Question

Discuss in general the professional integrity and ethical decision making relevant to engineering practices involving

1. liquid-liquid separation process

2. solid-liquid separation process

Perform a case study for each process and further elaborate the impact of the professional integrity and ethical decision making relevant to engineering practices on the public and society supported by real examples.

Answer 1

Solid - liquid separation process:

The two basic principles of solid-liquid filtration involve either separating liquids from solids or filtering solids from liquids, using one of two principles:

The solids will have a tendency to go one way and liquids the other (separation)

That use will be made of a hole smaller than the solids to be captured (filtration)

Still, more than 100 different types of equipment are available, many with their own variations.

Focusing on solid-liquid separation, suspended solids are removed from liquid either on the surface (cake filtration) or within the depth of the filter medium. The depth of the filter media can be the filter media itself, the cake or the filter aid. Regardless of the surface of depth filtration, three mechanisms exist for removal: inertial impact, diffusional interception or direct interception.

Particles in a fluid have a mass and velocity and therefore an associated momentum. As the liquid and entrained particles pass through a filter media, the liquid will take the path of least resistance and be diverted around the fiber. Because of their momentum, the particles tend to travel in a straight line, and as a result, particles located at or near the center of the flow line will strike or impact the fiber and are removed. Generally, larger particles will more readily deviate from the flow lines than smaller ones. In practice, because the differential densities of the particles and liquids are very small, this mechanism is less effective in liquid filtration.

For particles that have little mass, separation can result from diffusional interception. In this mechanism, particles collide with the liquid molecules, which cause the particles to move randomly around the fluid flow lines.

Such movements, observed only on a microscopic level, are called Brownian motion. Motion causes the smaller particles to deviate from the fluid flow lines and increases the likelihood of their striking the fiber surface and being removed. However, as with inertial impaction, this mechanism has only a minor role in liquid filtration.

Equally effective in liquids and gases, direct interception is the predominant mechanism for removing particles from liquids. In the depth of the filter medium (the medium itself, the cake or the filter aid, as stated previously), not only a single fiber or structure but also a rather tortuous path is visible. This tortuous path defines the pores or openings that will remove the solids. If they bridge across the structure or if two or more particles strike a pore simultaneously, particles smaller than the pore diameter might also be removed.

Both inertial impaction and diffusional interception are much less effective with liquids than with gases. Because the density of the particles will be typically closer to that of the liquid than to that of the gas, deviation of a suspended particle from the liquid flow line is much less, so impact on the structure of the medium is less likely. Moreover, impact to the surface of the filter media is not followed by adhesion of the particles to the surface of the filter media. Diffusional interception in liquids occurs only to a very limited extent because Brownian motion is not nearly as pronounced in liquids as it is in gases.

Liquid liqiud separation process:

In a liquid-liquid extraction unit, a liquid stream (carrier) containing the component(s) to be recovered (solute) is fed into an extractor, where it contacts a solvent. The two liquids must be immiscible or only slightly miscible; this allows them to form a dispersion, with one liquid dispersed as droplets in the other.

Mass transfer occurs between the droplets (dispersed phase) and the surrounding liquid (continuous phase). In order for the two liquids to be subsequently separated, they must have different densities. The droplets then accumulate above or below the continuous phase, depending on the liquids’ relative densities. The boundary between the continuous phase and the droplet dispersion is referred to as the interface, and can be at the top or bottom of the extraction column.

Professional integrity and ethical decision making to engineering practices:

Chemical engineering and, perhaps to a lesser degree, other kinds of engineering are topics of intense interest to contemporary ethicists and philosophers. In many cases, this scrutiny has been triggered by unfortunate safety or pollution incidents from the recent past in “our” process industries. In some circles, merely identifying oneself as a chemical engineer arouses negative associations that range from acid rain, asbestos, Bhopal, Chernobyl, chlorofluorocarbons, Exxon Valdez, DDT, Kepone, lead paint, Love Canal, mercury, PCBs, and author Rachel Carson’s “Silent Spring” to Three-Mile Island.

It is unfair, of course, to condemn an entire profession for the mistakes, poor judgment, or crimes of a few engineers or their employers; indeed, many engineers have made that point. Chemical engineering leaders and educators have worked hard to elevate or maintain the ethics of their colleagues and to enhance the image of our profession.

Virtually every chemical engineer will encounter ethical conflicts during his or her career while exerting control over forces that can affect health, lives, jobs, finances, and reputations. It is a heavy responsibility. No insurance reimbursement can compensate for the regret and guilt stemming from a lapse in judgment that causes injury, loss of life, or property damage. Because we are human, incidents will inevitably happen, but there is no need to despair over acts of fate that fell during our watch if we obey the rules and do our best.

