receiver systems (CRS) which use fields of mirrors (heliostats) focusing sunlight onto a central tower. The receiver often uses molten salt or Sodium (Na) as the heat transfer fluid.
  • Heat Transfer System: Circulates a fluid (like molten salts or Na) heated by the collectors to transfer thermal energy.
  • Thermal Energy Storage: Stores the collected heat, often using the heat transfer fluid itself in large insulated tanks, or sometimes using materials like rocks (especially in systems using hot air). This allows power generation even when the sun isn’t shining.
  • Power Generation Unit: Uses the stored heat to create steam, which drives a turbine connected to a generator, producing electricity (similar to conventional thermal power plants).

Operational challenges include the need for regular cleaning of mirrors and repairing potential damage to components.

Technologies for Cleaner Coal Utilization

Several technologies aim to reduce the environmental impact of using coal for energy generation:

  • Fluidized Bed Combustion (FBC): Coal particles are suspended alongside a sorbent material (like limestone) in upward-blowing jets of air during combustion. This promotes temperature homogeneity, allows for efficient capture of sulfur dioxide (SO2) by the sorbent, and reduces the formation of nitrogen oxides (NOx) compared to traditional boilers. Types include Atmospheric FBC (AFBC), Circulating FBC (CFBC), and Pressurized FBC (PFBC).
  • Coal Gasification: This process converts solid coal into a gaseous fuel called syngas (primarily Carbon Monoxide (CO) and Hydrogen (H2)) through controlled reactions with oxygen or air and steam. Pollutants can be removed from the syngas *before* combustion. The cleaned syngas is then typically burned in a gas turbine, often as part of an Integrated Gasification Combined Cycle (IGCC) plant, to generate electricity efficiently. Using air instead of pure oxygen results in lower heating value syngas (due to Nitrogen dilution) but can aid in NOx control during combustion.

Nitrogen Fertilizer Production: Haber-Bosch Process

The production of most nitrogen fertilizers begins with the synthesis of ammonia (NH3). This is primarily achieved through the Haber-Bosch process:

Nitrogen gas (N2), extracted from the air, is reacted with Hydrogen gas (H2), typically derived from natural gas (methane). This reaction occurs under conditions of high pressure (e.g., 150–350 atmospheres) and high temperature (e.g., 400–500 °C), in the presence of a solid catalyst (usually iron-based).

The resulting ammonia can be used directly as a fertilizer (e.g., anhydrous ammonia) or serve as a feedstock for other nitrogen fertilizers. For instance, to produce nitrate fertilizers (containing NO3-), ammonia is further processed through catalytic oxidation (often via the Ostwald process).

The Haber-Bosch process is highly energy-intensive. While nitrogen fixation (converting N2 into reactive forms like ammonia) also occurs naturally through certain bacteria, industrial production via Haber-Bosch now dominates and has significantly altered the global nitrogen cycle.