Concentrating of Sugar Syrup in Bioethanol Production Using Sweeping Gas Membrane Distillation

Bioethanol Production from Lignocellulosic Biomass-Challenges and Solutions

Regarding the limited resources for fossil fuels and increasing global energy demands, greenhouse gas emissions, and climate change, there is a need to find alternative energy sources that are sustainable, environmentally friendly, renewable, and economically viable. In the last several decades, interest in second-generation bioethanol production from non-food lignocellulosic biomass in the form of organic residues rapidly increased because of its abundance, renewability, and low cost. Bioethanol production fits into the strategy of a circular economy and zero waste plans, and using ethanol as an alternative fuel gives the world economy a chance to become independent of the petrochemical industry, providing energy security and environmental safety. However, the conversion of biomass into ethanol is a challenging and multi-stage process because of the variation in the biochemical composition of biomass and the recalcitrance of lignin, the aromatic component of lignocellulose. Therefore, the commercial production of cellulosic ethanol has not yet become well-received commercially, being hampered by high research and production costs, and substantial effort is needed to make it more widespread and profitable. This review summarises the state of the art in bioethanol production from lignocellulosic biomass, highlights the most challenging steps of the process, including pretreatment stages required to fragment biomass components and further enzymatic hydrolysis and fermentation, presents the most recent technological advances to overcome the challenges and high costs, and discusses future perspectives of second-generation biorefineries.

The Application of Open Capillary Modules for Sweeping Gas Membrane Distillation

The paper presents the sweeping gas membrane distillation realised by using the capillary module (length 1.1 m and area 0.1 m2) without housing (module shell). During the tests, the feed was flowing inside the hydrophobic polypropylene membranes. The studies were performed for two variants of process: with pre-heating (313–330 K) and without heating of the feed (brines). Under low gas flow (0.005 m/s) the evaporation performance varied in the range of 0.15–0.25 L/m2h, depending on the relative humidity (42–63%) and the air temperature (293–300 K). The application of feed pre-heating to 330 K led to an increase in the evaporation performance to 2.4 L/m2h. The permeate flux increased by 60% when the air flow velocities between the capillaries increased to 1.8–2.5 m/s. Increasing the feed flow rate from 0.1 to 0.59 m/s led to increase the permeate flux about 20% for feed temperature 293–310 K, and over 55% for feed temperature higher than 323 K.