What are the chemical engineer’s legal liabilities, and what constitutes “doing our best?” In the U.S., laws to protect safety, the environment, and people’s money are administered by the Occupational Safety and Health Administration (OSHA), the Environmental Protection Agency (EPA), and the Securities and Exchange Commission (SEC), among other agencies. Other countries have similar organizations, and, as in the U.S., legal guidelines are usually published widely in the workplace.

Keep in mind, however, that there is a difference between legality and ethics. On the one hand, a society’s rules change as its morality evolves. As a consequence, regulations ebb and flow; their nature and their impact are moderated by the weight of the public as it reacts to events, comes to a consensus, and forces legislation.

Ethical codes, on the other hand, tend to be less specific, and they change less dramatically. Their moral guidelines are more encompassing, but those guidelines require individual, person by person, interpretation. Such codes have been adopted by all major engineering societies, among them the American Institute of Chemical Engineers (AIChE), the American Soc. of Civil Engineers, the American Soc. of Mechanical Engineers, the Institute of Electrical and Electronics Engineers and the National Soc. of Professional Engineers.

The AIChE Code of Professional Ethics.

The chemical engineer who abides by this admirable code is indeed unlikely to do anything unethical or illegal.

Based on the ethics literature and more than 50 years of my own professional and personal experience, here are four prime observations:

Engineers cannot delegate ethical responsibility to anyone else

Ethical behavior is enhanced by effective communication

Ethical behavior is more likely when engineers are aware of their personal biases, and the limitations of their own knowledge

Ethical challenges never go away. No matter how old or how experienced, individuals and organizations must continually examine and sometimes reform their behavior.

The rest of this article delves deeper into each of those four points.

Real examples:

Let’s consider an example of an engineering model in which I was involved personally as an OR consultant. This model represents the so-called Waste Isolation Pilot Plant (WIPP), built near the town of Carlsbad in New Mexico (NM), USA; this WIPP stores nuclear waste. The client (patron) of this modeling effort is the Environmental Protection Agency (EPA) of the Department of Energy (DOE). The consultant (modeler) is Sandia National Laboratories in Albuquerque (NM). The other stakeholders become clear when I point out that this nuclear waste might leak away from the WIPP to the surface (this “plant” resembles an underground coal or salt mine, as it includes a “waste shaft” that is dug into the earth). Such leakage may endanger the health of human beings, so ethical issues certainly play a role. More precisely, not only the people now living near Carlsbad are at risk: future generations are at risk too. Therefore the model’s output (performance measure, criterion) is the chance of leakages in the next 10,000 years; this time horizon is stipulated by the EPA, so it is seems not open to scientific debate. Note that the local population also enjoys the benefits of new employment and business opportunities!

More specifically, the waste stored in this WIPP includes garments worn by medical personnel while treating cancer patients. So besides the risks and benefits for the people living in Carlsbad and other places now and in the future, there are benefits for these patients. Actually, the simulation model quantifies the chance of nuclear leakage; it does not quantify—let alone balance—the costs and benefits of all the different stakeholders (I shall return to the role of stakeholders). So—unlike some cost/benefit analyses—this study does not try to quantify the value of a human life (which is related to the question about “the worth of a songbird”; Funtowicz and Ravetz 1994).

Mathematically, the WIPP model includes many deterministic nonlinear differential equations plus some stochastic (random or chance) processes. These differential equations simulate the physical and chemical processes that are determined by the laws of nature governing the possible dissipation of the nuclear waste in the underground. The stochastic submodel (a so-called Poisson model) simulates human processes; e.g., after (say) 1,000 years, people may have forgotten about the WIPP, and start digging for precious metals in that area.

Based on the outcomes of this model, permission was granted to build the WIPP. Many more details can be found in the vast literature on this project (Helton 2009).

Later on, a different WIPP was modeled; namely, a WIPP for the waste created by the production of atomic bombs, to be built in the Yucca Mountain in Nevada. Obviously, the design and production of such bombs raises different ethical questions! Military applications of engineering and OR models will be discussed in a separate section below.

A recent urgent worldwide problem—that also involves engineers and has ethical implications—is global warming (the 2009 Copenhagen conference did not solve this problem). The Dutch “National Institute for Public Health and the Environment” (in Dutch: RIVM) developed a simulation model for this problem. Like in the WIPP example, the issue is the survival of future generations; that survival requires a sustainableworld. RIVM was confronted with the issue of validating their model, and selecting the really important factors among the many potential factors. It turned out that the model had some computer bugs (computer modules were called in the wrong order); furthermore, among the 281 potentially important factors, only 15 factors were found to be really important so they needed monitoring (Bettonvil and Kleijnen 1996; Kleijnen et al. 1992).