Wheat straw is an abundant lignocellulosic residue from wheat cultivation. It is composed of cellulose, hemicellulose, and lignin and offers several possibilities for valorisation. Nowadays, a growing interest in lignocellulosic biomass fractionation and lignin utilisation is observed. Alkaline pretreatment with NaOH is often applied to obtain a high-quality lignin fraction under milder conditions. In this study, alkaline pretreatment of wheat straw using a NaOH solution is simulated in Aspen Plus to determine mass and energy balances producing a lignin fraction. These balances were used as input to perform a life cycle assessment to screen and estimate the environmental impacts underlying 12 different scenarios. According to the impact assessment results, pretreatment with 2 % NaOH solution, reactor temperature 105 ºC, and solid biomass as the thermal energy source, as described in the base case, is the best compromise between low Global Warming, Eutrophication, Human Toxicity potentials, Blue Water Consumption, and resource efficiency.